Human beings internal need to have a kind of balance, this kind of balance called homeostasis. In humans' body, there is a normal condition which is the most optimum solute and water concentration in blood. Unmoral condition will lead to many illness and create mostly germ or bacteria, as a result the homeostasis in human body is very important.
Human beings control their milieu interne by nervous system and humoral regulation. Milieu interne is formed by extracellular fluid which is formed by lymph, plasma and tissue fluid (cybermilieu, nd). Humoral refers to the fluid of body, humoral regulation refers to the changing amount of different kind of fluid and controls the function of body. The nervous system especially the central nervous is the effector of the whole endocrine of human body, and the humoral regulation play an assisted role.
The definition of homeostasis is the maintenance of a constant internal environment by an organism (John, 2003, p267). Homeostasis is able to let cells function more efficiently and make people feel comfortable without pain. When the balance is broken, there will be negative feedback to adjust the internal reactions. Negative feedback is built by nervous and humoral system. Negative feedback means 'feeding back' the small amount of signal from a later part of the circuit to an earlier part (Randall, 1999). The degree of homeostasis is decided by several particular group, it is independent of the environment (John, 2003, p267).
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The main procedure of homeostasis is the endocrine control of kidney action. The kidney is one of the most important parts of excretory organs of vertebrates (John, 2003, p304). There are responsible for the filtration and selective reabsorption of materials (water, mineral salts, glucose, etc.) and the production of waste. In nearly all mammals, the kidneys are red-brown round structure, and are located at the back of enterocoelia. They receive blood oxygenated by the renal artery and are drained of deoxygenated blood by the renal vein. A tube called the ureter conveys excess water, salts, and nitrogenous compounds (urea and uric acid) as urine from each kidney to the bladder and hence to the exterior (John, 2003, p304). When kidney functions, the pressure in the kidney is decreased, and the apparatus which juxtaglomerular would secretes rennin into blood. Rennin will convert to angiotensinogen to angiotensin I and angiotensin I convert to angiotensin II. Angiotensin is a polypeptide that related to high blood pressure. Angiotensin I is an inactive decapeptide produced by the action of rennin, a kidney enzyme released when blood pressure is low. It has no physiological action, the active form angiotensin II is when enzyme-catalyzed removal of two terminal amino acids from angiotensin I. Angiotensin II can raise blood pressure by stimulating the constriction of the hormone aldosterone. (John, 2003, p34). When blood pressure is low, angiotensin I will produce by the action of rennin, a kidney enzyme released. Angiotensin II is formed by angiotensin I by the enzyme-catalyzed removal of two terminal amino acids from angiotensin I (John, 2003, p34), it is active form. Angio. Angiotensin II stimulates adrenal cortex which uses cholesterol as the starting material, the cells of the adrenal cortex secrete a variety of steroid hormones. The more aldosterone have the high pressure the blood has, because the function of it is increases the concentration of Na+ and decreases the concentration of K+. After this steps, angiotensin II will destroyed by proteinase enzymes. Here is a way to treat high blood pressure is that restrain angiotensin I change to angiotensin II. Beside this, the 'vasoconstriction of arteries to ensure normal filtration pressure in kidney' (Pickering, 2001, p86). Aldosterone is a kind of hormone secreted by the adrenal cortex. The hormone has an important effect on dealing with sodium and potassium by the kidney tubules. It can increase up kidney tubules reabsorb the sodium ion and discharge the potassium ion. The overall result is that sodium ion concentration in the blood rises, whereas potassium falls (John, 2003, p19). After these steps of kidney action, Na+ will be reabsorbed by distal convoluted tubules and collecting ducts (Pickering, 2001, p86). The volume of blood and the level of Na+ will be increased to restore normal blood pressure. These are complicated procedure of part of kidney which is related to blood, there is another part of function which is related to water.
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The picture below is a simulate picture of hypothalamus. The location of hypothalamus and the shape of it.
When life begins, the water concentration in the blood is low, so hypothalamus will control the posterior pituitary gland to release anti-diuretic hormone (Pickering, 2001, p86). Posterior pituitary gland is an organ which release growth hormone which affects protein metabolism; vasopressin which stimulates reabsorption of water from the kidney; adrenocorticotropic hormone which stimulates the secretions of the adrenal gland; gonadotropic hormone which stimulate gonad development; oxytocin which stimulates the uterine walls to contract during birth; prolactin which stimulates milk production by the mammary glands; and thyrotropin which stimulates the secretion of the thyroid glands. Anti-diuretic hormone has another name called vasopressin which stimulates reabsorption of water from the kidneys. What stimulates kidney to reabsorb water? The answer is the posterior pituitary gland. The pituitary gland is an endocrine gland 'in the vertebrate brain situated beneath the thalamencephalon behind the optic chiasma' (John, 2003, p437). The hormone of the pituitary gland control others internal secretion gland, therefore it is regarded as the main endocrine gland. After hypothalamus control posterior pituitary gland, it release anti-diuretic hormone. The hormone will increase the permeability of membranes of the collecting tube. The collecting ducts will functions facultative reabsorption of water by osmosis and these steps can increase water concentration in blood. However, everything has a positive and a negative side. If the concentration of water in blood is too high, something there will an inhibited action happen. The system will recycle the procedure again and if the concentration is ok, the kidney will function reabsorption of normal water concentration in blood (Pickering, 2001, p86). Everything will have a negative feedback, including kidney action. The simple principle of homeostasis is expound by the action of the nephron. The general idea of that is: firstly is the normal (optimum solute and water concentration in blood (Pickering, 2001, p86)), and there is a deviation from normal, after that the corrective mechanism is getting active to help to return to normal.
In conclusion, the most important part of human beings' homeostasis is endocrine control of kidney action. The flowing chart of the action is:
The main part:
1. Decreased pressure of kidney
2. Secretes rennin into blood
3. Rennin change to angiotensin I
4. Angiotensin I change to angiotensin II
5. a). Increase aldosterone
b). Filtration pressure in kidney
6. Reabsorption by distal convoluted tubules
Low water concentration
Release anti-diuretic hormone
Increased permeability of membrane
Reabsorption of water by osmosis
Increased water concentration