Renal physiology Flashcards
What are the 2 types of kidney nephrons
Cortical nephrons (70-80%)
Juxtamedullary nephrons (20-30%)
Cortical Nephrons
Glomeruli in outer cortex
Short-looped
Juxtamedullary nephrons (20-30%)
Glomeruli border on medulla
Long-looped
Paired with extensive vasa recta (specialised blood supply)
Renal Blood flow (RBF)
Renal blood flow (RBF) ~20% of cardiac output/min
πΉπ©π=πΉπ·π/(πβπππππππππ)
E.g
πΉπ©π=πππ/((πβπ.ππ)) = 1182 ml/min
What is renal blood flow NOT the same as?
Renal plasma flow
Glomerular filtration
~ 20% of Renal Plasma Flow
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
How many litres of fluid is filtered a day by GFR
~180L filtered/day
How much fluid is reabsorbed after GFR
~179L reabsorbed
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
Which 4 forces is net fluid movement
Glomerular hydrostatic pressure
(GHP; fluid out)
Glomerular colloid osmotic pressure
(pG; protein; fluid in)
Bowmanβs Capsule fluid pressure
(BCP; fluid in)
Bowmanβs Capsule colloid osmotic pressure (pB; ??)
Net filtration pressure (NFP) equation
GHP β (BCP + pG)
NFP = 60 β (18+32)
NFP ~ 10 mm Hg
As you go from the afferent to efferent arteriole what happens to the glomerular colloid osmotic pressure
The gradient increases
Glomerular hydrostatic pressure
As blood flows through afferent arteriole GHP forces fluid out
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)
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
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
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
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 β
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)
Doesnβt 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
- Reabsorption:
Water and solutes from tubular filtrate - Secretion:
Solute from blood and peritubular fluid into tubular fluid - Excretion:
Into urine
Drugs for Kidney
Thiazide diuretics
Bendroflumethiazide
-ve Na+/Cl- co-transporter
Loop diuretics Furosemide
-ve Na+-2ClβK+ ATPase
K+-sparing diuretics (Amiloride β Na+ channel)
(Spironolactone β 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
-Connβs syndrome
-Cushingβs?
b2-agonists
Alkalosis
Causes increased [K+]ECF
Insulin deficiency
Aldosterone deficiency
-(Addisonβs 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
Na
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 toβ¦.
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
