Ions, vitamins and minerals Flashcards
Define diffusion
Movement of atoms or molecules down their concentration gradient
Atoms or molecules intermingle due to random thermal motion
What are the following: mM, µM, nM, pM, fM
mM - millimolar 10-3 µM - micromolar 10-6 nM - nanomolar 10-9 pM - picomolar 10-12 fM - femtomolar 10-15
Describe diffusion across distances and of lipid soluble and water soluble molecules
Rapid over microscopic distances, slowly over macroscopic distances
Lipid soluble molecules can cross more easily than water soluble molecules
What is osmosis
Movement of water across a semi permeable membrane to an area of higher osmolarity (hypertonic)
How do molecules cross the epithelium to enter the bloodstream
Paracellular transport - between cells through tight junctions and lateral intercellular spaces
Transcellular transport - through epithelial cells
How can solutes cross a cell membrane
Simple diffusion
Facilitated transport
Active transport
What are the two types of transport proteins in membranes
Channel proteins that from aqueous pores to allow certain solutes through
Carrier proteins that bind to the solute and undergo a conformational change to transport it through
Channel proteins are faster than carriers
Define the two types of active transport and give examples
primary active = linked directly to cellular metabolism, using ATP e.g ATPases
secondary active = derives energy from the concentration gradient of other substances e.g. SGLT-1, bicarbonate/Cl-, Na+/H+
Define facilitated transport and give an example
Enhances rate of substance flow down the gradient e.g.GLUT-5 / GLUT-2
Describe water absorption in the gut
99% is absorbed
8L (SI) + 1.4L (LI)
Powered by ion absorption (passive diffusion)
Greatest amount absorbed in the jejunum
Describe the transport of Na+ from lumen to enterocyte
Drives standing gradient osmosis
proximal bowel - counter-transport with H+
Jejunum - Co-transport with amino acids, monosaccharides
Ileum - Co-transport with Cl-
Restricted movement through ion channels
How are chloride ions absorbed
Secondary active transport
Co-transport with Na+ in the ileum
Exchanged with bicarbonates in the colon
how are potassium ions absorbed
Passive transport
Diffuses via paracellular pathways in small intestine
Leaks between cells in the colon
Describe calcium absorption
In the duodenum and ileum
Calcium deficiency = increase absorption
Stimulated by vit D and parathyroid hormones
How is calcium transported across the apical membrane
Intestinal calcium-binding protein / IMcal (facilitated diffusion)
Ion channels
Passively due to a much greater extracellular concentration
Why is it important to keep calcium levels low and how is this done
Acts as an intracellular signalling molecule
Binds to calbindin in cytosol to prevent its action
PMCA has a high affinity but low capacity
What does vit D deficiency cause
Ricketts
Osteoporosis
How is vitamin D taken up
1, 25-dihydroxy D3 is taken up by enterocytes
What are the effects of vit D absorption
Enhances transport of calcium
Increases calbindin levels
Increases level of calcium ATPase in the basolateral membrane
What processes is iron critical for
Oxygen transport by RBCs Oxidative phosphorylation (ETC) (electron donor and acceptor)
What does iron present as in the diet
Inorganic iron (Ferric, Fe3+ or ferrous Fe 2+) As part of haem group i.e. in meat
Describe iron absorption
Only Fe 2+ can be absorbed
Vitamin C reduces Fe3+ to Fe2+ to aid absorption
Fe3+ forms insoluble salts with hydroxide, phosphate and bicarbonate
Describe the absorption of haem
Highly bioavailable Absorbed intact into enterocytes Occurs via the haem carrier protein 1 (HCP-1) Via receptor-mediated endocytosis Fe2+ liberated by haem oxygenase
Explain the process of iron uptake
Duodenal cytochrome B catalyses reduction of Fe3+ to Fe2+
Fe2+ transported via divalent metal transporter 1 (DMT-1) a H+ coupled co-transporter
Fe2+ moves via ferroportin (ion channe)l into blood
