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Urinary System
Introduction

1.
2.
3.
4.
Consists of
Two kidneys
Two ureters
One urinary bladder
One urethra
Introduction

Urine is excreted from each kidney
through its ureter and is stored in
the urinary bladder
Introduction

Urine is expelled from the body
through the urethra
Anatomy of Kidneys

Retroperitoneal organs
External Anatomy of Kidneys

Hilus – A vertical fissure near the
center of the concave medial border
External Anatomy of Kidneys

Ureters leave and blood vessels,
lymphatic vessels, and nerves enter
and exit at the hilus
Internal Anatomy of Kidneys

1.
2.
3.
4.
5.
6.
7.
Consists of
Cortex
Medulla
Pyramids
Papillae
Columns
Minor and Major calyces
Renal pelvis
Internal Anatomy of Kidneys

Nephron – functional unit of the
kidney
Blood and Nerve Supply of the
Kidneys

Blood enters the kidney through the
renal artery
Blood and Nerve Supply of the
Kidneys

Blood exits via the renal vein
Nephrons

1.
2.
Consists of
Renal corpuscle
Renal tubule
Renal Corpuscle

Where fluid is filtered
Renal Corpuscle
Consists of
1. Glomerulus
2. Glomerular Capsule
Renal Corpuscle

Glomerulus – capillary knot
Renal Corpuscle

1.
2.
3.
The glomerular capsule consists of
Visceral layer
Parietal layer
Capsular Space
Renal Corpuscle

The visceral layer consists of
modified simple squamous epithelial
cells called podocytes
Renal Corpuscle

The parietal layer consists of simple
squamous epithelium and forms the
outer wall of the capsule
Renal Corpuscle

Fluid filtered from the glomerular
capillaries enters the capsular space
Renal Corpuscle

Capsular space – the space between
the two layers of the glomerular
capsule
Renal Tubule

Filtered fluid passes through here
Nephron

1.
2.
3.
Renal tubule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Nephron

Distal convoluted tubules of several
nephrons drain into to a single
collecting duct
Nephron

Many collecting ducts drain into a
small number of papillary ducts
Nephron

These empty urine into the minor
calyces
Nephron

1.
2.
3.
Loop of henle consists of
Descending limb
Thin ascending limb
Thick ascending limb
Nephron

1.
2.
Two types of nephrons
Cortical nephron
Juxtamedullary nephron
Cortical Nephron

Has its glomerulus in the outer
portion of the cortex
Cortical Nephron

And a short loop of Henle that
penetrates only into the outer region
of the medulla
Juxtamedullary Nephron

Has its glomerulus deep in the cortex
close to the medulla
Juxtamedullary Nephron

Its long loop of Henle stretches
through the medulla and almost
reaches the papilla
Renal Tubule and Collecting Duct

Most of the cells of the distal
convoluted tubule have receptors for
ADH and aldosterone
Juxtaglomerular Apparatus (JGA)

Helps regulate blood pressure and
the rate of blood filtration by the
kidneys
Juxtaglomerular Apparatus (JGA)

1.
2.
Consists of
Juxtaglomerular cells
Macula Densa
Juxtaglomerular Cells

Located on an afferent arteriole
Macula Densa

Located on the distal convoluted
abutting the JG cells
Renal Physiology

Nephrons and collecting ducts
perform three basic processes while
producing urine
Renal Physiology
1.
2.
3.
Glomerular filtration
Tubular secretion
Tubular reabsorption
Glomerular Filtration

Glomerular filtrate - the fluid that
enters the capsular space
Glomerular Filtration

The principle of filtration – to force
fluids and solutes through a
membrane by pressure
Glomerular Filtration

Glomerular Filtration rate (GFR) –
the amount of filtrate formed by both
kidney per minute
Glomerular Filtration

GFR – 125ml/minute
Glomerular Filtration

This amounts of 180 liters of filtrate
per day
Glomerular Filtration

Because of further processing we
only excrete 1-2 liters of urine per
day
Glomerular Filtration

Only call it urine after it drips out of
the collecting ducts into the calyceal
system
Neural Autoregulation

Through the ANS
Neural Autoregulation

During extreme emergencies such as
shock, sympathetics to afferent
arterioles cause them to constrict
Neural Regulation

Blood flow into glomerular capillaries
is greatly decreased and GFR drops
Neural Regulation

Lowering of renal blood flow has two
consequences
Neural Regulation
1. Reduces urine output, which
conserves blood volume
Neural Regulation
2. It permits greater blood flow to
other body tissues
Neural Regulation

Severe hypotension can cause death
of part of the tubules, decreases
urine output, and kidney failure
Hormonal Regulation

With mild drops of BP sympathetics
stimulate renin secretion on JG cell
by targeting B1 receptors
Hormonal Regulation

Renin converts angiotensinogen to
angiotensin I
Hormonal Regulation

Angiotensin I is converted by
angiotensin converting enzyme to
angiotensin II
Hormonal Regulation

