Renal Physiology Flashcards
Cortical nephrons
- 80-85%
- Solute handling
- Peritubular capillaries
Juxtamedullary nephrons
- 15-20%
- make Concentrated Urine
- Peritubular Capillaries + Vasa Recta
Filtered freely at glomerulus:
Small, (+)
Not filtered freely at glomerulus:
Large
(-)
(Protein)
What pressure drives GFR?
Glomerular Capillary BP (P gc) vs. bowman’s space pressure vs. glomerular oncotic
Think of GFR as
- # filtering nephrons by surface area
* volume plasma filtered by nephrons
How much plasma gets filtered?
20%
~140 mL per minute
Blood plasma ratio
56% plasma
44% RBCs
Extreme Drop in BP
Neuro regulation GFR
- Sympa = afferent constricts
- Release renin
- Ang II constricts
Extreme BP rise
Neuro regulation GFR
- atria stretch = ANP released
- Mesangial cells in glomerulus relax
- UP surface area = UP GFR
Vasodilators
DILATE AFFERENT UP GFR *Prostaglandin E (PGE2) + Prostacyclin (PGI2) *NO *Bradykinin *DA *ANP + BNP (+ constrict EA)
Vasoconstrictors
CONSTRICT AFFERENT DOWN GFR *Sympathetic (a1/b1) *Ang 2 (+Efferent) = high dose *Endothelin *ADH
CONSTRICT EFFERENT
UP GFR
*Ang 2 = low dose
*ANP + BNP (+ dilate AA)
What med example need to measure GFR
Aminoglycosides
Limitations of GFR measurement
- creatinine partially secreted
- test underestimates it
- still not balanced
GFR ~ P crt
Inverse
GFR = 1/Pcrt
GFR = Ucrt*V/Pcrt
Filtration fraction =
GFR / renal perfusion
Filtration - reabsoption + secretion =
Clearance?
GFR ~ RPF
GFR (120 mL/min)= 20% of RPF (600mL/min)
Filtered Load
Mass getting out
GFR * Plasma conc
Filtration Fraction
Amount of total perfusion filtered (20%)
GFR/RPF
Lower than normal GFR?
Loss of nephrons
Collecting duct
Reabsorbs/Secretes
REABSORBS
- Bicarb
- Cl
- Na
- Urea
- Water
SECRETES
- H+
- NH4
- K+
Distal Tubule
Reabsorbs/Secretes
REABSORBS
- Na
- Water
- Bicarb
- Cl
SECRETES
*H+, NH4, K+
Loop of henle descending
reabsorbs
Water
NO SOLUTES
Loop of Henle
Thick ascending
Na
Cl
NO WATER
Thin Ascending
Reabsorbs
- Na
- Cl
NO WATER
PCT
Reabsorbs/Secretes
REABSORBS
- amino acids
- bicarb
- Cl
- Glucose
- Na
- peptides
- potassium
- urea
- water
SECRETES
*H+, Urate, NH4, Rx
Na reabsorbed in
- PCT (most) = co transpoerters (Cl)
- TALH (Na/K/2Cl)
- DCT (Na/Cl co)
- CD (ENaC)(aldosterone)
Lasix attacks
TALH
Na/K/Cl transporter
The Rock
Nothing excreted
K+
REABSORBED
- PCT (most) = Paracellular solvent drag
- TALH = transcellular (Na/K/2Cl)
REABSORBED/SECRETED
*DT =
secretion (principal cells-aldosterone);
reabsorption (a-intercalated cells H/K)
15-80% excreted
Ca2+
REABSORBS
- PCT (most) = paracellular solvent drag
- TALH = paracellular lumen positive reabsorption (K backleak)
- DCT = Ca2+ channel (PTH)
- CD
Almost nothing excreted
Aldo stimulated
*DCT = Principal cell K channel
ENaC
Na/K ATPase
=K loss, Na reabsorbed
Pi
REABSORBED
- PCT most = Na/Pi co
- PST = paracellular/transcellular (upreg if low Plasma Pi)
- DT = also upreged
Mg2+
*majority NOT reabsorbed PCT REABSORBED *PCT = solvent drag *TALH = solvent drag *DCT = Mg channel
Urea
- PCT ABSORB= passively reabsorbed
* LOOP SECRETE then ABSORB from CD
Water
REABSORB
- PCT
- tDLH
- NO ALH
- CD
Sodium controls
Volume
Slow movement (constriction/dilate of vessels to compensate)
Water controls
Osmolarity
Moves quickly, easy to regulate
Osmoreceptors
Controlling ADH
Hypothal = high plasma osmolarity ->release ADH + thirst
MOST SENSITIVE TO CONTROL OSMOLALITY = PRIMARY MODE OF REGULATION
Blood volume
controlling ADH
*large blood volume drop -> baroreceptors (vascular + carotid/AA) -> release ADH
LESS SENSITIVE THAN OSMORECEPTORS
Daily loss
1/2 liter = lungs
1/2 liter = skin
~1.6 water needed to excrete metabolic waste
ADH
Characteristic
- short t 1/2 (10-15min)
- Deep sleep
- exercise
- triggered by High Plasma Osmolarity
Amiloride blocks
Na/Cl channel in DCT
Thiazide effects
Increase sodium ENac Na excrete in early DCT
Late DCT = Na absorb/K excrete = LOSE K
Diuresis
Water
Large water intake = inhibits ADH secretion = UP urine volume
Osmotic diuresis
Ex: mannitol, excess glucose DM
CKD = less nephrons, more solute (can’t concentrate) + faster flow (can’t absorb/dilute)
Kidney maintain homeostasis of:
- blood volume (Na)
- Body fluid tonicity/osmolality (water, ion/nutrient excretion)
- Acid-base balance (bicarb)
- blood pressure (hormone-vascular tone + blood volume)
