Endocrine system Course outline Endocrine Glands & Hormones Glands of the endocrine system Hypothalamus and pituitary Hypothalamus gland Pituitary gland Thyroid gland Parathyroid gland Adrenal gland Pineal gland Endocrine Glands & Hormones The endocrine system consists of cells, tissues, and organs that secrete hormones. Endocrine glands are ductless organs that secrete their hormones directly into the surrounding fluid. Hormones secreted into the extracellular fluid diffuse into the blood. All endocrine cells are located within highly vascularized areas to ensure that their products enter the bloodstream immediately. Exocrine system: whose glands release their secretions through ducts. Functions Hormones play a critical role in the regulation of physiological processes include: Reproduction Growth and development of body tissues Metabolism Fluid, and electrolyte balance Blood sugar and blood pressure Use and storage of energy Responses to physical stress or trauma sleep Glands of the endocrine system The major glands of endocrine system are Hypothalamus Pituitary Thyroid Para thyroid Adrenal Pineal Thymus Pancreas Gonade ( Ovarium and Testis) Hypothalamus and pituitary The hypothalamus is located in the center of the brain. The hypothalamus and the pituitary gland are part of the diencephalon region of the brain. The hypothalamus–pituitary complex can be thought of as the “command center” of the endocrine system. This complex secretes several hormones that directly produce responses in target tissues, as well as hormones that regulate the synthesis and secretion of hormones of other glands. Hypothalamus and pituitary hypothalamus–pituitary complex coordinates the messages of the endocrine and nervous systems. A stimulus received by the nervous system must pass through the hypothalamus–pituitary complex to be translated into hormones that can initiate a response Hypothalamus The hypothalamus is a structure of the diencephalon of the brain located anterior and inferior to the thalamus. It has both neural and endocrine functions, producing and secreting many hormones. Nuclei of the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH) These hormones are transported to the posterior pituitary. Pituitary Gland (Hypophysis) Master gland lies in the middle cranial fossa,inferior to the hypothalamus. Connected to the hypothalamus by a thin stalk, the infundibulum(pituitary stalk). The pituitary gland is cradled within the sella turcica of the sphenoid bone of the skull. It consists of two lobes: The posterior pituitary (neurohypophysis) is neural tissue The anterior pituitary (adenohypophysis) is glandular tissue. Anterior lobe(adenohypophysis) There are three regions: the pars distalis is the most anterior, the pars intermedia is adjacent to the posterior pituitary, and the pars tuberalis is a slender “tube” that wraps the infundibulum. The secretion of hormones from the anterior pituitary is regulated by hormones secreted by the hypothalamus (Hormone-releasing & inhibiting factors) through vessels of Hypophyseal Portal System . Anterior lobe(adenohypophysis) Hypophyseal Portal System is bridge of capillaries(Within the infundibulum) connects the hypothalamus to the anterior lobe of pituitary gland. Hypothalamic hormones travel through a primary capillary plexus to the portal veins. Hormones produced by the anterior pituitary enter a secondary capillary plexus, then circulation. Anterior lobe(adenohypophysis) Secretes seven hormones: Growth hormone ( GH) Luteinizing hormone (LH) Follicle Stimulating hormone (FSH) Thyrotropin hormone (TSH) Prolactin (PRL) Adrenocorticotropic hormone ( ACTH) Melanocyte stimulating hormone ( MSH POSTERIOR LOBE(Neurohypophysis) Connected to hypothalamus through hypothalamo-hypophyseal tract(bridge of nerve axons). Stores hormones secreted by hypotha -lamic nuclei. The neurohypophysis receives a nerve supply from some of the hypothalamic nuclei (supraoptic & paraventricular). POSTERIOR LOBE(Neurohypophysis) The axons of hypothalamus nuclei convey their neurosecretion to the posterior lobe of pituitary gland through Hypothalamo-hypophyseal tract from where it passes into the blood stream. Paraventricular nuclei produce the hormone oxytocin. Supraoptic nuclei produce ADH. BLOOD SUPPLY OF PITUITARY GLAND Arteries : Superior & inferior hypophyseal arteries (branches of internal carotid artery) Veins : Hypophyseal veins drain into Cavernous Sinuses. Distribution of Arteries: Superior hypophyseal: supplies infundibulum & forms a capillary network from which vessels pass downward & form sinusoids into the anterior lobe of pituitary gland (hypophyseal portal system). Inferior hypophyseal: supplies posterior lobe of pituitary gland. Thyroid gland A butterfly-shaped organ. Located in the neck anterior to the trachea, just inferior to the larynx . Thyroid gland attached to arch of cricoid cartilage and to oblique line of thyroid cartilage. The medial region, called the isthmus, is flanked by wing-shaped left and right lobes. Each of the thyroid lobes are embedded with parathyroid glands, primarily on their posterior surfaces. Thyroid gland The tissue of the thyroid gland surrounded by a thin, fibrous capsule of connective tissue, and is composed mostly of thyroid follicles. The follicles are made up of a central cavity filled with a sticky fluid called colloid, surrounded by a wall of epithelial follicle cells. The colloid is the center of thyroid hormone production, and that production is dependent on the iodine (The essential component for hormone production). Blood supply Internal jugular vein and common carotid artery lie postero-lateral to thyroid. All thyroid arteries anastomose with one another on and in the substance of the thyroid, but little anastomosis across the median plane. The superior thyroid artery(anterior and posterior): Branch of the external carotid artery, which supplies the upper part of the thyroid gland. Blood supply The inferior thyroid artery, a branch of the subclavian artery, supplies the lower half of the thyroid. The superior and middle thyroid veins empties into the internal jugular vein. Inferior thyroid veins drain into the brachiocephalic veins. Parathyroid Glands Are tiny, round structures usually found embedded in the posterior surface of the thyroid gland. Four parathyroid glands, a superior and inferior pair on the left and right sides of the thyroid. Have a bean like shape. They secrete parathyroid hormone (PTH), (stimulates bones to release calcium into the blood & reduce secretion of calcium in urine by kidney. Adrenal glands The adrenal glands are pyramid-shaped organs that sit at the top of each kidney. They are wedges of glandular and neuroendocrine tissue adhering to the top of the kidneys by a fibrous capsule. Each adrenal gland consists of two structures: Outer adrenal cortex and an inner adrenal medulla. The adrenal glands have a rich blood supply and experience one of the highest rates of blood flow in the body. Adrenal glands They are served by several arteries branching off the aorta, including the suprarenal and renal arteries. Blood flows to each adrenal gland at the adrenal cortex and then drains into the adrenal medulla. Adrenal hormones are released into the circulation via the left and right suprarenal veins. Adrenal glands The adrenal cortex consists of glandular tissue secretes corticosteroids. The medulla of consists of nervous tissue secretes epinephrine and norepinephrine. The cortex it self is divided into three zones: the zona glomerulosa (Aldosteron), the zona fasciculata(cortisol), and the zona reticularis(Androgen). Pineal gland The pineal gland is small and pine cone shaped. located at the back of the diencephalon region in the brain, inferior but somewhat posterior to the thalamus. Pinealocyte cells (cells that make up pineal gland) secrete the melatonin, which is varies according to the level of light received from the environment. Melatonin regulate biological rhythms.
