Gastrointestinal Secretions and their Control Flashcards
What allows us to detect via b12?
Intrinsic factor
What are the water sources of inflow into the gut and outflow?
Inflow:
- Diet
- Saliva
- Gastric secretion
- Bile
- Pancreatic secretion
- Intestinal secretion
About 9L in and 9L out
Outflow:
- Small intestine absorption
- Colon absorption
- Faeces
What are the three phases of digestion? give details
- Cephalic
Thinking about food, presence of food in mouth: promote salivary and gastric secretions
Chewing to help breakdown food
Amylase in saliva initiates digestion of starch - Gastric
Stomach secretes (acid, pepsinogen) to repose to the presence of food in stomach
Gastric motility causes further mechanical breakdown or=f food particles
Digestion of protein starts - Intestinal
Food entering the small intestine gradually causes the release of hormones that inhibit gastric secretion and motility
Some of the same hormones provoke the release of biliary and pancreatic secretions into the duodenum
During this phase, most of the digestion takes place, followed by absorption of the nutrients
What are the controls of the 3 phases?
Cephalic phase is a neuronal controlled phase. Gastric is neuronally and hormonally controlled. Intestinal phase is hormonally and neuronally controlled.
Explain the first step in saliva production and secretion
- primary secretion made by acinar cells
- ultimately driven by Na pump on basolateral side of cells
Have a high chloride concentration inside cell so they leave into the lumen. Have lots of sodium outside the cell and these two ions have an opposite charge creating a gradient. Sodium wants to come into the cell which drags water with them - start of saliva production - several channels and transporters involved
- results in a watery secretion which is isotonic (same osmotic pressure) with plasma
Explain the second step in saliva production and secretion
Primary secretion is modified and it passes along the duct.
Some sodium and chloride reabsorbed from lumen into gland cells.
K+ and HC03- added to saliva.
Results in a bicarbonate rich hypotonic secretion (lower in water conc than blood).
Faster saliva flow means that the reabsorption of these ions will be less effective.
Except the ions mentioned, what are the other components of saliva?
- other ions, e.g. Ca2+, phosphate
- large molecule components: mucins (glycoproteins giving saliva consistency), lysozyme and amylase, released from acinar cells by exocytosis
- Immunoglobulin A: made by nearby plasma cells (B lymphocytes), binds to a receptor on the basolateral side of acinar cells, and transported into the lumen of the gland.
What are the 4 functions of saliva?
- lubricating food (for chewing and swallowing)
- amylase initiates starch digestion
- several of the other components have antimicrobial activities
- pH, and particular mix of Ca2+ and phosphate ions also contained in salvia, protect the teeth from demineralisation
What is the difference in the salivary secretions betqwwn glands?
Parotid: amylase > mucus
Submandibular: amylase
In basal and stimulated condition, which glands have the highest flow rates?
Basal = submandibular Stimulated = parotid
What affect does the ANS have on the salivary secretions?
- PS stimulation increases formation of the fluid and electrolyte components of saliva
- S stimulation increases release of macromolecular components.
Give details on oesophageal secretions
Widespread minor glands, which produce only mucus (just to lubricate food from mouth to stomach) Secretion is neurally controlled.
Explain the roles of the chief and parietal cells in gastric secretions
What else is produced in the stomach?
Chief cell produces pepsinogen (inactive form of pepsin).
Parietal cell produces HCL and intrinsic factor.
Other stuff produced in stomach = mucus from surface cell enterocytes, gastric lipase and water
What is the mechanism of acid secretion?
Uses active transport to pump H+ into the stomach lumen. H+ comes from the breakdown of carbonic acid and the proton pump moves it across.
ATP needed to drive H+ secretion into lumen against concentration gradient.
Cl- obtained from blood via exchanger on basolateral side of cell.
H+ secretion therefore results in net HCO3- movement into blood.
Net ion movement into lumen accompanied by water (by osmosis).
How is acid secretion increased in response to stimulation?
In resting condition = many of the proton pumps are confined to intracellular tubulovesicles.
On stimulation, the vesicles rearrange sonf sue with canaliculi continuous with lumen membrane, increasing surface area for HCl secretion.
(Vesicles in resting condition and proton pump sit in membrane of these vesicles. Vesicles fuse to luminal membrane to increase the number of proton pumps to drive H+ into stomach lumen)
