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*LSS Urinary Y1* > Flow and filtration > Flashcards

Flashcards in Flow and filtration Deck (39):

What proportion of CO goes to the kidneys?

Receives 20-25% CO in order to generate high pressure for ultrafiltration - achieved with direct aortic branching


What is the filtration fraction?

Ratio of renal plasma flow to amount of filtrate filtered by the glomerulus - normally 0.2 


What is normal Renal Blood Flow (RBF)?

approx. 1L/min


What is normal Renal Plasma Flow (RPF)?

approx. 0.6L min-1 (renal blood flow * (1-haematocrit))


What is the equation for Glomerular filtration rate?



Describe the process of Glomerular Filtration:

Passively occurs as fluid driven through semipermeable walls of glomerular capillaries into Bowman's capsule by cardiac hydrostatic pressures 


What is the filtration barrier?

Fenestrated capillary endothelia and semipermeable Bowman's capsule highly permeable to fluids and small solutes but not cells, proteins and drugs carried by proteins 


What is "freely filtered?"

Solute found at same conc in blood and filtrate


What is Primary urine?

Clear ultrafiltrate fluid free from blood and proteins


What is the glomerular filtration rate?

Amount of fluid filtered from the glomeruli into the Bowman's capsule per unit time (ml/min) - sum of rate of all functioning nephrons (loss of nephrons = \/ Kf = \/ GFR)


What is Kf?

Ultrafiltration coefficient and represents membrane permeability and surface area available for filtration - if changed then creates GFR imbalance, and kidney disease may reduce number of glomeruli and hence surface area and Kf


What is a normal GFR?



What will be the effect of drugs or hormones that dilate glomerular arterioles on Kf and hence GFR?

Increase Kf
Increase GFR


What does myogenic auto-regulation in glomerular arterioles allow?

Constant GFR;
VSMCs contract when smooth muscle stretched, so when afferent arterial pressures rise, vessel resistance does too, reducing the blood flow to keep the GFR constant


Describe four events that effect GFR:

Severe haemorrhage: decreases Pgc so will decrease GFR

Nephron tubule obstruction: increases Pt/decreases Kf so decreases GFR

Reduced [plasma proteins]: decreases πgc so increases GFR

Small BP increase: no effect due to myogenic autoregulation


What is the role of GFR in renal diagnostics?

Fall in GFR is cardinal feature of renal disease, and excretory proteins will build up in plasma; raised plasma [creatinine] diagnostic of renal disease, and excretion of other substances will be impaired, so may need to adjust drug dosage


What is the driving force of glomerular filtration?

Hydrostatic pressure in glomerular capillaries (Pgc)


What opposes hydrostatic pressure of glomerular capillaries?

Hydrostatic pressure of tubule (Pt) and Osmotic pressure of glomerular plasma proteins (πgc)


What equation describes net ultrafiltration?

Puf = Pgc - Pt - πgc


What factors effect GFR?

Pgc, πgc, Pt, Kf - can be hormonally or neurally controlled


What will happen to pressures in the kidney if there is an increase in arterial blood pressure?

Increased Pgc hence Puf and GFR increase


What happens if there is an increase in plasma protein concentration?

Increase in πgc hence Puf and GFR decrease


What will happen to Puf and GFR if there is a Ureteral obstruction?

Increases Pt therefore Puf and GFR decrease


What is renal clearance?

The extent to which substances passing through the kidneys are removed from the blood - no. Litres plasma that are completely cleared of the substance per unit time


What is the equation for working out renal clearance?

(urine concentration x rate of urine production)/concentration in plasma ml/min


How is GFR estimated?

Using clearance;
If a molecule is freely filtered and not reabsorbed/secreted than amount filtered = amount excreted 


What is Inulin?

A plant polysaccharide that is non-toxic, measurable in urine and plasma and freely filtered; must be transfused (usually 120ml min-1)


What is Creatinine?

An endogenous waste product from creatine in muscle metabolism, and amount released relatively constant; if renal function stable then amount in urine stable; High/Low creatinine = renal failure


How can renal plasma flow be estimated by clearance?

PAH (para aminohippurate) filtered and actively secreted in one pass of the kidney and should be 625ml min-1


What are the four ways water is removed from the body?

Skin/sweat: variable and uncontrollable (450ml/day)

Faeces: uncontrollable (100ml/day)

Respiration: uncontrollable (350ml/day)

Urine: variable and controllable 1500ml/day


What percentages of water filtered reach the Loop, DCT and enter urine?

30% reaches the dLoH, 20% reaches the DCT and 1-10% enters the urine 


Where are the Venous/Pulmonary baroreceptors?

Atria, Right Ventricle and Pulmonary vasculature


What are the responses of the Low-pressure system baroreceptors to hypotension?

Afferent fibres to brainstem increase vasopressin (ADH) release and increase SNS discharge


What are the responses of the Low-pressure system baroreceptors to hypertension?

Atrial stretch leads to ANP/BNP (Atrial + Brain) release


What is the renal response when high-pressure baroreceptors detect hypotension?

Afferent fibres to brainstem increase vasopressin (ADH) release and increase SNS discharge; JGA cells cause the release of renin


What is ANP and what does it do?

Atrial natriuretic peptide (ANP): made in the atria in response to atrial stretch; actions...

Vasodilation of renal vessels

Inhibition of sodium reabsorption in the PCT and CD

Inhibition of renin/aldosterone release

Reduction of BP


Describe ECF-BP feedback upon volume expansion in the Heart, Brain and Kidneys:

Heart: increases ANP/BNP to inhibit sodium reabsorption and renin release

Brain: reduces ADH to stop aldosterone production and sodium reabsorption

Kidneys: reduce renin secretion so less AGTII/aldosterone produced


Describe ECF-BP feedback upon volume contraction in the Heart, Brain and Kidneys:

Heart: decreases ANP/BNP to increase sodium reabsorption and renin release

Brain: increases ADH to increase aldosterone production and sodium reabsorption

Kidneys: increases renin secretion so more AGTII/aldosterone produced


How does blood flow change to increase GFR?

Afferent arteriole dilation to increase blood flow
Efferent arteriole constriction to increase pressure to increase overall Ultrafiltration and GFR