BCH Hormone Regulation of Carbohydrates Flashcards
Metabolism of carbohydrates is regulated by_________
Insulin and glucagon
Action of insulin
decrease plasma levels of glucose by promoting glucose uptake by tissue following an increase in plasma levels of glucose
Action of glucagon and other anti-insulin hormones
Name the other hormones
increases plasma levels of glucose
Hormones are: epinephrine, glucocorticoids, ACTH etc
Plasma insulin/glycogen ratio is delicately maintained for glucose homeostasis
Major organs dominant in CHO metabolism
liver
adipose tissue
muscle
brain
Function of major organs dominant in CHO and how they work together
These tissues contain sets of enzymes such that each organ is specialized for:
1. storage
2. use
3. and generation of specific fuels
These tissues act in concert with a coordinated network in which one tissue may provide a substitute for another or process compounds produced by the other
Hormone supporting insulin and glucagon (an its functions)
catecholamines
changes in plasma levels of this hormone make the body store energy or make energy available as the case arises
Chains of insulin are joined by________
intermolecular disulfide bonds at A7,B7 and A20, B19
There is also an intramolecular disulfide bond on A chain at 6th and 11th
Discuss Insulin
It is an anabolic hormone of the well-fed state and it is an important signal to stimulate the storage of excess nutrients such as glycogen and triglycerides
It is a polypeptide molecule of 51 arranged in 2 chains ( a and b)
Chain A has 21 aa
Chain B has 30 aa residues
Communication between tissues is mediated by________
- nervous signals
- variation in the hormonal level or
- availability of substitutes
Insulin is produced by what?
β cells of islets on langherhans of the pancreas
How does insulin mature?
In a cascade of cleavage from pre-proinsulin or proinsulin and finally insulin in response to increased blood glucose
Regulation of insulin and glucagon secretion to maintain glucose homeostasis
The amount of Insulin and Glucagon released by the pancreas are regulated so that hepatic glucose production is kept equal to the used glucose by peripheral tissues to maintain a delicate balance in the ins-glu ratio to maintain glucose homeostasis
insulin secretion is increased by
- glucose or carbohydrate
- amino acid
- certain GIT hormones e.g. CCK
insulin secretion is decreased/inhibited by
when there is a scarcity of dietary fuel, or a period of stress
Metabolic effects of insulin on carb metabolism
mainly promotes storage
Insulin is prominent in 3 tissues
liver
muscle
adipose tissue
the brain and RBC have no insulin receptors hence no insulin action is in them
action of liver and muscle
increase glycogenesis (glycogen synthesis)
decrease glycogenolysis
decrease gluconeogenesis
action of adipose and muscle
increase glucose uptake
Mechanism of action of insulin
Insulin binds to specific high affinity receptors in the cell membrane of most tissues including:
liver
muscle and
adipose, causing a cascade of reactions leading to its biological effects. Such reactions include:
Receptor recruitmen
signal transduction
dephosphorylation of enzymes etc
What is the hormone of the fasting state
Glucagon
Discuss glucagon
It is a polypeptide molecule of 29 aa arranged in a single chain of insulin. Glucagon is a catabolic hormone produced by alpha cells of the pancreatic Islets of langerhans in response to decrease plasma levels of glucose. It works in concert with the cathecols and corticosteroid to antagonize on the target tissues
Regulation of glucagon secretion
Glycogen responds to stimuli that signal actual or potential hyperglycemia
A decrease in plasma glucose Is the primary stimulus for glucagon release
A protein meal also stimulates glucagon release just as it has a counterforce to prevent hypoglycemia that may accompany increase insulin release
Paradoxically, in periods of stress, elevated levels of calthecoloamines also stimulates the production of glucagon in anticipation of increased utilization of glucose
Glycogen secretion is inhibited by
high levels of glucose and by insulin
