1. Maintaining Homeostasis
The Endocrine System
Maintaining Homeostasis

2. The Endocrine System Function: Maintains homeostasis using hormones.
An endocrine (ductless) gland secretes its products (hormones) directly into the blood stream.
Hormones are slow working but long lasting.
Hormones can only affect specific target cells.
What do we call glands that release their products through ducts to the outside of the body or into body cavities?
Exocrine glands Examples: Sweat, tears, & digestive juices

3. Endocrine Gland Locations (Fig. 39-2)
Hypothalamus
Thyroid
Pituitary gland
Pancreas
Parathyroid glands
Ovary
Thymus
Testis
Adrenal glands

4. II. Endocrine Gland Types & Functions
A. Pituitary – Secretes 9 hormones that directly regulate many body functions, & controls the actions of several other endocrine glands.
** The pituitary gland is controlled by the hypothalamus

5. Hypothalamus – Produces hormones that control the pituitary gland, & makes hormones stored in the pituitary gland.
Thyroid – Regulates the body’s metabolism using a hormone called thyroxine.
Too much thyroxine = hyperthyroidism and too little = hypothyroidism
What might the symptoms of each be?
Parathyroid – Releases parathyroid hormone which acts to maintain homeostasis of the calcium levels in the blood and bones.

6. Adrenal – Release epinephrine & norepinephrine which help the body respond to stress (flight or fight response).
Pancreas – produces insulin & glucagon which regulate the level of glucose in the blood.
Ovary – produces estrogen and progesterone. These produce primary and secondary sex characteristics and regulate the menstrual cycle and pregnancy.
Testis – produces testosterone for sperm production and primary and secondary sex characteristics.

7. III. How do hormones work?
There are two types of hormones:
Steroid hormones
1. Can cross the cell membrane directly into the cytoplasm and nucleus.
2. The hormone binds to a receptor protein inside the cell.
3. This hormone-receptor complex activates genes.
4. These genes code for proteins that carry out the actions associated with the hormone.
5. Estrogen, progesterone and testosterone are examples.
Steroid Hormone
Receptor
Hormone-receptor complex
Nucleus
DNA
Protein synthesis
mRNA

8. C. Nonsteroid hormones – Cannot pass through the cell membrane.
The hormone (first messenger) binds to a receptor on the cell membrane.
This activates an enzyme on the inner surface of the cell membrane.
The enzyme converts ATP into cyclic AMP (the second messenger).
The second messenger activates or inhibits enzymes.
These produce the hormones effects.
Human growth hormone and insulin
Hormone
Receptor
Cyclic AMP
Enzyme activities
Altered cellular function

9. Calcium and glucose levels
Concept Map
The Endocrine System
regulates
Growth
Water balance
Reproduction
Metabolism
Calcium and glucose levels
Response to stress
by means of the
by means of the
by means of the
by means of the
by means of the
by means of the
Pituitary
Ovaries
Testes
Thyroid
Pancreas
Adrenals
Parathyroids