glomerular filtration pressures #urinary

Glomerular Hydrostatic (Blood) Pressure: (HPg)

blood pressure within glomerulus

(HPg) function

• drives/pushes water + solutes out of glomerulus into capsular space OR renal corpuscle

• promotes filtration

the change in diameter of the afferent and efferent arteriole allows for …

BP changes

Blood Colloid Osmotic Pressure (OPg)

• osmotic pressure exerted by blood due to dissolved solutes (albumin)

• pulls/draws fluid back into glomerulus

oppose HPg → oppose filtration

Capsular Hydrostatic Pressure (HPc)

• pressure in glomerulus capsule due to amt of filtrate

• impedes the movement of additional fluid from blood into capsular space

Net Filtration Pressure (NFP) equation

HPg - OPg - HPc = NFP

NFP value positive = filtration

NFP value negative = no filtration

Glomerular filtration rate (GFR)

rate at which the volume filtrate is formed

relationship between NFP and GFR

direct relationship

increase NFP = increase GFR

decrease NFP = decrease GFR

increased NFP = increased GFP =

• more filtrate

• more fluid moving through tubules

• decreased filtrate reabsorption

• more substances excreted in urine

decreased NFP = decreased GFP =

• less filtrate

• less movement through tubules

• increased filtrate reabsorption

• less substances excreted in urine

relationship btwn glomerular hydrostatic pressure (HPg) and net filtration pressure (NFP)

• inc. HPg → inc. NFP → inc. GFR

• dec. HPg → dec. NFP → dec. GFR

influences if GFR

luminal diameter of afferent arteriole > change in blood flow

altering surface area of filtration membrane > change in filtrate formation

intrinsic control

processes within the kidney

renal auto-regulation; maintains GFR at normal lvls

extrinsic control

processes external to kidney

NS or hormonal regulation; increase or decrease GFR

intrinsic control 2 menchanisms

1. myogenic response

2. tubuloglomerular feedback mechanism

myogenic response

contraction and relaxation of smooth muscle in wall of afferent arteriole in response to changes in stretch

tubuloglomerular feedback mechanisms

• based on detection of NaCl lvls in tubular fluid

• “back up plan” if myogenic response isn’t sufficient

normal glomerular pressire when BP is within MAP range:

80-180 mm Hg

decreased systemic BP

< 80 mmHg

• results in vasodilation of afferent arteriole

• results in decreased glomerular BP and GFR

if too low, accumulation of waste in blood occurs.

decreasing GFR through Sympathetic Nervous System

during exercise or emergency

vasoconstriction > dec. blood flow through kidneys > decreased GFR

results in decreased GFR

granular cells of JG apparatus release renin > leads to angiotensin II production, stimulates contractions of mesangial cells

mesangial cell contractions decrease surface area of filtration membrane of glomerulus > less filtrate exits the glomerulus > dec. in GFR

net decrease in GFR results in

• decreased urine output

• increased blood volume and BP

results in increased GFR

• vasodilation of afferent arteriole > inc. blood flow through kidney

• inhibiting the release of renin > relaxes the mesangial cells

  • relaxation of cells increase glomerular filtration membrane surface area > more filtrate exits glomerulus

both tactics inc. GFR

Net increase in GFR results in

increases urine volume

decreased blood volume and BP

Maintaining GFR

INTRINSIC

• renal autoregulation maintains GFR

alters size in afferent arterioles in response to changes in system BP - keeps it within normal limits

Altering GFR

EXTRINSIC

• direct stimulation of sympathetic division cause vasocontriction of affferent arterioles to dec. blood flow into glomerulus.

• remin release w production of Ang II and contraction of mesangila cells that decrease surface area of glomerulus.

**GFR and urine production decrease

ANP increases GFR through vasodilation of afferent arteriole + inhibition of renin

** GFR and urine production increase