Lipid Digestion and Absorption of Calcium, iron and vitamins

Question 1

Name the 4 ingested lipids

Answer 1

Triacylglycerols
Phospholipids
Cholesterol
Fatty Acids

Question 2

Ingested lipids are either

Answer 2

Insoluble or poorly soluble

Question 3

Fats must be converted to what to be absorbed

Answer 3

Emulsion of small oil droplets

Question 4

What is the benefit of droplet

Answer 4

Increase SA to volume ratio

Increases oil water interface whereby digestion by lipases occur

Question 5

How are droplets stabilised

Answer 5

By chylomicrons

Adding protein to form a water soluble coat

Question 6

Where does lipid digestion of fat mainly occur

Answer 6

In the duodenum

Question 7

In the 2nd part of the duodenum what first comes into contact with the large fat droplets

Answer 7

bile providing bile salts which are produced in the liver and stored in the gallbladder

Question 8

what is the role of bile

Answer 8

Emulsify fat droplets from large ones to smaller ones

Question 9

A failure of bile salts can lead to

Answer 9

Steatorrhea - fat in faeces as not digested and absorbed

Secondary Vitamin Deficiencies - fat soluble vitamins not absorbed vitamin A, D, E, K

Question 10

what do bile salts allow

Answer 10

increased surface area for attack by pancreatic lipases

Question 11

What is required to allow pancreatic lipases access to fat droplets

Answer 11

Colipase which is activated by trypsinogen

Question 12

what are pancreatic lipases released in response to

Answer 12

cholecystokinin from I cells

Question 13

how are lipids absorbed

Answer 13

small and medium chain fatty acids –> diffusion through enterocyte, exit basolateral membrane and enter villus
large chain fatty acids and monoglycerides are resynthesised in the endoplasmic reticulum + subsequently incorporated into chylomicrons

Question 14

How are chylomicrons carried

Answer 14

They enter the lacteal (lymphatic vessel) travel to systemic circulation via lymphatic duct

Question 15

How is calcium absorbed

Answer 15

Via active and passive mechanisms
Active - duodenum and first part of jejunum
Na/Ca exchanger
CaATPase

Question 16

What 2 forms does iron exist in

Answer 16

ferrous Fe2+

ferric Fe3+

Question 17

what type of iron is most abundant from the diet

Answer 17

Fe3+

Question 18

how is most of the bodies iron carried

Answer 18

by haemoglobin

Question 19

is the daily loss of haemoglobin regulated or unregulated

Answer 19

daily loss of iron from the body = unregulated

long term = tightly regulated absorption across the duodenum

Question 20

Iron deficiency leads to

Answer 20

Microcytic anaemia

Question 21

Microcytic anaemia is problematic around the world especially for

Answer 21

women of child bearing age

Question 22

Iron excess effect

Answer 22

Toxic on body

Question 23

How is Fe2+ transported

Answer 23

Fe2+ transported across the apical membrane
transported to the basolateral membrane by a ‘molecular chaperone’
Fe2+ is then oxidised to Fe3+ and transported to tissues

Question 24

How is Fe3+ transported

Answer 24

Fe3+ is reduced to Fe2+
This is promoted by HCL within stomach, vit C, gastroferrin
Fe2+ influx via DMT1
H is brought into the cell
Some Fe2+ combines with cytoplasmic apoferratin and is stored as ferratin
Fe2+ is then oxidised to Fe3+ and transported to tissues

Question 25

Fe3+ can bind to transferrin leading to

Answer 25

ERythropoesis in bone marrow

Stored in liver