Nutrient digestion II - fat, vitamins and minerals

Question 1

What is a triacylglycerol?

Answer 1

Almost all ingested fat in form of triacylglycerol (glycerol + 3 stearic acids/fatty acids)

Question 2

What digests fat in the small intestine?

Answer 2

Pancreatic lipase

Question 3

What is emulsification?

Answer 3

Emulsification = dividing large lipid droplets into smaller droplets vie mechanical disruption and emulsifying agents (~1 mm diameter) ==> increased surface area and accessibility to lipase action.

Question 4

Describe characteristics of emulsifying agents

Answer 4

All emulsifying agents are amphiphatic molecules (i.e. polar (charged) and non-polar portions)
Non-polar portions associate with non-polar interior of lipid droplet leaving polar portions exposed at water surface.
Polar portions repel other small lipid droplets (also coated with bile salts/phospholipids) ==> prevent reforming into large droplets

Question 5

Describe a micelle

Answer 5

Micelle - fat transport molecule

Made up of bile salt + monoglycerides + fatty acids + phospholipids

Question 6

After entering cells, where are fatty acids and monoglycerides reformed into triacylglycerols?

Answer 6

Smooth endoplasmic reticulum

Question 7

What absorbs fats from chylomicrons in the small intestine?

Answer 7

Chylomicrons pass into lacteals (central core of villi, lymphatic vessels of the small intestine which absorb digested fats) between endothelial cells (cannot pass through capillary basement membrane), and are carried by the lymphatics to the thoracic ducts before entering the bloodstream

Question 8

List some fat soluble vitamins

Answer 8

A, D, E, K

Question 9

List some water soluble vitamins

Answer 9

B group, C and folic acid

Question 10

What is intrinsic factor?

Answer 10

Produced by stomach, allows B12 absorption in small intestines

Question 11

What is caused by B12 deficiency?

Answer 11

B12 deficiency ==> pernicious anaemia (failure of red blood cell maturation). Can take up to 3 years to present (=pernicious), as the body can naturally store enough B12 to last for 3 years, though it can also be caused by a deficiency in intrinsic factor. A deficiency in intrinsic factor can be caused by weakened stomach lining (atrophic gastritis) or autoimmune disease attacking the cellswhich produce intrinsic factor in the stomach.

Question 12

How is iron taken up by the intestines?

Answer 12

Iron transported across brush border membrane (via DMT1) into duodenal enterocytes, and taken up by ferritin and stored intracellularly

Question 13

How is iron held in the blood?

Answer 13

10% of ingested iron absorbed into blood

Stored in blood by transferrin, which delivers iron to the liver for haemoglobin production

Question 14

What influences ferritin expression intracellularly?

Answer 14

Bodies iron status

Question 15

What causes hyperaemia?

Answer 15

Hyperaemia ==> increased ferritin levels ==> more iron bound within enterocytes

Question 16

List the 5 functions of the stomach

Answer 16

• Temporary store of ingested material
• Dissolve food particles and initiate digestive process
• Control delivery of contents to small intestine
• Sterilise ingested material
• Produce intrinsic factor (for vitamin B12 absorption)