Intestine Anatomy PDF

INTESTINES Dr Ramya Rathan Asst Prof- Anatomy OBJECTIVES ▪ Differentiate between the Jejunum and the Ileum ▪ Explain the gross structure of the caecum ▪ Explain the Meckels Diverticulum ▪ Describe the features of vermiform appendix ▪ Describe the features of colon JEJUNUM AND ILEUM ▪ The jejunum and...

INTESTINES Dr Ramya Rathan Asst Prof- Anatomy OBJECTIVES ▪ Differentiate between the Jejunum and the Ileum ▪ Explain the gross structure of the caecum ▪ Explain the Meckels Diverticulum ▪ Describe the features of vermiform appendix ▪ Describe the features of colon JEJUNUM AND ILEUM ▪ The jejunum and ileum are suspended from the posterior abdominal wall by the mesentery and, therefore, enjoy considerable mobility. ▪ The jejunum constitutes the upper two-fifths of the mobile part of the small intestine, while the ileum constitutes the lower three-fifths. ▪ The jejunum begins at the duodenojejunal flexure. ▪ The ileum terminates at the ileocaecal junction. DIFFERENCES BETWEEN JEJUNUM AND ILEUM Feature Location Walls Lumen Mesentery Circular mucosal folds Jejunum Occupies upper and left parts of the intestinal area Ileum Occupies lower and right parts of the intestinal area Thicker and more vascular Thinner and less vascular Wider and often empty Narrower and often loaded a. Windows present b. Fat less abundant c. Arterial arcades, 1 or 2 d. Vasa recta longer and fewer a. No windows b. Fat more abundant c. Arterial arcades, 3 or 6 d. Vasa recta shorter and more numerous Larger and more closely set Smaller and sparse MECKEL’S DIVERTICULUM (DIVERTICULUM ILEI) ▪ Meckel’s diverticulum is the persistent proximal part of the vitellointestinal duct which is present in the embryo, and which normally disappears during the 6th week of intrauterine life. ▪ 1 It occurs in 2% subjects. ▪ 2 Usually, it is 2 inches or 5 cm long. ▪ 3 It is situated about 2 feet or 60 cm proximal to the ileocaecal valve, attached to antimesenteric border of the ileum. ▪ 4 Its calibre is equal to that of the ileum. ▪ 5 Its apex may be free or may be attached to the umbilicus, to the mesentery, or to any other abdominal structure by a fibrous band. LARGE INTESTINE ▪ The large intestine extends from the ileocaecal junction to the anus. ▪ It is about blind 1.5 m long, and is divided into the caecum (Latin blind pouch), the ascending colon, right colic flexure, the transverse colon, left colic flexure,the descending colon, the sigmoid colon, the rectum and the anal canal. ▪ In the angle between the caecum and the terminal part of the ileum, there is a narrow diverticulum called the vermiform appendix. FEATURES OF THE LARGE INTESTINE ▪ The large intestine is wider in calibre than the small intestine. The calibre is greatest at its commencement, and gradually diminishes towards the rectum where it is dilated to form the rectal ampulla just above the anal canal. ▪ The greater part of the large intestine is fixed, except for the appendix, the transverse colon and the sigmoid colon. ▪ The longitudinal muscle coat forms only a thin layer in this part of the gut. Looks like line going across intestine. The greater part of it forms three ribbon-like bands, called the taeniae coli. ▪ Small bags of peritoneum filled with fat, and called the appendices epiploicae (Greek to float on) are scattered over the surface of the large intestine, except for the appendix, the caecum and the rectum. These are most numerous on the sides of the sigmoid colon and on the posterior surface of the transverse colon. ▪ Sacculations: segments of the intestine ▪ Lymph from the large intestine passes through four sets of lymph nodes. ▪ a. Epicolic lymph nodes, lying on the wall of the gut. ▪ b. Paracolic nodes, on the medial side of the ascending and descending colon and near the mesocolic border of the transverse and sigmoid colon. ▪ c. Intermediate nodes, on the main branches of the vessels. ▪ d. Terminal nodes, on the superior and inferior mesenteric vessels. ▪ In carcinoma of the colon, the related paracolic and intermediate lymph nodes have to be removed. ▪ Their removal is possible only after the ligature of the main branch of the superior or inferior mesenteric artery along which the involved lymph nodes lie. It is necessary, therefore, to remove a large segment of the bowel than is actually required by the extent of the disease, in order to avoid gangrene as a result of interference with the blood supply. It is always wise to remove the whole portion of the bowel supplied by the ligated vessel. APPLIED ANATOMY ▪ Large intestine can be directly viewed by a procedure called colonoscopy. ▪ Diverticulum is a small evagination of mucous membrane of colon at the entry point of the arteries. Its inflammation is called diverticulitis CAECUM Features ▪ Caecum is a large blind sac (Latin blind) forming the commencement of the large intestine. ▪ It is situated in the right iliac fossa, above the lateral half of inguinal ligament. ▪ It communicates superiorly with ascending colon, medially at the level of caecocolic junction with ileum, and posteromedially with the appendix ▪ Dimensions ▪ It is 6 cm long and 7.5 cm broad. It is one of those organs of the body that have greater width than the length. ▪ The other examples are the prostate, pons and pituitary. ▪ Relations ▪ Anterior: Coils of intestine and anterior abdominal wall. ▪ Posterior ▪ 1 Muscles: Right psoas and iliacus. ▪ 2 Nerves: Genitofemoral, femoral and lateral cutaneous nerve of thigh (all of the right side). ▪ 3 Vessels: Testicular or ovarian. ▪ 4 Appendix in the retrocaecal recess. ▪ Vessels and Nerves ▪ The arterial supply of the caecum is derived from the caecal branches of the ileocolic artery. ▪ The veins drain into the superior mesenteric vein. ▪ The nerve supply is same as that of the midgut (T11 to L1; parasympathetic,vagus). ILEOCAECAL VALVE ▪ The lower end of the ileum opens on the posteromedial aspect of the caecocolic junction. The ileocaecal opening is guarded by the ileocaecal valve ▪ Structure ▪ The valve has two lips and two frenula. ▪ 1 The upper lip is horizontal and lies at the ileocolic junction. ▪ 2 The lower lip is longer and concave, and lies at the ileocaecal junction. The two frenula are formed by the fusion of the lips at the ends of the aperture. These are the left or anterior and the right or posterior frenula. The left end of the aperture is rounded, and the right end narrow and pointed. ILEOCAECAL VALVE ▪ Control and Mechanism ▪ 1 The valve is actively closed by sympathetic nerves, which cause tonic contraction of the ileocaecal sphincter. ▪ 2 It is mechanically closed by distension of the caecum. ▪ Functions ▪ 1 It prevents reflux from caecum to ileum. ▪ 2 It regulates the passage of ileal contents into the caecum, and prevents them from passing too quickly VERMIFORM APPENDIX ▪ Worm-like diverticulum arising from the posteromedial wall, of the caecum, about 2 cm below the ileocaecal orifice. ▪ Positions ▪ The appendix lies in the right iliac fossa. ▪ Although the base of the appendix is fixed, the tip can point in any direction, as described below. The positions are often compared to those of the hour hand of a clock (Figs 20.26 and 20.27). ▪ 1 The appendix may pass upwards and to the right. This is paracolic or 11 o’clock position. ▪ 2 It may lie behind the caecum or colon, known as retrocolic or 12 o’clock position. This is the commonest position of appendix, about 65%. VERMIFORM APPENDIX ▪ 3 The appendix may pass upwards and to the left. It points towards the spleen. This is the splenic or 2 o’clock position. The appendix may lie in front of the ileum (preileal) or behind the ileum (postileal). The preileal type is most dangerous type. ▪ 4 It may pass horizontally to the left (as if pointing to the sacral promontory) called promonteric or 3 o’clock position. ▪ 5 It may descend into the pelvis called pelvic or 4 o’clock position. This is the second most common position about 30%. 