digestive 3.pptxpfanatomy small intestine and
- 1. Small intestine •The small intestine is the longest part of the alimentary canal, and the si te of most enzymatic digestion and virtually all absorption of nutrients. •Most digestive enzymes that operate within the small intestine are secre ted not by the small intestine, but by the pancreas. •During digestion, the small intestine undergoes active segmentation mo vements, shuffling the chyme back andforth and maximizing its contact with the nutrient-absorbing mucosa. Peristalsis propels chyme through the small i ntestine in about 3-6 hours. •The small intestine has three subdivisions: the duodenum, jejunum and i leum. Although similar in general structure, each region has its characteristic features.
- 2. Duodenum •The duodenum is the shortest, widest and most fixed part of the small intestine. •It is so named because its length (approximately 25 cm) •It extends from the pylorus to the duodenojejunal flexure. •It is C-shaped around the head of the pancreas.
- 3. •The superior part passes upwards, backwards and laterally to the right side of the 1st lumbar vertebra above the head of the pancreas. •Posterior to it are the common bile duct and the inferior vena cava. Superior Part
- 4. •The descending part turns down along the right side of the 2nd and 3rd lumbar vertebrae. •Posterior to it are the right renal vessels, upper part of the right ureter and a variable amount of the right kidney. Descending Part
- 5. The hepatopancreatic ampulla (ampulla of Vater) (formed by the union of the terminations of the bile and pancreatic ducts) opens on the summit of the major duodenal papilla, which is on the internal surface of the posteromedial aspect of the descending part. There may be a smaller opening about 2cm above the major duodenal papilla; this is the opening of the accessory pancreatic duct and it is called minor duodenal papilla.
- 6. •The horizontal part crosses 3rd lumbar vertebra from right to left to become continuous with the fourth part. •The inferior vena cava, aorta, testicular or ovarian vessels, and the origin of the inferior mesenteric artery are situated posterior to it. Horizontal Part
- 7. •The duodenojejunal flexure is fixed by a fibromuscular band, Suspe nsory muscle of duodenum . • It passes from the right crus of the diaphragm at the right side of th e esophagus, behind the pancreas, and is attached to the duodenojeju nal flexure posteriorly. •The ascending part turns upwards and ends at the duodenojejunal flexure at the level of the 2n d lumbar verteb ra. Ascending Part
- 8. • Suspensory muscle of duodenum (ligament of Treitz), a surgic al landmark, descends from the right crus of diaphragm to duodenal ter mination.
- 9. Jejunum & ileum •The jejunum and ileum form sausage-like coils that hang from the posterior abdominal wall by a mesentery, which permits the coils to move freely and are framed by the large intestine. •The jejunum makes up the superior left part of this coiled intestinal mass. •The ileum makes up the inferior right part of this coiled intestinal mass. In addition, some coils of the ileum lie in the pelvis between the bladder and rectum or the uterus and rectum.
- 10. Jejunum and ileum Characteristic Jejunum Ileum Position Upper 2/5, upper left pa rt of abdominal cavity Lower 3/5, lower right p art of abdominal cavity Diameter Greater Less Wall Thicker Thin Circular folds Larger, numerous and l arge villi Fewer，smaller and les s abundant villi Vascularity Greater Less Color Deeper red Paler pink Lymphatic follicles Solitary Aggregated Fat in mesentery Less More
- 11. Large intestine •The large intestine frames the small intestine on 3½ sides, forming an open rectangle. •The large has the following subdivisions: cecum, vermiform appendix, colon, rectum, and anal canal. •The colon is further divided into ascending, transverse, descending, and sigmoid colon.
- 12. •Over most of its length, the large intestine exhibits three special features. •The teniae coli (colic bands) are three longitudinal strips, spaced at equal intervals on the surfaces of the cecum and colon. They are thickenings of the longitudinal layer of muscularis. •Because the teniae coli maintain muscle tone, they cause the large intestine to pucker into many sacs called the haustra of colon, which make the colon a typical sacculated appearance. •Attached to the teniae coli are many small pieces of fat covered by visceral peritoneum called the epiploic appendices. They vary greatly in size in different parts of the large intestine, and are often rudimentary or absent in the cecum, rectum and appendix.
