9.3 Flashcards
define homeostasis
the maintenance of a state of dynamic equilibrium through response of the body to internal and external stimuli
state the main homeostatic systems
control of heart rate
maintenance of pH
osmoregulation
thermoregulation
what is the equation for cardiac output
cardiac volume(dm^3) x heat rate (beats per min)
what is the average heart beat per minute and volume of blood per minute
70 times
4-6dm^3
how are fit people adapted to be good at exercise
they have a slower resting heartbeat and heart rate begins to increase when anticipating exercise
where is the cardiac control centre
medulla oblongata
where are baroreceptors found
sinuses in the carotid arteries and on the aorta
what are baroreceptors
mechanoreceptors that are sensitive to pressure changes
what are chemoreceptors
sensory nerve cells which respond to changes in CO2 levels in the blood
how do nerve impulses travelling down the sympathetic nerve from the cardiac center increase heartrate
release noradrenaline which stimulates the SAN which increases the frequency of signals from the pacemaker so the heart beats more quickly and the sympathetic nerve which passes into the ventricles increase the force of contraction
how do nerve impulses travelling down the parasympathetic nerve from the cardiac center decrease heartrate
release acetylcholine which inhibits SAN therefor slows down heart rate
what do baroreceptors do at rest
send a steady stream of signals back through sensory neurons to the cardiac center
what happens when exercise starts (involving baroreceptors)
blood vessels dilate (vasodilation) in response to adrenaline and blood pressure falls which reduces the stretch on the baroreceptors which reduces the stimulation from the baroreceptors to the cardiac control center which as a result sends signals along the sympathetic nerve to stimulate heart rate and increase blood pressure by vasoconstriction
how are baroreceptors involved in lowering blood pressure after exercise
when exercise stops blood pressure continues to increase so baroreceptors are stretched so send more impulses to the cardiac center which then sends impulses through the parasympathetic system to slow down heart rate and widen blood vessels in order to lower bloop pressure
where are chemoreceptors found
walls of aorta and carotid arteries
what happens when CO2 levels in the blood increase (involving chemoreceptors)
blood pH decreases and is detected by chemoreceptors
send impulses to cardiac center which increases impulses down the sympathetic nerve which increases heart rate, increasing blood flow to the lungs so more CO2 is removed
what happens when CO2 levels in the blood decrease (involving chemoreceptors)
blood pH rises and is detected by chemoreceptors which respond by reducing the number of impulses to the cardiac center which then reduces the number of impulses in the sympathetic nerve so heart rate returns to its intrinsic rhythm
where is adrenaline release from
adrenal medulla
what does adrenaline do
binds to receptors on target organs and SAN to increase frequency of excitation to increase heart rate
stimulates cardiac center to increase impulses to sympathetic neurons to increase heart rate
why is adrenaline needed to increase heart rate
to supply you with extra oxygen and glucose for the muscles and brain in case you need to fight or flight
define osmoregulation
the maintenance of a constant osmotic potential in the tissues of a living organism by controlling water and salt concentrations
what is deamination
the removal of the amino group from excess amino acids in the ornithine cycle in the liver which is then converted to ammonia then urea which can be excreted at the kidneys
what is the ornithine cycle
series of enzyme controlled reactions that convert ammonia from excess amino acids to urea in the liver
what are the main organs involved in osmoregulation
kidney and liver
where does deamination occur
the liver
what cells are involved in deamination
hepatocytes
summarise the ornithine cycle
ammonia, water and CO2 in
water and urea out
describe the kidneys
pair of dark reddish brown organs attached to the back of the abdominal cavity surrounded by a thick layer of fat involved in controlling the water potential of the blood that passes through them, removing substances that would affect the water balance
why are the kidneys surrounded by a thick layer of fat
to protect them from mechanical damage
what is the renal vein
carries blood away from the kidney after the removal of excess solutes and water
what is the renal artery
carries blood to the kidney
what is the ureter
carries urine from the kidney to the bladder
what is the urinary bladder
stores urine before micturition
what is the cortex of the kidney
rich capillary network making it a dark red colour containing Malpighian bodies of all the nephrons
what is the renal medulla
contains the loop of Henle from the nephrons
what is the pelvis of the kidney
the central chamber where urine arrives from the collecting duct
what is the juxtamedullary nephron
the long loop penetrates right through the medulla
what is the pyramid in kidneys
a collection of tubules, collecting ducts and blood vessels
what is the cortical nephron
loop which only just enters the medulla
what are the two main roles of the kidney
excretion (removal of urea)
osmoregulation
what is ultrafiltration
the process by which fluid is forced out of the capillaries in the glomerulus of the kidney into the kidney tubule through the epithelial walls of the capillary and the capsule
what is selective reabsorption
the process by which substances needed by the body are reabsorbed from the kidney tubules into the blood
what is tubular secretion
the process by which inorganic ions are secreted into or out of the kidney tubules as needed to maintain the osmotic balance of the blood
what are nephrons
microscopic tubules that make up most of the structure of the kidney
where are the cortical nephrons found
mainly in the renal cortex but they have a short loop of Henle which only just reaches into the medulla
where are juxtamedullary nephrons found
they have a long loop of Henle that penetrates right through the medulla
what is formed in ultrafiltration
tissue fluid
what do the bowmans capsule and glomerulus make up
Malpighian body
