The adrenal gland

what is the process of adrenal glands

the adrenal glands

he adrenal glands he two adrenal glands are named for their position in the body above (ad meaning "near") the kidneys (renal mean-g "kidney"). Each of these triangular glands has two parts 'with two different functions. The adrenal cortex  is the outer, yellowish portion of each adrenal gland. he word cortex comes from a Latin word meaning "bark" d is often used to refer to the outer covering of a tissue,organ, or gland. The adrenal medulla is the inner, reddishprortion of the gland and is surrounded by the cortex. Notsurprisingly, the word medulla comes from a Latin word caning "marrow" or "middle." 

The adrenal cortex 

As you may recall, the anterior pituitary gland secretes the hormone ACTH, adrenocorticotropic hormone. This hormone, as its name implies, stimulates the adrenal cortex to secrete a group of hormones known as corticosteroids. These steroid hormones act on the nucleus of target cells, triggering the cell's hereditary material to produce certain proteins. The two main types of corticosteroids produced by the adrenal cortex are the mineralocorticoids and the glucocorticoids. 

The mineralocorticoids are involved in the regulation of the levels of certain ions within the body fluids. The most important of this group of hormones is aldosterone. It affects tubules within the kidneys, stimulating them to reabsorb sodium ions and water from the urine that is being produced, putting these substances back into the blood-stream. The secretion of aldosterone is triggered when the volume of the blood is too low, such as during dehydration or blood loss. Special cells in the kidneys "monitor" the blood pressure. When the blood pressure drops, these cells secrete an enzyme that begins a chain of reactions ending with the secretion of aldosterone. Conversely, when the blood pressure is within a normal range, the cell "detectors" in the kidneys are not stimulated, the release of aldosterone is not triggered, and the kidney tubules are not stimulated to conserve sodium and water. 

 The glucocorticoids affect glucose metabolism, causing molecules of glucose to be manufactured in the body from non-carbohydrates such as proteins. This glucose enters the bloodstream, is transported to the cells, and is used for energy as part of body's reaction to stress.

Almost everyone is familiar with the term stress. And almost everyone can give examples of stressful situations: their boss "chewing them out" in front of co-workers, their kids fighting constantly with one another, or their sustaining a physical injury. The stress reaction was first described in 1936 by Hans Selye, a researcher who has since become the acknowledged authority on stress. Dr. Selye explained how the body typically reacted to stress—any disturbance that affects the body—and called this reaction the general adaptation syndrome. Over a prolonged period of stress, the body reacts in three stages: (1) the alarm reaction, (2) resistance, and (3) exhaustion. Contrary to maintaining homeostasis within the body, the general adaptation syndrome works to help the body "gear up" to meet an emergency. During the alarm reaction the body goes into quick action. Imagine that you just entered your place of work and your boss confronted you, accusing you—in front of the office staff—of making a costly mistake. Your body reacts with a quickening pulse, increased blood flow, and an increased rate of chemical reactions within your body. Why does your body react in this way? Although the adrenal cortex is involved in the stress reaction, the beginning of the story lies in an understanding of the middle section of the adrenal glands, the adrenal medulla.

The adrenal medulla 

The adrenal medulla is different from most other endocrine tissue in that its cells arc derived from cells of the peripheral nervous system and are specialized to secrete hormones. These cells arc triggered by the        au

tonomic nervous system, which controls involuntary “automatic" responses. The other major nervous tissues With direct endocrine function are the secretory portion of the hypothalamus in the brain and the posterior Pituitary just under the hypothalamus.

The two principal hormones made by the adrenal medulla are adrenaline and noradrenaline (also called epi. nephrine and norepinephrine). These two hormones are pl.'. manly responsible for the alarm reaction. The hypothalamus is responsible for sending the "alarm signal"  to the adrenal medulla. The hypo. thalamus picks up the alarm signal as it monitors changes in the emotions and carries it as nerve signals on tracts of neurons that connect the hypothalamus with the emotional centers in the cerebral cortex. It can therefore sense when the body perceives an emotional stress. It can also sense physical stress, such as cold, bleeding, and poisons in the body. The hypothalamus reacts to stress by readying the body for "fight or flight," first triggering the adrenal medulla to dump adrenaline and noradrenaline into the bloodstream. These hormones cause the heart rate and breathing to quicken, the rate of chemical reactions to increase, and glucose (stored in the liver) to be dumped into the bloodstream. In general, the actions of adrenaline and noradrenaline in-crease the amounts of glucose and oxygen available to the organs and tissues most used for defense: the brain, heart, and skeletal muscles.

The thyroid gland

what is the prolactin

Prolactin is another hormone secreted by the anterior pituitary. Prolactin works with estrogen, progesterone, and other hormones to stimulate the mammary glands in the breasts to secrete milk after a woman has given birth to a child. During the menstrual cycle, milk is not produced and secreted because prolactin levels in the bloodstream are very low. Late in the menstrual cycle, however, as the levels of progesterone and estrogen fall, the pituitary is stimulated by the hypothalamus to secrete some prolactin. This rise in prolactin, although not sufficient to cause milk production, does cause the breasts of some women to feel sore before menstruation. After menstruation, estrogen levels begin to rise, and prolactin secretion is once again inhibited. 