- 13. The cecum is situated in the right lower quadrant, where it lies in t he iliac fossa above the lateral half of the inguinal ligament. The caecum in most cases is completely covered with peritoneum a nd is therefore freely movable. But the posterior surface may be de void of peritoneum so that it is fixed to the posterior abdominal w all. Cecum
- 14. •When the cecum is distended, the anterior surface comes into contact with the anterior abdominal wall and may be palpated in the living subject. •When empty, its anterior surface is covered by coils of the small intestine. •The medial surfac is also related to coils of small intestine.
- 15. •The ileocecal orifice is a transverse slit in the posteromedial wall of the cecum. •This orifice is guarded by a valve composed of upper and lower folds which project into the cecal lumen. These folds form the ileocecal valve. •The ileocecal valve acts as a sphincter and relaxes at frequent intervals to allow a small amount of the ileal contents to pass through. The sphincter also prevents regurgitation of the cecal contents into the ileum, but not very effectively. •The orifice of the appendix, situated about 2 cm below the ileocecal orifice, is overlapped by a fold of mucous membrane which does not function as a valve to prevent the passage of the cecal contents into the appendix.
- 16. •The vermiform appendix is a worm-shaped blind tube. •Its base is attached to the cecum inferior to the ileocecal junction. Its apex is free. •The appendix varies in length from 2-23 cm, with a normal range of 7-12 cm. •Normally the appendix has a complete peritoneal covering; the proximal half is attached by mesentery, the mesoappendix; the distal half hangs free into the peritoneal cavity. Vermiform appendix
- 17. The position of the appendix varies considerably in different individuals and in the same individual from time to time. It may lie (i) in the retrocaecal fossa (the commonest position): (ii) entirely within the pelvis amongst the coils of the small intestine; (iii) close to the inguinal ligament; (iv) in front of or behind the terminal part of the ileum; or (v) to the lateral side of the cecum. When in the iliac fossa it is related to the iliacus and psoas major, and to the femoral nerve.
- 18. •Whatever the position of the tip of the appendix, the position of the base of the appendix normally lies deep to McBurney's point, which is at the junction of the lower and middle thirds of a line joining the right anterior superior iliac spine and the umbilicus.
- 19. Colon •The colon has several distinct segments. •The ascending colon ascends along the right side of the posterior abd ominal wall from the cecum, and reaches the level of the right kidney, where it makes a right-angle turn, forming the right colic flexure. •The ascending colon usually has no mesentery and is therefore relativ ely fixed. The upper part of the ascending colon is covered in front by coils of small intestine, but its lower part may come into direct contac t with the anterior abdominal wall.
- 20. •The transverse colon extends to th e left from the right colic flexure acr oss the peritoneal cavity. Directly an terior to the spleen, it bends acutely downward, forming the left colic fle xure. •The transverse colon is suspended b y the transverse mesocolon which pe rmits movement. •The left colic flexure is higher than the right and is in contact with the sp leen, the greater curvature of the sto mach, the tail of the pancreas and the anterior surface of the left kidney.
- 21. •The descending colon descends from the left colic flexure along the left side of the posterior abdo minal wall. After crossing the lef t iliac fossa, it becomes continuous with the sigmoid col on at the brim of the true pelvis. •Its upper part is placed deeply a nd is separated from the anterior abdominal wall by the termination of the transv erse colon and coils of the small intestine. When distended, its lower part freque ntly comes into contact with the anterior abdominal wall above t h inguinal ligament.
- 22. •Inferiorly, the colon enters th e true pelvis as S-shaped sigm oid colon. At the level of the third sacral verte bra, it continues to the rectum. •The sigmoid colon is suspen ded by the sigmoid mesocolo n. •The sigmoid colon lies deep i n the pelvis with coils of the s mall intestine separating it fr om the bladder in the male an d the uterus in the female.
- 23. The rectum is continuous proximally with the sigmoid colon at the level of 3rd sacral vertebra, and at the level of the tip of the coccyx it bends sharply backwards to become continuous with the anal canal. Rectum
- 24. •Even though the word rectum means “straight,” the rectum actually has several tight bends. •When viewed from anterior aspect, it is S-shaped and has three lateral curves. The upper and lower curves are usually convex to the right and the middle curve is convex to the left.