what material cannot pass through the pores in the glomerulus capillaries
blood cells and large plasma proteins
what is the bowmans capsule made up of and how are they adapted to their function
podocytes
they have extensions called pedicels that wrap around the capillaries forming slits that ensure any cells, platelets or large plasma proteins that have left the capillary do not get into the tubule
how does ultrafiltration work
high bp in the glomerulus capillaries because the diameter of the blood vessels coming into the glomerulus are larger than the blood vessels leaving
this high pressure squeezes blood out through pores in the capillary wall
bowmans capsule contains pedicels that ensure any cells, platelets or large plasma proteins do not enter the tubules
filtrate then enters the capsule containing the same concentration of substances as the blood plasma
does ultrafiltration require energy
no
what is removed from the blood in ultrafiltration
urea, water, glucose, salt, other substances
what is the proximal convoluted tubule
the first region of the nephron after the Bowmans capsule where over 80% of the glomerular filtrate is absorbed back into the blood
what adaptations does the proximal convoluted tubule have
covered in microvilli to increase surface area for reabsorption
lots of mitochondria for active transport of substances out of the nephron back into the blood
what is moved out of the nephron in selective reabsorption
glucose, vitamins, hormones, 85% of water and NaCl
how does selective reabsorption work
glucose, vitamins and 85% of Na+ are moved out of the tubule by active transport
water and Cl- moves out of the tubule passively into the intracellular spaces which then pass by diffusion into the extensive capillary network
the blood is constantly moving which maintains the concentration gradient
an isotonic solution with the tissue fluid is made in the tubule when it reaches the loop of henle
what is a countercurrent multiplier
a system that produces a concentration gradient in a living organism using energy from cellular respiration
what is the permeability of the descending limb
freely permeable to water but not permeable to sodium and chlorine
does active transport occur in the descending limb
no
what happens in the descending limb
water moves out of the descending limb via osmosis and into the blood because there is a low osmotic potential in the medulla as theres a high concentration of Na+ and Cl- ions when it reaches the hairpin the loop is very concentrated and hypertonic to the arterial blood
what is the permeability of the first section of the ascending limb
very permeable to Na+ and Cl-
not permeable to water
what happens in the ascending limb
first thin ascending limb, Na+ and Cl- move out of the tissue fluid into the medulla down the concentration gradient
second thicker ascending limb Na+ and Cl- are actively pumped out giving a high concentration of Na+ and Cl- in the medulla for the descending limb
water cannot move out of the ascending limb so fluid becomes less concentrated
what affects permeability of the distal convoluted tubule
ADH
what is the distal convoluted tubule
the section of the nephron after the loop of henle that leads into the collecting duct where balancing water needs of the body takes place
what is ADH
hormone produced in the hypothalamus stored in the posterior pituitary which increases permeability of the distal convoluted tubule and the collecting duct to water
what happens in the distal convoluted tubule if theres not enough salt in the body
sodium is actively transported out of the tubule and chlorine ions follow
water also moves out by osmosis if walls are permeable to water
what is the collecting duct
takes urine from the distal convoluted tubule to be collected in the pelvis of the kidney, the region of the kidney where most water balancing needed for osmoregulation occurs
how do kangaroo rats survive without drinking water
they produce water by oxidative reactions in their cells
how are desert animals adapted to reduce water lost in urine
large proportion of juxtamedullary nephrons
long loops of henle - long thin descending loop so more water is reabsorbed into the blood
more infoldings in the cell membranes of epithelial cells lining the tubules which increases surface area for a steeper concentration gradient to increase water reabsorbed
lots of mitochondria with densely arranged cristae to maximise cellular respiration for active transport of ions in or out of tubules
how does ADH work
binds to receptors on the membrane of tubule cells triggering reactions to form cAMP that acts as a second messenger to cause vesicles (containing water channels) within the cell lining to be inserted into the membrane making it permeable to water
what happens to the water channels when ADH levels decrease
levels of cAMP fall and water channels are withdrawn from the membrane and repackaged in vesicles making it impermeable to water
what could cause the blood to become more concentrated (decrease in water potential)
water shortage, sweating, salty food
what could cause blood to become less concentrated (increase water potential)
water loading
what happens when the blood becomes more concentrated (decrease in water potential)
detected by osmoreceptors in the hypothalamus
more ADH released from posterior pituitary
second convoluted tubule and collecting duct become more permeable to water
water potential restored back to normal
what happens when the blood becomes less concentrated (increase in water potential)
detected by osmoreceptors in the hypothalamus
less ADH released from posterior pituitary
second convoluted tubule and collecting duct become less permeable to water
water potential restored to normal
what type of feedback system does ADH have
negative feedback loop
what are osmoreceptors
sensory receptors in the hypothalamus that detect a change in the concentration of inorganic ions and therefor changes in osmotic potential of the blood
how does an increase in blood pressure affect the release of ADH
increase in blood pressure detected by baroreceptors in aortic and carotid arteries
resulting in less ADH being released from the posterior pituitary therefor second convoluted tubule and collecting duct are less permeable to water so increased volume of water lost in urine to reduce blood volume and pressure
