HOMEOSTASIS

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

WHAT HOMEOSTASIS IS AND WHY IT IS IMPORTANTWhy 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.

WHAT HOMEOSTASIS IS AND WHY IT IS IMPORTANTMammals and Birds = Endothermic – able to internally regulate body temp.They are able to maintain the internal temperature themselves, independent of outside environment.

OppositeReptiles, fish, invertebrates and amphibians = Ectothermic – unable to regulate body temp.The organisms body temp. varies with the environment. 

THE ADVANTAGES OF CONTROLLING BODY TEMPERATUREAdvantages of EndothermicEnzymes 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

THE STRUCTURE OF THE SKIN

Skin is obviously important for temp. regulation.

Two layers.  Top layer is EPIDERMIS

Lower layer is DERMIS

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?)

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

THE STRUCTURE OF THE SKIN

DERMISMost 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 

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.

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 TissueAdipose – contains oil which acts as insulation against heat loss and acts as energy storage.

THE STRUCTURE OF THE SKINSummary 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 raysHair follicles form when epidermis folds inwardsDermis – Formed from connective tissue.Contains Sweat Glands, blood vessels and nerve endings.Adipose Tissue – Fatty tissue containing oil.Insulates against the cold.  Energy storage.