Homeostasis Flashcards
What is homeostatsis
the maintenance of a constant internal environment
3 factors that affect homeostasis
Temperature
pH
blood glucose concentration
All examples of negative feedback
Why is low blood glucose bad
cell death as not enough glucose for respiration as involved in glycolysis
why is high blood glucose bad
blood water potential decreases, so water leaves cells by osmosis
Why is a low body temperature bad
not enough kinetic energy for enzyme substrate complexes to be formed
Why is a high body temperature bad
enzymes can denature so important enzyme controlled reactions cant occur
Why is a low pH or high pH bad
deviations in pH can cause enzymes to denature
Pathway of a negative feedback response
stimulus, receptor, CNS, effector, response
What is negative feedback
deviation from the optimum stimulates changes that result in a return the optimum
What is positive feedback and give an example
deviation from the optimum stimulates changes that result in an even bigger deviation from the optimum
contractions during labour, releases oxytocin, that results in even more contractions
What are factors that influence blood glucose concentration
Diet
exercise
insulin
glucagon
adrenaline levels
What is glycogenesis and when does it occur
excess glucose converted to glycogen by the LIVER
occurs when blood glucose is too high
What is glycogenolysis
breakdown of glycogen into glucose when blood glucose levels are too low
What is gluconeogenesis
glucose is created from non carbohydrate sources IN THE LIVER
for example amino acids and glycerol
occurs when glucose levels are still low despite glycogenolysis having occurred
What does insulin do and when is it secreted
It is secreted when Beta cells in the islets of Langerhans (in the pancreas) detect blood glucose levels that are too high
insulin attaches to receptors on target cells and changes the tertiary structure of channel proteins so more glucose is absorbed into the cells by facilitated diffusion
more protein carriers are incorporated into the membranes so even more glucose absorbed from the blood into the cells
Glycogenesis occurs
What does glucagon do and where is it produced
produced in the pancreas in response to low glucose levels
glucagon attaches to receptors on the surface of target cells
this stimulates adenylate cyclase to convert ATP into cyclic AMP (cAMP) which acts as a second messenger
cAMP activates an enzyme called protein kinase which hydrolyses glycogen to glucose
glucagon activates glycogenolysis and can also activate enzymes that are involved in gluconeogenesis
What is the second messenger molecule
a molecule that transmits signals inside of a cell when a molecule outside of the cell has bound to a receptor
What does adrenaline do in terms of blood glucose levels
Adrenaline attaches to receptors on the surface of target cells
this causes a G protein to be activated which converts ATP to cAMP
cAMP activates protein kinase which hydrolyses glycogen to glucose
so adrenaline stimulates glycogenolysis
What is type 1 diabetes and when does it start and what is the treatment
when the body is unable to produce insulin
starts in childhood
usually the result of an autoimmune disease in which beta cells are attacked by antibodies
main treatment is insulin injections
What is type 2 diabetes, when does it start and how should it be treated
receptors on target cells lose responsiveness to insulin
usually develops in adulthood due to obesity and poor diet
regulating carbohydrate consumption, increasing exercise
How is blood water potential controlled
osmoregulation
kidney (nephrons) and brain are involved
Structure of the nephron
cortex is top half
medulla is bottom half
renal
Structure of the nephron
cortex is top half
medulla is bottom half
renal artery brings blood to the kidneys
afferent arteriole takes blood to the glomerulus which is encased in the bowman’s capsule
proximal convoluted tubule which leads on to loop of Henle (descending and ascending limbs)
ascending limb leads to distal convoluted tubule and then to collecting duct then to the bladder
Steps of water reabsorption
ultrafiltration
selective reabsorption
loop of Henle
Distal Convoluted Tubule and collecting duct
What is ultrafiltration and where does it occur
occurs in glomerulus and Bowman’s capsule
blood enters kidneys via renal artery at HIGH PRESSURE
renal artery divides into afferent arteriole then glomerulus
water and soluble components are forced out of glomerulus down a pressure gradient and into Bowman’s capsule however proteins are left in the blood as are too large
this is called the GLOMERULAR FILTRATE
the pressure gradient is maintained as the efferent arteriole leaving the glomerulus being narrower than the afferent arteriole
What is selective reabsorption`
Glucose is reabsorbed by co transport from epithelial cells in proximal convoluted tubule to blood capillaries
this is carried out by actively transporting Na+, creating a low Na+ concentration in epithelial cells
Na+ moves in from the PCT lumen with glucose molecules by facilitated diffusion
glucose then diffuses into blood capillaries
What happens in the loop of Henle
Na+ actively transported out of the ascending limb, creating a low water potential in the interstitial space
the ascending limb is impermeable to water so water can only move out the descending limb by osmosis
water then enters the blood capillaries by osmosis as water potential in interstitial space is high
at the hairpin of the loop, Na+ ions naturally diffuse out as water potential is lowest here
What happens in the DCT and the collecting duct
Water moves out of DCT and collecting duct by osmosis
collecting duct runs parallel to loop of Henle, so ion concentration increases as you move down the medulla
So more water is reabsorbed into the blood by osmosis
What hormones alter the collecting ducts permeability
hypothalamus
posterior pituitary gland
anti diuretic hormone (ADH)
How can hormones alter the collecting ducts permeability
osmoreceptors in the hypothalamus detect blood water potential changes
when it falls, osmoreceptors shrink, causing release of ADH
ADH travels to posterior pituitary gland where its secreted into the blood
The blood travels to kidney and binds to receptors on the surface of collecting duct and activates the enzyme phosphorylase
this causes vesicles containing aquaporins to incorporate into the cell membrane
this increases water permeability and also urea permeability
urea and water leaves the collecting duct and is reabsorbed into the blood
