Abdomen Anatomy Lab Session PDF 2022

Abdomen Anatomy lab session, edition 2022. by Prof. Jerzy Gielecki MD, PhD and Anna Żurada MD, PhD 1 Abdomen and abdominal cavity The abdomen is the region of body between thorax and pelvis. 1.1 The abdominal cavity The abdominal cavity is defined as an anatomical space, which is limited by the musc...

Abdomen Anatomy lab session, edition 2022. by Prof. Jerzy Gielecki MD, PhD and Anna Żurada MD, PhD 1 Abdomen and abdominal cavity The abdomen is the region of body between thorax and pelvis. 1.1 The abdominal cavity The abdominal cavity is defined as an anatomical space, which is limited by the muscular diaphragm above (separating the abdominal cavity from the thoracic cavity) and the pelvic inlet below. Anteriorly, the abdominal wall is formed above by the lower part of the thoracic cage and below by the fasciae and following four pairs of muscles: 1. 2. 3. 4. 5. External oblique Internal oblique Transversus abdominis Rectus abdominis Pyramidalis (inconsistent) Posteriorly, the abdominal wall is formed by the fasciae and following muscles: 1. Psoas major and psoas minor* 2. Iliacus* 3. Quadratus lumborum *Psoas major, psoas minor and iliacus together form the iliopsoas muscle. The upper part of the lateral abdominal wall is also protected by lower part of the thoracic cage. 1.2 Surface landmarks of the abdominal wall For purposes of description, the abdomen is divided into nine compartments by the four planes: two horizontal and two sagittal. 1. Transpyloric plane transsects perpendicularly the midsagital plane half way between jugular notch and pubic symphysis. It is also marked by the level of L1. In addition, in that case another plane called the subcostal plane is used (through the lowest extension of the costal margin). 2. Transtubercular plane or the intertubercular plane unites left and right anterior superior iliac spines of the iliac crests. 3. Two vertical midclavicular lines extend from midpoint of the clavicle to the midinguinal point. 1 Fig. 1.1. Abdominal regions. TPP - transpyloric plane, ITP - intertubercular plane, VLR – right vertical line, VLL – left vertical line, A – right hypochondriac region, B – epigastric abdominal region, C – left hypochondriac region, D – right lumbar region, E – umbilical region, F – left lumbar region, G – right inguinal region, H – pubic region. 1.3 Surface landmarks of the abdominal wall Nine abdominal regions are formed between two horizontal planes and two vertical lines. The transpyloric (TPP) and intertubercular (ITP) planes separate three horizontal abdominal regions: 1. Epigastrial region (epigastrium) above the transpyloric plane. 2. Mesogastrial region (mesogastrium) between TPP and ITP planes. 3. Hypogastrial region (hypogastrium) beneath ITP plane. The left and right midclavicular lines and (as a continuation) midinguinal lines separate three horizontal abdominal regions (referer to the fig. 1.1 for the meaning of the capital letters below): 1. Two lateral abdominal regions: left = A+D+G and right = C+F+I. 2. Unpaired central abdominal regions: B+E+H. In the epigastrial regions two vertical lines separate: 1. Two hypochondriac regions on each side (A, C). 2. Epigastric abdominal region in the middle (B). In the mesogastrial region two vertical lines separate: 2 1. Two lateral regions or flanks at the lateral abdominal areas on each side (D, F). 2. Umbilical region in the middle (E). In the hypogastrial zone lines: VLR and VLL separate: 1. Two inguinal regions on each side (G, I), some authors call it as left and right hypogastric region. 2. Pubic region in the middle (H), some authors describe it as hypogastric region. 1.4 Musculature of the abdominal wall 1.4.1 Lateral group of abdominal muscles 1.4.1.1 The external oblique The external oblique muscle – the most superficial one - is located in the anterolateral portion (with the internal oblique and transversus abdominis) and it is the continuation of the intercostal external muscle. Its aponeurosis forms the anterior wall of the sheath of the rectus abdominis muscle. Origin: It arises from the outer surface of the lower eight ribs. Insertion: It inserts into the end of the xiphoid process, linea alba, pubic crest and the anterior half of the iliac crest. Fibres of this muscle run inferoanteriorly and medially. Action: Trunk flexion, expiration, compression of the contents of the abdominal cavity. Trunk rotation during contrlateral (unilateral) contraction. Blood supply: Posterior intercostal arteries, subcostal artery, deep circumflex iliac artery. Nerve supply: Intercostal nerves (T7- T11), Subcostal nerve (T12). Sensory: Iliohypogastric nerve (L1). 1.4.1.2 The internal oblique The internal oblique muscle is the middle one. It lies deeper to the external oblique and is the continuation of the internal intercostal muscle. Origin: It attaches to the lumbar fascia, anterior two-thirds of the iliac crest, inguinal ligament (lateral part). Insertion: The lower borders of the lower three ribs, costal cartilages, xiphoid process, the linea alba and the pubic symphisis. The fibres of this muscle run superoanteriorly and medially. Action: Trunk flexion, expiration, compression of the contents of the abdominal cavity. Trunk rotation during contrlateral (unilateral) contraction. Blood supply: Lower posterior intercostal arteries, subcostal artery, superior and inferior epigastric arteries, superficial and deep circumflex iliac arteries, posterior lumbar arteries. Nerve supply: Intercostal nerves (T7- T11), Subcostal nerve (T12). Sensory: Iliohypogastric nerve (L1). 1.4.1.3 The transversus abdominis The transversus abdominis muscle is the innermost muscle of the lateral group. There is transversus abdominis fascia beneath this muscle. Transversus abdominis fascia lies directly on the parietal peritoneum. Origin: It originates from the internal surfaces of the seventh to twelfth costal cartilages, lumbar fascia, iliac crest, lateral third inguinal ligament. Insertion: It inserts into the xiphoid process, linea alba and the pubic crest. Its fibers run horizontally. 3 Action: Expiration. Trunk rotation during contrlateral (unilateral) contraction. Blood supply: Lower posterior intercostal arteries, subcostal artery, superior and inferior epigastric arteries, superficial and deep circumflex iliac arteries. Nerve supply: Intercostal nerves (T7- T11), Subcostal nerve (T12). Sensory: Iliohypogastric nerve (L1). 1.4.2 Anterior group of abdominal muscles 1.4.2.1 The rectus abdominis Origin: Ascends from pubic symphysis, along pubic crest. Insertion: Xiphoid process, costal cartilages from fifth to seventh. 1.4.2.1.1 The rectus sheath Refer to the chapter 1.5 (The rectus sheath) for further details. It is situated inside the rectus sheath, which is formed by fusion and separation of the aponeuroses of the anterolateral abdominal musculature. The aponeurosis of the internal oblique muscle at the lateral margin of the rectus abdominis divides into two layers: anterior and posterior. The anterior layer of the internal oblique muscle and aponeurosis of the external oblique muscle form the anterior wall of the sheath. The anterior layer of the sheath is attached to the rectus muscle at three tendinous intersections (intersectiones tendineae). The posterior layer of the internal oblique muscle and aponeurosis of the transversus abdominis muscle form the posterior wall of the sheath. The posterior wall of the sheath ends at the level of line between the two anterior superior iliac spine, marked by a crescentic border- the arcuate line. Below and behind the rectus abdominis muscle lies only the transversalis fascia and parietal peritoneum. All aponeuroses of the anterolateral abdominal wall musculature form anterior wall. Both walls interlace in the midline to form the tendinous raphe, called the linea alba. Action: The rectus abdominis muscles flex trunk with the external, internal oblique and transversus abdominis. These three muscles also rotate trunk. All of them compress the abdominal viscera and assist the diaphragm during respiration. As the diaphragm contracts and descends during act of inspiration they relax and the viscera accommodate. These muscles assist also during expiration by pulling down the ribs and sternum. In some situations they contract together with the diaphragm (while the glottis is closed) and help in micturition, defecation, vomiting and parturition. Blood supply: Inferior epigastric artery anastomosing with superior epigastric artery. Also contributions from posterior intercostal, subcostal and deep circumflex arteries. Nerve supply: All muscles of the anterolateral abdominal wall are supplied by the inferior six thoracic intercostal nerves, subcostal, iliohypogastricus and ilioinguinalis nerves (last two branches from the lumbar plexus). 1.4.3 Posterior group of abdominal muscles 1.4.3.1 Quadratus lumborum The quadratus lumborum muscle (musculus quadratus lumborum) is an irregularly quadrilateral muscle which is located between the iliac crest, the twelfth rib and transverse process of the lumbar vertebra. 4 Origin: Iliac crest. Insertion: Inferior border of rib 12. Transverse processes of L1-L4. Action: Trunk extension. Stabilization of rib 12. Flexion of trunk (during contrlateral contraction). Blood supply: Lumbar artery, median sacral artery, subcostal artery. Nerve supply: Subcostal nerve, short branches of the lumbar plexus (anterior rami, L1-L4). 1.4.3.2 Psoas major Psoas major is a long fusiform muscle which passes laterally to the vertebral column along pelvic brim, beneath the inguinal ligament to the common tendon with the iliacus muscle. Origin: All transvese processes of the lumbar vertebrae. Insertion: Lesser trochanter of the femoral bone (as iliopsosas tendon). Action: Flexion and medial rotation of the thigh. Flexion of the trunk. Blood supply: Iliolumbar artery (lumbar branch). Nerve supply: Ventral rami of the lumbar spinal nerves. 1.4.3.3 Psoas minor Psoas minor a small, variable muscle which lies anteriorly to the psoas major muscle. Origin: Sides of the 12 thoracic vertebra and the 1 lumbar vertebra. Insertion: Iliopectineal (iliopubic) eminence, pecten pubis. Action: Weak flexion of the trunk. Blood supply: Lumbar arteries. Nerve supply: Branch (anterior ramus) of the first lumbar spinal nerve. 1.4.3.4 Iliacus Iliacus passes under the inguinal ligament laterally to the psoas with which it forms a common tendon. Origin: The upper two-thirds of the iliac fossa. Insertion: Lesser trochanter of the femoral bone. Action: Flexion and medial rotation of the thigh. Flexion of the trunk. Blood supply: Deep circumflex iliac artery, iliolumbar artery, femoral artery, obturator artery. Nerve supply: Femoral nerve (L1-L3). 1.4.3.5 Iliopsoas Iliopsoas is a large, compound muscle consisting of psoas major, psoas minor and iliacus parts. As a main flexor of the hip joint (thus, the lower limb) it will be further discussed in the lower limb lab session. 1.5 The rectus sheath 1.5.1 Superior part (upper ¾) Superior part (above the arcuate line) consists of: 5 Anterior wall formed by: o External oblique aponeurosis o Internal oblique aponeurosis (its anterior layer*) Posterior wall formed by: o Internal oblique aponeurosis (its posterior layer*) o Transverse abdominal muscle aponeurosis *Internal oblique aponeurosis is split into two layers: anterior and posterior. Here, the anterior layer covers the rectus abdominis anteriorly (in the front), and the posterior layer covers the rectus abdominis posteriorly (in the back). Fig. 1.2. Stucture of the superior part of the rectus sheath. Note the layers situated below and above the rectus sheath (e.g. peritoneum, transversalis fascia, superficial abdominal fascia). 