Ions, Vitamins and Minerals Flashcards
What is diffusion?
The process whereby atoms or molecules intermingle because of their random thermal motion.
How does diffusion differ across microscopic distances as opposed to macroscopic distances?
Diffusion occurs rapidly over microscopic distances, but slowly over macroscopic distances.
How do multicellular organisms bring individual cell within diffusion ranges?
By having circulatory systems
What does the cell membrane do between cells?
acts as a diffusion barrier, enabling cells to maintain cytoplasmic concentrations of substances different from their extracellular concentrations
Which molecules can easily cross the cell membrane barrier?
Lipid soluble (non-polar molecules)
What is meant by a hypotonic solution in terms of water concentration?
High water concentration
What is meant by a hypertonic solution in terms of water concentration?
Low water concentration
What is meant by paracellular transport?
through tight junctions and lateral intercellular spaces.
What is meant by transcellular transport?
Transcellular Transport - through the epithelial cells.
What methods can solutes use to cross cell membranes?
Simple diffusion
Facilitated diffusion
Active transport
What are the 2 types of transport proteins involved with active transport and describe how each works?
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.
what are four types of channel proteins?
- voltaged gated
- ligand-gated - intracellular and extracellular ligands
- mechanically gated
What are uniports?
Carrier mediated transport - one molecule moves in one direction
What are examples of uniports?
GLUT
VGCC
VGSC
What are symports?
Coupled transport mechanisms where the movement of one molecule down its concentration gradient provides energy for the movement of another against its concentration gradient
What are antiports?
Coupled transport where the movement of one ion power the movement of another in the opposite direction
What is an example of a symporter?
SGLT
What are examples of antiports?
Cl-/HCO3-
Na+ / H+
What is the difference between primary and secondary active transport?
Primary uses ATP but secondary uses the energy from the movement of another molecule
Give examples of primary active transporters and where they’re found
Na+ / K+ ATPase Pump - found in pancreas for pancreatic bicarbonate secretion and stomach for HCl secretion
Give examples of secondary active transporters and where they’re found
SGLT-1 co-tranpsorter (Small bowel absorption of monosaccharides)
HCO3-/Cl- counter transport (Pancreatic HCO3- Secretion)
Na+/H+ counter transport (Pancreatic HCO3- Secretion)
How are glucose and galactose absorbed?
Secondary active transport through SGLT
Where is glucose and galactose absorbed by secondary active transport?
enterocyte apical membrane
Why is it essential that glucose is absorbed via secondary active transport into enterocytes?
so it is effective when extracellular luminal concentrations are comparatively less than that in enterocytes
How is fructose absorbed?
Via facilitated diffusion using the carrier protein GLUT-5 on the apical membrane. Effective at relatively low concentrations of fructose in the lumen as tissue and plasma levels are low.
How does glucose exit through the basolateral membrane and what carrier protein is involved?
Facilitated diffusion, carrier protein is GLUT-2 (high capacity, low affinity facilitative transporter).
In what part of the GI system is the greatest amount of water absorbed?
Small bowel (especially in the jejunum)
Approximately how many litres of water are absorbed in the small and large bowel daily?
Small bowel - 8L
Large bowl - 1.4L
What drives the standing osmosis gradient?
Transport of Na+ from lumen into enterocyte.
what happens to the extracellular Na+?
Actively transported into the basolateral intercellular spaces by Na+ / K+ ATPase transport
how does standing gradient osmosis change as you travel down the intestine?
Becomes more efficient
How is the standing gradient osmosis created in the proximal bowel?
Counter transport in exchange for H+
How is the standing gradient osmosis created in the jejunum?
Co transport with amino acids and monosaccharides
How is the standing gradient osmosis created in the ileum?
Co transport with Cl-
How is the standing gradient osmosis created in the colon?
Restricted movement through ion channels
Explain how chloride ions are absorbed.
Cl- co-transported with Na+ within ileum, exchanged with HCO3- (Colon) into enterocytes. Co-transporter executed through secondary active transport on apical membrane.