Urinary System I: Kidneys and Urine Formation. Functions of the Urinary System Organs of the Urinary System The Kidney Coverings and Regions Blood Flow Nephrons: Glomeruli and Renal Tubules Urine Formation Urinalysis Ureters, Bladder, and Urethra.
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Unique: Incoming vessels enter as an arteriole, narrow into a capillary bedin the glomerulus, leave in an arteriole, and then break into the peritubular capillary bed before leaving as venus blood.
efferent afferent arterioles
Water is reclaimed from filtrate into venous circulation via peritubular capillaries
Glomerular capsule: parietal layer
• Glomerular capsule
of the glomerulus
Glomerular capsule: visceral layer
Highly infolded plasma
Proximal convoluted tubule cells
and thick ascending
L 0f H
Distal convoluted tubule cells
Loop of Henle
• Descending limb
• Ascending limb
Loop of Henle (thin-segment) cells
Mostly cuboidal epithelium with modifications in membrane surfaces
Collecting duct cells
NFP = HPg – (OPg + HPc)
= (push outwards - back pressure inwards)
Glomerular (blood) hydrostatic pressure
(HPg = 55 mm Hg)
Blood colloid osmotic pressure
(Opg = 30 mm Hg)
Capsular hydrostatic pressure
(HPc = 15 mm Hg)
angiotensinogen (a plasma globulin)
angiotensin converting enzyme (ACE)
Blood pressure in
afferent arterioles; GFR
blood vessels of
Granular cells of
apparatus of kidney
Stretch of smooth
muscle in walls of
Filtrate flow and
NaCl in ascending
limb of Henle’s loop
resulting in conversion
Macula densa cells
of JG apparatus
Release of vasoactive
Intrinsic mechanisms directly regulate GFR despite
moderate changes in blood pressure (between 80
and 180 mm Hg mean arterial pressure).
Extrinsic mechanisms indirectly regulate GFR
by maintaining systemic blood pressure, which
drives filtration in the kidneys.
Hormone regulated reabsorption of Ca2+ ( by PTH), water ( ADH) Na+ ( aldosterone and ANP)
Most reabsorption occurs here
Urea reabs. with ADH
Reduces the volume and saltiness of the filtrate
Na+, K+ resabsorbed
The salty outer medulla created by the ascending loop amplifies the extraction of water in the descending loop. Without countercurrent, much less water would be removed and therefore would be less efficient.
Loop of Henle
Renal function online animation
(a) Countercurrent multiplier.
The long loops of Henle of the
create the medullary
Countercurrent in Loop of Henle Peritubular Capillaries Maintains Salt Gradient
The saltier cortex created by the ascending vasa recta peritubular capillaries amplifies the extraction of water in the descending loop. Without countercurrent, much less would remain in the blood.
Online kidney physiology animation
(b) Countercurrent exchanger.
The vasa recta preserves the
medullary gradient while
removing reabsorbed water
Continuous ambulatory peritoneal dialysis (CAPD)