Physio Exam 3: Renal

What is the main homeostatic variable?

What is the main homeostatic variable?

ECF

The most important role in long-term regulation of BP is through control of ____

ECF volume

What is the functional unit of the kidney?

nephron

-each kidney has 500,000-800,000

What is the role and location of the Glomerulus?

Role: urine formation

Location: w/in the Bowman’s capsule

Where does the proximal tubule receive filtrate from?

Bowman’s Capsule

Loop of Henle parts:

U shaped tuble

-thin descending

-thin ascending

-thick ascending

How many distal tubules converge with the collecting duct?

6

What percentage of nephrons are Cortical? Juxtamedullary?

Cortical: 85%

Jux: 15%

Cortical nephron features:

-Glomeruli is in outer cortex

-loop of Henle are short

Juxtamedullary nephron features:

-Glomeruli deep in cortex

-loops of Henle are long

Do Juxtamedullary nephrons reabsorb (higher/lower) proportion of glomerular filtrate?

higher →salt conserving

When effective circulating blood volume is low, high proportion of renal blood flow is direct to the ____ to conserve _____

juxtamedullary nephrons; ECF

GFR is a ___ variable

constant

What is the threshold for GFR

60

-want high; lower than 60 → renal disease

Normal GFR

90+

Low GFR can lead to:

renal insufficiency

With mild CKD, GFR =

60-89

With moderate CKD, GFR =

30-59

With severe CKD, GFR =

15-29

How much filtrate is reabsorbed?

98-99%

Where is the rate of reabsorption highest?

proximal tubule

-reduces as flow becomes more distal

Where does fine control of excretion occur?

distal parts of tubule

Distal tubules are under ___ control

hormonal: Aldosterone, some ADH

Reabsorption

filtrate/nutrients from renal corpuscle → blood supply

Secretion

filtrate/nutrients from bloody supply → renal corpuscle

Kidneys receive ___ of CO

20-25%

What is needed to supply sufficient plasma for filtration?

High rate of RBF

RBF is

autoregulated

What can reduce RBF and why?

sympathetic vasoconstriction to conserve ECF

Glomerular capillary bed is supplied by ______ and drained via _______

afferent arteriole; efferent arteriole

The efferent arterioles supply the

peritubular capillary bed

Where do sites of vascular resistance occur? What is the purpose?

afferent and efferent arterioles to maintain pressure to drive filtration

Persistently low renal perfusion can lead to

acute renal failure

ARF occurs because of

low GFR lasting hours to days

CRF occurs because of

low GRF more than 3 months

What is the most common form of ARF

pre renal

pre renal ARF cause

any condition that results in renal hypoperfusion

(hypovolemia)

renal ARF cause

directly results in damage to renal parenchyma

(glomerular nephritis)

Post renal ARF cause

cause obstruction of urinary tract

(BPH)

Endocrine Fx of Kidneys

renin secretion, EPO secretion, activate vit D

Renin is released by the ___ in response to ____

juxtaglomerular apparatus; decrease in effective circulating BV

Renin cascade of events:

-Angiotensin II and Aldosterone release

-feedback regulation of GFR

-MOST important endocrine axis in control of ECF

EPO role

stimulate RBC formation due to low O2 levels

We can get vitamin D from:

ingestion or the sun

What produces inactive vit D

liver

function of vit D

promotes conservation of Ca2+

-increase Ca2+ mobilization in bones

-increase Ca2+ absorption in intestines

-reduce urinary Ca2+ loss

what hormone allows the kidney to activate vit D

PTH

Glomerular filtrate should not allow passage of

blood cells or plasma proteins

what is responsible for the net filtration pressure?

Starling’s Forces

Nephrotic Syndrome signs

severe proteinuria, hypoalbuminemia, generalized edema, hyperlipidemia

Nephritic Syndrome signs

hematuria, HTN, oliguria, azotemia

substance ____ are freely filtered

<10kDa

size of Albumin and its role

70dKa; largest contributor to plasma oncotic pressure

Can/should Albumin be filtered?

no due to its charge; NO!!

at pH 7.4 proteins carry a net ___ charge

negative

What 3 structures can a solute pass through?

-fenestrations

-Glomerular basement membrane

-Podocytes

Fenestrations

Glomerular capillary endothelial cell layer

-excludes ONLY blood cells

Basement membrane

fiber meshwork → sieve for macromolecules

-has a fixed NEGATIVE charge → repulses - particles

Podocytes

narrow filtration slits that are bridged by nephrin

-has a fixed NEGATIVE charge → repulses - particles

Net Filtration Pressure Equation

Favor - oppose

Pgc - (Pbc + Ogc)

What is the biggest factor that opposes filtration?

Oncotic Glomerular Capillary Pressure

Nephrotic syndrome:

Minimal change disease

Loss of nephrin → allows for loss of albumin

P(uf) represents

Pressure pushing fluid out of the glomerular capillary

K(f) represents

permeability of the filtration barrier

GFR formula

GFR= P(uf) x K(f)

P(uf) formula

P(uf)=P(gc)-P(bc)

Changes is afferent or efferent arteriolar tone alter:

vascular resistance and glomerular capillary hydrostatic pressure → changes in RBF and GFR

What hormone preferentially constricts afferent arterioles? What is the result of this?

NE

-reduces RBF, GFR, Na excretion

What hormone preferentially constricts efferent arterioles? What is the result of this?

Angiotensin II

-reduces RBF, but maintains GFR

Constriction of afferent arterioles results in

reduced RBF, P(gc), GFR

Dilation of afferent arterioles results in

increased RBF, P(gc), GFR

Mild constriction of efferent arterioles results in

reduced RBF

increased P(gc), GFR

Extreme constriction of efferent arterioles results in

reduced RBF, GFR

increase On(gc)

Dilation of efferent arterioles results in

reduced P(gc), GFR

increased RBF

Clearance is the volume of plasma rendered free of a given substance in ____

1 minute

What is a product of muscle metabolism?

Creatinine

Why is Cr production constant?

bc its a function of muscles mass

plasma Cr is a direct index of

GFR

The rate of Cr excretion varies with

GFR

Cr relationship with GFR

inverse

Filtered load

among of a substance filtered by unit time

Excretion rate

amount excreted per unit time

ER < FL =

reabsorption

ER > FL =

secretion

Fractional excretion

solute concentration as a percentage of filtered load

Clearance ratio

solute clearance : Cr clearance

-stems from fractional excretion

If you block NE what happens?

afferent arteriole dilates

Clearance of a solute may change as a function of

plasma concentration

Glucose is not normally found in the urine with ___

normal plasma concentrations

Renal threshold

when plasma solute concentration where solute first appears in urine

Splay

curve level off gradually

-variabiltiy in transport between nephrons

When plasma concentrations are high and your body can’t reabsorb it all, how does the body get rid of the excess?

Excretion

What are the only significant process affecting NaCl and H2O excretion?

Filtration and reabsorption

The early proximal tubule utilizes ___ to bring Na and nutrients into the wall and ____ to get the nutrients out

cotransporters; facilitated diffusion

The late proximal tubule utilizes ___ to get Na into the cell and H+ and formate out

Counter transporters (anitporter)

Loop diuretics are effective at the

thick ascending loop

Loop diuretics function

block Cl- —> inhibits Na/K/2Cl co transport

Thiazide diuretics are effective at the

Early distal tubule

Thiazide diuretics function

block Cl- —> inhibits Na/Cl co transport

K+ sparing diuretics are effective at the

Late tubule and Cortical collecting duct