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[ Pobierz całość w formacie PDF ]The Urinary System
26
Did you know...?
In ancient Greece, doctors checked the smell,
color, consistency, and taste of urine to help
diagnose an illness. Today we use more
sophisticated techniques.
Learning Outcomes
After completing this chapter, you should be able to do the following:
26-1
Identify the components of the urinary system, and describe the
functions it performs.
26-2
Describe the location and structural features of the kidneys,
identify major blood vessels associated with each kidney, trace
the path of blood flow through a kidney, describe the structure
of a nephron, and outline the processes involved in urine
formation.
26-3
Discuss the major functions of each portion of the nephron and
collecting system, and describe the primary factors responsible
for urine production.
26-4
Describe the factors that influence glomerular filtration
pressure and the rate of filtrate formation.
26-5
Identify the types and functions of transport mechanisms found
along each segment of the nephron, explain the role of
countercurrent multiplication, describe hormonal influence on
the volume and concentration of urine, and describe the
characteristics of a normal urine sample.
26-6
Describe the structures and functions of the ureters, urinary
bladder, and urethra; discuss the voluntary and involuntary
regulation of urination; and describe the micturition reflex.
26-7
Describe the effects of aging on the urinary system.
26-8
Give examples of interactions between the urinary system and
each of the other organ systems.
Clinical Notes
Analysis of Renal Blood Flow p. 969
Glomerulonephritis p. 975
Diuretics p. 991
Urinary Obstruction p. 998
Renal Failure and Kidney Transplantation p. 998
966
Unit 5
Environmental Exchange
An Introduction to the
Urinary System
body fluids, (2)
elimination
, the discharge of these waste
products into the environment, and (3) homeostatic regula-
tion of the volume and solute concentration of blood plasma.
The excretory functions of the urinary system are performed
by the two
kidneys
—organs that produce
urine
, a fluid con-
taining water, ions, and small soluble compounds. Urine
leaving the kidneys flows along the
urinary tract
, which
consists of paired tubes called
ureters
(u-RE-terz), to the
urinary bladder
, a muscular sac for temporary storage of
urine. On leaving the urinary bladder, urine passes through
the
urethra
(u-RE-thra), which conducts the urine to the ex-
terior. The urinary bladder and the urethra are responsible
for the elimination of urine, a process called
urination
or
micturition
(mik-choo-RISH-un). In this process, contrac-
tion of the muscular urinary bladder forces urine through the
urethra and out of the body.
ATLAS:
Embryology Summary 20: The De-
velopment of the Urinary System
In addition to removing waste products generated by
cells throughout the body, the urinary system has several
other essential homeostatic functions that are often over-
looked, including the following:
Most physiological wastes are removed by the urinary system.
In this chapter, we will consider the functional organization
of the urinary system and describe how the kidneys remove
metabolic waste products from the circulation to produce
urine. We also explain the major regulatory mechanisms con-
trolling urine production and concentration, and identify
how urine is transported to the urinary bladder and released
from the body through the urinary tract passageways.
26-1
Consisting of the kidneys,
ureters, urinary bladder, and
urethra, the urinary system has
three primary functions
The
urinary system
(
Figure 26–1
) has three major functions:
(1)
excretion
, the removal of organic waste products from
•
Regulating blood volume and blood pressure
, by adjusting
the volume of water lost in urine, releasing
erythropoietin, and releasing renin.
•
Regulating plasma concentrations of sodium, potassium,
chloride, and other ions
, by influencing the quantities lost
in urine and controlling calcium ion levels through the
synthesis of calcitriol.
•
Helping to stabilize blood pH
, by controlling the loss of
hydrogen ions and bicarbonate ions in urine.
•
Conserving valuable nutrients
, by preventing their
excretion in urine while excreting organic waste
products—especially nitrogenous wastes such as
urea
and
uric acid
.
•
Assisting the liver
in detoxifying poisons and, during
starvation, deaminating amino acids so that other tissues
can metabolize them down.
Kidney
Produces urine
Ureter
Transports urine
toward the
urinary bladder
Urinary bladder
These activities are carefully regulated to keep the compo-
sition of blood within acceptable limits. A disruption of any
one of them has immediate and potentially fatal consequences.
Temporarily stores
urine prior
to elimination
Urethra
Conducts urine to
exterior; in males,
transports semen
as well
CHECKPOINT
1. Name the three primary functions of the urinary
system.
2. Identify the components of the urinary system.
3. Define micturition.
See the blue Answers tab at the end of the book.
Anterior view
Figure 26–1
An Introduction to the Urinary System.
An
anterior view of the urinary system, showing the positions of its
components.
967
Chapter 26
The Urinary System
26-2
Kidneys are highly vascular
structures containing functional
units called nephrons, which
perform filtration, reabsorption,
and secretion
Renal artery
and vein
Suprarenal
gland
Diaphragm
Left kidney
11th and
12th ribs
Right
kidney
Lumbar
(L
1
)
vertebra
The kidneys are located on either side of the vertebral col-
umn, between vertebrae T
12
and L
3
(
Figure 26–2a
). The left
kidney lies slightly superior to the right kidney.
