Physiology Absorption Flashcards
(33 cards)
Define absorption.
Net passage of substances from the lumen across the epithelium to the interstitial fluid.
List the factors affecting absorption.
SA Motility Adequate digestion Penetration Removal of substances from interstitial space
Explain how the SA is maximized for absorption.
Circular folds, villi and microvilli present to increase SA.
Describe how motility is involved in absorption.
Segmentation - squeeze and squish for churning
Absorption is only possible if the molecule can come into contact with the epithelium.
Also need adequate contact time - cannot have too much motility.
Needs to be a balance between fast and slow movement.
Issues with motility result in diarrhoea or vomiting.
Explain why adequate digestion is needed for absorption.
Small pieces of food are needed for absorption
Brush border enzymes are needed
Breakdown of food is to create molecular units (small enough for absorption)
Explain the information regarding penetration involved in absorption.
Solubility/size
Transporters (in membrane)
Pathways (into and out of cells)
How do we move substances from the intersitial space?
We need gradients.
List some absorption mechanisms.
Diffusion/carrier/passive or active
What is key for absorption?
Na permeability and transport is key
What is key for secretion?
Cl ions
How is water absorbed?
Via an osmotic gradient
How are lipids absorbed?
Via diffusion
What is the key driver for absorption and secretion respectively?
Cl is key for secretion
Na is key for absorption
What structure is present for secretion and absorption respectively?
Villus is present for absorption
Crypt is present for secretion
Describe absorption in the mouth.
Minimal
Some drugs e.g. GTN under tongue due to good blood supply
Recreational drugs e.g. ketamine, tobacco chewing
What is absorbed in the stomach?
Aspirin
Ethanol
What are the main functions of the mouth and stomach?
Preparation for absorption
Where does the most absorption take place?
Small intestine (90%)
What is absorbed in the colon?
Water and sodium - swap water and sodium for K secretion.
Decreases faecal volume
Neuronal and hormonal control
Bacterial products - SCFA/vitamins
Drugs - rectal mucosa has good blood supply e.g. suppositories
Describe the absorption of sodium.
1000mmol/day - mostly from secretions
90% small intestine, solute co-transport
10% colon, K exchange?SCFA/ENaC
How much sodium is excreted in the faeces?
5-10mmol/day
Describe the absorption of water.
10L/day - mostly from secretions 90% SI, solute co-transport 1L in colon 0.1L in faeces Moves down osmotic gradient from Na absorption
Describe the absorption of carbohydrates.
Duodenum/jejunum = proximal absorption
Amylase –> disaccharides
Brush border enzymes for further breakdown –> monosaccharides
Absorbed as disaccharides and monosaccharides
Absorption by Na co-transport (GLUT 5 or SLGT1)
Describe how proteins are absorbed.
Come from our diet, sloughed cells, secretions
Pepsin, pancreatic proteases digest them into amino acids
Brush border peptidases
Amino acids with Na
Di/tri peptides also absorbed
