Urinary System
Urinary System
2 kidneys
 Two ureters
 Urinary bladder
 Urethra

Functions of the Urinary System

Formation of urine = kidneys
- rids body of waste products such as urea,
creatine and ammonia
• Elimination of urine= ureters, bladder, urethra
• Regulation of the volume of blood by excretion or
conservation of water
Regulation of the electrolyte content of the
blood
• Regulation of the acid-base balance of the
blood
•
Kidneys

Located in upper abdominal cavity on either side of
the vertebral column
 Are enclosed and protected by the lower rib cage
 Embedded in adipose tissue that act as cushion
and fibrous conn. Tissue which helps hold kidneys
in place
 Hilus: indention on the medial side of each kidney
- Renal artery= branch of the abdominal aorta
- Renal vein= returns blood to the inferior
vena cava
Internal Kidney Structure
The kidneys are composed of three
distinct areas:
 1. Renal cortex- outer layer
 2. Renal medulla- inner layer
 3. Renal pelvis- inner cavity

Internal Structure of Kidney

•
Renal cortex
- Outer tissue layer
- Made of renal corpuscles and
convoluted tubules (parts of nephron)
Renal medulla
- Made of loops of Henle and collecting
tubules
- Consist of wedge-shaped pieces
called renal pyramids
Internal Structure of Kidney

Renal pelvis
- Cavity formed by the expansion of the
ureter within the kidney at the hilus
- Funnel shaped extensions of the renal
pelvis called calyces
- Urine flows from the renal pyramids
into the calyces, then to the renal pelvis
and out into the ureter
The Nephron
Structural and functional unit of the
kidney
 Each kidney contains 1 million nephrons
 It is here that urine is formed
 2 major portions
- Renal corpuscle
- Renal tubule

The Nephron Cont.
3 basic functions
1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion
Renal Corpuscle
The renal corpuscles are the sites
where the process of urine formation
begins with a filtrate of blood plasma
 The renal corpuscle consist of a
glomerulus surrounded by a Bowman’s
capsule
 The glomerulus is a capillary network,
composed of an afferent and efferent
arteriole

Renal Corpuscle
Blood enters the glomerulus through the
afferent arteriole
 Blood leaves the glomerulus through
the efferent arteriole
 The glomerulus is suspended within the
Bowman’s capsule, and are supported
by podocytes within the Bowman space

Renal Tubule
Continues from the Bowman’s capsule, and
can be found in both the renal cortex and renal
medulla
 There are four parts of the renal tubule
 1. Proximal tubule, in the cortex, is the
beginning of the tubule; reabsorbs minerals and
nutrients from the tubular fluid and passes them
to blood

Renal Tubule
2. Loop of Henle, dips into the medulla
where it helps establish the hypertonic
saline environment within the medulla,
which allows for the recovery of water
 3. Distal convoluted tubule returns near
the corpuscle; it pumps ions and
molecules through its gradient

Renal Tubule
4. Collecting ducts collect urine from the
distal tubules (found in medulla)
 All parts are surrounded by peritubular
capillaries which arise from the efferent
arteriole

Glomerular Filtration
In glomerular filtration, blood pressure
forces plasma, dissolved substances,
and small proteins out of the glomeruli
and into Bowman’s capsule
 The fluid is no longer plasma but is
called renal filtrate

Tubular Reabsorption

Tubular reabsorption takes place from the
renal tubules into the peritubular capillaries.
 Peritubular capillaries arise from the efferent
arteriole, and receives materials reabsorbed
by the renal tubules
 Approx. 99% of renal filtrate is absorbed back
into the blood in the peritubular capillaries.
1% becomes urine
Four Mechanisms of
Reabsorption
1. Active transport- the cells of the renal
tubule use ATP to transport filtrate to
the blood
 2. Passive transport- negative ions that
are returned to blood are reabsorbed
 3.Osmosis- the reabsorption of water
follows the reabsorption of minerals
 4. Pinocytosis- occurs in the proximal
tubules, by enveloping small proteins

Tubular Secretion
Changes the composition of urine
 Substances are actively secreted from
the blood in the peritubular capillaries
into the filtrate in the renal tubules
 Waste products such as ammonia,
some creatine, and medication may be
secreted into the filtrate to be eliminated