The superior surface of each kidney is capped by a
suprarenal gland. The kidneys and suprarenal glands lie be-
tween the muscles of the dorsal body wall and the parietal
peritoneum, in a retroperitoneal position (
Figure 26–2b
).
Ureter
Inferior
vena cava
Iliac crest
Abdominal
aorta
Tips
&
Tricks
To visualize the kidneys’ retroperitoneal positions, think of
each kidney as a picture on the body wall that got covered
over by wallpaper (the parietal peritoneum).
Urinary
bladder
Urethra
The position of the kidneys in the abdominal cavity is
maintained by (1) the overlying peritoneum, (2) contact with
adjacent visceral organs, and (3) supporting connective tis-
sues. Each kidney is protected and stabilized by three concen-
tric layers of connective tissue (
Figure 26–2b
):
(a) Posterior view
Parietal
peritoneum
Renal
vein
Renal
artery
Stomach
Aorta
External
oblique
1.
The
fibrous capsule
, a layer of collagen fibers that cov-
ers the outer surface of the entire organ.
2.
The
perinephric fat capsule
, a thick layer of adipose tis-
sue that surrounds the fibrous capsule.
3.
The
renal fascia
, a dense, fibrous outer layer that an-
chors the kidney to surrounding structures. Collagen
fibers extend outward from the fibrous capsule through
the perinephric fat to this layer. Posteriorly, the renal fas-
cia fuses with the deep fascia surrounding the muscles of
the body wall. Anteriorly, the renal fascia forms a thick
layer that fuses with the peritoneum.
Pancreas
Pancreas
Ureter
Spleen
Spleen
Vertebra
Vertebra
Left
kidney
Fibrous
capsule
In effect, each kidney hangs suspended by collagen fibers
from the renal fascia and is packed in a soft cushion of adi-
pose tissue. This arrangement prevents the jolts and shocks of
day-to-day living from disturbing normal kidney function. If
the suspensory fibers break or become detached, a slight
bump or jar can displace the kidney and stress the attached
vessels and ureter. This condition, called a
floating kidney
,
may cause pain or other problems from the distortion of the
ureter or blood vessels during movement.
A typical adult kidney (
Figures 26–3
and
26–4
) is reddish-
brown and about 10 cm (4 in.) long, 5.5 cm (2.2 in.) wide,
and 3 cm (1.2 in.) thick. Each kidney weighs about 150 g
Renal
fascia
Quadratus
lumborum
Perinephric
fat
Psoas
major
Inferior
vena cava
(b) Superior view
Figure 26–2
The Position of the Kidneys.
(a)
A posterior view of
the trunk.
(b)
A superior view of a transverse section at the level
indicated in part (a).
ATLAS:
Plate 57a,b
(5.25 oz). The
hilum
, a prominent medial indentation, is the
point of entry for the
renal artery
and
renal nerves
, and the
point of exit for the
renal vein
and the ureter.
968
Unit 5
Environmental Exchange
Esophagus (cut)
Diaphragm
Left suprarenal gland
Inferior vena cava
Celiac trunk
Left kidney
Left renal artery
Right suprarenal gland
Right kidney
Left renal vein
Superior mesenteric artery
Hilum
Left ureter
Quadratus lumborum
muscle
Abdominal aorta
Iliacus muscle
Left common iliac artery
Psoas major muscle
Gonadal artery and vein
Peritoneum (cut)
Rectum (cut)
Urinary bladder
Anterior view
Figure 26–3
The Gross Anatomy of the Urinary System.
The abdominopelvic cavity (with the digestive organs removed), showing the
kidneys, ureters, urinary bladder, and blood supply to the urinary structures.
ATLAS:
Plates 61a; 62a,b
Renal cortex
Renal medulla
Renal
pyramids
Renal pyramid
Inner layer of
fibrous capsule
Renal sinus
Renal sinus
Connection to
minor calyx
Adipose tissue
in renal sinus
Minor calyx
Major calyx
Renal pelvis
Renal pelvis
Hilum
Major calyx
Hilum
Renal lobe
Minor calyx
Renal papilla
Ureter
Renal papilla
Renal columns
Ureter
Renal lobe
Fibrous capsule
Fibrous
capsule
(a)
(b)
Figure 26–4
The Structure of the Kidney.
(a)
A diagrammatic view of a frontal section through the left kidney.
(b)
A frontal section of the
left kidney.
ATLAS:
Plates 57a,b; 61b
969
Chapter 26
The Urinary System
Sectional Anatomy of the Kidneys
The fibrous capsule covering the outer surface of the kidney
also lines the
renal sinus
, an internal cavity within the kidney
(
Figure 26–4a
). The fibrous capsule is bound to the outer sur-
faces of the structures within the renal sinus, stabilizing the po-
sitions of the ureter and of the renal blood vessels and nerves.
