Alimentary mechanisms Flashcards
What is molar?
One mole per litre
What is millimolar? And units?
1/1000 moles. mM.
What is micromolar? And units?
1/million moles. uM.
nanomolar - units and what?
1/billion moles. nM.
picomolar - units and what?
1/10^12. pM.
femtomolar - units and what?
1/10^15. fM.
Which molecules can cross membranes more easily, lipid soluble or water soluble
lipid soluble
In osmosis, how does water move?
Movement of water from a hypotonic solution to hypertonic solution.
What do tight junctions help achieve?
Unidirectional flow of substances, by creating cell polarity: e.g. different membrane proteins are kept on different sides of a cell.
What is paracellular transport?
Passage between cells, through tight junctions and lateral intercellular spaces.
What is trans cellular transport?
Passage through the epithelial cells.
What are the two transport proteins involved in membrane transport? (x2) What are channel proteins?
Channel proteins and carrier proteins.
What are channel and carrier proteins?
(1) Channel proteins form aqueous pores allowing specific solutes to pass across the membrane: facilitated diffusion.
(2) Carrier proteins bind to the solute and undergo a conformational change to transport it across the membrane: facilitated diffusion
Which has faster transport, channel or carrier proteins
Channel proteins allow much faster transport than carrier proteins.
What type of ion channels are there (x4)
Voltage gated, extracellular Ligand gates, Intracellular ligand gates, mechanically gated (eg change in pressure)
What types of carrier-mediated transport proteins are there ?
Uniport, symport and antiporter. Symport and antiport are coupled transport.
What is a uniport, symport and antiport carrier?
UNIPORT: One molecule transported in one direction. SYMPORT: Two molecules transported in same direction. ANTIPORT: Two molecules, transported in opposite directions - usually to balance charge.
What are the two types of active transport?
Primary and secondary active transport.
What is primary active transport? What is 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.
What is facilitated transport/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. Uses channel and carrier-mediated diffusion proteins.
An example of primary active transport? (x2)
Na/K ATPase transport, H+/K+ ATPase transporter in stomach
Example of secondary active transport? (x3)
SGLT-1 cotransport (Na+, and glucose and galactose - when glucose in lower concentration in lumen than enterocyte), HCO3-/Cl- counter-transport, Na/H counter transport
Example of facilitated transport?
Glut-2,4,5 (Glut-5 carrier protein transports fructose on the enterocyte apical membrane; GLUT-2 is a carrier protein in the basolateral membrane so that glucose can exit from enterocyte into plasma.)
What percentage of ingested water is absorbed by GI tract?
99%
What is absorption of water powered by? Name for process?
Absorption of ions (Na+), called standing gradient osmosis
Where is the greatest proportion of water absorbed?
Small intestine, especially jejunum
Which molecules are incompletely absorbed?
Iron and Calcium
How much water a day absorbed by small intestine?
roughly 8L
How much water a day absorbed by Large intestine?
1.4L
Where does 8L liquid come from a day, if only drink 2L?
Drink 2L, Saliva 1.2L, Gastric secretions 2L, Bile 0.7L, Pancreas 1.2L, intestinal secretions 2.4L
Movement of sodium across the epithelial layer and their locations in the GI? (x5 mechanisms) Efficiency down the GI tract?
(1) Na+/H+ antiport (proximal bowel).
(2) Na+/Glucose co-transport (jejunum).
(3) Na+/Amino Acid Co-transport (Jejunum).
(4) Co-transport with Cl- (ileum).
(5) Some ion channles (colon)
(This all increases intracellular NA+ and becomes MORE EFFICIENT as you travel down intestine).
Transport of chloride? (x2 mechanisms)
(1) Cl- co-transported with Na+ (ileum) as already mentioned. (2) Exchanged with HCO3- (colon) into enterocytes. Both secondary active transport.
Transport of K+? (x2 mechanisms)
(1) K+ diffuses IN via paracellular pathways in small intestine. (2) K+ diffuses OUT out via paracellular pathways in colon. Passive transport and explains why you will find K+ in faeces..
