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Alimentary > Ions, vitamins and minerals > Flashcards

Ions, vitamins and minerals Flashcards

1
Q

Define diffusion

A

Movement of atoms or molecules down their concentration gradient
Atoms or molecules intermingle due to random thermal motion

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2
Q

What are the following: mM, µM, nM, pM, fM

A 
mM - millimolar 10-3
µM - micromolar 10-6
nM - nanomolar 10-9
pM - picomolar 10-12
fM - femtomolar 10-15
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3
Q

Describe diffusion across distances and of lipid soluble and water soluble molecules

A

Rapid over microscopic distances, slowly over macroscopic distances
Lipid soluble molecules can cross more easily than water soluble molecules

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4
Q

What is osmosis

A

Movement of water across a semi permeable membrane to an area of higher osmolarity (hypertonic)

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5
Q

How do molecules cross the epithelium to enter the bloodstream

A

Paracellular transport - between cells through tight junctions and lateral intercellular spaces

Transcellular transport - through epithelial cells

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6
Q

How can solutes cross a cell membrane

A

Simple diffusion
Facilitated transport
Active transport

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7
Q

What are the two types of transport proteins in membranes

A

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

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8
Q

Define the two types of active transport and give examples

A

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+

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9
Q

Define facilitated transport and give an example

A

Enhances rate of substance flow down the gradient e.g.GLUT-5 / GLUT-2

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10
Q

Describe water absorption in the gut

A

99% is absorbed
8L (SI) + 1.4L (LI)
Powered by ion absorption (passive diffusion)
Greatest amount absorbed in the jejunum

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11
Q

Describe the transport of Na+ from lumen to enterocyte

A

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

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12
Q

How are chloride ions absorbed

A

Secondary active transport
Co-transport with Na+ in the ileum
Exchanged with bicarbonates in the colon

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13
Q

how are potassium ions absorbed

A

Passive transport
Diffuses via paracellular pathways in small intestine
Leaks between cells in the colon

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14
Q

Describe calcium absorption

A

In the duodenum and ileum
Calcium deficiency = increase absorption
Stimulated by vit D and parathyroid hormones

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15
Q

How is calcium transported across the apical membrane

A

Intestinal calcium-binding protein / IMcal (facilitated diffusion)
Ion channels
Passively due to a much greater extracellular concentration

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16
Q

Why is it important to keep calcium levels low and how is this done

A

Acts as an intracellular signalling molecule
Binds to calbindin in cytosol to prevent its action
PMCA has a high affinity but low capacity

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17
Q

What does vit D deficiency cause

A

Ricketts

Osteoporosis

18
Q

How is vitamin D taken up

A

1, 25-dihydroxy D3 is taken up by enterocytes

19
Q

What are the effects of vit D absorption

A

Enhances transport of calcium
Increases calbindin levels
Increases level of calcium ATPase in the basolateral membrane

20
Q

What processes is iron critical for

A 
Oxygen transport by RBCs 
Oxidative phosphorylation (ETC)
(electron donor and acceptor)
21
Q

What does iron present as in the diet

A 
Inorganic iron (Ferric, Fe3+ or ferrous Fe 2+)
As part of haem group i.e. in meat
22
Q

Describe iron absorption

A

Only Fe 2+ can be absorbed
Vitamin C reduces Fe3+ to Fe2+ to aid absorption
Fe3+ forms insoluble salts with hydroxide, phosphate and bicarbonate

23
Q

Describe the absorption of haem

A 
Highly bioavailable
Absorbed intact into enterocytes
Occurs via the haem carrier protein 1 (HCP-1)
Via receptor-mediated endocytosis 
Fe2+ liberated by haem oxygenase
24
Q

Explain the process of iron uptake

A

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

25
Q

How is iron transported in the blood

A

Hephaestin (ferroxidase) converts Fe2+ to Fe3+
Fe3+ binds to apotransferin
Travels in the blood as transferrin

Binds to apoferritin in the cytosol -> ferritin micelle
Fe2+ oxidised to Fe3+ which crystallises within a protein shell
(stimulated by increased iron conc.)

26
Q

What is hepcidin

A

Major iron regulating protein

Suppresses ferroportin function to decrease iron absorption

27
Q

What are vitamins

A

Organic compounds that cannot be manufactured by the body but vital to metabolism.

28
Q

How are vitamins absorbed

A

Mainly passive diffusion
Fat soluble vitamins (A, D, E, K) transported to brush border in micelles.
K taken up by active transport.
Specific transport mechanisms for vitamin C (ascorbic acid), folic acid, vitamin B1 (thiamine), vitamin B12

29
Q

Where is vitamin B12 stored

A

Liver (2-5mg)

30
Q

What leads to pernicious anaemia

A

Impaired absorption of vitamin B12 which retards maturation of RBCs

31
Q

What is the function of R protein

A

vitamin B12 is freed by low pH and pepsin but its denatured by HCl
Vit B12 binds to R protein (haptocorrin) which is released in saliva and parietal cells
They are digested in the duodenum

32
Q

What is Intrinsic factor

A

vit B12 binding glycoprotein secreted by parietal cells
Resistant to digestion
Allows for B12 absorption
Complex binds to a cubilin receptor and taken up in the distal ileum

33
Q

How is vitamin B12 transported in the blood

A 
vitB12/IF complex broken down in the cell
B12 binds to transcobalamin II (TCII)
Travels to the liver via the blood
TCII receptors recognise TCII
Proteolysis in the liver
34
Q

What are the types of ion channel

A

Voltage-gated
Ligand-gated (extracellular)
Ligand-gated (intracellular)
Mechanically gated

35
Q

What are the types of carrier-mediated transport

A

Uniport - one direction of one molecule
Symport - movement of one molecule with another one
Antiport - movement of one molecule in exchange for another one

36
Q

How much water is drunk a day and where does the total volume of water absorbed come from

A

2L drinking a day

Largest amount is from gastric secretions (2L) but also from saliva, bile, pancreas and intestine

37
Q

What happens to the sodium that enters the enterocytes

A

Active transport into the lateral intercellular spaces by Na+K+ ATPase transport in the lateral plasma membrane

38
Q

What is the effect of an increase in intercellular sodium

A

Electric potential which transports CL- and HCO3- into the intercellular spaces
High concentration of ions in the space causes fluid to be hypertonic
Water flows through tight junctions into the intercellular space, increasing hydrostatic pressure
Fluid moves across the basement membrane into the capillaries

39
Q

How does calcium cross the basolateral membrane into the blood

A

Calcium is pumped across the basolateral membrane by calcium ATPase (PMCA) against the conc. gradient
High affinity but low capacity

Pumped by Na+/Ca2+ exchanger against conc. gradient
Low affinity but high capacity (needs large concentration)

40
Q

Why is it dangerous to have too much iron in the blood

A

Toxic in excess

No mechanism to actively excrete it

Alimentary (16 decks)

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