Hormones Flashcards
(26 cards)
Define hormone
A substance produced in minute amount at one site in a multicellular organism and transported to another site where it acts on target cells.
A chemical substance synthesised in small amounts by an endocrine tissue and carried in the blood to another tiddue, where it acts as a messenger to regulate the function of the tissue or organ
Define circulating hormones
Secreted to blood to target organ
Define autocrine hormones
hormones that bind to receptors on the same cell that secreted them
Define paracrine hormones
Hormones that bind to receptors on nearby cells
What is the endocrine system made of?
Hypothalamus Anterior pituatory posterior pituatory thymus gland pancreas (insulin, glucagon) pineal gland thyroid gland parathyroid glands adrenal glands gonads
What is hypoglycaemic?
Blood glucose is too low
Cause convulsions, coma
Mainly affects brain as it cannot metabolise fat
What is hyperglycaemic?
Blood glucose is too high
What is the normal blood glucose range?
3-5mM
What hormones maintain blood glucose levels?
Insulin and Glucagon
Called homeostasis
Outline how insulin works
Meal > Blood glucose rise > Insulin is released > return glucose levels to normal by glycogen storage and fat synthesis.
Outline how glucagon works
Fasting state > Glucagon released > promote release of glucose via breakdown of glycogen by liver.
Who discovered insulin?
1889, Oscar Monkowski
How does release of insulin affect skeletal muscles?
Increase: Glucose uptake, Glycogen synthesis
Decrease: Glycogen breakdown
How does release of insulin affect Fat cells?
Increase : Glucose uptake, Triacyglycerol synthesis
How does release of insulin affect liver?
Increase: Glycogen synthesis, FA synthesis
Decrease: Glucose release, glycogen breakdown
How does release of insulin affect the brain?
Stop eating
What does the islets of langerhands produce?
Insulin, Glucagon and somatostatins
Beta cells secret insulin
alpha cells secrete glucagon
delta cells secrete somatostatins
Outline insulin synthesis
Rough ER:
Preproinsulin > Proinsulin (Golgi) > Proteolytic cleavage > Insulin
What is the cleavage site of insulin?
Between A and F
How is preoproinsulin converted to proinsulin?
proteolytic cleavage of 23aa signal peptide
formation of 3 disulfide bonds
further cleavage removes the C peptide to produce mature insulin, composed of an A and B chain
When are GLUT2 transporters used?
For Beta-cells
When blood glucose rises
Glucose converted into G6P and enters glycolysis, TCA, and oxidative phosphorylation
This closes the ATP-gated K+ channels
Membrane depolarises, this opens voltage sensitive Ca2+ channels and Ca2+ floods in
The influx of Ca triggers fusion of the secretory granules with the plasma membrane and insulin release
How is insulin stored?
Secretory granules
Who sequenced insulin?
Fred Sanger
consists of 2 polypeptide chains, A, B. linked together by disufide bonds
What is the structure of insulin receptor?
2 units
alpha and B subunit linked by disulfide bond
a lie outside the cell, forming the binding site.
B has a transmembrane domain, and tyrosine kinase domain. Hence it phosphorylates tyrosine residues both itself and other proteins
