GI 2.1.1.pdf

TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal ANATOMY OF THE ABDOMINAL WALL, INGUINAL REGION AND HERNIAS 1 ABDOMINAL WALL ABDOMINOPELVIC CAVITY Abdominal and pelvic cavities are continuous but separated arbitrarily by the pelvic inlet (pelvic...

TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal ANATOMY OF THE ABDOMINAL WALL, INGUINAL REGION AND HERNIAS 1 ABDOMINAL WALL ABDOMINOPELVIC CAVITY Abdominal and pelvic cavities are continuous but separated arbitrarily by the pelvic inlet (pelvic brim) Upper part of abdominal cavity extends under thoracic cage, separated from thoracic cavity by diaphragm Bony landmarks: sternum, xiphoid process, costal margin, costal cartilages, iliac crest, iliac fossa, ASIS, pubic tubercle, pubic symphysis, thoracic and lumbar vertebrae, sacrum Visceral structures: stomach, duodenum, small intestine, large intestine, liver, pancreas, spleen, kidneys, ureters, urinary bladder, reproductive organs and abdominal vessels (on the posterior abdominal wall) 1 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal 9 REGIONS OF THE ANTERIOR ABDOMINAL WALL For descriptive purposes to allow precise location of underlying organs in relation to surface landmarks o E.g. liver lies in right hypochondriac region, crossing slightly over into epigastric region o E.g. stomach and spleen lies in left hypochondriac region Divided into: Right Epigastric – Left hypochondrium referred pain from foregut hypochondrium Right flank/ Umbilical – Left flank/ lumbar referred pain from midgut lumbar Right groin/ Hypogastric/ suprapubic – Left groin/ iliac iliac referred pain from hindgut Lines forming intersections: Subcostal plane Drawn just below subcostal margin (horizontal) Passes through inferior border of 10th costal cartilage Inter/ transtubercular Drawn between iliac tubercles plane (horizontal) Traverses L5 vertebrae Midclavicular planes Drawn from middle of clavicle to mid-inguinal point (between ASIS and top of (vertical, x2) pubic symphysis; different from midpoint of inguinal ligament) 4 QUADRANTS OF ABDOMEN For clinical purposes o E.g. liver and gallbladder, pylorus of stomach sit in right upper quadrant o E.g. stomach and spleen sit in left upper quadrant o E.g. cecum and appendix sit in right lower quadrant Lines forming intersection are drawn through the umbilicus to form the quadrants: o Transumbilical plane: horizontal, passes between L3 and L4 o Median/ sagittal plane: vertical (xiphoid process to pubic symphysis) 2 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal ANTERO-LATERAL ABDOMINAL WALL – SURFACE ANATOMY Dynamic, multi-layered, musculoaponeurotic wall that is mostly made of soft tissue Palpable surface features: xiphoid process, costal margin, iliac crest, ASIS, pubic symphysis, pubic tubercle ABDOMINAL WALL MUSCLES Anterior wall Paired vertical rectus abdominis muscles within rectus sheath Lateral wall 3 flat sheet muscles – external oblique, internal oblique, transversus abdominis Names suggest direction of fibres Posterior wall Post vertebral muscles (erector spinae group), psoas, quadratus lumborum (iliacus to 12th rib), and iliacus muscles (muscles of the lower limb) LATERAL ABDOMINAL WALL MUSCLES Consists of 3 separate flank sheet muscles (from superficial to deep): external oblique, internal oblique and transversus abdominis Continue anteromedially as aponeurotic sheets and contribute to rectus sheath, containing the rectus muscles Functions: Rotates vertebral column to contralateral side and bends trunk to ipsilateral site Compresses and depresses lower thoracic cavity, causing an increase in intra-abdominal pressure, which aids in expiration, evacuation of urine, faeces, parturition, and heavy lifting Protects intestines (other organs have their own support) and plays minor role in supporting viscera Weakly assists in flexion of trunk and helps maintain abdominal tone bilaterally External and internal obliques run in opposite directions to provide more strength to abdominal wall Neurovascular plane lies between internal oblique and transversus abdominis muscle layer Except inferior epigastric vessels: runs in rectus sheath between rectus abdominis and posterior rectus sheath above arcuate line; between transversus abdominis and transversalis fascia below arcuate line Muscle Description Origin Insertion External Possesses free posterior border External surface of Fans out to attach to: oblique Fibres directed downwards and forwards 5th to 12th ribs Xiphoid process Lower aponeurotic edge rolls inwards and (lower 8) Linea alba forms the inguinal (Poupart’s) ligament Pubic crest and which runs from the ASIS to the pubic pubic tubercle tubercle; towards midline, superficial Anterior half of inguinal ring (above inguinal ligament) iliac crest forms opening to the inguinal canal 3 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Internal Directed LATERAL: MEDIAL: oblique downwards Deep layer of thoracolumbar Lower margins of 10th and backwards fascia (attached to lumbar to 12th ribs (lower 3) vertebral spine) and costal cartilages Anterior 2/3 of iliac crest Xiphoid process Lateral half of inguinal ligament Rectus sheath Iliopsoas fascia Conjoint tendon Pubic crest Transversus Fibres runs MEDIAL: Xiphoid process abdominis horizontally Inner surface of 7th to 12th Linea alba from lateral to (lower 6) costal cartilages Pubic symphysis medial aspect Thoracolumbar fascia Conjoint tendon Anterior 2/3 of iliac crest Lateral 1/3 of inguinal ligament ANTERIOR ABDOMINAL WALL RECTUS ABDOMINIS Long strap muscle enclosed in the rectus sheath Possesses 2 heads (right and left) – 2 bands of paired vertical rectus abdominis muscles Divided into segments by 3 tendinous intersections on each side: o Attached to the anterior wall of the rectus sheath, providing stability within rectus sheath o At level of xiphisternum, umbilicus, and in between the 2 Linea semilunaris: lateral borders – where thoracic spinal nerves T7-T12 enter the rectal sheath à avoid making vertical incisions at this area (always do horizontal incisions) Linea alba: midline of abdomen, formed by interweaving aponeurosis from opposite sides and between superficial/ intermediate/ deep layers to form midline raphe, from xiphoid process to pubic symphysis – avoid vertical incision along linea alba as lateral wall muscles will pull on it, causing poor wound closure Lacks attachment to the posterior wall of the rectus sheath Origin (inferior attachment): pubic symphysis and pubic crest Insertion (superior attachment): xiphoid process, 5th to 7th costal cartilages Function: most powerful flexor of vertebral column (lower thoracic and lumbar) o External and internal obliques of both sides are important partners (assist) in this action Pyramidalis: small, insignificant triangular muscle anterior to the inferior part of rectus abdominis, attaches to anterior surface of pubis and anterior pubic ligament; ends in linea alba 4 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal RECTUS SHEATH Formed by aponeuroses of 3 flank muscles – transversus abdominis, internal and external oblique Arcuate line (linea semicircularis/ Douglas’ line): horizontal line that demarcates lower limit of posterior layer of the rectus sheath; occurs approximately midway of distance from umbilicus to pubic crest o Posterior wall of sheath is incomplete; below this line, rectus sheath is