7 - Function of the Stomach Flashcards
What are specialised cells that secrete hormones in the stomach called?
- Enteroendocrine cells, lettered e.g G, S, D
- Enterochromaffin like cells secrete histamine
How do hormones from the gut get into the systemic circulation?
- Paracrine: somatostatin from D cells on G cells inhibits gastrin
- Neurocrine: GRP from vagus nerve
What are the two families of hormones in the GI tract?
Gastrin Family
- Gastrin: from G cells in antrum. increase gastric acid secretion
- Cholecystokinin: I cell in duodenum and jejunum. Increase pancreatic/gallbladder secretions causing them to contract. Stimulated by fat and proteins
Secretin Family
- Secretin: S cells in duodenum. Stimulated by H+ and fatt acids. Increases HCO3 from gallbladder/pancreas to neutralise chyme. Inhibits gastric acid secretion
- GIP: In duodenum and jejunum, stimulated by sugars, aa and fa. Increase insulin and decrease gastric acid
What is the function of the stomach?
- Temporary store
- Start digestion physically and chemically by contraction (3 muscle layers) and hormones
- Innate immunity
What is the basic structure of the stomach?
- Mucosa made of gastric pits and glands containing lots of cells, e.g parietal, chief, mucous, enteroendocrine
- Simple columnar from stratified squamous in oesophagus
- Rugae
How do the different parts of the stomach differ in the way that they contract?
Upper: thin and creates basal tone
Lower: thicker and strong peristalsis every 20 seconds.
Stomach gores from larger to smaller so that liquid chyme is ejected but lumps left behind
What is the role of Brunner’s glands?
Submucosal gland in the duodenum that secretes alkaline mucus to neutralise chyme. They also lubricate the intestinal walls and provide the right environment for enzymes
What is the blood supply to the stomach?
Draw out the three branches of the coeliac trunk
- Splenic: goes behind stomach and above pancreas giving off to pancreas and greater curve of stomach by short gastric artery. Then gives off left gastroepiploic which anastomoses with right to supply greater curve
- Common Hepatic: gastroduodenal behind duodenum then gives off right epiploic and superior pancreaticoduodenal. Continues as proper hepatic to then give off left and right hepatics. Right then gives off cystic artery to gall bladder
- Left gastric artery: anastomoses with right gastric either from common/proper hepatic and supplies the lesser curve of the stomach
What is the issue with ulcers in the duodenum?
Can perforate the gastroduodenal artery behind the duodenum leading to vomiting blood and large haemorraghe
What is the venous drainage of the stomach?
All into portal vein from IMA joining splenic and splenic joining portal
How does the stomach prepare for an increase in volume before we have even started eating?
- Receptive relaxation
- Vagal innervation relaxes the stomach preventing reflux when swallowing
- Rugae can help distension
What is the chemical role of acid in the stomach?
- Denatures proteins so larger surface area for enzymes
- Disinfect stomach contents
- Activate proteases, e.g pepsinogen from chiefs, in the stomach lumen to prevent self digestion
What are some examples of enteroendocrine cells in the stomach and what do they secrete?
What is the distribution of enteroendocrine cells in the stomach, e.g parietal cells?
How is the secretion of HCl stimulated?
- Parietal cells
- Stimulated by gastrin (CCK receptor), histamine (H2) and ACh (Mcr)
- Produced when aa/peptide detected in stomach and when stomach is distended
How is the secretion of gastrin controlled?
- G-cells in antrum
- Peptides/amino acids in stomach lumen
- Vagal stimulation
- ACh
- GRP
- Stomach distension
How is the secretion of HCl inhibited?
- Reduced stomach distension
- Low pH in stomach as when food leaves food is a buffer for acid so pH drops. Stimulates D cells which secretes somatostatin to inhibit gastrin and histamine
- Reduced vagal activity
What stimulates chief cells?
- Gastrin on CCK
- Vagal innervation
- Pepsinogen released
What is an alkaline tide?
Shortly after a meal blood pH drops in venous blood as more HCl made so more bicarbonate secreted into venous blood
What are the phases of digestion?
- Cephalic: 30% HCl, direct stimulation by vagus nerve of G-cells (GRP). Due to parasympathetic stimuli e.g sight and smell. Also increases motility
- Gastric: 60% HCl. Distension of stomach activates vagus so parietal and G cells. AA and peptides stimulate G cells. Food acts as a buffer so no inhibition on gastrin. NS and Gastrin cause smooth muscle contractions
- Intestinal: 10% HCl. Chyme initially stimulates gastrin but then inhibited as presence of lipids activates enterogastric reflex. Vagal stimulation lowered and chyme causes CCK and secretin to be secreted
How does the stomach protect itself from its acidic environment?
- Mucin layer from foveolar cells
- HCO3 ions in mucus layer so alkaline
- Rich blood supply so any protons breaching mucus layer can be swept away. Kept rich by prostaglandins
- High turnover of epithelia
What is the nerve supply of the stomach?
- Parasympathetic: vagus nerve
- Sympathetic: T6-T9 spinal cord segments and passes to coeliac plexus via the greater splanchnic nerve
