80-85% Solute handling Peritubular capillaries

filtering nephrons by surface area volume plasma filtered by nephrons

Renal Physiology Flashcards by O lawformonde

Cortical nephrons

80-85%
Solute handling
Peritubular capillaries

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Juxtamedullary nephrons

15-20%
make Concentrated Urine
Peritubular Capillaries + Vasa Recta

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Filtered freely at glomerulus:

Small, (+)

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Not filtered freely at glomerulus:

Large
(-)
(Protein)

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What pressure drives GFR?

Glomerular Capillary BP (P gc) vs. bowman’s space pressure vs. glomerular oncotic

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Think of GFR as

# filtering nephrons by surface area

* volume plasma filtered by nephrons

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How much plasma gets filtered?

20%

~140 mL per minute

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Blood plasma ratio

56% plasma

44% RBCs

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Extreme Drop in BP

Neuro regulation GFR

Sympa = afferent constricts
Release renin
Ang II constricts

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Extreme BP rise

Neuro regulation GFR

atria stretch = ANP released
Mesangial cells in glomerulus relax
UP surface area = UP GFR

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Vasodilators

DILATE AFFERENT
UP GFR
*Prostaglandin E (PGE2) + Prostacyclin (PGI2)
*NO
*Bradykinin
*DA
*ANP + BNP (+ constrict EA)

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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)

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What med example need to measure GFR

Aminoglycosides

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Limitations of GFR measurement

creatinine partially secreted
test underestimates it
still not balanced

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GFR ~ P crt

Inverse

GFR = 1/Pcrt

GFR = Ucrt*V/Pcrt

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Filtration fraction =

GFR / renal perfusion

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Filtration - reabsoption + secretion =

Clearance?

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GFR ~ RPF

GFR (120 mL/min)= 20% of RPF (600mL/min)

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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

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)