formed by aponeurosis of all 3 muscles o Below the arcuate line, the rectus abdominis muscle is in contact with transversalis fascia Linea alba: where rectus sheaths meet in the midline Anterior wall is complete from xiphoid process and costal cartilages to pubic symphysis and crest Superior to External oblique aponeurosis (green) lies anterior to rectus abdominis umbilicus Internal oblique aponeurosis (orange) splits, forming anterior and posterior lamina that enclose the rectus abdominis Transversus abdominis aponeurosis (blue) lies posterior to rectus abdominis I.e. sheath is only formed by external and internal oblique aponeurosis Inferior to All 3 aponeurotic layers lie anterior to the rectus abdominis umbilicus Internal oblique and transversus abdominis aponeuroses merge and pass superficial (i.e. anteriorly) to the rectus muscle Rectus abdominis lies directly against transversalis fascia (posteriorly) Peritoneum of abdominal cavity lies posterior to fascia à muscle has weak support in this area 5 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal POSTERIOR ABDOMINAL WALL Contains posterior vertebral muscles and erector spinae group – function in stability and movement of vertebral column Lateral to vertebral bodies: psoas, quadratus lumborum and iliacus muscles Muscle Description Origin Insertion Function Psoas Muscle of Anterior surfaces Lesser trochanter of Flexion of trunk and hip joint major posterior and lower borders femur as iliopsoas External rotation abdominal wall of transverse tendon (together with Bends lumbar vertebral process of T12-L5 iliacus) columns Psoas Muscle of T12-L1 vertebrae Iliopectineal/ pubic Assists psoas major minor posterior and intervertebral eminence (arch) abdominal wall discs Iliacus Muscle of lateral Iliac fossa and Lesser trochanter of Flexion and external rotation pelvic wall crest; ala of sacrum femur as iliopsoas of hip joint muscle (together with Ipsilateral bending of trunk psoas major) Raising trunk from supine position Quadratus Muscle of Posterior part of 12th rib and transverse Bends trunk ipsilaterally lumborum posterior the iliac crest and processes of L1-L5 Fixes 12th rib and aids in abdominal wall iliolumbar ligament vertebrae expiration Lateral flexor of trunk LAYERS OF THE ABDOMINAL WALL Skin Superficial fatty layer (Camper fascia) Deep membranous layer (Scarpa fascia) – continues inferiorly into perineal region as Colles fascia (superficial perineal fascia) 3 flank muscles – external oblique (aponeurosis gives rise to external oblique fascia), internal oblique (gives rise to cremasteric fascia), transversus abdominis Transversalis fascia – gives rise to internal spermatic fascia Extraperitoneal connective tissue Parietal peritoneum Greater sac 6 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal NEUROVASCULATURE OF ABDOMINAL WALL ARTERIAL SUPPLY OF ABDOMINAL WALL Rectus Superior Terminal branch of internal thoracic artery, which is abdominis epigastric a branch of the subclavian artery artery Runs on the internal aspect of the sternum Enters rectus sheath from posterior aspect of rectus abdominis muscle Inferior Branch of external iliac artery, which is a branch epigastric from common iliac artery from abdominal aorta artery Runs between transversus abdominis muscle and transversalis fascia to enter rectus sheath, posterior to rectus abdominis Usually sited 1/3 of the way between the umbilicus and ASIS Both vessels enter rectus sheath and anastomose at the level of the umbilicus, forming a potential bypass to abdominal aorta, maintaining collateral circulation e.g. major block in abdominal aorta – bring collateral circulation from superior epigastric (subclavian) Flank Segmentally supplied by: muscles 7th to 11th intercostal arteries Subcostal arteries Lumbar arteries (L1-L4) Deep circumflex iliac arteries (from external iliac arteries) VENOUS DRAINAGE OF ABDOMINAL WALL Follows arterial supply Accompanying deep veins bear the same names as arteries LYMPHATIC DRAINAGE OF ABDOMINAL WALL There are no lymph nodes in the tissues of the abdominal wall except on the posterior abdominal region along the aorta, but there are lymphatic vessels Tissue Accompanying vein Draining nodes Above transumbilical plane Below transumbilical plane Superficial – lymphatic Subcutaneous veins Pectoral group of axillary LNs Superficial inguinal LNs drainage in quadrants Deep Deep veins (in extra- Mediastinal LNs External iliac and paraaortic peritoneal tissue) LNs 7 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal INNERVATION OF ABDOMINAL WALL Importance: referred pain, anaesthesia in surgery, direction in which nerves are travelling in (to prevent sensory and motor loss – support of abdominal wall) Anterior Motor nerves Segmentally supplied from T7-T12 and L1 spinal nerves abdominal T7-T12 Rectus abdominis wall T7-T11 External oblique T7-T12, L1 Internal oblique, transversus abdominis Dermatomes T7 Epigastrum (sensory to skin) T10 Umbilicus L1 Inguinal ligament Somatic To parietal peritoneum (outer) lining inner wall of abdomen: follows segmental sensory nerves that supply corresponding body wall areas innervation Visceral peritoneum (inner) has no somatic sensory innervation and is insensitive to pain Posterior Motor nerves Segmentally supplied from T12 and L1-L4 spinal nerves abdominal T12 (subcostal nerve) Anterior abdominal wall wall T12, L1-L4 Quadratus lumborum L1 (iliohypogastric, Parts of inguinal region (antero-lateral abdominal wall) ilioinguinal nerve) L2-L4 Psoas major L2-L4 (femoral nerve) Iliacus Lumbar plexus Mainly for lower limb (L1-L4) Provides some sensory branches to parietal peritoneum 8 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal 2 INGUINAL REGION INGUINAL REGION/ GROIN Inguinal ligament runs between anterior superior iliac spine and pubic tubercle Weak area given presence of many structures exiting and entering abdominal cavity into lower limb Clinically important due to common occurrence of hernias (more often in males than females) Femoral canal is below the inguinal canal INGUINAL CANAL Oblique passageway in lower part of anterior abdominal wall Present in both genders and about 4cm in length in adults Lies above medial half of inguinal ligament and extends from deep inguinal ring to superficial inguinal ring Deep inguinal ring Opening in transversalis fascia ~1.5 cm superior to midpoint of inguinal ligament Superficial inguinal ring Opening in external oblique aponeurosis Immediately superomedial to pubic tubercle In males: contain ilioinguinal nerve and spermatic cord; where testes descend through In females: contain ilioinguinal nerve and round ligament (descends through to attach to labia majora) Bordered by 4 walls (important!) Anterior External oblique aponeurosis (for whole length) Internal oblique muscle fibres (reinforce lateral 1/3) Floor Inguinal ligament – formed from rolled inferior (gutter-like) edge of external oblique aponeurosis Roof Arching fibres of internal oblique (for while length) Conjoint tendon (medially) Posterior Transversalis fascia Conjoint tendon (medially) Conjoint tendon: formed from the fusion of the lowest fibres of the internal oblique aponeurosis and transversus abdominis aponeurosis; attached medially to the linea alba Mid-inguinal point = halfway between pubic symphysis and ASIS – identify femoral artery (medial) Midpoint of inguinal ligament = halfway