Metabolic and Endocrine Control during Special Circumstances

Question 1

What are the anti-insulin hormones and why are they known by this term

Answer 1

Glucagon, adrenaline, growth hormone, cortisol

Their actions oppose that of insulins

Question 2

What is the normal glucose range in a healthy individual

Answer 2

4.0-6.0mmol/L

Question 3

What is hypoglycaemia

Answer 3

A reduction in blood glucose to 3.0mmol/L or lower

Question 4

What are the acute effects of hypoglycaemia

Answer 4

Weakness/tiredness

Palpitations

Changes in mood

Sweating

Headache

Sickness

Slurred speech

Can lead to unconsciousness and dead if untreated

Question 5

What is hyperglycaemia

Answer 5

Elevation of the fasting blood glucose above 7.0mmol/L

Question 6

What hormones are important in starvation and how do they act

Answer 6

Cortisol - stimulates gluconeogenesis, lipolysis and use of fatty acids instread of glucose by cells

Glucagon - stimulates gluconeogenesis and lipolysis

Anti-insulin hormones - stimulate ketone body production

Question 7

Why does maternal metabolism change during pregnancy

Answer 7

Ensure foetus is supplied with range of nutrients it requires

Ensure nutrients are supplied at appropriate rate for each stage of development

Ensure there is minimal disturbance to materal nutrient homeostasis

Ensure foetus is buffered from any major disturbances in materal nutrient supply

Question 8

What hormones are produced/involved in pregnancy

Answer 8

Maternal insulin

Oestrogens

Progesterone

Placental lactogen

Question 9

What is the role of materal insulin

Answer 9

Promotes uptake and storage of nutrients, largely as fat in maternal adipose tissue

Question 10

What are the foetal-placental hormones and what effect do they have

Answer 10

Human placental lactogen, progesterone, corticotropin releasing hormone

Have an anti-insulin effect

Question 11

What metabolic changes occur during the first half of pregnancy

Answer 11

Increase in maternal nutrient stores - increased insulin level to promote anabolic state

This is for the more rapid growth of foetus, birth and subsequent lactation

Question 12

What metabolic changes occur during the second half of pregnancy

Answer 12

Second half of pregnancy marked by increase in growth of placenta and foetus

Maternal metabolism adapts to meet increasing demands of foetal-placental unit by keeping nutrient concentration in maternal circulation relatively high

There is an increase in production of anti-insulin hormones

Question 13

How is nutrient concentration in materal circulation kept high during second half of pregnancy

Answer 13

Reduced maternal utilisation of glucose by switching tissues to use of fatty acids

Delayed disposal of maternal nutrients after meals

Release of fatty acids from stores built up during first half of pregnancy

Question 14

Due to the increased availability of fatty acids, what process is switched on during pregnancy

Answer 14

Maternal ketogenesis - ketone body production is switched on

Question 15

Where are the ketone bodies produced by maternal ketogenesis used

Answer 15

Used as a fuel by the developing foetal brain

Question 16

How is the increased insulin produced achieved by the cells of the pancreas during pregnancy

Answer 16

B-cell hyperplasia and hypertrophy

Insulin synthesis in B-cells increases

Question 17

What is gestational diabetes

Answer 17

Where the endocrine pancreas is unable to respond to metabolic demands of pregnancy and pancreas fails to release increased amounts of insulin required

There is a loss of control of metabolism, blood glucose increases and diabetes mellitus results

After birth, metabolic demands of pregnancy are removed and diabetes disappears as endocrine pancreas can respond normal demands

Question 18

What does the metabolic response to exercise ensure

Answer 18

Increased energy demands are met by mobilisation of fuel molecules from energy stores

Minimal disturbances to homeostasis by keeping rate of mobilisation equal to rate of utilisation

Glucose supply to brain is maintained

End products of metabolism are removed as quickly as possible

Question 19

What does the energy requirement of exercise reflect

Answer 19

The increased activity of skeletal and cardiac muscle, increased activity of respiratory muscle is less significant