1.5.2 Inferior part (lower ¼) Inferior part (beneath the arcuate line) consists of: Anterior wall formed by: o External oblique aponeurosis o Internal oblique aponeurosis (its anterior layer*) o Internal oblique aponeurosis (its posterior layer*) o Transverse abdominal muscle aponeurosis Posterior wall is absent here, with recuts abdominis lying directly on the thin transversalis fascia. *Internal oblique aponeurosis is split into two layers: anterior and posterior as mentioned above. Here, both the anterior and posterior layers cover the rectus abdominis anteriorly (in the front). Fig. 1.3. Structure of the inferior part of the rectus sheath. Note the layers situated below and above the rectus sheath (e.g. peritoneum, transversalis fascia, superficial abdominal fascia). Inside the rectus sheaths penetrate the superior (branch from the internal thoracic artery) and inferior (branch from the external iliac artery) epigastric arteries, adequate veins, terminal part of the inferior intercostal nerves, subcostal vessels. Also, inside the sheaths there may be situated two (each on each 6 side) pyramidal muscles (pyramidal in shape with base down). The pyramidal muscles can be spotted on top of the lower part of the rectus abdominis. 1.6 Fasciae of the abdominal wall Fasciae of the anterolateral wall consist of a superficial and a deep layer. The superficial layer lies under the skin and contains a various amounts of adipose tissue. The deep layer covers the superficial muscles and it is very difficult to separate it from them. Another fascia covers the internal surface of the anterolateral abdominal wall with the parietal peritoneum and is called the transversalis fascia. 1.7 Innervation of the anterolateral abdominal wall The skin, muscles and parietal peritoneum are supplied by the ventral rami of the lower six thoracic nerves (intercostal nerves and subcostal nerve), and also by the iliohypogastricus and ilioinguinalis nerves - branches of the lumbar plexus. They (except last two) pass forward between the internal oblique and transversus abdominis muscle, pierce the posterior wall of the rectus sheath and supply all of the muscles around. Next run through the anterior wall of the sheath and supply the skin too. The iliohypogastricus and ilioinguinalis nerves do not enter the rectus sheath. The first one passes through the aponeurosis of the external oblique and supplies the skin above the inguinal ligament. The second one emerges through the superficial ring and supplies skin below the inguinal ligament. 1.8 Arterial supply of the anterolateral abdominal wall 1. Superior epigastric artery - branch of the internal thoracic artery enters the upper part of the rectus sheath, descends behind that muscle and anastomise with the inferior epigastric artery. 2. Inferior epigastric artery - branch of the external iliac artery, runs upwards and medially, enters the lower part of the sheath, and ascends behind the rectus abdominis muscle, next anastomises with the superior epigastric artery. Both arteries supply the anterior part of the abdominal wall. 3. Between the superficial and deep fascia in front of the aponeurosis of anterolateral muscles ascend two superficial epigastric arteries each on each side, which arise from the right and left femoral arteries. These arteries anastomose with the terminal branches of the lateral thoracic artery. 4. Deep circumflex iliac artery: it is a branch of the external iliac artery, arises just above the inguinal ligament, runs upwards and laterally towards the anterior superior iliac spine and supplies the lateral abdominal wall. 5. Two lower intercostal and four lumbar arteries (branches from descending aorta) pass between the layers of the muscles and supply the lateral part of the abdominal wall. 7 Fig. 1.4. Branches of the external iliac artery and beginning of the femoral artery. Asterisk stands for the cremasteric artery in male or the artery of the round ligament of uterus in female. The border between the iliac and femoral arteries is crossing under the inguinal ligament and passing through the vascular space (ring on the picture). 1.9 Venous drainage of the anterolateral abdominal wall 1. Superficial network of veins radiates out from the umbilicus. It drains above into the lateral thoracic vein into the axillary vein, and below into the femoral vein via the superficial epigastric vein. 2. Around umbilicus are situated the paraumbilical veins, which pass along the round ligament and return blood straight to the portal vein. 3. Superior epigastric vein returns blood into the internal thoracic vein. 4. Deep circumflex iliac and inferior epigastric veins enter the external iliac vein. 5. Posterior intercostal veins drain into the azygos system and the lumbar veins return blood directly into IVC, however these veins are connected. 2 Internal surface of the lower part of the anterior abdominal wall 2.1 Folds of the anterior abdominal wall The peritoneum lining the lower part of the anterior abdominal wall and the transversalis fascia is raised into five folds. 1. Median umbilical fold is placed in median plane and ascends from the apex of the urinary bladder to the umbilicus. It contains the median umbilical ligament, a remnant of the urachus. 2. Right and left medial umbilical fold are located laterally to the median umbilical fold. Each fold contains the medial umbilical ligament (the obliterated part of the umbilical artery). 3. Lateral umbilical folds are situated laterally to the medial umbilical fold. Each of these two folds contains the inferior epigastric artery and vein. 8 2.2 Depressions of the anterior abdominal wall 1. Depression between folds A and B forms the right and left supravesical fossa. 2. Depression between folds B and C forms the medial inguinal fossa. 3. Depression at the lateral side of fold C forms the lateral inguinal fossa, which overlies the deep inguinal ring. The lateral inguinal fossa indicates the place where the processus vaginalis extended into the anterior abdominal wall during the descent of the testis. Depressions lying below the inguinal ligament and medially to the lateral inguinal fossa form the femoral fossa. 2.3 The inguinal triangle The inguinal triangle (of Hasselbach) is an area of potential weakness and, thus, is often the site of a direct hernia. The inguinal triangle is bounded by the: 1. Linea semilunaris - medially 2. Inguinal ligament - inferolaterally 3. Inferior epigastric vessels – superolaterally Fig. 2.1. Posterior view of the internal surface of abdominal wall. I) supravesical fossa, II) medial inguinal fossa, III) lateral inguinal fossa. 9 2.4 Borders of the inguinal canal The inguinal canal is an oblique passage through the lower part of the anterior abdominal wall and is present in both sexes. It is about one and half inches (4 cm) long, runs inferomedially from the deep inguinal ring (hole in fascia transversalis) to the superficial inguinal ring (hole in a aponeurosis of the external oblique), just superiorly and parallelly to the medial half of the inguinal ligament. 2.4.1 Deep inguinal ring The deep inguinal ring is oval shaped opening in the fascia transversalis, which lies about half inch above the midinguinal point. It is formed prenatally, when the processus vaginalis invaginates the transversalis fascia. It is related medially to the inferior epigastric vessels. Above and laterally, the arch fibres of the fascia transversalis bound it. 2.4.2 Superficial inguinal ring The superficial inguinal ring is a triangular shaped aperture in the aponeurosis of the external oblique muscle, which is palpable superiorly and laterally to the pubic tubercle. The pubic crest forms the base of this triangle. On the sides of the triangle are situated the medial and lateral crus which are formed by the aponeurosis of the external oblique muscle. The intercrural fibers from the inguinal ligament superomedially form an arch across the superficial ring. The superficial inguinal ring has: 1. 2. 3. 4. Anterior crus = intercrural fibres (prevent widening of the superficial inguinal ring) Posterior crus = reflected inguinal ligament Lateral crus = lateral fibres of the aponeurosis Medial crus = medial fibres of the aponeurosis 10 Fig. 2.2. Right superficial inguinal ring. 2.4.3 Walls of the inguinal canal The inguinal canal has four walls: 1. Anterior wall: the aponeurosis of the external oblique muscle. 2. Posterior wall: the transversalis fascia. It is reinforced in its medial third by the conjoint tendon (common tendon of the internal oblique and transversus abdominis muscles). 3. Inferior wall: the inguinal ligament and also at the medial end the lacunar ligament. 4. Superior wall: the arching lowest fibers of the internal oblique and transversus abdominis muscle. 11 Fig. 2.3. Walls of the inguinal canal. 2.5 Contents of the inguinal canal The inguinal canal contents differ depending on sex. In male the inguinal canal transmits: 1. 2. 3. 4. 5. 6. 7. Spermatic cord Testicular arteries, each of them arising from abdominalaorta Pampiniform plexus of veins, which coalesces into the testicular veins Vas deferens, the efferent duct of the testes Arteries of the vas deferens, each arising from the internal iliac artery Genital branch of the genitofemoral nerve Branch of the ilioinguinal nerve In female the inguinal canal transmits: 1. Round ligament of the uterus 2. Genital branch of the genitofemoral nerve 3. Branch of the ilioinguinal nerve 12 Fig. 2.4. Transverse section of the abdominal wall. A: median umbilical fold; B: medial umbilical fold; C: lateral umbilical fold; I.E.V: inferior epigastric vessels; R.M. – rectus abdominis muscle, M.U.L: medial umbilical fold, L.U.L: lateral umbilical fold. Clinical comments: We distinguish two kinds of inguinal hernia: indirect (oblique) and direct (straight). The indirect hernia is located within the whole inguinal canal. The indirect hernia passes the deep and superficial inguinal ring of inguinal canal. It is most common type of hernia (80% of inguinal hernia). The direct hernia passes through the inguinal triangle. It passes only through the superficial inguinal ring. 3 The peritoneum and peritoneal cavity 3.1 The peritoneum The peritoneum is a thin, serosus membrane which consists of a layer of sqamosus epithelium and divides into two parts: 1. Parietal peritoneum - lining the abdominal walls. 2. Visceral peritoneum - enclosing the abdominal viscera. A double-layer fold of peritoneum, which encloses an organ to the abdominal wall, is called a mesentery. The mesenteries are continuations of the visceral and parietal peritoneum. The mesenteries are formed by back-to-back layers of reflected peritoneum. They provide nerves and blood vessels to the viscera. These nerves, blood and lymph vessels and sometimes secretory ducts of glands are placed between layers of mesenteric peritoneum, thus they have no direct contact with peritoneal cavity. All viscera, which are covered around by peritoneum and fixed to the posterior abdominal wall by mesentery are situated intraperitoneally. Some viscera, which have not any mesentery, are situated extraperitoneally. Extraperitoneal viscera can be classified further as retroperitoneal and infraperitoneal. 1. Retroperitoneal are situated behind peritoneum. 2. Infraperitoneal are situated under peritoneum. 