The Excretory System
Chapter 23
What is the Urinary System?
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The purifying system for blood.
Blood passes through the urinary system in
order to be cleaned of toxins and poisons.
Organs of the urinary system include:
Kidneys – paired
Ureters – paired
Bladder – single
Urethra - single
The human excretory system
regulates the chemical composition
of body fluids by removing metabolic
wastes and retaining the proper
amounts of water, salts, and
nutrients. Components of this
system in vertebrates include the
kidneys, liver, lungs, and skin.
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By doing this, the excretory system allows
the body to maintain HOMEOSTASIS.
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Homeostasis is the body’s ability to maintain
a constant internal environment.
The Right
Kidney and
Adrenal Gland
CAT 
The Urinary System
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The KIDNEYS are found approximately 2 inches
from the vertebral column (3 fingerbreadths lateral).
The right kidney is LOWER than the left.
The superior edge of the left kidney is at T12. The
inferior edge of the right is at L3.
They are moveable during breathing. They move
approximately I inch in either direction.
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The URETER enters the bladder from below.
Which means that the bladder fills from the
bottom.
The URETHRA is central. It is approx. 1.5
inches long in females and 8 inches long in
males. This fact is important because the
length of a foley catheter differs in the sexes.
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A coronal section (frontal section) of the
kidney will reveal the junction of the ureter
and kidney form a funnel.
This area is called the RENAL PELVIS.
The renal pelvis contains the COLLECTING
TUBULES from the RENAL MEDULLA.
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The outer portion of the kidney is the RENAL
CORTEX. In humans, the renal cortex
extends between the RENAL PYRAMIDS.
Each pyramid branches into smaller funnels
called CALYX. Each calyx receives part of
the medulla. Each calyx has its own
pyramid.
The Nephron
The nephron consists of a cupshaped capsule containing
capillaries and the glomerulus,
and a long renal tube. Blood
flows into the kidney through the
renal artery, which branches into
capillaries associated with the
glomerulus. Arterial pressure
causes water and solutes from
the blood to filter into the
capsule. Fluid flows through the
proximal tubule, which include
the loop of Henle, and then into
the distal tubule. The distal
tubule empties into a collecting
duct. Fluids and solutes are
returned to the capillaries that
surround the nephron tubule.
The nephron has three functions:
 Glomerular filtration of water and solutes
from the blood.
 Tubular reabsorption of water and conserved
molecules back into the blood.
 Tubular secretion of ions and other waste
products from surrounding capillaries into the
distal tubule.
How do the nephrons work?
1.
The outermost layer of the
kidneys, the cortex, is
composed of approximately
1,250,000 structural units called
nephrons. Blood is carried to
the kidneys by the renal arteries,
which branch into smaller
arteries inside the cortex and
then lead to clusters of
capillaries called glomeruli.
2.
Each glomerulus is
surrounded by a "C"-shaped
structure called the
Bowman's Capsule. It is
here that materials such as
urea, salts, water, glucose, &
others pass from the blood
into the nephron.
3.
These materials (referred to as the
"filtrate") pass through the loop of
Henle. As the filtrate travels through
the loop of Henle, useful substances
are reabsorbed into the surrounding
capillaries (which connect to veins that
will transport the "clean" blood back to
the heart via the renal vein).
4.
About 180 liters of filtrate is produced each
day, but only 1.5 liters of urine. So as you
can see, most materials that initially enter the
nephron are reabsorbed, leaving only the
urea, salts, & some water in the
tubule. These metabolic wastes form urine,
which is transported to the renal pelvis by the
collecting tubule.
Minor
calyx
Renal
capsule
Major
calyx
Renal artery
Renal vein
Renal
pelvis
ureter
Renal
medulla
Renal pyramid
Renal cortex
Renal column
1.
Renal Vein
2.
Renal Artery
3.
Renal Calyx
4.
Medullary
Pyramid
5.
Renal Cortex
6.
