............................... THE ENDOCRINE SYSTEM AND ITS DISORDERS

Introduction. The organisms are born being small and then they grow and are changing the proportions of the body, ie they develop. There comes an age when the inactive reproductive organs become active and individuals are in an adult state. But, how do the bones cells know when they have begin to multiply bones to grow or when to stop? How do the sex organs know when they have to start their maturation? Clearly, these processes cannot be controlled by the nervous system, which is a system specialized in the quick responses. Well, for all this are responsible the hormones, substances that secrete the cells of the certain glands that release their products into the blood and are taken up by other cells. As you see, this is very similar to the communication between two neurons explained in the topic 13. In fact, many experts believe that the nervous system evolved from the endocrine system. The endocrine system have both animals and plants, while the nervous system is unique for the animals. Thanks to this animals control the displacement and capturing of the food.

Activities to do. Read the explanations on hormones and the endocrine system and perform the first Multiple Choice Test and the first Complete The Sentences. Then read the text on the control of the endocrine system and its disorders and perform the following Multiple Choice Test and Complete The Sentences and the Crossword.

1 . The hormones. Are the chemical substances released into the blood by certain glands, thus called internal secretion glands or endocrine, which act only on organs that have cells with specific receptors for them. These organs are the hormone's target organs. A receptor is a molecule specific special thanks to its structure can be combined with a certain hormone and thus initiate a series of reactions. The result is that specifically hormones control the internal activities of different cell types. This will regulate, for example, cellular metabolism, sexual maturation boy, adolescent growth or blood pressure. A specific receptor is a special molecule that thanks to its structure can be combined with a certain hormone and thus initiate a series of reactions. The result is that the hormones specifically control the internal activities of different cell types. This regulate, for example, the cellular metabolism, the sexual maturation of the boy, the adult growth or the blood pressure. Unlike the nervous system which originate a very quick response, such as for example raising an arm, and of a short duration, for example to maintain being up, the hormones produce a slow responses, such as for example bone growth, and of a long duration, for example the growth of these bones throughout adolescence.

2 . The endocrine system. Is the set of all endocrine glands. The main ones are: hypothalamus, hypophysis, thyroid, parathyroid, adrenal, pancreas, ovaries and testes.

Hypothalamus. It is a brain region that when receiving nerve impulses can produce various types of the hormones. Most of them act on the pituitary gland.

Hypophysis. It is a gland of the size of a pea that is located in the hypothalamus and attached to it. It secretes many different hormones, most of which act on other endocrine glands, thus it can be said that it practically controls all endocrine system. We can differentiate an anterior part called adenohypophysis and a posterior part called neurohypophysis. The picture below shows the hormones that are produced in each part and theirs function.

Thyroid. It is a gland located at the base of the neck. It produces the hormone thyroxine, which works by accelerating cell metabolism, and the hormone calcitonin, which helps the deposit of calcium in the bones.

Parathyroid. This gland is formed by four groups of cells located on the thyroid gland. It secretes parathyroid hormone, which causes the bones to release calcium into the blood.

Adrenal glands. They are two small glands located, each one of them, on a kidney. They produce the hormones aldosterone, which promotes sodium reabsorption in the kidneys, cortisol, which favors the passage of amino acids to glucose and adrenaline, which prepares the body for an action.

Pancreas. This gland besides of segregating the pancreatic digestive juice, which is why it is an exocrine gland, also is an endocrine gland, since it produces the hormone insulin which allows the cells to capture the glucose present in the blood.

Ovaries. These bodies in addition to the production of the ovules, also have endocrine gland function, because they produce hormones called estrogen that regulate female secondary sexual characteristics (high voice, mammary glands, wide hips, small hairy skin, etc..).

Testes (testicles). These organs besides of producing sperm also have the endocrine gland function, since the hormone testosterone regulates male secondary sexual characteristics (deep voice, increased muscle mass, skin with plenty of hairiness, etc..).

Multiple Choice Test (Spanish activity. Activity in English is under construction)

3. The hormonal control. The endocrine glands can have two types of stimuli: the nervous stimulation and the chemical stimulation.

1) The nervous stimulation. Certain internal or external conditions (sleep, fear, lack of affect, stress, noise, etc.) are captured by the brain which affect the hypothalamus, which sends, through the blood, the hormones which stimulate or hormones that inhibit the pituitary. This produce, or not, hormones that stimulate the target gland which releases its hormone into the bloodstream. As soon as its level increases slightly above the normal level, this excess causes that the hypothalamus no longer produce more hormone of excitation and, therefore, the pituitary does not produce more hormone of stimulation, which decreases the diana gland hormone production. This mechanism is called the feedback.

The hormones produced by the hypothalamus are called the releasing factors and the ones produced by the pituitary are called the trophic hormones.

Both of them are the neurohormones because they are produced by neurons.

4 . The diseases related to the hormonal system

Acromegaly. This disease is an excessive production of growth hormone in an adult. Its characteristic symptoms are excessive growth of hands, feet, chin, nose and other bones of the skull.

Goiter. This disease is an excessive production of the hormone thyroxine. It is characterized by an overgrowth of the thyroid, which implies a previous lump in the neck and exophthalmos (bulging eyes). Furthermore there is a hyperactivity, weight loss, insomnia and irritability.

Cretinism. This disease is a deficiency of thyroxine hormone during the infancy. The effects are severe mental deficiency, low metabolic rate, underdeveloped genitals and short stature. It can be caused by iodine deficiency in the diet or by inability to absorb it.

Diabetes mellitus. This disease is the lack or shortage of production of the hormone insulin. The symptoms are the excess of the glucose in the blood, increased urination, ketones in the breath, dizziness and fainting. The childhood type or type 1 may be due to a failure of the immune system which destroys its pancreatic cells producing insulin (autoimmune disease). The type 2 or adult is due to pancreatic disorders due to age.

Diabetes insipidus. It consists of a vasopressin hormone deficiency. The symptoms include increased urination and thirst.

Pituitary dwarfism. It is a poor growth due to the lack or shortage of production of growth hormone.

Pituitary gigantism. It is an overgrowth as a result of excessive growth hormone.

5. The standards to detect potential endocrine system disorders. If it takes too much time without doing anything to prevent a disorder of our endocrine system, the injuries can be very serious. Therefore we need to be aware of the symptoms and, when in doubt, have an endocrinology consult. The three most notable symptoms are:

• A child who does not grow at a normal rate may be suffering from a deficiency of the growth hormone.
• A child who grows at an excessive rate may be suffering from an excess of the growth hormone.
• A person who is constantly urinating, is very tired and has lost much weight may have the diabetes.
• A person with an increase in volume of the neck (goiter), an excessive prominence of the eye orbits, tachycardia and weight loss, may have goiter.

Crossword (Spanish activity. Activity in English is under construction)