13 According to complicated development of relations within embryonic cavity of body all viscera of abdominal and pelvic cavities in adult can be divided as follows: 1. Primarily intraperitoneal: organs which have always had their mesentery (e.g. jejunum, ileum, spleen). 2. Secondarily intraperitoneal: organs which have acquired mesentery during development (e.g. ovaries and uterine tubes). 3. Primarily extraperitoneal: organs which have never had mesentery (e.g. kidneys with ureters, suprarenal glands). 4. Secondarily extraperitoneal: organs which have lost their mesentery during development (e.g. almost whole duodenum, ascending and descending colon, pancreas). Fig. 3.1. Stages of development of secondarily intraperitoneal organ. Fig. 3.2. Development of secondarily extraperitoneal organ. 3.2 Mesenteries 14 Fig. 3.3. Transverse sections through primitive abdominal cavity (coeloma); left: on a level of duodenum; right: beneath duodenum. 3.2.1 Dorsal mesentery The dorsal mesentery persists throughout embryonic development and adult life. It suspends the entire abdominal gut from the posterior body wall (even in regions where the gut becomes secondarily retroperitoneal – as a secondary parietal peritoneum). The dorsal mesentery has following portions: 1. 2. 3. 4. 5. 6. 7. 8. Gastrophrenic ligament Gastrosplenic ligament Phrenicosplenic ligament Greater omentum Mesentery proper Mesoappendix Transverse mesocolon Sigmoid mesocolon 15 Fig. 3.4. Peritoneum of the upper part of the abdominal cavity. Fig. 3.5. Peritoneum of the left abdominal wall. 16 3.2.2 Ventral mesentery The ventral mesentery originates only in the superior part of abdominal cavity. Its inferior margin is attached to the umbilical region on the anterior abdominal wall and to the superior part of the duodenum posteriorly. The ventral mesentery has following portions: 1. Lesser omentum, which is formed by: a. Hepatoesophageal ligament b. Hepatogastric ligament c. Hepatoduodenal ligament 2. Coronary ligament 3. Left and right triangular ligaments 4. Falciform ligament 5. Round ligament of liver 6. Median umbilical fold 3.3 Peritoneal fold The peritoneal fold is a reflection of peritoneum, it covers for instance: the inferior epigastric vessels of the lateral abdominal wall. 3.4 Peritoneal recess The peritoneal recess is a tubular cavity, which is closed at one end and communicates freely with the rest of the peritoneal cavity on the other end. 3.5 Peritoneal ligament The peritoneal ligament. Is a double layer of peritoneum which connects two organs or organ with abdominal wall. It can contain blood vessels or other structures (biliary duct). 3.6 Lesser omentum The lesser omentum is attached to the stomach and part of the duodenum on the one end and to the liver on the other. It is a part of the ventral mesentery primarily placed behind the liver. Vide supra for parts of the lesser omentum. The lesser omentum (actually the hepatoduodenal ligament) contains: 1. Hepatic artery 2. Portal vein 3. Biliary duct The lesser omentum seperates the omental bursa from the rest of the abdominal cavity. 3.7 Greater omentum The greater omentum hangs down like an apron between the intestines and the anterior abdominal wall and consists of various amount of adipose and lymphatic tissue. It connects the stomach with the transverse colon and is built of four layers of dorsal mesentery usually grown into one. 17 3.8 Peritoneal cavity The space between the parietal and visceral peritoneum is called the peritoneal cavity. Capillary layer of the serous fluid can be found in the peritoneal cavity (peritoneal fluid as it is secreted by the peritoneum). It provides a lubricating film for parietal and visceral surfaces and facilitates free mobility of the viscera with minimal friction. The peritoneal cavity is the largest cavity of the human body and it has two sacs: 1. Greater sac 2. Omental bursa (lesser sac) The lesser and greater sacs are subdivisions of the peritoneal cavity separated by folds of peritoneum. The greater sac is also referred to as the general peritoneal cavity and forms greater part of this potential space. The peritoneal cavity can be divided into supracolic, infracolic and pelvic departments. The lesser sac represents the primitive right cavity of the coeloma. 3.8.1 Omental bursa (lesser sac) The omental bursa is situated: 1. Behind the stomach, 2. In front of the posterior abdominal wall The omental bursa has two parts: 1. Vestibule of the omental bursa which is located behind the lesser omentum. 2. Proper omental bursa that is located behind the posterior surface of the stomach. The omental bursa has three recesses: 1. Inferior recess - on the superior edge of the greater omentum, 2. Superior recess - between the inferior vena cava and caudate lobe of the liver. 3. Lienal recess - between the gastrolienal and lienorenal ligaments. The omental bursa has communication with the greater sac through an oval shaped window, the epiploic foramen. The epiploic foramen is bounded by two veins (caval & portal) and two organs (liver & duodenum), with following detailed boundaries: 1. Posteriorly – the inferior vena cava (covered by peritonum) 2. Anteriorly – the hepatoduodenal ligament with its all elements: a. Hepatic portal vein, b. Common bile duct c. Hepatic artery. 3. Superiorly – the caudate lobe of the liver. 4. Inferiorly – the superior duodenum. Clinical comments: The epiploic foramen is a potential place for intra-abdominal herniation. 18 Fig. 3.6. Anterior aspect of omental bursa situation. 19 Fig. 3.7. Sagittal section through the lesser sac. 20 3.8.2 Development of the omental bursa (lesser sac). Fig. 3.8. First stage of omental bursa forming. Fig. 3.9. Second stage of omental bursa forming. 21 Fig. 3.10. Third stage of omental bursa forming; development of greater omentum. 3.8.3 Peritoneal relations of organs of the abdominal cavity Organ Stomach Liver Pancreas Duodenum, 1st part Duodenum, 2nd, 3rd & 4th part Jejunum Ileum Cecum, terminal part Cecum, body Appendix Ascending colon Transverse colon Descending colon Sigmiod colon Rectum Relation Intraperitoneal Intraperitoneal Secondairly retroperitoneal (except tip of tail) Intraperitoneal Secondairly retroperitoneal Intraperitoneal Intraperitoneal Intraperitoneal Secondairly retroperitoneal Intraperitoneal Secondairly retroperitoneal Intraperitoneal Secondairly retroperitoneal Intraperitoneal Retroperitoneal 22 3.9 Development of the peritoneal cavity The primitive gut is divided into three parts: 1. Foregut: supplied by the coeliac artery. 2. Midgut: supplied by the superior mesenteric artery. 3. Hindgut: supplied by the inferior mesenteric artery. Fig. 3.11. Starting point for the rotations of primitive gastrointestinal tract: lateral view and coronary section. The foregut comprises future stomach and duodenum. Between layers of the ventral mesentery the liver develops as well as the gallbladder, the bile duct and ventral part of future pancreas. Within the dorsal mesentery at this level the dorsal pancreas is placed. Secretory ducts open to the loop of the foregut (duodenal loop). The midgut or the primitive intestinal loop gives origin to the small intestines, caecum, ascending colon and right two thirds of the transverse colon. At the apex of the loop there is an opening of the vitellointestinal duct. Its vestige forms ileal (Meckel's) diverticulum after redution of physiological umbilical hernia. The caudal border of blood supply given by the superior mesenteric artery is also the caudal border of the vagal innervation. The hindgut develops into the left third part of transverse colon, descending colon, sigmoid and rectum. 23 The primitive alimentary tract is attached to the abdominal walls by the ventral mesentery (to the anterior wall) and dorsal mesentery (to the posterior wall). Ventrally there is the mesentery only in the foregut region and it is attached to the abdominal wall above the umbilicus. Fig. 3.12. First stage of development of the stomach. Fig. 3.13. Forming of the greater omentum from the dorsal mesentery. 3.9.1 Rotation of the foregut The stomach undergoes accelerated growth in its dorsal part to produce the greater curvature. Differential growth pulls the mesogastrium to the left and produces the greater omentum. 1. Rotation of the stomach (90 degrees). The left surface of the stomach becomes the antero-superior and the right surface becomes the postero-inferior. Compare relations of the vagus nerve in the thoracic part and abdominal part. Most of the anterosuperior surface of the stomach is supplied by 24 vagal fibers coming from the left vagus nerve and most of the posteroinferior gastric surface from the right one. The right cavity of coeloma on a level of the stomach forms the omental bursa, which communicates with the greater sac by the epiploic foramen. 2. Rotation of a C-shaped loop of the duodenum (90 degrees). After this rotation the primitive dorsal mesentery of the duodenum lies against the posterior abdominal wall (except the first portion) and becomes secondarily retroperitoneal because the mesoduodenum fuses with the parietal peritoneum of the posterior wall. 3.9.2 Rotation of the midgut 3.9.2.1 First stage The first stage of rotation of the primary intestinal loop (midgut) is connected with a physiological umbilical herniation (6th-9th week). The abdominal cavity becomes temporarily too small for the developing gut because of the rapid hepatic and intestinal growth. The primary intestinal loop rotates 90 degrees counter clockwise around an axis provided by the superior mesenteric artery and the omphalomesenteric vitelline duct. In this stage the cranial limb of the primary intestinal loop comes to lie on the right and the caudal limb on the left side. Next primary intestinal loop rotates 90 degrees and at this stage produces “situs inversus” of the large intestine (the caecum develops in the superior part of the abdominal cavity). Fig. 3.14. Relations after 180 rotation around superior mesenteric artery. 3.9.2.2 Second stage The second stage of rotation of the primary intestinal loop is a result of the slower growth of the liver while the abdominal cavity becomes larger. Now, during the tenth week, the umbilical herniation is completely withdrawn. The jejunum is withdrawn first and the cranial limb of the primary intestinal loop develops intensively below its caudal limb. The caecum tends to lie to the right just below the liver. The caudal limb of the primary intestinal loop is withdrawn last. The primary intestinal loop lies now anteriorly. 25 Fig. 3.15. Relations after 270 rotation around superior mesenteric artery. 3.9.2.3 Third stage The third stage is connected with the development of the caecal regions. In this stage the appendix develops. The ascending and descending mesocolon fuse with the parietal peritoneum and these parts become the secondarily retroperitoneal. The dorsal mesogastrium grows and fuses with itself forming the greater omentum. Now, the greater omentum fuses with the transverse mesocolon and forms the gastrocolic ligament. 26 Fig. 3.16. Final effect of developmental changes in the abdominal cavity. 27 28 Fig. 3.17. Descending colon as the secondarily retroperitoneal organ, with fig. 4.2 repeated for comparison. 4 Extraperitoneal space The extraperitoneal space lies within the scope of both abdomen and pelvis part of the anatomy course. It is described in the “Pelvis, perineum and extraperitoneal space” part of lab sessions. 