between pubic tubercle and ASIS – identify deep inguinal ring 9 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal 3 HERNIAS An abnormal protrusion of an organ through the structure that usually contains the organ e.g. intestines Associated with positive cough impulse i.e. hernia is accentuated with increased intraabdominal pressure Components of a hernia: Sac Neck, body, fundus; arises from peritoneum Contents of sac E.g. bowel, bladder Defect Opening/ hole through which hernia has occurred Classification Reducible Sac can be returned to containing cavity by reducing the intra-abdominal pressure e.g. physical manipulation Irreducible Sac cannot be returned to containing cavity Obstructed Sac contains a blocked bowel e.g. by a twisting motion of the bowel, leading to constriction of the neck Strangulated Sac contains contents with a compromised blood supply, leading to tissue injury Typical clinical features (history) include a lump in the groin, may be transient or permanent, pain, vomiting, constipation and other associated conditions INGUINAL HERNIAS Indirect Defect always in internal ring (midway of inguinal ligament), which is always lateral to inferior epigastric vessels Hernia takes indirect path through abdominal wall via internal then external ring Defect is a dilated deep ring, allowing hernia to pass through the inguinal canal into the scrotum Most common type of hernia, tends to arise as a result of a developmental defect of inguinal canal where it fails to close properly Tends to occur in younger adults and children Direct Defect tends to through Hesselbach’s/ inguinal triangle, which is always medial to inferior epigastric vessels Hesselbach’s triangle: behind external ring of inguinal canal, bounded by linea semilunaris medially, inferior epigastric vessels superolaterally and inguinal ligament inferiorly Path of hernia goes straight through posterior wall of inguinal canal (which is weak) Rarely extends into the scrotum More common in older age group as abdominal wall in the inguinal triangle becomes weaker Associated with chronic straining (e.g. constipation) and with weak musculature of the area See image: view from inside 10 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal From external view, it is difficult to differentiate between direct and indirect hernia If severe, it is even more difficult to palpate to differentiate between the two Clinically not important to differentiate between the two, usually only determined during surgical procedures to decide course of action FEMORAL HERNIA Less common than inguinal hernias but have higher incidence of obstruction and strangulation More common in elderly and females than males, given that pelvic region is wider in females than males Path of defect goes into the femoral canal (below inguinal canal) Femoral canal borders: Superiorly Inguinal ligament Inferior Pectineus fascia Medially Lacunar ligament Laterally Femoral vein – main vein draining blood from LL to abdominal aorta A swelling below the inguinal ligament between ASIS and pubic tubercle likely suggests a femoral hernia On examination: o Appear inferolateral to pubic tubercle, as opposed to inguinal hernias that occur superomedially o Tend to be irreducible, hot and painful (if strangulated) 11 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal GUT AND PERITONEAL CAVITY 1 PERITONEUM AND PERITONEAL CAVITY Peritoneal Single continuous membrane of simple squamous epithelium (mesothelium) that lines the inner membrane abdominal wall, forming the abdominal cavity Visceral peritoneum covers suspended organs Parietal peritoneum lines the abdominal wall Both layers of the peritoneum are in continuity via the mesenteries Peritoneal Potential space between the 2 layers of the peritoneum cavity In real life, there is nothing in the peritoneal cavity proper apart from a small amount of fluid Mesenteries Peritoneal folds/ reflections attaching viscera (organ) to (posterior) abdominal wall Where components of GI tract are suspended Composed of 2 layers of peritoneum with thin layer of loose connective tissue between Act as conduit for vessels, nerves and lymphatics that supply viscera (mainly intestines, colon) The entire gut tube is suspended from a dorsal mesentery The foregut has a ventral mesentery containing the liver, which splits it into falciform ligament (sickle shape) and lesser omentum Falciform ligament keeps liver in position by attaching it to diaphragm and anterior body wall Omenta Double-layered peritoneal folds connecting stomach to other peritoneal organs Named after the curvature it is attached to Greater Lower part of the dorsal foregut mesentery extends downwards as a double fold omentum (4-layered) acting as an “apron” anterior to the gut structures (visceral Attaches to anterior surface of transverse colon and its mesentery peritoneum) Transverse mesocolon: attaches transverse colon to posterior body wall Composed of gastrorenal, gastrosplenic, gastrocolic and splenorenal ligaments Derived from dorsal mesogastrium 12 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Lesser Part of ventral foregut mesentery lying between liver and lesser curvature of omentum stomach (double-layered) Composed of: Hepatogastric ligaments: sheet-like; between groove for ligamentum venosum and lesser curvature of stomach Hepatoduodenal ligaments/ right free border: between porta hepatis and duodenum Transmits portal triad (hepatic portal vein, hepatic artery proper and bile duct) – between posterior abdominal wall and liver within the lesser omentum near its free edge (hepatoduodenal ligament), enclosing structures that pass through porta hepatis Free edge is present because the ventral mesentery ends at the start of midgut Pringle manoeuvre: surgical manoeuvre where large atraumatic haemostat is used to clamp the free border of the lesser omentum (hepatoduodenal ligament), interrupting flow of blood through the hepatic artery and portal vein to control bleeding from liver; must identify epiploic foramen to do this Derived from ventral mesogastrium ABDOMINOPELVIC CAVITY AND THE DIGESTIVE TRACT Abdominal part is where most gut structures are found; pelvic viscera found in the pelvic part Abdominal cavity extends into thoracic cage (below diaphragm), and into pelvic cavity From top to bottom: mouth and pharynx, oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (caecum, colon (ascending, transverse, descending, sigmoid), rectum, anal canal) 13 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Intraperitoneal Structures suspended from the abdominal wall by mesenteries structures Enveloped by mesentery – completely covered in peritoneum E.g. most of small intestine, transverse colon – enveloped by visceral peritoneum, allowing either for significant movement and shape changes due to intrinsic activity (e.g. stomach, bulb of duodenum, jejunum, ileum, transverse colon, sigmoid colon) or to accommodate passive changes in position, imposed by the adjacent, highly active diaphragm (e.g. liver, spleen, tail of pancreas) Retroperitoneal Lie between parietal peritoneum anteriorly and abdominal wall posteriorly structures Covered by mesentery only on anterior surface of organ E.g. kidneys, ureters, suprarenal glands, great vessels (abdominal aorta, IVC), nerves (lumbar plexus, sympathetic trunk), oesophagus, duodenum (except first part), pancreas (except