GI Intestinal Physiology. Flashcards
What is the total amount of body water?
40L
What is the water input into the GI tract?
9L/day
How much water is excreted in the GI tract and where?
7L/day- gastric acid 2.5, saliva 1.5L, Bilary 0.5L, Pancreatic 1.5L, Intestinal 1L/day
Where is the majority of water reabsorbed in the GI tract?
The small intestine.
How much water does the jejunum reabsorb?
5.5L/day it is the largest reabsorber of water.
How much water does the jejunum reabsorb?
5.5L/day it is the largest re-absorber of water.
What are the pathways for water re-absorption in the small intestine?
Paracellular and Transcellular.
What drives the paracellular root?
Solute driven pathway due to osmotic gradient out of SI. Na+ glucose pump.
What drives the transcellular root?
Solvent driven pathway via aquaporin molecules
How is Na+ absorbed in the SI?
Sodium moves by co-transport with either amino acids or glucose to be actively transported out of the SI.
How is K+ absorbed in the SI?
Down the electrochemical gradient it is a passive process.
How is HCO3- absorbed in the SI?
Pancreatic juice has high bicarbonate to neutralise gastric acid but some much be reabsorbed in SI to maintain balence.
1) In cell H2O+ CO2–> HCO3- + H+ By carbonic anhydrase.
2) HCO3- diffuses out of basolateral membrane to capillaries.
3) H+/K+ anitporter pumps H+ into stomach lumen
4) H+ + HCO3- in stomach lumen to H20 + CO2
How is Cl- absorbed in the SI?
Absorption of Cl- largely occurs through passive diffusion via a paracellualr route. Na+ resorption creates a lumen negative charge therefore a strong electrochemical gradient for passive resorption of Cl-.
Main absorption in duodenum and jejunum.
What micro-nutrients are absorbed in the duodenum?
Calcium, magnesium, iron, fat-soluble vitamins A and D, glucose.
What is absorbed in the jejunum?
Fat, sucrose, lactose, fat-soluble vitamins A and D, water-soluble vitamins like folic acid, proteins and amino acids, glucose.