Melanocyte-stimulating hormone (MSH)

 acts on cells in the skin called melanocytes, which synthesize a pigment called melanin. This pigment is taken up by epideimal cells in the skin, producing skin colorations from pale yellow(in combination with another pigment called carotene) to black. Variations are caused by the amount of pigment the melanocytes produce; this variation is genetically deter-mined and is an inherited characteristic.

The posterior pituitary 

The posterior lobe of the pituitary stores and releases two hormones that are produced by the hypothalamus: antidiuretic hormone (ADH) and oxytocin. ADH helps control the volume of the blood by regulating the amount of water reabsorbed by the kidneys. For example, receptors in the hypothalamus can detect a low blood volume by detecting when the solute concentration of the blood is high. When the hypothalamus detects such a situation, it triggers its specialized neurosecretory cells to make ADH. This hormone is transported within axons to the posterior pituitary, which releases the hormone into the bloodstreambinds to target cells in the collecting ducts of the nephrons of the kidneys, increasing their permeability. More water then moves out of these ducts and back into the blood, resulting in a more concentrated urine. ADH also acts on the smooth muscle surrounding arterioles. As these muscles tighten, they constrict the arterioles, an action that helps raise the blood pressure. Alcohol supresses ADH release, which is why excessive drinking leads to the production of excessive quantities of urine and eventually to dehydration.

 Oxytocin is another hormone of the posterior pituitary: it is produced in the hypothalamus and transported within axons to the posterior pituitary for secretion. In women, oxytocin is secreted during the birth process, triggered by a stretching of the cervix of the uterus at the beginning of the birth process. Oxytocin binds to target cells of the uterus, enhancing the contractions already taking place. The mechanism of oxytocin secretion is an example of a positive feed-back loop in which the effect produced by the hormone enhances the secretion of the hormone. For this reason, oxytocin is used by physicians to induce uterine contractions when labor must be brought on by external means. Oxytocin also targets muscle cells around the ducts of the mammary glands, allowing a new mother to nurse her child. The suck-ling of the infant triggers the production of more oxytocin, which aids in the nursing process and helps contract the uterus to its normal size.

what is the thyroid gland of human

The thyroid gland

Sitting like a large butterfly just below the level of the voice box, the thyroid gland can be thought of as your "metabolic switch." This gland secretes hormones that determine the rate of the chemical reactions of your body's cells. Put sim-ply, thyroid hormones determine how fast bodily processes take place.
 The thyroid hormones are thyroxine (T4) and triiodothyronine (T3). These hormones are called amines: single, modified amino acids. They are not considered to be "true" peptide hormones, however, because they act on the DNA of target cells as steroid hormones do. They are also unique because an inorganic ion—iodine—is part of their structures.

 Your body uses iodine in the food you eat to help make the thyroid hormones; the 3 or 4 in each hormone name refers to the number of atoms of iodine in each hormone. Foods such as seafood and iodized salt are good sources of dietary iodine. If the diet contains an insufficient amount of iodine, the thyroid gland enlarges. This condition is called a hypothyroid goiter. The hypothalamus and the thyroid gland work together to keep the proper level of thyroid hormone circulating in the bloodstream. This level is detected by the hypothalamus. A low level of thyroid hormones stimulates the hypothalamus to secrete a releasing factor—a chemical message—to the anterior pituitary. This message tells the pituitary torelease more TSH. The thyroid responds, thereby raising the blood level of T3 and T4 back to normal. This mechanism of action is an example of a negative feed-back loop in which the effect produced by stimulation of a gland "shuts down" the stimulus. Shutdown occurs when a sufficient effect has been produced, similar to the mechanism of a thermostat. In your home, your furnace is triggered to go on when the temperature goes below the thermostat setting. The furnace stays on until the house heats up to the desired level. The thermostat then signals the furnace to turn off.

In certain disease conditions the amount of thyroid hormones in the bloodstream cannot be regulated properly. If the thyroid produces too much of the thyroid hormones, a person may feel as though the "engine is racing," with such symptoms as a rapid heartbeat, nervousness, weight loss, and protrusion of the eyes

. This condition is called hyperthyroidism. On the other hand, if the thyroid produces too little of the thyroid hormones, a person may feel "run down," with such symptoms as weight gain and slow growth of the hair and fingernails. This condition is called hypothyroidism. Various factors can be the under-lying cause of such problems; often medication or surgery can correct the situation.

In addition to secreting the thyroid hormones, the thyroid gland secretes a hormone called calcitonin, or CT. This hormone works to balance the effect of another hormone called parathyroid hormone, or PTH. PTH regulates the concentration of calcium in the b
loodstream. Calcium is an important structural component in bones and teeth and aids in the proper functioning of nerves and muscles.

What is  The parathyroid glands

the parathyroid glands 

The parathyroid glands Embedded in the posterior side of the thyroid are the para-thyroid glands. Most people have two parathyroids on each of the two lobes of the thyroid. These are the glands that secrete PTH, which works antagonistically to CT to help maintain the proper blood levels of various ions, primarily calcium. Two of the many problems related to abnormal calcium levels in the blood are kidney stones and osteoporosis. If calcium levels in the blood remain high, tiny masses of calcium may develop in the kidneys. These masses, called kidney stones, can partially block the flow of the urine from a kidney. If calcium levels in the blood remain low, calcium may be removed from the bones, a disorder known as osteoporosis. Osteoporosis is most common in middle-aged and elderly women, who have stopped secreting estrogen at menopause . Estrogen stimulates bone cells to take calcium from the blood to build hone tissue.

