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Eye & Endocrine Alexia Hawley P 4 (major structures of eye (((Aqueous…

- - - - Aqueous Humor
      - Aqueous humor is a clear, watery fluid, contained in two chambers behind the cornea, that helps to bring nutrients to the eye tissues. It is produced by the ciliary body, a ring of tissue that sits behind the iris.
      - As it circulates, the aqueous fluid flows to the front part of the eye, where it is drained by the trabecular meshwork, a sponge-like filtering system located where the cornea and iris meet. After draining through the trabecular meshwork, the aqueous fluid then passes through a small duct, called the canal of Schlemm, and is absorbed into the bloodstream.
      - 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 Lens
      - The lens is composed of transparent, flexible tissue and is located directly behind the iris and the pupil. It is the second part of your eye, after the cornea, that helps to focus light and images on your retina.
      - Because the lens is flexible and elastic, it can change its curved shape to focus on objects and people that are either nearby or at a distance. The lens provides 25-35% of your eye's focusing power.
      - The ciliary muscles, which are part of the ciliary body, are attached to the lens and contract or release to change the lens shape and curvature.
    - - The Retina and Optic Nerve
      - The retina is the light-sensitive tissue that lines the inside surface of the eye, much like wallpaper. Cells in the retina convert incoming light into electrical impulses. These electrical impulses are carried by the optic nerve (which resembles your television cable) to the brain, which finally interprets them as visual images.
      - The macula is the small sensitive area in the center of the retina that provides clear central vision. The fovea is located in the center of the macula and provides the sharpest detail vision.
- - - - 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.
        
        The pituitary gland makes many hormones, such as:
        
        growth hormone, which stimulates the growth of bone and other body tissues and plays a role in the body's handling of nutrients and minerals
        
        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.
        
        Thyroid hormones are important because they help kids' and teens' bones grow and develop, and they also play a role in the development of the brain and nervous system.
        
        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.