The Endocrine System

Many diverse parts of the body work together in an amazingly complicated system of actions and reactions. Connecting these parts together and coordinating their actions is the job of the endocrine system.

Parts of the endocrine system

1.  Glands (nine total in a person).

2.  Hormones—chemical messages.

3.  Bloodstream—message delivery system.

Get the Message

Hormones are produced by specific endocrine glands but often function in cells all over the body. What makes the hormones message work only in the correct cells at the right time?

Receptors for specific hormones are located in target cells. The cell can turn the receptors on or off, plus the glands can change the amount of hormone released at a given time.

Feedback Mechanisms

Endocrine glands are controlled by feedback mechanisms that are similar to heating systems in homes. When the temperature goes below the thermometer setting, the thermostat sends a signal to the furnace and the heat starts. When the room reaches a comfortable temperature, the heat turns back off. In the body endocrine glands and their hormones are controlled the same way.

Example: The kidneys control water concentration in the blood. What signal tells the kidneys when to work? A hormone called ADH is secreted when blood water is low. ADH slows down the kidneys so less water is removed. When water in the blood is high, ADH is not secreted and the kidneys start to work again.


Major Glands and their Hormones

Gland

/ Location / Hormone / Action
Pituitary
/ base of brain / ADH / water balance; thirst
Oxytocin & Prolactin / milk production
FSH / egg release
LH / egg implantation
TSH / thyroid stimulation
ACTH / adrenal stimulation
GH / growth in cells
MSH / melanin production
Thyroid
/ neck / thyroxine / metabolism
calcitonin / decrease calcium in blood
Parathyroid / on thyroid / PTH / increase calcium in blood
Adrenal / on kidney / corticosteroids
(dozens of different types) / ion balance, nutrient absorption
epinephrine/norepinephrine (adrenaline) / “fight or flight”
Pancreas / near stomach / insulin / decrease blood glucose
glucagon / increase blood glucose
Testes / groin / testosterone / sex characteristics, sperm production
Ovaries / lower abdomen / estrogen / sex characteristics
progesterone / maintain uterus for pregnancy