L16 - Physiology of the Stomach - not finished Flashcards
What are the main structures of the stomach
what are the general functions of the 2 main parts
- body
- upper part knwon as fundus
- secretes mucus, pepsinogen, and HCl
- antrum
- secretes mucus, pepsinogen, and gastrim
- sphincters
- lower esophageal sphincter
- pyloric sphincter
name 1 to 4
name 5 to 9
what are the 3 types of cells that produce gastric juice
what do each of which produce
- zymongenic chief/peptic cells
- secrete pepsinogen
- parietal (oxyntic) cells
- secrete HCl
- goblet (neck) cells
- secrete mucous
how are parietal cells distributed
- more parietal cells are located in the body of the stomach
- none in the antrum
what are the functions of the stomach
- temporary storage of food
- mechanical digestion by stomach movements
- chemical digestion of proteins
- regulation of passage of chyme into small intestine
- secretion of intrinsic factor
- essential for absorption of vitamin B12
Describe the mechanical process in the stomach
- muscularis enables food to be chrurned
- particularly in the atrum
- where muscle wall is thicker
- more powerful contractions
- particularly in the atrum
- food mixed with gastric juices
- to produce chyme
what chemical acitivity occurs in the stomach
- proteins broken down by pepsin
- pepsin is only active in the acidic environment
- converted from pepsinogen by HCl
- gastric lipase breaks down fat at higher pH
- 5-6
In the formation of HCl, how is the H+ ion obtained
- carbon dioxide diffuses into the parietal cell
- and the enzyme carbonic anhydrase catalyses a reaction between the carbon dioxide and water to produce carbonic acid
- carbonic acid dissociates into bicarbonate ion and hydrogen ion
- and the bicarbonate ion is transported back into the blood stream
In the formation of HCl: How is the chlorine obtained and how is the HCl released from the parietal cells
- an ion exchange molecule in the plasma membrane exchanges bicarbonate going out for chloride coming in
- the hydrogen ions are actively transported into the duct of the gastric gland
- negatively charged chloride ions diffuse with the positively charged hydrogen ions
- potassium ions are counter transported into the parietal cell in exchange for hydrogen ions
- active process
why doesnt the stomach digest itself
what is the role of prostoglandins
- the mucosal barrier
- tight junctions between the mucosal epithelial cells prevents leakage of gastric juices onto underlying tissue
- mucous secreted by epithelial cells has a higher pH, providing localised neutralisation and physical barrier to acid
- prostaglandins increase mucoal thickness and stimulate bicarbonate production
what are the three phases of gastric secretion
- cephalic phase (increased secretion)
- stimulated by sight, smell, taste, though of food, or decreased blood glucose
- gastric phase (increased secretion)
- stimulated by stomach distension due to presence of food
- intestinal phase (decreased secretion)
- stimulated by digested proteins/fat in the duodenum
- presence of fat or low pH in duodenum inhibits gastric secretin
Describe the nerve impulses involved in the cephalic phase
- taste, smell, tactile sensation of food, or thought of food send nervous impulses to the medulla oblongata
- these impulses cause parasympathetic neurons via the vagus nerve to stimulate the secretion of HCl and pepsin in the stomach
- also results in secretion of gastrin from lower part
What happens when gastrin is released
- this hormone travels through the bloodstream and further stimulates HCl and pepsin secretion in the body of the stomach
Describe the nervous impulses in the gastric phase
- distension in the stomach activates a parasympathetic reflex via the medulla oblongata
- has a direct stimulatory effect on the gastric glands
- result is continued secretion of HCl and pepsin