5 Gastrointensinal tract 5.1 The stomach The stomach is the J-shaped part of the alimentary tract that occupies the epigastric and umbilical regions of the abdomen. It has two openings: the cardiac orifice where the abdominal part of oesophagus enters and the pyloric orifice which is guarded by the pyloric sphincter controlling the rate of discharge of stomach contents into the duodenum. 5.1.1 Subdivisions of stomach The stomach consists of four parts: 1. Fundus is the rounded uppermost part above the level of the oesophageal junction, projects above and to the left of cardiac orifice, and is related to the diaphragm (in most radiograms of the stomach this region appears empty, but it is full of air) 2. Cardia - cardiac portion is located in the close vicinity of the oesophagus, around the orifice. This opening receives the oesophagus and is called the cardiac orifice of the stomach. The cardiac notch (incisura cardiaca) is the notch between the fundus and oesophagus. 3. Body of the stomach constitutes the major portion of the stomach, which is located below the fundus. 4. Pyloric part, the pylorus is the terminal part of the stomach and it forms the opening into the duodenum - the pyloric orifice. The pyloric part is further subdivided into: a. Pyloric antrum with its angular incisura. b. Pyloric canal (narrow part, which separates the rest of the stomach from duodenum). c. Pyloric sphincter. Fig. 5.1. Pyloric region. 29 5.1.2 Curvatures The stomach has two curvatures: 1. The greater curvature: extends from the left of the oesophagus around the fundus to the pylorus. It forms the left border of the stomach and gives attachment to the gastrosplenic and gastrocolic ligaments. 2. The lesser curvature: is the right border and extends from the right oesophagus to the pylorus. 5.1.3 Surfaces The stomach has two surfaces: 1. The anterior surface has three zones: a. Zone of the liver left lobe b. Zone of the diaphragm c. Zone of the abdominal wall contact 2. The posterior surface is separated by omental bursa from: a. Zone of the diaphragm (bare area) b. Zone of the pancreas c. Zone of the spleen d. Zone of the left kidney e. Zone of the left suprarenal gland f. Zone of the transverse mesocolon & colon Fig. 5.2. Anterior surface of the stomach. 30 Fig. 5.3. Posterior surface of the stomach. 5.1.4 Ligaments The stomach has four ligaments: 1. 2. 3. 4. Hepatogastric ligament: ventral mesenterium Gastrophrenic ligament: dorsal mesenterium Gastrosplenic ligament: dorsal mesenterium Gastrocolic ligament: dorsal mesenterium 31 Fig. 5.4. Ligaments of the stomach. *The hepatocolic ligament is inconstant. 5.1.5 Relations Relations of the stomach to vertebral column: 1. Cardiac portion - on the level of the vertebra T10 2. Pylorus - on the level of the vertebra L1 The stomach is related to other viscera in the following way: 1. Anteriorly to the left costal margin, left pleura, lung, diaphragm and left lobe of liver. 2. Posteriorly it is related to the lesser sac (omental bursa – empty and thin pocket), and also it is related to the diaphram, spleen, left renal, left adrenal and transverse mesocolon. 3. Pylorus also contacts the inferior region of the quadrate lobe and the neck of the gall blader. The outermost layer is formed by the visceral peritoneum, which completely covers the stomach and leaves it's curvatures as omenta (lesser and greater). The stomach is also connected with the spleen by the gastrosplenic ligament (it contains the left gastroepiploic vessels) and with the diaphragm. 5.1.6 Muscular wall The muscular wall of the stomach is composed of three muscular layers: 1. Outer layer – longitudinal 2. Middle layer – circular. This layer forms the pyloric sphincter 3. Inner layer – oblique The innermost layer of the stomach wall is formed by mucous membrane with numerous folds. 32 5.1.7 Arterial supply of the stomach The arterial supply of the stomach consists mainly of two arterial arches: one on the lesser curvature and one on the greater curvature. The arterial arch on the lesser curvature is composed of: 1. Left gastric artery: branch from the celiac trunk. It passes along the lesser curvature downwards from the left. 2. Right gastric artery: branch from common (or proper, or left) hepatic artery. It passes along lesser curvature too, and anastomises with the left gastric artery. Another arterial arch is formed on the greater curvature (between layers of greater omentum) by junction of two arteries: 1. Left gastro-omental artery (left gastroepiploic artery): branch from splenic artery. Runs downwards along the greater curvature. 2. Right gastro-omental artery (right gastroepiploic artery): branch from gastroduodenal artery. Runs upwards. 3. The short gastric arteries: arise from splenic artery and pass between layers of the gastrosplenic ligament. Fundus of the stomach is supplied by these arteries. Fig. 5.5. Blood supply of the stomach. Splenic artery goes behind the stomach. 5.1.8 Venous drainage of the stomach The gastric veins lie together with the adequate arteries and all of them, just like all veins which drain the abdominal viscera return blood into the portal vein circulation. The right and left gastric veins join directly the portal vein, whereas the short gastric veins and the left gastro-omental vein (left gastroepiploic vein) drain into the splenic vein. The right gastro-omental vein (right gastroepiploic vein) joins the superior mesenteric vein. 33 5.1.9 Lymphatic drainage of the stomach The right and left gastric lymphatic nodes are situated just like adequate blood vessels and returns lymph into the coeliac nodes. The left and right gastroepiploic nodes drain lymph from the left part of the stomach. First group returns lymph into the splenic nodes around the splenic blood vessels. The second group drains into the pyloric lymph nodes. 5.1.10 Innervation of the stomach The parasympathetic fibres are derived from the anterior and posterior vagal trunks (formed by left and right vagus). The sympathetic fibres are derived from the celiac plexus (arise from T5-T8 segments). 5.2 Small intestine The small intestine occupies the greater part of the abdominal cavity by extending about 6.4 m between the pylorus and ileocecal junction. Physiological processes of secretion, digestion and absorption take place within this structure. Among other functions it also plays important role in immunological response to foreign organisms, viruses and substances. The small intestine has three parts: 1. Duodenum 2. Jejunum (length: 2.5 m) 3. Ileum (length: 3.7m) 5.2.1 Duodenum The duodenum, C-shaped part of the alimentary tract, courses around head of the pancreas and is the first and shortest portion of the small intestine. It is the widest and most fixed of three parts. It is divided into four segments and is located in the epigastric and umbilical regions of the abdomen on the posterior abdominal wall. The first three parts of the organ enclose the head of the pancreas while the fourth segment becomes continuous with the jejunum. Near the pylorus and duodenojejunal flexure, the surface is completely covered by the peritoneum; the remainder of the duodenum is retroperitoneal and relatively immobile. The organ measures about 24 cm. 5.2.1.1 Parts (segments) of the duodenum For convenience of description the duodenum is divided into four parts. 5.2.1.1.1 First duodenal segment First duodenal segment (at level L1) about 5 cm (2 inches) long is called also ampulla or bulb. The 1st part of the duodenum begins at the pylorus, in the transpyloric (subcostal) plane. This part has mesentery, is situated interaperitonealy. It is the most mobile part of duodenum. The first 2 cm has similar peritoneal relations to the stomach. The lesser omentum passes from the upper border and the greater omentum from the lower. The hepato-duodenal ligament is attached to the bulb. It is related to: 1. Frontally - quadrate lobe of the liver, gallbladder; 2. Posteriorly - common bile duct, hepatic artery and portal vein; 3. Below - head of pancreas 34 5.2.1.1.2 Second duodenal segment The second duodenal segment - descending part, descends from level L1 to L3, has no mesentery and just like the next two parts is located retroperitonealy. It is penetrated by the common bile and pancreatic ducts which pour their contents into the duodenum at the major duodenal papilla, which is guarded by the sphincter of hepatopancreatic ampulla. Sometimes the pancreatic duct ends as minor duodenal papilla. It is related to: 1. Anteriorly - transverse colon, liver and gallbladder 2. Posteriorly - right kidney and it's vessels, right suprarenal gland, IVC 3. Medially - head of the pancreas Fig. 5.6. Inner left surface of the descending part of duodenum. Fig. 5.7. Schematic drawing of ducts opening into the duodenum. 5.2.1.1.3 Third duodenal segment The third duodenal segment - horizontal part - level L3 - lies horizontally from the right to the left across L3 vertebra. The 3rd part of the duodenum lies on the head and uncinate process of the pancreas. 35 It crosses posteriorly: 1. 2. 3. 4. 5. 6. Right ureter Right psoas major muscle Testicular (or ovarian) artery Inferior vena cava Aorta Inferior mesenteric artery It is crossed anteriorly by: 1. Superior mesenteric artery 2. Superior mesenteric vein 3. Root of the mesentery 5.2.1.1.4 Fourth duodenal segment Fourth duodenal segment - ascending part runs upward from L3 to the left at the level of L2 and curves upwards along the left side of the aorta and the head of the pancreas on the left psoas major. It crosses over: 1. Psoas major muscles 2. Gonadal vessels 3. Sympathetic trunk It joins the jejunum at the duodenojejunal flexure on the level of the second lumbar vertebra and superiorly to that is situated the body of the pancreas and medially is the head of the pancreas. The duodenojejunal flexure is sometimes supported by a muscular slip - the suspensory muscle of the duodenum which comes from the right crus of the diaphragm. The suspensory ligament is a surgical landmark, it holds the ascending portion in place. Small peritoneal recesses are found on the left side of the 4th part of the duodenum and behind the adjacent part of the inferior mesenteric vein. 5.2.1.2 Arterial supply of the duodenum Arterial supply to the duodenum is from two sources. The upper half of the duodenum is supplied by the superior pancreaticoduodenal artery (from the gastroduodenal artery). The lower part is supplied by the inferior pancreaticoduodenal artery, which both arise from the superior mesenteric artery. These vessels anastomise and form anterior and posterior arcades, which are located between duodenum and pancreas. 1. Celiac trunk supplies the proximal duodenum: a. Right gastric artery b. Supraduodenal artery c. Gastroduodenal artery d. Retroduodenal arteries e. Anterior superior pancreaticoduodenal artery f. Posterior superior pancreaticoduodenal artery 2. Superior mesenteric artery supplies the distal duodenum: a. Anterior inferior pancreaticoduodenal artery b. Posterior inferior pancreaticoduodenal artery The anterior and posterior superior pancreaticoduodenal arteries anastomise with anterior and posterior branches of the inferior pancreaticoduodenal artery and form anterior and posterior arterial arches 36 around head of the pancreas. These arches are called the anterior and posterior pancreaticoduodenal arches. Fig. 5.8. Blood supply of the duodenum and the head of pancreas. 5.2.1.3 Venous drainage of the duodenum All veins draining the duodenum are tributaries of the portal vein system, mostly through the superior mesenteric vein. All veins follow corresponding arteries except the prepyloric vein, which ascends anteriorly to the pylorus and drains into the right gastric vein. It exactly marks the gastroduodenal junction. 