Lecture Eleven Endocrine system The endocrine system consists

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Lecture Eleven Endocrine system The endocrine system consists of cells, tissues, and organs that

Lecture Eleven Endocrine system The endocrine system consists of cells, tissues, and organs that synthesize and secrete hormones directly into the blood and lymph capillaries. As a result, the endocrine glands/organs are ductless, that is they do not have excretory ducts. Furthermore, the cells in most endocrine organs are arranged into cords and clumps, and surrounded by an extensive caplliary network. The hormones produced by the endocrine organs include peptides proteins, steroids, and amino acid. The hormones enter the blood vessels directly and are then transported in blood to distant target organs, where, via specific receptors, they influence the structure and function of their cells and tissues. The hormone receptors can be located either on the plasma membrane, cytoplasm, or nucleus of target cells. There also numerous exocrine organs that are associated with individual endocrine cells or endocrine tissues. Such mixed (endocrine-exocrine) organs are pancreas, kidneys, reproductive organs of both sexes, placenta, and gastrointestinal tract. There also distinct endocrine organs in the body. These include the hypophysis, or pituitary gland (described below), thyroid gland, adrenal (suprarenal) glands, and parathyroid glands.

Lecture Eleven ENDOCRINE ORGANS A- Hypophysis (pituitary) gland The hypophysis weights about 0. 5

Lecture Eleven ENDOCRINE ORGANS A- Hypophysis (pituitary) gland The hypophysis weights about 0. 5 g, and its normal dimensions in humans are about 10 x 13 x 6 mm. It lies in a cavity of the sphenoid bone. During embryogenesis, the hypophysis develops partly form oral ectoderm and partly from nerve tissue. The neural component arises as an evagination form the floor of the diencephalons. The oral component arises as an outpocketing of ectoderm from the roof of the primitive mouth of the embryo and grows cranially; forming a structure called Rathkes pouch Because of its dual origin the hypophysis actually consists of 2 glandthe neurohypophysis and the adenohypophsis- that are united anatomically but that have different functions. The neurohypophysis, the part of the hypophysis that develops form nerve tissue, consists of a large portion, the pars nervosa, and the smaller infundibulum or neural stalk. The neural stalk is composed of the stem and median eminence. The part of the hypophysis that arises from oral ectoderm I known as the adenohypophysis and is subdivided into 3 portions, a large pars distalis, or anterior lobe; a cranial part, the pars tuberalis, which surrounds the neural stalk; and the pars intermedia.

Lecture Eleven 1. Adenohypophysis * Pars Distalis The main components of the pars distalis

Lecture Eleven 1. Adenohypophysis * Pars Distalis The main components of the pars distalis are cords of epithelial cells interspersed with capillaries. The hormones produced by these cells are stored as secretory granules. The few fibroblasts that are present produce reticular fibers that support the cords of hormone-secreting cells. The pars distalies accounts for 75% of the mass of the hypophysis. 3 cells types in the pars distalis, chromophobes and 2 types of chromophils called basophils and acidophils according to their affinity for basic and acid dyes, respectively. The subtypes of basophil and acidophil cells are named for the hormones they produce. Chromophobes do not stain intensely and, when observed with an electron microscope, show 2 populations of cells. One has few secretory granules, and the other has none. The group with no secretory granules probably contains undifferenetiated cells and follicular cells. The long branching processes of follicular cells form a supporting network for the other cells. With the exception of the gonadotropic cell , which produces 2 hormones, the other cells produce only a single hormone.

Lecture Eleven Secretory hormones form the pars distalis Cell type Hormone produced or Main

Lecture Eleven Secretory hormones form the pars distalis Cell type Hormone produced or Main physiologic activity Somatotropic cell Somatotropin growth hormone Mammotropic cell Prolactin Promotes milk secretion Thyrotropic Thyrotropin (TSH) Stimulates thyroid hormone synthesis, storage and liberation Gonadotropic cell 1. Follicle stimulating hormone (FSH) 2. Luteinzing hormone (LH) Acts on growth of long bones by somatomedins synthesized in liver Promotes ovarian follicle development and estrogen secretion in women and stimulates spermatogenesis in men. Promotes ovarian follicle maturation and progesterone secretion in women and leyding cell stimulation andogensecretion in men

