GI Absorption Flashcards
The three types of digestions are brought about by?
Luminal - Enzymes secreted into lumen by gland/stomach/pancreas
Membrane - anchored enzymes (enterocytes) into brush border (dig/absorb coupling)
Cytosol - intracellular cytosolic breakdown (of tri/dipeptides to AA)
Absorption - Explain process, and my what mechanisms
Lumen –> E-Cell –> blood/lymph
by Diffusion / FT/AT
Membrane Transport: Passive
Diffusion - down gradient
Facilitated - transport mediated by protein
Absorption of water is ___ and determined by ____. This is unidirectional. In the small intestines water can be absorbed against an osmotic pressure gradient by ______ EXPLAIN!
*helps reabsorbs water
passive; osmotic gradient; standing gradient osmosis
Active transport pumps sodium in to lateral intercellular space creating a local osmotic gradient. (passive Cl- entry too); water follows –> enters cell + capillary.
What two ways does water use to enter cell?
Paracellular - through leaky intestinal tight junctions
Transcellular - through cells
Osmolarity?
of chemical compounds dissolved in liquid.
Electrolyte absorption in GI (sodium, potassium, chloride, bicarbonate)
Na: - Actively (sec) transported (removed from cell cytosol using Na+ pump)
K: Passively in SI; Colon [c] based
Cl: Passively
HCO3: Absorbed in Jejunum., but NET secretion in GI - neutralize acid
Electrolyte absorption in GI (sodium, potassium, chloride, bicarbonate) NET
SI: net absorber of water and all electrolytes. net secretor of bicarbonate
C: net absorber of water, Na+, Cl-, but is a net secretor of K+ and HCO3-
Solvent Drag
Solutes dissolved in water that is absorbed get absorbed too. No gradients involved; form or paracellular transport.
Calcium absorption in GI is ____ in ____, Ca is also absorbed in the ____
active; duodenum only via Trans-cellular pathway; jejunum
Explain Ca++ absorption in GI: Transcellular Pathway?
What vitamin stimulates and enhances this process?
Ca++ enters (FD) binds to calbindin; then diffusion via Ca++ATPase & Ca/Na Exchanger
Vitamin D
Explain Ca++ absorption in GI: Paracellular Pathway?
Is this pathway dependent on vitamin D?
Transport in vesicles, does not involved vitamin d.
Where is Magnesium absorbed? active or passive transport?
Absorbed actively in the ileum - mechanism poorly described; minor passive transport
Iron depletion leads to ____ because. _____. What is it called when you have a genetic defect that causes excessive absorption of iron
anemia; iron is used in RBC synthesis
idiopathic hemochromatosis
What are the two types of Dietary IRON; how is each absorbed?
H: Enterocyte uptake (via FD) H.oxygenase splits –> free Fe
NH: Ferric/Ferrous in sol’n
⁃ Ferric not soluble in neutral pH
⁃ reduced to Ferrous via Vit C
⁃ Brush Border reductase uptake