Human Endocrine System

• Hormone - A hormone is a chemical secreted by an endocrine gland and carried in the bloodstream to target organs where it performs a specific function.
• Functions of Hormones - The varying actions performed by hormones may be fast-acting (e.g. Adrenalin is a hormone that rapidly speeds up the heart and breathing rates when we get a fright), or may be slow-acting (e.g. Human Growth Hormone regulates the many body processes involved in growing from conception to death).
• Endocrine Glands - These glands are ductless, and secrete hormones directly into the bloodstream.
• Examples of Endocrine Glands - adrenal glands, thyroid gland, and ovaries and testes

ENDOCRINE GLAND	HORMONE SECRETED	TARGET ORGAN	EFFECT ON BODY
Pituitary	thyrotrophin	thyroid	controls secretion of thyroxin
	corticotrophin	adrenal glands	controls secretion of cortisol
	gonadotrophin	gonads	controls secretion of sex hormones
	human growth hormone	all cells	promotes body growth
	antidiuretic hormone	kidneys	promotes water reabsorption
	oxytocin	uterus	contracts uterus
	prolactin	breasts	controls breast milk secretion
Thyroid	thyroxine	all cells	controls metabolism
Parathyroid	parathyroid hormone	bones, kidneys	increases blood calcium
Adrenal	adrenaline ('fight or flight' hormone)	most cells	controls blood circulation, increases heart rate blood glucose and blood flow
	cortisol	most cells	controls metabolism of fats carbohydrates and proteins
	sex hormones	gonads	development of sex characteristics
Pancreas	insulin	all cells	lowers blood glucose
	glucagon	all cells	increase blood glucose
Gonads (Testes and Ovaries)	oestrogen	sex organs	female sex characteristics
	progesterone	sex organs	regulates menstrual cycle
	testosterone	sex organs, muscle	male sex characteristics, promotes growth

Homeostasis (Body Balance)

• Homeostasis - This is the tendency to maintain stability or uniformity in an organism's internal environment. A balance is maintained of temperature, and of chemicals such as water, salts and glucose.
• A Stimulus-Response Model

• Maintaining Human Body Temperature (37 °C)

1. If body temperature rises above 37 °C - The skin produces sweat which cools the body by using excess body heat to evaporate it. Also the body can consume cool drinks, find cool shade, radiate heat through the skin or by breathing out warm air, and by defecation or urination.
2. If body temperature falls below 37 °C - The muscles may shiver to produce heat through friction, skin muscles may contract to produce insulating air pockets next to the skin with 'goose bumps' and upright hairs, the body consumes warm drinks or finds warm shelter.

• Maintaining Water Balance
  Water is essential to the body for chemical reactions to take place within cells.
  The amount of water consumed in food and drink should equal the amount of water lost through breathing out, sweating, urination and defecation.
• Maintaining Salt Balance
  Excess salt in humans is excreted in both urine and sweat.