What happens to this high intracellular sodium?
Active transport of Na+ into the lateral intercellular spaces by Na+K+ATPase transport in the lateral plasma membrane, therefore [Na+] increases in intracellular space.
What happens to high intracellular chloride and HCO3-?
The movement of positive sodium out into intercellular spaces sets up an electrochemical gradient for negative ions (Cl- and HCO3-) which also move past basolateral membrane and into intercellular spaces.
What does movement of ions into intracellular spaces mean for standing gradient osmosis?
Creates a hypertonic intercellular fluid which drives transport of water from gut lumen to intercellular spaces by paracellular and transcellular pathways.
How does water and ions enter blood from intercellular spaces?
Movement of water into spaces increases pressure, which puts pressure on basement membrane, which forces water and ions into blood stream OVER the basement membrane (not basolateral membrane, but the basememnt membrane of the ECM).
Where is calcium absorbed?
Duodenum and Ileum
What happens to gut function when you have a Ca2+ deficient diet? Purpose?
Ca2+ deficient diet increases gut’s ability to absorb. This is compensatory - gut attempts to absorb more Ca2+ this way.
What stimulates calcium absorption? (x2)
Vit D and Parathyroid Hormone
How much ca2+ typically in diet?
1-6g/day
How much absorbed per day?
just under a gram
What is intracellular calcium concentration?
100nM/0.1mM
What is extracellular calcium concentration?
1-3mM. i.e. Calcium is found in high concentrations in the ECF, but low concentrations intracellularly.
What does high extracellular-low intracellular calcium mean for transport?
Doesn’t require energy for movement of calcium in cell.
How is calcium transported? (x2)
i) Intestinal calcium-binding protein (IMcal)- facilitated diffusion. ii) Ion channel
Why is ca2+ low in cytosol
acts as a signalling molecule
How is absorbed ca2+ prevented from acting as a signal?
Need to transport Ca2+ while maintaining low INTRAcellular concentrations. SO, binds to Calbindin in cytosol of enterocyte cell, preventing its action as an intracellular signal.
How is ca2+ transported across the basolateral membrance and into blood? (x2 mechanisms)
(1) Ca2+ pumped across basolateral membrane by plasma membrane Ca2+ ATPase (PMCA) against concentration gradient. PMCA has a high affinity for Ca2+ (but low capacity). High affinity maintains the very low concentrations of calcium normally observed within a cell. (2) Ca2+ also pumped across basolateral membrane by plasma membrane Na+/Ca2+ exchanger against concentration gradient. The Na+/Ca2+ exchanger has a low affinity for Ca2+ but a high capacity. Requires larger concentrations of Ca2+ to be effective. This means that it responds very quickly when there is an influx in Calcium.
How does Vit D help absorb calcium? (x3 functions) What diseases does deficiency lead to? (x2)
1, 25-dihydroxy D3 9the active form of Vitamin D) taken up by enterocytes: (i) Enhances the transport of Ca2+ through the cytosol; (ii) increases the levels of calbindin; (iii) Increases rate of extrusion across basolateral membrane by increasing the level of Ca2+ ATPase in the membrane. DEFICIENCY DISEASES: Deficiency causes rickets, osteoporosis.
What is the purpose of Iron? (x3)
(1) Iron can act as an electron donor and an electron acceptor. (2) Oxygen transport (red blood cells). (3) Oxidative phosphorylation (mitochondrial transport chain) - cytochromes.
What issue is there with iron absorption?
Too much is toxic, and the body has no way of actively excreting iron
What are the daily ingestion and absorption rates of iron?
Adult ingests approx 15-20mg/day but absorbs only 0.5-1.5mg/day.
Where is iron sourced in diet? (x2)
(1) INORGANIC IRON (Fe3+ ferric, Fe2+ ferrous) (2) as part of HEME (HAEM) GROUP (trapped in the meat that you eat in haemoglobin, myoglobin and cytochromes).
Which iron ion is absorbed
Fe 2+. Cannot Fe 3+