Sheet: Anatomy & Histology of The Small intestine

Done by: nisreen obeidat

Small intestine : narrow tube starts at the pyloric sphincter and ends at ileocecal junction ;its length =(5-7) m according to the tone of the muscles if relaxed it will be longer and if contracted it will be shorter

Position : epigastric & umbilical regions in the middle part of the abdomen

Consists of duodenum &jejunum &ileum

Remember : 4 organs in our body the length of them = 25 cm which are :

Ureter & male urethra & oesophagus & duodenum

Duodenum

C shape part of the small intestine ; the opening is to the left and surrounds the head of the pancreas

Can be divided to 4 parts:

1 : superior : 2 inches

2 : descending : 3 inches

3 : horizontal: 4 inches

4 : ascending : 1 inch

Superior part:

Directed to the right side superiority and backwards

The part that is adjacent to the pyloric sphincter is called the cab

The 1st inch is intra peritoneal where as the 2nd inch extra peritoneal

Relations of the 1st inch (same as stomach’s relations (

Sup : lesser omentum

Inf : greater omentum

Post : lesser sac & the pancreas

Ant : liver & greater sac & fundus of the gallbladder

Relations of the second inch

Sup : epiploic foramen

Inf : head of the pancreas

Post : common bile duct & portal vein & gastroduodenal artery

Ant : liver & greater sac & neck of the gallbladder

Descending part:

Descends at the right side of the vertebral column to the level of the third lumbar vertebra

This part is extra peritoneal

Relations :

Left : head of pancreas & superior pancreaticoduodenal Artery ( branch of gastroduodenal artery) & inferior pancreaticoduodenal aretery ( branch of superior mesentric artery

Posteriorly : right suprarenal gland & hilum of the right kidney & ureter & pelvis of ureter & right psoas muscle

Anteriorly : mesentry of the transverse colon & transverse colon & coils of the small intestine

In this part the ampulla of vater opens to duodenal papillae which is located in the midpoint down the length of the second part on the posteriomedial surface of this tube controlled by the sphincter of oddi

Cystic duct + hepatic duct >>> common bile duct common bile duct + major pancreatic duct >>> ampulla of vater

In 10% of people there is an accessory pancreatic duct that opens to the minor duodenal papillae

Note: common bile duct runs behind duodenum & pancreas

Horizontal part:

Running transversely across the posterior abdominal wall from the right side to the left side

Relations:

Anteriorly: superior mesentric artery & superior mesentric vein & coils of small intestine & mesentry of the small intestine

Posteriorly : right psoas muscle & right ureter & inferior vena cava & inferior mesentric artery & aorta & left psoas muscle

Superiorly : head of pancreas (uncinate process of pancreas (

Inferiorly : coils of the small intestine

Ascending part :

Ends at the level of the 2nd lumber vertebra

Posteriorly : left psoas muscle

Anteriorly : mesentry of small intestine & coils of small intestine

Left side : ureter & inferior mesentric vein

Ends at the duodenojejunal flexure and supported by the suspensory muscle & the end is intraperitoneal and directed downward & left

Jejunum = 2/5

Ileum = 3/5

Both are intra peritoneal and and have mesentry spread from doudenojejunal junction to ileocecal junction

The mesentry has arteries &veins & nerves & lymphatic vessels

Histology : Duodenum, jejunum, and ileum share the same wall structure formed by, a mucosa, a submucosa, a muscularis interna, a muscularis externa, and a serosa. The mucosa of the small intestine, comprising simple columnar epithelium and a lamina propria, forms finger-like projections, villi, which protrude into the lumen, and deep cavities, the crypts of Lieberkühn (intestinal glands) between the villi. The predominant cell in the epithelium is the absorptive enterocyte with microvilli on its apical membrane. Interspersed between the enterocytes are the oval, mucous goblet cells. Deep in the crypts the epithelium contains entero endocrine cells with granules (secrete hormones .(

