Renal physiology Flashcards by Maryam Mahmood

What are the 2 types of kidney nephrons

Cortical nephrons (70-80%)
Juxtamedullary nephrons (20-30%)

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Cortical Nephrons

Glomeruli in outer cortex
Short-looped

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Juxtamedullary nephrons (20-30%)

Glomeruli border on medulla
Long-looped
Paired with extensive vasa recta (specialised blood supply)

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Renal Blood flow (RBF)

Renal blood flow (RBF) ~20% of cardiac output/min

𝑹𝑩𝑭=𝑹𝑷𝑭/(𝟏−𝒉𝒂𝒆𝒎𝒐𝒄𝒓𝒊𝒕)
E.g
𝑹𝑩𝑭=𝟔𝟓𝟎/((𝟏−𝟎.𝟒𝟓)) = 1182 ml/min

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What is renal blood flow NOT the same as?

Renal plasma flow

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Glomerular filtration

~ 20% of Renal Plasma Flow

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What is GFR related to

arterial pressure and capillary properties
Blood enters afferent arteriole with RPF of 650ml/min into glomerulus > GFR ~125 ml/min) > out the efferent ateriole

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How many litres of fluid is filtered a day by GFR

~180L filtered/day

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How much fluid is reabsorbed after GFR

~179L reabsorbed

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What is GFR influenced by?

Net Filtration Pressure (NFP)
Hydrostatic pressures
Colloid osmotic pressures

Renal Blood Flow (RBF)
Autoregulation

Filtration coefficient (Kf; filter integrity/function)
Arteriolar endothelium
Glomerular podocytes
T2DM
Hypertension

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Which 4 forces is net fluid movement

Glomerular hydrostatic pressure
(GHP; fluid out)

Glomerular colloid osmotic pressure
(pG; protein; fluid in)

Bowman’s Capsule fluid pressure
(BCP; fluid in)

Bowman’s Capsule colloid osmotic pressure (pB; ??)

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Net filtration pressure (NFP) equation

GHP – (BCP + pG)

NFP = 60 – (18+32)

NFP ~ 10 mm Hg

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As you go from the afferent to efferent arteriole what happens to the glomerular colloid osmotic pressure

The gradient increases

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Glomerular hydrostatic pressure

As blood flows through afferent arteriole GHP forces fluid out

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What 3 parameters is GHP influenced by

Systemic arterial pressure
Tends to increase GHP and GFR
BUT renal auto-regulation minimises major change

Afferent arteriolar resistance
Generally reduces GHP and GFR

Efferent arteriolar resistance
Increased GHP, variable response in GFR (increase then decrease)

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What happens with increased resistance of afferent arteriole (constriction of afferent arteriole)

Causes Reduced Hydrostatic Pressure +
Reduced GFR in glomerulus
Hydrostatic pressure drops after blood flows through efferent arteriole causing a decrease in flow

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What happens with decreased resistance of afferent arteriole (dilation of afferent arteriole)

Causes increased Hydrostatic Pressure +
Increased GFR in glomerulus
Causes increased resistance in Efferent arteriole (partially constrict due to Ang II) > causes decreased HP and increased glomerular colloid osmotic pressure which causes increased fluid reabsorption

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What happens with decreased resistance of afferent arteriole (dilation of afferent arteriole) Part 2

Causes increased Hydrostatic Pressure which causes increased glomerular colloid oncotic pressure
Causes increased resistance in Efferent arteriole (severe constrict > lowers GFR) > causes decreased HP in Efferent arteriole leading to decreased flwo

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Renal Auto- regulation:

Intrinsic feedback mechanisms
Maintains near constant:
Renal blood flow
GFR

What does renal auto-regulation minimise the impact of?

systemic arterial pressure variations on RBF & GFR

What happens without autoregulation?

