1. Homeostasis
Shie Yu Hao (22)
Per Sheng Xiang (19)

2. Overall Outline The need for Homeostasis Structure of Mammalian Skin
Heat Production and Heat Loss

3. Small Facts How do they do this?
Emperor Penguin, largest of all Penguins, live in Antarctica. These birds breed in extremely low temperature that can drop to -40 degree Celsius.
The egg laid by the female is handed over to the male for incubation, and the egg cannot touch the ground or it will freeze immediately!
How do they do this?

4. Homeostasis Definition:
Homeostasis is the maintenance of a constant internal environment.
Why is there a need for this?
Conditions outside our body are constantly changing.
Body cells, however, must be kept at constant temperature and bathed in tissue fluid that is kept at a constant pH and water potential.

5. Constant body temperature
Enzymes in our body can only work within certain temperatures.
Thus, changes in body temperature too drastically may result in enzyme inactivation or even denaturation.
An example will be high fever, that is people suffering from high fever must consult doctors as high fever is highly fatal!
Note: Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure.

6. Constant pH and water potential
Drastic change in the pH of tissue fluid will affect enzyme reaction in the tissue cells and harm our body.
Composition of tissue fluid must be kept within very narrow limits, thus, any drastic change in water potential will affect our cells.
Do you know: 
Your kidneys help you regulate the water potential (osmotic pressure) in your blood.
When water potential increases, the osmotic pressure of blood will decrease and vice versa.

7. Homeostatic control of water potential
Normal water potential in blood (Norm)
Stimulus Water potential of blood decreases
(Due to loss of water through profuse perspiration)
Receptor (Hypothalamus stimulated)
Corrective Mechanism
More ADH released by pituitary gland
More water reabsorbed by kidney tubules Less water excreted
Urine is more concentrated
Less urine produced
Water potential of blood increases
When water potential decreases
Negative Feedback

8. Homeostatic control of water potential
Normal water potential in blood (Norm)
Stimulus Water potential of blood increases
(Due to large intake of water)
Receptor (Hypothalamus stimulated)
Corrective Mechanism
Less ADH released by pituitary gland
Less water reabsorbed by kidney tubules More water excreted
More dilute urine produced
Water potential of blood decreases
When water potential increases
Negative Feedback

9. Need for homeostasis
Homeostasis is the process that keeps body temperature constant and ensures that the composition of the body fluids is kept within narrow limits.
By ensuring a relatively stable internal environment, homeostasis allows an organism:
To be independent from changes of external environment.
Changes include blood and tissue fluid (mammals).

10. Homeostasis negative feedback
Homeostasis can help you respond to the drastic changes in your body by a receptor (detector).
Note: Your body reacts to bring about an opposite effect to changes!
Therefore, if the system is disturbed, the disturbance sets in motion a sequence of events that tends to restore the system to its original state.
This is the NEGATIVE FEEDBACK process!!
Note: A negative feedback response means that your body is gradually going back to normal.

11. More Facts
Organs or Structure that detects changes in body are called receptors/sensors.
Changes from normal condition is called stimulus.

12. Homeostasis Occurrence
There must be:
A stimulus, change in the internal environment
A receptor that detects the stimulus
An automatic/self-regulatory corrective mechanism: Brings about reverse effect of stimulus
Negative feedback to the receptor

13. Principle of homeostasis
Normal condition or set-point (Norm)
Stimulus (Condition rises above normal)
Receptor (Detects stimulus)
Self-regulatory corrective Mechanism
Condition decreases
Condition rises
Negative Feedback

14. Principle of homeostasis
Normal condition or set-point (Norm)
Stimulus (Condition decreases below normal)
Receptor (Detects stimulus)
Self-regulatory corrective Mechanism
Condition increases
Condition decreases
Negative Feedback

15. Examples of homeostasis in human
Regulating blood glucose concentration
Body cells need glucose for tissue respiration
Tissue respiration then provides cell with energy for vital activities
A drastic change in the blood glucose concentration can be VERY DANGEROUS!
Do you know: 
Glucose levels in your blood rise after a meal and fall during vigorous exercise or starvation.
So, how does our body keep the concentration of glucose in the blood constant?

16. Blood glucose concentration rises
Normal condition or set-point (Norm)
Stimulus
(Too much glucose in blood )
Receptor (Islets of Langerhans are stimulated)
Corrective Mechanism
Pancreas secretes more insulin.
Causes liver to convert glucose to glycogen
Blood glucose concentration falls
Negative Feedback

17. Blood glucose concentration falls
Normal condition or set-point (Norm)
Stimulus
(Too little glucose in blood )
Receptor (Islets of Langerhans are stimulated)
Corrective Mechanism
Pancreas secretes glucagon
Causes liver to convert glycogen to glucose
Blood glucose concentration increases
Negative Feedback

18. Structure of mammalian skin
Skin forms a protective coat over our body surface
Acts as an excretory organ
As well as a regulator of body functions
So, how does skin do all these stuffs??? Before you can answer this question, you must first learn about the structure of skin 

19. Structure of mammalian skin
Skin is composed of 2 different parts:
An outer part called the epidermis
An inner thicker part called the dermis

20. Dermis Upper part of Dermis is thrown into ridges
Rich supply of nerves and blood capillaries
These structures allow our skin to:
Detect changes in the temperature of the surrounding
Feel pain E.g. A needle pricks into your skin
Blush

21. Blood vessels in skin
A number of blood vessels are present in the dermis
Arterioles carries blood to these capillaries
Arterioles are controlled by nerves (Vasomotor nerves)
Vasomotor nerves brings about reflex contraction and dilation in Arterioles (Vasodilation)
When Arterioles dilates, more blood is sent to blood capillaries in your skin
Contraction of Arterioles, Vasoconstriction, reduces the amount of blood flowed through the capillaries in the skin (Causing you to become pale)
Do you know: 
Your skin will turn red when you blush is because of the numerous blood vessels in you skin dilate
Contraction and Dilation of you Arterioles help you to regulate body temperature!!!

