insulin and ketones SDL Flashcards
which hormones increase in the blood as a results of feed deprivation
- Glucagon
- Cortisol
- Epinephrine
- Growth hormone
when an animal enters negative energy balance, what storage form of lipid is broken down and what are the products
triglyceride is hydrolysed into glycerol and three fatty acids
what is the name of the process via which fatty acids are used to generate energy
beta oxidation
- occurs in the mitochondria of the liver
- generates ATP
- end product is acetyl coA
why are dairy cows in peak lactation likely to suffer from negative energy balance
The cow is struggling to produce huge amounts of milk when she is at peak lactation (3 to 6 weeks into lactation). Milk production requires glucose and the cow must make all of her own glucose via gluconeogenesis. Since milk production requires so much glucose, a relative deficiency of oxaloacetate develops. This inhibits movement of acetyl CoA into the TCA cycle (creates a “bottleneck” at the entrance to this metabolic pathway), which causes more acetyl CoA to be diverted into ketone production.
Why are ewes with twins/ triplets likely to suffer from a negative energy balance?
Milk production would be increased compared to an ewe with just one lamb = risk of ketosis increases with the number of foetuses and length of gestation
This means that the demand for energy by the foetuses is higher so the ewe needs to produce more glucose - the larger demand = negative energy balance - this is a problem as ruminants must produce all glucose themselves via gluconeogenesis
ruminants are particularly susceptible to ketosis because bacteria within the rumen consume all the glucose found in the feed. how then do ruminants generate glucose
ruminants are reliant on extensive and continuous gluconeogenesis for survival and productivity
explain why obesity would be likely to make ketosis worse
Negative energy balance is causing insulin levels to fall and the concentrations of the 4 hormones (glucagon, epinephrine, growth hormone and cortisol) to rise. This stimulates hormone-sensitive lipase (HSL), which breaks down triglyceride within the adipose tissues. This causes a large movement of fatty acids into the blood. These fatty acids are taken out the blood by the liver and should be used for energy via beta oxidation.
Animals (particularly ruminants) that are in negative energy balance develop a relative lack of oxaloacetate, which must combine with acetyl CoA in order for it to enter the TCA cycle.
Since the downstream pathway (entrance to the TCA cycle) is not keeping pace, there are two outcomes: 1) excess fatty acids are converted back into triglyceride and stored (causes hepatic lipidosis) or 2) they are used for energy via beta oxidation, but the excess acetyl CoA is diverted into ketones.
The more fatty acids being mobilized from the adipose tissues, the more acetyl CoA is diverted into ketones.
More fatty acids would be mobilized in an obese animal because:
1. There is a greater mass of stored triglyceride
2. The animal is likely to suffer from insulin resistance. The dampening effect of insulin on HSL will be lost and the enzyme will be more active.
what are the 3 ketones
- acetoacetate
- beta hydroxybutyrate
- acetone
why is ketosis more likely to occur in the insulin resistant animal
more fatty acids are mobilised from adipose tissues in response to negative energy balance.
which ketone is removed from the body via the respiratory tract
acetone
what enzyme is found within adipose tissues and aids lipolysis
hormone sensitive lipase
what hormones normally enhance the activity of hormone sensitive lipase
- corticotropin releasing hormone
- adrenaline
- noradrenaline
- glucagon
why does the activity of hormone sensitive lipase increase with insulin resistance
insulin usually supresses this enzyme to prevent lipolysis, therefore if insulin is no longer having an effect, it cant mediate lipolysis
what is metabolic acidosis
large quantities of ketones act as acids and lower the ph
which hormones normaly supresses hormone sensitive lipase activity
insulin