Lecture Eleven * Pars tuberalis The pars tuberalis is a funnel-shaped region surrounding the

Lecture Eleven * Pars tuberalis The pars tuberalis is a funnel-shaped region surrounding the infundibulum of the neurohypophysis. Most of the cells of the pars tuberalis secrete gonadotropins (folliclestimulating hormone and luteinizing hormone) and are arranged in cords alongside the blood vessels. * Pars intermedia The pars inermedia, which develops from the dorsal portion of Rathkes pouch is, in humans, a rudimentary region made up of cords and follicles of weakly basophilic cells that contain small secretory granules. The function of these cells is not known. 2. Neurhypophysis The part of the hypophysis that develops form nerve tissue consists of: Pars nervosa Infundibulum Median eminence

Lecture Eleven * Pars nervosa The pars nervosa, unlike the adenohypophysis dose not contain

Lecture Eleven * Pars nervosa The pars nervosa, unlike the adenohypophysis dose not contain secretory cells. It is composed of some 100. 000 unmyelinated axon of secretory neurn and supporting neuroglial cells called (pituicytes). The neuro secretions are transported a long the axons and accumulate at their endings in pars nervosa. Here they form structures known as (Herring bodies). Herring bodies contain neurosecretory granules that have a diameter of (100 -200 nm) and are surrounded by a membrane. The granules are released and enter the fenestrated capillaries; the hormones are than distributed to the general circulation. The neurosecretory material consist of two hormones both cyclic peptides mad up of nine amino acid. The hormones a have a slightly different amino acid composition which results in very different functions.

Lecture Eleven Cell of the neurohypophysis Although the neurohypophysis consists mainly of axons from

Lecture Eleven Cell of the neurohypophysis Although the neurohypophysis consists mainly of axons from hypothalamic neurons, about 25% of the volume of this structure consists of a specific type of highly branched glial cell called a pituicyte. Secretory hormones form the neurohypophysis Vasopressin (antidiuretic) hormone (ADH): The function of this hormone increase water permeability of kidney collecting duct and promotes vascular smooth muscle contraction. Oxytocin: Acts on contraction of uterine smooth muscle and the myoepithelial cells of mammary gland.

Lecture Eleven

Lecture Eleven

Lecture Eleven B. Adrneal (suprarenal) glands The adrenal glands are paired organs that lie

Lecture Eleven B. Adrneal (suprarenal) glands The adrenal glands are paired organs that lie near the superior poles of the kidneys, embedded in adipose tissue. They are flattened structures with a half-moon shape; in the human, they are about 4 -6 cm long, 1 -2 cm wide, and 4 -6 mm thick. Together they weight about 8 g, but their weight and size vary with the age and physiologic condition of the individual. Examination of a fresh section of adrenal gland shows it to be covered by a capsule of dense collagenous connective tissue. The gland consists of 2 concentric layers, a yellow peripheral layer, the adrenal cortex; and a raddish-brown central layer, the adrenal medulla. The dermal cortex and the adrenal medulla can be considered two organs with distinct origins, functions, and morphologic characteristics that become united during embryonic development. They arise from different germ layers. The cortex arises form the coleomic intermediate mesoderm; the demulla consist of cells derived form the neural crest, from which sympathetic ganglion cells also originate.

Lecture Eleven The general histologic appearance of the adrenal gland is typical of an

Lecture Eleven The general histologic appearance of the adrenal gland is typical of an endocrine gland in which cells of both cortex and medulla are grouped in cords along capillaries. The collagenous connective tissue capsule that coveres the adrenal gland sends thin septa to the interior of the gland as trabeculae. The stroma consists mainly of a rich network of reticular fibers that support the secretrory cells. 1. Adrenal cortex Because of the differences in disposition and appearance of its cells, the adrenal cortex can be subdivided into 3 concentric layers whose limits are usually not sharpy defined in humans: the zona glomerulosa, the zona fasciculate, and the zona reticularis. These layers occupy 15%, 65% and 7%, respectively, of the total volume of the adreal glands.

