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Page 1: No. 6 1. Small Intestine 1. Small Intestine 2. Great Intestine 2. Great Intestine.

No. 6No. 6

1. Small Intestine1. Small Intestine

2. Great Intestine2. Great Intestine

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Section 5 The Small IntestineSection 5 The Small Intestine The The small intestinesmall intestine—is a convoluted tube, extending —is a convoluted tube, extending

from the pylorus to the ileocecal valve, where it joins tfrom the pylorus to the ileocecal valve, where it joins the large intestine. It is the longest part of the digestive he large intestine. It is the longest part of the digestive tract, being 6tract, being 6 ~~ 7 m.7 m.

DivisionDivision: The small intestine can be divided into three : The small intestine can be divided into three regions that are not otherwise distinct from each otheregions that are not otherwise distinct from each other:r:

DuodenumDuodenum: a short, curved section which is devoid of : a short, curved section which is devoid of a mesentery and is named the duodenum.a mesentery and is named the duodenum.

JejunumJejunum, and , and IleumIleum: the long, greatly coiled part whi: the long, greatly coiled part which is attached to the posterior abdominal wall by the ch is attached to the posterior abdominal wall by the mesentery, and of which the proximal 2/5 constitutes mesentery, and of which the proximal 2/5 constitutes the jejunum, and the distal 3/5 the ileum.the jejunum, and the distal 3/5 the ileum.

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ⅠⅠ. The . The DuodenumDuodenum It is the shortest, widest and most fixed part of the It is the shortest, widest and most fixed part of the

small intestine, about 25 cm long. It has no small intestine, about 25 cm long. It has no mesentery, and thus is only partially covered with mesentery, and thus is only partially covered with peritoneum.peritoneum.

Its course presents a remarkably constant curve, Its course presents a remarkably constant curve, somewhat of the shape of an incomplete circle, which somewhat of the shape of an incomplete circle, which encloses the head of the pancreas.encloses the head of the pancreas.

It begins at the pylorus and ends opposite the second It begins at the pylorus and ends opposite the second lumbar vertebra in the jejunum.lumbar vertebra in the jejunum.

For descriptive purpose it is divided into four parts i.e. For descriptive purpose it is divided into four parts i.e. the superior part,the superior part, the descending part,the descending part, the horizontal part,the horizontal part, the ascending part.the ascending part.

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ⅠⅠ) The ) The Superior PartSuperior Part (first part) (first part)

It is about 3 cm long, and is the most It is about 3 cm long, and is the most movable of the four parts.movable of the four parts.

It begins at the pylorus, and It begins at the pylorus, and continues with its descending part at continues with its descending part at the area of the neck of the the area of the neck of the gallbladder, where it forms the gallbladder, where it forms the superior duodenal flexure.superior duodenal flexure.

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ⅡⅡ) The ) The Descending PartDescending Part (second (second part)part)

It is 8It is 8 ~~ 10 cm long, descends from the superior duod10 cm long, descends from the superior duodenal flexure, along the right side of the vertebral coluenal flexure, along the right side of the vertebral column, and at the border of third lumbar vertebra continmn, and at the border of third lumbar vertebra continues with its horizontal part, where it forms the inferior ues with its horizontal part, where it forms the inferior duodenal flexure.duodenal flexure.

The The common bile ductcommon bile duct from the liver and the from the liver and the pancrepancreatic ductatic duct from the pancreas join together to form the from the pancreas join together to form the hepatopancreatic ampulla (ampulla of Vater)hepatopancreatic ampulla (ampulla of Vater) , whic, which empties into the duodenum at the h empties into the duodenum at the major duodenal major duodenal papillapapilla. This opening is surrounded by a sphincter mu. This opening is surrounded by a sphincter muscle called thescle called the hepatopancreatic sphincter (sphincthepatopancreatic sphincter (sphincter of Oddi)er of Oddi) ..

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ⅢⅢ) The ) The Horizontal PartHorizontal Part (inferior or (inferior or third part)third part)

It is about 10 cm long, begins at the It is about 10 cm long, begins at the inferior duodenal flexure.inferior duodenal flexure.

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ⅣⅣ) The ) The Ascending PartAscending Part (fourth (fourth part)part)

It is about 2.5 cm long, ascends to the level of tIt is about 2.5 cm long, ascends to the level of the upper border of the second lumber vertebrhe upper border of the second lumber vertebra, where it turns ventrally at the a, where it turns ventrally at the duodenojejuduodenojejunal flexurenal flexure and is continuous with the jejunu and is continuous with the jejunum.m.

