Endocrinology : Endocrinology is a branch of medical science which deals with the study of different endocrine glands of the body.
Endocrine gland:Means ductless gland which directly poured their secretion into the blood.
Endocrine glands are:
1.Hypothalamus.
2.Pituitary gland.(a.Anterior pituitary gland,b.Posterior pituitary gland)
3.Thyroid gland.
4.Parathyroid glads.
5.Adrenal glands.
6.Pancrease.
7.Testis.
8.Ovaries
9.Placenta.(during pregnancy)
Coordination of the body functions by chemical messengers.
The multiple activities of the cells,tissues and organs of the body are coordinated by the interplay of several types of communication systems, including:
1.Neural, in which chemicals(neurotransmitters) are released at synaptic junctions and act locally to control cell function.
2.Endocrine, in which glands or specialized cells release into the circulating blood chemicals(hormones) that influence the function of cells at another location in the body.
3.Neuroendocrin, in which neurons substances:(neurohormones) that reach the circulating blood and influence the function of cells at another location in the body .
4.Paracrine, in which cells secrete substances that diffuse in to the extracellular fluid and affect neighboring cells.
5.Autocrine, in which a cell secretes substances that affect the function of the same cell by binding to the cell surface receptors.
For example, the adrenal medullae and the pituitary gland secrete their hormones primarily in response to neural stimuli.The neuroendocrine cells, located in the hypothalamus, have axons that terminate in the posterior pituitary gland and median eminence and secrete several neurohormones ,including antidiuretic hormone (ADH), oxytocin, and hypophysiotropic hormones, that control the secretion of anterior pituitary hormones. The endocrine hormones are carried by the circulatory system ti cells throughout the
body, including the nervous system in some cases, where they bind with receptors and initiate many body; for example,growth hormones causes growth in most parts of the body, and thyroxine increases the rate of many chemical reactions in almost all the body's cells.Other hormones affect only specific tissues called target tissues because only these tissues have receptors for the hormone.
physiological control effect on other cells of the body.
Classification of Hormone
1.Polypeptide and protein hormone
Polypeptide and protein hormones are stored in secretory vesicles until needed : Most of the hormones in the body are polypeptides
and proteins.These hormones range in size from small peptides with as few as three amino acids to protein almost 200 amino acids
long.In general, polypeptides with 100 or more amino acids are called proteins,and those with fewer that 100 amino acids are referred to as peptides.Protein and peptide hormones are synthesized on the rough end of the endoplasmic reticulum of the different
endocrine cells in the same fashion as most other proteins that are not biologically active and are cleaved to from smaller prohormones in the endoplasmic reticulum.These are than transferred to the golgi apparatus for packaging into secretory vesicles
cleave the prohomones to produce smaller, biologically active hormones and inactive fragments. The vesicles are stored within the
cytoplasm, and many are bound the cell membrane and the granular contents are extruded into the interstitial fluid or directly into the blood stream by exocytosis.
2.Steroid hormone
Steroid hormones are usually synthesized from cholesterol and are not stored : The chemical structure of steroid hormones is similar to cholesterol, and in most instances they are synthesized from cholesterol itself. They are lipid soluble and consist of three
cyclopenty1 ring combined into a single structure. Although there is usually very little hormone storage in steroid-producing endocrine cells, large stores of cholesterol esters in cytoplasm vacuoles can be rapidly mobilized for steroid synthesis after a stimulus. Much of the cholesterol in steroid-producing cells comes from the plasma, but there is also de novo synthesis of cholesterol in steroid-producing cells.Because the steroids are highly lipid soluble, once they are synthesized, they simply diffuse
across the cell membrane and enter the interstitial fluid and then the blood .
3.Amine hormone
Amine hormones are derived from tyrosine : The two groups of hormones derived from tyrosine, the thyroid and the adrenal medullary hormones, are formed by the actions of enzymes in the cytoplasmic compartments of the glandular cells.The thyroid hormones are synthesized and stored in the thyroid gland and incorporated into macromolecules of the protein thyroglobulin, which is stored in large follicles within the thyroid gland. Hormone secretion occurs when the amines are split from thyroglobulin and the free hormones
are than released into the blood stream.After entering the blood, most of the thyroid hormone combines with plasma proteins, especially thyroxine-binding globulin, which slowly releases the hormones to the target tissues.