Lecture Eleven The layer immediately beneath the connective tissue capsule is the zona glomerulosa,

Lecture Eleven The layer immediately beneath the connective tissue capsule is the zona glomerulosa, in which columnar or pyramidal cells are arranged in closely packed, rounded, or arched cords surrounded by capillaries. The next layer of cells in known as the zona fasciculate because of the arrangement of the cells in straight cords, one or two cells thick that run at right angles to the surface of the organ and have capillaries between them. The cells of the zona fasciculate are polyhedral, with a great number of lipid droplets in their cytoplasm. As a result of the dissolution of the lipids during tissue preparation, the fasciculate cells appear vacuolated in common histologic preparations. Because of their vacuolization, the cells of the fasciculate are also called spongyocytes. The zona reticularis, the innermost layer of the cortex, lies between the zona fasciculate and the medulla; it contains cells disposed in irregular cords that form an anastoimosing network. These cells are smaller than those of the other two layers. Lipofuscin pigment granules in the cells are large and quite numerous. Irregulalry shaped cells with pyknotic nuclei suggesting cell detah-are often found in this layer.

Lecture Eleven Cells of the adrenal cortex do not store their secretory products in

Lecture Eleven Cells of the adrenal cortex do not store their secretory products in granules; rather, they synthesize and secrete steroid hormones only upon demand. Steroids, being low-molecular-weight lipid-soluble molecules, can freely differed through the plasma membrane and do not require the specialized process of exocytosis for their release. Cells of the adrenal cortex have the typical ultrastructure of steroidsecreting cells.

Lecture Eleven Cortical Hormomes & their actions The steroids secreted by cortex can be

Lecture Eleven Cortical Hormomes & their actions The steroids secreted by cortex can be divided into 3 groups, according to their main physiologic actions: glucorticoids, mineralocorticoids, androgens. The zona glomerulosa secretes mineralocorticoids, primarily aldosterones that maintain electrolyte (eg, sodium and potassium) and water balance. The zona fasciculate and probably the zona reticularis secrete the glucocorticoids cotrisone and cortisol or, in some animals, corticosterone; these glucocorticoids regulate carbohydrate, protein, and fat metbolsim. These zones also produce androgens (mainly dehydroepiandrosterone) and perhaps estrogens in small amounts. The glucocorticoids, mainly cortisol and corticosterrone, exert a profound effect on the metabolism of carbohydrates, as well as on that of proteins and lipids. The mineralocorticoids act mainly on the distal renal tubules as well as on the gastric mucosa and the salivary and sweat glands, stimulating the absorption of sodium. They may increase the concentration of potassium and decrease the concentration of sodium in muscle and brain cells.

Lecture Eleven The defense system of the body and the adrenal cortex are closely

Lecture Eleven The defense system of the body and the adrenal cortex are closely associated because cortisol has anti-inflammatory properties via white blood cells and suppression of cytokines and is also an immunosuppressant. Dehydroepiandrosterone is the only sex hormone that is secreted in significant physiologic quantities by the adrenal cortex. Smaller amount of other androgens such as androstenedione, 11 betahydroxyandrostenedione, and testosterone, are also secreted. Dehydroxyandrostenedione, and testosterone, are also secreted Dehydroepiandrosterone androstenedione are weak androgens and exert their actions after conversion into testosterone in other parts of the body. 2 - Adrenal medulla The adrenal medulla is composed of polyhedral parenchymal cells arranged in cords or clumps and supported by a reticular fiber network. A profuse capillary supply intervenes between adjacent cords, and there a few parasympathetic ganglion cells. Medullary parenchymal cells arise from neural crest cells, as do the postganglionic neurous of sympathetic and parasympathetic ganglia. Parenchymal cells of the adrenal medulla can be regarded as modified sympathetic postganglionic neurons that have lost their axone and dendrites during embryonic development and have become secretory cells.