6 It may lie below the caecum (subcaecal) and may point towards the inguinal ligament called mid inguinal or 6 o’clock position. APPENDICULAR ORIFICE ▪ 1 The appendicular orifice is situated on the posteromedial aspect of the caecum 2 cm below the ileocaecal orifice. ▪ 2 The appendicular orifice is occasionally guarded by an indistinct semilunar fold of the mucous membrane, known as the valve of Gerlach. ▪ 3 The orifice is marked on the surface by a point situated 2 cm below the junction of transtubercular and right lateral planes. ▪ 4. McBurney’s point is the site of maximum tenderness in appendicitis. The point lies at the junction of lateral one-third and medial two-thirds of line joining the right anterior superior iliac spine to umbilicus ▪ Blood Supply ▪ Appendicular artery ▪ Blood from the appendix is drained by the appendicular, ileocolic and superior mesenteric veins, to the portal vein. ▪ Nerve Supply ▪ Sympathetic nerves : T9 and T10 segments ▪ Parasympathetic nerves : vagus. ▪ Lymphatic Drainage ▪ Most of the lymphatics pass directly to the ileocolic nodes. ASCENDING COLON ▪ 12.5 cm long and extends from the caecum to the inferior surface of the right lobe of the liver. ▪ Here it bends to the left to form the right colic flexure. ▪ Right Colic Flexure (Hepatic Flexure) ▪ Right colic flexure lies at the junction of the ascending colon and transverse colon. ▪ Here the colon bends forwards, downwards and to the left. ▪ The flexure lies on the lower part of right kidney. ▪ Anterosuperiorly, it is related to the colic impression on inferior surface of the right lobe of liver TRANSVERSE COLON ▪ Transverse colon is about 50 cm long and extend across the abdomen from the right colic flexure to the left colic flexure (splenic flexure). ▪ Actually, it is not transverse, but hangs low as a loop to a variable extent. It is suspended by the transverse mesocolon attached to the anterior border of pancreas, and has a wide range of mobility. ▪ Anteriorly, it is related to the greater omentum and to the anterior abdominal wall. ▪ Posteriorly, it is related to the second part of the duodenum, the head of the pancreas, and to coils of small intestine ▪ Left Colic Flexure (Splenic Flexure) ▪ Left colic flexure lies at the junction of the transverse colon and the descending colon. ▪ Here the colon bends downwards, and backwards. ▪ The flexure lies on the lower part of the left kidney and diaphragm, behind the stomach, and below the anterior end of the spleen. ▪ The flexure is attached to the eleventh rib (in the midaxillary line) by a horizontal fold of peritoneum, called the phrenicocolic ligament. ▪ This ligament supports the spleen and forms a partial upper limit of the left paracolic gutter. DESCENDING COLON ▪ Descending colon is about 25 cm long and extends from the left colic flexure to the sigmoid colon. ▪ It runs vertically up to the iliac crest, and then inclines medially on the iliacus and psoas major to reach the pelvic brim, where it is continuous with the sigmoid colon. ▪ The descending colon is narrower than the ascending colon. ▪ Anteriorly, it is related to the coils of small intestine. ▪ Posteriorly, it is related to the transversus abdominis, the quadratus lumborum, the iliacus and psoas muscles; the iliohypogastric, ilioinguinal, lateral cutaneous, femoral and genitofemoral nerves; the gonadal and external iliac vessels SIGMOID COLON (PELVIC COLON) ▪ Sigmoid colon is about 37.5 cm long, and extends from the pelvic brim to the third piece of the sacrum, where it becomes the rectum. ▪ It forms a sinuous loop, and hangs down in pelvis over the bladder and uterus. ▪ Occasionally, it is very short, and takes a straight course. ▪ It is suspended by the sigmoid mesocolon and is covered by coils of small intestine