Ions, Vitamins, Minerals Flashcards
Quantify the following units:
Molar (M) Milimolar (mM) Micromolar (uM) Nanomolar (nM) Picomolar (pM) Femtomolar (fM)
Mole (M) - one mole per litre
mM - 10^-3
uM - 10^-6
nM - 10^-9
pM - 10^-12
fM - 10^-15
Diffusion:
What is diffusion?
Diffusion occurs rapidly over what type of distances and slowly over what type of distances?
What do multicellular organisms evolve to bring individual cells within diffusion range?
What acts as a diffusion barrier?
What type of molecules diffuse easily? What type of molecules don’t?
Diffusion - process whereby atoms/molecules intermingle bc of their random thermal motion
Diffusion fast over microscopic distances
Diffusion slow over macroscopic distances
multicellular organisms evolve circulatory systems to bring individual cells within diffusion range
Cell membrane acts as diffusion barrier
Lipid soluble (non polar) molecules can diffuse more easily than water soluble (polar) molecules
How do molecules cross the epithelium to enter the bloodstream?
Paracellular transport- through tight junctions and lateral intercellular spaces
Transcellular transport - through the epithelial cells
Membrane transport:
Solutes can cross cell membranes by?
Types of transport proteins?
What type of transport protein transports solutes faster?
Solutes can cross cell membranes by:
- simple diffusion
- facilitated diffusion
- active transport
Two types of transport proteins:
Channel proteins - aqueous pores. Can have ion channels - specific to ions
Carrier proteins - binds to solute and undergoes conformational change to transport it across membrane. Can carry out uniport, symport or anti port
Transport much faster through channel protein than carrier proteins
Types of active transport?
What is facilitated transport/diffusion?
Active transport requires energy:
-Primary active transport - linked directly to cellular metabolism, uses ATP
-Secondary active transport - derives energy from conc grad of another substance that’s actively transported
Facilitated transport:
Enhances rate a substance can flow down its conc grad, doesn’t require energy
Examples of primary active transporters?
Examples of secondary active transporters?
Examples of facilitated diffusion?
Primary active transporters:
- Na+/K+ ATPase (pancreatic HCO3- secretion)
- H+/K+ ATPase (stomach - parietal cell)
Secondary active transporters:
- SGLT-1 co-transport (small bowel absorption of monosaccharides)
- HCO3-/Cl- counter transport (pancreatic HCO3- secretion)
- Na+/H+ counter transport (pancreatic HCO3- secretion)
Facilitated diffusion:
GLUT-5, GLUT-2 (small bowel absorption of monosaccharides)
Absorption of carbohydrates:
Via what type of transport are glucose and galactose absorbed?
Through what type of transporter protein?
When is this type of transport especially effective?
Absorption of glucose & galactose is by secondary active transport. Carrier protein = SGLT-1 on apical membrane
SGLT1 can transport glucose uphill against its conc grad (esp effective when glucose levels in the lumen are below those in the enterocyte)
How is fructose absorbed? Through what type of transporter protein if any?
What concs of fructose is this effective at?
Fructose is absorbed via facilitated diffusion
Carrier protein = GLUT-5 on apical membrane
Effective at relatively low concs of fructose in the lumen as tissue and plasma levels are low
How does glucose exit at the basolateral membrane?
Through what type of transporter protein if any?
Exit of glucose at the basolateral membrane is by facilitated diffusion
Carrier protein = GLUT-2, high capacity, low affinity facilitative transporter
Water & electrolytes:
What % of water presented to the GI tract is absorbed?
Absorption of water is powered by the absorption of what?
Where is the greatest amount of water absorbed?
How are many ions absorbed?
How are calcium and iron absorbed?
99% of the H2O presented to the GI tract is absorbed
Absorption of water is powered by the absorption of ions
Greatest amount of water is absorbed in the small intestine, esp the jejunum
Many ions slowly absorbed by passive diffusion
Calcium and iron are incompletely absorbed, this absorption is regulated
How much water is absorbed a day in the small bowel?
How much water a day is absorbed in the large bowel?
Water absorbed in small bowel : ~8L
Water absorbed in the large bowel: ~ 1.4L
Standing gradient osmosis:
Driven by what ion?
Transport of this ion becomes more efficient when?
Describe its transport at each of these locations:
- proximal bowel?
- jejunum?
- ileum?
