12: Physiology of digestion and absorption - lipids, calcium, iron and vitamins (updated Week 3)

Question 1

What type of lipid accounts for 90% of the fats we ingest?

Answer 1

Triglycerides

Question 2

Animal fats tend to be (saturated / unsaturated).

Answer 2

saturated

Question 3

Plant fats tend to be (saturated / unsaturated).

Answer 3

unsaturated

Question 4

Triglycerides and cholesterol are water ___.

Answer 4

insoluble

Question 5

Where does most fat digestion occur?

Answer 5

Small intestine

Question 6

Which enzyme digests triglycerides into monoglycerides and fatty acids?

Where is it secreted?

Answer 6

Lipase

Stomach and the pancreas

Question 7

Movements in the stomach mix food with the fat-digesting enzyme, gastric ___.

Answer 7

lipase

Question 8

Where in the GI tract is pancreatic lipase secreted?

Answer 8

Duodenum

Question 9

Which fluid, released by the liver, emulsifies fats in the small intestine?

Answer 9

Bile

Question 10

Chemicals found in pancreatic secretions ___ stomach acid to optimise enzyme action.

Answer 10

neutralise

Question 11

The presence of lipids in the duodenum triggers the release of which satiation signal?

Answer 11

CCK

Question 12

What is released by the gall bladder in response to CCK?

Answer 12

Bile salts

Question 13

How do bile salts aid in fat digestion?

Answer 13

Emulsify the lipids into smaller droplets with a greater surface area

Aids digestion by enzymes

Question 14

What does it mean for a molecule to be amphipathic?

Answer 14

Has both hydrophilic and hydrophobic parts

Allows bile to form an emulsion with lipids

Question 15

What does emulsification mean in terms of fat digestion?

Answer 15

Prevention of the fats sticking together, increases surface area, renders them easier to digest by pancreatic lipase

Question 16

Which ions, secreted in the pancreatic juice, neutralises the stomach acid and creates optimum conditions for digestive enzymes?

Answer 16

Bicarbonate ions (HCO₃^-)

Question 17

What is steatorrhoea?

Answer 17

Fat in faeces

indicates poor lipid absorption (e.g due to lack of bile salts)

Question 18

Emulsification of lipids allows a greater ___ ___ for the action of pancreatic lipase.

Answer 18

surface area

Question 19

If bile salts are bound to a lipid droplet, lipase won’t be able to bind.

Which coenzyme allows lipase to bind to lipids with bile salts attached?

Answer 19

Colipase

Question 20

What is a micelle?

Answer 20

Big aggregation of molecules with a hydrophobic core, presents lipids to lipases

Question 21

Micelles found in the duodenum tend to ___ lipid products of digestion.

Answer 21

accumulate

Question 22

a) Diffuse into enterocytes and then villus capillaries
b) Need to be resynthesised into triglycerides and transported to adipose tissue by chylomicrons in lymphatic tissue

short chain fatty acids, long chain fatty acids

match

Answer 22

Long chain fatty acids - b

Short chain fatty acids - a

Question 23

Which kind of lipid makes up chylomicrons?

Answer 23

Cholesterol

Question 24

Apolipoproteins are amphipathic and allow the packaging of ___ into ___ for transport in the ___ system.

Answer 24

triglycerides

chylomicrons

lymphatic

Question 25

By which process do chylomicrons leave an enterocyte?

Answer 25

**Exocytosis**

Question 26

Chylomicrons carry newly synthesised ___ into the lymphatic circulation.

Answer 26

**triglycerides**

Question 27

Which enzyme breaks down chylomicrons again once they have reached the venous circulation?

Answer 27

**Lipoprotein lipase**

Question 28

By which lymphatic duct do chylomicrons reach the left venous angle?

Answer 28

**Thoracic duct**

Question 29

Which protein, making up 50% of the plasma, **carries** lipids once they have been freed from chylomicrons by lipoprotein lipase?

Answer 29

**Albumin**

Question 30

**Chylomicron remnants** are converted to ___ \_\_\_.

Answer 30

**bile salts**

Question 31

Which drug inhibits the binding of **cholesterol** to the special protein found on the surface of enterocytes?

Answer 31

**Ezetimibe**

Question 32

**Cholesterol** is absorbed by enterocytes via the action of a specialised \_\_\_.

Answer 32

**protein**

Question 33

Which class of drug is used in conjunction with ezetimibe to treat hypercholesterolaemia?

Answer 33

**Statins**

Question 34

When calcium concentration is low, Ca²⁺ is absorbed (**passively / actively**).

Answer 34

**actively**

Question 35

When calcium concentration is high, Ca²⁺ absorption occurs **(passively / actively)**.

Answer 35

**passively**

Question 36

Which dietary component helps with the absorption of calcium into enterocytes?

Answer 36

**Vitamin D**

Question 37

The **exit** of calcium from enterocytes is coupled to the **entry** of sodium. Which transporter carries this out?

Answer 37

**NCX1** i.e sodium/calcium exchanger - this comes up a lot, remember it

Question 38

**Vitamins** increase the expression of which channels in enterocytes?

Answer 38

**Calcium** channels

Question 39

Which disorder may occur in people who have their stomachs removed? Why?

Answer 39

**Anaemia** Stomach acts to reduce Fe³⁺ to Fe²⁺ - if this doesn't occur iron ions aren't absorbable so person will be deficient in iron

Question 40

What vitamin acts as an antioxidant to stabilise the absorbable form of iron (Fe²⁺)?

Answer 40

**Vitamin C**

Question 41

What is the storage form of iron found in cells?

Answer 41

**Ferratin**

Question 42

Which vitamin has a vital role in the formation of red blood cells and brain function?

Answer 42

**Vitamin B₁₂**

Question 43

Which protein, released by **parietal cells** in the oxyntic mucosa, helps to prepare Vitamin B₁₂ for absorption?

Answer 43

**Intrinsic factor**

Question 44

Where is **intrinsic factor** secreted? Where does **intrinsic factor** bind with **Vitamin B₁₂**? Where is **Vitamin B₁₂** absorbed by endocytosis?

Answer 44

**Parietal cells** in oxyntic mucosa of stomach ## Footnote **Duodenum** **Terminal ileum**