PTH and CT work in the following way to keep calcium at an optimum level in the blood: If the calcium level is too low, PTH stimulates the activity of osteoclasts, or bone-destroying cells. These cells liberate calcium from the bones and put it into the bloodstream. PTH also stimulates the kidneys to reabsorb calcium from urine that is being formed and stimulates cells in the intestines to absorb an increased amount of calcium from digested food. CT acts antagonistically to PTH. When the level of calcium in the blood is too high, less PTH is secreted by the parathyroids and more a is secreted by the thyroid. The CT inhibits the release of calcium from bone and speeds up its absorption, decreasing the levels of calcium in the blood. These interactions of PTH and CT are an example of a negative feedback loop that does not involve the hypothalamus or pituitary gland. The level of calcium in the blood directly stimulates the thyroid and parathyroid glands .

the pituitary gland

How to controlling pituitary

The pituitary gland

The pituitary gland The pituitary is a powerful gland that secretes nine different hormones. Although it secretes so many hormones, it is amazingly tiny—about the size of a marble. The pituitary "marble" hangs from the underside of the brain, supported and cradled within a bony depression of the sphenoid bone. 

Controlling the pituitary: The hypothalamus

 The pituitary secretes seven major hormones from its larger front portion, or lobe, the anterior pituitary. It secretes two from its rear lobe, the posterior pituitary. The secretion of these hormones is regulated by a mass of nerve cells that lies directly above the pituitary, making up a small part of the "floor" of the brain. This regulatory nervous tissue, the hypothalamus, is connected to the pituitary by a stalk of tissue  . The hypothalamus uses information it gathers from the peripheral nerves and other parts of the brain to stimulate or inhibit the secretion of hormones from the anterior pituitary. In this way, the by pothalamus acts like a production manager, receiving in-  formation about the needs of the company's customers and regulating the production of products to satisfy those needs. The hypothalamus accomplishes its management job by producing releasing hormones that affect the secretion of specific hormones from the anterior pituitary. The hypothalmus also produces two hormones that do not regulate hormonal release in the pituitary. When they are needed by the body, the hypothalamus signals the pituitary to release them. 

The pituitary is a tiny gland that hangs from the  underside of the brain. The secretion of its many diverse hormones is controlled by a mass of nerve cells lying directly above it called the hypothalamus. The hypothalamus stimulates or inhibits the secretion of hormones from the pituitary by means of re-leasing hormones. In addition, the hypothalamus produces two hormones that it stores in the pituitary. 

The anterior pituitary

The seven hormones produced by the anterior pituitary regulate a wide range of bodily functions . Four of these hormones are called tropic hormones. The word tropic comes from a Greek word meaning "turning" and refers to the ability of tropic hormones to turn on or stimulate other endocrine glands. Of the four tropic hormones, two are gonadotropins. The gonads are the male and female sex organs, the testes and the ovaries. The gonadotropins are hormones that affect these sex organs (considered endocrine glands because they secrete sex hormones). The two gonadotropins are follicle stimulating hormone (FSH) and luteinizing hormone (LH). In females, FSH targets the ovaries and triggers the maturation of one egg each month. In addition, it stimulates cells in the ovaries to secrete female sex hormones called estrogens. In men, FSH targets the testes and triggers the production of sperm. LH stimu
lates cells in the testes to produce the male sex hormone testosterone. In females, a surge of LH near the middle of the menstrual cycle stimulates the release of an egg. In addition, LH triggers the development of cells within the ovaries that produce another female sex hormone—progesterone. (See Chapter 20 for the organs and processes of the reproductive system.)

  The two other tropic hormones are adrenocorticotropic hormone (ACTH) and thyroid-stimulating hormone (TSH). ACTH triggers the adrenal cortex to produce certain steroid hormones. The adrenal glands are located on top of the kidneys (see Figure 19-1). Each of these two glands has two distinct parts: an outer cortex and an inner medulla. ACTH stimulates the adrenal cortex to produce hormones that regulate the production of glucose from "non-carbohydrates" such as fats and proteins. Others regulate the balance of sodium and potassium ions in the blood. Still others contribute to the development of the male secondary sexual characteristics. TSH triggers the thyroid gland to produce the three thyroid hormones.. This endocrine gland is located on the front of the neck, just below the voice box (see Figure 19-1). Its hormones control normal growth and development and are essential to proper metabolism.
The front portion of the pituitary, the anterior pituitary, secretes seven hormones. Of these seven, four stimulate other endocrine glands and are called tropic hormones.
Growth hormone (GH) is produced by the anterior pituitary and works with the thyroid hormones to control normal growth. GH increases the rate of growth of the skeleton by causing cartilage cells and bone cells to reproduce and lay down their inter cellular matrix. In addition, GH stimulates the deposition of minerals within this matrix. GH also stimulates the skeletal muscles to grow in both size and number. In the past, children who did not produce enough GH did not grow to an average height; this condition is called hypo-pituitary dwarfism. However, in the past decade, scientists have been able to use the techniques of genetic engineering  to insert the human GH gene into bacteria to produce human GH. Currently.


