Anatomy Of Small And Large Intestine PDF

ANATOMY OF SMALL AND LARGE INTESTINE By: DR.MONIA ALI Small Intestine The small intestine is a long, tube-like organ that is responsible for the majority of nutrient absorption in the digestive system. It is divided into three sections: the duodenum, jejunum, and ileum. T...

ANATOMY OF SMALL AND LARGE INTESTINE By: DR.MONIA ALI Small Intestine The small intestine is a long, tube-like organ that is responsible for the majority of nutrient absorption in the digestive system. It is divided into three sections: the duodenum, jejunum, and ileum. The inner walls of the small intestine are lined with tiny finger-like projections called villi, which increase the surface area for nutrient absorption 1.Duodenum The most proximal portion of the small intestine. It runs from the pylorus of the stomach to the duodenojejunal junction. The duodenum can be divided into 4 parts: 1. Superior 3. Inferior 4. Ascending. Together these parts form a ‘C’ shape, D1 – Superior (Spinal level L1) -The first part lies in the transverse plane and begins anterolaterally to the right of L1 vertebral body, continuing the pylorus. -The proximal portion of the first part has a segment of the lesser omentum called the hepatoduodenal ligament attached to its superior surface, and the greater omentum attached to the inferior surface. D1 – Superior (Spinal level L1) Relations: Anteriorly: The quadrate lobe of the liver and the gallbladder. Posteriorly: The lesser sac (first inch only), the gastroduodenal artery, the bile duct and the portal vein, and the inferior vena cava. Superiorly: The entrance into the lesser sac (the epiploic foramen) Inferiorly: The head of the pancreas D2 – Descending (L1-L3) -The descending portion curves inferiorly around the head of the pancreas. -It lies posteriorly to the transverse colon, and anterior to the right kidney. -Internally, the descending duodenum is marked by the major duodenal papilla – the opening at which bile and pancreatic secretions to enter from the ampulla of Vater (hepatopancreatic ampulla). D2 – Descending (L1-L3) Relations: Anteriorly: Gallbladder and right lobe of the liver, transverse colon, transverse mesocolon (commencement), and coils of the small intestine. Posteriorly: Right kidney and right renal vessels, right edge of the inferior vena cava (IVC), and right psoas major muscle. Medially: Head of the pancreas. Laterally: From below upward, ascending colon, right colic flexure, and right lobe of the liver. D3 – Inferior (L3) -The inferior duodenum travels laterally to the left, crossing over the inferior vena cava and aorta. It is located inferiorly to the pancreas, and posteriorly to the superior mesenteric artery and vein. RELATION Anteriorly: Root of the mesentery, superior mesenteric vessels, and coils of the jejunum. Posteriorly: Right psoas major, right ureter, IVC, abdominal aorta, and right gonadal vessels. Superiorly: Head of the pancreas with its uncinate process. Inferiorly: Coils of the jejunum. D4 – Ascending (L3-L2) -After the duodenum crosses the aorta, it ascends and curves anteriorly to join the jejunum at a sharp turn known as the duodenojejunal flexure. -Located at the duodenojejunal junction is a slip of muscle called the suspensory muscle of the duodenum. -Contraction of this muscle widens the angle of the flexure, and aids movement of the intestinal contents into the jejunum. D4 – Ascending (L3-L2) RELATIONS: Anteriorly: Transverse colon and transverse mesocolon. Posteriorly: Left psoas major muscle, left sympathetic chain, left gonadal vessels, and inferior mesenteric vein. Superiorly: Body of the pancreas. On to the left: Left kidney and left ureter. On to the right: Upper part of the root of mesentery. *When we talking about structure of the abdomen we often encounter the terms ~ Retroperitoneal { } ~ intraperitoneal { } So, of these components the proximal portion of 1st part of duodenum and jejunum and ileum. Are intraperitoneal. Where the destal of 1st part of duodenum and 2nd, 3rd, 4th part of duodenum Are retroperitoneal  Blood supply The arterial supply of the duodenum is derived from two sources: 1-The celiac trunk gives off the common hepatic artery, which also gives rise to the supraduodenal artery supplying portions of the first and second duodenal parts, and the gastroduodenal artery, which has a branch called the superior pancreaticoduodenal artery, that supplies the first two parts of the duodenum up until the major duodenal papilla. 