tail), colon (ascending and descending only), rectum Secondarily retroperitoneal structures are initially suspended by posterior mesenteries which eventually fuse with body wall due to pressure from overlying organs e.g. duodenum, pancreas, colon (ascending, descending) COMPARTMENTS OF THE PERITONEAL CAVITY Peritoneal cavity is divided into greater sac and lesser sac (omental bursa) o Both representing capillary thin spaces but may enlarge when filled with fluid or gas e.g. ascites Liver is in ventral mesentery in the foregut region Initially, dorsal mesentery holds entire gut tube, while ventral mesentery is only in the foregut region As the liver grows, the mesentery twists and turns (to accommodate enlarging organs), trapping parts of the peritoneal cavity behind the liver and stomach (forming the lesser sac) o Liver moves to the right, while the dorsal mesentery and spleen move to the left, causing the original right side of the upper peritoneal cavity to now become posterior (lesser sac) Perforating ulcer in posterior wall of stomach would most likely cause peritonitis in lesser sac initially Below: embryo 5th week IUL 14 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Peritoneal cavity can be divided into many compartments o Surgically important – possible spread of material/ infection between compartments Greater sac is divided into supracolic and infracolic compartment by mesentery of transverse colon Infracolic compartment is divided into left and right compartments by mesentery of small intestine The right and left paracolic gutters lies on either side of the ascending and descending colon o Depression in that area of wall, acts as canal for drainage of fluid from supracolic compartment o Under normal circumstances, peritoneal space is filled with peritoneal fluid of approximately 50ml which usually moves upwards towards inferior side of diaphragm to be absorbed by vessels in the diaphragmatic wall and returned to venous circulation (left) o In a vertically standing patient, collection of fluid inferior to the diaphragm (e.g. pus and inflammatory exudate from liver abscess) flows through the paracolic gutter towards the pelvic cavity (right) Hepatorenal pouch of Morrison: separates liver from right kidney; where fluid tends to accumulate Omental/ epiploic foramen/ foramen of Winslow: foramen between greater and lesser sac; boundaries: Anterior Portal triad in hepatoduodenal ligament Inferior First part of duodenum Posterior IVC (peritoneum covering IVC) Superior Liver (caudate lobe) GUT TUBE Divisions of the gut tube – embryological basis Foregut Distal 1/3 of oesophagus to 2nd part of duodenum at entrance of bile duct (major duodenal papilla) Midgut 2nd part of duodenum to proximal 2/3 along transverse colon Hindgut Distal 1/3 of transverse colon to rectum Early development of the gut tube o The gut tube originates from endoderm and splanchnic mesoderm o By 4th week of intrauterine life, gut tube is enclosed within the intraembryonic coelomic cavity o Gut tube is covered by parietal peritoneum, suspends from mesogastrium (mesentery of gut) o Gut tube has dorsal mesentery (peritoneal fold) which suspends it from posterior abdominal wall 15 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal 2 ABDOMINAL VISCERA (ORGANS) ABDOMINAL OESOPHAGUS Pierces muscular part of the diaphragm at the right crus, at the level of T10 Contributes to lower oesophageal sphincter to prevent gastroesophageal reflux STOMACH Large muscular sac that holds food; parts of the stomach: Cardia Where contents of oesophagus empty into stomach Defined as the region following the z-line of the gastroesophageal junction (point at which epithelium changes from stratified squamous to columnar) Fundus Formed by upper curvature, lies directly inferior to left hemidiaphragm Body Joins oesophagus at cardia of stomach Narrows to form pyloric antrum which leads to pyloric canal Pylorus Lower section that facilitates emptying of contents into small intestine Pyloric sphincter: ring of smooth muscle at distal end of pyloric canal which prevents food from entering duodenum, controlling passage of food from stomach into duodenum; is a true anatomic sphincter Curvatures of the stomach Greater curvature Lies on the left; supplied by gastroepiploic/ gastroomental artery Lesser curvature Lies on the right; supplied by gastric arteries 16 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal SMALL INTESTINE DUODENUM Approximately 10-inched C-shaped structure with 4 parts Superior 2”/ 5cm; L1 – transpyloric plane Intraperitoneal proximally (first 2cm), retroperitoneal distally Duodenal cap: first part (seen in imaging), most frequent site of duodenal ulcers Passes anterior to bile duct, gastroduodenal artery, portal vein and IVC (clinical implications: a perforated duodenal ulcer may result in severe haemorrhage) Descending 3”/ 7-10cm; L1-L3 Contains entrance for common bile duct (major duodenal papilla) and accessory pancreatic duct (minor pancreatic duct); crossed by root of transverse mesocolon Inferior 3”/ 6-8cm; L3 Between superior mesenteric artery and vein anteriorly and IVC posteriorly Ascending 2”/ 5cm; L2 Terminates at duodenojejunal flexure, leading into jejunum (intraperitoneal) Lies between gastroduodenal and duodenojejunal junction Mostly retroperitoneal apart from most proximal and distal end Relations are clinically important as aneurysms can compress duodenum while peptic ulcers can erode into walls of vessels JEJUNUM AND ILEUM Entirely intraperitoneal organs that form remaining portion of small intestines, measuring ~20 feet Lies between duodenojejunal junction and ileocaecal junction Suspended by fan shaped mesentery with long free edge and short root o Root (red line) does not reflect length of intestine o Mesentery is directed obliquely from the duodenojejunal flexure at the left side of the second lumbar vertebra to the right sacroiliac joint Plicae circulares (circular inner folds): found in the mucosa, gradually decrease in number and become further apart in the distal part of the jejunum towards the ileum Lymphoid tissues (Peyer’s patches): abundant in the terminal ileum, but folds are significantly reduced 17 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Feature Jejunum Ileum Location Proximal 2/5 Distal 2/5 Jejunal loops are in left upper quadrant Ileal loops are in right lower quadrant and suprapubic region Lumen Wide-bored, thick-walled Smaller in diameter, thinner-walled Plicae circulares Closely arranged Reduced in number, further apart (but abundant lymphoid tissues (Peyer’s patches)) Arterial arcades Less prominent More prominent Vasa recta Longer Shorter Duodenum has 2 layers of vasa recta (anterior, posterior), jejunum and ileum have single LARGE INTESTINE Extends from the ileum to the anal canal; consists of: Caecum Intraperitoneal Ileocecal valve: folds of mucosa where small intestine (terminal ileum) joins large intestine Physiological (rather than true anatomical) sphincter that allows passage of food from ileum to large intestine, of little effectiveness Where gallstones from gallbladder can impact Appendix (3-5”): appendage of cecum Has its own short mesentery (mesoappendix) and blood vessels (important to identify mesoappendix for surgical removal) McBurney’s point roughly corresponds to most common location of base of appendix where it is attached to caecum; 