chapter 16-homeostasis Flashcards
homeostasis defintion
the maintenance of a constant internal environment within an organism
Importance of controlling pH and temperature
enzymes are sensitive to changes in pH and temperature so it is important that these factors are maintained in order for enzymes to function properly and not denature, to allow metabolic reactions to take place at a suitable rate
importance of controlling water potential
changes to water potential of the blood and tissues may cause cells to shrink or expand as a result of water entering or leaving by osmosis meaning cells cannot operate normally. Blood glucose concentration affects water potential
what is a feedback mechanism
a receptor responds to a stimulus created by the change brought about to the system by an effector
What happens when there is a fall in blood glucose concentration
1.stimulus detected by receptors on the cell surface membrane of alpha cells in the pancreas
2. alpha cells secrete glucagon which causes liver cells to convert glycogen to glucose which is released into the blood
3. blood glucose concentration increases
4. as blood circulates back into pancreas there is reduced stimulation of alpha cells
5. less glucagon secreted
What happens when there is a rise in blood glucose concentration
- stimulus detected by receptor on cell surface membrane of beta cells in the pancreas
- beta cells secrete insulin which increases the uptake of glucose by cells and its conversion to glycogen and fat
- blood glucose concentration decreases
- as blood circulates back into the pancreas there is reduced stimulation of beta cells
- less insulin secreted
benefit of separate negative feedback mechanisms
greater degree of homeostatic control
what happens when there is a rise in blood temperature
- stimulus detected by thermo receptors in hypothalumus
- more action potentials sent to heat loss centre
- more action potentials sent to skin
- vasodilation, sweating and lowering of body hairs leads to a fall in body temp
second messenger model-adrenaline
- adrenaline binds to a transmembrane protein receptor within the cell-surface membrane of a liver cell
- the binding of adrenaline causes the protein to change shape on the inside of the membrane
- this change of protein shape leads to the activation of adenyl cyclase which converts ATP to cyclic AMP
- the cAMP acts as a second messenger that binds to protein kinase enzyme changing its shape and therefore activating it
- protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cell by facilitated diffusion and into the blood through channel proteins
islets of langerhans
alpha cells- produce glucagon
beta cells- produce insulin
in the pancreas
glycogenesis
conversion of glucose into glycogen
occurs when blood glucose concentration is higher than usual
glycogenolysis
breakdown of glycogen to glucose
occurs when blood glucose concentration is too low
gluconeogenesis
production of glucose from other sources other than carbohydrate such as glycerol and amino acids
occurs when glycogen store is exhausted
importance of controlling blood glucose concentration
- glucose needed for respiration so if it falls too low cells will be deprived of energy and die
- if it rises too high it lowers the water potential causing osmotic activity that can cause dehydration
factors that influence blood glucose concentration
- directly from the diet in the form of glucose absorbed following the hydrolysis of carbohydrates
- from the hydrolysis in the liver of glycogen stored in liver and muscle cells (glycogenolysis)
- from gluconeogenesis
what happens when insulin binds with glycoprotein receptors
- a change in the tertiary structure of the glucose transport carrier proteins causing them to change shape and open allowing more glucose to diffuse into cells by FD
- causes vesicles containing proteins which glucose carrier proteins are made from to fuse with the cell-surface membrane. This increases the number of glucose transport channels
- activation of the enzymes that convert glucose to glycogen and fat
how does this lead to glucose blood concentration being lowered
- by increasing the rate of absorption of glucose into cells
- by increasing the respiratory rate of the cells which therefore uses up more glucose from the blood
- by increasing the rate of glycogenolysis in the cells of liver and muscles
type 1 diabetes
body is unable to produce insulin as a result of an autoimmune response
type 2 diabetes
glycoprotein receptors lose responsiveness to insulin or inadequate supply of insulin from pancreas
how is type 1 diabetes controlled
- injections of insulin- cannot be taken by mouth because it would be digested by the alimentary canal as it is a protein
how is type 2 diabetes controlled
- regulating the intake of carbohydrate in the diet and matching this to the amount of excersise
structure of the kidney
fibrous capsule- an outer membrane that protects the kidney
cortex- outer region made up of bowmans capsules, convoluted tubules and blood vessels
medulla- inner region made up of loops of henle, collecting ducts and blood vessels
renal pelvis- collects urine into the ureter
ureter- a tube that carries urine to the bladder
renal artery- supplies the kidney with blood from the heart via the aorta
renal vein- returns blood to the heart via the vena cava
structure of the nephron
bowman’s capsule- closed end at the start of the nephron which surrounds the glomerulus. inner layer made up of podocytes
proximal convoluted tubule- series of loops surrounded by blood capillaries. Walls made of epithelium with have microvilli
loop of henle- loop that extends from the cortex into the medulla of the kidney and back again. surrounded by capillaries
distal convoluted tubule- series of loops surrounded by fewer capillaries than proximal
collecting duct- a tube into which a number of distal covoluted tubules from a number of nephrons empty
how does ultrafiltration occur in glomerulus
- high hydrostatic pressure
- water and glucose pass out through small gaps in capillary endothelium and through capillary basement membrane
