lecture 7: urinary system (excretory system) Flashcards
why are kidneys important
maintain homeostasis
how many functions of the excretory system are there
5
name all 5 functions of excretory system
excretion
osmoregulation
produces erythropoietin
produces renin
activates vitamin D
describe excretion (functions of excretory system)
removal of nitrogenous waste products (urea)
describe osmoregulation (functions of excretory system)
regulating solute and water balance
maintains osmotic pressure
describe produces erythropoietin (functions of excretory system)
production of rbcs
describe produces renin (functions of excretory system)
enzyme that regulates blood pressure by activating angiotensin
which functions of excretory system regulate blood pressure
osmoregulation
produce renin
what is urea
nitrogenous waste
describe urea
made in liver by combining NH3 with CO2
~ 100 000x less toxic than ammonia
can be transported and stored at high concentrations
has a large impact on water balance (osmoregulation)
describe body’s strategy for osmoregulation
kidneys —> regulate composition of blood —> regulate composition of ISF —> regulate composition of cells
describe anatomy of urinary system
pathway of urine
kidneys —> ureters —> urinary bladder —> urethra
describe urinary bladder
stores urine
rugae for stretching
internal urethral sphincter (involuntary)
external urethral sphincter (voluntary)
describe kidneys
2 distinct regions =
outer renal cortex
inner renal medulla
contain nephrons and associated blood vessels
describe blood supply to kidneys
enters via renal artery and leaves via renal vein
20% of resting cardiac output passed through kidneys every minute
entire plasma volume is filtered 60 times per day
what are kidneys filled with
nephrons and collecting ducts are lined by transport epithelium that is specialized to reabsorb water and solutes to control composition of urine
what is a nephron
functional unit of kidney
how many nephrons does a kidney contain
around 1 million
name the 2 parts of a nephron
renal corpuscle
renal tubule
describe renal corpuscle
bowman’s capsule (nephron)
glomerular capillaries - glomerulus (stuck to nephron)
describe renal tubule
proximal convoluted tubule
nephron loop (loop of henle)
distal convoluted tubule
name the 3 processes of formation of urine
glomerular filtration
tubular reabsorption
tubular secretion
describe glomerular filtration (gen)
fluid is pushed out of glomerular capillaries into bowman’s capsule
mostly non selective (only depends on size)
describe tubular reabsorption
H2O and valuable solutes (glucose, amino acids, some salts) are reabsorbed back into blood
much more selective
describe tubular secretion
some solutes are selectively pumped by active transport into the nephron (some salts, H+, drugs)
describe collecting ducts
where fluid from nephron drains into
extend into medulla and drain into the renal pelvis (which drains into ureter)
describe pathway of blood supply of nephron
heart —> renal artery —> afferent arteriole —> glomerular capillaries —> efferent arteriole —> peritubular capillaries (proximal and distal) —> renal vein OR vasa recta (capillaries, loop of henle) THEN renal vein —> heart
describe exchange path (blood supply of nephrons)
via interstitial fluid
blood <—> ISF <—> nephron
when kidneys fail describe what to do (step before transplant)
dialysis
several times per week
blood flows out of body and is filtered by external device
you won’t pee
must be very aware about liquid composition
describe filtration (physical description)
specialized octopus like cells called podocytes form inner layer of bowman’s capsule and wrap around glomerular capillaries
spaces between foot-processes of podocytes are called filtration slits
describe filtration (specifics of how it works)
flow driven by high hydrostatic pressure (blood pressure) in glomerular capillaries
filtration slits act like a sieve that allow the passage of anything below a certain size
what is the composition of filtrate
same as blood except no blood cells or proteins
what is filtrate
water
salts
sugars
amino acids
nitrogenous waste
why is blood pressure high in glomerular capillaries
because the efferent arteriole has a smaller diameter than the afferent arteriole
what is reabsorbed from filtrate
99% of water
most of glucose, amino acids and vitamins
what is initial and final volumes (urinary system)
initial filtrate volume = 180L
final urine volume = 1.5L
describe what is reabsorbed in proximal tubule
NaCl and water
90% of bicarbonate (HCO3-): controls pH
nutrients (glucose, amino acids, etc)
K+
describe what is secreted in proximal tubule
some drugs and NH3 enter tubules from peritubular capillaries via ISF
H+ (helps control pH)
describe loop of henle (descending limb)
transport epithelium is permeable to H2O but NOT pet able to NaCl or other solutes
reabsorbs water
filtrate becomes more concentrated
describe loop of henle (ascending limb)
transport epithelium is NOT permeable to H2O but is permeable to NaCl
NaCl is reabsorbed
filtrate becomes more dilute
what can’t pass through the filtration slits
blood cells and proteins are too large
describe the reabsorption of NaCl and water in proximal tube
Na+ is actively transported out of tubule and positive charge is balance by transport of Cl-
water follows by osmosis
65% of volume is reabsorbed
describe the reabsorption of NaCl in the loop of henle (ascending limb)
as filtrate moves up the thin segment NaCl passively diffuses into ISF
in thick segment NaCl is actively transported into the ISF
what is reabsorbed in distal tubule
NaCl (actively pumped out to regulate levels in body)
water (reabsorbed passively by osmosis)
HCO3- (controls pH)
what is secreted in distal tubule
K+ (regulates k+ levels)
H+ (helps control pH)
describe collecting duct
transport epithelium is permeable to
water
region in inner medulla is also permeable to urea
what is reabsorbed in collecting duct
NaCl (actively transported across epithelium to regulate levels in body)