Question 20

Why is liver glycogen not used by muscles during exercise

Answer 20

It is used to prevent hypoglycaemia and associated impairment of CNS function

Question 21

What are the advantages of using muscle glycogen over circulating glucose

Answer 21

Availability not affected by blood supply

No need for membrane transport into muscle cells

Produces G-6-P without using ATP

Mobilisation can be very rapid - branched molecule

Question 22

What limits anaerobic metabolism of glucose in muscles

Answer 22

Accumulation of H⁺ and lactate

Question 23

How do H⁺ ions impair muscle function

Answer 23

H⁺ inhibits glycolysis

H⁺ interferes with actin/myosin interaction

H⁺ causes sarcoplasmic reticulum to bind calcium, inhibiting contraction

Question 24

What factors limit the use of fatty acids by muscles

Answer 24

Rate of lipolysis - rate of release from adipose tissue

Limited capacity of blood to transport fatty acids

Rate of fatty acids uptake into muscle cells and into muscle mitochondria

Fatty acid oxidation requires more oxygen/mole of ATP produced than glucose

Fatty acids only metabolised under aerobic conditions

Question 25

What is the metabolic response to short-duration, high intensity exercise and what controls this response

Answer 25

Metabolic response is rapid and largely confined to skeletal muscle that works anaerobically

Controlled by nervous system (NA) and some endocrine input (adrenaline)

Question 26

Describe the metabolic response to short-duration, high intensity exercise

Answer 26

Muscle ATP and C~P are used initially

Muscle glycogen is rapidly mobilised to provide ATP

G-6-P is metabolised by substrate level phosphorylation

Glycolysis is carried out under anaerobic conditions

Dramatic increase in rate of anaerobic glycolysis produced lactate and H⁺

H⁺ ions build up, producing fatigue

Question 27

What is the metabolic response to medium duration, medium intensity exercise

Answer 27

Initial spint uses muscle ATP, C~P and anaerobic glycogen metabolism

Long middle phase where ATP is produced aerobically from glycogen in muscle

Finial burst relying on anaerobic metabolism of glycogen

Question 28

What control the changes in metabolism that occur during long duration, low intensity exercise

Answer 28

Hormonal - insulin, adrenaline, growth hormone, glucagon, cortisol

Nervous system - noradrenaline

Question 29

What are the major features of the metabolic response that occur during long duration, low intensity exercise

Answer 29

Muscles work aerobically

Muscles can use all types of fuel molecules

Origin and type of fuel changes as exercise proceeds

Question 30

What fuel molecules are used during a marathon and during what points are they used

Answer 30

Initially muscle glycogen is used as major fuel

As marathon proceeds, there is increased utilisation of circulating blood glucose - replaced by glucose release from liver

Fatty acids can be used by muscle due to aerobic conditions

There are limited substrates for gluconeogenesis though so blood glucose level may fall

Question 31

How is the metabolic response during a marathon controlled - what is secreted and what is inhibited

Answer 31

Insulin secretion inhibited by adrenaline and noradrenaline

Noradrenaline, adrenaline and growth hormone levels increase rapidly

Glucagon and cortisol levels increase gradually

Question 32

What are the effects caused by changes in the endocrine system during a marathon

Answer 32

Fall in insulin/anti-insulin ratio causing:

Increased glycogenolysis in liver

Increased gluconeogenesis in liver - lactate and glycerol

Increased lipolysis in adipose

No effect on ketogenesis

Question 33

What is fatigue

Answer 33

Inability to maintain a given power output affecting the intensity and/or duration of exercise

Question 34

Give some biochemical causes of fatigue

Answer 34

Depletion of muscle glycogen

Accumulation of H+ in muscle

Dehydration

Question 35

What are the whole body reponses to prolonged exercise

Answer 35

Increased fuel consumption by muscles

Increased ATP production and utilisation by muscles

Increased heat production

Increased oxygen delivery - arteriole vasodilation

Increased removal of CO2, H+ and lactate

Increased cardiac output - beat faster, larger stroke volume

Redistribution of blood from to muscles, away from kidneys and gut

Changes in breathing - increased rate and depth

Question 36

What is training and what body systems does it primarly affect

Answer 36

Long term adaptations to improve capacity for physical work

Cardiovascular and musculoskeletal systems

Question 37

What are the cardiovascular changes due to training

Answer 37

More 2,3-bisphosphoglycerate

Heart beats slower for same cardiac output

Question 38

What are the musculoskeletal changes as a result of training

Answer 38

GLUT4 in cell membrane

Glycogen storage

Potential for oxidation metabolism - especially fatty acids

Number and size of muscle fibres

Vascularisation of muscles

Myoglobin content of muscle

Question 39

What are the benefits of exercise

Answer 39

Body composition changes - increased muscle, decreased adipose

Glucose tolerance improves - increased muscle glycogenesis

Insulin sensitivity increases

Blood TAGs decrease - increased HDL, decreased VLDL and LDL

BP falls

Feeling of well-being - psychological effect

Question 40

What are the two types of muscle and what exercise are they good for

Answer 40

Type 1 (red) - low intensity, high endurance

Type 2 (white) - high intensity, low endurance