Lecture Eleven Medullary parenchymal cells have abundant membrane-limited electron-dense secretory granules, 150 -350 nm

Lecture Eleven Medullary parenchymal cells have abundant membrane-limited electron-dense secretory granules, 150 -350 nm in diameter. These granules contain one or the other of the catecholamines, epinephrine or norepinephrine. The secretory granules also contain ATP, protein called chromogranins. A large body of evidence shows that epinephrine and norepinephrine are secreted by 2 different types of cells in the moedulla. Epinephrine-secreting cells have smaller granules that are less electron-dense, and their contents fill the granule. Norepinephrine-secreting cells have large granules that are more electron-dense; their contents are irregular in shape, and there is an electron-luncent layer beneath the surrounding membrane. About 80% of the catecholamine output of the adrenal vein is epinephrine. All adrenal medullary cells are innervate by cholinergic endings of preganglioic sympathetic neurons. Unlike the cortex, which dose not store steroids, cells of the medulla accumulate and store their hormones in granules.

Lecture Eleven

Lecture Eleven

Lecture Eleven C- Islest of Langerhans The islets of Langerhans are multihormonal endocrine microograns

Lecture Eleven C- Islest of Langerhans The islets of Langerhans are multihormonal endocrine microograns of the pancrease; they appear as rounded clusters of cells embedded within exocrine pancreatic tissue. Although most islets are 100 -200μm in diameter and contain several hundared cells, small islets of endocrine cells are also found interspersed among the pancreatic exocrine cells. There may be more than 1 million islets in the human pancreas, with a slight tendency for islets to be more abundant in the tail region. In sections, each islet consists of lightly stained polygonal or rounded cells, arranged in cords separated by a network of blood capillaries. In 3 -dimensional reconstructions, islets of Lagerhans are seen as around, compact masses of secretory epithelial cells pervaded by a labyrinthine network of blood caplillaries. Both the endocrine cells and the blood vessels are innervated by autonomic nerve fibers. A fine capsule of reticular fibers surrounds each islet, separating it from the adjacent exocrine pancreatic tissue.

Lecture Eleven Routine stains or trichrome stans allow the recognition of acidophils (alpha) and

Lecture Eleven Routine stains or trichrome stans allow the recognition of acidophils (alpha) and basophils (beta). Using immunocytochemical methods four types of cells-A, B, D, and Fhave been located in the islets. The ultrastructure of these cells resembles that of cells synthesizing polypeptides. The secretory granules of cells of the islets vary according to species studied. In human, the A cells have regular granules with a dense core surrounded by a clear region bounded by a membrane. The B (insulin-producing) cells have irregular granules with a core formed of irregular crystals of insulin in complex with zinc. The relative quantities of the 4 cell types found in islets are not uniform they vary considerably with the islets location in the pancreas

Lecture Eleven Table (cell types in human islets of Langerhans) Cell type Quanti ty

Lecture Eleven Table (cell types in human islets of Langerhans) Cell type Quanti ty A ~20% Usually in periphery Glucagons Acts on several tissues to make energy stored in glycogen and fat available though glycogenolysis and lipolysis; increases blood glucose content B ~70% Central region Insulin Acts on serval tissues to cause entry of glucose into cells and promotes decrease of blood glucose content D <5% Variable Smoatostatin Inhibits release of other islet cell hormones through local paracrine action F rare Variable Pancreatic polypeptide Not well established Position Hormone produced Hormonal function

Lecture Eleven

Lecture Eleven

Lecture Eleven D-Thyroid In early embryonic life, the thyroid is derived from the cephalic

Lecture Eleven D-Thyroid In early embryonic life, the thyroid is derived from the cephalic portion of the alimentary canal endoderm. Its function is to synthesize the hormones thyroxine (T 4) and triiodothyronine (T 3), which stimulate the rate of metabolism in the body. The thyroid gland, located in the cervical region anterior to the larynx, consists of 2 obels united by thousands of follicles that consist of spheres formed by simple epithelium whose lumen contains a gelatinous substance called colloid. In sections, follicular cells range from squamous to columnar and the follicles have an extremely variable diameter. The gland is covered by a loose connective tissue capsule that sends speta into the parenchyma. As these septa gradually become thinner they reach all the follicles, separated from one another by fine, irregular connective tissue composed mainly of reticular fibers. The thyroid is an extremely vascularized organ, with an extensive blood and lymphatic capillary network surrounding the follicles. Endothelial cells of these caplillaries are fenestrated, as they are in other endocrine glands. This configuration facilities the transport of molecules between the gland cells and the blood capillaries.

