Cortical nephron most abundant type of nephron 80

omitted, except for the vasa recta.
Cortical nephron
most abundant type
of nephron (80% this type)
Juxtamedullary nephron
long-looped nephron important in
establishing the medullary vertical
osmotic gradient (20% this type)
Fig. 14-5, p. 509

Nephron-­‐Tubular Component
• Bowman’s capsule
• Proximal tubule
• Loop of Henle
• descending limb
• ascending limb
• Distal tubule
• CollecFng duct

Simple model of kidney func1on
Filtra1on + Secre1on – Reabsorp1on = Excre1on
1 3 2 4
Fig 14-­‐21

Afferent
arteriole
Efferent
arteriole
Glomerulus
Bowman ’ s
capsule
Kidney
tubule
(entire
length,
uncoiled)
Urine excretion
(eliminated
from the body)
To venous system
(conserved
for the body)
Peritubular
capillary
20% of the
plasma that
enters the
glomerulus
is filtered
80% of the plasma
that enters the
glomerulus is
not filtered
and leaves through
the efferent arteriole
= Tubular secretion — selective movement of nonfiltered
substances from the peritubular capillaries into the tubular lumen
= Tubular reabsorption — selective movement of filtered
substances from the tubular lumen into the peritubular capillaries
= Glomerular filtration — nondiscriminant filtration of a protein-free
plasma from the glomerulus into Bowman ’ s capsule
GF
TR
TS
Fig. 14-6, p. 510
GF
125 ml/min
180 L/day
Ave plasma vol
= 2.75L
Therefore
kidneys filter
entire plasma
vol ~65X/day
TR: 178.5/180 L reabsorbed
125 ml/min fiiltered; 124 ml/
min reabsorbed

Glomeruli are beau1ful things

Glomerular Capillary Wall
1. A single layer of fla^ened endothelial cells perforated by
many pores.
2. Basement membrane is acellular and gela1nous composed of
collagen and glycoproteins; the collagen gives structureal
strength; the glycoproteins are nega1vely charged and repel
albumin and other plasma proteins which are also nega1vely
charged. Therefore plasma proteins are almost completely
excluded from the filtrate.
3. Any plasma proteins that do slip into the filtrate are picked
up by the proximal tubule by endocytosis-­‐degraded into amino
acids-­‐returned to blood.
4. Thus-­‐no proteins should be included in the urine!

Capillary pore
(fenestration)
Afferent arteriole Efferent arteriole
Glomerulus
Bowman ’ s
capsule
Lumen of
Bowman ’ s
capsule
Outer layer of
Bowman ’ s capsule
Proximal convoluted tubule
Inner layer
of Bowman ’ s capsule
(podocytes)
Lumen of
glomerular
capillary
Endothelial
cell
Basement
membrane
Basement
membrane
Podocyte
foot process
Filtration slit
Filtration
slit
Endothelial
cell
Filtration
slit
Lumen of
glomerular
capillary
Endothelial
cell
Capillary pore
fenestration)
Lumen of
Bowman ’ s capsule
Lumen of glomerular
capillary
Podocyte
foot process
Basement
membrane
1
3
2
Fig. 14-7a, p. 511
Afferent arteriole to each Bowman’s capsule is wider than the narrow efferent
arteriole (not shown below) which maintaines high blood P as a result of the
blood damming up in the glomerular capillaries—it’s the major force producing
glomerular filtraFon.

PODOCYTES of Bowman’s Capsule

Lumen of
glomerular
capillary
Podocyte
foot processes
Filtration
slit
Capillary pore
or fenestration
Basement
membrane
Lumen of
Bowman ’ s
capsule
Endothelial
cell
1
2
3
Fig. 14-7b, p. 511