- colon
Driven by Na+
-transport of Na+ from lumen into enterocyte-complex
Becomes more efficient as travel down intestine:
-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)
Absorption of other ions:
How is Cl- transported in:
-Ileum
-Colon
What type of transport is this?
How is K+ transported in small intestine and the colon?
What type of transport is this?
Cl- co-transported w Na+ (ileum), exchanged with HCO3- (colon) into enterocytes. - secondary active transport
K+ diffuses in via paracellular pathways in small intestine, leaks out between cells in colon
-passive transport
Standing gradient osmosis:
What happens to Intracellular sodium (in the enterocyte)?
Active transport of Na+ into the lateral intercellular spaces by Na+K+ATPase transport in the lateral plasma membrane
Standing gradient osmosis:
Why are Cl- and HCO3- transported into the intercellular spaces?
What causes the fluid in the intercellular spaces to be hypertonic?
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
Standing gradient osmosis:
How does water flow from the gut lumen into the intercellular space?
Water distending the intercellular channels causes what?
Ions and water moving across the basement membrane of the epithelium are carried away by what?
Osmotic flow of water from the gut lumen via adjacent cells, tight junctions into the intercellular space
Water dis tends the intercellular channels and causes increased hydrostatic pressure
Ions and water move across the basement membrane of the epithelium & are carried away by the capillaries
Calcium:
Where is Ca2+ absorbed?
What does a Ca2+ deficient diet result in?
What vitamin and hormone stimulates absorption of Ca2+?
How much calcium do we get from diet and secretions a day? How much is absorbed a day?
Duodenum and ileum absorb Ca2+
Ca2+ deficient diet increases guts ability to absorb
Vitamin D and parathyroid hormone stimulate absorption of Ca2+
Diet 1-6g/day, secretions 0.6g. Absorb 0.7g
Calcium:
What is low intracellular Ca2+ conc?
What is high extracellular fluid Ca2+ conc?
In the plasma?
In the lumen?
Low intracellular [Ca2+] approx 100 nM (0.1 uM)
-> can increase 10-100 fold during various cellular functions
High extracellular fluid [Ca2+] approx 1-3mM
- plasma [Ca2+] ~ 2.2-2.6 mM
- Luminal [Ca2+] varies in mM range
How are Calcium ions carried across apical membranes?
1) intestinal calcium binding protein (IMcal) - facilitated diffusion
2) ion channel
What are the implications for transport of Ca2+ into the cell from the lumen?
What are the implications for Ca2+ transport across the cell?
Implications for transport of Ca2+ into the cell from the lumen: Ca2+ acts as an intracellular signalling molecule
Implications for Ca2+ transport across the cell:
- need to transport Ca2+ while maintaining low intracellular concs
- binds to calbindin in cytosol, preventing its action as an intracellular signal
Calcium:
Via what plasma membrane transporter (1) are calcium ions pumped across the basolateral membrane?
Describe the affinity and capacity of this transporter for Ca2+
What is the benefit of this?
Ca2+ pumped across basolateral membrane by plasma membrane.
Ca2+ ATPase (PMCA) against conc grad
PMCA has a high affinity for Ca2+ (but low capacity)
Maintains the v low concs of calcium normally observed within a cell
Calcium:
Via what plasma membrane transporter (2) are calcium ions pumped across the basolateral membrane?
Describe the affinity and capacity of this transporter for Ca2+
What does this transporter require in order to be effective?
Ca2+ pumped across basolateral membrane by plasma membrane Na+/Ca2+ exchanger against conc grad
The Na+/Ca2+ exchanger has a low affinity for ca2+ but a high capacity. Requires larger concentrations of Ca2+ to be effective
Vitamin D:
What is vitamin D essential for?
What does a deficiency in vitamin D cause?
What are the consequences of 1,25-dihydroxy D3 being taken up by enterocytes?
Hint: enhances transport of? Increases levels of? Increases rate of?
Essential for normal Ca2+ absorption
Deficiency in vitamin D causes rickets, osteoporosis
1, 25-dihydroxy D3 taken up by enterocytes:
- enhances the transport of Ca2+ through the cytosol
- increases the levels of calbindin
- increases rate of extrusion across basolateral membrane by increasing the level of Ca2+ ATPase in the membrane
Iron:
What can iron act as?
What processes in the body is iron critical for?
Iron can act as an electron donor and an electron acceptor
Iron is critical for: Oxygen transport (RBCs) Oxidative phosphorylation (mitochondrial transport chain)
