Chapter 27
*Lecture Outline
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Chapter 27 Outline
• General Structure and Functions of the
Urinary System
• Kidneys
• Urinary Tract
• Aging and the Urinary System
• Development of the Urinary System
Functions of Urinary System
•
•
•
•
•
•
Removal of waste products from the
bloodstream
Production of urine
Storage and excretion of urine
Blood volume regulation
Regulation of erythrocyte production
Regulation of Blood Pressure
Urinary System
The urinary system is comprised of the
following structures:
• kidneys
• ureters
• urinary bladder
• urethra
Urinary System
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Diaphragm
Adrenal gland
Kidney
Renal artery
Renal vein
Inferior vena cava
Descending abdominal aorta
Ureter
Iliac crest
Psoas major muscle
Rectum
Uterus
Urinary
bladder
Urethra
(a) Anterior view
Latissimus
dorsi muscle (cut)
Lung
Ureter
11th rib
12th rib
Psoas major muscle
Right kidney
L2 vertebra
Iliac crest
Quadratus lumborum
muscle (cut)
Left kidney
Urinary bladder
Urethra
Figure 27.1
(b) Posterior view
a(right): © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel
Kidneys
• Located retroperitoneal on the posterior
abdominal wall
• The superior pole of the left kidney is at the
level of T12, whereas the superior pole of the
right kidney is about 2 cm lower to
accommodate the large size of the liver
• The kidneys have a concave medial border
called the hilum, where vessels, nerves, and the
ureter connect with the kidney
• The hilum is continuous with an internal space
called the renal sinus
Urinary System
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Diaphragm
Adrenal gland
Kidney
Renal artery
Renal vein
Inferior vena cava
Descending abdominal aorta
Ureter
Iliac crest
Psoas major muscle
Rectum
Uterus
Urinary
bladder
Urethra
(a) Anterior view
Figure 27.1
a(right): © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel
Urinary System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Latissimus
dorsi muscle (cut)
Lung
11th rib
Left kidney
12th rib
Ureter
Psoas major muscle
Right kidney
L2 vertebra
Quadratus lumborum
muscle (cut)
Iliac crest
Urinary bladder
Urethra
Figure 27.1
(b) Posterior view
Urinary System
Kidneys
Each kidney is surrounded and supported by several tissue
layers (from deepest to most superficial):
• Fibrous capsule—in direct contact with outer surface of
kidney
• Perinephric fat—provides cushioning and insulation to
the kidney
• Renal fascia—anchors kidney to posterior abdominal
wall
• Paranephric fat—outermost layer surrounding the
kidney between renal fascia and peritoneum
Kidneys
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Anterior
Stomach
Liver
Pancreas
Large intestine
Descending
abdominal aorta
Renal vein
Renal artery
Renal hilum
Body of
vertebra L2
Spleen
Inferior
vena cava
Peritoneum
Right kidney
Fibrous capsule
Perinephric fat
Left kidney
Renal fascia
Rib
Paranephric fat
Psoas major
muscle
Quadratus lumborum
muscle
Posterior
Figure 27.2
Regions of the Kidney
• Divided into an outer renal cortex and an
inner renal medulla
• Extensions of the renal cortex, called
renal columns, project into the renal
medulla and subdivide the medulla into
renal pyramids (medullary pyramids)
• A typical kidney contains 8–15 renal
pyramids
Regions of the Kidney
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Superior pole
Fibrous capsule
Renal cortex
Renal medulla
Renal column
Corticomedullary junction
Minor calyx
Renal papilla
Adipose connective
tissue in renal sinus
Renal sinus
Minor calyx
Major calyx
Renal artery
Renal pelvis
Renal vein
Renal pelvis
Major calyx
Renal pyramid
Renal pyramid
Renal lobe
Renal column
Ureter
Ureter
Inferior pole
Right kidney, coronal section
left: © Ralph T. Hutchings/Visuals Unlimited
Figure 27.3
Regions of the Kidney
• The wide base of the renal pyramid makes
contact with the cortex in a region called
the corticomedullary junction.
• The apex (tip) of the renal pyramid is
called the renal papilla.
Tubing within the Renal Sinus
• Each renal papilla projects into a hollow
funnel-shaped structure called the minor
calyx.
• Several minor calyces fuse to form a
major calyx.
• The major calyces fuse to form the renal
pelvis, which collects the total urine output
from one kidney and transports it into the
ureter.
