5. Ions, Vitamins and Minerals

Question 1

What do cell membranes act as?

Answer 1

Diffusion barrier, enabling cells to maintain cytoplasmic concentrations of substances different from their extracellular concentrations

Question 2

What is paracellular transport?

Answer 2

Transport through tight junctions and lateral intercellular spaces

Question 3

What is transcellular transport?

Answer 3

Through the epithelial cells

Question 4

What do tight junctions prevent?

Answer 4

Movement of proteins from the apical side to the lateral side

Question 5

What are the two types of transport proteins?

Answer 5

Channel proteins and carrier proteins

Question 6

What are the two forms of ion channels?

Answer 6

Closed and open

Question 7

How can ion channels be gated?

Answer 7

Voltage gated, Ligand-gated (intra and extracellular) and mechanically gated

Question 8

What are the two types of carrier-mediated transport?

Answer 8

Uniport, Coupled transport (symport and antiport)

Question 9

How much water presented in the GI tract is absorbed?

Answer 9

99%

Question 10

What powers the abosrption of water?

Answer 10

absoption of ions

Question 11

Where is the most water absorbed

Answer 11

Small intestine - jejunum

Question 12

How many litres of water is absorbed in the small intestine? a day

Answer 12

8 litres

Question 13

How many litres of water is absorbed in the large intestine per day?

Answer 13

1.4 litres

Question 14

Where and how much water is absorbed in a day?

Answer 14

Ingest - 2L

Saliva - 1.2L

Question 15

How much water does the small intestine absorb?

Answer 15

8L

Question 16

How much water does the colon absorb?

Answer 16

1.4L

Question 17

How is water absorbed?

Answer 17

Standing gradient osmosis

Question 18

How is water absorbed?

Answer 18

Standing gradient osmosis

Question 19

What is standing gradient osmosis driven by?

Answer 19

Na+, which is transported from the lumen into enterocytes raising intracellular sodium

Question 20

How is Na+ transported into cells?

Answer 20

Proximal bowel - Na+/H+ antiporter, Jejunum - Na+/glucose symporter, Na+/aa symporter
Ileum Na+/Cl- symporter
Colon - Na+ transporter

These all increase the intracellular concentration of sodium in the cell

Question 21

How does Cl- diffuse into cells?

Answer 21

Cl-/HCO3- antiporter

Na+/Cl- symporter

Question 22

How does K+ diffuse?

Answer 22

It diffuses in via paracellular pathways in the small intestine and leaks out between cells in colon. Passive transport

Question 23

What happens to Na+ inside of the cells?

Answer 23

It is pumped out by Na+/K+ ATPase resulting in an increase in the intercellular concentration of sodium.

Question 24

What effect does the increase in Na+ concentration have on negative ions?

Answer 24

In draws Cl- ions and HCO3- ions from the cell into the intercellular space. Overall there is an increase in the ion concentration in the intercellular space.

Question 25

How does an increase in ion concentration in the intercellular space affect the solution?

Answer 25

The solution becomes hypertonic drawing water in from the lumen

Question 26

What affect does water have in the intercellular channels?

Answer 26

It increases the hydrostatic pressure resulting in the movement of ions and water across the basement membrane of the epithelium

Question 27

Where is Ca2+ absorbed?

Answer 27

Dudoenum and Ileum

Question 28

What happens when Ca2+ diet is defiecient

Answer 28

Increases the guts ability absorb

Question 29

What stimulates Ca2+ absoption?

Answer 29

Vit D and parathyroid hormone

Question 30

How is Ca2+ carried across the apical membrane?

Answer 30

1) intestinal calcium-bining protein (IMcal) - facilitated diffusion 2) Ion channel

Question 31

How is the Ca2+ concentration kept low intracellularly?

Answer 31

By binding Ca2+ to calbindin in cytosol preventing its action as an intracellular signal

Question 32

How is Ca2+ pumped across basolateral membrane?

Answer 32

Plasma membrane Ca2+ ATPase PMCA has a high affinity for Ca2+ (but low capacity) Ca2+ can also be exchanged for sodium

Question 33

What effect does pumping Ca2+ across the basolateral membrane have?

Answer 33

It maintains the low intracellular concentration

Question 34

What is essential for Ca2+ absorption?

Answer 34

Vitamin D

Question 35

What does deficiency of vitamin D cause?

Answer 35

Rickets and osteoporossis

Question 36

Why is iron useful biologially?

