Metabolism in Health Flashcards
What are the two states of metabolism
- fed (absorptive) state (shortly after meal when new nutrients are available)
- fasted (post absorptive) state (body needs to draw upon its fuel stores)
what is the state of metabolism in the fed state
anabolic
-Nutrient molecules are used to provide energy stores or to
provide needs of growth and maintenance of cells and tissues
-But these needs mean that some molecules are used immediately
to provide energy
what is the state of metabolism in the fasted state
catabolic
-The body calls on the energy stores, so they become depleted
what determines the rate of different metabolic pathways
concentrations of substrates and products (direct or down- stream) of reactions determine their rate as does the activity of the relevant enzymes
What are the key hormones in regulating metabolism
Insulin
Glucose
Adrenaline and noradrenaline
What are the actions of these hormones mediated by
activation of intracellular protein kinases and phosphorylation of key regulatory proteins on tyrosine, serine or threonine residues – covalent modifications alter enzyme activities
is the majority of the pancreas’s function
exocrine function (digestive enzymes)
What factors drive the fed state
- Stimulates glycogen synthesis in liver and muscle
- Stimulates uptake of glucose into muscle and adipose tissue
- Stimulates glycolysis and hence fatty acid synthesis in liver
- Stimulates formation of triglycerides in fat tissue
- Stimulates protein synthesis in muscle
Actions of glucagon
alpha cells in the pancreas release it when glucose blood levels fall during the fasting stat e
what are its targets in the liver:
1. Stimulates release of glucose from glycogen
2. Stimulates gluconeogenesis but inhibits glucose incorporation into glycogen
Stimulates breakdown of triglycerides in fat tissue
What determines whether metabolism is in the fed or fasting state
the balance between circulating levels of insulin and glucagon
What secretes adrenaline and noradrenaline
the adrenal medulla and neurones of the sympathetic nervous system when blood glucose conc falls
what are the actions of adrenaline and noradrenaline
- they drive breakdown of glycogen and triglycerides
- their glycogenolytic action is mainly on muscle (producing glucose-6-P) rather than on liver
- The amines lower glucose uptake by muscle, so that fatty acids released by adipose tissue are used as fuel
- The amines also increase glucagon secretion and inhibit insulin secretion
what is blood glucose before and after a meal
80 mg/100 ml before
120 mg/100 ml after
what indicates hypoglycaemia
Lowered blood [glucose] (<3 mmol/litre)
What indicates hyperglycaemia
Elevated blood [glucose] (>11 mmol/litre)
How long can body fuel stores last
about 1-3 months of starvation, depending on level of physical activity
carb stores only a day or less (BG falls)
what is important to remember about triglycerides
have a limited ability to be converted to glucose
What happens during the first days of starvation
-Proteins potentially can yield glucose (gluconeogenesis), but these
need to be preserved as much as possible
- Muscle shifts from its use of glucose as a fuel to using fatty acids
released from adipose tissue (so sparing glucose for the brain)
- The liver uses fats mobilized from adipose tissue and pyruvate, lactate and alanine (from breakdown of protein) from muscle to make as much glucose as possible for export into the blood (for the brain)
What happens during the later days of starvation
After about 3 days large amounts of ketone bodies begin to be formed by the liver (as a consequence of breaking down fatty acids and limitations in the activity of the TCA cycle)
HOWEVER
Over the first few days of fasting the brain becomes more tolerant of lowered blood [glucose] and gains the ability to use ketone bodies to meet some of its fuel requirements.
- because the body uses less glucose, the need for amino acids to fuel gluconeogenesis is also reduced so there is a reduction in the rate at which muscle is broken down
What is the most common metabolic disease
Diabetes mellitus indicated by sugar in the urine
What are the two types of diabetes
Type 1 (insulin-dependent = juvenile onset) autoimmune where the beta cells of the pancreas are destroyed so little insulin can be secreted
Type 2 (non-insulin-dependent = insulin-resistant
= adult onset) associated lifestyle (little exercise, ready access to food and obesity), and there can be a genetic component
-Tissues are insensitive to the effects of insulin.
Effects of diabetes mellitus
- metabolism is largely similar to that seen during prolonged fasting
1. Glycolysis is slowed
2. Gluconeogenesis (new glucose) is stimulated (using amino acids produced by protein breakdown)
3. Fatty acids (from adipose tissue) are broken down and used to form ketone bodies
4. Newly formed glucose and ketone bodies pass into the blood
Why is diabetes associated with excessive urination
- In the glomeruli of the kidney glucose leaves the blood and passes into the urine along with ions and other relatively small molecules
- Normally
transporters in the proximal convoluted tubule reabsorb all the glucose and return it to the blood - In diabetes if the blood [glucose] rises beyond a certain level, the amount that passes into the kidney tubules is so great that the transporters cannot remove it all
- This glucose adds to the osmotic strength of the urine
- This makes it harder for the kidney to reabsorb water from the
urine - The result is that the urine volume is greatly increased
-It also explains why the urine of a diabetic contains glucose - In severe cases, acidic ketone bodies also appear in the urine (ketoacidosis) adding slightly to the osmotic strength.
-It also explains why the urine of a diabetic contains ketones
What damage can diabetes mellitus do long term if untreated
- Blood vessels (polyneuropathy)
- Eyes (Retinal blood vessels)
- Kidneys (urine infection; scarring and swelling in glomeruli leading to appearance of protein in the urine)
- Cardiovascular disease (largely a result of narrowing of blood vessels)
- Ketone bodies cause acidosis, which cannot be fully counteracted
As a result, an individual with uncontrolled diabetes can go into a coma as a result of low blood pH coupled with dehydration