Large increase in urine output (>40L/day)

Involves:
Afferent and efferent arterioles
Tubuloglomerular Feedback

GFR and autoregulation

Increased NaCl reabsorption at PCT > decreased NaVl sensed by Macula Densa cells in (DCT) > Autocoid secretion (PGE2, PGI2) > Causes decreased resistance in Afferent arteriole and increased GHP restoring GFR> Also causes release of Renin from juxtaglomerular cells > Causes RAAS > RAAS causes increased efferent arteriole resistance increasing GHP restoring GFR

What is the indicator for renal function

GFR

GFR, creatinine and Renal function

Requires plasma creatinine value
Creatinine filtration rate = GFR x [creatinine]plasma
Creatinine excretion rate ≅ creatinine production

Early stage renal failure

Significant decreased GFR > small increase in [creatinine]plasma

What is needed to figure out GFR the indicator of renal function

Requires plasma creatinine value: Clinically use estimated GFR (eGFR) Doesn’t consider creatinine tubular secretion

Drawbacks of GFR

Can overestimate GFR due to tubular creatinine secretion (10-15%) Creatinine metabolism reflection on lean body mass Ethnic correction removed Not validated in pregnancy

Factors that decrease GFR

D= Decreased I= Increased D Kf= Renal disease Diabetes mellitus Hypertension I BCP = Urinary tract obstruction (kidney stones) I pG = D RBF, I Plasma proteins D GHP = D Arterial pressure D R in Efferent = D ANG II (Due to ACEi/ ARB) I R in Afferent = NSAIDs

Four basic procces of kidney

1.Filtration: Glomerulus Water and solutes across glomerular capillaries 2. Reabsorption: Water and solutes from tubular filtrate 3. Secretion: Solute from blood and peritubular fluid into tubular fluid 4. Excretion: Into urine

Drugs for Kidney

Thiazide diuretics Bendroflumethiazide -ve Na+/Cl- co-transporter Loop diuretics Furosemide -ve Na+-2Cl--K+ ATPase K+-sparing diuretics (Amiloride – Na+ channel) (Spironolactone – aldosterone antagonist

Late distal and Cortical collecting tubules

Sensitive to ADH Impermeable to urea

3 cell types of Late distal and Cortical collecting tubules

Priniciple cells Type A intercalated cells Type B intercalated cells

Principal cells

Sensitive to ALDOSTERONE Na+ /H2O reabsorption Key role - K+ secretion I[K+]ECF > I Aldosterone; I Na+/K+ ATPase

Type A intercalated cells

Buffer acidosis H+ secreted K+ / HCO3- reabsorbed

Type B intercalated cells

Buffer alkalosis H+ reabsorbed K+ / HCO3- secreted

Factors that cause increased [K+]ECF

Insulin Hyperaldosteronism -Conn’s syndrome -Cushing’s? b2-agonists Alkalosis

Causes increased [K+]ECF

Insulin deficiency Aldosterone deficiency -(Addison’s disease) b2-antagonists Acidosis Cell lysis Exercise I ECF osmolarity Diet

Regulation of ECF volume: Basic system

I BV > I BP > I Renal excretion > Normal vol restored

What is the most abundant ECF ion

What does Sodium determine in ECF?

Osmotic pressure (osmolality) Volume

What regulates Blood Pressure and Volume

Baroreceptor reflexes (cardiovascular lecture slides) Negative feedback loops Short-term, continuous regulation Renal Involvement Juxtaglomerular Apparatus Macula densa (Renin/Angiotensin) Tubuloglomerular feedback

What is a renal response to expansion in ECF volume

ANP - Water/NaCl loss

ANP - peptide hormone

I ECF vol > I atrial stretch > D Hypothalamic ADH synthesis

ANP causes Afferent arteriole dilation leading to what?

Increased GFR

ANP inhibits Renin secretion leading to....

Decreased: Ang II Aldosterone secretion Systemic vascular resistance

ANP causes decreased DCT Na reabsorption leading to water

I Water secretion leading to pressure diuresis > Decreased ECF volume

ANP generally antagonises what?

Angiotensin II actions