11: Physiology of digestion and absorption - carbohydrates, protein

Question 1

What are the three main constituents of food?

Answer 1

Carbohydrates

Lipids

Proteins

Question 2

Which carbohydrate cannot be digested in the human GI tract?

Answer 2

Cellulose

Question 3

Lipids can be oxidised to generate energy. What else are they used for?

Answer 3

Cell membrane structure

Signal transduction

Question 4

What are proteins digested to obtain?

Answer 4

Essential amino acids

Question 5

If dietary protein is an exogenous source of protein, what are some examples of endogenous protein sources?

Answer 5

Digestive enzymes, mucin, dead cells being digested in the GI tract

Question 6

What is digestion?

Answer 6

Breakdown of larger molecules into smaller, absorbable molecules by enzymes

Question 7

Where do most digestive processes occur?

Answer 7

Small intestine

Salivary amylase and gastric pepsin don’t do all that much

Question 8

What name is given to the combined processes of digestion and absorption?

Answer 8

Assimilation

Question 9

All dietary carbohydrates need to be converted to ___ for absorption in the GI tract.

Answer 9

monosaccharides (e.g glucose, fructose)

Question 10

Which enzyme starts to digest carbohydrates for the first 30 minutes after ingestion?

Answer 10

Alpha amylase

Question 11

Where is alpha amylase produced?

Answer 11

Salivary glands (mainly parotids)

Pancreas

Question 12

What name is given to enzymes which break down long chain carbohydrates into monosaccharides?

Answer 12

Oligosaccharidases

e.g Lactase, Maltase

Question 13

Oligosaccharidases are (integral / peripheral) proteins found on the (lumenal / cytoplasmic) surface of the cell membrane.

Answer 13

integral , lumenal

Question 14

Which oligosaccharidase breaks down lactose into glucose and galactose?

Answer 14

Lactase

Question 15

Why may a person be unable to digest lactose?

Answer 15

Lactase insufficiency

Question 16

What is the cause of lactose intolerance?

Answer 16

Lactase insufficiency

Question 17

What causes primary lactase deficiency?

Answer 17

Genetic mutation in the gene which expresses lactase

Question 18

What is the cause of secondary lactase deficiency?

Answer 18

Damage / infection in the small intestine

Question 19

What is congenital lactase deficiency?

Answer 19

Inability to produce lactase (so inability to digest lactose) from birth

usually autosomal recessive

Question 20

What symptoms will be experienced by a person with lactose intolerance if they consume lactose?

Answer 20

Bloating

Abdominal pain

Flatulence

Diarrhoea (undigested lactose)

Question 21

Which transporter, found on the apical membrane of enterocytes, absorbs glucose and galactose with the aid of sodium?

Answer 21

SGLT1

Question 22

SGLT1 is a secondary active transporter - which ion facilitates the transport of glucose / galactose across the cell membrane of enterocytes?

Answer 22

Na⁺

Question 23

Which transporter carries fructose across the apical membrane of enterocytes?

Answer 23

GLUT5

Question 24

Which transporter allows the exit of all monosaccharides from enterocytes?

Answer 24

GLUT2

Question 25

**GLUT2** allows all monosaccharides to exit enterocytes by **(passive / facilitated)** diffusion.

Answer 25

**facilitated**

Question 26

Which transporter facilitates the action of GLUT2?

Answer 26

**Sodium potassium pump** as it keeps extracellular Na⁺ levels high

Question 27

How many sodium ions bind to SGLT1 to facilitate entry of 1 glucose / galactose molecule?

Answer 27

**2**

Question 28

Where in the small intestine does carbohydrate absorption occur?

Answer 28

**Duodenum** **Jejunum**

Question 29

In which three areas can **peptides** be digested into **amino acids**?

Answer 29

**Lumen** (by lumenal enzymes) **Brush border** (by brush border enzymes) **Intracellularly**

Question 30

Which enzyme starts to digest proteins in the stomach but is not essential for protein digestion?

Answer 30

**Pepsin**

Question 31

What are **exopeptidases**?

Answer 31

Enzymes which break bonds towards the ends of peptides to give individual amino acids

Question 32

What are **endopeptidases**?

Answer 32

Enzymes which break bonds in the centre of peptides to give small peptides

Question 33

Where are peptidases produced before they are secreted into the duodenum?

Answer 33

**Pancreas**

Question 34

Which ion is required to transport peptides into an enterocyte by facilitated transport?

Answer 34

**Na**⁺

Question 35

Other than Na⁺ dependent peptide transporters, what other ion can drive transport of peptides into enterocytes?

Answer 35

**H**⁺ (protons)

Question 36

**Exit** of amino acids from an enterocyte is facilitated by the action of which transporter?

Answer 36

**Sodium potassium pump**

Question 37

What are the two main types of digestion?

Answer 37

**Lumenal digestion** **Membrane digestion**

Question 38

What is the **brush border** of an enterocyte?

Answer 38

**Cell membrane**

Question 39

What type of digestion occurs at the brush borders of enterocytes?

Answer 39

**Membrane digestion**

Question 40

What are some **endopeptidases** found in the duodenum?

Answer 40

**Trypsin** **Chymotrypsin** **Elastase**

Question 41

Is **pepsin** an **endopeptidase** or an **exopeptidase**? Where is it found?

Answer 41

**Exopeptidase** **Stomach**