Fate of glucose

Question 1

Describe the change in glucose in the fasting state

Answer 1

~2-4 hrs after a meal blood glucose levels return to basal levels and continue to decrease until the next meal
Insulin levels decline and glucagon levels rise which triggers release of fuels from the body stored

Question 2

Describe how glucose is maintained in the fasting state

Answer 2

Liver produces glucose by glycogenolysis and by gluconeogenesis

Question 3

What occurs in starvation?

Answer 3

animal has a prolonged period of low glucose levels
lack of energy sources to maintain vital cells, especially nervous system tissues which can only use glucose as a substrate => coma + death

Question 4

What enzyme breaks down carbs in the mouth and SI?

Answer 4

amylase

Question 5

What is the effect of high blood glucose?

Answer 5

detected by Islets of Langerhans in the pancreas
beta cells release insulin
Insulin causes tissues to store glucose as either glycogen or fats to return blood glucose to normal levels

Question 6

What is the effect of low blood glucose?

Answer 6

Detected by islets of langerhans in pancreas
alpha cells release glucagon => mobilises glucose stores => returns blood glucose levels to normal

Question 7

What happens to glucose when they enter hepatocytes?

Answer 7

• can be oxidised and be used as energy source for hepatocyte
• converted to glycogen and stored (influenced by insulin)
• converted to TAG and exported out the liver

Question 8

what happens if TAGs get stored in the liver?

Answer 8

accumulation of fat in liver => prevents normal function => disease
e.g., fatty liver in cows, hepatic lipidosis in cats

Question 9

How does the liver secrete TAGs?

Answer 9

packages them with proteins, phospholipids and cholesterol into lipoproteins - VLDL
VLDLs secreted into blood streams

Question 10

What is the function of VLDLs (very low density lipoproteins)

Answer 10

Secreted in bloodstream from liver
some fatty acids from VLDL are taken up for immediate energy needs
Most are stored in adipose tissue as TAGs

Question 11

Clinical relevance: glucose and the CNS

Answer 11

Brain and neural tissues can only use glucose as substrate for energy
Glucose is major precurse of neurotransmitters
Clinical signs of low blood glucose are usually neurological

Question 12

How does the brain and other neural tissues use glucose for energy?

Answer 12

oxidize glucose via cellular respiration to generate ATP

Question 13

What is the lactate equation?

Answer 13

Lactate produces in anaerobic respiration
Lactate + NAD+ <=> pyruvate + NADH + H+

Question 14

Describe the cori cycle?

Answer 14

Lactate released from cells undergoing anaerobic glycolysis (usually muscle cells when O2 conc is low) taken up by liver and oxidised back to pyruvate
Pyruvate use to synthesise glucose (gluconeogenesis) which is returned to blood

Question 15

what is the cori cycle?

Answer 15

Cycling of lactate and glucose between peripheral tissues and the liver

Question 16

What is gluconeogenesis?

Answer 16

metabolic pathway that results in the generation of glucose from other products e.g., AAs, glycerol, fatty acids and lactate

Question 17

Where do the substrates used in gluconeogenesis come from?

Answer 17

Glycerol - from lipolysis of adipose TAGs
AAs - from breakdown of protein
Lactate - from anaerobic glycolysis in RBC cytosol

Question 18

Describe anaerobic glycoysis in the RBC

Answer 18

Glucose is only fuel for RBCs as they lack mitochondria
Glucose used to generate ATP in cytolosol via anaerobic glycolysis
Pyruvate form is converted to lactate and released into blood

Question 19

Describe the fate of glucose in muscles

Answer 19

Muscles can use glucose from blood or from their own glycogen stores
Convert glucose into lactate through glycolysis or oxidising it to CO2 and H2O

Question 20

Describe the fate of glucose in adipose tissues

Answer 20

Adipocytes oxidise glucose for energy
Adipocytes metabolise gluose to Acetyl CoA which can be turned into fat and stored

Question 21

what is function and action of epinephrine on glucose?

Answer 21

Mobilised fuels during acute stress
Stimulates glucose production from glycogen
Stimulates fatty acid release from adipose tissue

Question 22

What is the function and action of cortisol on glucose?

Answer 22

Provides for changing requirements over long-term
Stimulates AA mobilisation for muscle protein
Stimulates gluconeogenesis
Stimulates fatty acid release from adipose tissue

Question 23

where does the body get energy from in the starved state?

Answer 23

Body limits amount of AAs used for gluconeogenesis in order to preserve muscle mass
Relies of ketones as source of energy
As there is limited glucose, the brain must rely on using intermediate energy source ketone bodies
=> elevated levels of ketone body in blood = ketosis

Question 24

what is glucose sparing?

Answer 24

During starvation the brain uses ketone bodies as energy, therefore it needs less glucose
Glucose is still required for use by RBCs
Less glucose is used by the body to keep some ‘spare’
Liver needs to produce less glucose per hour during prolonged fasting than short periods

Question 25

How is protein spared during starvation?

Answer 25

decreased rate of gluconeogenesis
Reserves proteins for essential functions such as biosynthetic function and new protein synthesis

Question 26

Desribe the role of adipose tissue in starvation

Answer 26

Continues to bread down TAG stores to produce fatty acids and glycerol for energy
In liver fatty acids are converted to ketone bodies which are oxidised for energy

Question 27

How does ketonemia occur?

Answer 27

The rate of ketone body production exceeds rate at which they can be used

Question 28

Why is ketosis common in dairy cattle?

Answer 28

peak lactation has a high energy demand and cow is incapable of eating enough to support this
Body starts mobilising fats to provides energy => ketone production

Question 29

How does the body adapt to the starvation state?

Answer 29

The breakdown of protein becomes tissue or protein specific to guard against vital proteins/cells becoming depleted
This occurs due to elevated levels of cortisol

Question 30

Why do animals die of starvation?

Answer 30

Proteins become so depleted that heart, kidney etc stop functioning
Animal can develop infection and do not have adequate reserves to mount immune response
Deprived of vitamin and mineral precursors of coenzymes and other compounds necessary for tissue function
Lack of ATP and decreased electrolyte intake, electrolyte composition of cells or blood becomes incompatible with life