Gastrointestinal System Flashcards
What are the functions of the GI tract?
The absorption of nutrients and drugs
The digestion of food
Elimination
Mechanical and chemical digestion (breakdown of food into small so can be absorbed into circulatory system)
What are the regions of the GI tract?
Mouth
Oesophagus
Stomach
Small intestine
What are the accessory organs?
Liver
Salivary glands
Gall bladder
Pancreas
What is the role of the stomach?
Production of gastric juices
Digestion of proteins by digestive enzymes (pepsin)
Production of chyme
Peristalsis - mechanical digestion (muscle contraction starting at the oesophagus to move food down)
Gastric emptying (slowed down by presence of food in stomach and affects rate of absorption - affected by meal and population properties)
What is the role of the small intestine?
Completes digestion of nutrients in chyme
Major site of absorption of nutrients and orally administered drugs
Site of first pass metabolism of drugs (CYP3A4)
Movement of residues to the large intestine
Why is the small intestine a major site for absorption?
It has a large surface area and high perfusion
High exposure to enzymes and solubilisers
Receives secretions from the liver and pancreas
What gives the small intestine its large surface area?
It has villi, microvilli and mucosa
Why is it important for the small intestine to have a large surface area?
Dissolved drug is absorbed across the gut wall by passive diffusion
Enterocytes contain metabolic enzymes
Blood perfusing the lntestine goes to the liver via hepatic portal vein
What is coeliac disease?
Chronic autoimmune disorder of the small intestine
Inflammation process is triggered by the consumption of gluten foods
Causes atrophy of villi in small intestine epithelium
What is the role of the liver secretions?
Main site of metabolism of xenobiotics
It secretes bile which enters the duodenum via hepatic duct. Bile is stored in the gall bladder between meals.
Important for digestion of lipids.
What is the role of pancreas secretions?
Secretion of proteolytic enzymes - trypsin and chymotrypsin for digestion of proteins
Secretion of lipase for digestion of lipids
Secretion of HCO3- (bicarbonate) to neutralise stomach acid
How are carbohydrates digested?
Amylase breaks starch down into disaccharides (maltose and lactose)
Disaccharides broken down by enzymes in SI epithelial cells to monosaccharides (glucose and galactose).
These are then transported into blood.
How are proteins digested?
Pepsin in the stomach breaks down peptides into peptide fragments.
Trypsin and chymotrypsin (in SI) break down peptide fragments into amino acids.
These are actively transported to the epithelial cells.
How are lipids digested?
Emulsification - breaking up of fat globules into small lipid droplets.
Pancreatic lipase
Micelle formation - for transport of lipids
What is the role of the large intestine?
Reabsorption of water and salts from chyme
Mixing and propulsion of contents
indigestible residue and liquid is eliminated as faecal waste
