Urinary System
Human Anatomy
Chapter 23
• I. Kidneys
• The kidneys perform the
following functions:
excretion of urea (from
amino acid breakdown),
uric acid (nucleic acid
turnover), and creatine
(from creatine phosphate
breakdown). It also
disposes of waste and
excess ions, it regulates
blood volume and its
chemical make up, it
affects blood pressure
and red blood cell
formation
(erythropoetin- hormone
to stimulate blood
production). People can
survive with just one
kidney.
•
•
A. Gross anatomy
• 1. Location and external
anatomy - The kidneys
appear to be bean shape,
both the left and right
kidney lie against the
posterior abdominal wall
above the ilium and are
protected by the lower two
ribs. The renal hilus is the
location where blood
vessels and nerves enter
the kidney. Superior to
each kidney is the adrenal
gland.
•The kidneys are
surrounded by the
renal capsule
(dense connective
tissue), the
adipose capsule
(contains perirenal
fat), and the most
external
membrane is renal
fascia. There is
some fat that lies
close to the
kidneys called
pararenal fat, both
fat layers cushion
and support the
kidneys.
• 2. Internal gross anatomy- The following features can be seen with the
naked eye in dissection. The most superficial region is the renal cortex
which is lighter in color than the deeper region called the renal medulla. The
renal medulla is divided into sections called renal pyramids, the renal
columns (extensions of the cortex) lie in between the renal pyramids. The
minor calices collect urine and merge into major calices which are branches
that converge to form the renal pelvis (superior part of the ureter). The renal
pelvis joins the ureter.
Microscopic View of Renal Cortex (Shows nephron)
Microscopic view of Renal Medulla
•
3. Gross vasculature and nerve supply- The kidneys have a rich blood
supply (see figure 23.3, 23.9, 23.10 for summary). The largest blood
vessels are the renal arteries and veins. They eventually become
segmental arteries, then lobar, then interlobar. They narrow more and
become arcuate, they are called interlobular ateries again and finally reach
the nephron as affarent and efferent arterioles. They then wrap around the
nephron as pritubular capillaries and vasa recta. As this point they are
veins and have the same names as the ateries: interlobular, arcuate, and
renal vein. The renal plexus serves the nerves supply of the kidney carrying
autonomic NS fibers. The sympathetic fibers control the diameters of the
kidney arteries and influence uriniferous tubules.
•3. Gross vasculature and nerve supply- The kidneys have a rich blood supply
(see figure 23.9 for summary). The largest blood vessels are the renal arteries
and veins. They eventually become segmental arteries, then lobar, then
interlobar. They narrow more and become arcuate, they are called interlobular
ateries again and finally reach teh nephron as affarent adn efferent arterioles.
They then wrap aroudn the nephron as pritubular capillaries and vasa recta. As
this point they are veins and have the amse as teh ateries: interlobular, arcuate,
and renal vein. The renal plexus serves the nerves supply of the kidney
carrying autonomic NS fibers. The sympathetic fibers control the diameters of
the kidney arteries and influence uriniferous tubules.
•
•
•
B. Microscopic anatomy of the
kidneys-This section examines the
uriniferous tubules composed of the
nephron and the collecting tubule.
We will also look at urine production.
1. Mechanisms of urine productionurine production has three stages:
•
a. Filtration- blood filtrate enters the
nephron, it resembles blood plasma
and it is further processed to create
urine. Note that normally NO blood
cells or large proteins enter as part of
filtrate.
•
b. Reabsorption- along the nephron
beneficial molecules such as
nutrients, water, and essential ions
are reclaimed. These are returned
into the blood.
•
c. Secretion- Undesired molecules
are actively removed and passed
along the tubules of the nephron on
their way to become urine.
• 2. The nephron- the filtering unit of the kidney contain various
sections that perform different functions.
• a. Nephron types- cortical nephrons are the most abundant type.
Most of the nephron is located within the cortex and only a small
portion of the loop of Henle enters into the medulla. About 15% of
the nephrons are juxtamedullary nephrons because the Loop of
Henle extends well into the renal medulla, these are used to
produce highly concentrated urine.
