Chapter 19a
The Kidneys
About this Chapter
• Anatomy of the urinary system
• Overview of kidney function
• Homeostasis
• pH
• Electrolytes
• fluid
• Filtration
• Reabsorption
• Secretion
• Excretion
• Micturition
Functions of the Kidneys
• Regulation of extracellular fluid volume and
blood pressure
• Regulation of osmolarity
• Maintenance of ion balance
• Homeostatic regulation of pH
• Excretion of wastes
• Production of hormones
Anatomy: The Urinary System
THE URINARY SYSTEM
Kidney
Ureter
Urinary bladder
Urethra
(a) The urinary system
Figure 19-1a
Anatomy: The Urinary System
Diaphragm
Left adrenal gland
Inferior vena cava
Left kidney
Right kidney
Renal artery
Ureter
Aorta
Renal vein
Peritoneum
(cut)
Urinary
bladder
Rectum
(cut)
(b) The kidneys are located retroperitoneally
at the level of the lower ribs.
Figure 19-1b
Anatomy: The Urinary System
Nephrons
Cortex
Polycystic kidney
Medulla
Renal pelvis
Ureter
Capsule
(c) The kidney, in cross section.
Figure 19-1c
Anatomy: The Urinary System
Arterioles
Nephrons
Cortex
Medulla
(i) Some nephrons dip deep
into the medulla.
Figure 19-1i
Anatomy: The Urinary System
Efferent arteriole
Juxtaglomerular
apparatus
Peritubular
capillaries
Peritubular
capillaries
Glomerulus
Afferent
arteriole
Glomerulus
(capillaries)
Vasa recta
Collecting
duct
Loop of
Henle
(g) One nephron has two arterioles
and two sets of capillaries.
(h) Juxtamedullary nephron
with vasa recta
Figure 19-1g–h
Anatomy: The Urinary System
Figure 19-1d–e
Anatomy: The Urinary System
STRUCTURE OF THE NEPHRON
Glomerulus
Cut edge of
nephron tubule
(f) The capillaries of the glomerulus form a
ball-like mass.
Figure 19-1f
Anatomy: The Urinary System
Bowman’s
capsule
Proximal tubule
Descending
limb of loop
begins
Distal tubule
Ascending
limb of loop
ends
Collecting
duct
Descending
limb
(j) Parts of a nephron
Ascending
limb
Loop of
Henle
To bladder
Figure 19-1j
Kidney Function
• Filtration, reabsorption, secretion, and
excretion
Distal tubule
Peritubular capillaries
Efferent
arteriole
Glomerulus
Afferent
arteriole
Bowman’s
capsule
Proximal
tubule
KEY
= Filtration: blood to lumen
= Reabsorption: lumen to blood
Loop
of
Henle
Collecting
duct
To renal
vein
= Secretion: blood to lumen
= Excretion: lumen to external
environment
To bladder and
external environment
Figure 19-2
Kidney Function
Table 19-1
Kidney Function
• The urinary excretion of substance depends
on its filtration, reabsorption, and secretion
Glomerulus
Efferent
arteriole
Peritubular
capillaries
To renal vein
Tubule
Afferent
arteriole
Bowman’s
capsule
Amount
Amount –
reabsorbed
filtered
To bladder and
external environment
+
Amount
secreted
=
amount of solute
excreted
Figure 19-3
The Filtration Fraction
Efferent arteriole
80%
Afferent
arteriole
1 Plasma volume
entering afferent
arteriole = 100%
Peritubular
capillaries
2 20% of
volume
filters.
Bowman’s
capsule
4 >99% of plasma
entering kidney
returns to systemic
circulation.
3 >19% of fluid
is reabsorbed.
5 <1% of
volume is
excreted to
external
environment.
Remainder
of nephron
Glomerulus
Figure 19-4
The Renal Corpuscle
Thick
ascending
limb of
loop of
Henle
Efferent
arteriole
Bowman’s
capsule
Capsular
epithelium
Podocyte
Proximal
tubule
Glomerular
capillary
Afferent
arteriole
Lumen of
Bowman’s
capsule
(a) The epithelium around glomerular
capillaries is modified into podocytes.
Figure 19-5a
The Renal Corpuscle
Foot process
of podocyte
Filtration slit
Pores in
endothelium
Basal lamina
Capillary
lumen
Filtered
material
Lumen of
Bowman’s
capsule
(d) Filtered substances pass
through endothelial pores
and filtration slits.
Figure 19-5d
The Renal Corpuscle
Podocyte
Lumen of
Bowman’s
capsule
Glomerular
capillary
Podocyte
foot
processes
Capillary
endothelium
Mesangial
cell
(c) Podocyte foot processes surround each
capillary, leaving slits through which filtration
takes place.
Figure 19-5c
Forces that Influence Filtration
• Hydrostatic pressure (blood pressure)
• Colloid osmotic pressure
• Fluid pressure created by fluid in Bowman’s
capsule
Filtration
• Filtration pressure in
the renal corpuscle
depends on
hydrostatic pressure,
and is opposed by
colloid osmotic
pressure and
capsule fluid
pressure
Efferent
arteriole
15 mm Hg Pfluid
30 mm Hg 
Net filtration
pressure =
10 mm Hg
PH 55 mm Hg
Afferent
arteriole
Glomerulus
Bowman’s
capsule
PH
–

–
Pfluid
55
–
30
–
15
= net filtration pressure
= 10mm Hg
KEY
PH = Hydrostatic pressure (blood pressure)
 = Colloid osmotic pressure gradient
due to proteins in plasma but not
in Bowman’s capsule
Pfluid = Fluid pressure created by fluid in
Bowman’s capsule
Figure 19-6
Filtration
• Autoregulation of glomerular filtration rate
takes place over a wide range of blood
pressures
Figure 19-7
Filtration
• Resistance changes in renal arterioles alter
renal blood flow and GFR
Figure 19-8a
Filtration
Figure 19-8b
Filtration
Figure 19-8c
GFR Regulation
• Myogenic response
• Similar to autoregulation in other systemic
arterioles
• Tubuloglomerular feedback
• Paracrine control by macula densa
• Hormones and autonomic neurons
• By changing resistance in arterioles
• By altering the filtration coefficient
• Surface area
Juxtaglomerular Apparatus
Bowman’s capsule
Efferent arteriole
Ascending
limb of loop
of Henle
Glomerulus
Macula densa cells
Proximal tubule
Granular cells
Afferent arteriole
(a)
Endothelium
(b)
Figure 19-9
Tubuloglomerular Feedback
1
Glomerulus
Distal tubule
GFR increases.
Efferent arteriole
2 Flow through tubule increases.
Bowman’s capsule
3 Flow past macula densa increases.
Macula densa
4
1
5
Granular cells
4
Paracrine from macula
densa to afferent arteriole
Afferent arteriole
2
3
Proximal
tubule
5 Afferent arteriole constricts.
Resistance in afferent
arteriole increases.
Collecting
duct
Hydrostatic pressure
in glomerulus decreases.
GFR decreases.
Loop
of
Henle
Figure 19-10, steps 1–5 (4 of 4)