22 - Metabolism in Context Flashcards
What are the main fuel sources for the body?
What hormones are involved in changing fuel concentrations?
If the body is in low levels of glucose what other energy source can they use?
- Fatty acids, which can be converted to ketone bodies for the brain
- Only red blood cells can’t use fatty acids as no mitochondria
At different points after eating, what supplies the fuel supply for the body?
What does insulin stimulate and inhibit?
What is the feeding fasting cycle?
Individuals who eat regular meals have regular metabolic changes
What happens in starvation?
- Initially glucagon maintains glucose level by breakdown of liver glycogen
- Then reduction of glucose stimulates release of ACTH and therefore cortisol increases
- Brain becomes adapted* to use ketones for fuel and kidneys begin to contribute to gluconeogenesis
Why does urea synthesis fall during starvation?
Brain becomes adapted to using ketone bodies so the need to use protein for gluconeogenesis falls so less nitrogen released and therefore urea in urine falls
Why does late stages starvation lead to death?
Due to loss of muscle mass, e.g loss of respiratory muscle mass can lead to serious respiratory infections
What is the usual gain of weight in pregnancy and what causes this increase in weight?
Therefore, mother has to alter her metabolism and endocrine system to deal with increased demands of fetus and placenta
Why does the mother’s metabolism have to change in pregnancy?
- Rate of transfer of nutrients depends on concentration in blood
- Foetus needs nutrients at an appropriate rate for each stage of development
- Foetus needs to be buffered from any major distrubance in mother’s nutrient supply
What are the hormones involved in the long term adaptive response of the mother’s metabolism in pregnancy?
- Maternal insulin
- Foetal-placenta unit: oestrogens, progesterone, placental lactogen
What are the major metabolic changes that occur in the first half of pregnancy?
Concentration of insulin increases as pregnancy proceeds and promotes uptake and storage of nutrients and fat in adipose tissue for later
What hormones are from placental origin and what is their importance?
- Human placental lactogen
- Progesterone
- CRH
Have an antiinsulin effect and increase ACTH and therefore cortisol concentration
What are the major metabolic changes that occur in the second half of pregnancy?
- Effectively the overall concentration of insulin decreased due to more antinsulin produced
How does maternal insulin secretion increase in pregnancy?
- Increased appetite so increase in glucose intake
- Oestrogens and progesterone increase sensitivity of pancreatic beta cells so there is hyperplasia and hypertrophy of beta cells so increase in insulin synthesis
What does the foetal brain use for fuel?
- Ketone bodies from maternal ketogenesis
- Increased availability of fatty acids and decreased insulin:anti insulin ratio results in ketogenesis being activated in the liver
What is gestational diabetes?
- Increased metabolic demand in pregnancy means pancreas beta cells have to undergo hypertrophy and hyperplasia to secrete more insulin.
- Some mothers cannot produce enough insulin to keep up with demand so uncontrolled metabolism
- After birth when metabolic demands and hormones removed the diabetes goes away
What is gestational diabetes a warning sign for?
Mothers that develop this are more likely to acquire type II DM later in life
What are the complications with gestational diabetes?
- Increased risk of miscarriage
- Increased risk of congenital malformation
- Fetal macrosomia so shoulder dystocia
- Associated with hypertension and preeclampsia
Risk of complications lowered if diagnosed and managed
What is preeclampsia?
Having a high blood pressure and protein in urine as there has been damage to an organ system
What are the risk factors for developing gestational diabetes and how is this condition managed?
When the body is exercising there is a change in metabolism, what is this to ensure?
- Increased energy demand of skeletal and cardiac muscle are met by mobilising energy stoes
- Minimal disturbances to homeostasis so rate of energy utilisation mathes rate of energy mobilisation
- Glucose supply to brain maintained
- End products of metabolism removed ASAP
What does the magnitude of change in metabolism depend on in exercise?
- HIT short: anaerobic metabolism
- LIT long: aerobic metabolism
Therefore, need different energy supplies
What is the rate of ATP turn over in skeletal muscle in a 100m sprint and how is it synthesised?
- Muscle ATP stores last 2 seconds
- ATP then synthesised from creatine stores for 5 seconds
- Beyond this further ATP must be supplied by glycolysis and oxidative phosphorylation so fuel stores have to be mobilised
How does ATP synthesis differ from a 100m sprint when doing up to 2 mins of exercise?
- Complete oxidation glycogen can sustain 60 mins of exercise
- Lactic acid end product can sustain 2 mins HIT exercise
Why can anaerobic metabolism of glucose only occur for a short period of time?
Produces lactic acid and the H+ ions cause issues like:
- Inhibition of glycolysis
- Interferes with actin/myosin interactions
- H+ causes sarcoplasmic reticulum to bind calcium an prevent contraction
Why are fatty acids use limited in muscles for fuel?
- Fatty acid oxidation requires more O2 per pole of ATP produced than glucose
- Rate of fatty acid uptake into muscles cells and their mitochondria
- Can only be metabolised under aerobic conditions
Describe the metabolic response to short duration high intensity exercise, e.g 100m sprint.
- Muscle ATP and C-P used initially for 5 seconds
- Muscle glycogen rapidly mobilised to provide G-6-P for 5 seconds
- Glycolysis occurs under anaerobic conditions as oxygen supply inadequate
(control of this is usually the sympathetic nervous system e.g NA)
Describe the metabolic response to medium duration medium intensity exercise, e.g 1500m run.
Describe the metabolic response to long duration low intensity exercise, e.g 1500m run.
Muscles work aerobically and can use all types of fuel molecules, the type of fuel changes as exercise proceeds. Control of this is mainly hormonal, e.g insulin, cortisol, and some nervous.
How do athletes prepare for a marathon in terms of their energy stores?
They eat lots of carbs after exercise to promote storage of glucose as muscle glycogen rather than lipid. Boosts their glycogen stores
How do hormones control metabolism in a marathon?
- Increase glycogenolysis in liver
- Increase gluconeogenesis in liver (lactate and glycerol)
- Increase lipolysis in adipose tissue
- No effect on ketogenesis in liver as insulin still present
What is the definition of fatigue and what causes it?
Inability to maintain a power output affecting the intensity and/or duration of exercise
- Depletion of muscle glycogen
- Accumulation of H+ in muscle
- Dehydration (no sweating, less heat loss, increase temp)
What are whole body, not just metabolic, responses to exercise?
What are whole body, not just metabolic, responses to training?
Long term adaptions to improve capacity for physical work, minimal changes to respiratory system but lots of changes to CVS and MSK
What are the benefits of exercise?
What are the differences between type I and type II muscle fibres?