2-The SMA {superior mesenteric artery} on the other hand, gives off a branch called the inferior pancreaticoduodenal artery, which supplies the other two parts of the duodenum, distal to the major duodenal papilla. The superior and inferior pancreaticoduodenal arteries give anterior and posterior branches that connect with each other, forming anastomoses between the celiac trunk and the SMA.  Venous drainage The veins of the duodenum drain alongside the arteries and venous blood is collected by the splenic and superior mesenteric vein which eventually drain into the hepatic portal vein. lymphatic drainage To the pancreatoduodenal and superior mesenteric nodes >> drain into the celiac lymph nodes. Nerve Supply The small intestine receives its nerve supply primarily from the enteric nervous system, which is a complex network of nerves that regulates the gastrointestinal tract. The enteric nervous system consists of both intrinsic and extrinsic nerves. The extrinsic nerves that supply the small intestine include: Vagus nerve (cranial nerve X) and the pelvic splanchnic nerves. These extrinsic nerves help control various functions such as motility, secretion, and blood flow within the small intestine. Intrinsic nerves are part of the enteric nervous system itself and are responsible for coordinating peristalsis, regulating local blood flow, and modulating secretions in the small intestine. Jejunum and Ileum we have the jejunum which is the second part of the small intestine, beginning at the duodenojejunal flexure, where the small intestine becomes intraperitoneal again. And after the jejunum, there’s the ileum, which is the third and final part of the small intestine. There is no clear visible demarcation between the jejunum and ileum, but when we divide the abdominopelvic cavity into four quadrants, we can see that the jejunum is mostly situated in the left upper quadrant while the ileum is mostly in the right lower quadrant. Iliocecal Valve The ileum opens into the large intestine, where the cecum and ascending colon join together. Possible functions of the ileocecal fold include preventing reflux from the cecum to the ileum, and regulating the passage of contents from the ileum to the cecum.  Blood supply The arterial blood supply for the jejunum and ileum is provided by the SMA. The arterial supply to the jejunum includes: jejunal arteries from the SMA The arterial supply to the ileum includes: ileal arteries from the SMA, and an ileal branch from the ileocolic artery (from SMA).  Blood supply The difference between the jejunum and ileum comes in: Jejunum: has fewer arcades with larger loops and longer vasa recta, Ileum: has more arcades with shorter loops and shorter vasa recta. LARGE INTESTINE The colon The colon (large intestine) is a distal part of the gastrointestinal tract, extending from the cecum to the anal canal. Anatomically, the colon can be divided into four parts :– Ascending: » Caecum » Vermiform appendix Transverse Descending Sigmoid The colon averages 150cm in length. The Large Intestine The large intestine can easily be distinguished from the small intestine by: 1. Taeniae coli, three thickened bands of longitudinal muscle. 2. The sacculations of its walls between the taeniae, called haustra. 3. Appendices epiploicae (omental appendages), the small pouches of omentum filled with fat. 4. Much greater caliber. Three Teniae Coli Thickened bands of smooth muscle representing most of the longitudinal coat. These begin at the base of the appendix as the thick longitudinal layer of the appendix splits to form three bands. The teniae run the length of the large intestine, merging again at the rectosigmoid junction into a continuous longitudinal layer around the rectum. Appendix Epiploica Fat-filled pockets of peritoneum projecting from the visceral peritoneum on the surface of the large intestine There are many appendices epiploices on the large intestine (except the rectum) ; also known as omental appendage. Haustra Multiple pouches in the wall of the large intestine. Haustra form where the longitudinal muscle layer of the wall of the large intestine is deficient; also known as: sacculations  THE CAECUM The sac-like caecum is the 1st part of the large intestine and is obviously continuous with the Ascending colon The caecum is a broad blind pouch and is 5 to 7 cm in length. It is located in the right lower quadrant, where it lies in the iliac fossa, inferior to the ascending colon The ileum