Ions, vitamins and minerals Flashcards
What is molar, mM, µM, nM, pM and fM and thei conversions?
Molar = one mole per litre
Millimolar (mM) 10-3 Micromolar (µM) 10-6 Nanomolar (nM) 10-9 Picomolar (pM) 10-12 Femtomolar (fM) 10-15
What is diffusion?
Is it faster over macroscopic or microscopic distances?
- The process whereby atoms or molecules intermingle because of their random thermal motion.
- Diffusion occurs rapidly over microscopic distances, but slowly over macroscopic distances.
What is a hypotonic solution?
Solution that has less solute and more water than another solution
What is the pathway of water in osmosis (tonicity of solutions)?
hyptonic ->isotonic->hypertonic
What are the two broad types of transport?
Transcellular - through epithelial cells
Paraceullular - through tight junctions and lateral intercellular spaces
Which membrane transporters are faster - channel or carrier protein?
channel protein
What are some types of ion channels?
Ion channels can be voltage gated, ligand gated, mechanically gated
What are the types of carrier protein mediated transport?
Uniport -one
Symport - cotransported
Antiport - counter transport
What is primary active transport and give an example?
Linked directly to cellular metabolism (ATP powered)
E.G. Sodium Potassium ATPase
What is secondary active transport and give an example?
Derives energy from concentration gradient of another substance actively transported
E.G. Bicarbonate/Chloride counter-transport, SGLT-1
What is the importance of facilitated diffusion?
Enhances rate a substance can flow down a concentration gradient
so it can reach equilibrium.
E.G. GLUT-5, GLUT-2
How are glucose and galactose absorbed?
- Absorption of glucose & galactose is by secondary active transport
Carrier protein = SGLT-1 on apical membrane. - SGLT1 can transport glucose uphill against its concentration gradient (so effective when glucose at levels in the lumen are below those in the enterocyte)
How is fructose absorbed?
- Absorption of fructose is by facilitated diffusion
- Carrier protein = GLUT-5 on apical membrane.
- Effective at relatively low concentrations of fructose in the lumen as tissue and plasma levels are low
How does glucose exit the enterocyte and enter the blood?
- Exit of glucose at the basolateral membrane is by facilitated diffusion. Carrier protein = GLUT-2, a high-capacity, low-affinity facilitative transporter.
What % and volume of water is absorbed by the GI tract and how?
Which part of the GI tract absorbs the most water?
- 99%
- It is absorbed by the action of ion absorption
- Most water is absorbed in the small intestine (especially the jejunum)
How are many ions absorbed and are Ca2+ and iron completely absorbed?
Many ions absorbed slowly by passive diffusion and Ca2+ and iron are incompletely absorbed due to regulation.
How much water is absorbed by the small and large intestine?
SI - 8L
LI - 1.4 (DAILY)
Where does the water in the GI tract come from?
- Ingestion (2L)
- Saliva (1.2L)
- Gastric secretions (2L)
- Bile (0.7L)
- Pancreas (1.2L)
- Intestine (2.4L)
What is the name of the process by which water is reasborbed?
Standing gradient osmosis (driven by Na+)
How does sodium enter enterocytes?
Sodium gets into the cells via different methods depending on location of the enterocyte:
- Proximal bowel uses counter transport for H+
- Jejunum uses cotransport with amino acids, monosaccharides
- Ileum uses cotransport with Cl-
- Colon uses restricted movement through ion channels
- Cl- is cotransported with Na+ in the ileum and exchanged with HCO3- in the colon
Describe the standing gradient osmosis
High intracellular sodium is controlled by:
- Active transport of Na+ into lateral intercellular spaces by Na+/K+ATPase
- Cl- and HCO3- transports into the intercellular space by electrochemical gradient of Na+
- High concentration of ions in intercellular spaces (hypertonic)
- Osmotic flow of water from the gut lumen via adjacent cells, tight junctions into the intercellular space
- 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
Calcium absorption - where does majority occur, what does a calcium deficiency do to absorption, what stimulates its absorption, how much is absorbed daily, and at rest what are the relative concentration of intra and extracellular calcium?
- Most absorption of calcium occurs in the duodenum and ileum
- A calcium deficiency increases the gut’s ability to absorb calcium
- Vitamin D and parathyroid hormone stimulate absorption of calcium
- Even though we ingest 1-6g of calcium a day, we only absorb about 0.7g of it
- This is because it is regulated
- At rest, there is a low (nm) intracellular concentration and a high (micromole) extracellular concentration
How is calcium transported across the apical membrane?
Absorption via 2 types of transporter:
- Facilitated diffusion – IMcal (intestinal calcium binding protein)
- Ion channel
How is calcium transported whilst maintaining low intracellular concentrations (because it is a signalling molecule)?
- Binds to calbindin in cytosol to make it inactive
- Calcium pumped out of basolateral surface by:
Ca2+ATPase (PMCA) - PMCA has a high affinity but low capacity
- Maintains the low intracellular concentration.
- It is also pumped out by Na+/Ca2+ exchanger against its concentration gradient
- It has a low affinity but high capacity so needs larger concentrations of calcium to be effective (hence it works before the PMCA to reduced the large calcium amounts)