Segmental
Artery
7.
Interlobar
Artery
8.
Arcuate
Artery
9.
Arcuate Vein
10.
Interlobar
Vein
11.
Segmental
Vein
12.
Renal
Column
13.
Renal
Papillae
14.
Renal Pelvis
15.
Ureter
1.
Renal Capsule
2.
Renal Cortex
3.
Renal Medulla
4.
Renal Pyramid
5.
Renal Pelvis
6.
Renal Column
7.
Renal Calyx
8.
Ureter
The Right
Kidney and
Adrenal Gland
Adult normal kidney with a
renal cyst.
A much larger cyst at the
upper pole of the kidney
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There are approximately 8-10 calyces and a pyramid
for each one in each human kidney.
The functional unit of the kidney is the NEPHRON.
There are about 2.5 million nephrons in each kidney.
The ADRENAL GLANDS (suprarenal glands) are
endocrine glands found on the superior portion of
each kidney. They secrete EPINEPHRINE and
NOREPINEPHRINE.
The Layers of the Kidney
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Each layer has a specific job
1. Cortex - nephrons for filtration
2. Medulla – collecting layer
3. Pelvis – collecting tubules come together
Suprarenal
glands
Suprarenal
glands
Kidney
Renal
vessels
urachus
urachus
Trigone
Is this a male or
ureter female?
Bladder
Prostatic Urethra
Trigone of
Prostate Gland
bladder
Ureter
1 – epithelium
2 – connective tissue
3 – smooth muscle
Lumen
What is in Urine?
Urea – derived from the breakdown of
amino acids (building blocks of
proteins).
Uric Acid – results from the turnover
of nucleic acids.
Creatinine – formed by the breakdown
of creatine phosphate (found in
muscle)
Other functions of the urinary system
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Regulation of the volume and chemical
makeup of the blood.
Maintenance of the proper balance between
water and salts and between acids and
bases.
Ureters
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Carry urine from the kidneys to the bladder.
Begin as a continuation of the RENAL
PELVIS in the kidney.
Bladder
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A collapsible muscular sac that store urine.
Lies on the pelvic floor, posterior to the pubic symphysis.
The bladder lies anterior to the rectum in males.
In females, it lies anterior to the vagina and uterus.
Ureters enter the bladder at the POSTEROLATERAL ANGLES.
The apex of the bladder (anterior angle) has a fibrous band
called the URACHUS (remnant of the embryonic urinary canal).
The inferior angle drains into the URETHRA.
In males, the PROSTATE GLAND lies directly inferior to the
bladder surrounding the urethra.
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Inside the bladder are the two openings
where the ureters enter. When combined
with the opening of the urethra, a triangle is
formed known as the TRIGONE.
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The wall of the bladder has three layers:
1.
Mucosa – distensible epithelium
Thick Muscle (Detrusor Muscle) –
intermingled smooth muscle fibers
Fibrous Adventitia
2.
3.
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When empty, the bladder collapses into a
pyramid shape.
As urine accumulates, the walls distend and
stretch. There is no increase in internal
pressure until there is about 300mL of
accumulated urine.
A full bladder holds about 500mL of urine.
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At the junction between the bladder and urethra, the
DETRUSOR MUSCLE forms the INTERAL
URETHRAL SPHINCTER.
The sphincter keeps the urethra closed when urine is
not being passed. It prevents “dribbling”.
Involuntary action – smooth muscle.
The EXTERNAL URETHRAL SPHINCTER
surrounds the urethra in a sheet of muscle called the
UROGENITAL DIAPHRAGM.
The EUS is what humans use to voluntarily delay
urination. Therefore, it is skeletal muscle.
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The urethra is of different lengths in each sex.
Males – 20 cm long. Has three regions:
a. Prostatic urethra
b. Membranous urethra – in the urogenital
diaphragm.
c. Penile urethra (spongy)
The urethra opens into the EXTERNAL URETHRAL
ORIFICE.