1 glomerulus receives feedback on status of its own

1 glomerulus receives feedback on status of its own downstream tubular fluid
and adjusts filtration rate accordingly -
This regulates filtrate composition, stabilizes renal function, compensates for
fluctuations in blood pressure
Macula densa: sense Na, K, Cl 
secrete ATP
Mesangial cells: ATP  Adenosine
Granular cells : Adenosine 
contraction of G. cells  constricts
afferent arteriole
* mesangial cells also contract  further
constricting afferent arteriole
Juxtaglomerular Apparatus
@ end of nephron loop/start of DCT where folds back
into/meshes w/ afferent & efferent arterioles of same
nephron

23-33
Renal Autoregulation - Tubuloglomerular Feedback,
continued
Juxtaglomerular Apparatus ( JGA
) - components
Macula densa,
patch of sensory cells in nephron loop
If GFR is high  filtrate contains more NaCl  macula densa absorbs more
NaCl  secretes ATP  nearby mesangial cells convert ATP to Adenosine
 Adenosine stimulates granular cells to contract
Granular (juxtaglomerular) cells:
modified smooth muscle cells;
wrapped @ arterioles (close to macula densa)
Adenosine  sm. muscle contracts  afferent arteriole constricts  blood
flow  adjusts GFR  Remains relatively constant
Mesangial cells
also contract, constricting capillaries  further limit GFR
ALSO
When BP  , Granular cells secrete Renin
JGA is component of Renin-Angiotensin-Aldosterone system’
This system controls blood volume and pressure

23-35
Tubuloglomerular Feedback = Negative Feedback Control
of GFR
DCT can absorb Na & Cl, Tubuloglomerular feedback prevents system
overwhelming capacity of DCT to absorb Na & Cl and prevent excess loss of
Na, Cl and H
2
O in urine

23-36
How is glomerular filtration rate regulated?

Renal Autoregulation
Sympathetic Control
Hormonal Control
Sympathetic nerve fibers richly innervate renal
blood vessels
Sympathetic input plus adrenal epinephrine constrict
afferent arterioles during strenuous exercise OR acute
conditions, e.g., circulatory shock
Reduces GFR   urine output  maintains plasma volume
Redirects blood from kidneys to heart, brain, & skeletal muscles
GFR may be as low as a few milliliters per minute

23-37
When BP   detected by carotid and aorta
baroreceptors  sympathetic nervous system
 granular cells release Renin
Renin-Angiotensin-Aldosterone System
system of hormones that helps regulate blood
pressure and GFR
Renin converts angiotensinogen 
angiotensin I

Renin-Angiotensin-Aldosterone System
In lungs and kidneys, angiotensin-converting enzyme
(ACE) converts angiotensin I to angiotensin II
Angiotensin II (ANG II), hormone that increases BP