The kidney itself has an outer cortex and an inner
medulla. The
renal cortex
is the superficial portion of the
kidney, in contact with the fibrous capsule. The cortex is red-
dish brown and granular. The
renal medulla
consists of 6 to
18 distinct conical or triangular structures called
renal pyra-
mids
. The base of each pyramid abuts the cortex, and the tip
of each pyramid—a region known as the
renal papilla
—
projects into the renal sinus. Each pyramid has a series of fine
grooves that converge at the papilla. Adjacent renal pyramids
are separated by bands of cortical tissue called
renal
columns
, which extend into the medulla. The columns have
a distinctly granular texture, similar to that of the cortex. A
renal lobe
consists of a renal pyramid, the overlying area of
renal cortex, and adjacent tissues of the renal columns.
Urine production occurs in the renal lobes. Ducts within
each renal papilla discharge urine into a cup-shaped drain
called a
minor calyx
(KA-liks). Four or five minor calyces
(KA-li-sez) merge to form a
major calyx
, and two or three ma-
jor calyces combine to form the
renal pelvis
, a large, funnel-
shaped chamber. The renal pelvis, which fills most of the renal
sinus, is connected to the ureter, which drains the kidney.
Urine production begins in microscopic, tubular struc-
tures called
nephrons
(NEF-ronz) in the cortex of each renal
lobe. Each kidney has roughly 1.25 million nephrons, with a
combined length of about 145 km (85 miles).
between the cortex and medulla of the kidney. Each arcuate
artery gives rise to a number of
cortical radiate arteries
,
also called
interlobular arteries
, which supply the cortical
portions of the adjacent renal lobes. Branching from each
cortical radiate artery are numerous
afferent arterioles
,
which deliver blood to the capillaries supplying individual
nephrons (
Figure 26–5b,c
).
From the capillaries of the nephrons, blood enters a net-
work of venules and small veins that converge on the
cortical
radiate veins,
also called
interlobular veins
(
Figure 26–5a,c
).
The cortical radiate veins deliver blood to
arcuate veins
;
these in turn empty into
interlobar veins
, which drain di-
rectly into the
renal vein
; there are no segmental veins.
The kidneys and ureters are innervated by
renal nerves
.
Most of the nerve fibers involved are sympathetic postgan-
glionic fibers from the celiac plexus and the inferior splanch-
nic nerves.
l
pp. 534, 545
A renal nerve enters each kidney
at the hilum and follows the tributaries of the renal arteries to
reach individual nephrons. The sympathetic innervation (1)
adjusts rates of urine formation by changing blood flow and
blood pressure at the nephron and (2) stimulates the release
of renin, which ultimately restricts losses of water and salt in
the urine by stimulating reabsorption at the nephron.
CLINICAL NOTE
Analysis of Renal Blood Flow
The rate of blood flow
through the kidneys can be estimated by administering the
compound
para-aminohippuric acid (PAH)
, which is
removed at the nephrons and eliminated in urine. Virtually
all the PAH contained in the blood that arrives at the
kidneys is removed before the blood departs in the renal
veins. Renal blood flow can thus be approximated by
comparing plasma concentrations of PAH with the amount
secreted in urine. In practice, however, it is usually easier to
measure the glomerular filtration rate (p. 981).
Blood Supply and Innervation
of the Kidneys
Your kidneys receive 20–25 percent of your total cardiac out-
put. In normal, healthy individuals, about 1200 mL of blood
flow through the kidneys each minute—a phenomenal
amount of blood for organs with a combined weight of less
than 300 g (10.5 oz)!
Each kidney receives blood through a
renal artery
, which
originates along the lateral surface of the abdominal aorta near
the level of the superior mesenteric artery (
Figure 21–24a
,
pp. 755–756). As it enters the renal sinus, the renal artery pro-
vides blood to the
segmental arteries
(
Figure 26–5a
). Segmen-
tal arteries further divide into a series of
interlobar arteries
,
which radiate outward through the renal columns between the
renal pyramids. The interlobar arteries supply blood to the
arcuate
(AR-ku-at)
arteries
, which arch along the boundary
The Nephron
Each nephron (
Figure 26–6
) consists of a renal tubule and a
renal corpuscle. The
renal tubule
is a long tubular passage-
way which may be 50 mm (1.97 in.) in length. It begins at the
renal corpuscle
(KOR-pus-ul), a spherical structure consist-
ing of the
glomerular
(Bowman)
capsule
, a cup-shaped cham-
ber approximately 200 mm in diameter, and a capillary
network known as the
glomerulus
.
Blood arrives at the renal corpuscle by way of an afferent
arteriole. This arteriole delivers blood to the
glomerulus
(glo-MER-u-lus; plural,
glomeruli
), which consists of about
50 intertwining capillaries. The glomerulus projects into
the glomerular capsule much as the heart projects into the
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