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The Urinary System
Major Organs of the Urinary System
• Kidneys- a pair of glandular
organs which remove waste
products from the blood to
form urine.
• Ureters-muscular tubes which
convey urine from the kidneys
to the urinary bladder.
• Urinary Bladder-muscular
sac which stores urine until
micturation can occur.
• Urethra-tubelike structure
which conveys urine from the
urinary bladder to outside the
body.
Kidneys
Location:
• Reddish brown bean shaped organ
located retroperitoneally.
• Imbedded in the parietal
peritoneum of the abdominal
cavity against the deep muscles of
the back
• Held in position by connective
tissue (renal fascia) and
surrounded by adipose tissue
(renal fat)
• Located between the 12th thoracic
and 3rd lumbar vertebrae
• The left kidney is usually 1-2 cm
higher than the right.
• It is encased in a tough fiberous
capsule called the tunica fibrosa
Structure of the kidney
• Lateral surface is convex
• Medial surface is concave
• A medial depression is a hollow
chamber called the renal sinus
• The entrance to the sinus is called
the hilum.
• Thru it pass the blood vessels,
nerves, lymphatic vessels and the
ureter.
• The superior end of the ureter is
expanded to form a funnel shaped
part called the renal pelvis.
• The renal pelvis is divided into
major calyces and further divided
into minor calyces (calyx)
Kidney Structure (cont)
• There are several projections of
kidney tissue into the renal sinus
which form the kidney wall.
• These projections are called the
renal papilla and each are pierced
by tiny openings into a minor
calyx
Kidney is divided into 2 regions:
Medulla- inner portion composed of
collecting ducts and loops of
Henle , has a striated appearance
Cortex-outer portion, composed of
nephrons which give it a grainy
appearance. Some of the cortex
dips into the medulla to form
columns.
Renal Blood Vessels
• Supplied by the renal artery.
• Enters the kidney thru the
hilum and breaks into smaller
arteries called afferent
arterioles.
• Venous blood is returned in a
series of veins and passes out
of the kidney through the renal
veins.
The Nephron
• Functional unit of the kidney
• Some 1 million per kidney
• This is where the waste products
are removed from the blood.
Composed of 2 parts:
Renal corpuscle-composed of a
tangled cluster of blood capillaries
called the glomerulus.
Renal Tubule-consists of a long tube
that is surrounded by blood
capillaries called the peritubular
capillaries.
• Leads away from Bowman’s
capsule and becomes highly coiled
and is called the PCT. (proximal
convoluted tubule)
Renal Tubule (cont)
• This tubule then dips and rises
again to form a loop called The
Loop of Henle.
• The tubule then becomes
highly convoluted again to form
the DCT. (distal convoluted
tubule)
• It is shorter and not as coiled as
the PCT.
• Several DCT’s merge to form a
larger tube called a Collecting
Duct.
• Which passes into the renal
medulla becoming larger and
larger as it merges with other
collecting ducts.
Functions of the Nephron
• Removal of waste substances from
the blood.
• Reabsorption of water and
electrolyte concentrations.
Blood Supply of the Nephron
• The afferent arteriole supplies
blood to the glomerulus.
• Blood from the glomerulus leaves
by way of the efferent arteriole.
• The efferent arteriole then branches
into a complex of freely
anastomosing network of capillaries
that surround the renal tubule
called the peritubular capillary
system.
Urine Formation
Urine is the end product of the
kidneys:
• Urine contains wastes, excess
water, and excess electrolytes.
Glomerular Filtration
• The liquid forced from the
glomerulus is actually blood
plasma, once it enters Bowman’s
capsule it is referred to as
glomerular filtrate.
• There are no large proteins or red
blood cells in glomerular filtrate.
• It contains: water, glucose, amino
acids, urea, uric acid, sodium,
chlorine, potassium, and calcium
ions.
Glomerular filtration
• It is squeezed out of the
glomerulus at a rate of 125/ml
a min.
• 180 liters a day or 45 gallons a
day.
• The entire content of blood
plasma filters through the
glomeruli about 60 times a day.
• The nephrons of the kidneys
make up 2 square meters of
surface area about the size of
the human skin.
• The glomerulus filters this
glomerular filtrate and
Bowman’s capsule receives it.
Tubular Reabsorption
• The reabsorption into the blood of
water, glucose, and electrolytes to
maintain proper blood content of
these substances.
• PCT reabsorbs water by osmosis.
• The passive transport of glucose,
sodium, potassium, chlorine, and
amino acids also occurs here.
• Descending Loop of Henle active
transport of sodium and chlorine
occurs.
• Ascending Loop of Henle active
transport of chlorine and the
subsequent passive transport of
sodium.
Tubular reabsorption (cont.)
• DCT- active transport of water
only.
• This occurs in the presence of
ADH (antidiuretic hormone)
which increases the absorption
of water.
