[Physiology] Nutrient Digestion and Absorption 2

Question 1

what form is almost all ingested fat in

Answer 1

triacylglycerol

Question 2

where does all fat digestion take place

Answer 2

small intestine

Question 3

what causes fat digestion to take place in the small intestine

Answer 3

pancreatic lipase

Question 4

how do triacylglycerols appear

Answer 4

large lipid droplets that are insoluble in water

Question 5

what is lipase

Answer 5

water soluble enzyme

Question 6

what is problematic with pancreatic lipase

Answer 6

digestion can only take place at surface of droplet ⇒ very slow

Question 7

what does lipase break triacylglyceride down into

Answer 7

monoglyceride + 2 fatty acids

Question 8

what is emulsification

Answer 8

dividing large lipid droplets into smaller droplets (~1 mm diameter)

Question 9

what is the benefit of emulsification

Answer 9

⇒ increased surface area and accessibility to lipase action.

Question 10

what does emulsification require

Answer 10

Mechanical disruption
Emulsifying agent

Question 11

what causes mechanical disruption

Answer 11

smooth muscle contraction within the muscularis externa of the stomach - grinds and mixes lumenal contents

Question 12

what is an emulsifying agent

Answer 12

Bile salts + phospholipids secreted in bile

amphiphatic molecules with polar and non polar portions

Question 13

what do non polar portions associate with

Answer 13

non-polar interior of lipid droplet

leaves polar portions exposed at the surface

Question 14

what do polar portions do to other small lipid droplets

Answer 14

prevent reforming into large droplets

Question 15

is emulsification alone enough to enhance absorption of lipase digestion

Answer 15

no it is still very slow

Question 16

what enhances this absorption further

Answer 16

formation of micelles

Question 17

what are micelles

Answer 17

similar to emulsion droplets but much smaller (4-7 µm diameter)

Micelle = bile salt + monoglycerides + fatty acids + phospholipids

Question 18

Micelle =

Answer 18

bile salt + monoglycerides + fatty acids + phospholipids

Question 19

where are polar portions located on a micelle

Answer 19

the surface

Question 20

where are non polar portions located

Answer 20

micelle core

Question 21

what happens as soon as a micelle touches the lipid membrane

Answer 21

they are absorped they are fat

Question 22

micelle breakdown

Answer 22

release of small amounts of free fatty acids (FFA) and monoglycerides into solution ⇒ diffusion across plasma membrane of absorbing cells

Question 23

what happens once the micelle enters the acid microclimate

Answer 23

acids within take on that hydrogen ion, and they lose their charge and that releases them from the micelle fatty acids and monoglycerides being absorbed and they go into the microclimate region.
anything that doesn’t get absorbed gets taken up into micelle.
keeps moving around until ultimately all of the fatty acids and monoglycerides have eventually be taken up across the apical membrane.
having no charge they will then cross the lipid membrane much more readily.

Question 24

what happens after the fatty acids and monoglycerides enter the SER

Answer 24

they are reformed into triacylglycerols (by enzymes located within the sER)

Question 25

what are the reformed triacylglycerol droplets coated with

Answer 25

amphiphatic protein (emulsification)

Question 26

How are Triacylglycerol droplets transported through cell

Answer 26

vesciles formed from the SER membrane processed through Golgi apparatus until reaching the basolateral membrane where they are exocytosed into extracellular fluid at serosal membrane

Question 27

what are extrecellular fat droplets known as

Answer 27

Chylomicrons

Question 28

chylomicrons

Answer 28

(also contain phospholipids, cholesterol & fat-soluble vitamins) ~1 µm diameter

Question 29

what can chylomicrons not do

Answer 29

can’t get through the tight junctions at the end of the endotherlial cells that make up the capillaries there -cant go into your blood, which is good because you don’t want fat going into your circulatory system. Instead they pass into lacteals - branch of your lymphatic system.

Question 30

once chylomicrons are in the lymphatic system where do they end up

Answer 30

thoracic duct

Question 31

what do chylomicrons pass into instead of blood

Answer 31

lacteals

Question 32

what are the two classes of vitamins

Answer 32

Fat-soluble vitamins
Water-soluble vitamins

Question 33

what are the fat soluble vitamins

Answer 33

A, D, E, K

Question 34

what are the Water-soluble vitamins

Answer 34

B group, C and folic acid

Question 35

what is vitamin B12

Answer 35

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

Question 36

what is pernicious anaemia

Answer 36

B12 deficiency (failure of red blood cell maturation)

Question 37

how much of daily ingested iron is absorbed across intestine into blood

Answer 37

10%

Question 38

how is iron transported across brush border enzymes

Answer 38

(via DMT1) into duodenal enterocytes

Question 39

why do divalent metals require a transporter

Answer 39

These are extremely toxic and corrosive if unbound.

Question 40

where does the vast majority of iron go

Answer 40

protein complex known as ferratin

Question 41

if the iron does not get incorporated into ferritin what happens

Answer 41

it goes to the basolateral membrane, and then it gets transported across the basolateral membrane via a protein called IREG 1
Once it goes into blood it binds to another protein called transferrin

Question 42

what is ferritin expression regulated by

Answer 42

the bodys iron status

Question 43

hyperaemia results in

Answer 43

increased ferritin levels in the duodenal enterocytes ⇒ more iron bound in enterocytes

Question 44

anaemia results in

Answer 44

decreased ferritin levels ⇒ more iron released to blood