5.2.1.4 Lymphatic drainage of the duodenum The anterior lymph vessels drain superiorly to the pancreaticoduodenal lymph nodes along the splenic artery and vein. From the lower part of the anterior surface, lymph is returned to the pyloric lymph nodes. Efferent vessels pass to the celiac lymph nodes. 5.2.2 The midgut (jejunum & ileum) The small bowel is supported by the mesentery proper and is situated below the transverse colon mainly in the central abdomen. The inferior part may extend into the pelvis. The peritoneal portion of the small bowel averages 7 m, varying 5 - 11 m. The jejunum is the upper two-fifths of the small intestine. We can't identify clearly the border between jejunum and ileum. There is gradual change from one part to the other. The jejunum and ileum share blood supply, innervation, mesenteric support and functions. The small intestines are attached to the posterior abdominal wall by the mesentery and between two layers of peritoneum pass jejunal, illeal blood vessels, lymphatic vessels, nerves, also fatty tissue. Thanks to the 37 mesentery, loops of jejunum and ileum are very mobile, except proximal and distal parts (shorter mesentery). The space, where the visceral peritoneum is continuous with the parietal peritoneum is called the root of mesentery. The root of mesentery is 15 cm long and extends from left side L2 to the right sacroiliac joint. It crosses posteriorly: 1. 2. 3. 4. 5. 6. Horizontal part of duodenum Abdominal aorta IVC Right psoas major muscle Right ureter Right testicular or ovarian vessels. Localisation Diameter Linear measures Wall Vascularisation Arcades Arteriae rectae Fat in mesentery Plicae circulares Peyer's patches Jejunum the left lateral region of abdominal cavity 2 - 4 cm two-fifths thick, heavy greater large loops, few long less well developed few Ileum the pelvic cavity 2.5 - 3 cm three-fifths thin, light less short loops, many short more rudimentary many Fig. 5.9. Distinguishing characteristics of the jejunum and ileum. 38 Fig. 5.10.Comparison of jejunum and ileum. 5.2.2.1 Arterial Supply of Jejunum and Ileum All blood is coming to jejunum and ileum through the branches of the superior mesenteric artery, which arises from abdominal aorta at a level of L1 vertebra, 1 cm below the coeliac trunk. The superior mesenteric artery subdivides into many branches: jejunal and ileal arteries, which forms arches called arterial arcades. There are lots of anastomoses between blood vessels, which are formed by three levels of arterial arcades. Straight vessels arise from these arcades and since then there are no anastomoses between them. They pass to the visceral border of the mesentery. 39 5.2.2.2 Venous drainage of jejunum and ileum The superior mesenteric vein drains all blood from jejunum and ileum. It runs with the corresponding artery in front to the root of the mesentery and unites with the splenic vein to form the portal vein. 5.3 The coeliac trunk The celiac trunk is a short (about 1 cm), thick trunk which arises from the anterior surface of the aorta (level L1) and divides immediately into three branches: 1. Left gastric artery the smalles tone, passes upward to the left, next to the cardiac orifice of the stomach, runs downwards along the lesser curvature and anastamoses with the right gastric artery. 2. Common hepatic artery runs upward and to the right to the pyloric part of the stomach, next runs between the layers of the lesser omentum to the liver. It gives off: a. Right gastric artery b. Gastroduodenal artery c. Hepatic artery proper 3. Splenic artery - the biggest one, passes horizontally to the left, behind the peritoneum along the upper border of the pancreas and supplies it. This branch gives off: a. Short gastric arteries b. Left gastroepiploic (gastro-omental) artery anastomises with right gastroepiploic (gastroomental) artery (from the gastroduodenal artery) on the lesser curvature. 5.4 The superior mesenteric artery The superior mesenteric artery, next unpaired branch, arises also from the anterior surface of the aorta 1 cm below coeliac trunk at the level lower 1/3 of L1. It runs forwards between the pancreas and first part of duodenum (crosses in front of that), descends between layers of mesentery to the right iliac fossa. From the superior mesenteric artery arise: 1. 2. 3. 4. 5. Inferior pancreaticoduodenal artery Jejunal and ileac arteries Ileocolic artery Right colic artery Middle colic artery Branches from the superior mesenteric artery supply: a part of the duodenum, all the small intestine, the large intestine until right two-thirds of the transverse colon. 40 Fig. 5.11. Blood supply given by the superior mesenteric artery. 5.5 The large intestine (large bowel) The large intestine is subdivided into: 1. Caecum with appendix 2. Colon (ascending, transverse, descending and sigmoid) 3. Rectum The length of the large intestine, from cecum to anus, can vary between 100 to 200 cm with a normal length of about 150 cm. The large intestine consist of: 1. Caecum 2. Vermiform appendix (*) 3. Ascending colon 41 4. 5. 6. 7. 8. Descending colon Transverse colon Sigmoid colon Rectum (*) Anal canal (*) The above parts except indicated by the asterisk (*) are characterized by: 1. Fat-filled tags over its surface, 2. Three bands of the teniae coli - the longitudinal layer of muscle layer, 3. The haustra which are sacculated wall of the bowel. 5.5.1 Caecum The blind pouch of caecum measuring 6 cm in length and 8 cm in diameter lies superficially to the iliopsoas muscle within the right iliac fossa. The cecum is usually enveloped by the peritoneum, but mesentery is not present. The vermiform appendix projects from the dorsomedial aspect of the pouch while the ileocecal valve, the ileocecal orifice occurs on the medial side of the cranial portion of the cecum. Clinical comments: Localisation of the original point of the vermiform appendix in the projection on the abdominal wall: 1. Mc Burney's point - half of the diameter between the anterior superior iliac spine and umbilicus. 2. Lanza's point - left 1/3 of the diameter between the right and left anterior superior iliac spine. 5.5.2 Colon 5.5.2.1 Ascending colon The ascending colon is located in the right lumbar region. This segment represents a specific region of the colon which projects superiorly for 15-20 cm between the cecum and the inferior surface of the liver and laterally to the gallbladder. Right colic flexure is located at level of L2 and sixth right rib. Right colic flexure is connected sometimes with the liver by the hepato-colic ligament. Impression of the right colic flexure is marked on the visceral surface of the liver. 1. Anterior surface and partly sides of the ascending colon are covered by: a. Peritoneum b. Midgut 2. Posterior aspect of the ascending colon is related to: a. Right kidney b. Iliacus muscle c. Quadratus lumborum muscle 3. Medial aspect is related to: a. Partly to the psoas major muscle b. Midgut 4. Posterior aspect of the ascending colon is related to the lateral wall of the abdominal cavity. 42 Fig. 5.12. The right colic flexure and features of the colon. 5.5.2.2 Transverse colon In distance of about 30 cm from the right colic flexure the transverse colon passes to the splenic or left colic flexure. The real lenght of that part of the clolon is bigger then the distance between the both flexures (40 to 50 cm), because the middle part of the transverse colon bends inferiorly with the apex of the curvature sometimes reaching the cavity of the true (lesser) pelvis. The left colic flexure is connected to the diaphragm by the phrenicocolic ligament which supports the spleen at the level of the eleventh left rib. There is also the gastrocolic ligament between the stomach and the transverse colon. The diameter of the transverse colon is smaller than that of the ascending segment. 1. Cranially, the transverse colon relates to, from right to left: a. Liver b. Gallbladder c. Stomach d. Spleen 2. Posterior aspect of the ascending colon is related to: a. Descending part of the duodenum 43 b. Head of the pancreas c. Left kidney 3. Anterior surface of the tube is covered by: a. Major omentum 4. Inferior aspect of the ascending colon is related to: a. Midgut 5.5.2.3 Descending colon The third part or descending segment of the colon (colon descendens) passes inferiorly 28 cm along the left hypochondriac, lateral and inguinal regions between the left colic flexure and the pelvic brim. 1. Anterior border, medial and lateral side of the organ are related as the ascending colon (see above). 2. Posterior aspect is free of peritoneum and relates to: a. Left kidney b. Diaphragm c. Three muscles of the posterior abdominal wall (quadratus lumborum, partly psoas major and iliacus). 5.5.2.4 Sigmoid colon The sigmoid colon is S-shaped. It begins at the point where the descending colon crosses the medial aspect of psoas major muscle and the external iliac vessels. This fourth part of the colon descends about 40 cm to the level of the vertebrae S3. The sigmoid descends along the left pelvic wall to reach the pelvic floor where it passes almost horizontally to the right. The junction of the two segments constitutes the narrowest part of the colon. The sigmoid colon relates to: 1. Pelvic coils of ileum 2. Urinary bladder 3. Uterus (in women) The sigmoid mesocolon encircles this peritoneal fold that attaches it to the pelvic wall. 44 Fig. 5.13. The sigmoid colon and folds of its mucous membrane which can be observed in sigmoidoscopy. 5.5.3 Rectum The rectum is this segment of the large intestine which projects 12 to 14 cm between the sigmoid colon (at S3) and anus. The rectum is divided into two parts: rectal ampulla and anal canal. 5.5.3.1 Rectal ampulla The rectal ampulla is a dilatation of the rectum and is located just superiorly to the pelvic diaphragm. The rectum passes through a hiatus in the pelvic diaphragm formed mainly by the levator ani muscle to become the anal canal. Peritoneum covers the front and sides of the upper part of rectum and only the front of the middle part. The lower rectum is free of a peritoneal lining since peritoneum swings anteriorly over the bladder in male, and over the back of the vagina and uterus in female. In addition, the rectum is also free of taeniae coli. 5.5.3.2 Anal canal The anal canal The 3 cm long anal canal extends between the pelvic diaphragm (levator ani muscle) and the external aperture known as anus. The anorectal junction at the level of the pelvic diaphragm (S3) is marked by the presence of the muscular sling of the puborectalis muscle around its posterior surface. Inferiorly to the levator ani muscle, the anal canal is surrounded by the musculature of the external anal sphincter. Internal sphincter - this involuntary muscle is a continuation of the circular muscle coat of the rectum. It surrounds the upper two-thirds of the anal canal and is innervated by the pelvic plexus. Sympathetic stimulation contracts the muscle. External sphincter - this encircles the lower two-thirds of the anal canal and is arranged in the deep, superficial and subcutaneous parts (from above downwards). o Deep part - surrounds the middle part of the anal canal. It has no bony attachment but is reinforced by the fibres of levator ani. Functionally this is an essential part of the anal sphincter. 