Nutrient digestion and absorption 2

Question 1

in what form is almost all fat ingested

Answer 1

triacylglycerol

Question 2

where does all fat digestion take place

Answer 2

small intestine

Question 3

what enzyme is responsible for digestion of fats in the small intestine

Answer 3

pancreatic lipase

Question 4

what do triacylglycerols present as

Answer 4

large lipid droplets which are insoluble

Question 5

what is a water soluble enzyme

Answer 5

lipase

Question 6

where is the only place digestion can take place for a droplet

Answer 6

on the surface
slow process

Question 7

when triacylglycerol is digested by lipase what is formed

Answer 7

monoglyceride and 2 fatty acids

Question 8

what do bile salts act as

Answer 8

emulsifiers or surfactants

Question 9

emulsification

Answer 9

ividing large lipid droplets into smaller droplets (~1 mm diameter) ⇒ increased surface area and accessibility to lipase action.

Question 10

what does emulsification require

Answer 10

Mechanical disruption of large lipid droplets into small droplets.

Emulsifying agent - prevents small droplets reforming into large droplets.

Question 11

mechanical disruptor

Answer 11

Smooth muscle contraction grinds and mixes lumen contents.

Question 12

Emulsifying agent

Answer 12

Amphiphatic molecules (ie polar (charged) and non-polar portions)

Question 13

where is bile released

Answer 13

duodenum

Question 14

what prevents fats reforming into large droplets

Answer 14

Polar portions repel other small lipid droplets (also coated with bile salts/phospholipids) ⇒ prevent reforming into large droplets

Question 15

what can enhance absorption of lipid digestion

Answer 15

formation of micelles

Question 16

what are micelles

Answer 16

similar to emulsion droplets but much smaller

Micelle = bile salt + monoglycerides + fatty acids + phospholipids

Question 17

what makes up a micelle surface

Answer 17

polar portions (bile salts)

Question 18

what makes up a micelle core

Answer 18

non polar portions

Question 19

Micelle breakdown

Answer 19

release of small amounts of free fatty acids (FFA) and monoglycerides into solution

then diffuse acriss plasma membrane of absorbing cells

Question 20

Dynamic equilibrium

Answer 20

between fatty acids and monoglycerides in solution and in micelles - retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption.

Question 21

what does the ER contain

Answer 21

triacylglycerol synthetic enzymes

Question 22

what is released from basolateral membrane of epithelial cells

Answer 22

chylomicron

Question 23

chylomicron

Answer 23

Chylomicrons are composed of a main central lipid core that consists primarily of triglycerides, however like other lipoproteins, they carry esterified cholesterol and phospholipids

doesnt absorb through blood, to move in blood they must go in certain forms eg low density lipoprotein or HDL

Question 24

what happens after entering epithelial cells

Answer 24

fatty acids and monoglycerides enter smooth endoplasmic reticulum (sER) where they are reformed into triacylglycerols (by enzymes located within the sER)

Question 25

what happens inside the epithelial cell

Answer 25

Triacylglycerol droplets coated with amphiphatic protein (inside the cells) ⇒ emulsification

Question 26

how are Triacylglycerol droplets transported through cell

Answer 26

in vesicles formed from sER membrane

Question 27

what happens after Triacylglycerol droplets are transported through vesciles

Answer 27

processed through Golgi apparatus and exocytosed into extracellular fluid at serosal membrane (basolateral membrane)

Question 28

how are chylomicrons transported

Answer 28

pass into lacteals between endothelial cells (cannot pass through capillary basement membrane)

Question 29

what are the two classes of vitamins

Answer 29

Fat-soluble vitamins: A, D, E, K

Water-soluble vitamins: B group, C and folic acid

Question 30

how are fat soluble vitamins absorbed

Answer 30

Follow same absorptive path as fat

Question 31

how are water soluble vitamins absorbed

Answer 31

Either absorbed by passive diffusion or carrier-mediated transport.

Question 32

how is vitamin B12 absorbed

Answer 32

Binds to intrinsic factor in stomach to form complex which is absorbed via specific transport mechanism in distal ileum.

Question 33

what is vitamin B12 deficiency known as

Answer 33

pernicious anaemia

Question 34

pernicious anaemia

Answer 34

(failure of red blood cell maturation)

Question 35

Pernicious

Answer 35

delayed / harmful effect / comes over different stages / happens over time - can take 3 years to have symptoms - failure of red blood cell to mature hard for blood cells to carry O2

Question 36

how much of daily ingested iron is absorbed

Answer 36

10% the rest in faeces

Question 37

how is iron transported

Answer 37

across brush border membrane (via DMT1) into duodenal enterocytes

Question 38

what are iron ions incorporated into

Answer 38

ferritin (protein-iron complex ⇒ intracellular iron store)

Question 39

what does unbound iron after transporting across serosal membrane bind to

Answer 39

transferrin

Question 40

hyperaemia

Answer 40

too much iron in blood

increased ferritin levels ⇒ more iron stored and bound in enterocytes

Question 41

anaemia

Answer 41

⇒ decreased ferritin levels ⇒ more iron released to blood

Question 42

why is unbound iron harmful

Answer 42

Free iron is iron that is not bound; it is the most dangerous kind of iron because free iron can cause oxidative damage to organs, nourish harmful bacteria, change DNA or help to spread cancer.