Ions, Vitamins and Minerals Flashcards
K+ absorption
Moves passively into small intestine lumen paracellularly
Tends to move out of large intestine passively= high K+ conc in faeces
Osmosis
Solution changes from what to what?
Hypotonic → Isotonic→ Hypertonic
Methods of molecules entering bloodstream?
Adaptations to allow this?
Paracellular
through tight junctions and lateral intercellular spaces.
Transcellular
through the epithelial cells.
Tight junctions go all the way round the cell
Some tight junctions= tighter than others
Fixes membrane bound proteins into boundaries to help localise them to parts of the membrane= carries out function better
Types of transport proteins
Faster one?
Channel proteins form aqueous pores allowing specific solutes to pass across the membrane.
Carrier proteins bind to the solute and undergo a conformational change to transport it across the membrane.
Channel proteins = faster transport than carrier proteins which has to undergo conformational change.
Types of ion channels
Examples?
Voltage gated
Ligand-gated (extracellular ligand) (e.g. hormone)
Ligand-gated (intracellular ligand) (e.g. secondary messengers bind+ open them)
Mechanically gated (e.g. increased pressure)
Types of carrier-mediated transport
Functions?
Uniport
Symport
Antiport (Counter-Transport) (trying to balance charge)
Symport+ Antiport= coupled transport, used in secondary active transport
Examples of Primary active transporters
Examples Secondary active transporters
Examples of Facilitated transport /facilitated diffusion transporters
Na+/K+ ATPase, H+/K+ ATPase
SGLT-1 co-transport, HCO3-/Cl- counter transport, Na+/H+ counter transport
GLUT-5, GLUT-2
Absorption of water+ ions process
Draw diagram
(slide3, lecture 6)
Driven by?
Driven by Na+
1. Transport of Na+ from lumen into enterocyte
Becomes more efficient as travel down intestine:
2. Counter-transport in exchange for H+ (proximal bowel)
3. Co-transport with amino acids, monosaccharides (jejunum)
4. Co-transport with Cl- (ileum)
5. Movement through ion channels (colon)
6. Cl- co-transported with Na+ (ileum), exchanged with HCO3- (colon) into enterocytes. Both secondary active transport.
7. K+ diffuses in via paracellular pathways (between cells instead of across cells) in small intestine, leaks out between cells in colon. Passive transport.
8. Active transport of Na+ into the lateral intercellular spaces by Na+K+ATPase transport in the lateral plasma membrane
9. Cl- and HCO3- transported into the intercellular spaces due to electrical potential created by the Na+ transport.
10. High conc of ions in the intercellular spaces causes the fluid there to be HYPERTONIC
11. Osmotic flow of water from gut lumen via adjacent cells, tight junctions into the intercellular space.
12. Water distends the intercellular channels and causes increased hydrostatic pressure.
13. Ions and water move across basement membrane of the epithelium +carried away by the capillaries.
% H2O presented to GI tract= absorbed?
99%
Greatest amount of water absorbed where?
Jejenum
Calcium absorption process?
Implications of conc. gradient?
Draw it (slide 2, lecture 6)
Low intracellular Ca2+ but high extracellular fluid concentrations= Passive transport (goes easily down conc. gradient)
- Ca2+ carried across apical membrane by:
i) Intestinal calcium-binding protein (IMcal) facilitated diffusion.
ii) Ion channels (don’t need to know specifics) - Ca2+ acts as an intracellular signalling molecule- don’t want to kick off intracellular signalling pathways, Need to transport Ca2+ while maintaining low intracellular concentrations.
- Binds to calbindin in cytosol, preventing its action as an intracellular signal. (But at high conc. on other side= need active transport)
- Ca2+ pumped across basolateral membrane by plasma membrane Ca2+ ATPase (PMCA) against concentration gradient.
- PMCA has a high affinity for Ca2+ so even low conc. Ca it is still effective (but low capacity)= Maintains the very low concentrations of calcium normally observed within a cell.
- Ca2+ also pumped across basolateral membrane by plasma membrane Na+/Ca2+ exchanger against concentration gradient. (secondary active transport)
- The Na+/Ca2+ exchanger has a low affinity for Ca2+ but a high capacity (opposite to ATPase). Requires larger concentrations of Ca2+ to be effective but high capacity= works quickly
Ca2+ deficient diet=?
Increases gut’s ability to absorb.
What stimulates Ca2+ absorption?
Vit D
Parathyroid hormone
Vitamin D absorption process?
Effects?
Importance?
Taken up by enterocytes
Enhances the transport of Ca2+ through the cytosol
Increases the levels of calbindin
Increases rate of extrusion across basolateral membrane by increasing the level of Ca2+ ATPase in the membrane.
Normal Ca2+ absorption
Deficiency= Rickets in children, Osteoporosis in adulta.
Iron function?
Act as an electron donor and an electron acceptor