urine formation 2 Flashcards
what are the 3 basic processes of urine formation?
glomerular filtration
tubular secretion and tubular reabsorption.
what produces glomerular filtrate?
blood pressure forces water and most solutes in blood plasma towards walls of glomerular capillaries, producing glomerular filtrate.
what 3 pressure does glomerular filtration depend on?
1) glomerular blood hydrostatic pressure (HP)promotes filtration
2) capsular HP (opposes filtration),
3) blood colloidal osmotic pressure (BCOP), due to proteins in plasma (opposes)
does afferent or efferent arteriole have higher resistance and increases BP upstream in glomerulus?
Efferent arteriole.
where are mesangial cells positioned?
between capillaries.
mesangial cells (intraglomerular) do what?
decrease surface area of capillaries so glomerular filtration decreases.
what is globular filtration rate defined as (GFR)?
amount of filtrate formed in all renal corpuscles of both kidneys each minute. 105/125/min. female/male
150-180 L/ day of filtration but since 99% is returned to blood, how much is actually excreted?
1-2 litres.
what keeps GFR relatively constant by renal autneural and hormone regulation ?
Homeostasis.
What do severe blood loss and High blood pressure do to GFR?
Severe blood loss - decreases GFR
high blood pressure - doesn’t increase much
what does atrial natriuretic peptide (ANP) do?
It opposes the renin-angiotensin system.
Net filtration pressure =
Glomerular blood hydrostatic pressure - capsular HP- blood colloidal osmotic pressure.
Describe the chain that happens when glomerular capillaries become damaged/pereable
Plasma proteins enter glomerular filtrate, leads to
Decreased BCOPressure, leads to
H2O drawn out of blood, leads to
Increased Net FP, leads to
Decreased blood volume & increased interstitial fluid volume, leads to
Oedema
what happens during tubular reabsorption?
filtered fluid flows along the renal tubule and through the collecting duct.
Tubule and duct cells return 99% of filtered water and useful solutes to blood flow through peritubular capillaries.
How do tubule and duct cells return 99% of filtered water and solutes to blood flow?
through peritubular capillaries.
Tubular reabsorption goes through what process to reclaim back into blood?
selective process.
In tubular reabsorption, transport across membranes may be one of 3…
-Active 1 - uses ATP, Na+, bicarbonate ions (stabilises blood pH).
-Active 2- uses ion’s electrochemical gradient, glucose , AAs
-Passive, urea, lipid soluble non polar components, H2O
What does ‘transport maximum Tm’ do?
it reflects number of carriers available to transport substance (except Na+).
What happens during tubular secretion?
Tubule and duct cells remove substances from the blood in the peritubular capillaries and transports them into the fluid in the renal tubules, eg wastes, drugs (penicillin , morphine) and excess ions.
What is tubular secretion a backup for?
for the material not filtered out in the glomerulus.
There is hormonal regulation for what processes of urine formation?
tubular reabsorption and secretion.
how to determine the rate of urinary excretion of any solute.
rate of glomerular filtration - rate of reabsorption + rate of secretion.
which is excreted more, glucose or urea?
Urea.
if the filtration- reabsorption - secretion is disrupted , is it fatal?
Yes, you can die.
What controls production of dilute and concentrated urine?
antidiuretic hormone - ADH,also called vasopressin.
What is the Osm/kg of dilute and concentrated urine?
dilute urine - 65 Osm/kg
concentrated urine - 1200Osm/kg
extracellular urine - 300Osm/kg
What happens if antidiuretic hormone (ADH) is absent from urine production?
Urine will contain high ratio of water to solutes (dilute urine), as principal cells of collecting duct are impermeable to water.
What happens if antidiuretic hormone (ADH) is present in urine production?
water is reabsorbed back into blood (concentrated urine) due to osmotic gradient maintained by :
1) differences in solute & water permeability
2)countercurrent flow.
If too little water in blood, how does the body return to normal?
1) hypothalamus detects little water in blood
2) pituitary gland releases ADH
3) kidneys maintain blood water level
4) so less water is lost in urine (urine more concentrated)
5) blood water levels return to normal