opens into its superior part at the ileocaecal junction. About 2.5 cm inferior to this, the vermiform appendix opens into its medial aspect. Unlike the ascending colon above it, the cecum is intraperitoneal. THE VERMIFORM APPENDIX This is a narrow, worm-shaped blind tube. It is variable in length, averaging 8 cm. It joins the caecum about 2.5 cm inferior to the ileocaecal junction and is relatively longer in infants and children than in adults. The appendix has its own short triangular mesentery, called the mesoappendix.This suspends it from the mesentery of the terminal ileum. The position of the body of the appendix is variable: retrocaecal or retrocolic (65%), pelvic (31%), subcaecal (2.3%) and rarely anterior or posterior to the terminal ileum. The base of the appendix is fairly constant and usually lies deep at the junction of the lateral and middle 1/3 of the line joining the ASIS and the umbilicus (McBurney's point). The three taeniae coli of the caecum converge at the base of the appendix and form a complete outer longitudinal coat for it. ASCENDING COLON It is located in the right paracolic gutter and covered by the peritoneum on the front and sides, which binds it to the posterior abdominal wall. Its posterior surface is located on 3 muscles: – Iliacus , – Quadratus Lumborum – Transversus abdominis. Anteriorly it is related to the coils of the small bowel and right edge of the greater omentum. RIGHT COLIC FLEXURE Junction of the ascending colon and the transverse colon. Right colic flexure lies anterior to the lower part of the right kidney and inferior to the right lobe of the liver Also known as: hepatic flexure. TRANSVERSE COLON It is the longest (20 inch/50 cm in length) and most mobile part of the large intestine. It stretches from the right colic flexure (in right lumbar region) to the left colic flexure (in the left hypochondriac region). Strictly speaking transverse colon isn’t transverse but creates a dependent loop in front of loops of small intestine between the left and right colic flexures. The lowest point of loop generally goes up to the level of umbilicus but might occasionally extend into the pelvis. Therefore, the transverse colon is generally ‘U’ shaped DIFFERENCES BETWEEN THE RIGHT TWO-THIRD AND LEFT ONE-THIRD OF THE TRANSVERSE COLON Right two-third of Left one-third of Features transverse colon transverse colon Development From midgut From hindgut Middle colic artery, a branch Left colic artery, a branch Arterial supply of superior mesenteric of inferior mesenteric artery (artery of midgut) artery (artery of hindgut) By pelvic splanchnic Nerve supply By vagus nerves nerves LEFT COLIC FLEXURE Junction of the transverse colon and descending colon. Left colic flexure lies anterior to the left kidney and inferior to the spleen; also known as: splenic flexure DESCENDING COLON The descending colon is longer (25 cm), narrower, and more deeply found than the ascending colon. It goes from the left colic flexure to the very front of the left external iliac artery in the level of pelvic brim where it becomes continuous with the pelvic colon (sigmoid colon). It’s covered by the peritoneum on the front and sides (Retroperitoneal)  SIGMOID COLON (PELVIC COLON) The sigmoid colon is around 15 inches (37.5 cm) long and attaches the descending colon with the rectum. It’s S shaped and therefore its name, sigmoid colon (G. Sigma = S-shaped alphabet). It goes from the lower end of descending colon in the left pelvic inlet to the pelvic surface of the 3rd section of sacrum, where it becomes continuous with the rectum. In the pelvis it is located in front of the bladder and uterus, below the loops of ileum. The sigmoid colon is suspended from the pelvic wall by a large peritoneal fold termed sigmoid mesocolon.  PARACOLIC GUTTERS The paracolic gutters are two spaces between the ascending/descending colon and the posterolateral abdominal wall. These structures are clinically important, as they allow infective material that has been released from abdominal organs to accumulate elsewhere in the abdomen.  