1/3 of distance from ASIS to umbilicus; refers to the point of maximum tenderness in appendicitis Apex of appendix is variable, commonly retrocaecal or pointing towards pelvis Ascending colon Retroperitoneal; runs upwards, to right of liver, taking a sharp bend (right colic/ hepatic flexure – inferior compared to left colic flexure) to continue as transverse colon Transverse colon Intraperitoneal – normally suspended in a mesentery Runs across abdominal cavity near to spleen to form left colic/ splenic flexure Descending colon Retroperitoneal Sigmoid colon Intraperitoneal – most mobile region Rectum Retroperitoneal; pierces levator ani to pass into perineum, descending within concavity of sacrum (showing 3 lateral curvatures) becoming the anal canal at the anorectal junction Arterial supply: superior and middle rectal arteries, from the IMA Innervation: autonomic nervous system Sympathetic: L1-L2 via hypogastric plexus Parasympathetic: S2-S4 (pelvic splanchnic), mainly sensitive to stretch 18 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Anal canal Guarded by involuntary internal sphincter and voluntary external sphincter External sphincter formed by deep, superficial and subcutaneous muscle groups that bring faecal continence to anal canal However, skeletal muscle sphincter surrounding anal canal is less important than puborectalis sling (part of levator ani) – forms a sharp angle at anorectum junction; tonically active, keeps rectum at sharp bend If pelvic diaphragm is damaged (e.g. during episiotomy – surgical cut in muscular area between vagina and anus during childbirth to enlarge vaginal opening), puborectalis may be affected, resulting in incontinence Pectinate/ dentate line: divides superior 2/3 and inferior 1/3 of anal canal; located at lower border of anal columns and developmentally Hilton’s white line/ intersphincteric groove: slightly inferior to pectinate line; landmark for the intermuscular border between internal and external anal sphincter muscles and transition point of epithelium between anal canal and anus/ perianal skin Arterial supply: inferior rectal artery, a systemic artery arising from the internal pudendal artery, which branches from the internal iliac artery Innervation: somatic nervous system (inferior rectal branches of pudendal nerve, S2-S4), mainly sensitive to injury e.g. sharp sensations Main features to distinguish large intestine: taenia coli, haustra, appendices epiploicae (fatty tags) Taenia coli muscles 3 long bands of muscles formed from modified muscular wall (part of longitudinal layer in muscularis externa) that end over the caecum and come together at the appendix (important for locating appendix during surgery by tracing the taenia coli on the caecum) Haustra Large sacculations formed by outpouchings of intestinal wall Appendices epiploicae Fatty tags on the outside of large intestine 19 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal 3 NEUROVASCULATURE OF THE GUT ARTERIAL SUPPLY OF THE GUT Arises from 3 unpaired arteries that are direct branches off the anterior of the abdominal aorta All blood vessels are retroperitoneal COELIAC TRUNK (T12) Supplies entire foregut (abdominal oesophagus, stomach, proximal part of duodenum), its derivatives (liver, part of pancreas), and spleen (not part of alimentary system, but shares supply from coeliac trunk) 3 main branches: o Left gastric artery o Splenic artery: (highly tortuous) o Common hepatic artery: on the right side; further divides into gastroduodenal artery and hepatic artery proper which supplies the liver Structures behind the stomach and liver – “block” of structures that form posterior relations of liver and stomach, is part of retroperitoneum o Includes duodenum, pancreas, right kidney, great vessels o Pathology can be communicated within this area Arteries of the stomach Origin Supplies Left gastric Coeliac trunk Distal oesophagus, lesser curvature Right gastric Hepatic artery proper Lesser curvature (right portion) Left gastro-omental/ gastro-epiploic Splenic artery Greater curvature (left portion) Right gastro-omental/ gastro-epiploic Gastroduodenal artery Greater curvature (right portion) Short gastric Splenic artery Fundus of stomach 20 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal SUPERIOR MESENTERIC ARTERY (L1) Branches from abdominal aorta at level of L1, just inferior to origin of coeliac trunk Supplies midgut – all of intestines from distal part of duodenum through 2/3 of transverse colon Divides into branches that usually anastomose with each other o Middle colic artery: supplies transverse colon o Right colic artery: supplies ascending colon o Ileocolic/ ileocecal artery: supplies caecum and appendix, and part of ileum § Gives off appendicular artery: end artery with no anastomoses – if blocked, necrosis o Ileal arteries: supplies ileum o Jejunal arteries: supplies proximal part of jejunum Pancreas receives blood supply from both coeliac trunk and SMA INFERIOR MESENTERIC ARTERY (L3) Supplies only small area of gut hence smaller size of artery Supplies hindgut (transverse colon from left colic flexure to upper part of rectum, including descending colon and sigmoid colon) via 3 main branches: o Left colic artery: supplies descending colon (bifurcates into ascending and descending branches) o Sigmoid branches: supplies sigmoid colon o Superior rectal artery: supplies rectum; effective terminal branch Anastomose with superior mesenteric artery at the site of the splenic/ left colic flexure – junction of the mid and hindgut à change from SMA to IMA arterial supply at this level 21 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal VENOUS DRAINAGE OF GUT Differs from arterial supply as most of venous blood from the gut initially enters hepatic portal system Venous blood channels through portal vein, which enters liver o Inferior mesenteric vein drains into splenic vein behind body of pancreas o Superior mesenteric vein joins splenic vein to form the portal vein behind neck of pancreas Liver processes nutrients of venous blood which is then collected into the hepatic vein which drains into the inferior vena cava to be returned to the systemic circulation Portal-systemic anastomoses are formed between portal veins and adjacent systemic veins in 4 areas in the abdominal cavity Portal vein Systemic vein Left gastric vein Oesophageal vein (branch of azygos vein) Superior rectal vein (drains large intestine) Inferior rectal vein Paraumbilical vein Epigastric vein Colic veins Posterior abdominal veins Liver or portal obstruction due to increased portal venous pressure (as in liver cirrhosis) causes these veins to dilate widely, leading to severe venous haemorrhage from oesophagus or rectum if ruptured (especially first 2 anastomoses) 22 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal LYMPHATIC DRAINAGE OF GUT Follows arterial supply; all these nodes are connected to each other Lymph nodes are grouped around abdominal aorta Lymphatic channels drain to LNs named after corresponding artery supplying respective parts of gut (branches of abdominal aorta) o Coeliac nodes o Superior mesenteric nodes o Inferior mesenteric nodes (paraaortic nodes) – drains distal part of large intestine and rectum Lymph channels connect lymph nodes and drain lymph upwards toward cisterna chyli, an elongated lymphatic sac located anterior to L1-L2 bodies, from which