The effects of pregnancy and exercise on metabolism Flashcards
Describe the metabolic and hormonal response to pregnancy
The metabolism of all major maternal nutrients are affected during pregnancy - the magnitude of the effect depending on the stage of pregnancy.
These changes are long-term adaptive responses to maternal metabolism that are hormonally mediated
Why is the environment in which the foetus develops controlled by the maternal metabolism?
The rate of transfer of nutrients across the placenta to the foetus is dependent on their concentration in the maternal circulation
Why does maternal metabolism need to change as pregnancy proceeds?
So:
- The foetus is supplied with the range of nutrients it requires
- Nutrients are supplied at the appropriate rate for each stage of development
- Minimal disturbances to maternal nutrient homeostasis
- Foetus is buffered from any major disturbances in maternal nutrient supply
What maternal hormones are involved in the long-term adaptive responses of maternal metabolism?
Insulin
What hormones produced by the foetal-placental unit are involved in the long-term adaptive responses of maternal metabolism?
Corticotropin releasing hormone (CRH) Oestrogen Progesterone Placental lactogen etc...
What is the role of maternal insulin in controlling changes to maternal metabolism during pregnancy?
Its concentration in the maternal circulation increases as pregnancy proceeds and it acts to promote the uptake and storage of nutrients, largely as fat in maternal adipose tissue
Placental hormones become increasingly important as pregnancy proceeds. They have a number of effects on maternal metabolism. In general what do these effects largely achieve?
Anti-insulin effects - impaired glucose uptake in maternal adipose and muscle
What are the general metabolic changes to maternal nutrient homoeostasis during the first 20 weeks of pregnancy?
Increasing insulin:anti-insulin ratio increases maternal nutrient stores in preparation for the more rapid growth of the foetus, birth and subsequent lactation
What is the second half of pregnancy characterised by?
A marked increase in the growth of placenta and foetus
The demands of the foetal-placental unit for nutrients in the second half of pregnancy are met by keeping the concentration of nutrients in the maternal circulation relatively high. How is this achieved?
- Reducing the maternal utilisation of glucose by switching tissues to the use of fatty acids
- Delaying the disposal of maternal nutrients after a meal
- Releasing fatty acids from the stores built up during the first half of pregnancy
How is the concentration of nutrients in the maternal circulation raised in the second half of pregnancy?
Maternal insulin increases to rise but this is met by an even faster rate of increase in foetal-placental unit anti-insulin hormones, which produces a decrease in the insulin:anti-insulin ratio
Why are more ketone bodies produced in the maternal liver in the second half of pregnancy?
Due to the reduced insulin: anti-insulin ratio and greater availability of fatty acids (mobilisation of maternal adipose tissue) to the liver, ketone body production is switched on in the maternal liver
What use is there of the extra ketone bodies during pregnancy?
Used as fuel by developing foetal brain
Both basal and stimulated insulin production normally increases throughout pregnancy. How is this extra demand met by the pancreatic beta cells?
Beta-cell hyperplasia
Beta-cell hypertrophy
Rate of insulin synthesis in beta-cells increases
Why does gestational diabetes occur?
Endocrine pancreas is unable to meet the extra demands of pregnancy and the pancreas fails to release the increased amounts of insulin required. Consequently there is a loss of control of metabolism, blood glucose levels rise and diabetes results
What happens to women who have gestational diabetes after they have given birth?
Increased metabolic demands of pregnancy removed
Hormone levels change
Endocrine pancreas can now respond sufficiently
Diabetes disappears.
Women who have gestational diabetes are at a higher risk of what, compared to women who didn’t develop it?
Type 2 diabetes
Why are some women high risk for gestational diabetes?
They have a high baseline of insulin resistance. Insulin resistance increases during pregnancy and so a high baseline can result in it increasing over the threshold where diabetic symptoms occur
In general, what does the body need to do during exercise?
- Meet the acute oxygen and fuel demands of cardiac and skeletal muscle
- Remove end-products of metabolism
What does the metabolic response to exercise need to ensure?
- Increased demands of skeletal and cardiac muscle are met by mobilisation of fuel molecules from energy stores
- Minimal disturbances to homeostasis by keeping the rate of mobilisation equal to the rate of utilisation
- Glucose supply to the brain is preserved (prevent hypoglycaemia)
- End products of metabolism are removed as quickly as possible
What is the magnitude and nature of the metabolic response dependent on?
- Type of exercise (muscles used)
- Intensity and duration of exercise
- Physical condition and nutritional status of the individual
Under high intensity activities of short duration (e.g. 100m sprint) what conditions does the skeletal muscle have to work under?
Anaerobic conditions as the supply of oxygen to muscle is inadequate to maintain aerobic metabolism
Under low intensity activities of longer duration (e.g. marathon), what conditions does the skeletal muscle work under?
The supply of oxygen to muscles is adequate to allow aerobic metabolism
The increased energy requirements of exercise chiefly reflect the increased activity of which muscle(s)?
Skeletal and cardiac muscles (increased activity of respiratory muscle is less significant)
The ATP present in muscle in theory would be used up very quickly in a 100m sprint (approximately 2 seconds!) but it does not fall below 20% because it is regenerated by a variety of mechanisms.
(i) How is ATP initially regenerated in muscle?
(ii) What fuel is used next to replenish ATP?
(i) Creatine phosphate
(ii) Muscle glycogen
During medium duration medium intensity exercise (1500m) the body regenerates ATP using a mixture of aerobic (60%ish) and anaerobic (40%ish) metabolism of glycogen. What types of metabolism occur in these three stages of the race?
- Initial sprint
- Long middle phase
- Final finishing burst
- Uses muscle ATP, creatine phosphate and anaerobic glycogen metabolism
- ATP produce aerobically from glycogen - relies on adequate supply of oxygen to muscles
- Anaerobic metabolism of glycogen, producing lactate
During a marathon the carbohydrate stores in the body are insufficient to meet the energy requirements of muscle cells, what do they start to oxidise instead?
Fatty acids