 Sandy Allen is shown here with her mother, brother, an dog. Giantism is caused by the over secretion of growth hormone.

this laboratory-made hormone is being used successfully treating growth disorders caused by hyposecretion (UN production) of GH in children. The opposite problem also occur: during the growth years, some children pr too much GH. This hypersecretion (overproduction) cause the long bones to grow unusually long (Figure 19-and result in a condition known as giantism. In adults, h persecretion of GH causes the bones of the hands and fa to thicken, resulting in a condition known as acromegaly .

Human Hormones

what is the hormone

Shooting up in the locker room with anabolic steroids has caused the downfall of many winners. These controversial drugs are really synthetic hormones, chem. icals that affect the activity of specific organs or tissues. The various hormones of the body all affect their "target" tissues in unique ways. Anabolic steroids affect the body in ways similar to the male sex hormone testosterone and stimulate the buildup of muscles. But along with building a championship body, anabolic steroids strikingly change the body's metabolism.

                                                                 

 Female athletes on steroids experience side effects such as shrinking breasts, a deepening voice, and an increase in body hair. Male athletes find that their testicles shrink. some users also experience life-threatening kidney and liver damage. Youngsters who take these drugs risk stunting their growth, since anabolic steroids cause bones to stop growing prematurely. And a great deal of controversy still surrounds claims that anabolic steroids can cause psychological effects such as "steroid rage," a state of mind in which users attack people and things around them. Today, scientists still lack solid scientific data regarding all aspects and consequences of anabolic steroid use. How-ever, it is clear that their use is risky at the least—and may put users in the cemetery rather than in the winner's circle.

  what is the human endocrine system

Endocrine gland and their hormone

A hormone is a "chemical messenger" sent by a gland to other cells of the body. Traditionally, animal hormones have been described by scientists as the chemical products of glands that travel within the bloodstream to all parts of the body, causing an effect on specific cells, or target organs, far removed from that gland. Glands are individual cells or groups of cells that secrete substances. Their secretory portions are made up of specialized epithelial cells (see Chapter 9). The glands that secrete hormones spill these chemicals directly into the bloodstream and are called endocrine, or "ductless," glands. Glands that secrete other substances such as digestive enzymes or sweat route their secretions to specific destinations by means of ducts. In this way, for example, the digestive enzyme pancreatic amylase flows directly from the pancreas to the small intestine and goes nowhere else. Glands having associated "ductwork" are called exocrine glands.

Today, most scientists have expanded their definition of hormones to include any chemical produced by one cell that causes an effect in another. Included in this description, then, are substances such as neurotransmitters chemicals produced by the axon end of a nerve cell that travel to and bind with the dendrite end of an adjacent nerve cell, con-tributing to the propagation of the nerve impulse along that neuron (see Chapter 15). Such chemicals are often called local hormones because they affect neighboring target cells. The human body produces many local hormones; they are described later in this chapter.

 Hormones are "chemical messengers" secreted by cells that affect other cells. Hormones that travel within the bloodstream and affect cells in another part of the body are called endocrine hormones. Hormones that do not travel within the bloodstream but only affect cells lying near the secretory cells are called local hormones.

The 10 different endocrine glands of the human body make over 30 different hormones. Together, these glands are called the endocrine system (Figure 19-1). The endocrine system works with the nervous system to integrate the functioning of the various tissues, organs, and organ systems of the body. The nervous system sends messages to muscles and glands, regulating muscular contraction and glandular secretion. The hormones of the endocrine system, on the other hand, carry messages to virtually any type of cell in the body. The messages of the endocrine hormones are varied but can be grouped into four categories: 

1. Regulation: Hormones control the internal environment of the body by regulating the secretion and excretion of various chemicals in the blood, such as salts and acids.

 2. Response:Hormones help the body respond to changes in the environment and cope with physical and psycho-logical stress. 

3. Reproduction: Hormones control the female reproductive cycle and other reproductive processes essential to conception and birth and control the development of sex cells, the reproductive organs, and secondary sexual characteristics (those that make men and women different) in both sexes. 4. Growth and development: Hormones are essential to the proper growth and development of the body from conception to adulthood. 

Once molecules of a hormone are released into the bloodstream, they travel throughout the body. Although hormone molecules may pass billions of cells, specific hormones only affect specific cells called target cells. Hormones recognize target cells because they bind to receptor molecules embedded within the cell membrane or located within the cytoplasm of the cell. The binding of a hormone molecule to a receptor molecule activates a chain of events in the target cell that results in the effect of the hormone being expressed. 

Two major classes of endocrine hormones work within the human body: peptide hormones and steroid hormones. Peptide hormones are made of amino acids, but the amino acid chain length varies greatly from hormone to hormone. The smallest are actually modifications of the single amino acid tyrosine. Somewhat larger are short peptide hormones that are several amino acids in length. Polypeptide hormones have chain lengths of several dozen or more amino acids, such as the hormone insulin. Even larger are protein hormones that may have over 200 amino acids with carbohydrates attached at several positions. 

