digestive system 2

STOMACH
The stomach is the expanded part of the digestive tube it received the food from the esophagus , mixing and partial digestion of the food in the stomach by the its gastric secretions produce pulpy fluid mix called chyme, the chyme then passes in to the small intestine for further digestion and absorption .The stomach divided in to three region :

1-cardiac region (cardia)
The part which are near the esophageal orifice that have the cardiac glands.

2-pyloric region(pylorus)
The part proximal to the pyloric sphincter which contain the pyloric glands.

3-fundic region (fundus) The largest part of the stomach which is situated between the cardia and the pylorus and contain the fundic or gastric glands.



MUCOSA
the mucous membrane (mucosa)of the empty stomach is thrown in to deep irregular longitudinal folds called rugae the surface of the epithelium is simple columnar which invaginates in to lamina propria to form gastric pits , into these pits empty the million of gastric glands largely branched tubular types the thickness of mucosa due to the presence of these gastric glands.
The gastric glands are of the three types located in different region in the stomach :
1-cardiac glands located in the narrow ring shaped region when the stomach joins with the esophagus
2-the gastric or fundic glands shaped through out the body and fundus of the stomach
3-the pyloric glands confined to the pyloric region where the stomach joins the small intestine
The cells lining the gastric glands are:
1-mucose secreting surface epithelium cells (simple columnar)
2-chief zymogenic cells that produce the digestive enzymes pepsin and lipase
3-partial (oxyntic) cells that produce hydrochloride acid
4-mucous neck cells limited to the initial (neck) regions
5-enteroendocrine cells located in the base of the gastric glands they secret the secretin ,gastrin.





SUBMUCOSA
Composed of blood vessels and nerves (meissners sub mucosal plexus) with loosely arranged collagenous and elastic fibers.

MUSCULARIS EXTERNA
Has 3 layers of smooth muscle inner oblique , middle circular ,outer longitudinal layer Auerbaches myenteric nerve plexus lies between circular and longitudinal muscle layers

SEROSA
Covering by loose connective tissue surrounded by mesothelium

REGIONAL DIFFRENCES IN STOMACH

1-CARDIAC REGION
In the small cardiac region the glands are the least numerous because the cardia of the stomach is limited to collar wide around the esophageal orifice , they have rather wide , open, deep pits ,that continue into short , coiled glands lined with mucous type cells the glands occupy the lamina propria and the base rest on muscularis mucosa.






2-FUNDUC OR BODY REGION
in the body and the fundus the glands called fundic glands are the most numerous because these regions occupy about three fourths of stomach, fundic glands are narrow , shallow pits, long tubules , the pits are lined with surface mucous – type cells the small irregular neck mucous cells , mucous neck cells produce intermediate product between serous and mucous secretions , the body of elongated fundic gland is lined with partial and chief cells , the chief cells are most numerous they are also called zymogenic cells , they are concentrated in the in the lower part of the fundic glands , the basal part of the cells is basophilic





3-PYLORIC REGION

It is continuous with the duodenum the pyloric glands resemble with cardiac glands but has deeper pits and more branching and coiling of the tubular glands they contain parietal cells and gastrin secreting cells among the mucous like cells that line the pyloric glands .

SMALL INTESTINE
Small intestine extends from the stomach to the large intestine a distance about 6-8 m has 4 layers resemble the pattern of the GI tract it divided to 3 regions (duodenum , jejunum , and ileum )small intestine has 3 principle functions :
1- complete the digestion of the food by action of the enzyme.
2-absorbed the finished product of digestion into the blood and lymph vessels.
3-synthesized and release hormone.

MUCOSA
Plicae circularis the mucosal surface of the small intestine undergoes several specializations to increase the surface area the first of these modifications the permanent spiral or circular mucosal folds that extends through out the length of the organ called plicae circularis they greatly increase the mucosal area they reach maximum development in the duodenum and upper jejunum and gradually disappear in the ileum .
Villi are long finger like or leaf like projections of the mucosa that extends in to the gut lumen , they are cover by simple columnar epithelium resting on surface membrane , intestinal glands (crypts lieberkuhn) other mucosal modifications that increase the surface area , these are straight , un branched , tubular glands ,located in the base of the villi and the muscularis mucosa.
Microvilli is the striated border of the lining epithelial cells composed of parallel rows of microvilli of even height , they extend from the cell border like brush bristles, hence the term brush border is a synonym for striated border each microvillus covered by cell plasma membrane , in the center of the microvillus are many longitudinal fine microfilaments some of these microfilaments are actin filaments ,
Lamina propria the loose reticular connective tissue of the lamina propria forms the core of each villus and fill the potential space between the intestinal glands collections of small lymphocytes form lymph nodules with or without the germinal centers the nodules increase in size and number until in the ileum they form large aggregations called payers patches.



MUSCULARIS MUCOSA
It is thin has 2 layers of smooth muscle inner circular and outer longitudinal layer these layers separate the lamina propria from the submucosa , penetrated with meissners plexus .


SUBMUCOSA

Large zone compose of areolar connective tissue surrounding larger blood and lymph vessels and nerve plexuses (meissners plexus) and also contain peyers patches in lamina propria contain no glands except in the duodenum.

MUSCULARIS EXTERNA
Large , has 2 layers inner circular and outer longitudinal of smooth muscle between this 2 layers are frequent parasympathetic (Auerbach plexus),these muscle also facilitate the mixing of food with the digestive enzymes

SEROSA
Single layer of mesothelium cells resting on thin layer of loose connective tissue ,blood and lymph and nerve traverse the serosa




REGIONAL DIFFRENCES IN SMALL INTESTINE

DUODENUM
It is extends from the pyloric end of the stomach to its junction with the jejunum it is has burners gland in the sub mucosa , leaf shape villi , adventitia and termination of bile and pancreatic ducts.
Bruner s glands are mucous compound tubular largely in the sub mucosa but occasionally in lamina propria, their mucin secreting cells are low columnar type , the secretion is strongly alkaline which neutralizes the acidic chyme of the stomach and thus protect the duodenal mucosa from auto digestion , Bruner s glands contain urogastrone , a peptide hormone that inhibits the HCL production in the stomach also called human epidermal growth factor(HEGF).
The rather short broad leaf shaped villi are most numerous in the duodenum.




JEJUNUM
Has no really distinctive features , although the finger like villi are the tallest , if the histological section of small intestine dose not contain submucosal glands Bruner s glands or aggregates of lymph nodules in the lamina propria (payers patches) the organ is probably Jejunum.


ILEUM
The ileum has only one diagnostic feature: the presence of many aggregates of lymph nodules in the lamina propria( payers patches) the lymph nodules are usually pear shaped with tier rounded dome shaped apices directed toward the lumen covered by single layer of epithelium there is evidence that these cells are transport antigens from the lumen to the lymphoid follicles these cells have been designated as follicle associated epithelium (FAE).