bound hormones cannot easily diffuse across the capillaries and gain access to their target cells and are therefore biologically inactive until they dissociate from plasma proteins.The relatively large amounts of hormones bound to proteins serve as reservoirs, replenishing the concentration of free hormones
from an outgrowth of the hypothalamus. Control of pituitary secretion by the hypothalamus : Almost all the secretion of pituitary gland are controlled by eithre hormonal or nervous signals from the hypothalamus. Secretion from posterior pituitary is controlled by yhe nerve signals originate in the hypothalamus and terminate in the posterior pituitary. In contrast, secretion by the anterior is controlled by the hypothalamic releasing or hypothalamic inhibitory hormones secreted within the hypothalamus itself and than conducted to the anterior pituitary through minute blood vessels. In the anterior pituitary, these releasing and inhibitory hormones act on the glandular cells to control their secretion.The hypothalamous in turn recives signals from many sources in the nervous system.Thus,when a person is exposed to pain a portion of the pain signal is transmitted into the hypothalamus.Likewish,when a person experiences some powerful depressing or exciting thought,a portion of the signal is transmitted into the hypothalamus. O1factory stimuli denoting pleasent or unpleasant smells transmit strong signal components directly and through the amygdaloid nuclei into the hypothalamus. Even the concentration of the nutrients,electrolytes, water and various portions of the hypothalamous.Thus the hypothalamous is a collecting center for information concerning the internal well being of the body and turn much of this information is used to control
secretions of the many globally important pituitary hormones.
hormone receptors are unresponsive as a result of loss-of-function mutations of the gane for the receptors.The resulting condition is is known as growth hormone insensitivity or Laron dwarfism.Plasma IGF-I is markedly reduced,along with IGFBP-3,which is also growth hormone-dependent.
2.Psychosocial dwarfism or the kasper hauser syndrome:Chronic abuse and neglect can also cause dwarfism in children.This condition is known as phychosocial dwarfism or the kasper hauser syndrome,named for the patient with the first reported case 3.Achondroplasia:Achondroplasia,the most common from of dwarfism in humans,is characterized by short limbs with a normal trunk. It is an autosomal dominant condition caused by a mutation in the gene that codes for fibrohlast growth factor receptor 3 (FGFR3).
This member of the fibroblast growth receptor family is normally expressed in cartilage and the brain.
Endocrine gland:Means ductless gland which directly poured their secretion into the blood.
Endocrine glands are:
1.Hypothalamus.
2.Pituitary gland.(a.Anterior pituitary gland,b.Posterior pituitary gland)
3.Thyroid gland.
4.Parathyroid glads.
5.Adrenal glands.
6.Pancrease.
7.Testis.
8.Ovaries
9.Placenta.(during pregnancy)
Coordination of the body functions by chemical messengers.
The multiple activities of the cells,tissues and organs of the body are coordinated by the interplay of several types of communication systems, including:
1.Neural, in which chemicals(neurotransmitters) are released at synaptic junctions and act locally to control cell function.
2.Endocrine, in which glands or specialized cells release into the circulating blood chemicals(hormones) that influence the function of cells at another location in the body.
3.Neuroendocrin, in which neurons substances:(neurohormones) that reach the circulating blood and influence the function of cells at another location in the body .
4.Paracrine, in which cells secrete substances that diffuse in to the extracellular fluid and affect neighboring cells.
5.Autocrine, in which a cell secretes substances that affect the function of the same cell by binding to the cell surface receptors.
For example, the adrenal medullae and the pituitary gland secrete their hormones primarily in response to neural stimuli.The neuroendocrine cells, located in the hypothalamus, have axons that terminate in the posterior pituitary gland and median eminence and secrete several neurohormones ,including antidiuretic hormone (ADH), oxytocin, and hypophysiotropic hormones, that control the secretion of anterior pituitary hormones. The endocrine hormones are carried by the circulatory system ti cells throughout the
body, including the nervous system in some cases, where they bind with receptors and initiate many body; for example,growth hormones causes growth in most parts of the body, and thyroxine increases the rate of many chemical reactions in almost all the body's cells.Other hormones affect only specific tissues called target tissues because only these tissues have receptors for the hormone.
Hormone
Hormone is a chemical substance that is secreted into the internal body fluid by one cell or group of cells and exerts aphysiological control effect on other cells of the body.
Classification of Hormone
1.Polypeptide and protein hormone
Polypeptide and protein hormones are stored in secretory vesicles until needed : Most of the hormones in the body are polypeptides
and proteins.These hormones range in size from small peptides with as few as three amino acids to protein almost 200 amino acids
long.In general, polypeptides with 100 or more amino acids are called proteins,and those with fewer that 100 amino acids are referred to as peptides.Protein and peptide hormones are synthesized on the rough end of the endoplasmic reticulum of the different
endocrine cells in the same fashion as most other proteins that are not biologically active and are cleaved to from smaller prohormones in the endoplasmic reticulum.These are than transferred to the golgi apparatus for packaging into secretory vesicles
cleave the prohomones to produce smaller, biologically active hormones and inactive fragments. The vesicles are stored within the
cytoplasm, and many are bound the cell membrane and the granular contents are extruded into the interstitial fluid or directly into the blood stream by exocytosis.