ANATOMICAL RELATIONS Anterior Posterior Ascending colon Small intestine Iliacus and quadratus lumborum Greater omentum Right kidney Anterior abdominal wall Iliohypogastric and ilioinguinal nerves Transverse colon Greater omentum Duodenum Anterior abdominal wall Head of the pancreas Jejunum and ileum Descending Small intestine Iliacus and quadratus lumborum colon Greater omentum Left kidney Anterior abdominal wall Iliohypogastric and ilioinguinal nerves Sigmoid colon Urinary bladder Rectum Uterus (females only) Sacrum upper vagina (females only) Ileum  Arterial Supply As a general rule, midgut-derived structures are supplied by the superior mesenteric artery , and hindgut-derived structures by the inferior mesenteric artery. – The colon is supplied by the following arteries: 1. Ileocolic artery 2. Right colic artery 3. Middle colic artery 4. Left colic artery 5. Sigmoidal arteries. 6. Superior rectal artery VENOUS DRAINAGE The veins emptying the colon follow the arteries. The veins accompanying the ileocolic, right colic, and middle colic arteries join the superior mesenteric vein, while the veins, accompanying the branches of inferior mesenteric artery, join the inferior mesenteric vein. The superior and inferior mesenteric veins ultimately drain into the portal vein flow.  BLOOD SUPPLY TO THE COLON Ascending The lower smaller part of the colon ascending colon is supplied by the ileocolic artery. its bigger upper part is supplied by the right colic artery. Transverse The right two-third of the transverse colon colon is supplied by the middle colic artery. The left one-third by the left colic artery. Descending The left colic artery. colon Sigmoid The sigmoidal branches of the inferior colon mesenteric artery and superior rectal artery THE LYMPHATIC DRAINAGE The lymphatic drainage of the colon is medically very essential because carcinoma of the colon propagates via lymphatic route. There are numerous colic lymph nodes, which drain the lymph from the colon. These nodes have common routine of distribution. – Epiploic nodes, are small nodules and are located on the wall of the colon. – Paracolic nodes, is located quite close to the marginal artery (of Drummond), i.e., along the medial edges of the ascending and descending colons and along the mesenteric edges of transverse and sigmoid colons. – Intermediate colic nodes, is located along the ileocolic, right colic, middle colic and left colic, arteries, and drain into terminal nodes. RECTUM Begins at the 3rd sacral vertebra as a continuation of the sigmoid colon and ends at the recto anal junction about 2-3 cm anterior to and slightly below the tip of the coccyx. It descends within the sacrococcygeal concavity, at first running posteriorly and then curving anteriorly. Anteroposterior flexures=2 Lateral flexures=3 RECTUM Extends approximately 15 cm above the external anal margin. Its upper diameter is similar to that of the sigmoid colon, but more inferiorly it becomes dilated as the rectal ampulla. Unlike the sigmoid colon, the rectum has no sacculations, appendices epiploicae or taeniae coli. Upper third-covered by peritoneum anteriorly and laterally. Middle third-covered only anteriorly. Lower third-no peritoneal covering.  S3 1 inch infront of coccyx SHAPE (FLEXURES) OF RECTUM - Anteroposterior curve - 3 flexures 1. Upper concave to left 2. lower concave to left 3. Middle concave to right 3 folds of rectum  males females Anterior o Rectovesical pouch containing o Recto-uterine pouch, coils of ileum and sigmoid colon coils of ilium and o Base of urinary bladder. sigmoid colon o Ampulla of vas deference o Posterior wall of o Seminal vesicles vagina. o Prostatic gland o Terminal part of ureter. Posterior Muscles As males o Piriformis, LevatorAni, Coccygeus Bones o Sacrum, Coccyx Vessels o Superior Rectal Artery and Median Sacral Artery Laterally LevatorAni, Coccygeus, Pararectal As males Fossa 46 1. Superior rectal artery-the continuation of IMA It supplies the rectum and upper half of anal canal. 2. Middle rectal artery-arises from the anterior division of internal iliac artery 3. Inferior rectal artery -arises from internal pudendal artery 49 1. Superior rectal vein continues up as inferior mesenteric vein which drains into the splenic vein ( ) 2. Middle rectal vein drains into internal iliac vein ( ). 3. Inferior rectal vein drains into internal pudendal vein ( ). Superior, middle, and inferior rectal veins anastomose with each other in submucosa of rectum and anal canal. the dilation of the veins at the site of anastomosis 51  Tributary of superior rectal Above white line Generally painless Tributary of inferior rectal Below white line Generally painful  Lymph Drainage of Rectum 1.Upper half drains to para rectal L.Ns which drain to inferior mesenteric L.Ns. 2.Lower half drains to internal iliac lymph nodes.  