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 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.
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 .
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.