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