The terminal part of the duodenum and the duThe terminal part of the duodenum and the duodenojejunal flexure are usually described and odenojejunal flexure are usually described and fixed in position by the fixed in position by the suspensory muscle of suspensory muscle of duodenumduodenum (suspensory muscle, or (suspensory muscle, or ligament ligament of Treitzof Treitz). ).

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ⅡⅡ. The . The JejunumJejunum The next 2.5 m or so of the small intestine is the jejunum.The next 2.5 m or so of the small intestine is the jejunum.

This portion is suspended in the abdominal cavity by a This portion is suspended in the abdominal cavity by a

mesentery.mesentery.①①It has a diameter of about 4 cm, and is thicker, redder anIt has a diameter of about 4 cm, and is thicker, redder an

d more vascular than the ileum.d more vascular than the ileum.②②The circular folds of its mucous membrane are large and The circular folds of its mucous membrane are large and

thickly set, and its villi surpass those of the ileum in size.thickly set, and its villi surpass those of the ileum in size.③③The The aggregated lymphatic folliclesaggregated lymphatic follicles are almost absent i are almost absent i

n the upper part of the jejunum; in the lower part they arn the upper part of the jejunum; in the lower part they are fewer and smaller than those in the ileum and tend to e fewer and smaller than those in the ileum and tend to assume a circular form.assume a circular form.

④④The most part of jejunum lies in the umbilical region, but The most part of jejunum lies in the umbilical region, but it may extend into any of the surrounding areas.it may extend into any of the surrounding areas.

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ⅢⅢ. The. The Ileum Ileum

The ileum is the remaining 3.5 m or The ileum is the remaining 3.5 m or so of the small intestine. Like the so of the small intestine. Like the jejunum, the ileum, is suspended jejunum, the ileum, is suspended from the posterior body wall by a from the posterior body wall by a mesentery.mesentery.

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① ① It has a diameter of 3.5 cm, and its wall is thinner than that of tIt has a diameter of 3.5 cm, and its wall is thinner than that of the jejunum.he jejunum.

② ② A few circular folds are present in the upper part of the ileum, bA few circular folds are present in the upper part of the ileum, but they are small and disappear almost entirely towards its lower ut they are small and disappear almost entirely towards its lower end.end.

③ ③ the aggregated lymphatic follicles are, however, large and morthe aggregated lymphatic follicles are, however, large and more numerous than those in the jejunum.e numerous than those in the jejunum.

④ ④ For the most part the ileum is situated in the hypogastric and pFor the most part the ileum is situated in the hypogastric and pelvic regions. The lower portion of the ileum usually lies in the peelvic regions. The lower portion of the ileum usually lies in the pelvis.lvis.

It ends in the right iliac fossa by opening into the medial side of tIt ends in the right iliac fossa by opening into the medial side of the junction of the cecum and ascending colon.he junction of the cecum and ascending colon.

The jejunum and ileum are attached to the posterior abdominal The jejunum and ileum are attached to the posterior abdominal wall by an extensive fold of peritoneum, termed the wall by an extensive fold of peritoneum, termed the mesenterymesentery, , which allows of very free movement, so that each coil can accomwhich allows of very free movement, so that each coil can accommodate itself to changes in form and position.modate itself to changes in form and position.

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Section 6 The Large IntestineSection 6 The Large Intestine

The The large intestinelarge intestine, which is about 1.5 , which is about 1.5 m long, 6.5 cm in diameter, extends from long, 6.5 cm in diameter, extends from the ileocecal valve to the anus. Its certm the ileocecal valve to the anus. Its certain parts are attached to the posterior aain parts are attached to the posterior abdominal wall by its mesocolon.bdominal wall by its mesocolon.

It is so named because its diameter in mIt is so named because its diameter in most regions is greater than that of the smost regions is greater than that of the small intestine.all intestine.

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The characteristics of the large intestineThe characteristics of the large intestine: The l: The large intestine differs considerably in structure, arge intestine differs considerably in structure, appearance, size and arrangement from the sappearance, size and arrangement from the small intestine: It has a greater caliber; for the mall intestine: It has a greater caliber; for the most part, it is more fixed in position.most part, it is more fixed in position.

The outstanding features are as the follows, wiThe outstanding features are as the follows, with the exceptions of the cecum, the vermiform th the exceptions of the cecum, the vermiform appendix and the rectum.appendix and the rectum.

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1. 1. colic bandcolic band: Its longitudinal muscular fibers form three c: Its longitudinal muscular fibers form three colic bands.olic bands.

