Homeostasis Flashcards
What is homeostasis?
Maintainance of the internal environment of an organism within restricted limits, via physiological control systems.
What are the features of control systems?
Receptor - detects deviations from optimum
Coordinator - transfers information
Effector - carries out a response
What is negative feedback?
Negative feedback counteracts changes to restore a system to its original level.
What is positive feedback?
Positive feedback exaggerates a change, increasing deviation from the original level.
What happens if blood glucose concentration is too low or too high?
If it is too low, cells will not be able to respire and will die. If it is too high, the water potential of blood will decrease, and water will move out of cells via osmosis.
What factors affect blood glucose concentration?
Diet and exercise.
Where is adrenaline released and in response to what?
What are the groups of cells that detect changes in blood glucose concentration called?
Islets of Langerhans
What is the role of alpha and beta cells?
Alpha cells detect decreases in blood glucose concentration and produce glucagon.
Beta cells detect increases, and release insulin.
What are glycogenolysis, glycogenesis, and gluconeogenesis?
Glycogenolysis: conversion of glycogen to glucose.
Glycogenesis: conversion of glucose into glycogen.
Gluconeogenesis: conversion of glycerol and amino acids into glucose.
Describe the action of insulin.
Insulin binds to complementary receptors on the cell-surface membrane of cells throughout the body, causing vesicles to increase the number of glucose channel proteins in the membrane. This increases the amount of glucose that can enter the cell via facilitated diffusion, decreasing blood glucose concentration.
In liver cells, insulin activates enzymes that catalyse glycogenesis, further decreasing blood glucose concentration.
Describe the action of glucagon.
Glucagon binds to receptors on the cell-surface membrane of liver cells, and activates enzymes which catalyse glycogenolysis and gluconeogenesis. The glucose produced moves into the blood via facilitated diffusion, decreasing blood glucose concentration.
Where is adrenaline produced and released?
Adrenaline is produced in the adrenal glands in response to stress.
Describe the action of adrenaline.
The action of adrenaline involves the second messenger model. Adrenaline, the first messenger, binds to a complementary receptor on the cell-surface membrane of a liver cell, activating adenylate cyclase, which converts ATP into cyclic AMP. cAMP, the second messenger, binds to a protein kinase enzyme, and activates it, catalysing glycogenolysis. The glucose produced moves into the blood via facilitated diffusion.