water (passively by osmosis, driven by NaCl and urea gradient)
describe filtrate in collecting duct
filtrate becomes more concentrated as it moves down collecting duct
allows kidneys to excrete hyperosmotic urine and conserve water
what is osmolarity
concentration of solutes
mOsm/L
for blood = 300mOsm/L
why is osmolarity of urine max 1200mOsm/L
limited by max concentration of surrounding kidney tissues
max concentration of solutes in inner medulla is 1200mOsm due to NaCl and urea
name 2 types of nephrons
juxtamedullary nephrons
cortical nephrons
describe juxtamedullary nephrons
20% of nephrons
loop of henle is long and extends deep into medulla
can create steep osmotic gradient in kidney to produce urine that is hyperosmotic to the body
name and briefly describe the 3 steps/parts to creating concentrated urine
i - countercurrent multiplier: creates osmotic gradient
ii - countercurrent exchange: preserves osmotic gradient
iii - collecting ducts: adjusts urine osmolarity
describe countercurrent multiplier
loop of henle
ascending and descending limbs
flow of fluid multiples power of NaCl pumps (pumps out more NaCl)
describe countercurrent multiplier (loop of henle - ascending limb)
NaCl is pumped out to create osmotic gradient in kidney
filtrate becomes less concentrated as it moves up
describe countercurrent multiplier (loop of henle - descending limb)
osmotic gradient causes water to leave the filtrate by osmosis
filtrate becomes more concentrated as it moves down
describe countercurrent exchange
vasa recta - highly permeable to water and solutes
blood flow is very slow to allow enough time for exchange to occur between blood and ISF
blood can deliver nutrients and reabsorb water/solutes without disrupting osmotic gradient in kidney
explain countercurrent exchange (exchange between blood and ISF)
allows blood to remain isosmotic to ISF
most solutes that move into the blood (as flows downwards) move back out (as flow upwards)
describe collecting ducts (creating concentrated urine)
adjust osmolarity of urine
nephrons use energy to produce an osmotic gradient in the kidney
NaCl and urea are the primary solutes that create the gradient
nephrons using energy to produce osmotic gradient in kidney allows what
allows max amount of water to be extracted from urine as it passes through collecting duct
describe hormonal control of urine production (gen)
composition of urine can be modified based on needs of body
hormones control the osmolarity, salt concentration, volume and hydrostatic pressure of blood
name all the hormones that control urine production (4)
ADH (antidiuretic hormone)
angiotensin II (RAAS)
aldosterone (RAAS)
ANF (atrial natriuretic factor)
name the hormones that cause water retention
ADH
angiotensin II
aldosterone
name the hormones that cause water loss
ANF
describe ADH (site of production, target and effect)
s - hypothalamus (stores/released by pituitary gland)
t - epithelium of distal tubule and collecting duct
e - increase permeability to H2O (increase reabsorption)
name the stimuli that could cause hormone to change something about the urine
changes in blood pressure
changes in blood osmolarity
describe angiotensin II (site of production, target and effect)
s - liver (activated by renin, a kidney enzyme)
t - arterioles, proximal tubule, adrenal glands
e - vasoconstriction, increase NaCl reabsorption (H2O follows), aldosterone production
describe aldosterone (site of production, target and effect)
s - adrenal glands
t - distal tubules
e - increase NaCl reabsorption (H2O follows)
describe ANF (site of production, target and effect)
s - walls of atria
t - kidney, collecting ducts, adrenal glands
e - inhibits renin release, inhibits NaCl reabsorption, inhibits aldosterone release
describe ADH
osmoreceptors in hypothalamus are stimulated when blood rises above 300mOsm/L (set point)
causes more ADH to be released into blood
ADH increases H2O reabsorption at distal tubule and collecting duct to decrease urine volume
what can bring osmolarity back to set point
ONLY intake of water can bring osmolarity back to set point
ADH only prevents further increase above set point
ADH is an example of what type of feedback
negative
how does ADH work
increases H2O reabsorption by incresing number of aquaporins in collecting duct epithelium
aquaporins are integral membrane proteins that allow passage of water by facilitated diffusion
what does RAAS stand for
renin-angiotensin-aldosterone system
describe RAAS (3 steps/statements)
i - renin is an enzyme that initiates chemical reactions to convert angiotensin into angiotensin II
ii - angiotensin II is a hormone that increases blood volume and pressure
iii - aldosterone is a hormone that is released by adrenal gland (stimulated by angiotensin II)
describe angiotensin II
drop in blood pressure triggers release of renin in JGA
angiotensin II increases blood volume and pressure
how does angiotensin II increase blood volume and pressure
vasoconstriction of arterioles
increase NaCl reabsorption (H2O follows) in proximal tubule
stimulating release of aldosterone
what does JGA stand for
juxtaglomerular apparatus (in kidney)
describe aldosterone
increase NaCl reabsorption (H2O follows) in distal tubules
released from adrenal glands (endocrine glands on top of kidneys)
describe ANF
released by walls of atria in response to high blood volume and pressure
opposes the RAAS mechanism to lower blood pressure and volume
what does ANF inhibit
renin release
aldosterone release
reabsorption of NaCl in collecting ducts
what effect does alcohol have on urine
alcohol inhibits ADH (ADH - lowers urine production) so alcohol increases urine production
excessive water loss or inadequate intake of water causes dehydration
stimuli = increases osmolarity and decreases blood pressure
response = ADH & RAAS
excessive loss of body fluids (water and salts) due to blood loss or diarrhea
stimuli = decreases blood pressure
response = RAAS
