Download DigesCve System

Diges&ve System University of Pavia Small Intes&ne •  It consists of Duodenum, Jejunum and Ileum. •  It extends from the distal end of the pyloric canal to the Ileocecal valve and has approximately a length of 5-­‐6 m (7 in cadavers). •  The Duodenum lies mostly in the Upper Peritoneum, the Jejunum and Ileum occupy the central and lower parts of the Abdominal cavity. •  They are aPached to the posterior abdominal wall by a mesentery which allows considerable mobility of the loops of the small bowel. Duodenum •  The adult Duodenum is 20/25cm long and it’s par&ally covered by peritoneum: the proximal 2,5 cm is intraperitoneal and the remainder is retroperitoneal. It forms an elongated “C”. •  For descrp&ve porpouses it’s divided into 4 parts. •  First Part: It’s the most mobile one and it’s approximately 5cm long. It’s con&nuos proximally with the duodenal con&nua&on of the Pylorus and ends at the Superior Duodenal Flexure. •  It’s peritoneum covered and forms the anterior wall of the Epiploic Foramen. •  The Lesser Omentum is aPached to its upper border and the Greter Omentum to its lower one. •  It lies anterior to the Gastroduodenal Artery, Common Bile Duct and Portal Vein and the anterosuperior head of the Pancreas. It’s also posterior to the neck of the bladder. Second Part: It’s 8 to 10cm long. It starts at the Superior Duodenal Flexure and runs inferiorly as a gentle curve. It than turns sharper medially into the Inferior Duodenal Flexure, which marks its junc&on with the third part. It’s peritoneum covered only on its upper anterior surface. It lies posterior to the neck of the bladder and is crossed anteriorly by Transverse Colon. It lies anteriorly to the hilum of the Right Kidney, the Right Renal Vessels and the edge of the Inferior Cava. Medially are present the head of the Pancreas and the Common Bile Duct. (Most common loca&on of duodenal diver&cula). The pancrea&c duct and common bile duct enter the descending duodenum through the major duodenal papilla. Minor duodenal papilla is the entrance for the accessory pancrea&c duct Third Part: It starts at the Inferior Duodenal Flexure and is approx. 10 cm long. The lower por&on of its anterior aspect is covered by the Peritoneum which is reflected anteriorly from the posterior layer of the origin of Small Bowel Mesentery. It’s anterior to the Urether, Right Psoas Major, Gonadal Vessels, Inferior Cava and Abdominal Aorta. Fourth part: It’s 2,5cm long. It starts just to the le9 of the Aorta, runs superiorly, and laterally to L2 and turns sharply anteroinferiorly at Duodenujejunal Flexure to become con&nuos with the Jejunum. Posteriorly are present the Aorta, Sympathethic trunk, leU and right Gonadal Vessels and sits on the leU Psoas Major. Posterolaterally are present the LeU Kidney and the LeU Urether; anteriorly the leU Lateral Transverse Mesocolon and Transverse Colon, which separates it from the stomach. At its leU lateral end, it becomes progressively covered in peritoneum, such as it’s suspended by a double fold of peritoneum, the Ligament of Treitz, which may contain the Suspensory muscle of the duondenum. Jejunum •  the small intes&ne is usually between 5.5 and 6m long, 2.5m of which is the jejunum •  It has a median external diameter of 4cm and an internal of 2,5cm. •  In supine posi&on usually occupies the Upper LeU Infracolic compartment. •  It’s vascularized by Jejunal branches of the Superior Mesenteric Artery. Ileum •  It has a median external diameter of 3,5cm and an internal one of 2cm and have a thinner wall the Jejunum. 2–4 m long •  The Plicae Circularis become progressively less obvious in distal mucosa. •  It lies mainly in the Hypogastric region and Right Iliac Fossa. Fig. 66.7 Endoscopic appearance of the terminal ileum. It extends from the Ileocecal Valve to the anus. Cecum Ascending Colon Transverse Colon Descenidng Colon Sigmoid colon Rectum and anal canal Large Intes&ne Parts of the large intestine are:
Cecum – the first part of the large intestine
Taeniae coli – three bands of smooth muscle
Haustra – bulges caused by contraction of taeniae coli
Epiploic appendages – small fat accumulations on the viscera
Appendix (or vermiform appendix; also cecal (or caecal) appendix;
also vermix
Locations along the colon are:
The ascending colon
The right colic flexure (hepatic)
The transverse colon
The transverse mesocolon
The left colic flexure (splenic)
The descending colon
The sigmoid colon – the v-shaped region of the large intestine