The lamina propria consists of loose connective tissue and blood vessels. central lymph vessel, the lacteal, is present in the lamina propria of each villus . Large lymphoid aggregates Peyer’s patches (unencapsulated lymphoid nodules), occur in the submucosa throughout the intestines but mainly in the ileum; M cells form part of the epithelium covering the Peyer’s patches. The jejunum and ileum are histologically identical, except for their villi and the presence of Paneth cells . The villi of the jejunum are tall and cylindrical, while they are short and cylindrical in the ileum . Paneth cells have eosinophilic cytoplasmic granules and occur in clusters at the bases of crypts. are especially found in the jejunum and have very prominent granules, they secrete digestive enzymes

Nerve supply of the intestine The myenteric plexus (or Auerbach's plexus) provides motor innervation to both layers of the muscular layer of the gut, having both parasympathetic and sympathetic input (although present ganglionar cell bodies belong to parasympathetic innervation, fibers from sympathetic innervation also reach the plexus ( , The submucous plexus has only parasympathetic fibres and provides secretomotor innervation to the mucosa nearest the lumen of the gut

Peyers patches

Ileum

Chylomicrons transport lipids absorbed from the intestine to adipose, cardiac, and skeletal muscle tissue, where their triglyceride components are hydrolyzed by the activity of the lipoprotein lipase, allowing the released free fatty acids to be absorbed by the tissues.

Villus

Histology of Duodenum MUCOSA: LINED BY SIMPLE COLUMNAR EPITHELIUM WITH FINE MICROVILLI and MUCOUS SECRETING GOBLET CELLS. The inside surface of duodenum is thrown INTO LARGE FOLDS OR FINGER LIKE PROJECTIONS CALLED VILLI.’PLYCA CIRCULARIS’ IS A MUCOSAL FOLD WITH A CORE OF SUBMUCOSA. LAMINA PROPRIA: Contains Crypts of Lieberkühn (TUBULAR INTESTINAL GLANDS ) CRYPTS OF LIEBERKUHN CONSISTS OF FOLLOWING CELLS,

1. STEM CELLS: ACTIVE,UNDIFFERENTATED CELLS FOUND AT THE BASE OF LAMINA PROPRIA.

2. GOBLET CELLS: SECRETE MUCOUS. 3. ENTERO ENDOCRINE CELLS:

PRESENT ABOVE THE STEM CELLS.ALSO CALLED AS ‘ARGENTAFFIN CELLS’ SINCE THEY ARE STAINED BY SILVER SALTS. They produce and release hormones in response to a number of stimuli. Hormones may be distributed as local messengers. They may also stimulate a nervous response.

4. PANETH CELLS: ZYMOGENIC CELLS, PRODUCING DIGESTIVE ENZYMES AND LYSOZYMES (an antimicrobial enzyme produced by animals that forms part of the innate immune system( MUSCULARIS MUCOSA/INTERNA: Circular muscle layer SUBMUCOSA: MADE UP OF LOOSE AREOLAR CONNECTIVE TISSUE. PRESENCE OF NUMEROUS MUCOUS SECRETING BRUNNER’S GLANDS.

MUSCULARIS EXTERNA: CONSISTS OF OUTER LONGITUDINAL AND INNER CIRCULAR PARASYMPATHETIC GANGLION CELLS OF MYENTERIC PLEXUS CAN BE SEEN. SEROSA: OUTER MOST LAYER MADE UP OF FEW CONNECTIVE TISSUE CELLS AND FIBRES, COVERED BY MESOTHELIUM OF VISCERAL PERITONEUM. FUNCTIONS: VILLI HAS ABSORPTIVE FUNCTION. MICROVILLI INCREASE THE SURFACE AREA OF ABSORPTION. BRUNNER’S GLANDS SECRETE ALKALINE FLUID RICH IN HCO3‾. MUSCULARIS EXTERNA HELPS IN CHURNING FOOD PARTICLES SEROSA IS SUPPORTIVE AND PROTECTIVE

Duodenum

Duodenum