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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

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 (or 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

Endocrine

  • Maintaining Human Body Temperature (37oC)
  1. If body temperature rises above 37oC - 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 defaecation or urination.
  2. If body temperature falls below 37oC - The muscles may shiver to produce heat through friction, skin muscles may contract to produce insulating air pockets next to the skin with 'goosebumps' 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 defaecation.
  • Maintaining Salt Balance

Excess salt in humans is excreted in both urine and sweat.