45 o Superficial part - surrounds the lower part of the anal canal. It is attached to the anococcygeal body posteriorly and the perineal body anteriorly. o Subcutaneous part - this is a thick ring of muscle surrounding the anal orifice. 5.5.3.3 Topographical relations The relations of the rectum in the two sexes are as follows: M F Coils of ileum Coils of sigmoid Rectovesical pouch Rectouterine pouch Fundus of urinary bladder Seminal vesicles Ducti deferentes Prostate (dorsal aspect) Sacrum Piriformis muscle Sacral plexus of nerves Sympathetic trunk + + + + + + + + + + + + + + + + + + The relations of the anal canal in the two sexes are as follows: M F Perinea body Bulb of penis Vagina (cauda) Puborectalis m. Fat (ischioanal fossa) + + + + + + + + 5.6 Inferior mesenteric artery The inferior mesenteric artery projects from the aorta at the level of L3, passes downwards to the left iliac fossa and supplies: one-third part of the transverse colon, descending colon, sigmoid, superior part of the rectum. 5.6.1 Branches of inferior mesenteric artery It gives off following branches: 1. Left colic artery anastomises with the middle colic artery to supply the transverse colon 2. Two sigmoid arteries 3. Superior rectal artery 46 Fig. 5.14. The inferior mesenteric artery and organs supplied by it. 5.7 Liver The liver, the largest organ of the body, is the center of metabolic processes. It is supplied with blood from the portal vein (unoxygenated, sometimes nutrient - rich and toxic) and the hepatic artery (oxygenated). The blood drains to the hepatic vein, and then to the inferior vena cava. The liver secretes bile to the biliary tree. The bile is formed by the bile pigments (breakdown products of haemoglobin) and the bile salts, that aid in digestion by emulsification of the fats. The normal adult organ weighs about 3 pounds (1.5 kg) in male and slightly less in female (1.3 kg). The liver rests in the right hypochondriac and epigastric regions of the abdomen, extending frequently into the left hypochondrium. The greater part is situated under cover of the ribs and costal cartilages (level of T9 - L2) and is also in contact with the diaphragm. The upper surface is convex, modelled to undersurface of the domes of the diaphragm. The visceral surface (postero-inferior) is modelled by the adjacent viscera and is irregular in shape. It contacts with the oesophagus, stomach, duodenum, right colic flexure, right kidney, right suprarenal gland and gallbladder. 5.7.1 Surface of the liver The liver is wedge-shaped and has two surfaces: 47 1. Diaphragmatic surface is divided into: a. Superior surface b. Posterior surface (bare area) c. Right lateral surface 2. Visceral or inferior surface has h-shaped fissure of the liver. It is divided into three lines: two sagittal and one transverse (the porta hepatis) a. Left sagittal line (the interlobar fissure) contains: i. Fissure for the round ligament ii. Fissure for the ligamentum venosum b. Right sagittal line contains: i. Fossa for gallbladder - anteriorly ii. Groove for the inferior vena cava - posteriorly c. The porta hepatis contains: i. Portal vein ii. Common hepatic duct iii. Hepatic artery proper All elements of the porta hepatis are located in the hepatoduodenal ligament as the hepatic pedicle in the following order: 1. Portal vein lies posteriorly to the common hepatic duct & the hepatic proper artery. 2. Common hepatic duct and the common bile duct lies anteriorly and to the right. 3. Hepatic proper artery lies anteriorly and to the left. 5.7.2 Lobes of the liver The liver has four lobes: 1. Right lobe, the largest lobe of the liver, forms about 2/3 of the entire organ. The right and left lobes function separately. 2. Left lobe, much smaller than the right, forms only about 1/3 of the entire organ. In situ it appears significantly thinner and flattened from above downwards. 3. Quadrate lobe is below the porta hepatis and between the round ligament & the gallbladder. The quadrate lobe is functionally part of the left lobe because it receives blood from the left hepatic artery and drains into the left hepatic duct. The quadrate lobe is located on the anterior and inferior aspect of the organ where it is bordered by the fossa for the gallbladder, on the right, ligamentum teres, on the left, and the porta hepatis, posteriorly. 4. Caudate lobe lies between the interlobal fissure and the inferior vena cava, above the porta hepatis. It communicates with the right lobe by the caudate process but is functionally part of the right and left lobes because it receives blood from the right and left hepatic arteries and drains into the right and left hepatic duct. The right and the left lobe are separated by: 1. Round ligament 2. Groove of the inferior vena cava 3. Fissure for the ligamentum venosum The liver is made up of liver lobules. The central vein of each lobule is tributary of the hepatic veins. In the spaces between the lobules are portal canals. These contain branches of the hepatic artery (which carries 48 oxygenated blood) and portal vein (carries venous blood containing products of digestion absorbed from gastrointensine tract). Fig. 5.15. Anterior surface of the liver. 5.7.3 Ligaments of the liver The liver has two parts of the ventral mesenteric attachments. 1. Its anterior part is formed by: a. Coronary ligament with the bare area between two layers of the peritoneum b. Hepatic veins and the inferior vena cava pass through the bare area c. Right triangular ligament is the right extremity of the coronary ligament d. Left triangular ligament is the left extremity of the coronary ligament e. Falciform ligament is sickle shaped and extends from the diaphragm and the anterior abdominal wall. Its inferior free edge contains the round ligament, which is the remnant of the obliterated umbilical vein. 2. Its posterior part forms the lesser omentum: a. Hepatoduodenal ligament contains in the hepatic pedicle b. Gastrohepatic ligament 49 Fig. 5.16. Inferior surface of the liver. 5.7.4 Relations of the liver surfaces 1. Relations of the diaphragmatic surface: The liver is separated by the diaphragm from the heart, lungs and pleura. The bare area is related to the inferior vena cava and the right suprarenal gland. 2. Relations of the visceral surface: The left lobe is in contact with the abdominal oesophagus and the stomach. The caudate lobe and gallbladder are related to the 1st part of the duodenum superiorly and to the transverse colon inferiorly. The caudate process forms the upper boundary of the epiloic foramen. The right lobe is related to the right colic flexure and the right kidney. 5.7.5 The biliary tracts 5.7.5.1 Internal hepatic bile tracts 1. Hepatocytes secrete bile into canaliculi. 2. Canaliculi unite to form intrahepatic bile ducts (canaliculi biliferi, in a portal triad). 3. Intrahepatic ducts unite and form interlobular ducts. 4. Interlobular ducts join each other to form the left and right hepatic ducts. 5.7.5.2 External hepatic bile tree: 5. Left and right hepatic ducts leave the lobes of the liver and join to form: 6. Common hepatic duct. 7. Common hepatic duct is joined by the cystic duct from the gallbladder, which enters the hepatoduodenal ligament to pass towards the porta hepatis to form the common bile duct. Precibum (before eating) bile passes through the cystic duct to be stored and concentrated in the gallbladder. 50 8. Postcibum bile passes from the gallbladder via the cystic duct and common bile duct to the hepatopancreatic ampulla (it is also joined here by the main pancreatic duct). The common bile duct has four portions: 1. In the lesser omentum it contributes to the hepatic pedicle. 2. Behind the duodenum it is anterior to the portal vein and accompanied by the gastroduodenal artery on its left side. 3. Behind the head of the pancreas it lies on the inferior vena cava. 4. The intramural portion is formed by the confluence of the common bile duct and the main pancreatic duct. As mentioned above, both the common bile duct and the main pancreatic duct form hepatopancreatic ampulla, which opens to the descending part of duodenum at the major duodenal papilla. It is the narrowest part of the common bile duct. 5.7.6 Gallbladder The gallbladder is a piriform sac (8 cm long, 3 cm wide) located in the gallbladder fossa on the inferior (visceral) surface of the right lobe of the liver (level T12-L2). The gallbladder represents the major reservoir for bile storage (30 to 50 ml). The organ is divided into fundus (3 cm wide), body and the neck. The inferior (ventral) and lateral surface of the organ are covered by peritoneum. The superior border of the organ comes in contact and attaches, via areolar connective tissue, to the fossa of the gallbladder which is located on the liver. Parts of the gallblader are as follows: 1. Body: it forms the greatest part of the organ and comes in contact with duodenum (first and second part). 2. Fundus: normally located at the junction of the right ninth costal cartilage within the linea semilunaris (and lateral border of rectus abdominis m.) It projects slightly passing the anterior surface of the liver to touch the transverse colon. 3. Neck: (about 1 cm) touches the superior region of the duodenum (first part) before it narrows to become the cystic duct (4 cm). The gallbladder is supplied by the cystic artery, branch of the right hepatic artery. Clinical comments: The gallbladder concentrates and stores bile and adds mucous to it. Overconcentration of the bile and changes in its contents may result in the precipitation of bile components, leading to concretions forming gallstone (cholelithus; state with presence of gallstones is termed cholelithiasis). Gallstones can be visible in an ordinary radiograph. Gallstones irritate the cystic mucosa (cholecistitis – inflammation of the gallbladder) and results in the erosion of the wall of the gallbladder. The gallstones are most often found in overweight, multiparous women over the age of 40 (4-F - fat, fertile, female, forty). 51 Fig. 5.17. The biliary system. 5.7.7 Blood supply of the liver The liver has a double blood supply (in terms of blood that flows into the liver): 1. From the hepatic artery (oxygenated blood). It is a private system. 2. From the portal vein(!!!) (venosus blood). It is a public system. The private system provides arterial, oxygenated, nutritious blood to the liver. The proper hepatic artery is a continuation of the common hepatic artery (branch of the coeliac trunk) and runs between layers of the lesser omentum, in the hepatoduodenal ligament. Near the porta hepatis (transverse fissure of the liver) it is divided into right and left hepatic arteries. The public system provides functional blood supply to the liver coming from intestines. The portal vein also passes between layers of the lesser omentum (also in the hepatoduodenal ligament) and at the right end of the porta hepatis it terminates by dividing into right and left branches. Please refer to the chapter 7 (Portal circulation) when learning about the portal vein. 5.7.7.1 Venous drainage of the liver Venous drainage for both systems (the private and public system) consists of the hepatic veins (usually 3 in number). They are formed by the union of the central veins in its lobules and join inferior vena cava while it passes just behind or even pierces the liver. These vessels drain venous blood from the liver. 52 Fig. 5.18. The portal circulation. 5.7.8 Lymphatic drainage of the liver Lymphatic vessels drain the liver and enter the hepatic lymph nodes at the porta hepatis. The efferent vessels pass to the coeliac nodes. Some of the deep vessels follow the hepatic veins to the phrenic lymph nodes. 