Human endocrine system

Unable to pass through the cell membrane, peptide hormones bind to receptor molecules embedded in the cell membrane of target cells. The binding of hormone to a receptor triggers an increase in that cell's production of a compound referred to as a second messenger. A second messenger triggers enzymes that cause the cell to alter its the endocrine glands pictured  in this diagram secrete chemical messengers that travel through the bloodstream to affect other cells in the body

How peptide hormones work

functioning in response to the hormone  For example, prolactin stimulates cells of the mammary glands to produce milk. Target cells respond as enzymes "go into action" catalyzing reactions that produce the components of mother's milk. Other types of hormone responses include the secretion of substances from target cells and the closing or opening of certain "protein doors" within target cell membranes. Cyclic adenosine monophosphate (cyclic AMP for short), a "cousin" of ATP (see Chapter 6), acts as a second messenger to many cells. Besides cyclic AMP, other second messenger molecules have been discovered.

 Once inside the cell, peptide hormones bind to the cell membrane and trigger an increase of second messenger com-pounds within the cell, such as cyclic AMP. The second Messenger in turn activates enzymes that alter the cell's function in response to the hormonal message. 

                          How steroid hormones work

Steroid hormones are all made from cholesterol, a lipid synthesized by the liver. You know cholesterol as that "dietary devil" present in certain foods such as eggs, dairy products, and beef. A characteristic of steroid hormones is their set of carbon rings. Steroid hormones, being lipid soluble, pass freely through the lipid bilayer of the cell membrane. Once inside a cell, these hormones bind to receptor molecules located within the cytoplasm of target cells. Together, the hormone-receptor complex moves into the nucleus of the cell, causing the cell's hereditary material, or DNA, to trigger the production of certain proteins . In Steroid hormones are able to pass through the cell membrane without the aid of a receptor molecule. Inside the cell, they bind with receptor molecules. The hormone-receptor complex then enters the nucleus of the cell, where it acts on DNA to produce proteins. These proteins control physiological processes such as growth and development. 

A simple feedback loop

In response to a stimulus, an endocrine gland releases a specific hormone that acts on a specific target tissue. The effect of the hormone on the target tissue either causes the gland to release more of the hormone (positive feedback) or causes the gland to slow or stop its production of the hormone (negative feedback). 

response to the sex hormones estrogen or testosterone, for example, the proteins produced are those involved in such processes as the development and maintenance of female or male sexual characteristics. 

Two main classes of endocrine hormones are pep-tide hormones and steroid hormones. Both travel within the bloodstream to all parts of the body but affect only certain target cells. Peptide hormones bind to receptors on the cell membrane of target cells and ultimately trigger enzymes that alter cell functioning. Steroid hormones bind to receptors within the cytoplasm of target cells and ultimately cause the hereditary material of the cell to produce specific proteins.

The production of hormones is regulated by a mechanism called a feedback loop. In general, hormonal feedback loops work in the following way: endocrine glands are initially stimulated to release hormones. Stimulation of an endocrine gland occurs in one of three ways:

 1. Direct stimulation by the nervous system: The sensation of fear, for example, can cause the autonomic nervous system to trigger the release of the hormone adrenaline from the adrenal medulla. 2. Indirect stimulation by the nervous system by means of re-leasing hormones: The hypothalamus is a specialized portion of the brain that produces and secretes releasing hormones. Some releasing hormones stimulate the re-lease of other hormones; some prevent the release.

 3. The concentration of specific substances in the bloodstrecon. The blood level of a substance such as glucose or calcium. for example, may signal an endocrine gland to "turn ow, or "turn off"

 After an endocrine gland secretes its hormone into the bloodstream, the hormone travels throughout the body via the circulatory system and interacts with target tissues. The target tissues cause the desired effect to be produced. This "effect" acts as a new stimulus to the endocrine gland (Figure 19-4). Put simply, the body "feeds back" information to each endocrine gland after it releases hormone. In a positive feedback loop, the information that is fed back causes the gland to produce more of its hormone. In a negative feed. back loop, the feedback causes the gland to slow down or to stop the production of its hormone. Most hormones work by means of negative feedback loops. (Specific examples of feedback mechanisms and interactions are discussed throughout this chapter.) 

keeping human new brain cells

How to keeping human brain cells

So it turns out that your brain is a nursery: every day, it seems, new brain cells are born. But it seems that your brain doesn't always keep these newborn neurons. Just like all other babies, they need special care to survive. And it's not pampering: your newborn neurons, scientists are finding, need to be challenged, exercised, and run hard. 

If you don't use those new cells, they will disappear. Animal research shows that most of these cells die within a couple of weeks unless that brain is challenged to learn something new and, preferably, something hard that involves a great deal of effort. And new is key here as well: just repeating old activities won't support new brain cells.

 Scientists still don't really know why or what the heck the new neurons are doing or even why we make them. Are they made to replace dying cells? One theory is that they are backup, produced just in case they are needed. This idea suggests that your brain calls for reinforcements when new brain cells are available to aid in situations that tax the mind, and that a mental workout can buff up the brain much as physical exercise builds up the body

 In animal studies, scientists found that between five thousand and ten thousand new neurons arise in the rat hipclocampus every day (it's not known how many we humans make, or how often). The birth rate depends on some environmental factors. Heavy alcohol consumption slows the production. for example, whereas exercise increases it. Rats and mice that log time on a running wheel kick out twice as many new cells as do mice that lead a more sedentary life. Even eating antioxidant-rich blueberries seems to goose the generation of new neurons in the rat hippocampus, as do exciting changes in their cages or new toys to pique their interest.