Answer 36

Acts as an electron donor and an electron acceptor

Question 37

What is the process of iron critical for?

Answer 37

Oxygen transport | Oxidative phosphorylation

Question 38

What iron can you absorb?

Answer 38

Fe2+ not Fe3+

Question 39

List iron present in the diet?

Answer 39

1) Inorganic iron | 2) As part of heme

Question 40

What reduces Fe3+ to Fe2+?

Answer 40

Vitamin C

Question 41

How is heme absorbed into the enterocyte?

Answer 41

Heme carrier protein 1 (HCP-1) and via receptor mediated endocytosis

Question 42

How is Fe2+ libereated from heme?

Answer 42

Heme oxygenase

Question 43

How does Fe2+ move into the blood from the basolateral membrane?

Answer 43

Via ferroportin

Question 44

What happens to Fe2+ when it reaches the blood?

Answer 44

Converted back to Fe3+ by hephaestin.

Question 45

What does Fe3+ bind to in the blood

Answer 45

apotransferrin

Question 46

What is the Fe3+ apotransferrin complex called?

Answer 46

Transferrin

Question 47

In the duodenum how is Fe3+ reduced to Fe2+?

Answer 47

Duodenal cytochrome B

Question 48

What is the major iron regulating protein?

Answer 48

Hepcidin -supresses ferroportin

Question 49

What is ferritin?

Answer 49

A globular protein complex capable of storing up to 4,000 iron ions. Fe2+ is oxidised to Fe3+ which crystallises in the protein shell.

Question 50

How is ferritin produced?

Answer 50

Fe2+ binds to apoferritin in cytosol

Question 51

What are vitamins?

Answer 51

Organic compounds that cannot be manufactured by the body

Question 52

What are the fat soluble vitamins?

Answer 52

A, D, E, K

Question 53

What vitamin does the liver have a lage store of?

Answer 53

B12 (2-5mg)

Question 54

What does the impaired absorption of vitamin B12 cause?

Answer 54

Retarded maturation of RBC - pernicious anaemia

Question 55

How is the denaturation of B12 in the stomach avoided?

Answer 55

Binds to R protein (haptocorrin) released in saliva and parietal cells

Question 56

Where are R proteins digested?

Answer 56

Duodenum

Question 57

What binds to vit B12 in the small intestine (duodnum)

Answer 57

IF - B12/IF complex is resistant to digestion

Question 58

What does the vit B12/IF complex bind to?

Answer 58

Cubilin receptor in the distal ileum where it is absorbed

Question 59

Once in the cell what happens to vit B12/IF complex?

Answer 59

Broken down possibly in the mitochondria

Question 60

How does B12 cross the basolateral membrane?

Answer 60

Transcobalamin II

Question 61

How does the vit B12 travel to the liver?

Answer 61

Bound to TCII

Question 62

How does the liver take up the complex of vit B12?

Answer 62

TCII receptors, then protelysis breaks down TCII

Question 63

What are channel proteins?

Answer 63

Form an aqueous pore allowing specific solutes to pass across the membrane

Question 64

What are carrier proteins?

Answer 64

Bind to the solute and undergo a conformational change to transport it across the membrane

Question 65

Which transport protein is faster - Carrier or channel?

Answer 65

channel

Question 66

What is the difference between primary and secondary active transport?

Answer 66

Primary active transport uses ATP to power transport whereas secondary active transport uses energy derived from the concentration gradient of another substance

Question 67

What are examples of a primary active transporter?

Answer 67

Na+/K+ ATPase | H+/K+ ATPase

Question 68

What are examples of a secondary active transporter?

Answer 68

SGLT-1 co transporter HCO3-/Cl- counter trasnport Na+/H+ Counter transporter

Question 69

What are examples of facilitated transport?

Answer 69

GLUT-5 and GLUT-2

Question 70

How are many ions absorbed?

Answer 70

Slowly by passive diffusion

Question 71

What does 1,25-dihydroxy D3 do when taken up by enterocytes?

Answer 71

Enhances Ca2+ transport through the cytosol Increases calbindin levels Increases the level of Ca2+ ATPase in the basolateral membrane

Question 72

How are fat soluble vitamins transported to the lumen in the GI tract?

Answer 72

In micelles

Question 73

What is the function of ferritin?

Answer 73

Binds many irons and transports it in the intestinal lumen so it can be excreted in the faeces