The endocrine system regulates long-term changes in the body through glands that release chemical substances called hormones directly into the bloodstream. Hormones control homeostasis, metabolism and growth, reproductive functions, water balance, heart rate and blood pressure, immune function, and more. Hormones are either steroid hormones that diffuse through cell membranes or nonsteroid hormones that bind to receptors on cell surfaces or inside cells. The endocrine glands include the thyroid, parathyroid, adrenal, pituitary, pancreas, ovaries, testes, and placenta.

2. Endocrine system
• An endocrine gland produces and
releases chemical substances that
signal changes in other parts of the
body.
• Endocrine glands release substances
directly into the bloodstream.
• The endocrine system regulates long-
term changes in the body such as
growth and development.

3. Composition :

4. Functions :
• 1. Controls homeostasis
• 2. Maintains water balance
• 3. Controls uterine contractions
• 4. Controls milk production
• 5. Regulates ions (calcium, sodium, potassium)
• 6. Regulates metabolism and growth
• 7. Regulates heart rate and blood pressure
• 8. Monitors blood glucose levels
• 9. Aids the immune system
10. Reproductive functions

5. Chemical Classificaton of Hormones
Steroid Hormones:
• Lipid soluble
• Diffuse through cell membranes
Endocrine organs
• Adrenal cortex
• Ovaries
• Testes
• placenta
Nonsteroid Hormones:
• Not lipid soluble
• Received by receptors external to
the cell membrane
Endocrine organs
• Thyroid gland
• Parathyroid gland
• Adrenal medulla
• Pituitary gland
• pancreas

6. Hormone Actions
• “Lock and Key” approach: describes the interaction between the
hormone and its specific receptor.
• Receptors for nonsteroid hormones are located on the cell membrane
• Receptors for steroid hormones are found in the cell’s cytoplasm or in its
nucleus