Stomach Flashcards
If a hormone is secreted from the stomach, where does it end up?
Peptides released from endocrine cells into portal circulation (venous system). They then pass through the liver to enter the systemic circulation. This means that, in the end they end up pretty close to where they were released from.
What are paracrine hormones?
Hormones that act locally and diffuse short distances
What are the main gastrointestinal hormones?
Gastric family:
-Gastrin and Cholecystokinin (CCK)
Secretin family:
-Secretin and Gastric inhibitory polypeptide (GIP)
What does CCK do?
Released by I cells in the duodenum to increase pancreatic and gall bladder secretions.
Stimulated by fat and protein
This works because the Gall bladder contracts which stimulates the pancreas.
What does secretin do?
Released by S cells in duodenum
Stimulated by H+ and fatty acids
Increases HCO3 from pancreas / gall bladder and decreases gastric acid secretion
What does GIP do?
GIP = gastric inhibitory polypeptide
Released by cells in the duodenum and jejunum
Stimulated by sugars, amino acids and fatty acids
It increases insulin and decreases gastric acid secretion
What are the basic functions of the stomach?
Receives food - short term storage
Disrupt food - vigorous contractions of the smooth muscle
Continue / commence digestion
Disinfect
Where is the stomach?
Upper left quadrant
Lying somewhat under left lobe of liver
How is the stomach designed to prevent reflux?
Right crust of diaphragm and angle at which the stomach sits means that substances will go into the fundus rather than into the oesophagus.
What are rugae?
Temporary folds in the stomach (only there when it is empty)
What types of cells are in the stomach epithelia?
Mucous cells (secrete mucus) Parietal cells (secrete HCl and intrinsic factor) Chief cells (secrete pepsinogen and chymosin) G cells (secrete gastrin)
What is the role of the stomach smooth muscle?
There is an extra oblique layer of muscle to allow for mechanical digestion.
Contractions - mix / grind contents and move contents along.
Upper stomach - sustained contractions to create basal tone.
Lower stomach - strong peristalsis mixes stomach contents, contractions every 20 seconds or so (coordinated) proximal to distal.
Why is shape of muscles important?
Larger part is proximal and smaller part is distal.
This means that the contents accelerates so that lumps are left behind (separates contents) and only liquid chyme is ejected into the duodenum. This ejection occurs roughly 3 times per minute.
What are the three main branches of the coeliac trunk?
Splenic artery
Left gastric
Common hepatic artery
What is the venous drainage of the stomach?
Portal vein to liver
Then hepatic vein into IVC
What is receptive relaxation?
tells stomach stuff is coming so it can relax and create pressure.
Fatally mediated relaxation of the stomach. This allows food to enter the stomach without raising intra-gastric pressure too much. It prevents reflux of the stomach contents during swallow. Also, the gastric mucosal folds (rugae) allow distention.
Why is the stomach acidic?
Unravel proteins
Activates proteases (Pepsinogen to pepsin) - stops us digesting ourselves
Disinfects stomach contents.
What does the stomach secrete?
HCL (parietal cells)
Intrinsic factor (parietal cells)
Mucus / HCO3- (mucus cells)
Pepsinogen (chief cells)
What are some important cells in the stomach and what do they produce?
Parietal cells - HCl and intrinsic factor
G cells - Gastrin
Enterochromaffin like cells (ECLs) - Histamine
Chief cells - pepsinogen
D cells - somatostatin
Mucous cells - Mucus and bicarbonate
How do we control HCL production?
Parietal cells that secrete HCl are stimulated by gastrin, histamine and ACh.
How do we control gastrin secretion?
G cells located in Antrum
G cells stimulated by:
- peptides / aminos cids
- Vagus nerve (stimulated by ACh and GRP) can activate parietal and G cells
How do we inhibit HCL production?
Inhibit G cells.
When food leaves the stomach, pH drops as old acts as a buffer.
This low pH activates D cells which release somatostatin.
This somatostatin inhibits G cell (and ECL cells) which therefore reduces the distension of the stomach and therefore the vagal activity.
How exactly is HCL produced
Split water to make H+
Anion antiport protein bring Cl- into Stomach lumen and out using CL- channel protein.
H+ leaves via H+/K+ ATPase (protein pump)
This means H+ and Cl- an make HCl.
What are the three phases of digestion?
Cephalic
Gastric
Intestinal
