chandimakumara007@gmail.com

1. Edexcel IGCSE
Human Biology
Chapter 08
Homeostasis and Excretion
chandimakumara007@gmail.com

2. Introduction
• Homeostasis refers to the ability of keeping the conditions of
the internal environment of the body relatively constant
• Homeostasis regulates the;
―Body temperature
―pH
―Water
―Salts (Na+, K+)
―Glucose concentration
―Blood pressure
• Internal environment refers to the blood together with tissue
fluid

3. Consequences of incorrect homeostasis
• Changing body temperature – enzymes can get
denatured
• Changing pH - enzymes can get denatured
• Increased water – fluid overload of the body leads to
heart failure
• Increased salts (Na+, K+) - fluid overload of the body,
Arrhythmia
• Increased glucose concentration - Diabetes
• Increased blood pressure – Hypertension, Stroke
• Increased wastes (urea) - Toxicity

4. Urine
• Healthy adult produces
― 1.5 dm3 urine per day
― 40g of waste products per every litre of urine
• Nitrogenous waste in urine - urea, ammonia
• Why every animal has to excrete a nitrogenous waste product ??
― Carbohydrates and fats only contain C,H,O elements and can be
stored as glycogen
― Protein has element of ‘N’ and excess cannot be stored
― Protein is broken down to Amino acids in the liver, then converted in
to glycogen as a storage by producing urea as the waste product
― Urea is filtered in the kidneys
― Kidney serves as an excretory organ as well as a homeostatic organ

5. Urinary system

6. Components of the Urinary system
• Renal artery – where the not filtered blood enters to the
kidneys at a high pressure
• Renal vein – filtered blood is transported to the heart via
inferior vena cava
• Ureters – Urine is transported from kidneys to the bladder
• Bladder –
―stores of urine
―Has two muscular sphincters
Lower sphincter– voluntary
Upper sphincter- Involuntary
• Kidneys

7. The Kidneys

8. Anatomy of the Kidney
• Renal cortex –
– Contents
―tiny blood vessels branches from renal artery
― tubules of the nephrons
• Renal medulla –
– Contents
• Loop of henles’
• Pyramids where the tubules get connected and opens to the pelvis
• Renal Pelvis
– Connects with ureters

9. Nephron

10. Functions of the nephron
• Bowman’s capsule - hollow cup
of cells at the start of the
nephron
• Glomerulus
― ball of blood capillaries
surrounds bowman’s capsule
― Receives blood through
afferent arteriole which has a
larger diameter
― Removes blood through
efferent arteriole which has a
smaller diameter
― This creates a resistance in
the glomerulus and pressure
forces fluid towards the
capsule

11. Functions of the nephron
• Glomerulus continued…..
― filtration occurs through three layers;
 capillary cell wall
 basement membrane – act as a filter allows only water, ions and small
molecules to pass
 capsule cell wall
― Glomerulus filtrate
―The fluid enters capsule space after ultrafiltration
―180 dm3 per day, but only 1.5 dm3 is lost as urine due to reabsorption
― Ultrafiltration – Filtering different sized molecules under
pressure

15. Questions
• Explain the filtration and reabsorption of following
substances before producing urine
– Proteins
– Blood cells
– Glucose
– Na+
– Urea
– Water( flow rate)
• Why camels have a long loop of Henle while beavers
have a shorter one ?

16. Control of the body’s water content
Q. Explain the
regulation of
body water
content of the
ADH hormone

17. Control of the body’s water content
Increased
concentration
in the blood
Detected by
the
Hypothalamus
Posterior
pituitary gland
Increased ADH
secretion
Increased the
water
reabsorption in
tubules in the
Kidneys
What will happen if someone drinks a large amount of water ?
Decreased
concentration
in the blood
Detected by
the
Hypothalamus
Posterior
pituitary gland
Decreased
ADH secretion
Decreased the
water
reabsorption in
tubules in the
Kidneys

18. Oral Rehydration Therapy (ORT)
• Microorganisms can
cause diarrhoea and
vomiting which leads
to dehydration and
loss of electrolytes
• ORT can simply
prevent deaths from
fluid or
electrolyte(Na+/K+)
imbalance

19. Kidney Failure
• Kidneys helps to remove toxic wastes from the blood
• One can survive with one kidney, but not by none
• If both kidneys are not functioning one must undergo
one of these options;
– A kidney transplant
– Renal dialysis

