Excretory System: Anatomy and Function of Kidneys and Nephrons

EXCRETORY SYSTEM NUTRITION

OBTAINING
Digestive system
Nutrients
Respiratory
system
Oxygen

DISTRIBUTING
Circulatory
system
Nutrients and oxygen
and collecting waste
products and carbon
dioxide

ELIMINATING
Excretory system
Waste products
Respiratory
system
Carbon dioxide

Excretory Products and Organs

What are the excretory products
of the various excretory organs?

EXCRETORY SYSTEM

Excretion is the elimination of waste products which result from the metabolic activity of cells.
Without excretion, the waste products would accumulate and become toxic.

Liver
Urinary system
Respiratory system
Sweat glands

THE URINARY SYSTEM

Adrenal gland
Kidneys
Adrenal glands - Endocrine system
These endocrine glands secrete
hormones such as adrenaline and
corticosteroids.

Renal
vein
Renal
artery
Inferior vena cava
Aorta
Urinary bladder
Ureters
Urethra

The renal artery enters and
the renal vein leaves the
kidneys on its concave side.

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KIDNEYS

Cortex: outer layer
Medulla
Renal pelvis

The renal pelvis is the
innermost part of the
kidney. It is funnel-shaped
and connected to the ureter.

The medulla is the striated middle layer of the
kidney. This is split into triangular sections
called renal pyramids or Malpighi's pyramids.

Kidney
Unfiltered
blood
Filtered
blood
Ureter
Urine exits
to bladder

Each kidney contains approximately one million
nephrons. These units filter the blood and produce urine.

Nephron Structure

Nephron
Glomerulus
Filtered
blood
Tubule
Unfiltered
blood
Collecting duct
Urine exits duct

Glomerulus
Filtered
blood
Bowman's capsule
Distal convoluted
tubule
Unfiltered
blood
Proximal
convoluted tubule
Cortex-medulla
junction
I
-
Venule
Collecting duct
Loop of
Henle
Peritubular
capillary
network

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Urine flows into renal pelvis

NEPHRONS

Bowman's capsule is a hollow, cup-shaped sac
surrounding a ball of capillaries called the
glomerulus. This structure is inside the renal
cortex.

Convoluted tubules are twisted tubes. They may
be proximal convoluted tubules running from
Bowman's capsule to the loop of Henle or distal
convoluted tubules running from the loop of
Henle to the collecting duct.

The loop of Henle is a U-shaped tube located
between the proximal and distal convoluted
tubules. This part of the nephron enters the
medulla of the kidneys.

URINARY TRACT

Ureters

They are two 25 cm-long, narrow tubes.
They take urine from the kidneys to the urinary bladder.

Ureter
Smooth muscle
layers
-Internal sphincter
External sphincter

Urinary bladder

Expandable, muscular organ. Up to
half a litre of urine collects here,
although it can store up to two litres.

Urethra

It connects the urinary bladder with the
outside and has two sphincters to control
the output of urine. The internal sphincter is
under involuntary control while the external
one is under voluntary control.

right kidney
left kidney
ureters
bladder
urethra

1
Bowman's capsule
Filtered
blood
Distal convoluted
tubule
Unfiltered
blood
2
K+
3
Proximal
convoluted tubule
Cortex-medulla
junction
I
-
Venule
Collecting duct
2
Loop of
Henle
Peritubular
capillary
network
Urine flows into renal pelvis
4

THE EXCRETORY PROCESS

1. Absorption: liquid passes from the blood in
   the glomerulus into the Bowman's capsule. This
   process filters out water, waste products (urea),
   vitamins, amino acids, mineral salts and glucose.
2. Reabsorption: substances such as water,
   glucose, amino acids and mineral salts are
   returned to the blood from the tubules and the
   loop of Henle.
3. Some substances, such as potassium ions (K+),
   pass from the interstitial fluids into the final
   part of the nephron.
4. Urine is produced and flows to the renal pelvis.

THE EXCRETORY PROCESS

1. Urine flows continuously from the ureters into the
   bladder.
2. Urination: when the bladder is full, urine flows
   through urethra from the bladder to the outside of the
   body. This process is controlled by two small muscles
   called sphincters at the top and bottom of the urethra.

Kidney
Kidney
(inside
view)
Renal
pelvis
Ureter
5
Bladder
Opening of
ureter
(ureteral orifice)
Internal
sphincter
Urethra
External
sphincter
6

THE URINE

Composition of Urine

Urine is a clear, yellow liquid composed of:

• 95% water.
• 3% of toxic substances, such as urea and uric
  acid.
• 2% of mineral salts, mainly sodium and
  potassium.

Functions of Urine

• Eliminate toxic waste from the body.
• Regulate the levels of ions in the blood.
• Balance fluid levels.
• Regulate blood volume and pressure.

What does urea
come from?