Alimentary system 6 - Ions, minerals and vitamins Flashcards Preview

LSS 2 > Alimentary system 6 - Ions, minerals and vitamins > Flashcards

Flashcards in Alimentary system 6 - Ions, minerals and vitamins Deck (19)
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1
Q

What is paracellular transport?

A

Through tight junctions and lateral intercellular spaces

2
Q

What is transcellular transport?

A

Through the epithelial cells

3
Q

List the types of channels

A
  • Voltage gated
  • Ligand-gated (intracellular/extracellular)
  • Mechanically gated
4
Q

Describe the process of carbohydrate absorption

A
  • Glucose and galactose by secondary active transport (SGLT-1)
  • Fructose by facilitated diffusion (GLUT-5)
  • Exit the basolateral membrane by facilitated diffusion (GLUT-2)
5
Q

Compare daily water absorption in the small intestine and large intestine

A
  • Small intestine 8L

- Large intestine 1.4L

6
Q

Describe the process of standing gradient osmosis

A
  • Transport of Na+ into enterocytes (exchange for H+, co-transport with amino acids, glucose, and chloride, some movement through ion channels)
  • Cl- exchanged with bicarbonate ions to enter enterocytes
  • Potassium diffuses through paracellular pathways (passive)
  • Sodium actively transported into intercellular spaces by sodium/potassium ATPase
  • Cl- and bicarbonate transported into intercellular spaces due to electric potential created by sodium transport
  • Water follows as the fluid is hypertonic
7
Q

Describe the absorption of calcium in the large intestine

A
  • Stimulated by vitamin D and parathyroid hormone
  • Carried across the apical membrane by intestinal calcium-inding protein (IMcal), and through ion channels
  • Bound by calbindin to prevent intracellular signalling
  • Pumped out the basolateral membrane by plasma membrane calcium ATPase (or sodium/calcium exchanger in high conc)
8
Q

List the effects of vitamin D on enterocytes

A
  • 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.
9
Q

Describe absorption of heme into the enterocyte

A
  • Absorbed intact into the enterocyte by heme carrier protein 1
  • Fe2+ is liberated by heme oxygenase
10
Q

Describe the process of iron uptake into the enterocytes

A
  • Duodenal cytochrome B catalyses reduction of Fe3+ to Fe2+
  • Fe2+ transported by divalent metal transporter 1 (H+ coupled transporter)
  • Carried to basolateral membrane, where it moves via ferroportin into the blood
11
Q

Describe the two processes that happen to iron following movement through ferroportin in the intestine wall

A
  • Fe2+ converted to Fe3+ by Hephaestin (copper dependent ferroxidase)
  • Fe3+ binds to apotransferrin and travels in the blood as transferrin
    OR
  • May also bind to apoferritin in cytosol to form a ferritin micelle in the cytosol
  • Fe2+ converted to Fe3+ which crystallises within protein shell
  • Single ferritin molecule stores up to 4000 iron ions
12
Q

Describe the action of hepcidin

A

Regulates iron and suppresses ferroportin

13
Q

What happens following iron/ferritin storage in the enterocyte?

A
  • Irreversibly bound
  • No transport to plasma
  • Lost in the intestinal lumen and excreted into faeces
14
Q

Define vitamin

A

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

15
Q

How are vitamins transported?

A
  • Passive diffusion

- Fat soluble vitamins (ADEK) transported in micelles. K is taken up by active transport

16
Q

Why is vitamin B12 important?

A
  • Stored in the liver

- Impaired absorption means issues maturing red blood cells (pernicious anaemia)

17
Q

How is vitamin B12 transported through the stomach?

A
  • R protein binds to vitamin B12 to prevent denaturing in the stomach
  • Also called haptocorrin (released in saliva and parietal cells)
18
Q

What binds to vitamin B12 after R protein?

A
  • Intrinsic factor
  • Binds to B12 following digestion of R protein in the SI
  • Cubilin recognises intrinsic factor in the ileum, and the complex is taken up into the cell
19
Q

What happens following entry of the vitamin B12/intrinsic factor complex entering the cell?

A
  • Complex broken down
  • B12 binds to transcobalamin II and crosses the basolateral membrane and travels to the liver
  • Taken up into the liver by TCII receptors
  • Proteolysis breaks down TCII inside the cell