4. The urinary system is one of the
excretory systems of the body. It
consists of the following structures:
• Kidneys, which secrete urine
• Ureters, which convey the urine from the
kidneys to
• The urinary bladder where urine collects and
is temporarily stored
• Urethra through which the urine is discharged
Urinary system
5. Ureters
Tubes that convey urine from the kidneys to the
urinary bladder
They are about 25 to 30 cm long with a diameter
of about 3 mm
The ureters propel the urine from the kidneys
into the bladder by peristaltic contraction of the
smooth muscle
Innervated by ANS
6. The urinary bladder is a reservoir for urine.
Trigone
Contains opening for the urethra
Rugae absent
Each ureter, as it enters the bladder, courses obliquely
through the detrusor muscle and then passes another 1 to
2 centimeters beneath the bladder mucosa before
emptying into the bladder
The Urinary bladder
Bladder wall has 4 layers;
1. Mucosa → transitional epithelium → has folds “rugae”.
2. Submucosa → loose connective tissue.
3. Smooth muscle layer → Detrusor muscle → the main muscle of
micturition.
4. Serosa
7. • Urine is transported through the ureters.
• Urine is propelled through the ureter and into the bladder
by the help of peristalsis.
• Peristalsis is thought to be initiated by pacemaker cells in
the renal pelvis.
• Sympathetic stimulation → inhibits peristalsis.
• Parasympathetic stimulation → enhance peristalsis.
UrineTransportfrom Kidney to Bladder
8. The lower urinary tract = bladder + urethra
Functionsof the LowerUT
Functions of the bladder &
urethra
Urine storage Voiding (Micturition)
Store without leakage Empty when appropriate
Wall relaxed
with closed
outlet
Wall
contracts
with open
outlet
9. Micturition = the process by which the urinary bladder
empties when it becomes full.
Micturition is a visceral function → under control of the
autonomic nervous system.
When the volume of urine in the urinary bladder exceeds 200 to 400 mL,
pressure within the bladder increases considerably, and stretch receptors
in its wall transmit nerve impulses into the spinal cord.
These impulses propagate to the lower part of the spinal cord and trigger
a reflex called the micturition reflex.
Micturition
10. • It is a autonomic reflex that can be facilitated or inhibited
by higher centres.
• Occurs in two steps:
1. Progressive filling of the bladder until a threshold is reached.
2. At the threshold, a nervous reflex is initiated “micturition reflex” to empty the
bladder.
• If the conditions for emptying are favourable → emptying
will occur.
• If the conditions for emptying are unfavourable → reflex is inhibited,
however, there is the conscious desire to urinate.
The MicturitionReflex
13. Nervous Connections of Urinary Bladder
The principal nerve supply of
the bladder is by way of the
pelvic nerves
Connecting with cord
segments S-2 and S-3
Contains both sensory
nerve fibers and motor
nerve fibers
Motor parts are
parasympathetic fibers
Skeletal motor fibers
transmitted through the
pudendal nerve
Hypogastric nerve carrying
sympathetic discharge
Effects more related to the
blood vessels
15. The MicturitionReflex
Filling of bladder Stretches the wall Stimulate stretch receptors
Signals are carried through
pelvic nerve to sacral center
Excite parasympathetic
efferent and inhibit pudendal
discharge
16. • An autonomic spinal
reflex.
• Is controlled by higher
CNS centres;
• Brain stem (Pons).
• Cerebral cortex.
• Control is either
inhibitory orfacilitatory.
• Voluntary.
The MicturitionReflex
18. Components of Urine
The urine volume eliminated daily in an average adult is 1 to 2 liters.
Water accounts for about 95% of the total volume of urine.
In addition to urea, creatinine, potassium, and ammonia, typical solutes normally
present in urine include uric acid as well as sodium, chloride, magnesium, sulfate,
phosphate, and calcium ions.
If the disease alters body metabolism or kidney function, traces of substances not
usually present may appear in the urine, or normal constituents may appear in
abnormal amounts.
19. Albumin
A normal constituent of blood plasma that usually appears in only very small
amounts in urine because it is too large to be filtered.
The presence of excessive albumin in the urine, albuminuria, indicates an increase
in the permeability of filtering membranes due to injury or disease, increased blood
pressure, or damage to kidney cells.
Glucose
Glucosuria, the presence of glucose in the urine, usually indicates diabetes mellitus.
Red blood cells
Hematuria, the presence of hemoglobin from ruptured red blood cells in the urine,
can occur with (erythrocytes) acute inflammation of the urinary organs due to
disease or irritation from kidney stones, tumors, trauma, and kidney disease.
Abnormal Constituents in Urine
20. Conti…
White blood cells
The presence of white blood cells and other components of pus in the urine, referred
to as pyuria, indicates (leukocytes) infection in the kidneys or other urinary organs.
Ketone bodies
High levels of ketone bodies in the urine, called ketonuria, may indicate diabetes
mellitus, anorexia, starvation, or too little carbohydrate in the diet.
