Ions, Vitamins and Minerals Flashcards
How does water move down a concentration gradient
How can molecules cross the epithelium to enter the bloodstream
Paracellular transport through tight junctions and lateral intercellular spaces
Transcellular transport through epithelial cells
What are channel protein
What are carrier proteins
What are the two types of co-transported ion
What is the difference between primary active transport and secondary active transport
Primary - linked with ATP
Secondary - derives energy from concentration gradient of another substance that is actively transported
Example of primary active transport
Example of secondary active tranport
SGLT-1 co transport in small bowel absoprtion
HCO3/Cl in pancreatic HCO3 secretion
Na/H counter transport in pancreatic HCO3 secretion
Example of facilitated transport
How are glucose and galactose absorbed
How is fructose absobred
Facilitated diffusion
GLUT-5 on apical membrane
How does glucose exit the basolateral membrane
Facilitated diffusion
Glut-2 high capacity low affinity
Where is water being absorbed coming from
How is water absorbed
Driven by Na
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)
How is Cl absorbed
How is K absorbed
Diffuses via paracellular pathways in small intestine
Passive transport
What happens to Na after being used for secondary active transport
Active transport into lateral intercellular spaces by Na K ATPase transport in the lateral plasma membrane
What happens when Na moves into intercellular space
Intercellular spaces causes fluid to be hypertonic
Osmotic flow of water from gut lumen via adjacent cells, tight junctions into the intercellular space
Water distends the intercellular channels and causes increased hydrostatic pressure
What stimulates calcium absorption
How is calcium carried across apical membrane
What are teh implications for Ca transport transport across the cell
Need to transport Ca while maintaing low intracellular concetrations
Binds to calbindin in cytosol
How is Ca pumped across basolateral membrane by plasma membrane
PMCA has a high affinity for Ca but low capacity
Ca (ATPase)
Also pumped by Na/Ca which has low affinity but high capacity ( requires larger concentrations)
What is the rold of 1,25-dihydroxy d3
Enhances transport of Ca
Increases levels of calbindin
Increase rate of extrusion across basolateral membrane by increasing Ca ATPase
What is iron essnetial for
Oxygen transport
Oxidative phosphrylation
How is iron presented in the diet
Facts about iron
How is heme absorbed
Heme carrier protein 1 (HCP-1) and via receptor-mediated endocytosis
Fe liberated by Heme oxygenase
How is iron uptook
Duodenal cytochrome B catalyzes the reduction of Fe3 to Fe2 in the process of iron absorption
Fe2 transported via divalent metal transporter (DMT-1) , H coupled cotransporter
Fe2 binds to unkown factors carried to basolateral membrane via ferroportin ion channel
Hephaestin is a transmembrane copper-dependent ferroxidase converts 2 to 3
Fe3 binds to apotransferrin, travels in blood as transferrin
Facts about ferritin
Binds to apoferritin in cytosol to form ferritin micelle
Ferritin molecule can store up to 4000 iron
In excess diertary iron absorption, porduce more ferritin
Globular portein complex
Fe crystallises within protein shell
What happens to ferritin stored in enterocytes
Prevents absorption of too much iron
How are fat soluble vitamins (A,D,E,K) transported
K taken up by active transprot
Others transported to brush border
What happens during impaired absorption of vit B12
Retards the maturation of RBC - pernicious anaemia
Most b12 bound to proteins
How is denaturation of B12 in stomach avoided
Binds to R portein (haptocorrin) released in saliva and from parietal cells
R proteins digested in duodenum
What is the intrinsic factor
Vit B12 binding glycoprotein secreted by parietal cells
Resistatnt to digestion
Vit B12/IF binds to cubilin receptors, taken up in distal ileum
What happens to B12 once in cell
Vit B12/IF complex broken
B12 binds to protein transcobalamin II (TCII)
Travels to liver bound to TCII
TCII receptors on cells allow them to uptake complex
Proteolysis breaks down TCII inside cell
Where is the greatest amount of water absorbed
Small bowel, jejunum
How much iron is absorbed
5% inorganic iron
20% of heme iron
