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Hormonal Communication
Hormones are important messages both within the brain and between the brain and the body.
In addition to the nervous system, the endocrine system is a major communication system of the body. While the nervous system uses neurotransmitters as its chemical signals, the endocrine system uses hormones. The pancreas, kidneys, heart, adrenal glands, gonads, thyroid, parathyroid, thymus, and even fat are all sources of hormones. The endocrine system works in large part by acting on neurons in the brain, which controls the pituitary gland. The pituitary gland secretes factors into the blood that act on the endocrine glands to either increase or decrease hormone production. This is referred to as a feedback loop, and it involves communication from the brain to the pituitary to an endocrine gland and back to the brain. This system is very important for the activation and control of basic behavioral activities, such as sex; emotion; responses to stress; and eating, drinking, and the regulation of body functions, including growth, reproduction, energy use, and metabolism. The way the brain responds to hormones indicates that the brain is very malleable and capable of responding to environmental signals.
The brain contains receptors for thyroid hormones (those produced by the thyroid) and the six classes of steroid hormones, which are synthesized from cholesterol — androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, and vitamin D. The receptors are found in selected populations of neurons in the brain and relevant organs in the body. Thyroid and steroid hormones bind to receptor proteins that in turn bind to DNA and regulate the action of genes. This can result in long-lasting changes in cellular structure and function.
The brain has receptors for many hormones; for example, the metabolic hormones insulin, insulin-like growth factor, ghrelin, and leptin. These hormones are taken up from the blood and act to affect neuronal activity and certain aspects of neuronal structure.
In response to stress and changes in our biological clocks, such as day and night cycles and jet lag, hormones enter the blood and travel to the brain and other organs. In the brain, hormones alter the production of gene products that participate in synaptic neurotransmission as well as affect the structure of brain cells. As a result, the circuitry of the brain and its capacity for neurotransmission are changed over a course of hours to days. In this way, the brain adjusts its performance and control of behavior in response to a changing environment.
Hormones are important agents of protection and adaptation, but stress and stress hormones, such as the glucocorticoid cortisol, can also alter brain function, including the brain’s capacity to learn. Severe and prolonged stress can impair the ability of the brain to function normally for a period of time, but the brain is also capable of remarkable recovery.
Reproduction in females is a good example of a regular, cyclic process driven by circulating hormones and involving a feedback loop: The neurons in the hypothalamus produce gonadotropin-releasing hormone (GnRH), a peptide that acts on cells in the pituitary. In both males and females, this causes two hormones — the follicle-stimulating hormone (FSH) and the luteinizing hormone (LH) — to be released into the bloodstream. In females, these hormones act on the ovary to stimulate ovulation and promote release of the ovarian hormones estradiol and progesterone. In males, these hormones are carried to receptors on cells in the testes, where they promote spermatogenesis and release the male hormone testosterone, an androgen, into the bloodstream. Testosterone, estrogen, and progesterone are often referred to as sex hormones.
In turn, the increased levels of testosterone in males and estrogen in females act on the hypothalamus and pituitary to decrease the release of FSH and LH. The increased levels of sex hormones also induce changes in cell structure and chemistry, leading to an increased capacity to engage in sexual behavior. Sex hormones also exert widespread effects on many other functions of the brain, such as attention, motor control, pain, mood, and memory.
Sexual differentiation of the brain is caused by sex hormones acting in fetal and early postnatal life, although recent evidence suggests genes on either the X or Y chromosome may also contribute to this process. Scientists have found statistically and biologically significant differences between the brains of men and women that are similar to sex differences found in experimental animals. These include differences in the size and shape of brain structures in the hypothalamus and the arrangement of neurons in the cortex and hippocampus. Sex differences go well beyond sexual behavior and reproduction and affect many brain regions and functions, ranging from mechanisms for perceiving pain and dealing with stress to strategies for solving cognitive problems. That said, however, the brains of men and women are more similar than they are different.
Anatomical differences have also been reported between the brains of heterosexual and homosexual men. Research suggests that hormones and genes act early in life to shape the brain in terms of sex-related differences in structure and function, but scientists are still putting together all the pieces of this puzzle.
How LASIK Surgery is done
LASIK, or "laser-assisted in situ keratomileusis," is the most commonly performed laser eye surgery to treat myopia (nearsightedness), hyperopia(farsightedness) and astigmatism.
Like other types of refractive surgery, the LASIK procedure reshapes the cornea to enable light entering the eye to be properly focused onto the retina for clearer vision.
In most cases, laser eye surgery is pain-free and completed within 15 minutes for both eyes. The results — improved vision without eyeglasses or contact lenses — can usually be seen in as little as 24 hours.
If you're not a good LASIK candidate, a number of other vision correction surgeries are available, such as PRK and LASEK laser eye surgery and phakic IOL surgery. Your eye doctor will determine if one of these procedures is suitable for your condition and, if so, which technique is best.
Want a visual? View our LASIK slide show!
How Is LASIK Surgery Performed?
