The kidneys and urinary system remove waste from the body through urine. The kidneys contain over a million nephrons that filter blood to form urine. Urine regulates water, salt, and pH levels in the blood. It contains nitrogenous wastes like urea and ammonia, produced when proteins breakdown. The urine is transported from the kidneys to the bladder via ureters, stored in the bladder, and exited through the urethra.

1. EXCRETORY SYSTEM (urinary)
• I INTRODUCTION
• Excretion rids body waste substances,
particularly end products of metabolism.
• Several organs assist in the excretory
process but the kidneys which are a part of
the urinary systemare the primry organs of
excretion.

2. EXCRETORY SYSTEM contd.
• Urine is formed by more than one million
nephrons in each kidney which not only
serves to rid the body of nitrogenous
wastes, but also to regulate the water
content, the salt levels, and the pH of the
blood.
• USE pp. 243 & 244 of the lab manual.

3. EXCRETORY SYSTEM CONTD.
• I EXCRETORY PROCESS IN HUMAN BODY
• 1. Lungs--carbon dioxide
• 2. Sweat-Glands--urea (in small
quantities.
• 3. Digestive Tract-excess Calcium,and
• iron from the small intestine.
• 4. Kidneys--Nitrogenous wastes , (urea)
• 5. Liver--Bile pigments

4. EXCRETORY SYSTEM contd.
• Proteins are broken down into amino acids.
• They may be used to produce new protein
or they may be deaminated in the liver to
form ammonia.
• Ammonia is toxic and is converted in the
liver to urea. This is delivered to the
kidneys by the blood. (ON BOARD)

5. EXCRETORY SYSTEM contd.
• FUNCTIONS OF EXCRETORY SYSTEM
• 1. Excretion of nitrogenous products of
metabolism in urine.
• 2. Maintenance of the proper water
balance in the body.
• 3. Maintenance of the proper conc. Of
salts.
• 4. Regulation of pH in the blood.

6. EXCRETORY SYSTEM contd.
• URINARY SYSTSEM
• 1. Kidneys--(bean shaped organs about
4”X2”. They are reddish brown in color.
• 2. URETERS--(tubes which convey the urine
• to the bladder.)
• 3. URINARY BLADDER--(hollow muscular
organ that can hold up to 600 mls. Of urine.
• 4. URETHRA--(tube that runs from bladder
to body surface. Drains the bladder.)

7. EXCRETORY SYSTEM contd.
• ANATOMY & FUNCTION OF THE KIDNEY
• 1. CORTEX--Layer that lies next to outside
of kidney. Contains the nephrons, the
filtering units of the kidneys.
• 2. MEDULLA--The inner layer of the
kidney.It consists of thousands of
collecting tubules. Forms pyramids &
calyx. 3. PELVIS--Hollow collecting
chamber.

8. EXCRETORY SYSTEM contd.
• The formation of urine by the nephron
results from 3 physiological activities that
occur in different regions of the nephron:
• I F I L T R A T I O N
• 1. Blood pressure forces small molecules
• from the glomerulus into Bowman’s
• capsule.
• 2. The glomerular filtrate (20 percent of

9. EXCRETORY SYSTSEM contd.
• 3. This glomerular filtrate , collected in
Bowman’s capsule is carried to the renal
tubule .
• 4. 80 per cent of the blood (serum protein
& blood cells) is carried by the efferent
vessel to the network of veins sorounding
the renal tubule.
• This is accomplished by blood pressure.

10. EXCRETORY SYSTEM contd.
• II. SELECTIVE REABSORPTION
• 1. Cells in the walls of the proximal
convoluted tubule reabsorb whatever
substances are needed and pass them out
into the venous capillaries sorrounding the
tubule.
• 2. The tubule is able to select for
reabsorption just the amount of any one
substance needed by the blood.

11. EXCRETORY SYSTEM contd.
• 3. Reabsorbed materials are:
• (a) electrolytes
• (b) glucose sugar
• © water (80 per cent absorbed at the
• loop of Henle.
• 4. This is accomplished by diffusion and
active transport.

12. EXCRETORY SYSTEM contd.
• III. SECRETION
• In the distal convoluted tubule
substances not needed in the blood, are
transferred out of the blood from the
venous capillaries into the the tubule. The
tubule then secretes these into the filtrate.
• Substances excreted are: (1) water (2salts
(3) urea (4) Uric ascid (5) creatinine
• All are excreted from the body in the urine.