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
Diabetes type 2
Non insulin dependant disease
Insulin is produced but the insulin receptors in the target cells are unresponsive so insulin has no effect
Symptoms of diabetes
High thirst
Large volume of urine production
Poor vision
Osmoregulation
Osmoreceptor cells in the hypothalamus of the brain detect fall in water potential
ADH secreted into capillaries by posterior pituitary gland
ADH travels to kidneys in blood and increases the permeability of the cells of the distal convoluted tubule and collecting duct to water
ADH causes vesicles bound with aquaporin proteins to fuse with the cell surface membrane of cells of the distal convoluted tubule and collecting duct
1-formation of glomerular filtrate
Produced by ultrafiltration
Blood in the glomerulus is under high hydrostatic pressure because the afferent arteriole is wider than the efferent arteriole
Forces water and small substances such as glucose ions and urea through the pores in capillary endothelium and through the basement membrane into the bowman’s capsule
2 selective reabsorption
Where all of the glucose, some water and some ions get reabsorbed into the blood stream
Na+ are actively transported out of epithelial cells lining the proximal convoluted into the blood
Lowers the sodium ion concentration in the cells
Sodium ions move from the lumen of the proximal convoluted tubule into the cells taking glucose either them via co transport
The glucose concentration increases inside the cell and glucose moves via facilitated diffusion in the blood
3- control of blood water potential
The loop of henle acts as a counter current multiplier
Na+ actively transported out of the ascending limb of the loop of henle into the surrounding medulla
Ascending limb is impermeable to water
This decreases the water potential of the medulla
Water moves out of the filtrate in the descending limb and the collecting duct by osmosis into the medulla
Water reabsorbed into the blood via capillaries
Animals that live in dry environments
Have a thicker medulla and longer loop of henle
4-reabsorption of water by the distal convoluted tubule and the collecting ducts
Distal convoluted tubule makes final adjustments, reabsorbs water and salts and changes permeability of wall
Collecting duct lowers water potential further down the medulla
Water moves out of the collecting duct via osmosis
Water then reabsorbed into the blood
Everything left in the collecting duct becomes urine
Permeability can change