the thoracic duct arises INNERVATION OF THE ABDOMINAL VISCERA Abdominal viscera is supplied by autonomic nervous system (sympathetic and parasympathetic) Parasympathetic Regulate reflex gut function (peristalsis), main nerve fibres arise from vagus nerve (CN X – up to left colic flexure) and pelvic splanchnic nerves (S2-S4 – supplies hindgut) Sympathetic Mediates pain Main nerve fibres arise from the thoracic splanchnic nerves (T5-T12) and lumbar splanchnic nerves (L1-L2), which arise from the sympathetic chain Thoracic splanchnic nerves are divided into the greater splanchnic nerve (T5-T9), lesser splanchnic nerve (T10-T11) and least splanchnic nerve (T12) Sensory – Sensory fibres running with the parasympathetic fibres (vagus, sacral) are involved in reflex autonomic regulation of gut function (visceral afferents) control of the gut Sensory fibres running with the sympathetic fibres (T1-L2) mediate pain – any pathology in the gut is perceived through sensory fibres travelling in the sympathetic pathway Sensory fibres are the most important – where pain sensation is perceived Autonomic nerves are routed via plexuses along the abdominal aorta and its branches, before nerve fibres reach the respective viscera Some exceptions include parasympathetic fibres in the pelvic region that go directly to the visceral organs 23 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal GUT HISTOLOGY I GENERAL STRUCTURE OF THE GUT (FROM LUMEN OUTWARDS) 9m long muscular tube extending from the mouth to the anus Functions mainly in digestion, absorption and elimination Gut wall conforms to general plan composed of 4 distinctive layers that show minor variations Mucosa Epithelium Mainly columnar, except in the oesophagus and distal anal canal, where it is stratified squamous Lamina Non-epithelial tissue; consists of connective tissues (which help to support the propria surface lining epithelium and glands), nerves, blood vessels and diffused population of inflammatory cells (lymphocytes and plasma cells form aggregates at certain areas and are part of the mucosa immune system) Muscularis Thin layer of muscle separating mucosa from submucosa, consists of layers: mucosae Inner circular Layered arrangement important to maintain mobility of Outer longitudinal mucosa and for expelling of glandular secretions Points where mucosa undergoes abrupt transition: gastroesophageal junction, gastroduodenal junction, ileocaecal junction and rectoanal junction Mucosa shows modification reflecting its function Protective Non-keratinising stratified squamous Protects against potential frictional trauma e.g. passage of food during mastication and swallowing, or during passage of faeces through anal canal Found in oral cavity, pharynx, oesophagus, anal canal Secretory Epithelium dips into lamina propria to form simple or branched tubular glands that are closely packed; glands produce various combinations of acid and digestive enzymes to facilitate digestion of food and secrete mucous to protect mucosa Found in stomach 24 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Absorptive Mucosa forms villus projective – increase SA of mucosa, with intervening crypts (short glands); in the duodenum, some crypts extend through muscularis mucosae to form submucosal glands (Brunner’s glands) Found in small intestine Absorptive/ Mucosa arranged into closely packed, straight tubular glands consisting of cells protective specialised for water absorption, and mucous-secreting goblet cells that lubricate the passage of faeces Found in large intestine Submucosa Layer of loose connective tissue layer (collagenous, adipose) through which neurovasculature runs through – contains larger blood vessels, lymphatics, nerves that physically support mucosa Enteric nervous system: submucosal/ Meissner’s plexus Glands may be present in certain areas of the gut e.g. oesophagus, duodenum Muscularis Thick layer of muscle which powers movement of gut tube; arrangement of the 2 layers is externa/ important in maintaining the peristaltic movement of the gut propria Smooth muscle bundles are arranged in tight and loose helices around the gut wall Perpendicular action of muscle layers collectively results in peristaltic movement Inner circular Contractions lead to constriction of gut lumen Outer longitudinal Contractions shorten the gut length, pushing food forward Enteric nervous system: myenteric/ Auerbach plexus between the two layers Variations Skeletal muscles in upper oesophagus and anal canal instead of smooth muscle Extra inner oblique layer within the stomach Taenia coli (longitudinal layer that form long bundles) in the colon Localised thickening of circular muscle to form sphincters e.g. pyloric sphincter, internal anal sphincter Adventitia/ Adventitia = layer of connective tissue where the peritoneum is absent, e.g. oesophagus, rectum, serosa is in continuity with surrounding tissue Serosa = outermost layer of gut, connective tissue supporting serous membrane (visceral peritoneum i.e. flattened simple squamous epithelium – single cell layer of mesothelial cells), continuous with mesenteries; carries blood vessels and nerve Mesentery Double-layered peritoneal structure that suspends the gut tube Conduit for all blood vessels, lymphatics and nerves Note that the enteric nervous system is the intrinsic nervous system of the gut 25 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal ENTERIC NERVOUS SYSTEM Largely autonomic, comprising an extensive meshwork of neurones in the gut wall Forms a diffuse neuroendocrine system that controls gut peristalsis, epithelial secretion, absorption and blood flow (known as the second brain) Nerve plexus consists of neurones and ganglion cells o Ganglion cells are recognisable by large round nucleus with nucleoli and basophilic cytoplasm Submucosal/ Meissner plexus: postganglionic sympathetic fibres arising from superior mesenteric plexus Myenteric/ Auerbach plexus: larger clusters of parasympathetic ganglion cells Interstitial cells of Cajal: stellate myoid cells around the nerve plexuses o Represent pacemaker cells of the gut – initiate contraction of smooth muscle and are modulated by the autonomic nervous system (particularly parasympathetic) o Difficult to visualise in regular H&E section but stain brown with the immunohistochemical marker c-kit; around nerve plexuses and in the muscularis layer OESOPHAGUS Strong muscular tube that conveys food from oropharynx to stomach Lined by non-keratinising stratified squamous epithelium which performs a protective function Submucosa contains mucous glands (similar to salivary glands; most prominent in upper and lower thirds) which helps to lubricate mucosa during passage of food and has abundant elastin fibres that allow for considerable distention during passage of food bolus Muscularis externa comprises usual inner circular and outer longitudinal layers Upper third Skeletal muscle fibres – initiation of swallowing is voluntary Middle third Mix of skeletal and smooth muscle fibres Lower third Smooth muscle fibres – strong peristaltic reflex conveys bolus into stomach Note that muscularis mucosae has no role in propelling food bolus Adventitia present, except for lower part of oesophagus – intra-abdominal and thus covered by serosa Arrows indicate muscularis mucosae (stratified squamous, right), submucosal glands, and muscularis propria (inner circular, outer