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UNIT B: Human Body Systems
Chapter 8: Human Organization
Chapter 9: Digestive System
Chapter 10: Circulatory System and
Lymphatic System
Chapter 11: Respiratory System
Chapter 12: Nervous System
Chapter 13: Urinary System: Section 13.2
Chapter 14: Reproductive System
UNIT B Chapter 13: Urinary System
Chapter 13: Urinary System
What is the role of the kidneys in the
body?
How would problems in the
collecting ducts of the nephrons
cause kidney failure?
Born with Bad Kidneys. The kidney on the left
is normal. The kidney on the right is from a
person who has polycystic kidney disease
(PKD). In PKD, cysts form within the collecting
ducts of the nephrons, which can lead to kidney
failure. A kidney transplant is required to treat
PKD.
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Polycystic kidney disease seems to
cause more serious problems in
people of African descent, especially
those who have sickle cell disease.
Sickle cell is mainly a disease of the
red blood cells. What does this have
to do with the kidneys?
UNIT B Chapter 13: Urinary System
Section 13.2
13.2 Anatomy of the Kidney and Excretion
The kidney’s blood supply
is supported by many
branches of the renal vein
and renal artery.
Figure 13.3 Anatomy of the
kidney. a. A lengthwise section of
the kidney showing the blood
supply. Note that the renal artery
divides into smaller arteries, and
these divide into arterioles. Venules
join to form small veins, which form
the renal vein.
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UNIT B Chapter 13: Urinary System
A kidney has three regions.
• Renal cortex: outer,
granulated layer
• Renal medulla: contains
cone-shaped tissue masses
called renal pyramids
• Renal pelvis: central space
that is continuous with the
ureter
Figure 13.3 Anatomy of the kidney.
c. The same section as (a) without the
blood supply. Now it is easier to
distinguish the renal pelvis, medulla,
and cortex, which connects with the
ureter.
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Section 13.2
UNIT B Chapter 13: Urinary System
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Section 13.2
Figure 13.3 Anatomy of the kidney. a. A lengthwise section of the kidney showing the blood supply.
Note that the renal artery divides into smaller arteries, and these divide into arterioles. Venules join to
form small veins, which form the renal vein. b. An enlargement showing the placement of nephrons.
c. The same section as (a) without the blood supply. Now it is easier to distinguish the renal pelvis ,
medulla, and cortex, which connects with the ureter. d. A lengthwise section of an actual kidney.
UNIT B Chapter 13: Urinary System
Anatomy of a Nephron
The kidney is composed of
over 1 million nephrons, also
known as renal or kidney
tubules.
Figure 13.3 Anatomy of the
kidney. b. An enlargement showing
the placement of nephrons.
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Section 13.2
UNIT B Chapter 13: Urinary System
Blood Supply in a Nephron
Each nephron has it own blood
supply.
• From the renal artery, an
afferent arteriole leads to the
glomerulus, a knot of
capillaries inside the
glomerular capsule
• Blood leaving the glomerulus
enters the efferent arteriole,
which takes blood to the
peritubular capillary network,
before exiting through the
renal vein
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Section 13.2
Figure 13.4 Nephron anatomy. a. You can trace the path of
blood through a nephron by following the black arrows.
UNIT B Chapter 13: Urinary System
Parts of a Nephron
Glomerular capsule
(Bowman’s capsule)
• Inner layer composed of
cells called podocytes
• Spaces between podocytes
allow small molecules from
the glomerulus to enter the
glomerular capsule
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Section 13.2
UNIT B Chapter 13: Urinary System
Parts of a Nephron
Proximal convoluted tubule
(PCT)
• Lined with cuboidal
epithelial cells that have
packed microvilli to
increase the surface area for
reabsorption
o Also contain several
mitochondria to carry
out active reabsorption
of substances
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Section 13.2
UNIT B Chapter 13: Urinary System
Parts of a Nephron
Loop of Henle
• Also known as the loop of
the nephron
• Consists of a descending
limb and an ascending
limb
• Lined with simple
squamous epithelium
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Section 13.2
UNIT B Chapter 13: Urinary System
Parts of a Nephron
Distal convoluted tubule (DCT)
• Composed of cuboidal
epithelial cells that lack
microvilli but have many
mitochondria
• Helps move molecules from
the blood into the tubule
(tubular secretion)
• The DCTs of many nephrons
enter one collecting duct
• Collecting ducts carry urine
to the renal pelvis
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Section 13.2
UNIT B Chapter 13: Urinary System
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Figure 13.4 Nephron anatomy.