Beginning: It begins one inch below and anterior to the tip of the coccyx at the recto-anal junction. Course: It runs down and backwards. Termination: It ends at the anus.  The upper part of the anal canal is lined by mucosa similar to that lining the rectum and is distinguished by a number of longitudinally oriented folds known as anal columns, which are united inferiorly by crescentic folds termed anal valves. Superior to each valve is a depression termed an anal sinus.  The anal valves together form a circle around the anal canal at a location known as the pectinate line (Dentate line) , which marks the approximate position of the anal membrane in the fetus. Inferior to the pectinate line is a transition zone known as the anal pecten, which is lined by nonkeratinized stratified squamous epithelium. The anal pecten ends inferiorly at the anocutaneous line (“white line”), or where the lining of the anal canal becomes true skin. Internal anal sphincter: -It is the thickened inner involuntary circular muscle layer of the anal canal. -Surrounds the upper 3/4th of the anal canal, extending from ano-rectal junction till the white line. Nerve supply: autonomic External anal sphincter: -Striated voluntary muscle fibers.  Blood supply, nerve supply and lymph drainage of anal canal: Upper part Lower part Blood -It is supplied by -It is supplied by: supply superior rectal artery. 1. Middle rectal artery of and - It is drained by internal iliac artery. venous superior rectal vein 2. Inferior rectal artery of drainage (portal circulation). internal pudendal artery. -The corresponding veins drain into internal iliac vein (systemic circulation.) Nerve Above pectinate line by Below pectinate line by supply autonomic nerve fibers. inferior rectal nerve (Sensitive to pain &touch). Lymphatic Above pectinate line Below the pectinate line into drainage into internal iliac LNs. superficial inguinal LNs.  Congenital Megacolon/Hirschsprung Disease It happens when neural crest cells don’t migrate and create the myenteric plexus (parasympathetic ganglia) in the sigmoid colon and rectum during embryonic development. This state ends in absence of peristalsis. Consequently the normal proximal colon becomes grossly dilated because of the fecal retention causing abdominal distension. The constricted section normally corresponds to rectosigmoid junction.  Cancer (Carcinoma) of Colon Cancer of colon (really large intestine) is a top cause of death in the Western world. Comparatively common in those who are above 50 years old and nonvegetarian. Slow growing tumor and causes constriction of the colon. In advanced cases, it spreads to the liver via portal vein circulation. If diagnosed early, hemicolectomy (partial resection of the colon) is carried out to heal the patient.  Diverticulosis The diverticulosis includes the herniation of the lining mucosa via the circular muscle between the teniae coli. The herniation takes place where the circular muscle coat is the feeblest, i.e., where it is pierced by the blood vessels. The inflammation of diverticula is named diverticulitis  Volvulus It’s a clinical illness, where a portion of gut rotates (clockwise/anticlockwise) on the axis of its mesentery. It typically happens because of adhesion of antimesenteric border of the gut to the parietes or some other viscera. It might correct itself spontaneously or the rotation may continue until the blood supply of the gut is cut off leading to ischemia. The sigmoid colon is susceptible to volvulus due to extreme freedom of its mesentery- the pelvic mesocolon.  Intussusception It is a clinical condition where a proximal section of the bowel invaginates into the lumen of an adjoining distal section. This might cut off the blood supply to the bowel and cause gangrene. The different forms of intussusception are ileoileal, ileocaecal, and colocolic. The ileocaecal intussusception is the most typical form.  Appendicitis Appendicitis is acute inflammation of the appendix, and is the most common cause for acute, severe abdominal pain. The abdomen is most tender at McBurney’s point – one third of the distance from the right anterior superior iliac spine to the umbilicus. This corresponds to the location of the base of the appendix. Initially, the appendicitis causes a vague pain in the periumbilical region. As the appendix swells, it irritates the parietal peritoneum, and causes severe pain in the right lower quadrant. If the appendix is not removed, it can become necrotic and rupture, resulting in peritonitis (inflammation of the peritoneum).