 Elizabeth Gould (a discoverer of neurogenesis in adults), Tracy Stars, and colleagues have been examining the connection between learning and neurogenesis by studying the brains of rats and the importance of hard learning. In their experiments, they first injected the animals with BrdU (bromodeoxyuridine), a drug that marks only brand-new cells. A week later, they recruited half of the treated rats for a training program and let the rest lounge around their home cages. 

The rats enrolled in Rodent University were given an cyeblink course: an animal hears a tone and then, sonic fixed time later (usually 500 milliseconds, or half a second), gets hit in the eye with a puff of air or a mild stimulation of the eyelid, which causes the animal to blink After several hundred trials, the animal learns to connect the tone with the stimulus, anticipate when the stimulus will arrive, and

The birth of brain cells

what you need to know  about neurogenesis

Neurogenesis

We've all heard the warnings: If you (fill in the blank) you'll kill brain cells. And because scientists believed until very recently that you were born with all the brain cells you'd ever have, that was a fairly dire warning. You broke it, and you were stuck with the results.

 Recently we've been able to relax a bit, because we know that our brain makes new cells in at least two sections: the detente Cyrus of the hippocampus, a structure involved in learning and memory, and the olefactory bulbs. And it may in fact create new neurons elsewhere in the brain; we don't know for certain yet.

 Most of this research has been done on animals, but some human studies have confirmed the finding. Studies were done on terminal cancer patients who generously agreed to be injected with a marker for new cell production and to offer their brains for study after their death. The autopsies showed that even in the face of aging and death, their brains continued to produce new neurons to the very end. Chemotherapy could give us an idea of what happens when we don't make new neurons. Chemotherapy impairs the cell division needed for making new cells, and people who have had chemotherapy treatment for cancer and some other serious diseases often complain about a syndrome sometimes referred to as chemobrain. They have trouble with the kinds of learning and remembering that everyone finds challenging, such as juggling multiple projects while trying to process new information. 

Because having a ready supply of new neurons on tap could help to keep your brain intellectually limber, scientists are looking for ways to exploit this to prevent or treat disorders that bring about cognitive decline. Meanwhile, they've found that these new brain cells disappear if you don't use them.

what to need to know about neuroplasticity

neuroplasticity 

 Scientists have long known that the brain can change itself. In fact, your brain is probably changing every microsecond in response to experiences, both external and internal. Those changes come mainly from the growth of new connections and networks among neurons, particularly among newborn neurons.

 We've known that different kinds of experiences lead to changes in brain structure, with more activity in the networks used most. In musicians, for example, the parts of the brain ddclicated to playing their instruments are disproportionately larger than in nonmusicians or in musicians who play a different instrument. A decade-old study of London taxi drivers skilled at navigation in the city center showed the same effect: they had larger hippocampi than nondrivers, reflecting the huge amount of data they needed to have at hand. Moreover, the longer they drove complicated routes around the city, the larger their hippocampi grew.

 Also, brains apparently riddled with blank areas or plaque and other signs of Alzheimer's disease have come from people functioning very well into late old age. Indeed, some brains lacking a hemisphere—the entire half of a brain—can function quite well.

 We also know the brain can sometimes repair itself after devastating injury, bypassing dead areas to create new connections. ABC news correspondent Bob Woodruff, critically injured by a roadside bomb in 2006 while covering the war in Iraq, suffered a brain injury so severe that part of his skull was permanently removed, and he was kept in a medically induced coma for more than a month. Few believed he would walk again, let alone work as a reporter. After more than a year of intensive therapy, which included relearning speech to

what is important or reasons to take care of human brain

 Centenarians—individuals one hundred years or older—are the fastest growing age group in the United States, and experts predict there may be as many as 1 million by 2050.

 If you're sixty years old (or younger) today, you could be in that group. And if you want your mind to be there along with you, take good care of your brain.

 You'll have plenty of company near your age: people aged eighty and older are the fastest-growing portion of the total population in many countries. By 2040, the number of people sixty-five or older worldwide will hit 1.3 billion, according to the National Institute on Aging, which announced the figures. And within ten years, there will be more people aged sixty-five and older than children under five in the world for the first time in human history.

 The most rapid increase will be in developing countries. By 2040, they will be home to more than 1 billion people aged sixty-five and over-76 percent of the projected world total. If you reach one hundred years, you are sure to live in interesting times, an old blessing (or curse) of the Chinese (who, incidentally, will have the world's largest population of elders by 2040). This global aging will change the social and economic nature of the planet and present some difficult challenges. Interesting times, indeed.

overcome aphasia, he made a hard-hitting documentary about the plight of injured soldiers and the deficits in government care. And then he went back to work as a reporter—in Iraq. Certainly Woodruff benefited from the kind of very expensive and intense treatment not available to all of us. Nevertheless, his recovery shows how remarkably able the brain is, especially because his was not a young brain: he was forty-four at the time of his injury. What we did not know for certain until recently is that what you think and feel also physically change your brain, such as intellectual

challenges, deliberate brain training, anxiety, and joy. So it seems there is a biological basis to mind training: you can learn skills aimed at changing your brain just as you learn repeated activities to change your body. Meditation is a brain-changing example. Studies show that regular practice of meditation results in physical as well as mental and emotional changes. In long-time practitioners of meditation, the two hemispheres become more balanced, the trigger-happy amygdala shows less reaction to emotional sounds, and the many brain regions involved in focused attention show greater activity (see "Boosting Your Brain with Meditation," p. 31).