Other Functions of Kidney

1. Secretion of renin- when blood pressure
decreases cells in the afferent arteriole
secrete the enzyme renin; which triggers the
renin-angiotensin mechanism and the
production of aldosterone
 2. Secretion of erythropoietin- stimulates the
red bone marrow to increase the rate of RBC
production; which increases oxygen carrying
capacity
Other Functions

3. Activation of vitamin D- vitamin D is
converted to calciferol by the kidneys.
Calciferol increases the absorption of
calcium and phosphate in the small
intestine
Dialysis

Separation of large particles from
smaller ones through a selectively
permeable membrane
Hormones that affect kidneys
Antidiuretic hormone (ADH)- Increases
reabsorption of water
 Aldosterone- increases reabsorption of
Na and excretion of K+
 Atrial natriuretic hormone (ANH)Decreases reabsorption of Na+

Renal Failure

Inability of the kidney to function properly
3 Causes
1. Prerenal- problem is before the kidneys,
decrease blood flow (hemorrhage)
2. Intrinsic- problem is in kidneys (bacterial
infections)
3. Postrenal- problem is after kidney,
obstruction of urine flow (kidney stones)
Floating Kidney

A floating kidney is one that has moved
out of its normal position. If a ureter
becomes twisted or kinked, urine cannot
flow properly. This could lead to urine
backing up into the renal pelvis, and
Bowman’s capsule, ultimately causing
permanent kidney damage.
Ureters
Ureters extend from the hilus of a
kidney to the lower, posterior side of the
urinary bladder
 The smooth muscle in the walls of the
ureter contracts in peristaltic waves to
propel urine toward the urinary bladder

Urinary Bladder
The urinary bladder is a muscular sac
below the peritoneum and behind the
pubic bone
 In women, the bladder is inferior to the
uterus
 In men, the bladder is superior to the
prostate gland

Urinary Bladder

The mucosa of the bladder is transitional
epithelium, which permits expansion without
tearing the lining.
 When the bladder is empty, the mucosa
appears wrinkled; the folds are called rugae
and permit expansion
 The trigone is a triangular area on the floor of
the bladder, it has no rugae and does not
expand
 The points of the triangle are the two ureters
and the urethra
Urinary Bladder
The detrusor muscle is the smooth
muscle layer of the bladder which
contracts and decreases its volume
 The muscle fibers of the detrusor form
the internal urethral sphincter or
sphincter of the bladder (involuntary)

Urethra
The urethra carries urine from the
bladder to the exterior
 The external urethral sphincter is made
of skeletal muscle (voluntary)
 In women the urethra is 1 to 1.5 inches
long
 In men the urethra is 7 to 8 inches long,
and carries semen as well as urine

Micturition (Urination Reflex)
The urination reflex is a spinal cord
reflex in which voluntary control can
occur
 The stimulus for the reflex is stretching
of the detrusor muscle of the bladder
 The bladder can hold as much as 800ml
of urine, but the reflex is activated
around 200 to 400 ml
 When the limit is reached impulses
travel to the sacral spinal cord

Aging
With age the number of nephrons
decrease, often by half
 The urinary bladder decreases in size
and tone
 The chance of infection also increases,
because of residue left behind during
micturiiton

Kidney Stones
Kidney stones are crystals of the salts
that are present in urine, and block the
flow of urine in the ureter
 Kidney stones are most likely to form in
the renal pelvis

Urinary Tract Infection
Infection of a part of the urinary system
 Symptoms include burning or painful
urination
 If chronic, scar tissue forms and impairs
function

Bright’s disease
Inflammation of the glomeruli
 Caused by bacteria
 Endothelial space becomes highly
permeable to blood and protein

Renal Failure


1.
2.
3.
Acute is a decrease in glomerular
filtration
Chronic is the irreversible decline in
glomerular filtration
Diminished- up to 75%
Renal- 75%
End stage- 90%
Causes edema, acidosis, anemia
Polycystic kidney disease
Inherited disorder (1:1000)
 Tubules become filled with cyst
 Apoptosis occurs in tubule cells

Diabetes Insipidus
Excretion of very dilute urine
 Patients exhibit extreme thirst
 The cause of DI is the defect in the
production of ADH
