1. The Endocrine System 11(a)

2. Overview of the Endocrine System Two organ systems enable the body to communicate with itself in order to maintain homeostasis: Nervous System: Acts quickly. Endocrine System: Composed of endocrine glands. Acts slowly (minutes to years!). – Hormone: A chemical messenger that travels through the bloodstream to a target cell. – Hormones alter a cells metabolism (DNA expression, enzymes). – Endocrine glands operate by negative feedback.

4. There are two types of hormones:

5. Hormone Action Steroid Hormones: Synthesized from Cholesterol. – Examples: Testosterone, Estrogen, Cortisol – How it works: – Lipid-soluble (why?), meaning it can easily pass through membrane. Because the membrane is made of lipids too! – Steroid hormones easily pass through membrane and the nucleus. They can cause your DNA to be expressed (transcription & translation).

6. Hormone Action Non-Steroid (Peptide) Hormones: Synthesized from amino acids (proteins). – Examples: Insulin, Antidiuretic Hormone (ADH), Thyroid Stimulating Hormone (TSH) – How it works: – Cannot pass through cell membrane. Must bind with receptor protein (Receptor-Hormone Complex). – Receptor Complex triggers a Secondary Messenger known as cAMP (cyclic AMP). – Since cAMP is on the inside of the cell and the hormone is not, cAMP causes changes to the cells metabolism.

8. Hormone Action Again, cAMP acts as a messenger. It must be quickly broken down by the enzyme phosphodiesterase so that cAMP’s activity is short-lived. **Caffeine Blocks phosphodiesterase**. What is the effect on cAMP? – cAMP doesn’t get broken down. What is the effect on a person? – Prolonged action of the hormone (more alert, etc.)

10. Endocrine Glands 1.Hypothalamus – Essentially tells the pituitary when to secrete. 2.Pituitary – Activated many of the following hormones 3.Thyroid – Thyroxin - Metabolism 4.Pancreas – Insulin, Glucagon 5.Adrenal Gland – Epinephrine 6.Ovaries – Estrogen 7.Testes – Testosterone

11. Review There are two types of hormones: – Steroid Hormones – Non-Steroid Hormones – Which one is faster?