Anatomy of endocrine system
- 2. GLANDS: An organ which secretes particular chemical substances for use in the body or for discharge into the surroundings. There are three types of glands in our body: Endocrine glands Exocrine glands Heterocrine glands
- 3. EXOCRINE GLANDS Exocrine glands are glands that secrete their products into ducts EXAMPLE: Sweat glands Salivary glands Mammary glands Digestive glands
- 4. ENDOCRINE GLANDS Glands that secrete their product (hormones) directly into the blood rather than through a duct EXAMPLE: Pituitary gland Thyroid gland Parathyroid gland Adrenal glands Pineal gland
- 5. • in addition several organs and tissues are not endocrine glands exclusively but contain cells that secrete hormones include • Hypothalamus • Thymus • Pancreas • Ovaries • Testes • Kidneys • Stomach • Liver • Small intestine • Skin • Heart • Adipose tissue • placenta
- 6. Pituitary gland & Hypothalamus • Pituitary gland or Hypophysis was called the master endocrine gland. • Pituitary gland itself has a master – Hypothalamus • Hypothalamus is the major link between the nervous and endocrine systems. • Cells in the hypothalamus synthesize at least nine different hormones. • Pituitary gland secretes seven • These two combine together play important roles in the regulation of virtually all aspects of growth, developmet, metabolism and homeostasis
- 7. • The pituitary gland is a pea shaped structure measuring 1- 1.5cm in diameter • The pituitary gland or hypophysis lies in the hypophyseal fossa of the sella turcica of the sphenoid bone. • It attaches to the hypothalamus by a stalk, the infundibulum. • It has anatomically and physiologically separate portions Anterior pituitary Posterior pituitary • The anterior pituitary lobe also called the adenohypophysis, accounts for about 75% of the total weight of the gland and is composed of epithelial tissue. • The anterior pituitary consists of two parts in an adult; • Pars distalis- is the larger portion • Pars tuberalis – forms a sheath around the infundibulum
- 9. • Posterior pituitary lobe also called the neurohypophysis, is composed of neural tissue • It also consists of 2 parts oPars nervosa – the larger bulbar portion o infundibulum. o a third region of the pituitary gland is the pars intermedia atrophies during human fetal development and ceases to exit as a separate lobe in adults.
- 10. Anterior pituitary • The anterior pituitary or adenohypophysis secretes hormones that regulate a wide range of bodily activities from growth to reproduction. • Release of anterior pituitary hormones is stimulated by releasing hormones and suppressed by inhibiting hormones by hypothalamus
- 11. Hypophyseal Portal system • Hypothalamic hormones reach the anterior pituitary through a portal system. • In portal system blood flows from one capillary network Portal vein Second capillary network
- 12. • The superior hypophyseal arteries, the branch of the internal carotid arteries bring blood into the hypothalamus. • At the junction of the median eminence of the hypothalamus and the infundibulum, these arteries divide into a capillary network called the primary plexus of the hypophyseal portal system. • From the primary plexus the blood flows into the hypophyseal portal vien that passes down the outside of the infundibulum. • In the anterior pituitary, the hypophyseal portal veins divide again and form another capillary network called the secondary plexus of the hypophyseal portal system
- 13. • Above the optic chiasm are clusters of specialized neurons called neurosecretory cells • They synthesize the hypothalamic releasing and inhibiting hormones in their cell bodies and package the hormones inside vesicles, which reach the axon terminals by axon transport. • Nerve impulses stimulate the vesicles to undergo exocytosis. • The hormones diffuse into the primary plexus of the hypophyseal portal system • Hypothalamic hormones flow with the blood through the portal vein into the secondary plexus. • Hypothalamic hormones act on anterior pituitary cells • hormones secreted by anterior pituitary cells pass into the secondary plexus capillaries, which drain into the hypophyseal veins and out into general circulation. • Anterior pituitary hormones travel to target tissues throughout the body.
- 16. Types of anterior pituitary cells and their Hormones Types of anterior pituitary cells: Somatotrophs Thyrotrophs Gonadotrophs Lactotrophs corticotrophs
- 17. Somatotrophs: • Secrete hGH also known as somatotropin • Human growth hormone in turn stimulates several tissues to secrete insulin like growth factors , hormones that regulate general body growth and regulate aspects of metabolism Thyrotrophs: • Secrete TSH also known as thyrotropin • TSH controls the secretions and other activities of the thyroid gland Gonadotrophs: • Secrete 2 gonadotropins; FSH (follicle stimulating hormone), LH (luteinizing hormone) • They stimulates the secretion of estrogen and progesterone and the maturation of oocytes in the ovaries • they stimulate sperm production and secretion of testosterone in the testes
- 18. Lactotrophs: • Secrete prolactin (PRL), which initiates milk production in the mammary glands. • Corticotrophs : secrete adrenocorticotropic hormone, (ACTH), also known as corticotropin • stimulates cortex to secrete glucocorticoids such as cortisol • Some corticotrophs remnants of the pars intermedia, also secrete Melnocyte- stimulating hormone(MSH)
- 20. Posterior Pituitary • Posterior pituitary or neurohypophysis does not synthesize hormones, it does and store 2 hormones • It consists of axons and axon terminals of more than 10,000 hypothalamic neurosecretory cells. • The cell bodies of the neurosecretory cells are in the paraventricular and supraoptic nuclei of the hypothalamus • Their axons form hypothalamohypophyseal tract. • This tract begins in the hypothalamus and ends near blood capillaries in the posterior pituitary • The neuronal cell bodies in the supraoptic nucleus produce antidiuretic hormone also called vasopressin
- 22. • The axon terminals in the posterior pituitary are associated with specialized neuroglia called pituicytes • After their production the cell bodies of neurosceretory cells oxytocin and antidiuretic hormone are packaged into secretory vesicles, which moves by fast axonal transport to the axon terminals in the in the posterior pituitary • Where they are stored until nerve impulses trigger exocytosis and release of the hormones • Blood is supplied to the posterior pituitary by the inferior hypophyseal arteries, which branch from the internal carotid arteries. • In the posterior pituitary, the inferior hypophyseal arteries drain into the capillary plexus of the infundibular process • A capillary network that receives secreted oxytocin and ADH • From this plexus, hormones pass into the posterior hypophyseal veins for distribution to target cells in other tissues.