The Human Endocrine System

1. What are hormones?

• Hormones are chemicals that regulate cells in the body. They are usually produced in one place but affect cells in another area.

2. How do hormones travel?

• Hormones are secreted into the blood and the circulatory system carries them to other body organs.

3. Nontarget vs target hormones?

• Nontarget hormones affect many different types of cells.

• Examples: growth hormone, insulin, epinephrine (adrenalin)

• Target hormones have a target, a specific type of cell that they act upon.

• Examples: parathyroid hormone, gastrin

4. NS vs Endocrine System

• Nervous system allows the body to adjust very quickly to changes in the environment.

• Endocrine system maintains control over a longer period of time.

5. Connection between systems?

• The hypothalamus in the brain controls the pituitary gland with nerve impulses.

• The pituitary gland stimulates other glands to produce hormones that affect the nerve activity of the hypothalamus.

6. Hormones affect all cells?• Hormones do not affect all cells. It depends

on the type of receptors the cell has and the number of them.

• Ex. A cell can have a receptor for hormone A, but not hormone B, A will affect that cell but B wouldn’t.

• Ex. Liver and muscle cells have lots of receptors for insulin; bone cells have few receptors for insulin, insulin has a greater effect on liver and muscle than on bone.

7. Two types of hormones

• Steroid hormones – made of cholesterol and soluble in fat.

• Examples are sex hormones (estrogen, testosterone) and cortisol

• Protein hormones – made of chains of amino acids and soluble in water.

• Examples are insulin, growth hormone, epinephrine

8. Action of Steroid Hormones• Hormone diffuses through cell membrane

(because they are soluble in fat) of target cell

• Hormone combines with receptor molecule

• They move into the nucleus and attach to DNA

• DNA activates a gene to produce a specific protein to cause the desired hormonal effect.

Action of Steroid Hormones

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Action of Steroid Hormones

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9. Action of Protein Hormones

• Hormone attaches to receptor on cell membrane of target cell (can’t pass through membrane because not fat soluble)

• This causes cyclic AMP to be formed • Cyclic AMP activates enzymes in the

cytoplasm which triggers ribosomes to create a specific protein to cause the desired hormonal effect

Action of Protein Hormones

Action of Protein Hormones

10. Two messenger system

• The action of protein hormones is often referred to as a “two messenger system”.

• The hormone that arrived at the cell is the first messenger.

• The Cyclic AMP within the cell is the second messenger.

Negative Feedback

• Is a type of control system that regulates hormone production

• Works similar to a thermostat on your furnace

• When the desired change is detected, the original action is inhibited

Negative Feedback