2. 2. haustras of colonhaustras of colon: Since the colic bands are shorter tha: Since the colic bands are shorter than the circular muscular coat, the colon is puckered and sacn the circular muscular coat, the colon is puckered and sacculated, the sacculations being known as haustras of colon.culated, the sacculations being known as haustras of colon.

3. 3. epiploic appendicesepiploic appendices: Small, peritoneum—covered, adip: Small, peritoneum—covered, adipose projections, termed epiploic appendices, are found scaose projections, termed epiploic appendices, are found scattered over the free surface of the whole of the large intestittered over the free surface of the whole of the large intestine.ne.

The large intestine is divided into several parts:The large intestine is divided into several parts: the cecum,the cecum, colon,colon, rectum,rectum, anal canal.anal canal.

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ⅠⅠ. The . The CecumCecum

The large intestine begins as a blind pouThe large intestine begins as a blind pouch called the cecum, which receives the ich called the cecum, which receives the ileum of the small intestine.leum of the small intestine.

It is about 6 cm long and 7.5 cm wide. It iIt is about 6 cm long and 7.5 cm wide. It is a blind pouch of the closed end is direcs a blind pouch of the closed end is directed downward, and it opens above into tted downward, and it opens above into the ascending colon.he ascending colon.

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ⅡⅡ. The . The Vermiform AppendiVermiform Appendixx

It is a narrow, worm shaped tube, which springIt is a narrow, worm shaped tube, which springs from the posteromedial wall of the cecum, 2 s from the posteromedial wall of the cecum, 2 cm or less below the end of the ileum. It is abocm or less below the end of the ileum. It is about 9 cm long and about 1.5 cm wide.ut 9 cm long and about 1.5 cm wide.

The appendix is variable in position.The appendix is variable in position. Most commonly, the tip lies retrocecally or haMost commonly, the tip lies retrocecally or ha

ngs over the brim of the lesser pelvis.ngs over the brim of the lesser pelvis. The wall of the appendix contains numerous lyThe wall of the appendix contains numerous ly

mphatic nodules.mphatic nodules.

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ⅢⅢ. The . The ColonColon

It may be considered in four parts: It may be considered in four parts: the ascending,the ascending, transverse,transverse, descending,descending, sigmoid.sigmoid. The large intestine extends upward from the ceThe large intestine extends upward from the ce

cum as the cum as the ascending colonascending colon.. The ascending colon is not supported by a mesThe ascending colon is not supported by a mes

entery; instead, it lies tightly against the posteentery; instead, it lies tightly against the posterior wall of the abdomen.rior wall of the abdomen.

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Just beneath the liver, the ascending colon beJust beneath the liver, the ascending colon bends sharply to the left nds sharply to the left ((right colic flexureright colic flexure)) and and crosses the abdominal cavity as the crosses the abdominal cavity as the transverstransverse colone colon. This portion of the colon is suspende. This portion of the colon is suspended by a mesentery called the mesocolon.d by a mesentery called the mesocolon.

In the vicinity of the spleen, the transverse colIn the vicinity of the spleen, the transverse colon bends downward on bends downward ((left colic flexureleft colic flexure)) and fo and forms the rms the descending colondescending colon. .

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The descending colon, like the ascending coloThe descending colon, like the ascending colon, is retroperitoneal.n, is retroperitoneal.

Where the descending colon reaches the left pWhere the descending colon reaches the left pelvic brim, it curves to the midplane via an S-selvic brim, it curves to the midplane via an S-shaped haped sigmoid colonsigmoid colon..

The sigmoid colon is closely surrounded by peThe sigmoid colon is closely surrounded by peritoneum, which forms a mesentery, the ritoneum, which forms a mesentery, the sigmsigmoid mesocolonoid mesocolon..

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The position and shape of the sigmoid colon vThe position and shape of the sigmoid colon vary very much, and depend on:ary very much, and depend on:

① ① its length, its length, ② ② the length and freedom of its mesocolon, the length and freedom of its mesocolon, ③ ③ the condition of distension, the condition of distension, ④ ④ the condition of the rectum and bladder.the condition of the rectum and bladder. Usually it is relatively free within the lesser pelUsually it is relatively free within the lesser pel

vis below the small intestinevis below the small intestine

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ⅣⅣ. The . The RectumRectum

It is continuous with the sigmoid colon aIt is continuous with the sigmoid colon at the level of the third sacral vertebra. It it the level of the third sacral vertebra. It is about 12 cm long and its upper part has about 12 cm long and its upper part has the same diameter as the sigmoid colos the same diameter as the sigmoid colon (about 4 cm in the empty state), but its n (about 4 cm in the empty state), but its lower part of the rectum is dilated to forlower part of the rectum is dilated to form the m the ampulla of rectumampulla of rectum..

