GI physiology 4 (small + large intestine) Flashcards
Why are muscle contractions important?
They mix the stomach content, ensure the luminal content is in contact with epithelial cells and transport chyme
What are the two types of contraction in the small intestine?
Segmentation and Peristalsis
What is the function of segmentation?
To mix content in the intestine
What is the migrating motility complex?
Propulsive movements that ‘sweep’ the intestine clean between meals- it removes bacteria and sloughed off epithelial cells
How is the contraction in the small intestine controlled?
via pacemaker cells
What are pacemaker cells?
Specialised neurones that can generate slow waves that then contract the smooth muscle
What else is released that effects the membrane potential of the smooth muscle?
peptides and other neurotransmitters
Where are most carbohydrates and proteins broken down?
The small intestine
What are some adaptations of the small intestine?
Folds in the inner surface (mucosa), villi with microvilli (all to increase surface area)
What is the structure of enterocytes?
They contain an apical membrane that is in contact with the intestinal lumen, Tight junctions that connect adjacent enterocytes and a basolateral membrane that acts as extracellular space
How does absorption work in the small intestine?
Nutrients are transferred from the lumen, across the apical membrane (if they are organic)
Transcellular absorption
absorption through the cell through the enterocytes (organic nutrients)
Paracellular absorption
Inorganic ions and water diffusing through tight junctions that connect the enterocytes
What are the two phases of digestion?
Luminal and membranous, they are both catalysed by enzymes
Where and how are carbohydrates digested?
By amylase, in the proximal part of the stomach
Where does the final degradation of proteins into amino acids occur?
In the membrane of the stomach
How are fats broken down in the small intestine?
Fats are emulsified by bile produced from the pancreas, FFA’s and monoglycerides then diffuse into the epithelial cell where they become chylomicrons and enter the lymph vessel
Levels of Absorption of calcium in the small intestine
It is essential that the level of calcium within cells remains low so calcium is bound to a protein during its transport from the apical membrane to the basolateral
What is the function of calcitrol?
Increases the number of channels in the apical membrane and increases synthesis of the transporter proteins so more calcium is taken up
Absorption of sodium
All sodium is re-absorbed, co-transported with glucose
Absorption of potassium
Mostly absorbed via diffusion through the apical membrane in the gut
Where does microbial digestion occur?
In the large intestine, it is most of benefit to simple stomached herbivores (e.g horses/ rabbits)
What occurs to Carbohydrates in the large intestine?
they are degraded to VFA’s by microorganisms, these can then be absorbed by the epithelium
What happens with the excess acid after VFA production in horses? (too many VFA’S produced)
large amounts of HCO3- produced in the pancreas and ileum are transferred to the LI to neutralise the acids
