Introduction to the functions of the GIT Flashcards
DIGESTION:
What occurs to the stomach when food is digested?
What does the stomach then do to digest the food? What does this form?
What substances are used to relax/expand the fundus?
- For first hour, food is just stored, not mixed with acid. The fundus and body relaxes to allow for max. storage.
- Antrum mixes/grinds food with gastric secretions - forms chyme.
- VIP and NO
What are the constituents of gastric secretions? Where are they released from? What’s their role?
Outline the process of Pepsin formation from Pepsinogen in chief cells
- Mucus - Goblet cells - lubricates and acts as a barrier, protecting stomach and colon
- Lipase - fat digestion (converts TG’s → FA + Glycerol)
- Intrinsic factor - Parietal cells - Vit B12 absorption
- HCl - Parietal cells - important in defence
- Pepsin - Chief cells - protein digestion and Pepsinogen conversion
- Pepsinogen from chief cells is an inactive enzyme. In acidic conditions, Pepsinogen → Pepsin (active enzyme). Once some pepsin is made, acidic conditions are NO LONGER NEEDED to convert more pepsinogen.
PARACRINE SECRETIONS:
Where are they secreted from?
Where do they act?
Example is SOMATOSTATIN:
Where are they released from? What do they do? What is its release mediated by?
- From cells in the mucosa
- Act locally on adjacent cells
- Somatostatin - from D cells - inhibits Gastrin release from G cells. Gastrin is used to promote acid secretion from the parietal cells, so Somatostatin works to reduce acid secretion and the risk of ulcerations - its release is mediated by PH.
EXOCRINE SECRETIONS:
Where do exocrine secretions occur in the GIT? What do they release?
- Salivary glands release mucus. Gastric glands that release HCl, Pepsin, mucus. Pancreas that releases Bicarbonates and enzymes. Liver that releases bile acids.
ENDOCRINE SECRETIONS:
What do they do?
What are the endocrine secretions in the GIT? Where are they released from?
What is the role of Secretin?
- Go directly into the blood and bind to target tissue receptors
- Gastrin from G cells in antrum. Secretin from S cells in duodenal mucosa. Cholecystokinin from the duodenal mucosa. Insulin from β-cells.
- Stimulates the pancreas and gallbladder to release a bicarbonate base for acid neutralisation.
ABSORPTION:
Where does it mainly occur? Why?
Where does fluid absorption occur?
What can occur if there are problems with fluid secretion and reabsorption?
- Small intestines - to get nutrients from food into the blood.
- Small and large bowel (Colon absorbs 90% of water)
- Diarrhoea or Constipation
MOTILITY:
What is it?
What is its importance?
EXCRETION:
How can substances be excreted from the body?
How do the indigestible substances leave the body?
- Movements of muscular walls of GIT to move food along
- It moves food into the different areas that have different roles in food digestion and excretion e.g. storage, absorption, excretion.
- In saliva, bile, faeces, vomit.
- In the faeces e.g. tomato skin
Why is defence so important in the gut?
What can happen if there’s damage to the mucosal barrier?
What are the defence mechanisms used?
- Intestines is the largest mucosal surface, so is exposed to many foreign antigens. It’s the largest lymphoepithelial organ, which means that the epithelial cells also carry out immune functions.
- Toxins can enter the blood - infection
- • Look, smell, and taste of food can tell us if it’s harmful
• Vomit reflex - remove “bad” food from system
• HCl in stomach kills most harmful bacteria
• Natural flora prevents colonisation of bacteria
• Aggregation (clustering) of lymphoid tissue (Peyer’s patches) allow for immune response to food-borne antigens
What is the role of the liver in metabolism?
Used in carbohydrate, nitrogen and lipoprotein metabolism. It produces Bile and excretes Bilirubin (made from RBC breakdown) - high bilirubin levels may indicate liver problems.