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Sacral flexure and perineal flexure of the rectuSacral flexure and perineal flexure of the rectumm::

From its origin it descends, following the concFrom its origin it descends, following the concavity of the sacrum and coccyx, forming an antavity of the sacrum and coccyx, forming an anteroposterior curve known as the eroposterior curve known as the sacral flexursacral flexuree of the rectum. It thus passes at first downwa of the rectum. It thus passes at first downwards and backwards, then downwards, and finards and backwards, then downwards, and finally downwards and forwards to become continlly downwards and forwards to become continuous with anal canal by passing through the puous with anal canal by passing through the pelvic diaphragm.elvic diaphragm.

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The anorectal junction is situated 2The anorectal junction is situated 2 ~~ 3 3 cm in front of and slightly below the tip cm in front of and slightly below the tip of the coccyx. From this level, which in tof the coccyx. From this level, which in the male is opposite the apex of the prosthe male is opposite the apex of the prostate, the anal canal passes downwards aate, the anal canal passes downwards and backwards from the lower end of the nd backwards from the lower end of the rectum, the backward bend of the gut at rectum, the backward bend of the gut at the anorectal junction being termed the the anorectal junction being termed the perineal flexureperineal flexure of the rectum. of the rectum.

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The peritoneum covers the upper 1/3 of the reThe peritoneum covers the upper 1/3 of the rectum on its front and sides, the middle third octum on its front and sides, the middle third on its front only, and does not cover anywhere n its front only, and does not cover anywhere of the lower third.of the lower third.

In the empty state of the rectum, the mucous In the empty state of the rectum, the mucous membrane of its lower part presents a number membrane of its lower part presents a number of longitudinal folds which are effaced by disteof longitudinal folds which are effaced by distension of the rectum. Besides, there are three pnsion of the rectum. Besides, there are three permanent ermanent transverse folds of rectumtransverse folds of rectum ( (semilusemilunar rectal foldsnar rectal folds))..

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ⅤⅤ. The . The Anal CanalAnal Canal

The terminal 3 to 4 cm of the large The terminal 3 to 4 cm of the large intestine is called the anal canal. This intestine is called the anal canal. This region is located below the pelvic region is located below the pelvic diaphragm and thus is outside the diaphragm and thus is outside the pelvis.pelvis.

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Morphology of the anal canalMorphology of the anal canal:: In the lower part of the canal the mucous memIn the lower part of the canal the mucous mem

brane present 6brane present 6 ~~ 10 vertical folds, the 10 vertical folds, the anal canal columnsolumns..

The lower ends of these columns are joined toThe lower ends of these columns are joined together by small crescentic valve-like folds of mgether by small crescentic valve-like folds of mucous membrane, the anal valves, above each ucous membrane, the anal valves, above each of which lies a small recess or of which lies a small recess or anal sinusesanal sinuses..

The line along which the anal valves are situatThe line along which the anal valves are situated is termed the ed is termed the dentate linedentate line..

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The succeeding part of the anal canal extends The succeeding part of the anal canal extends for about 1 cm below the anal valves, and is knfor about 1 cm below the anal valves, and is known as the own as the anal pectenanal pecten..

Below the lower border of the anal pecten, theBelow the lower border of the anal pecten, there is the re is the white linewhite line, it is the transitional zone b, it is the transitional zone between the anal mucous membrane and the aetween the anal mucous membrane and the anal skin. It can be felt in the digital examinational skin. It can be felt in the digital examination of the anal canal because it lies at the intervn of the anal canal because it lies at the interval between the al between the sphinctersphincter ani internusani internus and th and the e sphincter ani externussphincter ani externus..

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The walls of the anal canal are surrounded by The walls of the anal canal are surrounded by a complex of muscular sphincters, which can ba complex of muscular sphincters, which can be divided into internal and external parts. At the divided into internal and external parts. At the anorectal junction the circular muscle coat oe anorectal junction the circular muscle coat of the rectum becomes considerably thickened f the rectum becomes considerably thickened (5-8 mm) to form the sphincter ani internus. T(5-8 mm) to form the sphincter ani internus. The sphincter ani externus surrounds the whole he sphincter ani externus surrounds the whole length of the anal canal; it is usually described length of the anal canal; it is usually described as consisting of three parts and composed of sas consisting of three parts and composed of striated muscle.triated muscle.

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