Metabolism Physiology Flashcards
What are the majority of ingested lipids?
90% triglycerides
What are ingested lipids made of?
Essential (eg alpha-linolenic and linoleic acid) and non-essential fatty acids
Where are ingested lipids broken down?
10-30% in stomach
Rest is broken down in duodenum and upper jejunum.
Bile salts are absorbed in the terminal ileum.
Can ingested lipids be used as a source of ATP?
Yes they are energy dense, provide more than double the ATP than from glucose.
What happens to the faeces if bile salts secretion is reduced?
Lipids in the faeces increases because bile salts are required to solubilize fats and aid their absorption.
When can BMR be lower?
During sleep
For every 1 degree C rise in body temp, what happens to the cerebral metabolic rate?
Increases by 8%
What is BMR?
BMR is the energy output of an individual per unit time at rest, at room temperature
It must also be measured 12-14 hr after their last meal (a time when one is said to be thermoneutral).
What can measure BMR?
A wet spirometer (measures indirectly)
What does an ergometer measure?
Energy expenditure whilst active.
What hormones antagonise insulin-induced hypoglycaemia?
- adrenaline
- noradrenaline
- glucagon
- GH
- cortisol
What effect does insulin have on protein anabolism?
It facilitates it.
Insulin is the only major anabolic hormone and stimulates synthesis of proteins, fat and glycogen.
What does insulin do to glycogen synthesis?
It promotes it
In anaerobic metabolism, how much lactate is produced from one glucose?
Each glucose is converted to 2 pyruvate, therefore makes 2 molecules of lactate
How do anaerobic and aerobic metabolism compare in speed of release of ATP?
Glucose metabolism to lactate releases ATP at least as TWICE as fast as mitochondrial metabolism and can optimally provide energy for 1.5 mins of maximal muscle activity.
After exercise what happens to lactate?
80% is reconverted to glucose in the liver via the Cori cycle
What happens to lactate in the kidney?
It is actively reabsorbed by the nephron to a transport max of 75mg/min
Why can adrenaline cause hyperglycaemia?
It stimulates glucagon secretion and stimulates gluconeogenesis
How can thyroid stimulating hormone cause hyperglycaemia?
Thyroid hormone stimultaes: increased glucose absorption from the gut, glycogenolysis and gluconeogenesis.
What effect do thiazide diuretics have on blood glucose?
Hyperglycaemia.
Thiazide diuretics commonly precipitate Type 2 diabetes.
What does administration of glucagon do to blood glucose?
Hyperglycaemia
What do beta blockers do to blood glucose levels?
They can cause hypoglycaemia under GA
What does glucagon do?
Stimulates gluconeogenesis, glycogenolysis and lipolysis.
What receptor does glucagon act through?
Via G-protein linked receptors
Where is glucagon made?
Pancreatic alpha cells
How does glucagon affect growth hormone?
It stimulates secretion of GH
What inhibits glucagon release?
- alpha stimulation
- insulin
- glucose
- ketones
- phenytoin
- somatostatin
What stimulates glucagon release?
- cortisol
- infection
- theophylline
- other phosphodiesterase inhibitors
What happens in starvation?
Glycogenolysis occurs and the liver begins to use fatty acids as a source of energy.
As glycogen is depleted, gluconeogenesis increases using amino acids from the breakdown of muscle protein. Glycogen is not replenished until return of nutrients, this restorative process is under control of cortisol.
The brain cannot survive without glucose but other tissues can adapt to using ketone bodies as a fuel.
Free fatty acids undergo beta oxidation to produce ATP in the mitochondria. Glucose cannot be formed from fatty acids.
What do insulin and GH have directly opposing effects on?
- fat catabolism
- glucose utilisation
- fat anabolism
- glycogen production
What does GH and insulin do to fat?
Causes fat breakdown
Insulin stimulates fat deposition
What do GH and insulin do to glucose utilisation?
GH inhibits glucose utilization
Insulin stimulates glucose absorption
How do GH and insulin affect protein synthesis?
They both promote protein anabolism
What do insulin and GH do to glycogen?
Insulin stimulates glycogen deposition.
GH encourages glycogenolysis.
What happens to glucagon levels in starvation?
They go up as body enters a catabolic phase with increased glycogenolysis
What causes ketoacidosis in starvation?
The accumulation of acetyl-CoA
What can the majory of amino acids be converted to for ketosis?
After deamination can be converted to acetyl-coA from which acetoacetate can be formed.
What does the liver convert fatty acids to in ketosis?
Fatty acid degradation occurs largely in the liver where acetyl-CoA is formed leading to acetoacetate production. This is transported at low levels but with efficient flux to the rest of the body.
What is ketosis?
The presence of excessive levels of acetoacetate, beta-hydroxybutyrate or acetone in the blood - due to high fat diet/diabetes/starvation.
What limits entry of acetyl-CoA into the citric acid cycle in ketosis?
Oxaloacetate is needed to receive acetyl CoA into the citric acid cycle.
How does ketoacidosis cause hyponatraemia?
Ketoacids are easily excreted by the kidney but being strong acids they are excreted combined with Na+ from the extracellular fluid. The resultant hyponatraemia leads to an increased acidosis beyond that occasioned by the direct rise in ketoacid levels.