2.Steroid hormone
Steroid hormones are usually synthesized from cholesterol and are not stored : The chemical structure of steroid hormones is similar to cholesterol, and in most instances they are synthesized from cholesterol itself. They are lipid soluble and consist of three
cyclopenty1 ring combined into a single structure. Although there is usually very little hormone storage in steroid-producing endocrine cells, large stores of cholesterol esters in cytoplasm vacuoles can be rapidly mobilized for steroid synthesis after a stimulus. Much of the cholesterol in steroid-producing cells comes from the plasma, but there is also de novo synthesis of cholesterol in steroid-producing cells.Because the steroids are highly lipid soluble, once they are synthesized, they simply diffuse
across the cell membrane and enter the interstitial fluid and then the blood .
3.Amine hormone
Amine hormones are derived from tyrosine : The two groups of hormones derived from tyrosine, the thyroid and the adrenal medullary hormones, are formed by the actions of enzymes in the cytoplasmic compartments of the glandular cells.The thyroid hormones are synthesized and stored in the thyroid gland and incorporated into macromolecules of the protein thyroglobulin, which is stored in large follicles within the thyroid gland. Hormone secretion occurs when the amines are split from thyroglobulin and the free hormones
are than released into the blood stream.After entering the blood, most of the thyroid hormone combines with plasma proteins, especially thyroxine-binding globulin, which slowly releases the hormones to the target tissues.
Transport of hormones in the blood
Water-soluble hormones are dissolved in the plasma and transported from their sites if synthesis to target tissues, where they diffuse out of the capillaries, into the interstitial fluid,and ultimately to target cells. Steroid and thyroid hormones, in contrast, circulate in the blood mainly bound to plasma proteins. Usually less than 10 per cent of steroid or thyroid hormones in the plasma exist free in solution. For example, more than 99 per cent of the thyroxine in the blood is bound to plasma proteins. However, proteinbound hormones cannot easily diffuse across the capillaries and gain access to their target cells and are therefore biologically inactive until they dissociate from plasma proteins.The relatively large amounts of hormones bound to proteins serve as reservoirs, replenishing the concentration of free hormones
Anterior pituitary gland
Physiological anatomy of pituitary gland : The pituitary gland,also called the hypophysis, is a small gland - about 1 cm in diameter and 0.5 to 1 gm in weight that lies in the sella turcica at the base of the brain and is connected with the hypothalamus by the pituitary stalk. The pituitary gland is divided into two parts. Anterior pituitary or adenohypophysis and posterior pituitary or neurohypophysis between them a relatively avascular zone,called pars intermedia which is almost absent in human being. Anterior pituitary develops from rathke's pouch which is an embryonic invagination of pharyngeal epithelium and posterior pituitary developsfrom an outgrowth of the hypothalamus. Control of pituitary secretion by the hypothalamus : Almost all the secretion of pituitary gland are controlled by eithre hormonal or nervous signals from the hypothalamus. Secretion from posterior pituitary is controlled by yhe nerve signals originate in the hypothalamus and terminate in the posterior pituitary. In contrast, secretion by the anterior is controlled by the hypothalamic releasing or hypothalamic inhibitory hormones secreted within the hypothalamus itself and than conducted to the anterior pituitary through minute blood vessels. In the anterior pituitary, these releasing and inhibitory hormones act on the glandular cells to control their secretion.The hypothalamous in turn recives signals from many sources in the nervous system.Thus,when a person is exposed to pain a portion of the pain signal is transmitted into the hypothalamus.Likewish,when a person experiences some powerful depressing or exciting thought,a portion of the signal is transmitted into the hypothalamus. O1factory stimuli denoting pleasent or unpleasant smells transmit strong signal components directly and through the amygdaloid nuclei into the hypothalamus. Even the concentration of the nutrients,electrolytes, water and various portions of the hypothalamous.Thus the hypothalamous is a collecting center for information concerning the internal well being of the body and turn much of this information is used to control
secretions of the many globally important pituitary hormones.
Dwarfism
Most instances of dwarfism result from generalized deficiency of anterior pituitary secretion during childhood.In general,all the physical parts of the body develop in appropriate proportion to one another, but the rate of development is greatly decreased.A child who has reached the age of 10 years may have the bodily development of a child of 4 to 5 years, and the same person on reaching the age of 20 years may have the bodily development of a child of 7 to 10 years. 1.Laron dwarfism:In this group of dwarfed children,the plasma growth hormone concentration is normal or elevated but their growthhormone receptors are unresponsive as a result of loss-of-function mutations of the gane for the receptors.The resulting condition is is known as growth hormone insensitivity or Laron dwarfism.Plasma IGF-I is markedly reduced,along with IGFBP-3,which is also growth hormone-dependent.
2.Psychosocial dwarfism or the kasper hauser syndrome:Chronic abuse and neglect can also cause dwarfism in children.This condition is known as phychosocial dwarfism or the kasper hauser syndrome,named for the patient with the first reported case 3.Achondroplasia:Achondroplasia,the most common from of dwarfism in humans,is characterized by short limbs with a normal trunk. It is an autosomal dominant condition caused by a mutation in the gene that codes for fibrohlast growth factor receptor 3 (FGFR3).
This member of the fibroblast growth receptor family is normally expressed in cartilage and the brain.
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