20. Kidney Transplant
• Operation where a patient receives another person’s kidney
• Kidney will be selected from a closed relative or from a patient is at a
vegetative state
• Transplanted kidneys can be rejected from the recipients immune system
• To avoid the rejection, following actions will be taken;
– Tissue typing
• donated kidney will be taken from a genetically closed person (identical twin is
the best donor)
– Recipient will receive immune suppressive drugs
• It may increase the risk of getting infections
– Bone marrow of the patient is treated with radiation to reduce
production of WBC
• success rate 80%, survival longer than 3 years
• While people waiting for a kidney transplant they undergo renal dialysis
Watch this video : https://www.youtube.com/watch?v=fELn4Fe9Ccc

21. Renal Dialysis
• Renal dialysis machine(kidney machine) filters blood to remove urea,
other wastes and excess salts
• The filter is a special dialysis membrane called visking tubing which has
tiny hole in it to pass small molecules ( water, ions, urea) but not larger
molecules ( proteins, blood cells)
• Blood from the patient flow on one side of the membrane and watery
liquid called dialysis solution flows on the other side in the opposite
direction
• Urea and unwanted salts diffuse through the holes in to the dialysis
fluid
• Dialysis fluid is replaced with fresh solution all the time and after
several hours patients blood has been cleaned of toxic waste
• Before the dialysis, an operation is carried out to join an artery to the
vein, which raises the blood pressure
• A tube then permanently connected to the vein to receive cleaned
blood

22. Renal Dialysis contd…
• The used dialysis fluid is then discarded
• While the process, kidney machine prevent air bubbles coming
in, regulates temperature and oxygenation
• Time consuming and an unpleasant process
• A patient may need to clean blood for many hours and for 2 to 3
times per week
• Kidney transplant is a much better option than the renal dialysis
Watch this video :
https://www.youtube.com/watch?v=IQKQ4eoKfTg

24. Control of body temperature
• Homoeothermic (warm blooded) – Ability to keep their body
temperature constant, despite the changes in the temperature
of their surroundings ( Ex: Humans, birds)
• Homoeothermic animals can regulate temperature by the
physiological changes ( producing or losing heat). So they are
also called as endotherms (heat from inside)
• Endotherms uses;
– heat from the chemical reactions in the cells and control the
temperature by sweating and blood flow to the skin
– Use behavioral changes to warm up the bodies
• Penguins – huddling
• Humans - clothing

25. Control of body temperature contd..
• All the other animals are cold blooded as they can’t regulate
their temperature ( Ex: reptiles)
• Coping strategies used by reptiles to survive in the change of
temperature
– Cold weather - lying in the sun
– Hot weather – staying in cold places in the ground
• Importance of regulating temperature;
– provide enzymes to work efficiently
– avoid denaturing

27. Structure of the skin

28. The skin and temperature control
• Functions of the skin;
1. Protect from mechanical damage
2. Protect from microorganisms
3. Acting as an impermeable layer to prevent loss of
water
4. Acting as a sense organ
• Pain receptor
• Temperature receptor
• Pressure receptor
5. Controlling heat loss from body surface

29. Structure of the skin
• Epidermis
– Outer layer consists of dead cells
– Prevents water loss
– Act as a barrier for the outside microorganisms
• Dermis
– Middle layer
– Contains sensory receptors, sweat glands, small blood vessels,
hair follicles
• Hypodermis
– fat layer that stops heat loss
– Acts as a energy store

30. Monitoring Body Temperature
• Thermoregulatory centre in the hypothalamus monitors the
temperature in the body via a negative feed back system
• Thermal sensation of the skin is notified to this centre through
nerve impulses
• Thermoregulatory centre;
– Implement behaviours in hot or cold weather
• Sunny – going under a shade
• Hot – having a cool drink
– Regulates vasodilatation under the skin
– Regulates sweat glands under the skin
– Regulates skeletal muscles to produce heat (shivering)
– Increase the metabolism of the body and produce more heat

32. Thermal regulation of the skin

33. Increasedbodytemperature
Sweat glands
Produce a greater
amount of sweat
Latent heat of
vaporisation
Evaporation removes
heat on the surface
Relaxation of the
hair erecter muscles
Hair lies flat on the
skin
More heat will be
lost
Vasodilation
Blood flows through
the capillary loops
Radiates heat
outside
decreased
metabolism
Generating less heat
Behavioral actions
Going to a shade
having a cold drink

34. Decreasedbodytemperature
Sweat glands Reduced sweat production Less evaporation
Contract hair erecter
muscles
Hair pulled upright on the
skin
heat will be saved
Vasoconstriction in
sphincter muscles in
arteriole walls
Reduced blood flow to the
capillary loops
Heat will be saved
Increased metabolism Generating more heat
Heat is distributed all over
the body
Shivering of skeletal
muscles
Generating more heat
Heat is distributed in the
body
Behavioral actions
Putting up warm cloths
having a hot drink