1. The Urinary System
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2. The Urinary System
Learning Outcomes:
• List the parts of the Urinary System.
• State the function of the kidneys.
• Outline the gross structure of the kidneys.
• Describe the structure of a nephron.
• Name the four processes involved in urine formation
and describe the action of each.
• Describe the process of urine formation.
• State the composition of urine.
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3. The Urinary System
• Also called the excretory system.
• Excrete, remove and eliminate metabolic waste
products from the blood.
• Regulate volume, acid-base balance and
electrolyte composition of body fluids.
• Blood supply – renal artery and renal vein.
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4. The Urinary System
The main excretory system and consists of the
following structures:
• 2 kidneys (secrete urine)
• 2 ureters (convey urine from the kidneys to the
bladder)
• 1 urinary bladder (collects urine)
• 1 urethra (through which urine is discharged)
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5. The Kidneys
Main functions of kidneys are:
• Removal of nitrogenous waste material, certain salts
and excess water from the blood.
• Secretion of waste products in the form of urine.
• Production and secretion of erythropoietin, the
hormone that controls formation of red blood cells.
• Production and secretion of renin, an enzyme that
helps in the control of blood pressure.
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6. Structure of the Kidney
• A bean shaped organ app. 10cm long and 5 cm wide, 2.5
cm thick and weigh 150 g.
• Extend from the 12th thoracic vertebra to the 3rd lumbar
vertebra.
• Rt. Kidney is slightly lower than Lt. kidney.
• A protective layer of fat (adipose capsule) around the
organ.
• An outermost layer of fascia (connective tissue) anchors
the kidney to the peritoneum and abdominal wall.
• Medial border – hilum, where the renal artery, renal vein
and ureter connect with the kidney.
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7. Gross structure of the Kidney
Divided into 3 areas of tissues:
• A fibrous capsule, surrounding the kidney.
• The cortex, a reddish brown layer of tissue, below
the capsule and outside the pyramids.
• The medulla, the innermost layer, consisting of pale
conical-shaped striations, the renal pyramids.
• The hilum – concave medial border of the kidney
where blood and lymph vessels, the ureter and
nerves enter.
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8. Gross structure of the Kidney
• The renal pelvis – the funnel-shaped structure
that acts as a receptacle for the urine formed by
the kidney.
• Calyces – cuplike extensions of renal pelvis
surrounding the tips of the pyramids and collects
urine.
• Urine in pelvis passes down the ureters to the
bladder.
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9. Structure of the Kidney
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10. The Nephron
• The nephron is the structural and functional unit of the
kidney.
• Consists of a specialized tubular structure and closely
associated blood vessels.
• Responsible for the formation of urine.
• Each kidney contains 1,000,000 nephrons that filter the
blood and form urine.
• About 99% of the initial filtrate from the glomerulus is
reabsorbed by the nephron and returned to the blood
in the peritubular capillaries.
• When nephrons are damaged they are not replaced or
regenerated.
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11. The Nephron
• About one third of the nephrons in a kidney must be
functional to ensure survival of the organ.
The parts of the nephron are as follows:
• Bowman's capsule - This closed end at the beginning of
the nephron is located in the cortex.
• Proximal convoluted tubule or proximal tubule - The first
twisted region after the Bowman's capsule; it is in the
cortex.
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12. The Nephron
• Loop of Henle - A long, hairpin loop after the proximal
tubule, it extends from the cortex down into the
medulla and back.
• Distal convoluted tubule or distal tubule - This second
twisted portion of the nephron after the loop of Henle
is located in the cortex.
• Collecting duct - This long straight portion after the
distal tubule that is the open end of the nephron
extends from the cortex down through the medulla.
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13. The Nephron
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14. Formation of Urine
• A complete process, involving many exchanges
between blood stream and kidney tubules.
• There is ample time for exchange to take place
as fluid filtered from the blood travels through
the twists and turns of the nephron.
• The processes allow the kidney to “fine tune”
body fluids as they adjust the composition of the
urine.
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15. Formation of Urine
Four processes occurring in successive portions of the
nephron accomplish the function of urine formation.
• Glomerular filtration allows diffusible materials (water
and small molecules) to pass from the blood into the
nephron.
• Tubular reabsorption moves useful substances
(glucose, amino
acids,sodium, calcium, potassium, phosphate and
chloride) back into the blood while keeping waste
products (urea and uric acid) in the nephron for
elimination.
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16. Formation of Urine
• Tubular secretion moves additional substances from
the blood into the nephron for elimination.
Movement of hydrogen ions is one means by which
the pH of body fluids is balanced.
• The countercurrent mechanism concentrates the
urine and reduces the volume excreted. The pituitary
hormone ADH allows more water to be reabsorbed
from the nephron.