How to changes in human brain 

Epigenetics 

Scientists are finding one of the ways your brain changes itself is by actually changing your genes—or more correctly, by the acting out (or not) of certain genes—in the process of epigenesis. We know that your genome is the total deoxyribonucleic acid (DNA) that you inherit from your ancestors and contains the instructions for making your unique body and brain. Another layer of information, called the epigenome, is stored in the proteins and chemicals that surround and stick to the DNA. It's a kind of chemical switch that determines which genes are activated (or not): it tells your genes what to do and where and when.

Researchers have discovered that the epigenome can be affected by many things, from aging and diet to environmental toxins to even what you think and feel. This means that even your experiences can literally change your mind by chemically coating the DNA that con
trols a function. The coating doesn't alter the underlying genetic code; rather, it alters specific gene expression, shutting down or revving up the production of proteins that affect your mental state.

 Epigenetics helps explain the gap between nature and nurture that has long puzzled scientists: why some illnesses and traits pop up in one but not both identical twins who have the same DNA, or why these traits skip a generation. It also helps explain neuroplasticity.

One researcher describes DNA as a computer hard disk, with certain areas that are password protected and others that are open. Epigenetics is the programming that accesses that material, writes Jolt Walter of Saarland, Germany, on the Web site Epigenome. 

Epigenetics can profoundly affect your health and, it seems, your happiness, changing not only your vulnerability to some diseases such as cancer but also your mental health. Scientists have found, for example, that a mother rat's nurturing, through licking and loving behavior that boosts the expression of a gene that eases anxiety and stress, bolsters emotional resilience in her newborn pups. They've also found that distressing events can turn off the expression of genes for brain cell growth protein and thereby trigger depression, and that epigenetic changes may also underlie the pathology of schizophrenia, suicide, depression, and drug addiction. 

The acting-out process of changeable genes—gene expression—is quite complicated and a new area of intense research. Just recently biologists have found that epigenetic changes may be heritable—passed on to your descendants—just as your DNA is. They have also found that altering gene expression with drugs or environments that provide more intellectual stimulation can improve learning and memory in cognitively impaired animals. Future therapies for memory disorders in humans might work in a similar way. It's a promising area with much to be learned. In 2008, the National Institutes of Health invested $190 million in the five-year Roadmap Epigenomics Program to pursue some of these promising fields of research.

Human changeable brain

what is the changeable brain

When you woke up today, you were a new person literally. Many of the cells in your body had replaced themselves with younger versions, and your brain has been busy as well. Scientists have discovered your brain is a work in process. Every day, it seems, your brain makes new neurons in at least some sections, and almost every second, your brain is changing its networking in response to what you experience, think, feel, and need. In fact, your brain can even direct changes to some of your genes, turning them off or on.

Then Your brain is hardwired and unchangeable, and you're born with all the brain cells you'll ever have. Good luck, because when they're gone, they're gone.

 NOW: Who knew? Your brain creates new neurons in some areas and new networks, even into old age, and it changes physically in response to your actions, thoughts, and emotions. Your genes are not your destiny—or at least not all of it.

 Tomorrow: Well be able to direct changes: stimulate new brain cells and networks where and when we need them; turn genes off and on at will to repair brain damage, restore function, and optimize performance; and rewire our brains to manipulate memory and even reverse dementia and mental retardation.

 The revolutionary findings about your brain's remarkable ability to change itself are barely a decade old. Biologists had long believed that the creation of brain cells was completed at or shortly after birth, and that the rest of your life was a slow slide into brain cell loss. In the 1990s, scientists rocked the field of neurobiology with the startling news that the mature mammalian brain is capable of sprouting new neurons in the hippocampus and the ole factory bulbs, and that it continues to do so even into old age. This process is called neurogenesis.

 Scientists also confirmed what was long suspected: your brain is not hardwired. It can reinvent itself, as it were, by creating new path-ways to reroute, readjust, and otherwise change the networking and connections, sometimes even substituting one area for another. When one part of your brain goes south—from a stroke or trauma, for exampleother sections can sometimes take over some of those functions. Your brain also changes to reflect what you learn, do, and think. In fact, your brain is physically rearranging its networks just about every minute of every day. That's neuroplasticity.

 Then they discovered that your actions, thoughts, feelings, or environment can change your genes—more specifically, whether certain genes are expressedaltering brain function; character traits; and risk of some diseases, from cancer to schizophrenia. That's epigenetics.

brain science is a big business

why important the brain science

In fact, it has spawned a whole new industry. Three hot neurotech areas that promise major changes in brain research in the near future are neuroimaging, neuropharmacology, and neurodevices such as brain implants. And they are thriving. The Neurotechnology Industry Report for 2008 shows 2 billion people worldwide suffering from a brain-related illness, with an annual economic burden of more than $2 trillion. Globally, in 2008, more than 550 public and private companies participated in a neurotech industry where revenues rose 9 percent to $144.5 billion overall, with neuropharmaceuticals reporting earnings of $121.6 billion, neurodevices revenues of $6.1 billion, and neurodiagnostics revenues of $16.8 billion.

