9 Ions, Vitamins and Minerals Flashcards
Q: mM µM nM pM fM
A: Millimolar (mM) 10-3 Micromolar (µM) 10-6 Nanomolar (nM) 10-9 Picomolar (pM) 10-12 Femtomolar (fM) 10-15
Q: What is diffusion? How does speed vary? (2) How have multicellular organisms evolved? to?
A: The process whereby atoms or molecules intermingle because of their random thermal motion
Diffusion occurs rapidly over microscopic distances, but slowly over macroscopic distances.
Multicellular organisms evolve circulatory systems to bring individual cells within diffusion range
Q: What does the cell membrane act as in terms of diffusion? allowing? Which molecules can cross easily?
A: The cell membrane acts as a diffusion barrier, enabling cells to maintain cytoplasmic concentrations of substances different from their extracellular concentrations
Lipid soluble (non-polar) molecules can cross more easily than water soluble (polar) molecules
Q: What is osmosis?
A: water movement from hypotonic -> isotonic -> hypertonic ACROSS semipermeable membrane
Q: How does the epithelium of the gut form a continuous layer? What else does this structure do? What determines the molecules that can cross the epithelium to enter the bloodstream?
A: tight junctions form between enterocytes- different proteins that connect cells together
allows differentiation between apical and basolateral membrane as proteins can’t move freely between the regions
depends on ‘tightness’- not consistent throughout the gut -> have varying leakiness/selectivity on what can pass between cells
Q: What are the 2 ways molecules can cross the epithelium to enter the blood?
A: Paracellular Transport
through tight junctions and lateral intercellular spaces.
Transcellular Transport through the epithelial cells (absorbed at apical side of cell and exocytosed on other (basolateral))
Q: What are the 3 ways that solutes can cross cell membranes? What are the 2 types of protein involved? Speed comparison? Control comparison?
A: simple diffusion, facilitated transport or active transport. Two types of transport proteins involved.
1) Channel proteins form aqueous pores allowing specific solutes to pass across the membrane. 2) Carrier proteins bind to the solute and undergo a conformational change to transport it across the membrane. Channel proteins allow much faster transport than carrier proteins but channel proteins allow much less control - only allow things to move DOWN electrochemical gradient
Q: What are the 4 types of ion channel?
A: can be gated to some degree- can be open or closed
- voltage gated
- ligand-gated (extracellular ligand) eg H binding
- ligand-gated (intracellular ligand) - secondary intracellular signals eg cAMP or Ca2+
- mechanically gated eg pressure transducers and stretch receptors
Q: What are the 3 types of carrier mediated transport?
A: uniport- allows the movement of 1 molecule in 1 direction
coupled transport:
symport- allows the movement of 2 molecules in one direction
antiport=counter transport: allows movement of 2 molecules in opposite directions (often of molecules with same charge= prevent disturbance of electrochemical equilibrium)
Q: What are the 3 types of membrane transport in terms of energy? Describe.
A: Active transport requires energy:
- 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 = currency is often Na+
Facilitated transport /facilitated diffusion:
-enhances the rate a substance can flow down its concentration gradient. This tends to equilibrate the substance across the membrane and does not require energy
Q: Give 2 examples of Primary active transporters.
A: Na+/K+ ATPase
H+/K+ ATPase (in stomach- H+ put into gastric fluid)
Give 3 examples of Secondary active transporters.
A: SGLT-1 co-transport (sodium/glucose)
HCO3-/Cl- counter transport (in pancreas)
Na+/H+ counter transport (in pancreas)
Q: Give 2 examples of Facilitated transport /facilitated diffusion transporters. we have already covered in the course.
A: GLUT-5, GLUT-2
Q: By which process are glucose and galactose absorbed by enterocyte? Via? When is this effective? why?
A: by secondary active transport (carrier protein and electrochemical gradient)
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)
- energy is being inputted in form of Na+ coming down its electrochemical gradient
Q: By which process is fructose absorbed by enterocyte? Via? When is this effective? why?
A: 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
Q: By which process does glucose exit an enterocyte? Via? How does glucose vary between plasma and tissue/enterocyte?
A: Exit of glucose at the basolateral membrane is by facilitated diffusion. Carrier protein = GLUT-2, a high-capacity, low-affinity facilitative transporter.
Glucose between plasma and tissue/enterocyte generally equilibrated.
Q: What percentage of H2O presented to the GI tract is absorbed? What powers this absorption? speed? Where in the GI tract is the greatest amount of water absorbed?
A: 99%
by the absorption of ion- Many ions slowly absorbed by passive diffusion
in the small intestine, esp the jejunum
Q: What can describe calcium and iron absorption? means?
A: Calcium and iron are incompletely absorbed by specific mechanisms, and this absorption is regulated
Q: Approximately, how many litres of water a day is absorbed by 2 named organs? Compare. How does this compare to how much we drink?
A: Approximately 8 litres of water a day absorbed in the small intestine.
Approximately 1.4 litres of water a day absorbed in the large intestine (works harder and content is more solid)
we don’t drink that much, the rest of the water absorbed is from secretions
Q: Name 6 contributors to the water in our gut (predominantly reabsorbed). Include how many litres they put into gut?
A: ingest 2L
saliva 1.2L
gastric secretions 2L (stomach)
bile 0.7L
pancreas 1.2L
intestinal 2.4L
Q: What drives the water absorption in the gut? DIAGRAM. How does it create this environment? (4) Include the absorption of 3 other ions.
What occurs next to the ions? What does this change? What happens to water? (3)
What occurs to the driving force?
A: Na+ primarily
4 mechanisms that put Na+ into enterocytes and increase intracellular concentration
- Counter-transport in exchange for H+ (proximal bowel)
- Co-transport with amino acids, monosaccharides (jejunum) (SGLT-1)
- Co-transport with Cl- (ileum) (opposite charges = equalises)
- Restricted movement through ion channels (colon) (on its own through aqueous pore/ ion channel)
- Cl- co-transported with Na+ (ileum)
- Cl-exchanged with HCO3- (colon) into enterocytes. Both secondary active transport.
- K+ diffuses in via paracellular pathways (tight junctions) in small intestine, leaks out between cells in colon. Passive transport
- Cl- and HCO3- transported into the intercellular spaces due to electrical potential created by the Na+ transport.
- High conc of ions in the intercellular spaces causes the fluid there to be 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.
What happens to this intracellular sodium?
Active transport of Na+ into the lateral intercellular spaces by Na+K+ATPase transport in the lateral plasma membrane
Q: What is standing osmotic gradient?
A: reabsorption of water against the osmotic gradient in the intestines
Q: Where does the majority of Ca2+ absorption occur? How can Ca2+ in your diet affect gut absorption? What stimulates absorption? (2) Usually?
A: Duodenum and Ileum absorb Ca2+
Ca2+ deficient diet increases gut’s ability to absorb.
Vit D and parathyroid hormone stimulate absorption.
usually don’t need to stimulate lots as diet contains so much
secretions 0.6g. Absorb 0.7g so we only need 0.1g, BU T out diet is 1-6g/day,
Q: What’s the concentrationof Ca2+ in intracellularly? why? extracellularly? (2)
A: Low intracellular [Ca2+] approx 100 nM (0.1µM)
(but can increase 10– to 100-fold during various cellular functions)
=> try and keep low as it’s an intracellular signaller
High extracellular fluid [Ca2+] approx 1-3mM.
(Plasma [Ca2+] approx 2.2-2.6mM)
(Luminal [Ca2+] varies inmM range)