- 25. •These curves are represented as three transverse folds of the rectum, which are formed by the mucous membrane, submucosa and circular muscle layer of the rectal wall. •The most constant transverse fold of the rectum is middle one situated anteriorly and to the right just below the level of the reflection of the peritoneum from the rectum to the bladder or vagina. •These folds can be recognized on examination of the rectum in the living subject with a proctoscope, and the main fold may be felt on digital examination.
- 26. •These transverse folds prevent feces from being passed along with flatus (gas). •The dilated lower part of the rectum is called the rectal ampulla, which supports and holds the fecal mass before defecation. •Normally, distension of the rectum arouses the desire to defecate.
- 27. The relations of the rectum are important since many of the adjacent structures can be palpated from its lumen by an examining finger. Posteriorly, the rectum is related to the lower three sacral vertebrae and coccyx. The anterior relations of the rectum differ in the two sexes. In the male, the rectum is related to the seminal vesicles, the terminations of the ductus deferens, urinary bladder and prostate gland. Of these structures the prostate gland can readily be felt by digital examinatio n in the living subject.
- 28. •In the female, the rectum is related to the uterus and vagina. The cervix of the uterus is readily palpable as a rounded knob projecting backwards. The ovaries lie anterolateral to the rectum and may sometimes be felt by digital examination.
- 29. •The anal canal is the terminal part of the large intestine. •About 3 cm long, it begins at the level of the tip of the coccyx, where the rectum passes through the levator ani. As the levator ani form the pelvic floor, thus, the anal canal lies entirely external to the abdominopelvic cavity. •It passes downwards and backwards and ends at the anus. •Laterally the canal is separated from the fat of the ischiorectal fossa by the levator ani and the external sphincter. The presence of fat in the fossa allows the canal to dilate during the passage of fecal mass. Anal canal
- 30. •The lining membrane of the anal canal forms six to ten vertical folds called the anal columns. •The lower ends of the anal columns are joined together by pocketlike folds of mucous membrane, the anal valves. •The space between an anal valve and the anal wall is called an anal sinus. •The function of the anal columns and valves is not known. Interior of anal canal
- 31. •The inferior comb-shaped limit of the valves forms an irregular line known as the pectinate (dentate) line. •This line indicates the junction of the superior part of the anal canal (derived from the hindgut) and the inferior part (derived from the proctodeum). •Because the mucosa superior to this line is innervated by visceral sensory fibers, it is relatively insensitive to pain. Inferior to the pectinate line, however, the mucosa is sensitive to pain because it is innervated by somatic nerves.
- 32. •The anal canal is surrounded by an internal an al sphincter of smooth muscle and an external a nal sphincter of skeletal muscle. •The internal anal sphincter contracts involunta rily, whereas the external anal sphincter contracts voluntarily to inhibit defecation, both to prevent feces from leakin g from the anus between defecations and to inh ibit defecation during emotional stress. •Kids learn to control the external anal sphincte r during toilet training.
- 33. •The internal anal sphincter is a thickening of the circular muscle of the gut wall. •The external anal sphincter is usually described as tripartite, but there is no very clear distinction between the three parts. The subcutaneous part is deep to skin and does not affect anal continence. The superficial part is attached posteriorly to the coccyx. It encircles the anal canal to be inserted into the central tendon of the perineum. The deep part has no bony attachment and encircles the upper part of the internal anal sphinc
- 34. The tonic contractions of the external and internal anal sphincters keep the anus and anal canal closed, and are inhibited during defecation. The external anal sphincter is stronger than the internal anal aphincter, which appears to be unimportant for normal fecal continence since complete surgical division of the internal anal sphincter does not result in incontinence. If the external anal sphincter is paralysed, however, sphincter control is lost. In addition to the sphincter, the lower part of the rectum and the upper part of the anal canal are supported by the puborectalis, which passes around their lateral and posterior sides like a sling. Contraction of the puborectalis causes the angle between the rectum and anal canal to become more acute. Thus, its contraction is an important factor in preventing passage of feces from the rectum to the anal canal.