 The military has a hefty investment in this as well. Neurotechnology and research will help the thousands of soldiers returning from wars with severe brain injuries or missing limbs. Advances will also perfect the toolbox for warfare. Neuroenhancers will keep soldiers and fighter pilots awake and alert for days, and will fine-tune and juice up mental focus and reflexes. Brain-machine interfaces could create new weapons and allow exploration into deep space and other hostile territory. And neuroimaging could allow us to see into brains to predict and possibly control behavior and thoughts.

How your brain works the short version

A refresher on brain basics will help set the context for the detailed chapters that follow. Your brain is three pounds of flesh, nerves, and fluid that looks like a big walnut but is much softer. Its billion or so specialized cells called neurons communicate and form networks through chemicals (especially those called neurotransmitters) and minuscule electrical charges that pass over the tiny gaps, or synapses, between them. The overall brain is often described in three parts: the primitive brain, the emotional brain, and the thinking brain.

  The primitive brain

 the brain stem or hindbrainsits at the top of the spine and takes care of the automated basics, such as breathing, heartbeat, digestion, reflexive actions, sleeping, and arousal. It includes the spinal cord, which sends messages from the brain to the rest of the body, and the cerebellum, which coordinates balance and rote motions, like riding a bike and catching a ball. Above this, your brain is divided into two similar, but not identical, hemispheres connected by a thick band of fibers and nerves called the corpus callosum. Each side functions slightly differently than the other does, and for reasons not yet understood, the messages between the hemispheres and the rest of our body crisscross, so that the right brain controls our left side and vice versa.

 The emotional brain

The emotional brain, or limbic system, is tucked deep inside the bulk of the mid brain and acts as the gatekeeper between the spinal cord and the thinking brain in the cerebrum above. It regulates survival mechanisms such as sex hormones; sleep cycles; hunger; emotions; and, most important, fear, sensory input, and pleasure. The amygdala is our sentry, the hippo campus is the gateway to short-term memory, and the hypothalamus controls your biological clock and hormones, while the thalamus passes along sensory information to the thinking centers in the cortex above. The basal ganglia surround the thalamus, and are responsible for voluntary movement. The so-called pleasure center, or reward circuit, is also based in the limbic system, involving the nucleus accumbens and ventral tegmental area.

 the thinking brain

The thinking brain the part we usually see when we picture a brain and what is sometimes called the crown jewel of the body—sits on the top, where it controls thoughts, reasoning, language, planning, and imagination. Vision, hearing, speech, and judgment reside here as well. But let's be honest. In spite of enormous research advances, scientists still have a pretty rudimentary understanding of brain function and how it relates to your thoughts, feelings, and actions. There are frequent announcements about how the sources of some emotions and functions have been "mapped" in the brain, but most of these should be qualified: brain researchers are still trying to figure out much of what goes on between your ears. But they're gaining on it.

the process of brain

why important of brain for human

introduction of brain

We know more about the brain today than ever before, and a perfect storm of events is supporting even more and better brain knowledge and better brains.

There is a tremendous surge of research on the brain and tremendous pressure to learn more, and learn it faster, from an aging generation with the will and the means to force these advances: boomers.

The first of the boomers, the largest ever demographic group and (even with the recession) the best off financially, are hitting old age, and a group that never took no for an answer is not going gently into that good night; instead, it is kicking, screaming, and raging for a better aging brain. Billions are being expended on brain research, especially in areas related to dementia, memory loss, and other conditions of aging.

The National Institutes of Health (NIH) alone spent $5.2 billion, nearly 20 percent of its total budget, on brain-related projects in 2008. With this expanded funding, researchers are making sweeping inroads in both understanding and manipulating the brain.

We've learned more about the brain in the past fifty years than the preceding fifty thousand, and the cooperation among the sciences over the next two decades may even surpass that record. Brain research has moved beyond psychology, psychiatry, and neurology, and married the so-called wet and hard sciences: biology, biochemistry, and chemistry now cohabit with physics, engineering, electronics, computer science, material sciences, statistical analysis, and even information technologies, with advances

 in technology contributing ever-better, smaller, faster, and smarter devices and techniques. Scientists and futurists are predicting what will have changed by mid century:

• Computer chips or mini-microprocessors in the brain will expand memory; control symptoms of brain disease, from Parkinson's disease to depression and anxiety; and wireless receive and transmit information so that you won't need a cell phone or a computer to stay in touch.

• Brain surgery will be a thing of the past except in the most severe cases. Advanced neurhimaging will identify mental illness and brain disease before symptoms show and in general be used to "read" minds and predict and control behavior. Microscopic robots—nanobots—will enter your bloodstream to diagnose and repair brain damage. Protein molecules will travel your brain in a similar way to turn on or off brain cells or genes responsible for brain diseases.

• Neurohenhancers from drugs to digital devices will boost memory and mind function in healthy people—and equally powerful drugs will help block painful or traumatic memories. That could mean growing new brain cells to replace neurons damaged by disease or slipping your kids a memory pill while they cram for Advanced Placement calculus.

• Alzheimer's disease, other dementias, and perhaps even mental retardation will be preventable, curable, and even reversible in many people.

• Those who are paralyzed will regain limb and spinal cord function, and thought-driven spare parts will abound, from prosthetic limbs and vision with lifelike function to prosthetic brain chips to store data and perhaps even duplicate neural networks.