BCH Hormone Regulation of Fats Flashcards
What are fats?
Fatty acid esterified with glycerol to form triacylglycerol (TAG)
Describe fats
Fats are simple lipids, organic compounds poorly soluble in water but soluble in organic solvents. Fats form the bulk of adipose tissues (adipocytes) free fatty acid and TAG contribute significantly to the energy requirements in the body
Fat molecules are a large store of energy and an average 70 KG man has 15 KG of fat in the body and….135,000 kcal of energy by far the largest of energy in the body
Transport of TAG
TAG in the food are transported from the intestine as chylomicrons into the liver for storage.
The three fatty acids are transported to various tissues re-esterified and stored as tag in tissues such as adipose muscle
Fat metabolism organs and function
Liver
Adipose tissue
muscle
brain
These tissues Contain different sets of enzymes for:
storage
Use
And generation of fuel
These tissues do not work in isolation but their activities are so integrated in a network that one tissue may provide the substitute for another, or process compounds produced by another organ
Communication among tissues is controlled by
the availability of substrates
hormones
and the nervous system
Starvation or fasting
Starvations fosters thoughts if miss you the second after the absorptive period
What is the absorptive period
The. 2 to 4 hours after the ingestion of a normal meal
What occurs during fasting
In the absence of food the plasma level of glucose, amino acids and TAG fall causing a decrease of ins/gly ratio as occurs in the fed state.
The decrease in insulin/glycogen ratio and the decrease in availability of circulating substrates with degradation of glycogen, TAG and protein makes the fasting/starvation period a catabolic one
This sets in motion an exchange of substrates among the body tissues where the fuels are principally utilized mainly liver, muscle adipose tissue and the brain
Describe the exchange of substrates during fasting
This exchange divided by two priorities
- They need to sustain adequate blood levels of glucose for the use of the brain erythrocytes and other glucose requiring tissues
- The need to mobilize FFA from adipose tissue and the synthesis of ketones from the liver for the use by all other tissues for energy requirement
Discuss the fat reserve of a 70 KG man
An average 70 KG man normally has a reserve of 15 KG fat six KG protein and 0.2 KG carbohydrate (as glycogen) these are equivalent to 135,000 kcal, 24,000 kcal and 800kcal of energy respectively
The fat stores alone are enough to meet energy needs for about three months.
Why is Protein is normally not an energy source
Protein is normally not an energy source as it has other important functions in the body such as the structural components of the body, enzymes etc
Therefore only about 1/3 of the body protein to be utilized for energy beyond which vital organs are fatally impaired
Fat stores alone are enough to meet energy needs for how long?
About three months
The regulation of intermediary metabolism in the fasting state like in the fed state is controlled by four mechanisms
- Availability of substrates
- allosteric regulation of enzymes (activating or inhibitory)
- Covalent modification of enzymes
- Induction expression of enzyme synthesis
Are substrates available by the diet in the fasting state? Explain why?
In the fasting state, substrates are not available by the diet but from catabolism of stores and or tissue eg. glucose is from glycogen, FFA and glycerol from the TAG in adipose tissue, amino acid from proteolysin
Also in the fasting state most of the enzymes regulated by covalent modification are phosphorylated and inactive
What happens to the liver tissue During Fasting?
- Increase in glycogen degradation: Hepatic glycogen are virtually consumed in under 24 hours of fasting/starvation
- The obligatory glucose requirements of the brain, RBCs and other organs are met by gluconeogenesis. Gluconeogenesis plays an important role in maintaining blood glucose during both overnight and prolonged fasting. The liver first uses glycogen degradation and then gluconeogenesis to maintain optimal glucose levels for energy metabolism.
Glucose formed during gluconeogenesis is derived from glucogenic amino acids, lactate from the muscle and glycerol from the adipose tissue.
In the first week of fasting 150 g of protein is utilized for gluconeogenesis
Increase in glucagon in plasma result in an increase includes glucogenolysis and an increase in gluconeogenesis
- Increase in FFA oxidation provides an ADP and ATP for gluconeogenesis
- Increase in the synthesis of ketone bodies for use by peripheral tissues and brain thus reducing the need for gluconeogenesis from amino acids thus preserving protein
What happens to the skeletal muscle During Fasting?
Resting muscle uses FFA as a fuel, in contrast exercising muscle uses glucose from glycogen stores.
As the glycogen reserves are depleted by starvation and exercise, FFA from TAG become the energy source.
There is a decrease in glucose uptake because of decreased insulin.
Initially, the muscles uses fatty acids from adipose tissue and ketones as fuel, later ketones are spared and fatty acids are oxidized (used) exclusively.
This causes an increase in Ketone in blood for the use of the brain.
Thus as Ketone is increasing in blood, for brain use, the muscle is the decreasingly utilizing the compounds.
During the first few days there is a rapid breakdown of muscle protein providing amino acid for gluconeogenesis in the liver.
After several weeks, the rate of muscle proteoglycan declines paralleling a decline in the need for glucose used by the brain which has now begun using ketone bodies
What happens to the brain During Fasting?
Initially uses glucose
In prolonged fasting (2-3 weeks) glucose is spared and ketones become the fuel used by the brain thus sparing proteolysin and muscle wasting
What happens to the kidney during Fasting?
Kidney plays a role in prolonged starvation
50% of Gluconeogenesis occurs in the kidney in late fasting.
The kidney also provides compensation for the acidosis that accompanies the increased production of Ketone bodies in the blood.
The nitrogen byproduct of the enzymatic process in the kidney, picks hydrogen ions from Ketone body dissociation and is excreted in the urine as urea decreasing the acid load of the body