Regions of the Kidney
Figure 27.3
Arterial Supply to the Kidney
• Blood enters kidneys by the renal
arteries.
• Within the renal sinus, the renal arteries
branch into segmental arteries.
• Segmental arteries branch into interlobar
arteries.
• Interlobar arteries branch into arcuate
arteries.
• Arcuate arteries branch into interlobular
arteries.
Blood Supply to the Kidney
Figure 27.4
Arterial Supply to the Kidney
• As interlobular arteries enter the kidney cortex,
they extend small branches called afferent
arterioles.
• The afferent arterioles enter a structure called
the renal corpuscle and form a tuft (ball) of
capillaries called the glomerulus.
• Some plasma is filtered out of the capillaries into
the capsular space within the renal corpuscle.
• The remaining blood exits the glomerulus and
the renal corpuscle as the efferent arteriole.
Blood Supply to the Kidney
Figure 27.4
Capillary Supply to the Kidney
Efferent arterioles branch into one of two
capillary networks:
• Peritubular capillaries—surround the
convoluted tubules and reside primarily in
the cortex
• Vasa recta—associated mainly with the
nephron loop and primarily reside in the
medulla
Blood Supply to the Kidney
Figure 27.4
Venous Return from the Kidney
• The peritubular capillaries and vasa recta drain
into a network of veins.
• The smallest veins are the interlobular veins.
• Interlobular veins merge to form arcuate veins.
• Arcuate veins merge to form the interlobar
veins.
• Interlobar veins merge in the renal sinus to form
the renal vein in each kidney.
Blood Supply to the Kidney
Figure 27.4
Nephrons
•
•
The nephron is the functional filtration unit of
the kidney.
There are approximately 1.25 million nephrons
in each kidney. The nephrons form urine
through three interrelated processes:
–
–
–
•
filtration
tubular reabsorption
tubular secretion
The final product is the formation of urine.
Two Types of Nephrons
1. Cortical nephrons—about 85% of all
nephrons; the bulk of the nephron
structures reside in the kidney cortex and
only a relatively small component enters
the kidney medulla
2. Juxtamedullary nephrons—their renal
corpuscle lies near the corticomedullary
junction and their long nephron loops
extend deep into the medulla
Two Types of Nephrons
Figure 27.5
Structural
The nephron is comprised of the following
components:
• renal corpuscle
• proximal convoluted tubule
• nephron loop
• distal convoluted tubule
Components of the Nephron
Figure 27.5
Renal Corpuscle
•
Composed of two structures:
– glomerulus—a thick tangle of fenestrated capillaries
– glomerular capsule—an epithelial covering over the
glomerulus
•
•
Corpuscle has a vascular pole, where the
afferent arteriole enters and the efferent
arteriole exits
Also has a tubular pole, where the proximal
convoluted tubule exits
Renal Corpuscle
Figure 27.6
Glomerular Capsule
Comprised of two layers:
1. Visceral layer—directly overlies and
comes in contact with the glomerulus;
comprised of specialized cells called
podocytes
2. Parietal layer— formed from a simple
squamous epithelium
Figure 27.6
Glomerular Capsule
Figure 27.6
Podocytes
• Have long processes called pedicels that wrap
around the glomerular capillaries but do not
completely ensheathe it.
• The pedicels are separated from each other by
thin spaces called filtration slits.
• The filtration slits and the fenestrated capillary
wall makes up the filtration membrane, which
mostly leaks indiscriminate contents from the
plasma into the capsule.
• It is the role of the remainder of the nephron to
adjust the contents of the urine.
Podocytes Covering the
Glomerular Capillaries
Figure 27.6
Proximal Convoluted Tubule
• Begins at tubular pole of renal corpuscle
• Walls comprised of simple cuboidal epithelium
with tall microvilli
• Cells reabsorb almost all nutrients leaked
through the filtration membrane
• Reabsorbed nutrients and water enter the
peritubular capillaries and are returned to the
general circulation in the vascular system
Nephron Components
Figure 27.5
Nephron Loop
Nephron loop (loop of Henle) projects into the
medulla. Each loop has two limbs:
1. Descending limb—extends from the
cortex into the medulla
2. Ascending limb—returns from medulla
into cortex
Both limbs facilitate reabsorption of water and
solutes.
