1. What is excretion?
The elimination of metabolic waste products
Faces include excretory products, because they include metabolic wastes ( bile and mucus).
Excretions are toxic and must be removed, because high concentrations can damage the body tissues.

2. Importance of excretion
it helps in the maintenance of salt balance in the blood.
helps in the removal of metabolic waste that may be poisonous to the organism.

3. Removal of unwanted Substances
Carbon dioxide
Removed during exhalation
In gaseous exchange, carbon
dioxide diffuses from capillaries into the alveoli of lungs.
The carbon dioxide rich air then expelled into the atmosphere.

4. Water
In excess water can be very harmful to the organism. (put strain on heart)
A small amount is removed from the body during exhalation as water vapour.
As we sweat we lose water.
Urine contains a large amount of water and is expelled during urination.

5. Salts and ions
Released from body during sweating and urination.
Nitrogenous wastes
Released during urination via kidneys
A small amount is released in our sweat.

6. The Skin The largest organ of the body.
The only organ comes in a variety of colours.
Covers our entire body and protects it from the outer environment.
Has two major layers :
Epidermis on top
The dermis below

7. The Epidermis Thinner than dermis Has several layers. Top layer called
cornified layer.

8. Epidermis Malpighian layer
Layer of cells which produce the pigment melanin
Melanin gives the skin and hair its colour.
Melanin protects us from ultraviolet rays in sunlight.

9. Epidermis Cornified layer Top layer of skin. Made of dead cells.
Protects the softer living cells below.

10. Dermis Made mainly of connective tissue Blood vessels
Transport substances and help to regulate body temperature.
Nerves
Carry messages to and from brain.
Muscle fibres (erectile muscles)
Attached to hair follicles so that hairs can stand up or lie down.

11. Dermis Sebaceous glands
Secrete an oily substance onto surface of the skin, which help keep the hair flexible and waterproof the epidermis.
Sweat glands
Secrete sweat.
Sweat evaporates to keep the body cool.
Sweat also contain water, salts and urea (excretory products).

12. Regulation of body temperature
Heat loss to cool the body
Vaso-dilation – arterioles
near surface of skin
enlarge in diameter.
The larger volume of
blood carried in the
blood vessels will carry
more heat, which lost through the skin

13. Sweating
This is a response made by the body to excessive heat in the surroundings.
Infections and strenuous can also increase your body temperature.
Evaporation of sweat cools the body.
The water in sweat evaporates from the surface of the skin.

14. Heat is taken from the body to change liquid sweat to vapour, causing cooling.
Sweating itself does not cool the body.
It is the evaporation of sweat which has this effects.
When sweat cannot evaporate in badly ventilated rooms, or in humid air,
great discomfort can be caused.

15. Fans can help by blowing the water vapour away from the skin surface.
This increase the rate of evaporation.

16. Keeping the body Warm
Vasoconstriction
When the body is cold, the blood vessels reduces their diameter.
Blood vessels then carry less blood.
When less blood is carried, less heat is lost through the skin.

17. Shivering This is a response made by the body to cold.
The muscles under the skin quickly contract and relax.
The muscles are working hence heat is released as respiration increases.

18. Subcutaneous Fat
The layer of fat acts as an insulating layer against cold.
Fat is a poor conductor of heat .
The subcutaneous layer holds heat within the body.

19. Clothing
This acts as an insulator to keep the body warm.
Hair
Fur in animals acts as an insulator, trapping air to keep them warm.
Man does not have enough hair to keep them warm.
Some warmth may be retained by hair on the head.

20. N.B Hyperthermia This is a condition where the body temperature rises and the regulatory mechanisms fail to cool it. Hypothermia When the body temperature is uncontrollably lowered and regulating mechanisms fail. Heat and temperature Heat is a form of energy while temperature is a degree of hotness.

21. What is homeostasis?
This is the way constant conditions in the body are maintained in spite of changes from the surrounds.
These mechanisms work to maintain normal conditions in the body.
Example
Blood water content
Blood glucose level
Body temperature

22. How Does Homeostasis Work ?
The optimum, normal level for a factor that needs to remain constant is called the set point.

23. Receptors in the body detect any deviation from the set point, either up or down, and send the information to a control centre.

24. The control centre then sends messages to an effecter, which takes action to bring the level of the factor back towards to set point.

25. Homeostasis of Water Balance
Our body fluid always remain constant.
Whether we drink a little or a lot of water.
The kidneys are responsible for the water balance.
Water that enters the cells blows them up, like an inflated balloon (turgid).

26. If the body fluids become less concentrated than body cells.
Water enters body cell.
If the cells take in too much water they may burst open. .

27. Should water leave the cells then they lose this support and deflate.
If the body fluids becomes more concentrated then water leave the cells.
The control of water balance in the cells is known as osmoregulation.

28. Control of Water Content by ADH
Control of water content in the blood is maintained by the hypothalamus.
When the hypothalamus detect a high blood concentration it simulate the posterior pituitary gland.
The posterior pituitary gland then produce antidiuretic hormone (ADH)

29. ADH stimulate the kidneys to increased reabsorption of water from the filtrate back into the blood.

30. Homeostasis of the Blood Sugar Content
Whether we eat a lot of little carbohydrate, the blood sugar level must be kept constant.
Insulin and glucagon from the regulate blood sugar level/concentration.

31. Excess Sugar
When blood sugar concentration rises, receptors in the islets of Longerhans of the pancreas detected the increase.
Beta (b) cells then produce the hormone insulin.
This occur after a large meal containing carbohydrate.
Insulin make liver convert excess
sugar to glycogen.

32. This glycogen is then stored in the liver.
Insulin also convert some sugar to fat.

33. Low Blood Sugar Level
Alpha cells in the islets of langerhans secrete the hormone glucagon.
Glucagon make liver break down glycogen back to glucose.
This restores normal sugar level in the blood.

34. NB Insulin lowers the blood sugar concentration and glucagon increases it.

35. The Kidneys
The kidneys are attached inside the back of the abdomen.
The are bean shaped.
They receive blood rich in waste by the renal artery.
Deoxygenated ,but purer ,blood is collected by the renal vein and passed back to the heart by the posterior vena cava.

36. The Nephron
This is the functioning unit of the kidneys.
Each kidney contain about 1 million nephrons.

37. Bowman’s Capsule
Renal artery (afferent arteriole) create a high blood pressure in the capillaries of the glomerulus.

38. The pressure forces fluids into the bowman’s capsule (filtrate).

39. Filtrate contains useful substances such as water, salts, glucose.
Waste products such as urea.

40. Proximal Convoluted Tubule
Reabsorb useful substances such as glucose, salts and water.

41. Loop of Henle
Descending limb mainly allows water to leave into blood capillaries.
Ascending limb mainly
allow surrounding
capillaries to reabsorb
salts.

42. Distal convoluted Tubule and Collecting Duct
Fine-tune body fluid composition.
Control body pH levels.
ADH stimulates more
reabsorption of water from
The distal convoluted tubule
And collecting duct.

43. Stages in the Formation of Urine
Filtration under pressure in the capsule.
Selective reabsorption of the useful substances from the tubules.
More waste can be added to the tubules by the capillaries them.
Water is removed or added to the collecting ducts from the loop of henle.
Urine passes to the pelvis and ureter.
Blood with plasma at the correct concentration passes out in the renal vein.