Tubular Secretion
• The addition of materials to the
glomerular filtrate from the
blood.
• This process provides 2
functions.
1. Controls the blood pH.
2. Rids the body of certain
materials. Hydrogen and
ammonia are secreted into the
filtrate.
Urine Composition
Water -95%
Other electrolytes 1%
Urea- 2.5%
Uric acid .3%
Sodium chloride 1% Other substances .2%
Urea is ammonia and carbon dioxide stuck
together. Nitrogenous waste produced by
protein catabolism.
Uric acid can form insoluble crystals,
components of kidney stones and cause
gout.
• These figures can vary depending on diet.
Characteristics:
Volume- urine production is 1-3 liters a day.
pH- varies from 5.0-7.8
Elimination of Urine
After being formed, urine passes
from the collecting ducts thru
openings in the renal papillae
and enters the major calyces of
the kidney.
From there it passes thru thru the
renal pelvis and is conveyed by
the ureter to the urinary
bladder.
It is excreted outside the body via
the urethra
The Ureters
Paired tubular organs 10 in. length
Superior end is expanded to form a
funnel shaped renal pelvis
Inferior end joins the urinary bladder
from underneath
It conveys urine from the kidney to the
urinary bladder.
Composed of 3 layers
1. mucous coat- inner, transitional
epith.
2. Muscular coat- smooth muscle,
circular and longitudinal planes,
peristalsis helps convey urine.
3. Fibrous coat- serous epithelium
and connective tissue. Outer layer
The Urinary Bladder
• Hollow, distensible, muscular organ
• Located within the pelvic cavity
behind the pubic symphysis
• In male, lies against the rectum
posteriorly.
• In female, contacts the anterior
walls of the uterus and vagina.
The bladder is somewhat spherical,
when empty the inner wall is highly
folded.
• As it fills with urine the walls
become smoother and it swells and
extends upward into a dome.
Urinary bladder
• The floor of the bladder internally is
called the trigone.
• It has an opening at each of its angles.
• The upper corners are the ureters and
the lower corner is the urethra.
Bladder wall consists of 4 layers:
1. Mucous coat-transitional epi.,
adapted for stretching and shrinking.
2. Submucous coat-connective tissue
w/ lots of elastic fibers
3. Muscular coat-course bundles of
smooth muscle in all planes
• Detrusor muscle-contraction of this
muscle forces urine out of the
bladder. Parasympathetic control.
4. Serous coat-serous epithelium
w/some fibrous connective tissue
The Urethra
Function- to convey urine from the urinary
bladder to outside the body.
• Lined w/mucous membrane and large
amounts of smooth muscle. Contains many
mucous glands.
• In female, 1.6 to 2 in. in length
• In male, around 8 in. in length,
functions as both a urinary canal and as a
passageway for cells and secretions of the
male reproductive system.
Divided into 3 segments:
1. Prostatic urethra- thru prostate gland.
2. Membranous urethra-external urethral
sphincter located here. Controls urination
3. Penile urethra- thru the penis, exits the
body thru the external urethral orifice
Micturation
• Process by which urine is expelled from
the urinary bladder.
• It involves the contraction of the detrusor
muscle and is aided by the contraction of
the abdominal muscles.
• Relaxation of the ext. urethral sphincter
voluntary
• The need to urinate is stimulated by
distention of the bladder as it fills with
urine.
• Micturation reflex center located in the
sacral segments of the spinal cord.
• Reflex can be overridden by parts of the
cerebral cortex and midbrain. 3-4 yrs of
age. Potty training
• Hypothalamus and pons may assist in this.
• Bladder may hold up to 800-1000ml
need to urinate at 150ml.
feeling uncomfortable at 300ml.
Disorders and Diseases of the Urinary Tract
Nephritis- inflammation of the nephron.
• Glomerular- glomerulus
• Pylenonephritis- inflammation of the
renal pelvis
• Proteinuria, glycosuria, hematuria
Gout- uric acid crystals form in the joints.
arthritis, swelling, pain in lower
extremities.
Hemodialysis- machine removes waste
products from the blood. Takes the
place of healthy kidneys. Has to be
done every 3 days or so.
Renal Caliculi (Kidney Stones)
• Caused by uric acid combining with
calcium oxalates, calcium phosphate,
or magnesium phosphate which form
crystals within collecting ducts, renal
pelvis or ureter.
• This blocks the flow of urine, backing
up the system decreasing urine
production.
• If stone passes into the ureter it may
stimulate severe pain. Which usually
begins in the region of the kidney
and tends to radiate to the pelvis or
legs, or groin.
Lithotripsy
Medical procedure used to break
up kidney stones by
bombarding them with ultrasound waves or a blast of ultra
sound.
UTI (urinary tract infection)
• More common in women that men
due to the shortness of the
urethra.
• Usually a streptococcus or
E. coliform bacteria.