22. Hair
Hairs are embedded in the dermis, but they are produced by the epidermis.
Malpighian layer of the epidermis sinks into the dermis, forming a hollow tube called hair follicle.
Each hair grows in a hair follicle.
Hair papilla (mass of tissue containing blood capillaries and nerves) are found at the base of the hair follicle.
Covered with epidermal cells that constantly divides (Pushes new cells upwards)
Cells being pushed upwards soon dies and harden, which form hair 

23. Hair erector muscles are attached to the hair follicles
These muscles can contract, causing:
The hairs to “stand on its ends”
The skin to be raised around the hair, producing the characteristics “goose pimples” in humans
Do you know: 
Hair can be specialized for particular purposes.
The whiskers or vibrissae of cats and dogs can help them sense objects.
The long stiff spines of porcupines are modified hairs used for protection.

24. Sweat glands Each sweat gland is a coiled tube formed by a
down-growth of the epidermis
Forms a tight knot in the dermis
Richly surrounded by blood capillaries
Secreted sweat flows through a sweat duct and a sweat pore to the skin surface
Secreted sweat contains mainly water, dissolved salt (sodium chloride) and small amount of urea
Sweat contains metabolic waste products such as urea, skin is considered an excretory organ

25. Sweat secretes continuously
Amount of sweat produce, however, varies
It may be produced in very small quantities which evaporates almost immediately Or
When more sweat is produced, it appears as droplets on your skin or as “running streaks” of liquid in extreme cases
Note: Sweat is a mean by which your skin regulates body temperature

26. Sensory receptors Parts of body that detect changes in the
environment or stimuli are called sensory receptors
Nerves ending found in the epidermis and dermis
are simple sensory receptors
Enable us to sense (PPT)- Thermoreceptors:
Pain
Pressure
Temperature changes in the external environment

27. Sub-cutaneous fat
Beneath the dermis are several layers of adipose cells, where fats is stored
Fat in these cells also serves as an insulating layer, preventing heat loss

28. Skin Acts as: A Protective outer covering of the body
A Regulatory of body temperature
An Excretory organ
A Sense organ
Skin contains of an outer epidermis and a thick inner dermis
In short, JUST REMEMBER: PRESS! 

29. Heat Production How does your body gain heat? Definition:
Heat is produced within you body as a result of metabolic activities such as tissue respiration
Lots of tissue respiration takes place in the muscles and liver
Thus, large amount of heat are set free in these organs
Heat is then distributed to all parts of your body by the blood
Do you know: 
You can also gain extra heat by eating hot food, exercising, from the sun’s radiation or from warm air on very hot days
If these heat is not lost to the surrounding, you may die of overheating

30. Heat Loss How does your body lose heat? Heat is lost:
Through you skin by radiation, convection and to a limited extent, conduction
By evaporation of sweat from the surface if your skin
In the faeces, urine and in the air that is exhaled
Do you know: 
Certain parts of your skin contain shunt vessels. These vessels connect the skin arterioles with the venules.
They control the amount of blood flowing through your skin capillaries.
When shunt vessels constrict, more blood reaches the capillaries in your skin, which increase the amount of heat loss. When shunt vessels dilate to allow more blood to enter them, less blood flows to the capillaries in your skin, thereby decreasing the amount of heat loss. Hence, shunt vessels affect heat loss through skin surface.

31. Regulating body temperature
Hypothalamus in our brain monitors and regulates body temperature
Hypothalamus receives information about temperature changes in the external environment from temperature receptors in skin
Also monitors temperature of blood passing through it

32. Human body temperature rises
Normal condition or set-point (Norm)
Stimulus
(Blood and skin temperature increases)
Receptor
Temperature in skin detects change and send nerve impulses to brain
Hypothalamus in brain is stimulated and sends nerve impulses to relevant body parts
Corrective Mechanism
Arterioles in skin dilate, shunt vessels constrict, more blood flows to blood capillaries in the skin, increasing heat loss
Sweat glands more active, more sweat produced, sweat evaporated and more latent heat lost
Rapid breathing (helps remove heat)
Metabolic rate decreases (decrease heat produced)
Blood temperature decreases to the norm
Negative Feedback

33. Human body temperature falls
Normal condition or set-point (Norm)
Stimulus
(Blood and skin temperature decreases)
Receptor
Temperature in skin detects change and send nerve impulses to brain
Hypothalamus in brain is stimulated and sends nerve impulses to relevant body parts
Corrective Mechanism
Arterioles in skin constrict, shunt vessels dilates, less blood flows to blood capillaries in the skin, decreasing heat loss
Sweat glands less active, less sweat produced and less latent heat lost
Shiver, if very cold (Contraction of skeletal muscles)
Metabolic rate increases (decrease heat produced)
Blood temperature increases to the norm
Negative Feedback

34. Results Constant body temperature
Extra heat produced is removed at a faster rate so that there is no appreciable rise in body temperature
Heat is gained at a faster rate when surrounding temperature drops too low

35. Thank You !