Section 13.2
UNIT B Chapter 13: Urinary System
Section 13.2
Urine Formation
Urine formation is divided into the following processes:
• Pressure filtration: water, salts, nutrients, and wastes
move from the glomerulus to the inside of the glomerular
capsule
• Selective reabsorption: nutrient and salt molecules are
actively reabsorbed from the convoluted tubules into the
blood of the peritubular capillary network
• Tubular excretion: certain molecules are actively
secreted from the blood in the peritubular capillary
network into the convoluted tubules
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UNIT B Chapter 13: Urinary System
Figure 13.5 Processes in
urine formation. The
three main processes in
urine formation are
described in boxes and
colour-coded to arrows
that show the movement
of molecules into or out of
the nephron at specific
locations. In the end, urine
is composed of the
substances within the
collecting duct (see blue
arrow).
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Section 13.2
UNIT B Chapter 13: Urinary System
Pressure Filtration
Pressure filtration occurs when
blood enters the afferent arteriole
and the glomerulus.
• Due to blood pressure, water
and small molecules move
from the glomerulus to the
inside of the glomerular
capsule
o These filterable blood
components form the
glomerular filtrate
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Section 13.2
UNIT B Chapter 13: Urinary System
Section 13.2
Selective Reabsorption
In selective reabsorption, nutrients and ions from the glomerular
filtrate in the convoluted tubules are reabsorbed into the blood of
the peritubular capillary network.
Examples:
• Na+ ions are actively reabsorbed into the blood, with Cl- ions
following passively
o This reabsorption of salt (NaCl) results in water moving
passively from the tubule into the blood
• Glucose and amino acids are actively reabsorbed into the blood
almost exclusively at the proximal convoluted tubule
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UNIT B Chapter 13: Urinary System
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Section 13.2
UNIT B Chapter 13: Urinary System
Section 13.2
Selective Reabsorption
The glomerular filtrate that enters the proximal convoluted tubule
is divided into two portions.
• Reabsorbed filtrate components: reabsorbed from the tubule
into blood
• Nonreabsorbed filtrate components: continue to pass through
the nephron to be processed into urine (become the tubular fluid
that enters the loop of Henle)
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UNIT B Chapter 13: Urinary System
Section 13.2
Tubular Excretion
Tubular excretion is another way substances are removed
from blood in the peritubular capillary network and added to the
tubular fluid.
• Hydrogen ions, potassium ions, creatinine, and certain drugs
are removed by active transport from the blood in the
peritubular capillary network into the convoluted tubules
• The resulting urine contains:
o Substances that have undergone glomerular filtration but
have not been reabsorbed
o Substances that have undergone tubular excretion
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UNIT B Chapter 13: Urinary System
Section 13.2
Check Your Progress
1. Identify the parts of a nephron that are found in the
renal cortex and the renal medulla.
2. Explain the difference in microscopic structure which
suggests that the PCT, but not the DCT, is specialized
for reabsorption.
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UNIT B Chapter 13: Urinary System
Section 13.2
Check Your Progress
3. Explain how the kidney uses the processes of diffusion,
passive transport, and active transport.
4. Explain where in the nephron, and by what process,
glucose is normally returned from the glomerular
filtrate to the blood.
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UNIT B Chapter 13: Urinary System
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Section 13.2
UNIT B Chapter 13: Urinary System
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Section 13.2