5.7.9 Innervation of the liver Liver receives sympathetic fibres via hepatic plexus, the largest derivative of the coeliac plexus, which receives fibres from the right vagal and phrenic nerves. Branches of the hepatic plexus lay between layers of the lesser omentum and enter the liver also at the porta hepatis. 5.8 Pancreas The pancreas is an endocrine (secrets glucagon and insulin) and exocrine (produces pancreatic juice that enters the duodenum via pancreatic duct) gland. It is 12-14 cm long, and weighs about 80 g. The pancreas is a retroperitoneal organ which passes, from right to left, transversely across the posterior surface of the stomach. It lies within the epigastric and left hypochondriac regions of the abdomen at the level of L1 - L2. It is subdivided into four parts: 1. Head: The head of the pancreas is surrounded by the first three duodenal segments and is overlapped anteriorly by the pyloric region of the stomach. A part of the head extends to the left, behind the superior mesenteric vessels and is called uncinate process. The head is related posteriorly to the IVC and the aorta. 2. Neck: The superior mesenteric vessels pass behind the neck of the pancreas. 3. Body: The body is triangularly shaped in cross section, crosses the midline and is related posteriorly to the vertebral column, aorta, splenic vessels, left kidney and left suprarenal gland. 4. Tail: The tail comes in contact with hilus of the spleen. Anteriorly the pancreas is related to the transverse colon, mesocolon, lesser sac and the stomach. 53 The pancreas, as an exocrine gland, produces pancreatic juice which enteres into the duodenum through the pancreatic duct. The internal secretions: glucagon and insulin enter the blood. The common bile duct passes posteriorly to the first duodenal segment and to the head of pancreas. The main pancreatic duct begins in the tail and runs throughout the length of the gland and usually opens with common bile duct into hepatopancreatic ampulla. Sometimes the pancreatic duct opens alone into hepatopancreatic ampulla minor, which can be situated above the first one. The accessory pancreatic duct (ductus pancreaticus accessorius) is variable, it drains part of the head and usually joins the main pancreatic duct. 5.8.1 Arterial supply of the pancreas The pancreas is supplied by the superior and inferior pancreaticoduodenal arteries, and also by the rami pancreatici (short branches from the splenic artery). 1. The superior pancreaticoduodenal arteries are branches from the gastroduodenal artery. They descend and anastomose with the anterior and posterior branches of the inferior pancreaticoduodenal artery and form the anterior and posterior arterial arches around the head of the pancreas. These arches are called the anterior and posterior pancreaticoduodenal arcades. 2. The inferior pancreaticoduodenal artery is a branch from the superior mesenteric artery. It ascends and divides into anterior and posterior branches. 3. Short branches from the splenic artery. 5.8.2 Venous drainage of the pancreas Veins of the pancreas join the portal circulation. They empty into the portal vein, splenic vein and superior mesenteric vein, but mostly to the splenic vein. 5.8.3 Innervation of the pancreas The main fibres are carried by the splanchnic nerves. Sympathetic and parasympathetic nerves reach the gland by running along the arteries from celiac and superior mesenteric plexuses. 5.9 Spleen The spleen is a lymphatic organ located in the left hypochondriac region of the abdomen. The organ participates in hemopoiesis during the fetal period. In the adult, the spleen filters blood, removes iron from fragmentation of red blood cells, produces lymphocytes and antibodies and stores blood. The adult organ weighs 180 g and measures 12 x 8 x 4 cm. Its long axis lies along the 10th rib (level T11-L1) and crosses the midaxillary line. It is related to the ninth, tenth and eleventh ribs. The spleen has a capsule surrounded by peritoneum, which passes from it at the hilum as the gastrosplenic ligament (carrying short gastric arteries and right gastroepiploic artery) to the greater curvature of the stomach and to the posterior body wall over the left side of the diaphragm as the phrenicosplenic ligament and to the left kidney as splenorenal ligament (the lower portion of the phrenicosplenic ligament). 54 Fig. 5.19. Visceral surface of the spleen. Fig. 5.20. Localization of the spleen in the abdominal cavity. 5.9.1 Relations of the spleen The spleen is related: 1. Anteriorly: to the stomach, the tail of the pancreas, and the left colic flexure. 2. Posteriorly: to the diaphragm. 3. Medially: to the left kidney. 55 Fig. 5.21. Relation of the spleen to the rib cage. 5.9.2 Arterial supply of the spleen The spleen is supplied by the splenic artery the largest branch of the celiac trunk. It divides into 5 or 6 branches, which enter the hilum of the spleen. It is interesting that each branch of the splenic artery supplies the individual element of the spleen and there are no anastomoses between them. Therefore, any obstruction in one of these branches results in death of one region of the splenic tissue. 5.9.3 Venous drainage of the spleen The splenic vein is formed by many tributaries which emerge from hilum of the spleen. The splenic vein is one of the three veins which form the portal vein. 5.9.4 Lymphatic drainage of the spleen All lymph from the spleen is transported along splenic vessels to the pancreaticosplenic lymph nodes. 5.9.5 Innervation of the spleen Nerves of the spleen are derived from the celiac plexus and pass around branches of the splenic artery. 6 Abdominal aorta Origin: The abdominal aorta is a continuation of the descending part of the thoracic aorta below the diaphragm and begins at level Th12. 56 End: It terminates on the body of the fourth lumbar vertebra, where it divides into two terminal branches, the common iliac arteries and small unpaired middle sacral artery (arteria sacralis mediana). Course: The abdominal aorta descends from the aortic opening of the diaphragm (at level T12) on the front and to the left of vertebral column. 6.1 Topographic relations of the abdominal aorta: 1. On the right side are situated IVC, azygos vein, thoracic duct. 2. On the left side the duodenojejunal flexure, left crus of the diaphragm, 3. Anteriorly the lesser omentum, stomach, duodenum, root of the mesentery, pancreas, left renal vein, celiac plexus. 4. Posteriorly bodies of the vertebrae and intervertebral discs, anterior longitudinal ligament. 6.2 Branches of the abdominal aorta For purposes of description branches of the aorta are divided into two groups: visceral branches that supply abdominal viscera, and parietal branches, that supply abdominal wall. 6.2.1 Visceral branches Visceral branches of the abdominal aorta are subdivided into paired and unpaired branches. 6.2.1.1 Paired visceral branches: 1. Middle suprarenal arteries: arise from lateral sides of aorta almost on the same level just like the coeliac trunk, pass to suprarenal glands and supply them. 2. Renal arteries: large trunks that arise from sides of the aorta just below the superior mesenteric artery and run horizontally to the kidneys. The right one and also longer one, crosses anteriorly to the vertebral column and behind IVC. It gives off: a. The inferior suprarenal arteries 3. Testicular (or ovarian) arteries: arise from the aorta just below the renal arteries at the level L2. Each of them runs obliquely downwards in the front of the psoas muscle (right one anteriorly to IVC), crosses anteriorly the ureter, genitofemoralis nerve and inferiorly the external iliac artery. Fig. 6.1. Paired branches of the abdominal aorta (lumbar arteries not shown). 57 6.2.1.2 Unpaired visceral branches 1. Coeliac trunk: short (about 1-2 cm), thick trunk which arises from the anterior surface of the aorta (level L1) and divides immediately into three branches: a. Left gastric artery the smallest branch. It passes upward to the left, next to the cardiac orifice of the stomach, runs downwards along the lesser curvature and anastomises with the right gastric artery. b. Common hepatic artery runs upward and to the right to the pyloric part of the stomach, next runs between the layers of the lesser omentum to the liver as the hepatic artery proper. It gives off: i. Gastroduodenal artery c. Splenic artery - the biggest one, passes horizontally to the left, behind the peritoneum along the upper border of the pancreas and supplies it. This branch gives off: i. Short gastric arteries ii. Left gastroepiploic artery (left gastroomental artery) anastomises with the right one (from the gastroduodenal artery) on the greater curvature of the stomach 2. Superior mesenteric artery, next unpaired branch, arises also from the anterior surface of the aorta 1 cm below coeliac trunk at the level lower 1/3 of L1. It runs forwards between the pancreas and the first part of duodenum (crosses in front of that), descends between layers of mesentery to the right iliac fossa. From the superior mesenteric artery arise: a. Inferior pancreaticoduodenal artery b. Jejunal and ileac arteries c. Ileocolic artery d. Right colic artery e. Middle colic artery Branches from the superior mesenteric artery supply a part of the duodenum, all small intestines, large intestines until right two-thirds of the transverse colon. 3. Inferior mesenteric artery arises from the aorta at the level L3, passes downwards to the left iliac fossa and supplies: left one-third part of the transverse colon, descending colon, sigmoid, superior part of the rectum. It gives off following branches: a. Left colic artery which anastomises with the middle colic artery to supply the transverse colon b. Sigmoid arteries c. Superior rectal artery 6.2.2 Parietal branches All of parietal branches are paired, and are as follows: 1. Inferior phrenic artery: arises just below diaphragm and supplies inferior surface of the diaphragm. It gives off: a. Superior suprarenal artery 2. Lumbar arteries:, four pairs arise from the abdominal aorta on the level L1- L4. They pass laterally behind quadratus and psoas major muscles. All these arteries supply posterior abdominal wall. 58 Fig. 6.2. Branches of the abdominal aorta and their relation to the inferior vena cava. 7 Portal circulation The portal circulation begins as a capillary plexus in the viscera and ends in the capillary circulation within the liver. There is only one blood vessel like that in all human body, which begins and ends as a capillary circulation. 7.1 Portal vein The portal vein drains blood from the lower end of the oesophagus to the upper end of the anal canal, from pancreas, gallbladder, bile duct and from the spleen. Origin: It is an about 6 cm long venous channel, formed behind the neck of the pancreas by the union of the splenic and superior mesenteric veins. End: At the porta hepatis it normally divides into the right and left terminal branches, which enter the corresponding lobes of the liver. Course: Portal vein projects towards the liver beginning deeply to the neck of the pancreas, next coursing behind the first part of the duodenum, then along the free border of the lesser omentum where it lies inferiorly to the common bile duct and the hepatic artery (the bile duct along the free edge and the artery to the left of the duct). At the porta hepatis the hepatic ducts are superficial to the arteries which, in turn, are superior to the portal vein. The quadrate lobe is always superior (ventral) to the caudate lobe and is separated from this lobe by the intervention of the portal vein and its associated structures (bile duct and hepatic arteries) and/or the gallbladder. 