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17. The Path of the Formation of Urine
• Blood enters the afferent arteriole, passes through the
glomerulus, to Bowman’s capsule.
• In Bowman’s capsule, it becomes filtrate (blood minus
RBC and plasma proteins) continues through the
proximal convoluted tubule to the collecting tubule (by
now, 99% of filtrate has been reabsorbed)
• App. 1 ml of urine is formed per minute and travels all
the way down to bladder for excretion.
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20. Normal Constituents of Urine
• Nitrogenous waste
products – urea, uric
acid, and creatinine.
• Electrolytes – sodium
chloride, sulfates and
phosphates.
• Pigment – from bile
compounds, foods and
drugs.
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21. Composition of Urine
• Water 96%
• Urea 2%
• Uric acid
• Creatinine
• Ammonia
• Sodium
• Potassium 2%
• Chlorides
• Phosphates
• Sulphates
• Oxalates
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22. Ureter, Bladder, Urethra
Learning Outcomes:
• Describe the Ureter, Bladder and Urethra.
• State the functions of ureter, bladder and
urethra.
• Describe the physiological processes of
micturition.
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23. Ureters
• Two long, narrow tube (1/4 inch wide and 10 to
12 inches long) carrying urine from the kidneys
to the bladder.
• When the muscles contract, peristalsis is
initiated, pushing urine down the ureter into the
urinary bladder.
• When urine accumulates and the pressure in the
bladder rises, the ureters are compressed and
the openings occluded to prevent reflux of urine
back into the kidney.
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24. Cross Section of Ureter
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25. Structure of the Ureters
Consists of 3 layers of
tissue:
• An outer covering of
fibrous tissue.
• A middle muscular layer
consisting of interlacing
smooth muscle fibres.
• An inner layer, the
mucosa, composed of
transitional epithelium.
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26. Function of Ureter
• Propel urine from the
kidneys into the bladder by
peristaltic contraction of
the smooth muscle layer.
• Occurs several times per
minute, increasing in
frequency with the volume
produced.
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27. Urinary Bladder
• A hollow, muscular, pear shaped organ for
storage of urine.
• Can stored up to 500 mls of urine.
• Lies in the pelvic cavity.
• When distended, the bladder rises into the
abdominal cavity.
• Voiding takes place by contractions of the
bladder, which forces urine through the urethra
and to the outside opening, the urinary meatus.
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28. Structure of the Urinary Bladder
The bladder wall is composed of three layers:
• An outer layer of loose connective
tissue, containing blood and lymphatic vessels
and nerves, covered on the upper surface by the
peritoneum.
• A middle layer of interlacing smooth muscle
fibres and elastic tissue called the detrusor
muscle.
• A inner layer of mucosa, composed of
transitional epithelium.
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29. Cross Section of Urinary Bladder
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30. Structure of the Urinary Bladder
• The trigone is a triangular-shaped region in floor
of bladder.
• Marked by the openings of the two ureters and
urethra.
• As the bladder fills with urine, it expands
upward, leaving the trigone at the base
stationary.
• This prevents stretching of the ureteral openings
and possible backflow.
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31. The Urethra
• A canal extending from neck of
bladder to external urethral
orifice.
• Longer in the male (8-10
inches) than in female (4
inches).
• External urethral orifice is
guarded by the external
urethral sphincter (voluntary
control).
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32. Structure of the Urethra
The walls consist of three layers of tissue.
• The muscle layer is continuous with that of the bladder.
It is mainly elastic tissue and smooth muscle
fibres, under autonomic nerve control.
• The submucosa is a spongy layer containing blood
vessels and nerves.
• The mucosa is continuous with that of the bladder in
the upper part of the urethra. The lower part consists of
stratified squamous epithelium, continuous externally
with the skin of vulva.
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33. Micturition
• Urination (micturition) involves physiological
processes within the urinary tract and the brain.
• The slight need to urinate is sensed when urine
volume reaches about one-half of the bladder's
capacity.
• The brain suppresses this need until a person initiates
urination.
• Neurons in the brain and in smooth muscle of the
bladder govern the detrusor muscle; it is not
controlled voluntarily.
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34. Micturition
• The nervous system stimulates the detrusor muscle
to contract into a funnel shape and expel urine, once
a person initiates urination.
• Pressure in the bladder increases and the detrusor
remains contracted until the bladder empties.
• Once empty, pressure falls and the bladder relaxes
and resumes its normal shape.
• Normally, the detrusor muscle contracts and relaxes
according to the volume of urine in the bladder and
the initiation of urination.
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35. CLINICAL CONNECTION
• Nephroptosis
• Kidney transplant
• Loss of plasma proteins in urine causes edema
• Glucosuria
• Diuretics
• Dialysis
• Cystoscopy
• Urinary incontinence
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