• b. Renal corpuscle- this is the site of filtration. The
network of capillaries at this site is the glomerulus, it has
afferent and efferent capillaries (no venuoles). These are
surrounded by the glomerular capsule (Bowman’s
capsule). The cells of the glomerular capsule are called
podocytes. This site has fenestrations on the capillaries
and filtration slits within podocytes, making it highly
permeable.
c. Tubular section-connecting to
the renal corpuscle are the tubules
responsible for reabsorption and
secretion. First is the proximal
convoluted tubule (cortical
nephron) it is surrounded by
peritubular capillaries. The
proximal convoluted tubule goes
into a long loop called the Loop of
Henle. There is a descending and
ascending limb. The ascending
limb connects to the distal
convoluted tubule which connects
to the collecting tubules. Blood
vessels in the Loop of Henle are
called vasa recta, they are
involved in concentrating urine.
• 3. Collecting tubulesthese collect urine from
several nephrons and run
into the medulla where
they merge with other
collecting tubules to form
papillary ducts that empty
into minor calyces. When
the body dehydrates the
collecting tubules become
more permeable and allow
water to be reabsorbed,
reducing urine volume and
increasing its
concentration.
• .
• 4. Juxtaglomerular apparatus- a structure that regulates blood
pressure by releasing a hormone called rennin as a response to
falling blood pressure. This causes an increase in blood solute
concentration which leads to an increase blood volume and thus
increased blood pressure.
• 5. Interstitial connective tissue- layers of connective tissue that
surround the uriniferous tubules and contain cells that release
hormones to influence blood pressure and red blood cell production
II. Ureters – Tubules
that carry urine from the
kidney to the bladder.
A. Gross Anatomyabout 10 inches long,
runs from the renal
pelvis and reaches the
bladder medially on its
posterior wall. It enters
at an oblique angle to
prevent back flow.
Forma two points of the
trigone.
B. Microscopic
anatomy- this tube has
three layers: mucosa,
muscularis, and
adventitia. Urine
reaches the bladder
through peristalsis. The
muscle contractions
seem to be guided by a
reflex response.
III. Urinary bladdera muscular sac that
stores urine. It can
collapse when
empty and expand
enough to enter
into the abdominal
cavity. In males it
lies anterior to the
rectum and in
females it lies
anterior to the
uterus and vagina.
It also has three
layers: the mucosa,
muscularis, and
adventitia
IV. Urethra- a thin tube that drains the urine
out of the body from the bladder. It is short
in females and long in males. In females
the opening of the urethra lies posterior to
the clitoris and anterior to the anus. The
male urethra opens at the tip of the penis
and carries both urine and semen. An
involuntary sphincter muscle keeps the
urethra closed when there is no urine, a
voluntary sphincter constricts urine flow
until the appropriate time to void.
V. Micturition- Urination or voiding occurs when pressure in the bladder
is increased either by bladder muscle and/or abdominal muscle
contraction. This action is controlled by the brain, the
parasympathetic neurons stimulate contraction of the muscle to
induce voiding and the sympathetic branch stimulates the sphincter
to prevent micturition.
VI. Disorders of the urinary system
• A. Urinary tract infections- these are more common in women than in
men. In women they most often result from intercourse because it brings
bacteria into the urethra and spermacides kill the natural living bacteria in
the vagina. In men it can arise from long-term catheterization. The infection
can spread from the bladder up the ureters and to the kidneys. The
symptoms include frequent micturition accompanied by a burning sensation
and fever. These infections are treated with antibiotics.
• B. Renal Calculi- commonly known as kidney stones, they form when
calcium, magnesium, or uric acid salt precipitate and accumulate. They
cause pain when they obstruct a ureter. Kidney stones are caused by
different factors but one of them is dehydration. Treatment includes
ultrasonic shock wave therapy.
• C. Cancer of Urinary Organs
• 1. Bladder cancer- five times more common in men than in women, the
cancer arises from the transitional epithelial cells of the mucosa. It can arise
from exposure to tar in tobacco smoke, chemicals, and artificial sweetners.
Blood in urine is a sign of bladder cancer.
• 2. Kidney cancer- arises from epithelial cells of the uriniferous tubules or
renal pelvis. It is more common in men than in women. Risk factors include
obesity, high blood pressure, and a high protein diet. By the time it is
detected the tumor has metastasized and since it is resistant to cancer
treatment, the person only has months to live.