Angiotensin II causes efferent
arteriole to constrict more than
afferent arterioles, maintaining
filtration
Hormonal Regulation

Angiotensin II also leads to the
formation of aldosterone
Hormonal Regulation

Aldosterone causes sodium and
water retention and potassium
excretion
Principles of Renal Transport

Reabsorption – returns most of the
filtered water and many of the
filtered solutes (such as glucose,
sodium, etc.) to the bloodstream
Principles of Renal Transport

Tubular secretion – the transfer of
materials from the blood and tubule
cells into tubular fluid
Principles of Renal Transport

Tubular secretion helps control blood
pH and helps eliminate other
substances from the body
Principles of Renal Transport

Solute reabsorption drives water
reabsorption
Reabsorption in the Proximal
Convoluted Tubule

The majority of the solute and water
reabsorption from filtered fluid
occurs in the proximal convoluted
tubules
Reabsorption in the Proximal
Convoluted Tubule

Reabsorption of Na and other solutes
creates an osmotic gradient that
promotes reabsorption of water by
osmosis
Reabsorption in the Proximal
Convoluted Tubule

1.
2.
3.
4.
5.
6.
7.
8.
Proximal convoluted Na transporters
promote reabsorption of organic solutes
such as
Glucose
Amino acids
Bicarbonate ions
Water
Na
K
Cl
Other ions and vitamins
Secretion of NH3 and NH4 in the
Proximal Convoluted Tubule

The deamination of the amino acid
glutamine by PCT cells generates
NH3 and new HCO3-
Secretion of NH3 and NH4 in the
Proximal Convoluted Tubule

Most NH3 quickly binds to H+ and
becomes NH4+
Secretion of NH3 and NH4 in the
Proximal Convoluted Tubule

NH4+ can substitute H+ aboard the
Na+/H+ antiporters and be secreted
into tubular fluid
Reabsorption in the Loop of Henle

Water reabsorption is not directly
coupled with sodium reabsorption
Reabsorption in the Loop of Henle

In the descending limb, water is
reabsorbed via osmosis
Reabsorption in the Loop of Henle

As water is reabsorbed from the
descending limb, the osmolality of
the filtrate increases
Reabsorption in the Loop of Henle

In the ascending limb, Na+, K+, Clsymporters reclaim Na+, Cl-, and K+
ions from the tubular lumen fluid.
Reabsorption in the Loop of Henle

As sodium and chloride are
reabsorbed from the ascending limb,
the osmolality of the filtrate
decreases
Reabsorption in the DCT

As fluid flows along the DCT,
reabsorption of Na+ and Clcontinues due to Na+ - Clsymporters
Reabsorption in the DCT

The DCT serves as the major site
where parathyroid hormone
stimulates reabsorption of Ca2+ and
excretion of phosphate
Reabsorption and Secretion in the
Collecting Duct

Aldosterone increases Na+ and water
reabsorption as well as K+ secretion
by the collecting ducts and late distal
convoluted tubules
Reabsorption and Secretion in the
Collecting Duct

Some cells secrete H+ into the
filtrate and reabsorb HCO3- into the
bloodstream
Reabsorption and Secretion in the
Collecting Duct

These cells help maintain body fluid
pH by excreting excess H+ when the
pH is too low or by reabsorbing less
HCO3- when the pH is too high.
Reabsorption and Secretion in the
Collecting Duct

ADH regulates water reabsorption by
increasing permeability in the
Collecting Duct and DCT
Production of Dilute and
Concentrated Urine

The rate at which water is lost from
the body depends mainly on ADH
Production of Dilute and
Concentrated Urine

When ADH level is very low, the
kidneys produce dilute urine and
excrete excess water
Production of Dilute and
Concentrated Urine

When ADH level is high, the kidneys
secrete concentrated urine and
conserve water
Ureters

Each of the two ureters connects the
renal pelvis of one kidney to the
urinary bladder
Urinary Bladder

Located in the pelvic cavity posterior
to the pubic symphysis
Urinary Bladder

In the floor of the urinary bladder is
a small, smooth triangular area, the
trigone.
Urinary Bladder

The ureters enter the urinary bladder
near two posterior points in the
triangle
Urinary Bladder

The urethra drains the urinary
bladder from the anterior point of the
triangle
Urinary Bladder

In the area around the opening to
the urethra, the circular fibers of the
muscularis form the internal urethral
sphincter
Urinary Bladder

The internal urethral sphincter
contracts in response to
sympathetics, and relaxes in
response to parasympathetic
stimulation
Urinary Bladder

Below the internal sphincter is the
external urethral sphincter, which is
composed of skeletal muscle
Urethra

A tube leading from the floor of the
urinary bladder to the exterior
Urethra

Functions to discharge urine from the
body
Urethra

The male urethra also serves as the
duct for ejaculation of semen
Incontinence

A lack of voluntary control over
urination
Retention

Failure to void urine completely or
normally