Lecture Eleven The major regular of the anatomic and function a state of the

Lecture Eleven The major regular of the anatomic and function a state of the thyroid gland is thyroid-stimulating hormone (thyrotropin), which is secreted by the anterior pituitary. The morphologic appearance of thyroid follicles varies according to the region of the gland its functional activity. In the same gland, larger follicles that are full of colloid and have a cuboidal or squamous epithelium are found alongside follicles that are lined by columnar epithelium. Despite this variation, the gland is considered hypoactive when the average composition of these follicles is squamous. Thyrotropin stimulates the synthesis of thyroid hormone, increases the height of the follicular epithelium, and decreases the quantity of the colloid and the size of the follicles. The cell membrane of the basal portion of follicular cells is rich in receptors for thyrotropin. The thyroid epithelium rests on a basal lamina. The follicular epithelium exhibits all the characteristics of a cell that simultaneously synthesizes, secretes, absorbs, and digests proteins. The basal part of these cells rich in rough endopasmic reticulum. The nucleus is generally round and situated in the center of the cell. The apical pole has a discrete Golgi complex and small secretory granules with he morphologic characteristics of follicular colloid. Abundant lysosomes, 0. 5 -0. 6μm in diameter, and some largo phasgosomes are found in this region.

Lecture Eleven The cell membrane of the apical pole has a moderate number of

Lecture Eleven The cell membrane of the apical pole has a moderate number of microvilli. Mitochondria ad cisternae of rough endoplasmic reticulum are dispersed throughout the cytoplasm. Another type of cell, the parafollicular, or C, cell, is found as part of the follicular eptheiul or as isolated clusters between thyroid follicles. Parafollicular cells are somewhat larger than thyroid follicular cells and stain less intensely. They have a small amount of rough endoplasmic reticulum, long mitochondria, and a large Goligi complex. The most striking feature of these cells is their numerous small (100 -180 nm in diameter) granules containing hormone. These cells are responsible for the synthesis and secretion of calcitonin, a hormone whose main effect is to lower blood calcium levels by inhibiting bone resorption. Secretion of calcitonin is triggered by an elevation in blood calcium concentration.

Lecture Eleven

Lecture Eleven

Lecture Eleven E. Parathyroid glands The parathyroids are 4 small glands -36 mm-with a

Lecture Eleven E. Parathyroid glands The parathyroids are 4 small glands -36 mm-with a total weight of about 0. 4 g. They are located behind the thyroid gland, one at each end of the upper and lower poles, usually in the capsule that covers the lobes of the thyroid. Sometimes they are embedded in the thyroid gland. The pararthyroid glands are derived from the pharyngeal pouches-the superior glands form the fourth puch and the inferior glands from the third pouch. They can also be found in the mdeiastinum, lying beside thymus, which originates from the same pharyngeal pouches. Each parathyroid gland is contained within a connective tissue capsule. These capsules send septa into the gland, where they merge with the reticular fibers that support elongated cordlike clusters of secretory cells. The endocrine cells of the parathyroid are arranged in cords. These are 2 types of cells: the chief, or principal, cells and the oxyphil cells.

Lecture Eleven The chief cells are small polygonal cells with avesicular nucleus and pale-staining,

Lecture Eleven The chief cells are small polygonal cells with avesicular nucleus and pale-staining, slightly acidophilic cytoplasm. Electron microscopy shows irregularly shaped granules (200 -400 nm in diameter) in their cytoplasm. They are the secretory granules containing parathyroid hormone, which is a polypeptide in its active form. Oxyphil cells constitute a smaller population. They are larger polygonal cells, and their cytoplasm contains many acidophilic mitochondria with abundant cristae. The function of the oxyphil cells is not known. With increasing age, secrtory cells are replaced with adipocytes. Adipose cells constitute more than 50% of the gland in older people.