Nephron Components
Figure 27.5
Distal Convoluted Tubule
• Found in renal cortex
• Secretes K+ and H+ from peritubular
capillaries into tubular fluid
Nephron Components
Figure 27.5
Nephron Components
Nephron Components
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Efferent
arteriole
Proximal
convoluted
tubule
Renal
corpuscle
Renal
corpuscle
Distal
convoluted
tubule
Distal
convoluted
tubule
Afferent
arteriole
Collecting
duct
Proximal
Convoluted
tubule
LM 100 x
(b) Histology of renal cortex
Nephron loop
Tall microvilli
Short, sparse microvilli
Nucleus
Mitochondria
Proximal convoluted tubule
(a) Nephron components
Basement
membrane
(c) Convoluted tubule epithelia
Thick limbs of
nephron loops
Collecting ducts
Thin limbs of
nephron loops
Figure 27.7
Vasa recta
LM 100x
(d) Histology of renal medulla
b: © Dr. Alvin Telser; d: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Distal convoluted tubule
Juxtaglomerular Apparatus
The juxtaglomerular apparatus is important in
regulation of blood pressure and is comprised of
the following components:
• juxtaglomerular cells—modified smooth
muscle cells of the afferent arteriole located at
the vascular pole of the renal corpuscle
• macula densa—group of modified epithelial
cells in the distal convoluted tubule that come in
contact with the juxtaglomerular cells
Juxtaglomerular Apparatus
Figure 27.6
Innervation of the Kidney
• Innervated by a mass of sensory and
autonomic fibers collectively called the
renal plexus, which enters the kidney at
the hilum
• CN X = Vagus (parasympathetic)
• Pain from kidneys is usually referred to
dermatomes T10–T12
Urinary Tract
Composed of the following components:
• ureters
• urinary bladder
• urethra
Urinary System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diaphragm
Adrenal gland
Kidney
Renal artery
Renal vein
Inferior vena cava
Descending abdominal aorta
Ureter
Iliac crest
Psoas major muscle
Rectum
Uterus
Urinary
bladder
Urethra
(a) Anterior view
Figure 27.1
a(right): © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel
Ureters
•
•
•
Fibromuscular tubes that conduct urine from
the kidney to the urinary bladder
Originate at the renal pelvis as it exits the
hilum of the kidney then enter the
posterolateral wall of the base of the urinary
bladder
Wall of ureter has three layers:
1.
2.
3.
mucosa
muscularis
adventitia
Ureters
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Mucosa
Mucosa
Lamina
propria
Muscularis
Adventitia
Transitional
epithelium
Mucosa
Muscularis
Lumen
Adventitia
LM 18x
(a) Ureter cross section
(b) Histology of ureter
b: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Figure 27.8
Urinary Bladder
• Main function is reservoir for urine
• Located immediately posterior to pubic
symphysis
• In females, the urinary bladder lies
anteroinferior to the uterus and directly
anterior to the vagina
• In males, the urinary bladder lies anterior
to the rectum and superior to the prostate
gland
Urinary Bladder
Comparison of an empty and filled urinary
bladder:
Figure 27.9
Urinary Bladder
• The posteroinferior triangular area of the
urinary bladder is called the trigone.
• It is defined by the two ureteral opening
and the urethral opening.
Urinary Bladder Trigone
Figure 27.9
Wall of Urinary Bladder
Four tunics form the wall of the urinary bladder:
1. Mucosa—transitional epithelium that lines the
internal surface of the bladder; rugae allow for
distension of bladder
2. Submucosa—supports urinary bladder wall
3. Muscularis—three layers of smooth muscle
called detrusor muscle; an internal urethral
sphincter muscle is present at the urethral
opening
4. Adventitia—outer layer of areolar connective
tissue
Urinary Bladder Trigone
Figure 27.9
Urethra
•
•
The urethra is a fibromuscular tube that
originates at the neck of the urinary
bladder and conducts urine to the
exterior of the body.
Two sphincters control the release of
urine from the urinary bladder in to the
urethra:
1. internal urethral sphincter
2. external urethral sphincter
Urethra
Figure 27.10
Female Urethra
• Has the single function of transporting
urine to the exterior of the body
Figure 27.10
Male Urethra
•
•
Has two functions–urinary and
reproductive–because it serves to
transport both urine and semen
Partitioned into three segments:
1. prostatic urethra
2. membranous urethra
3. spongy urethra
•
Ends as an opening called the external
urethral orifice
Male Urethra
Figure 27.10
Development of the Urinary System
Figure 27.11
Development of the Urinary System
Figure 27.12