Metabolism - Lecture Twenty-Four

Question 1

What are the specialised structures that create a vast surface area for absorption?

Answer 1

Villi and microvilli (brush border)

Question 2

Sugar transport

Answer 2

Sugars are highly water soluble and cannot simply diffuse across cell membranes so they require specific transporter proteins that are anchored in the membrane to form ‘pores’

Question 3

What are the two types of sugar transport?

Answer 3

Active transport - against the concentration gradient (requires ATP energy)
Facilitative transport - down the concentration gradient

Question 4

What sites does the GLUT 1 transporter distribute?

Answer 4

Everywhere

Question 5

What sites does the GLUT 2 transporter distribute?

Answer 5

Liver, pancreas, kidney and intestinal epithelia

Question 6

What sites does the GLUT 3 transporter distribute?

Answer 6

Brain

Question 7

What sites does the GLUT 4 transporter distribute?

Answer 7

Muscle and adipose tissue

Question 8

What sites does the SGLT 1 transporter distribute?

Answer 8

Intestinal epithelia

Question 9

What does glucose transport by SGLT 1 involve?

Answer 9

Simultaneous transport of sodium ions

Question 10

Absorption of peptides

Answer 10

There is very little absorption of peptides longer than four amino acids

Question 11

How does the absorption of di- and tri- peptides in the small intestine occur?

Answer 11

By co-transport with H+ ions via membrane transporter PepT1

Question 12

What happens to di- and tri- peptides once they are absorbed into the small intestine?

Answer 12

They are further digested into the individual amino acids by cytoplasmic peptidases and exported from the epithelial cells into the blood circulation

Question 13

Absorption of amino acids from the gastrointestinal tract

Answer 13

From the lumen of the small intestine by transepithelial transport.

Question 14

Transepithelial transport

Answer 14

Transepithelial transport is a semi-specific Na+ dependent transport system

Question 15

Na+ dependent carries

Answer 15

Transport both Na+ and an amino acid

Question 16

Types of Na+ dependent carriers

Answer 16

Neutral AA, proline, hydroxyproline, acidic AA, basic AA (Lys, Arg) and cistine

Question 17

Uptake of intact proteins from gastrointestinal tract

Answer 17

Occurs only in a few circumstances, e.g. new born animals, such as uptake of immunoglobulins in colostral milk- acquisition of passive immunity

Question 18

Lactose intolerant

Answer 18

Lactase enzyme deficiency (genetic basis), causes bloating, flatulence and diarrhoea due to fermentation of lactose by intestinal bacteria so they need to avoid lactose in diet

Question 19

Examples of disease affecting digestive organs

Answer 19

Pancreatitis, stomach (or peptic) ulcers, cystic fibrosis and coeliac disease

Question 20

Pancreatitis

Answer 20

Leads to inappropriate activation of zymogens (proenzymes), resulting in “self-digestion”

Question 21

Stomach (or peptic) ulcers

Answer 21

Due to the breakdown of the mucosa which normally protects against protease action

Question 22

Cystic fibrosis

Answer 22

Causes malabsorption and thick mucous secretions which block the pancreatic duct and secretion of pancreatic enzymes and can be aided by taking supplements containing pancreatic enzymes i.e. ‘pancreatin’, a pancreas extract

Question 23

Coeliac disease

Answer 23

Causes malabsorption and is a disease of the small intestine where the body reacts against gluten protein that is present in wheat. Antibodies react with transglutaminase, villi are flattened and nutrients are not absorbed which leads to gastrointestinal symptoms.

Question 24

Digestion of dietary nucleic acid polymers

Answer 24

DNA and RNA are subject to partial acid hydrolysis in the stomach

Question 25

Intestinal endonuclease enzymes

Answer 25

Hydrolyse the phosphodiester bonds linking individual nucleotides

Question 26

Exonuclease enzyme

Answer 26

Release individual nucleotides (nucleoside monophosphate

Question 27

How are individual nucleotides absorbed?

Answer 27

Via nucleotide transporters