longitudinal) respectively 26 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal GASTROESOPHAGEAL JUNCTION Where mucosa of tract undergoes abrupt transition from protective stratified squamous epithelium to tightly packed glandular secretory mucosa Muscularis mucosa is continuous across junction, although less easily seen in the stomach where it lies immediately beneath the base of the gastric glands Underlying submucosa and muscularis propria continued uninterrupted beneath mucosal junction Point of physiological sphincter, involving 4 complementary factors: o Diaphragmatic contraction o Greater intra-abdominal pressure than intragastric pressure being exerted upon abdominal part of oesophagus o Unidirectional peristalsis o Maintenance of correct anatomical arrangements of structures Malfunction of sphincter allowing reflux of gastric acid into lower oesophagus results in heartburn and metaplasia with time o Barrett’s oesophagus: stratified squamous epithelium of lower oesophagus becomes columnar mucus-secreting o High risk of dysplasia and invasive adenocarcinoma of generally poor prognosis STOMACH Distensible organ that may retain food for >2h for mechanical and chemical breakdown to form chyme Adipose tissue of lesser and greater omentum is attached along lesser and greater curvature of stomach; lymph nodes and large blood vessels lie within omental fatty tissue Mucosa Significant changes to reflect secretory function Muscularis mucosa demarcates mucosa from submucosa Gastric mucosa is thrown into gastric rugae – prominent longitudinal folds that allow for distension Submucosa Loose connective tissue, highly vascular, extends into gastric rugae Submucosal glands are absent Muscularis externa 3 layers including additional innermost oblique layer Pyloric sphincter: thickening of circular muscle (of muscularis externa) at pylorus Serosa 27 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal GASTRIC MUCOSA There are 2 epithelial compartments in the gastric mucosa: Superficial Gastric pits formed by pale mucous-secreting columnar cells of surface epithelium foveolae layer that dip down into the lamina propria; occupy about ¼ of the thickness of mucosa Relatively uniform throughout stomach, secrete mucous Deeper Gastric specialised glands (1-7) underlying the pits and open into the gastric pits glandular layer Major differences in thickness and composition in different regions of the stomach Secrete gastric juices, a watery secretion containing: Hydrochloric acid: pH 0.9-1.5 Pepsin: hydrolyses proteins into polypeptide fragments Mucus: protect against self-digestion of stomach mucosa (maintained at a higher pH than the gastric juice by secretion of bicarbonate ions by gastric surface mucous cells) Histological zones of the stomach mucosa Cardia Thicker foveolar layer with deeper pits Small area of mucous-secreting glands surrounding the entrance of the oesophagus May measure only a few millimetres or be incomplete or absent altogether Fundus, Thinner foveolar layer with short gastric pits Body Most of mucosa here is composed of the glandular layer – specialised gastric glands filling mucosa; cells secrete HCl and intrinsic factor Ratio of pits:glands is about 1:3 Pylorus/ Thicker foveolar layer with deeper pits that occupy about half the thickness of the pyloric pyloric mucosa, lined almost exclusively by mucus-secreting cells (PS = pyloric sphincter) antrum Underlying layer of simple mucous glands in deeper third of mucosa Pyloric glands are branched and coiled Associated endocrine cells (G cells) secrete gastrin when stimulated by the presence of food in the stomach; gastrin promotes the secretion of pepsin and acid by the gastric glands of the fundus and body, and enhances gastric mobility Ratio of pits:glands is about 1:1 28 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Main cells: chief cells/ peptic cells/ zymogen cells and parietal cells/ oxyntic cells Chief More numerous bluish staining cells, secrete precursors of pepsin, renin, and lipase cells More cuboidal and more numerous towards lower half of the glands Parietal Distributed along length of glands but tend to be more numerous in isthmus of glands cells Large ovoid cells with central round nucleus and bright eosinophilic (oxyntic) granular cytoplasm, scattered among chief cells Secrete gastric acid (HCl) and intrinsic factor (glycoprotein necessary for absorption of vitamin B12) Secretion is triggered by the activation of H2 receptor by histamine Gastrin and acetylcholine can also stimulate secretion via different receptors Canaliculi: invaginations into cytoplasm – luminal membrane modification Once receptors are activated, proton pumps actively transport H+ into the canalicular lumen to bind to Cl- to form HCl Acid production can hence be blocked at various stages – therapeutic basis of H2 receptor blockers and PPIs (right: top arrow is a parietal cell, bottom arrow is a chief cell) With few neuroendocrine cells, regenerative cells and mucous neck cells (third image, red arrows) Principal secretions of gastric epithelial cells Surface lining cells, mucous neck cells Mucous – prevent acid from digesting the mucosa Parietal cells HCl and gastric intrinsic factor Chief cells Precursors of pepsin, renin, and lipase Diffuse neuroendocrine cells Hormones – gastrin, somatostatin, secretin, cholecystokinin (DNES – scattered endocrine cells) GASTRODUODENAL JUNCTION Termination of pylorus and site of strong muscular pyloric sphincter formed by thickening of the circular layer of the muscularis Marks sharp transition from glandular secretory type mucosa of stomach to villus absorptive type mucosa of duodenum Circular and longitudinal layers of muscularis between pylorus and duodenum are continuous 29 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal SMALL INTESTINES Principal site for absorption of digestion products Mucosa is distinguished by presence of villi (which increase absorptive surface; tend to be longest in the duodenum and become shorter towards the ileum) lined by: Columnar Have eosinophilic cytoplasm around oval nucleus epithelium Reflect absorptive function; basally situated with accentuation along luminal border absorptive cells of cells forming the striated brush border (enterocytes) Numerous microvilli, which are evenly spaced surfaced projections to increase mucosal SA for absorption, can be seen on electron microscopy (third image) Overlying layer of glycocalyx may be highlighted using mucin stain (second image – mucous cells also highlighted in pink) Goblet cells – Secrete mucin for lubrication of intestinal contents and protection of the interspersed epithelium; proportion of which increases distally Characteristic shape Mucin appears unstained on H&E sections Lymphocytes Scattered, appear as small blue dots Crypts of Lieberkuhn: simple tubular glands that lie deep to the villi, open into intervillous spaces; contains regenerative cells, DNES and Paneth cells at the base o Paneth cells produce lysosomes, defensins, phospholipase A and immunoglobulins, and have phagocytic capabilities; contain dense eosinophilic apical granules (red arrow) 30 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Peyer’s patches: follicles formed by aggregates of lymphoid cells in ileum, especially distal ileum o Intraepithelial lymphocytes provide defence against invasive organisms o Present