Homeostasis and excretion

Homeostasis and excretion

1. the maintenance of a constant internal environment

2. Homeothermic/endoithermic animals can keep their temperature almost constant even though their environment changes

3. Poikilothermic/exothermic animals cannot

4. Temperature Regulation

   • Top layer - epidermis
     • Cells in the epidermis were made in the MALPIGHIAN LAYER Cellls ar constantly dividing by mitosis. The new cells made move towards the surface of the skin as they go they die and fill up with a protein - KERATIN forming the CORNIFIED LAYER.
       • Some cells in the epidermis contain a dark brown pigment - MELANIN. This absorbs harmful UV rays in sunlight
     • The epidermis folds in forming hair follicles. hairs are made of keratin.
       • A SEBACEOUS GLAND opens from the side of each hair follicle these make an oily substance called SEBUM which keeps the hair and skin soft and supple
   • Bottom layer - dermis
     • Mostly made of connective tissue which contains elastic fibres and collagen fibres.
     • Sweat glands secrete sweat
     • Blood vessels and nerve endings
     • A layer of fat called ADIPOSE TISSUE below the dermis helps insulate the body
   • The HYPOTHALAMUS is a part of the brain that coordinates the activities of parts of the body that can bring about temperature change
     • It acts as a thermostat and works by sending electrical impulses along nerves to parts of the body
     • When hot.....
       • Hair lies flat
       • Vasodilation
       • Sweat
     • When cold......
       • Muscles work
       • Metabolism may increase
       • Hair stands up
       • Vasoconstriction
     • Negative Feedback
       • Where the hypothalamus stops the skin from acting to reduce or conserve heat

5. Control of blood glucose content

   • Cells need steady supply of glucose to carry out respiration
   • Carried out by the LIVER and PANCREAS
     • Scattered throughout the pancreas are ISLETS OF LANGERHANS. They make two hormones called glucagon and insulin
       • Insulin lowers blood sugar
         • the liver cells absorb glucose from the blood. Some is used for respiration, but some is stored in the liver as the insoluble polysaccharide glycogen
       • Glucagon raises blood sugar
         • The liver cells break down glycogen into glucose

6. Excretion

   • Deamination
   • Kidneys -Ultra filtration

7. the removal of toxic materilals, the waste products of metabolism andsubstances of excess requirements