Homeostasis Flashcards
What is homeostasis
Homeostasis is the maintenance of a stable/constant internal environment
Control mechanism
Receptor detects any deviation from the set point and informs the controller
Controller usually the brain coordinates information from various receptors and sends instruction to an appropriate effector
Effector brings about the changes needed to return the system to the set point
This creates a feedback loop
Negative feedback
Means that when there is an increase/decrease from the set point the opposite effect is instigated and produces a response that returns the value back to the norm
Positive feedback
Occurs when a deviation from an optimum causes even greater deviation from the normal
Eg birth contractions
Thermoregulation and ph
If body temp is too low enzyme controlled reactions take place too slowly
If body temp is too high enzymes could be denatured
If blood ph deviates from optimum enzymes may become denatured
Endotherms- maintain body temp by both physiological and behavioural means
(Mammals, birds and some fish)
Ectotherms-maintain body temp by behavioural means only
(Reptiles, amphibians and most fish)
Low and high levels of blood glucose
Hypoglycaemia-very low levels of blood glucose
Hyperglycaemia- very high levels of blood glucose - impacts cells of the nervous system more frequently
Insulin
Insulin binds to complimentary receptors on cell surface membrane of target cells
Controls the uptake of glucose by regulating the addition of glucose carrier proteins in the surface membrane of target cells
Insulin also activates enzymes that stimulate the conversion of glucose to glycogen so decreases blood glucose
Secreted by beta cells
Glucagon
Glucagon binds to receptors on the cell surface membrane of target cells
Activates enzymes involved in the hydrolysis of glycogen to glucose
Activates enzymes involved in the conversion of glycerol and amino acids into glucose
Increases blood glucose levels and secreted by alpha cells
Second messenger model
(Adrenaline and glucagon)
Adrenaline and glucagon both bind to transmembrane protein receptors on the surface of the target cell membrane - first messenger
Hormone receptor complex is formed to change tertiary structure
The hormone receptor complex activates adenylate cyclase and results in the conversion of atp to cyclic amp - second messenger
Second messenger causes a series of chemical reactions that produce the required rapid response
cAMP is the second messenger and activates protein kinase enzymes which produce a cascade of chain of reactions that catalyse the conversion of glycogen to glucose
Role of glucagon
Hormone that catalyses hydrolysis of glycogen to glucose
Role of glycogen
Energy storage carbohydrate found in liver and muscles
Glycogenolysis
Glycogen hydrolysed to glucose
Glycogenesis
Glucose to glycogen
Gluconeogenesis
Glucose from amino acids and glycerol
Type 1 diabetes
Insulin dependant disease
Severe insulin deficiency due to autoimmune killing of beta cells