Ions, Vitamins and Minerals

Question 1

How does water move down a concentration gradient

Question 2

How can molecules cross the epithelium to enter the bloodstream

Answer 2

Paracellular transport through tight junctions and lateral intercellular spaces

Transcellular transport through epithelial cells

Question 3

What are channel protein

Question 4

What are carrier proteins

Question 5

What are the two types of co-transported ion

Question 6

What is the difference between primary active transport and secondary active transport

Answer 6

Primary - linked with ATP

Secondary - derives energy from concentration gradient of another substance that is actively transported

Question 7

Example of primary active transport

Question 8

Example of secondary active tranport

Answer 8

SGLT-1 co transport in small bowel absoprtion

HCO3/Cl in pancreatic HCO3 secretion

Na/H counter transport in pancreatic HCO3 secretion

Question 9

Example of facilitated transport

Question 10

How are glucose and galactose absorbed

Question 11

How is fructose absobred

Answer 11

Facilitated diffusion

GLUT-5 on apical membrane

Question 12

How does glucose exit the basolateral membrane

Answer 12

Facilitated diffusion

Glut-2 high capacity low affinity

Question 13

Where is water being absorbed coming from

Question 14

How is water absorbed

Answer 14

Driven by Na

Counter transport in exchange for H (proximal bowel)

Co transport with amino acids, monosaccharides (jejunum)

Co transport with Cl (ileum)

Restricted movement through ion channels (colon)

Question 15

How is Cl absorbed

Question 16

How is K absorbed

Answer 16

Diffuses via paracellular pathways in small intestine

Passive transport

Question 17

What happens to Na after being used for secondary active transport

Answer 17

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

Question 18

What happens when Na moves into intercellular space

Answer 18

Intercellular spaces causes fluid to be hypertonic

Osmotic flow of water from gut lumen via adjacent cells, tight junctions into the intercellular space

Water distends the intercellular channels and causes increased hydrostatic pressure

Question 19

What stimulates calcium absorption

Question 20

How is calcium carried across apical membrane

Question 21

What are teh implications for Ca transport transport across the cell

Answer 21

Need to transport Ca while maintaing low intracellular concetrations

Binds to calbindin in cytosol

Question 22

How is Ca pumped across basolateral membrane by plasma membrane

Answer 22

PMCA has a high affinity for Ca but low capacity

Ca (ATPase)

Also pumped by Na/Ca which has low affinity but high capacity ( requires larger concentrations)

Question 23

What is the rold of 1,25-dihydroxy d3

Answer 23

Enhances transport of Ca

Increases levels of calbindin

Increase rate of extrusion across basolateral membrane by increasing Ca ATPase

Question 24

What is iron essnetial for

Answer 24

Oxygen transport

Oxidative phosphrylation

Question 25

How is iron presented in the diet

Question 26

Facts about iron

Question 27

How is heme absorbed

Answer 27

Heme carrier protein 1 (HCP-1) and via receptor-mediated endocytosis Fe liberated by Heme oxygenase

Question 28

How is iron uptook

Answer 28

Duodenal cytochrome B catalyzes the reduction of Fe3 to Fe2 in the process of iron absorption Fe2 transported via divalent metal transporter (DMT-1) , H coupled cotransporter Fe2 binds to unkown factors carried to basolateral membrane via ferroportin ion channel Hephaestin is a transmembrane copper-dependent ferroxidase converts 2 to 3 Fe3 binds to apotransferrin, travels in blood as transferrin

Question 29

Facts about ferritin

Answer 29

Binds to apoferritin in cytosol to form ferritin micelle Ferritin molecule can store up to 4000 iron In excess diertary iron absorption, porduce more ferritin Globular portein complex Fe crystallises within protein shell

Question 30

What happens to ferritin stored in enterocytes

Answer 30

Prevents absorption of too much iron

Question 31

How are fat soluble vitamins (A,D,E,K) transported

Answer 31

K taken up by active transprot Others transported to brush border

Question 32

What happens during impaired absorption of vit B12

Answer 32

Retards the maturation of RBC - pernicious anaemia Most b12 bound to proteins

Question 33

How is denaturation of B12 in stomach avoided

Answer 33

Binds to R portein (haptocorrin) released in saliva and from parietal cells R proteins digested in duodenum

Question 34

What is the intrinsic factor

Answer 34

Vit B12 binding glycoprotein secreted by parietal cells Resistatnt to digestion Vit B12/IF binds to cubilin receptors, taken up in distal ileum

Question 35

What happens to B12 once in cell

Answer 35

Vit B12/IF complex broken B12 binds to protein transcobalamin II (TCII) Travels to liver bound to TCII TCII receptors on cells allow them to uptake complex Proteolysis breaks down TCII inside cell

Question 36

Where is the greatest amount of water absorbed

Answer 36

Small bowel, jejunum

Question 37

How much iron is absorbed

Answer 37

5% inorganic iron 20% of heme iron