•  It extends from the Ileocecal valve to the anus. It lies in a curve that tends to form a border around the loop of the small intes&ne. It begins in the Right Iliac Fossa as the Caecum becomes con&nuos with the Ascending Colon, which passes in the Right Hypocondrial region. It blends at the Inferior aspect of the Liver, where it forms the Hepa&c Flexure to become Transverse Colon. It proceeds with an anteroinferior convec&on un&l it reaches the Le9 Hypocondrium where it curves inferiorly to the Splenic Flexure and becomes the Descending Colon which con&nuos throughout the Le9 Lumbar and Iliac regions to become the Sigmoid Colon in the Iliac Fossa. It becomes the rectum by forming the Anal Canal at the level of the Pelvic floor. It’s 1,5 m long and its caliber gradually diminishes. It develops as a fully mesenteric organ, in par&cular: •  The Caecum may be within the retroperitoneum; •  The Ascending Colon usually develops as a fully retroperitoneal structure; •  The Transverse emerges from the retroperitoneum and forms the Transverse Mesocolon and than rebecomes retroperitoneal at the Splenic Flexure; •  The Rectum enters the Pelvis as a retroperitoneal structure. The Haustra are the small pouches caused by saccula&on, which give the colon its segmented appearance. The Taenia coli runs the length of the Large Intes&ne. Because the Taenia Coli is shorter than the Intes&ne, the Colon becomes sacculated between the Taniae, forming the haustra&ons. Haustral contrac&ons are slow segmen&ng movements that occur every 25 minutes. One haustrum distends as it fills, which s&mulates muscles to contract, pushing the contents to the next haustrum. Caecum It’s a large blind pouch lying in the Right Iliac Fossa below the Ileocecal valve, con&nuos proximally with the distal Ileum and distally with the Ascending Colon. The blind endning vermiform Appendix usually arises on its medial side at the level of the Ileal opening. Its length is approximately of 6 cm. It rests posteriorly on the Right Iliacus and Psoas Major. Posteriorly lies the Rectocaecal recess which frequently contains the Vermiform Appendix. It’s usually en&rely peritoneum covered. The Vermiform Appendix is a narrow vermiform tube which arises from the posteromedial Caecal wall, approx. 2cm below the end of the Ileum. The commonest posi&on are retrocecal, retrocolic, pelvic, decending over the pelvic brim, in rela&on to the Right Uterine Tube and Ovary in female. The Acute Appendici&s is a consequence of increased intraluminal pressure and reten&on of infected contents which allows acute suppura&on to occur. Ascending Colon •  It’s 15 cm long and narrower than the Caecum. It ascends to the inferior surface of the Right Lobe of the Liver on which it makes a shallow depression and tha turns abruptly toward to the le9, at the Hepa&c Flexure. •  It’s a retroperitoneal organ covered anteriorly on both sides by peritoneum. Its posterior surface is separated by loose connec&ve &ssue from the Iliac Fossa, the Iliolumbar ligament, Quadratus Lomborum, the aponeurosis of Transversus Abdominis and anterior perirenal fascia of the Right Kidney. Lateral Femoral Cutaneus Nerve usually lies posteriorly as it crosses the Quadratus Lomborum laterally. Anteriorly is in contact with the loops of the Ileum, the Greater Omentum and Anterior Abdominal wall. The Right lobe of the Liver is superior and anterolateral. The second part of the Duodenum is medial and the Gallbladder anteromedial. Transverse Colon It’s approximately 50cm long and extends from the Hepa&c Flexure across into the Le9 Hypocondrium, where it curves posteroinferiorly below the Spleen at the Splenic Flexure. It’s o9en described as an inverted arch with a posterosuperior concavity. It’s usually a]ached to the Greater Curvature of the Stomach by the Gastrocolic ligament, which is in con&nuity with the Greater Omentum. Behind and below it lies on the descending part of the Duodenum, head of the Pancreas, Upper bowel of Small Mesentery. The Mesocolon allows a good mobility of the Transverse Colon, and occasionally the Colon may be interposed between the Liver and the Diaphragm, in a condi&on known as Chilaidi4’s Syndrome. Chest X-­‐ray of obvious Chilaidi&'s sign, or presence of gas in the right colic angle between the liver and right hemidiaphragm. may occur in pa&ents with a long and mobile colon (dolichocolon), chronic lung disease such as emphysema, or liver problems such as cirrhosis and ascites. Descending Colon •  It’s approximately 25cm long. •  It descends through the Le9 Hypocondrium and Lumbar Region, ini&ally following the lateral border of the Le9 Kidney, and than descending in the angle between the Psoas Major and Quadratus Lomborum to the Iliac Crest. It curves inferomedially, lying anteriorly to the Iliacus and Psoas Major, to become the Sigmoid Colon at the level of Iliac Crest. It lies on the retroperitoneum, covered anteriorly on both sides by peritoneum. Its posterior