59 7.1.1 Portal vein tributaries: 1. Splenic vein, inferior and superior mesenteric veins – these three vessels form the main trunk, (inferior mesenteric vein usually joins the splenic vein first). All of them accompany innominate (same name) arteries in their previous course. 2. Paraumbilical veins 3. Left and right gastric vein 4. Cystic vein 5. Prepyloric vein - it is only vein of the stomach, which has no innominate artery. 7.1.1.1 Splenic vein tributaries: 1. Short gastric veins 2. Left gastroepiploic vein 3. Usually - inferior mesenteric vein 7.1.1.2 Superior mesenteric vein tributaries: 1. Right gastroepiploic vein 2. Jejunales and ilei veins 3. Ileocolic vein 4. Right colic vein 5. Middle colic vein 6. Inferior pacncreatoduodenal vein 7. Rarely - inferior mesenteric vein 7.1.1.3 Inferior mesenteric vein tributaries: 1. Left colic vein 2. Sigmoid veins 3. Superior rectal vein 7.2 Anastomoses between portal and systemic veins The portal venous system communicates with the systematic venous system in several locations. These anastamoses are very important clinically, particularly when the portal circulation is obstructed (e.g. in case of hepatic cirrhosis). In such situation venous pressure is increased (portal hypertension), blood is partly reversed and through anastamoses gets into the systemic venous system. It is possible as the portal venous system has no valves. These communications are as follows: 1. Esophageal branches of the left gastric vein (drain lower part of oesophagus and join the portal vein) anastomise with the oesophageal veins draining the middle part of that organ into the azygos vein (joins superior vena cava). 2. Anal canal is drained partly by superior rectal veins (return blood through the inferior mesenteric vein, splenic vein to the portal vein) and partly by the middle and inferior rectal veins (through the internal iliac vein and next IVC) 3. Paraumbilical veins drain straight into the portal vein, however they also anastomise with superficial veins of the anterior abdominal wall, which drain to the external iliac veins and next to IVC. 4. Veins, which drain the colon, duodenum and pancreas; return blood through the inferior mesenteric vein, splenic vein and gastroepiploic vein to the portal vein. They also anastomise with the lumbar, renal and phrenic veins (systemic tributaries). 60 8 Inferior vena cava The inferior caval vein - IVC is a main vein of the lower part of the body (under the diaphragm). Origin: It begins on the level L5 as result of junction between two common iliac veins about 2.5 cm to the right of the median plane. The origin of the inferior vena cava is located inferiorly to the bifurcation of the abdominal aorta. End: Right atrium of the heart Course: IVC ascends to the diaphragm and passes through with the right phrenic nerve on the level of T8 vertebra. IVC returns blood from the lower limbs, most of the abdominal wall and partly from the abdominopelvic viscera. 8.1 Topographical relations of IVC IVC is surrounded by: 1. On the left side - the abdominal aorta, 2. On the right side - the psoas major muscle and right ureter, 3. Behind - head of the pancreas and portal vein (vena portae) The IVC crosses posteriorly: 1. 2. 3. 4. Right common iliac artery, Root of the mesentery, Right testicular or ovarian artery, Horizontal part of duodenum. The IVC crosses anteriorly: 1. 2. 3. 4. Right lumbar arteries, Right renal artery, Right medial suprarenal artery, Right inferior phrenic artery. 8.2 Tributaries of IVC Abdominal tributaries of the IVC: 1. Parietal branches: a. Inferior phrenic veins, b. Ascending lumbar vein (partly). 2. Visceral branches: a. Hepatic veins, b. Suprarenal veins, c. Renal veins, d. Right testicular or ovarian vein, e. Right and left common iliac vein, f. Middle sacral vein – IVC is a continuation of the middle sacral vein. 61 8.3 Communications with superior vena cava The IVC venous system communicates with the superior vena cava (SVC) venous system in several locations. These communications are as follows: 1. Lumbar veins return blood into IVC and partly via ascending lumbar veins into the azygos vein system and next into the SVC. 2. Superior vena cava receives blood from superior epigastric vein through internal thoracic vein and brachiocephalic vein. IVC receives blood from the inferior epigastric vein through the external iliac vein and common iliac vein. Both superior and inferior epigastric veins anastomise in the umbilical region. 3. Superficial epigastric vein drains into IVC via femoral, external iliac and common iliac veins. The superficial epigastric vein anastomises with the thoracoepigastric veins which return blood into the lateral thoracic vein and axillar, subclavian and brachiocephalic veins. All of them drain into SVC. 9 Lymphatic drainage of the intestinal tract and retroperitoneal space The intestinal mucosa is richly supplied with lymphatics which drain via submucosal and subserous plexuses to nodes on the surface of the viscus. These drain into intermediate groups of nodes arranged along arteries (in the mesentery or on the abdominal wall) which in turn drain to one of three groups of the pre-aortic nodes arranged about the origins of the coeliac, superior and inferior mesenteric arteries. The lymph vessels of the anterior abdominal wall pass to the axillary, anterior mediastinal and superficial inguinal nodes. The abdominal viscera and posterior abdominal wall drain to the aortic nodes which are subdivided into pre-aortic and para-aortic groups: 1. Pre-aortic nodes - are arranged around the origins of the three arteries supplying the alimentary tract and its derivatives, and drain the corresponding structures. Their efferents unite to form the intestinal lymph trunk which enters the cisterna chyli. 2. Para-aortic nodes - lay alongside the aorta around the origins of the paired lateral arteries. They drain the posterior abdominal wall, the kidneys, the suprarenals and the gonads and, through the common iliac nodes, the pelvic viscera and lower limbs. Their efferents unite to form the right and left lumbar lymph trunks. Common iliac lymphatic nodes receive lymph from external and internal lymphatic lymph nodes. These nodes drain into lumbar lymph nodes. Common iliac lymphatic nodes receive through external and internal lymphatic nodes almost all lymph drained from lower limbs, pelvis and deep tissue of the perineum. Lumbar lymphatic nodes (aortic lymphatic nodes) are situated around the abdominal aorta and IVC. These nodes receive afferent lymph from common iliac lymphatic nodes, also from paired viscera in the abdominal cavity and from some pelvic viscera. Next, lymph is returned into lumbar trunks (trunci lumbales). Coeliac lymphatic nodes, which are located near celiac trunk, receive lymph from unpaired viscera of the abdominal cavity. The coeliac group drains the stomach and proximal duodenum, the liver, spleen and pancreas. It also drains the superior and inferior mesenteric groups of nodes. Efferent vessels pass to the cisterna chyli through the intestinal trunks. 62 The inferior mesenteric group - drains the distal one third of the transverse colon, the descending and the pelvic colon and the upper part of the rectum. The superior mesenteric group - drains the distal half of the duodenum, the jejunum, ileum, caecum and appendix, and the ascending and proximal transverse colon. 9.1 Cisterna chyli The union of the intestinal trunks and lumbar trunks forms a dilated sac (cistern, reservoir of chyle), which is called the cisterna chyli. The cisterna chyli is about 5 cm long and 6 mm wide. It lies on the right side of the bodies of L1 and L2 vertebrae. The cisterna chyli is situated posteriorly to the right crus of the diaphragm. At this place the thoracic duct (ductus thoracicus) begins. It is the biggest lymphatic vessel in a human body. Thoracic duct arises from the superior margin of the cisterna chyli and ascends to the aortic opening in the diaphragm. Refer to the thorax lab session for the thoracic duct information. 10 Autonomic Nervous System in Abdomen and Pelvis Like elsewhere it is composed of sympathetic and parasympathetic parts: 10.1 Sympathetic part The sympathetic part is derived from the thoracic, lumbar and sacral sympathetic trunks, the fibres passing mainly through the coeliac, aortic, hypogastric and pelvic plexuses. 1. Lumbar sympathetic trunk enters the abdomen by passing under the medial arcuate ligament and descends on the medial margin of psoas to the pelvic brim. It usually has four ganglia. Branches: a. Somatic branches: pass to the lumbar nerves (grey rami communicantes). b. Visceral branches: pass to the aortic plexus and also descend anteriorly to the common iliac vessels to the hypogastric plexus. c. Vascular branches: pass to the common iliac artery. 2. Sacral sympathetic trunk - descends on the pelvic surface of the sacrum medially to the anterior sacral foramina to join its fellow in front of the coccyx at the ganglion impar (unpaired ganglion). It is continuous under the iliac vessels with the abdominal sympathetic trunk above. It has four or five small ganglia. Branches: a. Somatic branches - pass to the sacral nerves (grey rami communicantes). b. Visceral branches - pass to the pelvic plexuses. 3. Celiac plexus - is formed by the two intercommunicating celiac ganglia which lie on each side of the coeliac artery. Each ganglion receives greater, lesser and the least splanchnic nerves from the thoracic sympathetic trunk and branches pass down on the front of the aorta to form aortic plexuses. From the coeliac and aortic plexuses, postsynaptic fibres pass with branches of the aorta to supply the upper part of the alimentary tract, its derivatives, the kidneys, and the gonads. Presynaptic fibres pass trough the plexus and end in the suprarenal glands (medullary part). 4. Aortic plexus - lies on the front of the lower abdominal aorta and receives branches from the coeliac plexus and the lumbar sympathetic trunk. Postsynaptic fibres pass along the inferior mesenteric artery to the lower abdominal viscera. It gives branches to the hypogastric plexus. 5. Hypogastric plexus - lies in the midline below the aortic bifurcation. It is formed of branches from each lumbar sympathetic trunk and the aortic plexus. It divides into the right and left branches which descend to the: 63 6. Pelvic plexuses - each of which lies on the side wall of the rectum and is formed by branches from the hypogastric plexus, and the sacral sympathetic trunk. It gives postsynaptic supply to the pelvic viscera. 10.2 Parasympathetic part The parasympathetic part - this is derived from CNX - the vagal (anterior and posterior gastric nerves) and the pelvic splanchnic (S2, S3, S4) nerves. 1. Anterior and posterior gastric nerves - are a mixture of both vagi. They are distributed through the coeliac plexus and along the branches of the aorta to the alimentary tract and its derivatives as far as the splenic flexure. 2. Pelvic splanchnic nerves - pass to the hypogastric and pelvic plexuses. From the hypogastric plexus some fibres ascend to the inferior mesenteric artery and are distributed along it to supply the gut distal to the splenic flexure. From the pelvic plexuses fibres are distributed to the pelvic viscera. 64 11 Reference charts 11.1 Abdominal aorta branches flowchart 65