Ions, Vitamins And Minerals Flashcards
What does molar mean?
One mole per litre
How can molecules cross the epithelium to enter the blood stream?
Para cellular transport - through tight junctions and lateral intercellular spaces
Trans cellular transport - through the epithelial cells
What are the ways solutes can cross a membrane?
Simple diffusion
Facilitated transport
Active transport (primary -ATP, or secondary -energy from another substances conc gradient that is actively transported)
Transport proteins include: channel proteins (can be openable), carrier proteins
Transport through channel proteins is in general quicker
What are the types of carrier mediated transport?
Uniport - only requires transported molecule
Symport- transported molecule and co transported ion go in the same direction
Antiport- transported molecule and co transported ion go in opposite direction
These last two are forms of coupled transport
How is the absorption of carbohydrates done (glucose and galactose)?
Absorption of glucose and galactose
Secondary active transport
Carrier protein = SGLT-1 on apical membrane
SGLT-1 can transport glucose against its conc gradient (useful if glucose in the lumen is low)
Absorption on basolateral membrane is by facilitated diffusion
Carrier proteins = GLUT-2, high capacity, low affinity
Concentration between plasma and enterocytes is generally equilibreated
How is absorption of carbohydrates done (fructose)?
Fructose
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
What are some facts about water and electrolytes in terms of absorption?
99% of water in the GI tract is absorbed
The absorption of water is powered by the absorption of ions
Greatest amount of water is absorbed in the small intestine (esp jejunum)
Many ions are slowly absorbed by simple diffusion
Calcium and iron are incompletely absorbed
Approx 8L ow water are absorbed a day in the small bowel, and 1.4L in the large bowel
Where does the water we absorb come from?
We invest about 2L a day
Saliva produced gives about 1.2L
Gastric secretions produce about 2L
Bile 0.7L
Pancreatic juice 1.2L
Intestinal 2.4L
The absorption of water is through a standing gradient osmosis, what does this entail?
Driven by Na+
Transport of sodium ions from the lumen into Enterocyte. Becomes more efficient as you travel down the intestine:
Proximal bowel - counter transport in exchange for H+
Jejunum- co transported with amino acids and monosaccharides
Ileum - cotransport with Cl-
Colon - restricted movement through ion channels
This sodium is then transported into the lateral intercellular spaced by the sodium potassium ATPase
What is the absorption of Cl- and K+ like (separate)?
Cl-:
Co transported with Na+ (ileum)
Exchanged with HCO3- (colon)
(Both secondary active transport)
K+:
Defuses in via paracellular pathways in small intestine, leaks out between cells in colon
Passive transport
How does the standing gradient osmosis effect water?
Cl and bicarbonate are Transported into the intercellular spaces due to potential created by the sodium transport
The high concentration of ions in the intercellular spaces causes the fluid there to be hypertonic ( so water drawn into intercellular spaces)
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 I carried away by the capillaries
What is an overview of the absorption of calcium?
Duodenum and ileum absorb Ca2+
A calcium deficient diet increases the guts ability to absorb it
Vitamin D and parathyroid hormone stimulate absorption
Diet 1-6 g/day, secretions 0.6g. Absorb 0.7g
How can calcium ions be absorbed into the blood?
Using vitamin D via the Paracellular tight junctions (diffusion)
Facilitated diffusion Into the cells via a channel protein.
Then binds to calbindin (prevents its action as an intracellular signal)
Calbindin can either be presented to a channel protein
Or exchanged for sodium via another channel
Vitamin D has a strong role in the transcription of the calcium transporters and absorption of calcium
How is calcium absorbed into blood (better slide)?
Cancium ions carried across apical membrane by:
Intestinal calcium binding protein (IMcal) - facilitated diffusion
Ion channel
Ca2+ is then pumped across basolateral membrane by plasma membrane calcium ATPase (PMCA) against conc gradient
PMCA has a high affinity for Ca2+ but low capacity
Maintains very low conc of calcium usually in cell
OR
Calcium pumped across basolateral membrane by plasma membrane Na+/Ca2+ exchanger against conc gradient
The Na*/Ca2+ exchanger has a low affinity for calcium but a high capacity. It requires large concentrations of calcium to be effective
What is the role of vitamin D in calcium absorption?
Essential for normal calcium absorption
Deficiency causes Rickets or osteoporosis
1,25-dihydroxy cholecalciferol taken up by enterocytes:
Enhances the transport of calcium through the cytosol
Increases the level of calbindin
Increases the rate of extrusion across Bazel lateral membrane by increasing the level of calcium ATPase in the membrane