surface is in rela&on to the Anterior Perirenal fascia of Gerota of the Le9 Kidney. Sigmoid Colon •  It begins below the pelvic inlet and ends as the Rectum. It forms a mobile loop which lies on the Lesser Pelvis. It’s usually completely invested in Peritoneum and aPached to the Lower Abdominal wall and posterior wall of the Abdominal Pelvis by the fan-­‐shaped Sigmoid Mesocolon. Laterally are the Le9 External Iliac Vessels, the Obturator Nerve and Ovary or Vas Deferens. Posteriorly the Le9 External and Internal Iliac Vessels and Gonadal Vessels, Ureter, Piriformis and Sacral Plexus. Anteroinferiorly is present the Bladder in male and the Uterus in female Rectum •  It’s con&nuos with the Sigmoid Colon at S3 level at the Upper end of the Anal Canal. It descends along the Sacrococcygeal concavity at the Sacral Flexure of the Rectum, ini&ally inferoposteriorly and than inferoanteriorly, to join the anal canal by passing through the Pelvic Diaphragm. The Anorectal junc&on is 2-­‐3cm in front of and slightly below the &p of the coccyx; •  It has a length of approximately 15cm above the External Anal margin and inferiorly it becomes dilated as the Rectal Ampulla. The upper third is covered by peritoneum on its anterior and lateral aspect. It’s related anteriorly to the Sigmoid Colon or Urinary Bladder in females. The middle third is peritoneum covered only on its anterior aspect. The peritoneum is reflected onto the Urinary Bladder in males to form the Rectovescical Pouch of Douglas. The level of this reflec&on is approx. 7,5 cm from the anorectal junc&on in male and 5,5 cm in female. Rela&ons: Laterally: Pararectal Fossa and its contents. Anteriorly: Sigmoid Colon, Terminal ileum, Upper parts of base of the Bladder in male, or cervix/body of the Uterus and Upper Vagina in female Anal Canal •  It begins at the anorectal junc&on and ends when become con&nuos with the skin of perineum. It lies in front of and slightly below the &p of the coccyx. •  The Anal Canal consists of an inner epithelial lining, vascular subepithelium, the Internal and External Anal sphincters and fibromuscolar suppor&ng &ssue. It’s 2 to 5 cm long in adult. Anteriorly, the middle third is aPached to the perineal body, which separates it from the membraneous urethra and penile bulb in male and lower vagina in female. Laterally and posteriorly it’s surrounded by loose adipose &ssue within the ischioanal fossa (this offers a poten&al pathway for spread of perineal sepsis from one side to another Posteriorly is aPached to the coccyx by the Anococcygeal ligament. The Anal Canal is encircled by internal and external anal sphincter, separated by the longitudinal layer, and has connec&ons superiorly to puborectalis and the Transversus Perinei And so, to get oriented… The small intestine is
divided into three structural
parts:
Duodenum 26 cm in length
Jejunum 2.5 m
Ileum 3.5 m
duodenum
Brunner’s or duodenal glands produce a mucus-­‐rich alkaline secre&on (containing bicarbonate) in order to: 1) protect the duodenum from the acidic content of chyme 2) provide an alkaline condi&on for the ac&va&on of the intes&nal enzymes thus promo&ng absorp&on 3) lubricate the intes&nal walls. IC B Intes&nal crypts (IC) Submucosal seromucous (Brunner's) glands (B) and muscularis externa (ME). The fate of the gut epithelial cell depends on the direc&on of their movement. Cells that migrate to the villi differen&ate into enterocytes, goblet cells (~5%) or endocrine cells (~1%), producing secre4n (bicarbonate) and cholecystokinin (pancrea&c enzymes and bile secre&on), they are characterized by quick turnover, with a life-­‐span seldom exceeding 48 hours. Cells directed downwards into the depth of the crypts differen&ate into Paneth cells. These cells with life-­‐span reaching 21 days produce lysozyme and defensins and are involved in protec&on of the gut. Enterocyte intes&nal absorp&ve cells, are simple columnar epithelial cells found in the small intes&nes and colon. A glycocalyx surface coat contains diges&ve enzymes. Microvilli on the apical surface increase surface area for the diges&on and transport of molecules from the intes&nal lumen. PANETH CELLS… α-­‐defensins, known as cryptdins in mice 2
3
duodenum
1
6
5
4
4
Jejunum
5
6
1
3
2
ILEUM WALL
ILEUM
3
*
L
V
1
*
2
*
aggregated lymphoid nodules in the digestive system
(Peyer's patches)
INTESTINAL VILLI
c
e
*
*
a
*
e
a
Paneth cells are found in the small intes4ne but not in the large intes4ne. LARGE INTESTINE
CECAL APPENDIX
CECAL APPENDIX
4’
4’
5
6
3
1
5
5
2
5
4
CECAL APPENDIX
1
2
5
3
4’
4
4
A
B
4’
RECTUM
1
3
2
4
The anus, the last few cen4meters of the diges4ve tract, is lined with stra4fied squamous, usually kera4nized disappearance of the crypts and goblet cells