Endocrine System PDF

Endocrine system Endocrine system Endocrine system : Composed mainly of ductless glands that its secretion are passed directly into blood circulation They secrets special materials (hormone) which has an effect upon a particular tissue or organ or by the body as a whole the effected organ by hormone...

Endocrine system Endocrine system Endocrine system : Composed mainly of ductless glands that its secretion are passed directly into blood circulation They secrets special materials (hormone) which has an effect upon a particular tissue or organ or by the body as a whole the effected organ by hormone is called target organ due to presence of receptor in the organ for the hormone There are 2 types of receptors : Membranous Cytoplasmic Also there are 2 types of hormones : Steroids Peptides Endocrine system Endocrine system : Endocrine system The steroids : can enter the cell passing from cell membrane to the cytoplasm and effect the DNA of the cell The peptides : are the majority of hormones which effect membrane like insulin, glucagon… Hormones with the nervous system control the physiological activities of the body so they consider as single system called (neuro endocrine system) The endocrine glands are either as a complete separated glands like the pituitary gland and thyroid gland Or may be associated with other exocrine gland like islets of Langerhans Or associated with complexed organ such as in kidney, testis and ovary Some are present as an isolated groups with other tissue like the enteroendocrine cells. Endocrine system Thyroid gland: Position : its located in the anterior part of the upper neck in front of the larynx and trachea. Its resembles the wings of butterfly opened. It consists of 2 lobes joined by the isthmus. Histology of thyroid gland: Thyroid gland is consist of follicles which consist of single layer of cuboidal cells in lumen of follicle there is a colloid gelatinous material that stored in it The colloid contains the thyroglobulin, which react with the iodine, after reabsorption of it from the lumen, to form T4 and T3-Tri iodothyronine then T4 (thyroxine) and T3 secreted on the blood. Endocrine system Thyroid gland: Endocrine system Thyroid gland: Between the follicles, there is another cell type which are the (parafollicular cell) or (clear cells) or (C cells) they are large stain lightly found single or as cluster These cells responsible for synthesis and secretion of calcitonin which lowers blood calcium level. The pituitary gland controls the thyroid secretion through a hormone (thyroid stimulating hormone -TSH-). The (TSH) stimulates the thyroid to synthesis and secrete T4 and T3 which have a negative feedback on the secretion of TSH from the anterior pituitary. Endocrine system Parathyroid glands : The parathyroids are 4 small groups of endo-crinal tissue They are situated behind the thyroid gland. 2 groups behind each lobe They are covered by C.T capsule which cover the thyroid gland. The C.T. from septa that separate the cells into cords and clumps. Type of cells : Chief cell : the majority Oxyphil cells : only few The parathyroid glands secrets the parathyroid hormone (PTH) which increase the blood calcium. In case of 𝑐𝑎+2 deficiency, the PTH increases the Ca in blood by dissolving the calcium of the bone. Endocrine system Adrenal (suprarenal glands): They are pair of glands located in the anterior upper pole of the kidney They are covered by C.T. capsule and the capsule sends septa to the anterior as trabeculae while the stroma consists mainly of reticular fibers that support the secretory cells. The adrenal glands are flattened structures consists of 2 layers: peripheral cortex & a central medulla. The cortex secrets a series of hormones called corticosteroids. The medulla secrets adrenaline and which increasing heart rate and blood pressure. Endocrine system Adrenal (suprarenal glands): Cellular Arrangement : The adrenal cortex can be subdivided into 3 layers :Zona glomerulosa: just beneath the C.T. capsule, the cells are arranged in cords and chains or arches. Zona fasciculata: the middle layer, the cells are arranged in longitudinal chains parallel to each other. Zona reticularis: the inner most layer, lies between zona fasciculate and medulla, it cells has no distinct arrangement. Endocrine system Adrenal (suprarenal glands): Cellular Arrangement : Endocrine system Adrenal (suprarenal glands): Cellular Arrangement : Medulla : Consist of secretory cells polyhydral in shape, arranged in cords or clumps and supported by reticular fibers network. We can see also ganglionic cells (sympathetic) because the gland is under the control of sympathetic nervous system. The secretory cells (chromaffin cells) secrets "catecholamine" which stored in secretory granules inside it. Endocrine system Pituitary gland (Hypophysis) : It is the most important gland in the body, its connected to the hypothalamus at the base of the brain The pituitary gland consist of 2 parts: Adenohypophysis : originates from oral ectoderm Neurohypophysis : originate from nervous tissue The adenohypophysis consist of 3 regions : Pars distalis Pars intermediate Pars tuberalis Endocrine system Pituitary gland (Hypophysis) : The neurohypophysis : Pars nervosa or posterior pituitary : they are no secretory cell on it only it contains unmyelinated axons of neurosecretory cells which their bodies found in supra optic and paraventricular nuclei. There secretion is carried by their own axons posteirior pituitary only contain supporting cells to the unmyelinated axons, these cells are called pituicytes Infundibulum : connect the pituitary gland with the hypothalamus Endocrine system Pituitary gland (Hypophysis) : Adenohypophysis : Pars tuberalis : funnel-shaped surrounds the infundibulum of neurohypophysis, it cells secrets FSH and LH hormones Pars intermedia: secrets MSH which transport to the skin to increase the number of melanosomes Pars distalis: make the greater part of the pituitary gland, it composed of secretory cells which can differentiated as 2 types according to the color and affinity to staining Chromophobe : don't stain darkly Chromophil : have the affinity to be stained and can be differentiated into acidophils and basophils Endocrine system Pituitary gland (Hypophysis) : Adenohypophysis : Acidophils secretion : Somatotropes (HGH) human growth hormone coordinates growth Mammotropes (prolactin) stimulate milk secretion from mammary gland Basophils secretion : Thyrotropes secret thyroid stimulating hormone TSH Gonadotropes FSH , LH Corticotropes secret adrenocorticotropic hormones ACTH which promotes growth of adrenal cortex Endocrine system Pituitary gland (Hypophysis) : Pars intermedia MSH skin Endocrine system Hypothalamus : Its located in the lower central part of the brain Its important in regulation of metabolism and body temperature It secrets hormones that stimulate or suppress the release of hormones in the pituitary gland The hypothalamus also secrets a hormone called somatostatin , which cause pituitary stop the release of growth hormone. Pineal body : Is located in the middle of the brain, it secrets a hormone called melatonin which may help regulate wake - sleep cycle of the body. Endocrine system Adrenal cortex : Derived from mesoderm, consist of 3 layers: Zona Glomerulosa (15% of cortex) secrets mineral corticoids (Aldosterone) Maintenance of electrolyte and water balance Regulated by renin-angiotensin system Zona fasciculate (78% of cortex) secrets glucocorticoids-cortisol prepares body for energy demands. Zona reticularis (7% of cortex) secrets gonado corticoids Adrenal medulla : Chromaffin cells secrets epinephrine (80%) and nore epinephrine (20%) Endocrine system Thyroid gland : Para follicular cells : secrets calcitonin which inhibit osteoclast activity and stimulate osteoblast activity adding 𝐶𝑎+2 to bony matrix, works in opposition to para thyroid hormone Para thyroid hormone: decrease calcium stimulates secretion, para thyroid hormone stimulate osteoclast to degrade bone and raise blood 𝐶𝑎+2