An image of a man from the waist up changes to a skeletal view
with some organs and glands visible.
The glands that make up the endocrine system produce chemical messengers called hormones
that travel through the blood to other parts of the body.
A box to the right of the screen will show enlargements of highlighted areas
from the larger image. The first is the brain.
Important endocrine glands include the pituitary,
A dot above the bridge of the nose is shown.
thyroid.
A gland is shown in the middle of the neck.
parathyroid,
Two glands resembling a pair of wings are shown attached to the thyroid.
thymus,
An elongated gland is shown in front of the heart.
and adrenal glands.
Two glands are shown, one on top of each kidney.
There are other glands that contain endocrine tissue and secrete hormones,
including the pancreas, ovaries, and testes.
The pancreas is shown in the front of the abdomen between the kidneys.
The endocrine and nervous systems work closely together.
The brain sends instructions to the endocrine system.
Signal arcs spread down from the head.
In return, it gets constant feedback from the glands.
Circles like radio waves spread out from the thymus.
The two systems together are called the neuro endocrine system.
The main image changes to a cut view of the man's head.
A small round object dangles below the brain just in front of the brain stem.
The object -- looking like two bulbs -- and area above it enlarge.
The area above is labeled hypothalamus.
The hypothalamus is the master switchboard.
It's the part of the brain that controls the endocrine system.
That pea-sized structure hanging below it is the pituitary gland.
It's called the master gland because it regulates the activity of the glands.
The hypothalamus sends either hormonal or electrical messages to the pituitary gland.
Signals are represented by arrows.
In turn, it releases hormones that carry signals to other glands.
The main image goes back to the skeletal view.
The image of the pituitary below the hypothalamus remains in the box.
The system maintains its own balance.
When the hypothalamus detects the rising level of hormones from a target organ,
Arcs rise to the hypothalamus.
It sends a message to the pituitary to stop releasing certain hormones.
When the pituitary stops, it causes the target organ to stop producing its hormones.
The box is removed from the screen, and the main image returns
to the original image of a man from the waist up.
The constant adjustment of hormone levels lets the body function normally.
This process is called homeostasis.