Role of Liver in Metabolism

Question 1

When is the early postprandial stage?

Answer 1

shortly following food digestion

Question 2

When is glucose taken up by liver?

Answer 2

When dietary glucose component high in blood

Question 3

When glucose enters circulation, where is it taken up in order to replenish glycogen stores?

Answer 3

Liver, muscle, glial cells brain

Question 4

What is excess glucose in the blood converted to when taken up by liver?

Answer 4

Triaglycerides (fats)

Question 5

Define signalling role of insulin

Answer 5

“Store signal” –> increase transport of glucose into adipose tissue cells
Activation of enzymes that catalyse production of fatty acids from glucose derivatives
Inhibition of lipolysis

Question 6

Where is insulin released from

Answer 6

Pancreas

Question 7

Insulin is released in response to what?

Answer 7

High glucose & low glucagon

Question 8

Summarise insulin’s actions

Answer 8

Increase glucose use
Inc carb and fat storage
Inc protein synthesis
THEREFORE lowers blood glucose/ FA/ AA levels

Question 9

What is the primary stimulus for insulin secretion?

Answer 9

Inc blood glucose conc

Question 10

Which cells release insulin?

Answer 10

Islet B cells of pancreas

Question 11

Lipids are precursors to the formation of ___ + ___ through the ____ cycle

Answer 11

Lipids are precursors to the formation of fatty acids + glycerol through the B oxidation cycle

Question 12

How many/few of the carbohydrates that ruminants ingest are absorbed directly as sugars from the GIT

Answer 12

Very few!

Question 13

What process aids the absorption of dietary carbohydrates in ruminant diets?

Answer 13

Fermented by microbes –> short chain VFA’s –> absorbed across ruminal mucosa

Question 14

What are the three VFA’s primarily produced by ruminal fermentation of carbohydrates?

Answer 14

70% acetic acid
20% propionic acid
10% butyric acid

Question 15

How is butyric absorbed and metabolised?

Answer 15

Metabolised by mucosal epithelium to ketone body B-hydroxybutyrate (BHBA) –> utilised directly by tissues as an energy sources

Question 16

How is acetic acid absorbed and metabolised?

Answer 16

Acetic acid –> acetate –> blood –> peripheral tissues and mammary gland –> oxidation to generate energy, metabolism into long chain fatty acids for lipid storage

Question 17

How does propionic acid differ from butyric acid and acetic acid?

Answer 17

Proprionic acid is GLUCOGENIC whereas other two are KETOGENIC

Question 18

Which cells in the body are most dependant on glucose as an energy source?

Answer 18

Neurons

Question 19

How do animals maintain blood glucose levels?

Answer 19

1. Utilise circulating glucose
2. Mobilise stored glycogen
3. Produce glucose by converting non-carbohydrate sources to glucose through gluconeogenesis

Question 20

During gluconeogenesis, oxaloacetate is made into what?

Answer 20

Glucose

Question 21

Triaglycerides are lipolysed into __ and __

Answer 21

glycerol and free fatty acids

Question 22

Free fatty acids are made into __ during B oxidation

Answer 22

acetyl CoA

Question 23

How do tissues spare glucose when circulating glucose levels are low?

Answer 23

By metabolising lipids rather than glucose as their energy source

Question 24

Which blood parameters stimulate hepatic glycogenolysis?

Answer 24

A high glucagon:insulin ratio

Catecholamines e.g. adrenaline

Question 25

During a fast, how do blood hormone levels respond to a decrease in blood glucose?

Answer 25

Inc insulin secreted & decreased glucagon secreted –> reduced hepatic synthesis of glycogen and triglycerides –> if blood glucose falls below a threshold …> hepatocytes begin to mobilise glycogen reserves –> release of glucose into blood

Question 26

How soon after food deprivation are hepatic glycogen stores usually depleted?

Answer 26

24hrs

Question 27

After depletion of hepatic glycogen stores, an animal is reliant on _____ for energy

Answer 27

gluconeogenesis

Question 28

How do muscles produce energy during a fast?

Answer 28

Glycogenolysis

Question 29

What stimulates glycogenolysis

Answer 29

Adrenaline

Question 30

Can skeletal myocytes release glucose derived from glycogen stores directly into circulation?

Answer 30

No- they use it themselves

Question 31

Glucose undergoes ____ in muscle cells to produce ATP and ___ or ___

Answer 31

Glucose undergoes anaerobic glycolysis in muscle cells to produce ATP and pyruvate or lactate

Question 32

What is the main organ in which gluconeogenesis occurs?

Answer 32

liver

kidneys also play a significant roles, especially during starvation

Question 33

Which hormones promote gluconeogenesis?

Answer 33

Glucocorticoids e.g. cortisol, glucagon & growth hormone

Question 34

Which 5 substrates can be used to generate glucose via gluconeogenesis?

Answer 34

Pyruvate
Lactate
Glycerol
Proprionate (derived from rumen fermentation)
Amino acids (derived from tissue protein stores, e.g. skeletal muscle)

Question 35

Which is the most important amino acid used for gluconeogenesis in the liver?

Answer 35

Alanine

Question 36

What is most of the alanine used for in hepatic gluconeogenesis?

Answer 36

Transamination into pyruvate –> release into blood –> uptake by hepatocytes –> glucose production