Metabolism

Question 1

How do lipids enter systemic circulation?

Answer 1

Via the lymphatic system

- they by pass the liver as they are too big

Question 2

What are the two metabolic phases in carnivores and omnivores (describe them)?

Answer 2

1. absorptive state - Energy derived from oxidation of absorbed nutrients
2. post-absorptive state - Energy derived from oxidation of stored nutrients

Question 3

Where are galactose and fructose converted to glucose?

Answer 3

In the liver

Question 4

What is the constant level of plasma glucose?

Answer 4

5mmol/l

Question 5

When glucose is converted to tri-glycerides, what is most of it exported to blood as? What is the purpose of this?

Answer 5

very low density lipoproteins

• to distribute tri-glycerides to other tissues

Question 6

How are lipids made water soluble?

Answer 6

By binding to proteins

Question 7

What are the 4 major types of lipids bound to proteins?

Answer 7

1. Chylomicrons
2. Very low density lipoproteins (VLDL)
3. Low density lipoproteins (LDL)
4. High density lipoproteins (HDL)

Question 8

What % of amino acids are taken up by the liver and what are they used for?

Answer 8

75%

• protein synthesis
• converted to keto acids to provide energy to liver cells

Question 9

What happens to the ammonia produced when amino acids are degraded in herbivores?

Answer 9

urea is transported to fore-stomach or secreted in saliva and used for microbial protein synthesis

Question 10

How does the liver maintain plasma glucose levels?

Answer 10

1. mobilising glycogen stores

2. producing glucose from other sources

Question 11

How does the liver respond when plasma glucose declines due to it being used by tissues?

Answer 11

• reducing anabolic activities

- Mobilising glycogen stores to release glucose into the blood

Question 12

What is gluconeogenesis?

Answer 12

Glucose synthesised from non-carbohydrate sources

• performed by liver and kidneys
• pyruvate is the substrate

Question 13

Which are the only diet group that absorb sufficient glucose from their diet?

Answer 13

omnivores

Question 14

What is the cori cycle?

Answer 14

In post-absorptive state skeletal muscle also starts glycogenolysis

• glucose is oxidised to pyruvate/lactate to enter bloodstream
• then converted to glucose by liver

Question 15

Why is nervous tissue and fetuses heavily dependent on glucose for energy compared to other sources?

Answer 15

Have a very low uptake of FFA’s so cant covert them to VLDL

Question 16

What is the importance of ruminants synthesising ketone bodies from butyrate?

Answer 16

Butyrate inhibits gluconeogensis from pyruvate which is essential for producing the glucose they lack in their diet

Question 17

What is the role of insulin in regulation of carbohydrate metabolism?

Answer 17

• increases uptake of glucose as it stimulates glycogenesis

Question 18

What is the role of adrenaline in carbohydrate metabolism?

Answer 18

stimulates glycogenolysis in liver which maintains plasma glucose

Question 19

How does glucagon regulate protein metabolism?

Answer 19

Acts in the post-absorptive state

• increased uptake in liver
• proteins degraded into amino acids that can be used in gluconeogenesis

Question 20

In what state is the insulin:glucagon ratio high?

Answer 20

Absorptive state

Question 21

In ruminants what serve as the pre-cursors for glucose in the absorptive state and post-absorptive state?

Answer 21

1. propionic acid/amino acids

2. amino acids/glycerol