Hormones u Chemical messengers carried in the blood plasma u Affect cells with the correct receptors = target cells u Secreted into the blood by endocrine glands

Main endocrine glands

Adrenaline u Stress hormone u From adrenal glands u Prepares for “fight or flight” u Eg. diverts blood to the muscles u Raises heart and breathing rate

Homeostasis u Maintaining a steady internal environment u Controlled by negative feedback mechanisms u Provides the optimum conditions for cells

Homeostasis u Controlled by pancreas / liver u Too little cells cannot respire u Too much and cells lose water by osmosis u Controlled by kidneys u Too little / too much causes osmotic problems u Controlled by the skin u Too cold and reactions are slow u Too hot and enzymes denature Blood Glucose Water content Temperature

Thermoregulation u Mammals and birds = homeothermic u Optimum conditions for enzymes u Thermostat in the hypothalamus

Skin 1. Hair 2. Capillary 3. Sweat gland 4. Fat

When it’s cold u Keeps blood away from skin u Reduces heat loss u Muscles contract and relax u Friction generates heat u Metabolic reactions generate heat u Trap insulating layer of air VasoconstrictionShivering Increased liver activity Hairs stand up

When it’s hot u Blood passes next to surface u Increases heat loss u Heat from body evaporates water u Water leaves and takes energy u and opposite of what you do when it’s too cold VasodilationSweating

Blood Glucose Levels u Insulin u Produced by pancreas in response to high blood glucose levels u Makes cells take up glucose from the bloodstream u Makes the liver convert glucose to glycogen u Therefore lowers blood glucose

Blood Glucose Levels u Glucagon u Produced by pancreas in response to low blood glucose levels (Glucose gone) u Makes the liver convert glycogen to glucose u Therefore increases blood glucose

Removal of waste = excretion u Alveoli / lungs u Kidneys Carbon dioxide Water Salt / urea

The excretory system

The kidney 1. Renal artery 2. Nephron 3. Renal vein 4. Ureter

Structure of a nephron Bowman’s capsule First coiled tubule Loop of Henlé Second coiled tubule Collecting duct

Bowman’s capsule

The formation of urine 1. Filtration under pressure (water, ions and small molecules enter nephron) 2. Reabsorption (Useful molecules reabsorbed into blood) 3. Reabsorption of water (water reabsorbed to conserve it) u A hormone (ADH) released from the brain causes more water to be reabsorbed into the blood 1 2 3

The effect of ADH