Ions, Vitamins, Minerals Flashcards
(47 cards)
What is paracellular transport?
through tight junctions and lateral intercellular spaces.
What is Transcellular transport?
through the epithelial cells.
What are channel proteins and carrier proteins?
- 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.
- Carrier proteins bind to the solute and undergo a conformational change to transport it
- Channel proteins allow much faster transport than carrier proteins.
What types of gated channel proteins are there?
Voltage gated
Ligand gated - extracellular ligand
Ligand gated - intracellular ligand
Mechanically gated
What is the difference between primary active transport and secondary active transport?
Primary active transport is linked directly to cellular metabolism (uses ATP to power the transport).
Secondary active transport derives energy from the concentration gradient of another substance that is actively transported.
Examples of primary active transporters?
Na+/K+ ATPase (Pancreatic HCO3- Secretion)
H+/K+ ATPase (Stomach – Parietal Cell)
Examples of secondary active transporters?
SGLT-1 co-transport (Small bowel absorption of monosaccharides)
HCO3-/Cl- counter transport (Pancreatic HCO3- Secretion)
Na+/H+ counter transport (Pancreatic HCO3- Secretion
Examples of facilitated diffusion transporters?
GLUT-5, GLUT-2 (Small bowel absorption of monosaccharides)
How is glucose and galactose absorbed ( carbohydrates )?
Absorption of glucose & galactose is by 2o active transport (carrier protein & electrochemical gradient). Carrier protein = SGLT-1 on apical membrane.
Why is the SGLT1 transporter useful?
SGLT1 can transport glucose against its gradient
- it is effective when glucose at levels in the lumen are below those in the enterocyte.
How is fructose absorbed?
Facilitated diffusion : GLUT-5 carrier protein on apical membrane
- Effective at relatively low concentrations of fructose in the lumen as tissue and plasma levels are low.
How is glucose secreted out?
facilitated diffusion.
Carrier protein = GLUT-2, a high-capacity, low-affinity facilitative transporter.
- Glucose between plasma and tissue/enterocyte generally equilibrated.
Where is water absorbed the most and how?
The greatest amount of water is absorbed in the small intestine, esp the jejunum.
The absorption of water is powered by the absorption of ions.
99% of the H2O presented to the GI tract is absorbed.
Many ions slowly absorbed by passive diffusion.
Calcium and iron are incompletely absorbed, and this absorption is regulated.
How much water is absorbed in the small and large bowel?
Approximately 8 litres of water a day absorbed in the small bowel.
Approximately 1.4 litres of water a day absorbed in the large bowel.
How much water is absorbed in the small and large bowel?
Approximately 8 litres of water a day absorbed in the small bowel.
Approximately 1.4 litres of water a day absorbed in the large bowel.
How is the osmosis gradient created?
Driven by Na+
Transport of sodium from lumen into enterocytes becomes more efficient as it travels down the intestine
How is does Na+ absorption change going down the intestine?
Becomes more efficient as travel down intestine:
- Counter-transport in exchange for H+ (proximal bowel)
- Co-transport with amino acids, monosaccharides (jejunum)
- Co-transport with Cl- (ileum)
- Restricted movement through ion channels (colon)
Describe the absorption of Chlorine ions and potassium ions?
Cl- co-transported with Na+ (ileum), exchanged with HCO3- (colon) into enterocytes.
Both secondary active transport
K+ diffuses in via paracellular pathways in small intestine, leaks out between cells in colon.
Passive transport.
What happens to intracellular sodium?
Active transport of Na+ into the lateral intercellular spaces by Na+K+ATPase transport in the lateral plasma membrane
Why is the fluid in between intracellular spaces hypertonic?
High concentrations of ions in the fluid
Due to Cl- and HCO30 transported into the spaces by the electrical potential generated by Na+ transport
- Water distends the intercellular channels and causes increased hydrostatic pressure.
Ions and water move across the basement membrane of the epithelium and are carried away by the capillaries.
What absorbs calcium ions?
Duodenum and Ileum absorb Ca2+
Ca2+ deficient diet increases gut’s ability to absorb
Vit D and parathyroid hormone stimulate absorption
Diet 1-6g/day, secretions 0.6g. Absorb 0.7g
What are the normal calcium concentrations intra and extra cellular?
Low intracellular [Ca2+] approx 100 nM (0.1µM)
(but can increase 10 to 100-fold during various cellular functions).
High extracellular fluid [Ca2+] approx 1-3mM.
(Plasma [Ca2+] approx 2.2-2.6mM)
(Luminal [Ca2+] varies inmM range)
What is the calcium transporter?
Ca2+ carried across apical membrane by 2 methods :
- Intestinal calcium-binding protein (IMcal)- facilitated diffusion.
- Ion channel
What are the implications for transport of Ca2+ into the cell from the lumen?
Ca2+ acts as an intracellular signalling molecule.