throughout small intestines but fairly inconspicuous in the duodenum Lacteal capillaries run in the centre of the villous and absorb dietary fats in the form of chylomicrons, which form chyle that is emptied into larger lymphatic vessels Plicae circulares (valvulae conniventes/ folds of Kerckring): circular/ transverse folds of the mucosa that are covered with villi; most prominent and numerous in the jejunum and proximal ileum but are generally absent in the proximal duodenum and distal ileum; distinguishes small intestine from large intestine Muscularis mucosae: lies immediately beneath the mucosal crypts; separates mucosa from submucosa, which extends into and forms the core of the plicae circulares Brunner’s glands: submucosal glands exclusively found in duodenal submucosa (distinctive) o Ducts pass through muscularis mucosae to open into the crypts between the mucosal villi o Secrete alkaline mucous material in response to the presence of chyme in the duodenum so as to neutralise gastric acid and pepsin o Other secretions: lysozyme, epidermal growth factor Top arrow = muscularis mucosa, glands beneath the muscularis mucosa are submucosal glands (bottom arrow) – distinctive feature of duodenum Muscularis propria consists of inner circular and outer longitudinal layer ILEOCAECAL JUNCTION Marked by cone-shaped ileocaecal valve consisting of thickened extension of the muscularis propria that provides robust support for the mucosa Area of abrupt transition in lining of valve from small intestinal villiform pattern to glandular epithelial COLON Principal function: recovery of water and salt from faeces, and propulsion of increasingly solid faeces to rectum prior to defecation Mucosa is distinct in that it lacks villi and is incompletely folded in the non-distended state but does not exhibit distinct plicae circulares; lined by: Columnar epithelial with Absorb water surface absorptive cells More numerous in proximal colon Goblet cells secrete Numerous, increase in numbers towards the distal end to help in mucous lubrication of faecal material which becomes increasingly dehydrated Colon has highest concentration of goblet cells in the epithelial lining Crypts of Lieberkuhn seen as regularly spaced tubular glands, formed by dipping of epithelium into the lamina propria and extending into prominent muscularis mucosa (which touches the bases of glands) Inflammatory cells are scant and scattered in the lamina propria, which fills the space between the glands Paneth cells may be found in the proximal colon, but is always considered metaplastic in the distal colon (descending colon, sigmoid and rectum) and may be an indication of inflammatory bowel disease 31 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal APPENDIX First arrow: muscularis propria and serosa Second arrow: prominent lymphoid aggregates/ follicles in submucosa and mucosa – bluish area, distinctive in appendix Third arrow: inner layer of mucosa Fourth arrow: central lumen Small, blind-ended tubular sac extending from the caecum, just distal to the ileocaecal junction General structure conforms to that of the rest of the large intestine, but the most characteristic feature (particularly in the young) is the presence of masses of lymphoid tissue that diffusely infiltrate the mucosa and submucosa with much less closely packed mucosal glands o Lymphoid tissue forms follicles that often contain germinal centres and bulge into the lumen of the appendix and are invested by simple epithelium of M cells Most common disorder affecting the appendix is acute appendicitis, which presents with severe abdominal pain, initially centred in the middle of the abdomen and then later localizing to the right iliac fossa; fairly common acute surgical emergency that if left untreated, may rupture and discharged infected pus into the peritoneal cavity, resulting in acute peritonitis ANORECTAL JUNCTION Area of abrupt transition from glandular epithelium of rectum (short, dilated terminal portion of the large intestine that exhibits the same mucosa as the rest of the large bowel but has even more numerous goblet cells) to stratified squamous epithelium of anal canal Branched tubular circumanal glands open at the junction into small pits at the distal ends of the anal columns (of Morgagni), which is formed by longitudinal folds of the mucosa Demarcated by pectinate (dentate) line ANAL CANAL – TERMINAL PART OF GI TRACT (LAST 2-3CM) Mucosa: epithelium undergoes a gradual transition to skin Upper part Simple columnar mucosa (continuation), also has goblet cells that secrete mucous (for lubrication and also makes the faeces solid) Mid part Stratified squamous epithelium – more protective function Lower part Skin (keratinised) – contains sebaceous glands and large apocrine sweat glands Submucosa contains numerous vascular structures, forming the internal haemorrhoidal plexuses Muscularis externa contains the circular muscle which forms the internal anal sphincter 32 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal GUT ASSOCIATED LYMPHOID TISSUE (GALT) Mucosal lymphoid tissue seen as scattered follicles or aggregates as in ileal Peyer’s patches along GI tract, including Waldeyer’s tonsillar ring, Peyer’s patches and diffusely distributed lymphoid cells and plasma cells in the lamina propria Epithelium overlying dome-shaped structures are specialised for antigenic uptake M (microfold) cells: o Epithelial cells overlying the follicles which transport luminal antigens to subjacent lymphoid follicles scattered among normal epithelial cells o Show numerous microfolds instead of microvilli that transport luminal antigens to subjacent lymphoid follicles and mesenteric lymph nodes o Do not secrete digestive enzymes or mucus, and lack thick surface of glycocalyx In addition to lymphoid follicles, there are numerous plasma cells within lamina propria of small bowel Villus epithelium shows intraepithelial T lymphocytes which are also present within the lamina propria Act as sites for initiation of immune response against ingested pathogens Ileum: left arrow shows numerous lymphoid follicles as dense blue structures (Peyer’s patches), right arrow shows villi 33 TBL 2.1.1T – Anatomy of the abdominal wall, inguinal region and hernias, gut and peritoneal Part of GI tract Type of epithelium Main cell type of epithelium Other distinctive features Oesophagus (a) Stratified squamous Squamous cells Submucosal glands Body/ fundus of Glandular, straight Surface mucous cells Lymphoid cells are sparse stomach (b) tubular Neck mucous cells No lymphoid aggregates Parietal cells Chief (peptic) cells – only at fundus Pylorus and Glandular, coiled, Mucous cells Lymphoid cells are sparse cardia (c) branched tubular May be occasional parietal cells No lymphoid aggregates Duodenum (d) Glandular with villi and Enterocytes with microvilli Brunner’s gland crypts of Lieberkuhn Goblet cells Plicae circulares Paneth cells (after distal duodenum) Jejunum and Glandular with villi and Enterocytes with microvilli Peyer’s patches become ileum (e) crypts of Lieberkuhn Goblet cells more prominent distally Paneth cells Plicae circulares Colon and Glandular, straight Goblet cells Taeniae coli rectum (f) crypts Absorptive cells Appendix (g) Glandular, straight Goblet cells Prominent lymphoid tissue crypts Tall columnar cells Anus (h) Stratified squamous Squamous cells Columns of Morgagni 34