The Sclera
The sclera is a tough white outer coating of fibrous tissue that covers your entire eyeball (all the way around) except for the cornea. The muscles that move the eye are attached to the sclera. The name sclera comes from the Greek word "skleros," which means "hard."

The Iris and the Pupil
The iris is a ring-shaped membrane inside the eye that surrounds an opening in the center, called the pupil. The iris contains muscles that allow the pupil to become larger (open up or dilate) and smaller (close up or constrict). The iris regulates the amount of light that enters your eye by adjusting the size of the pupil opening.

The Choroid
The choroid is a dark brown membrane that is rich with blood vessels, located between the sclera and the retina. It supplies blood and nutrients to the retina and nourishes all of the other structures within the eye.

The Vitreous
The vitreous is the jelly-like substance that fills the inside of the back part of the eye. Over time, the vitreous becomes more liquid and can detach from the back part of the eye

Hypothalamus: The hypothalamus is in the lower central part of the brain. It links the endocrine system and nervous system. Nerve cells in the hypothalamus make chemicals that control the release of hormones secreted from the pituitary gland. The hypothalamus gathers information sensed by the brain (such as the surrounding temperature, light exposure, and feelings) and sends it to the pituitary. This information influences the hormones that the pituitary makes and releases.

Pituitary: The pituitary gland is at the base of the brain, and is no bigger than a pea. Despite its small size, the pituitary is often called the "master gland." The hormones it makes control many other endocrine glands.

prolactin, which activates milk production in women who are breastfeeding

thyrotropin , which stimulates the thyroid gland to make thyroid hormones

corticotropin which stimulates the adrenal gland to make certain hormones

antidiuretic hormone, which helps control body water balance through its effect on the kidneys

oxytocin , which triggers the contractions of the uterus that happen during labor

The pituitary also secretes endorphinschemicals that act on the nervous system and reduce feelings of pain. The pituitary also secretes hormones that signal the reproductive organs to make sex hormones. The pituitary gland also controls ovulation and the menstrual cycle in women.

Thyroid: The thyroid is in the front part of the lower neck. It's shaped like a bow tie or butterfly. It makes the thyroid hormones thyroxine . These hormones control the rate at which cells burn fuels from food to make energy. The more thyroid hormone there is in the bloodstream, the faster chemical reactions happen in the body.

Parathyroids: Attached to the thyroid are four tiny glands that work together called the parathyroids . They release parathyroid hormone, which controls the level of calcium in the blood with the help of calcitonin which the thyroid makes.

Adrenal Glands: These two triangular adrenal glands sit on top of each kidney. The adrenal glands have two parts, each of which makes a set of hormones and has a different function:

The outer part is the adrenal cortex. It makes hormones called corticosteroids that help control salt and water balance in the body, the body's response to stress, metabolism, the immune system, and sexual development and function.

The inner part is the adrenal medulla It makes catecholamines , such as epinephrine . Also called adrenaline, epinephrine increases blood pressure and heart rate when the body is under stress.

Pineal: The pineal body, also called the pineal gland, is in the middle of the brain. It secretes melatonin a hormone that may help regulate when you sleep at night and when you wake in the morning.

Reproductive Glands: The gonads are the main source of sex hormones. Most people don't realize it, but both guys and girls have gonads. In guys the male gonads, or testes , are in the scrotum. They secrete hormones called androgens the most important of which is testosterone These hormones tell a guy's body when it's time to make the changes associated with puberty, like penis and height growth, deepening voice, and growth in facial and pubic hair. Working with hormones from the pituitary gland, testosterone also tells a guy's body when it's time to make sperm in the testes.

A girl's gonads, the ovaries , are in her pelvis. They make eggs and secrete the female hormones estrogenand progesterone . Estrogen is involved when a girl starts puberty. During puberty, a girl will have breast growth, start to accumulate body fat around the hips and thighs, and have a growth spurt. Estrogen and progesterone are also involved in the regulation of a girl's menstrual cycle. These hormones also play a role in pregnancy.

Pancreas: The pancreas makes insulin and glucagon , which are hormones that control the level of glucose, or sugar, in the blood. Insulin helps keep the body supplied with stores of energy. The body uses this stored energy for exercise and activity, and it also helps organs work as they should.