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*LSS Urinary Y1* > Flow and filtration > Flashcards

Flow and filtration Flashcards

1
Q

What proportion of CO goes to the kidneys?

A

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

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2
Q

What is the filtration fraction?

A

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

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3
Q

What is normal Renal Blood Flow (RBF)?

A

approx. 1L/min

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4
Q

What is normal Renal Plasma Flow (RPF)?

A

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

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5
Q

What is the equation for Glomerular filtration rate?

A

GFR = RPF x FF

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6
Q

Describe the process of Glomerular Filtration:

A

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

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7
Q

What is the filtration barrier?

A

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

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8
Q

What is “freely filtered?”

A

Solute found at same conc in blood and filtrate

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9
Q

What is Primary urine?

A

Clear ultrafiltrate fluid free from blood and proteins

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10
Q

What is the glomerular filtration rate?

A

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)

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11
Q

What is Kf?

A

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

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12
Q

What is a normal GFR?

A

120ml/min

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13
Q

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

A

Increase Kf

Increase GFR

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14
Q

What does myogenic auto-regulation in glomerular arterioles allow?

A

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

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15
Q

Describe four events that effect GFR:

A

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

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16
Q

What is the role of GFR in renal diagnostics?

A

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

17
Q

What is the driving force of glomerular filtration?

A

Hydrostatic pressure in glomerular capillaries (Pgc)

18
Q

What opposes hydrostatic pressure of glomerular capillaries?

A

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

19
Q

What equation describes net ultrafiltration?

A

Puf = Pgc - Pt - πgc

20
Q

What factors effect GFR?

A

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

21
Q

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

A

Increased Pgc hence Puf and GFR increase

22
Q

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

A

Increase in πgc hence Puf and GFR decrease

23
Q

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

A

Increases Pt therefore Puf and GFR decrease

24
Q

What is renal clearance?

A

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

25
Q

What is the equation for working out renal clearance?

A

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

26
Q

How is GFR estimated?

A

Using clearance;

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

27
Q

What is Inulin?

A

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

28
Q

What is Creatinine?

A

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

29
Q

How can renal plasma flow be estimated by clearance?

A

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

30
Q

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

A

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

Faeces: uncontrollable (100ml/day)

Respiration: uncontrollable (350ml/day)

Urine: variable and controllable 1500ml/day

31
Q

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

A

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

32
Q

Where are the Venous/Pulmonary baroreceptors?

A

Atria, Right Ventricle and Pulmonary vasculature

33
Q

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

A

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

34
Q

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

A

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

35
Q

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

A

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

36
Q

What is ANP and what does it do?

A

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

37
Q

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

A

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

38
Q

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

A

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

39
Q

How does blood flow change to increase GFR?

A

Afferent arteriole dilation to increase blood flow

Efferent arteriole constriction to increase pressure to increase overall Ultrafiltration and GFR

*LSS Urinary Y1* (4 decks)

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