Homeostasis refers to the maintenance of a constant internal environment in the body, keeping factors such as temperature, water concentration, and glucose levels stable despite changes in the external environment. This allows cells to function efficiently and prevents damage. Endothermic animals like mammals and birds internally regulate their body temperature, while ectothermic animals like reptiles rely on external temperatures. The skin plays an important role in homeostasis through its structure - the epidermis contains cells that protect the body and produce melanin and keratin, while the dermis contains sweat glands, blood vessels, and nerves that help regulate temperature.

1. HOMEOSTASIS

2. WHAT HOMEOSTASIS IS AND WHY IT IS
IMPORTANT
• Homeostasis – the maintenance of a constant internal environment
Although the outside environment is always changing (think weather),
The cells inside almost always the same all the time.
Temp., amount of water, glucose concentration

3. WHAT HOMEOSTASIS IS AND WHY IT IS
IMPORTANT
Why is Homeostasis important?
Temp.
To help cells work efficiently. 37 degrees helps enzymes work at the optimum rate.
Water.
Cells are not damaged by absorbing/losing too much water by osmosis.
Glucose.
Constant glucose conc. Means always enough fuel for energy.

4. WHAT HOMEOSTASIS IS AND WHY IT IS
IMPORTANT
Mammals and Birds = Endothermic – able to internally regulate body temp.
They are able to maintain the internal temperature themselves, independent of outside
environment.
Opposite
Reptiles, fish, invertebrates and amphibians = Ectothermic – unable to regulate body
temp.
The organisms body temp. varies with the environment.

5. THE ADVANTAGES OF CONTROLLING BODY
TEMPERATURE
Advantages of Endothermic
Enzymes can always work very efficiently. Metabolism can occur even when cold
outside.
Can be active (can move) in cold weather.
However,
Endothermic animals need to eat much more than Ectothermic.
Needs to gain energy, from respiration

6. THE STRUCTURE OF THE SKIN
Skin is obviously important for temp. regulation.
Two layers. Top layer is EPIDERMIS
Lower layer is DERMIS

7. THE STRUCTURE OF THE SKIN
Epidermis - Cells at the base of the epidermis divide (mitosis).
These new cells move towards surface = die and fill up with keratin (protein)
(top layer of skin is made up of dead cells = Cornified Layer)
This Cornified Layer protects living cells below. How? Because it is Hard and
Waterproof.
Constantly sheading and being replaced. (Soles of feet thicker....WHY?)

8. THE STRUCTURE OF THE SKIN
Some epidermis cells contain a pigment call Melanin (dark brown)
Melanin absorbs harmful ultraviolet rays, to stop damage to living cells below.
Hair follicles are formed by the epidermis folding inwards. Hair is made of Keratin

9. THE STRUCTURE OF THE SKIN
DERMIS
Most of Dermis is formed by connective tissue (separates/connects different
organs/tissues, not clearly defined shape – containing few cells, collagen and elastic
tissues)
As people get older the fibres lose their elasticity

10. THE STRUCTURE OF THE SKIN
DERMIS. Sweat glands are contained in the dermis. Secrete Sweat (mostly water, with
salts and urea dissolved in it)
From sweat gland – through sweat duct – out through sweat pores.
Sweating helps with temp. regulation.

11. THE STRUCTURE OF THE SKIN
DERMIS. Also in Dermis: -
Blood vessels and nerve endings (sensitive to touch/pain/pressure/temp.)
Detect changes in environment
Below Dermis is Fat Layer of Adipose Tissue
Adipose – contains oil which acts as insulation against heat loss and acts as energy
storage.

12. THE STRUCTURE OF THE SKIN
Summary of Skin Structure
Epidermis - New cells form by mitosis.
New cells move to surface and die forming Cornified Layer. Protects living cells below.
Contains Melanin to protect from UV rays
Hair follicles form when epidermis folds inwards
Dermis – Formed from connective tissue.
Contains Sweat Glands, blood vessels and nerve endings.
Adipose Tissue – Fatty tissue containing oil.
Insulates against the cold. Energy storage.