First, your eye surgeon uses either a mechanical surgical tool called a microkeratome or a femtosecond laser to create a thin, circular "flap" in the cornea.The surgeon then folds back the hinged flap to access the underlying cornea (called the stroma) and removes some corneal tissue using an excimer laser.
This highly specialized laser uses a cool ultraviolet light beam to remove ("ablate") microscopic amounts of tissue from the cornea to reshape it so it more accurately focuses light on the retina for improved vision.
For nearsighted people, the goal is to flatten the cornea; with farsighted people, a steeper cornea is desired.
Excimer lasers also can correct astigmatism by smoothing an irregular cornea into a more normal shape. It is a misconception that LASIK cannot treat astigmatism.
How Lungs Work
Why are the lungs important?
Oxygen, a basic gas, is needed by every cell in your body in order to live. The air that comes into the body through the lungs contains oxygen and other gases. In the lungs, the oxygen is moved into the bloodstream and carried through the body. At each cell in the body, the oxygen cells are exchanged for waste gas called carbon dioxide. The bloodstream then carries this waste gas back to the lungs where the waste gas is removed from the blood stream and then exhaled from the body. This vital process, called gas exchange, is performed automatically by the lungs and respiratory system.
Oxygen, a basic gas, is needed by every cell in your body in order to live. The air that comes into the body through the lungs contains oxygen and other gases. In the lungs, the oxygen is moved into the bloodstream and carried through the body. At each cell in the body, the oxygen cells are exchanged for waste gas called carbon dioxide. The bloodstream then carries this waste gas back to the lungs where the waste gas is removed from the blood stream and then exhaled from the body. This vital process, called gas exchange, is performed automatically by the lungs and respiratory system.In addition to gas exchange, the respiratory system performs other roles important to breathing. These include:
- Bringing air to the proper body temperature.
- Moisturizing the inhaled air to the right humidity.
- Protecting the body from harmful substances. This is done by coughing, sneezing, filtering, or swallowing them.
- The sense of smell.
The Parts of the Respiratory System and How They Work
AIRWAYS
The SINUSES are hollow spaces in the bones of the head. Small openings connect them to the nose. The functions they serve include helping to regulate the temperature and humidity of air breathed in.
The SINUSES are hollow spaces in the bones of the head. Small openings connect them to the nose. The functions they serve include helping to regulate the temperature and humidity of air breathed in.
The NOSE is the preferred entrance for outside air into the respiratory system. The hairs that line the wall are part of the air-cleaning system.
Air also enters through the MOUTH, especially in people who have a mouth-breathing habit or whose nasal passages may be temporarily obstructed, as by a cold or during heavy exercise.
The THROAT collects incoming air from the nose and mouth and passes it downward to the windpipe (trachea).
The windpipe divides into the two main BRONCHIAL TUBES, one for each lung, which subdivide into each lobe of the lungs. These, in turn, subdivide further.
Lungs and Blood Vessels
The right lung is divided into three LOBES, or sections. Each lobe is like a balloon filled with sponge-like tissue. Air moves in and out through one opening -- a branch of the bronchial tube.
The right lung is divided into three LOBES, or sections. Each lobe is like a balloon filled with sponge-like tissue. Air moves in and out through one opening -- a branch of the bronchial tube.
The left lung is divided into two LOBES.
The PLEURA are the two membranes, actually one continuous one folded on itself, that surround each lobe of the lungs and separate the lungs from the chest wall.
The PLEURA are the two membranes, actually one continuous one folded on itself, that surround each lobe of the lungs and separate the lungs from the chest wall.
The bronchial tubes are lined with CILIA (like very small hairs) that have a wave-like motion. This motion carries MUCUS (sticky phlegm or liquid) upward and out into the throat, where it is either coughed up or swallowed. The mucus catches and holds much of the dust, germs, and other unwanted matter that has invaded the lungs. You get rid of this matter when you cough, sneeze, clear your throat or swallow.
The smallest subdivisions of the bronchial tubes are called BRONCHIOLES, at the end of which are the air sacs or alveoli.
The CAPILLARIES are blood vessels that are imbedded in the walls of the alveoli. Blood passes through the capillaries, brought to them by the PULMONARY ARTERY and taken away by the PULMONARY VEIN. While in the capillaries the blood gives off carbon dioxide through the capillary wall into the alveoli and takes up oxygen from the air in the alveoli.
Muscles and Bones
The DIAPHRAGM is the strong wall of muscle that separates the chest cavity from the abdominal cavity. By moving downward, it creates suction in the chest to draw in air and expand the lungs.
The DIAPHRAGM is the strong wall of muscle that separates the chest cavity from the abdominal cavity. By moving downward, it creates suction in the chest to draw in air and expand the lungs.
The RIBS are bones supporting and protecting the chest cavity. They move to a limited degree, helping the lungs to expand and contract.
Keeping Lungs Healthy
Taking good care of yourself every day will help keep your lungs healthy. Good health habits like eating a balanced diet, exercising and reducing the stress in your life will help you breathe easier.
