Flashcards in Hormones Controlling Plasma Nutrients Deck (28):
What is insulin and glucagons role in the post-absorptive state?
Storage of nutrients after absorption
The maintenance of plasma nutrient concentrations
What are the physiological aspects of calorie buffering?
Short term stores (glucose, glycogen) osmotically active
Longer term stores (lipids) are osmotically inert
Lipid is a high calorie density (ideal) storage form
What is the role of insulin and glucagon hormones?
Fat deposition/mobilisation in the short term
Insulin causes storage of glucose and fats
Glucose conversation for brain function in extreme conditions- glucagon mobilises fats and provides glucose
What are the actions of insulin
Lowers blood glucose concentrations
Stimulates amino acid incorporation into proteins in muscle and into fatty acids in the liver
Increased glucose and amino acid in the liver conversion to fatty acids then lipoproteins which exit to blood
Increased glucose oxidation to fatty acids in the adipocytes, stored as triglycerides, with lipolysis prevented
What does insulin lower blood glucose for?
Facilitating glucose diffusion into skeletal muscle, liver cells, adipocytes, but NOT brain (always able to obtain glucose)
Reducing hepatic glucose output by:
- Stimulating glycogen synthesis
- Inhibiting glycogenolysis
How do liver and dietary lipoproteins enter adipocytes?
Through lipoprotein lipase action
What are the net results of action of insulin?
Fatty acids incorporated into long term (adipocyte) store
Glucose becomes liver/ muscle glycogen or adipocyte fat
Amino acids incorporated into skeletal muscle or liver protein or become liver fatty acids
How is insulin secretion controlled?
Increase in plasma glucose increases insulin secretion. Beta cells of pancreatic islets assumed to have a glucose receptor. Surge of calcium ion into cells stimulates insulin release. On prolonged fasting, insulin levels negligible
Oral glucose has an insulinotrophic effect via GIP
A rise in plasma amino acids increases release
Increased sympathetic activity inhibits release
Increased parasympathetic activity increases release
Delta cell somatostatin inhibits release
Increasing glucagon levels stimulate release
Ketone bodies from liver produced by prolonged fasting stimulate insulin release
What is the physiological control of glucagon secretion?
Decrease in blood glucose stimulates glucagon release
Insulin inhibits glucagon release
Increased plasma amino acid concentrations increase glucagon release
NB increased plasma amino acids also enhance insulin release. Glucagon is also released to counteract hypoglycaemia during amino acid uptake by muscle
Amino acids in the intestinal lumen cause CCK release which increases glucagon release
Increased sympathetic activity stimulates release of glucagon as does an increase in plasma adrenalin
What effect does adrenaline have on sympathetic stimulation?
Glycogen breakdown to lactate in skeletal muscle with export to liver
Liver gluconeogensis (also from muscle lactate)
Directly inhibits insulin release
Directly increases glucagon release
What is the action of cortisol on plasma nutrients?
Peripheral insulin antagonist
Has a permissive effect: plasma levels do not normally rise except under physiological stress e.g. broken limb
Permissive effect on liver gluconeogenesis and adipocyte lipolysis enzymes
What does the action of cortisol on plasma nutrients permit?
The rise in plasma glucose and fatty acids caused by other hormones
What does anterior pituitary hormones do?
Increases adipocyte sensitivity to lipolytic agents e.g. adrenaline
Increases liver gluconeogenesis
Reduces insulin stimulated facilitated diffusion of glucose into cells
What does anterior pituitary hormone increase?
Plasma glucose and fatty acids concentrations
What does low blood glucose (hypoglycemia) stimulate?
Secretion of glucagon from alpha cells of the pancreatic islets
What does glucagon act on?
Hepatocytes (liver cells)
What happens when glucagon acts on liver cells?
Accelerates the conversion of glycogen into glucose (glycogenolysis) and to promote formation of glucose from lactic acid and certain amino acids (gluconeogenesis)
What happens as a result of glucagon acts on hepatocytes?
Release glucose into the blood more rapidly, and blood glucose level rises
What happens if blood glucose continues to rise?
High blood glucose level (hyperglycemia) inhibits release of glucagon (negative feedback)
What does high blood glucose (hyperglycemia) stimulate?
Inhibits release of glucagon (negative feedback)
What does insulin act on the body to facilitate?
To accelerate diffusion of glucose into cells
To speed conversion of glucose into glycogen (glycogenesis)
To increase uptake of amino acids by cells
To increase protein synthesis
To speed synthesis of fatty acids (lipogenesis)
Slow the conversion of glycogen to glucose
Slow the formation of glucose from lactic acid and amino acids (gluconeogenesis)
What happens as a result of insulin acting on the body?
Blood glucose level falls
What happens if blood glucose level drops below normal?
Low blood glucose inhibits release of insulin (negative feedback) and stimulates release of glucagon
What are the four cell types in the pancreatic islets?
What do Alpha cells secrete?
What do Beta cells secrete?
What do Delta cells secrete?