Brenda - Hormones and Metabolism Flashcards
What is the control centre for the endocrine system?
The hypothalamus
How does the endocrine system work?
(4)
Hypothalamus receives and integrates signals from the nervous system
The hypothalamus then releases regulatory hormones
These pass directly to the nearby pituitary gland
Anterior and posterior pituitary gland release hormones which regulate the endocrine tissue (amplification)
What are the two classifications of hormones?
Protein based hormones
Lipid based hormones
Where are the receptors for protein based hormones?
Receptors for these exist on plasma membranes
What are the receptors for lipid based hormone?
Receptors for these exist inside the cell
List the three classifications of hormones
Peptide hormones
Amino acid derivatives
Lipid derivatives
What are peptide hormones?
(3)
Relatively short
Defined amino acid chains
e.g. insulin and glucagon
What are amino acid derivative hormones?
Hormones derived from tyrosine
e.g. epinephrine, norepinephrine (catecholamines) and thyroxine and triiodothyronine (thyroid hormones)
What are lipid derivative hormones?
(2)
Steroid hormones derived from cholesterol
e.g. testosterone, oestradiol, progesterone, cortisol, aldosterone
What four hormones regulate glucose?
Insulin
Glucagon
Adrenaline
Cortisol
What does insulin do?
Signals that blood glucose levels are too high
What does glucagon do?
Signals that blood glucose levels are too low
What does adrenaline do?
Signals tissues that extreme bursts of activity are imminent
What does cortisol do?
Cortisol mediates the response to chronic stress
What is blood glucose maintained at?
4.5mM
What are the four pancreatic cells in the islets of Langerhans?
a cells
B cells
Delta cells
Gamma cells
What do alpha cells do?
Produce glucagon
What do beta cells do?
Produce insulin
What do delta cells do?
Produce somatostain
What do gamma cells do?
Produce a polypeptide with unknown function
Write a note on insulin synthesis
(3)
Insulin gene encodes preproinsulin (precursor of insulin)
During translation, the signal peptide is cleaved to form proinsulin
During packaging in granules by Golgi, proinsulin is cleaved into insulin and C peptide
How does glucose control the release of insulin from Beta cells?
(4)
Glucose concentrations in blood rise -> GLUT2 transports glucose into beta cells -> its converted into G6P and enters glycolysis
Aerobic oxidation of glucose causes an increase in intracellular ATP which closes ATP dependent potassium ion channels
The membrane becomes depolarised and causes calcium channels in the plasma and ER membranes to open
An influx of calcium induces release of insulin stored in granules by exocytosis
What does GLUT2 do?
GLUT2 transports glucose into beta cells
What does aerobic oxidation of glucose do?
(2)
Causes an increase in intracellular ATP
This closes ATP potassium ion channels
What happens when ATP potassium ion channels close?
(2)
The membrane becomes depolarised
This causes calcium channels in the plasma and ER membranes to open
What happens when the calcium channels open?
(2)
There is an influx of calcium
This induces release of insulin stored in granules
What is glucagon?
(2)
A 29 amino acid polypeptide hormone
Produced by alpha cells in the pancreas
What does glucagon promote?
(3)
Glycogenolysis
Gluconeogenesis
Release of glucose to the blood from the liver cells
What is glycogenolysis?
The breakdown of glycogen to glucose
What is gluconeogenesis?
Synthesis of glucose from lactic acid and noncarbohydrates
What are the two types of liver cells?
Kupffer cells (phagocytes)
Hepatocytes
What do hepatocytes do?
Transform dietary nutrients into fuels and precursors and export them
What do the hepatocytes do in a protein-rich diet?
Hepatocytes increase their synthesis of enzymes for amino acid catabolism and gluconeogenesis
What do hepatocytes do in a carbohydrate rich diet?
(2)
Levels of gluconeogenesis enzymes drop
Hepatocytes increase their synthesis of enzymes for carbohydrate synthesis and fat synthesis
How does insulin affect liver metabolism?
(7)
It stimulates the uptake of glucose by the muscle, liver and adipose tissue
In the liver it activates glycogen synthase and converts glucose into glycogen
Glucose is also broken down into acetyl coA
It activates enzymes responsible for converting glucose into pyruvate and pyruvate into acetyl-coA
If acetyl-CoA is not oxidised further via the TCA cycle it is used for fatty acid synthesis
Triacylglycerides are synthesised from these fatty acids in the liver and transported to muscle and adipose tissue by VLDL
Insulin also stimulates the conversion of fatty acids absorbed from the small intestine into triacylglycerides
What does insulin stimulate fatty acids to do?
Stimulates the conversion of fatty acids absorbed in the small intestine into triacylglycerides
What happens if the liver doesn’t oxidise acetyl-CoA?
It is used for fatty acid synthesis for muscle and adipose tissue
