Endocrine System Notes PDF

UNIT 3.11 ENDOCRINE SYSTEM Mutalife F. Mweemba Outline  Structural organs of the endocrine glands of the human body; ◦ hypothalamus, pituitary gland, pineal glands ◦ thyroid gland, parathyroid gland, adrenal glands ◦ pancreas, gonads Objectives  By the end of the lecture, l...

UNIT 3.11 ENDOCRINE SYSTEM Mutalife F. Mweemba Outline  Structural organs of the endocrine glands of the human body; ◦ hypothalamus, pituitary gland, pineal glands ◦ thyroid gland, parathyroid gland, adrenal glands ◦ pancreas, gonads Objectives  By the end of the lecture, learners should be able to: 1. Describe the structure of the endocrine glands 2. Discuss the actions of the hormones secreted by the glands 3. Explain the influence of the hypothalamus on the lobes of the pituitary gland 4. Outline the hormones produced by the endocrine glands 5. State the functional anatomy of the endocrine system 6. Clinical anatomy Organs of endocrine glands  Over view  The nervous system and endocrine system work together to monitor and adjust physiological activities.  In general, the nervous system performs short-term “crisis management,” and  the endocrine system regulates longer-term, on going metabolic processes. Endocrine system  Defn - is a control system of ductless glands that secrete hormones within specific organs.  made up of glands that produce and secrete hormones,  Hormones act as "messengers," and are carried by the bloodstream to different cells in the body, which interpret these messages Cont…  Hormones are chemical substance produced in the body that regulate; ◦ metabolism, ◦ growth and development, ◦ tissue function ◦ sexual function ◦ plays a part in sleep and mood cycle Cont…  The system includes all of the endocrine cells and tissues of the body.  Endocrine cells are glandular secretory cells that release hormones.  Hormones are organized into 4 groups based on chemical structure: ◦ Amino acid derivatives ◦ Peptide hormones ◦ Steroid hormones ◦ Glycoprotein hormones Cont…  hormones act on target cells with receptors for those hormones at a: ◦ distance from the site of their secretion. ◦ Or only a short distance away  glands are often also target organs for other hormones  Endocrine activity is controlled by endocrine reflexes that are triggered by:  Humoral stimuli ◦ hormones secreted in direct response to changing levels of certain chemicals in blood  Hormonal stimuli ◦ secretes several hormones that control the secretion of other endocrine glands  Neural stimuli ◦ hormones secreted due to direct nervous stimulation  hormones are carried in the blood to target cells throughout the body. Endocrine organs Cont…  Besides the specialized endocrine glands many other organs specialized for other functions, such as the; ◦ heart, thymus, gut, kidneys, testis, and ovaries,  contain various endocrine cells  Hypothalamus  Part of the brain and the pituitary gland are major sites where the nervous and endocrine systems interact.  hypothalamus regulates the secretory activity of the pituitary gland.  Indeed, the posterior pituitary is an extension of the hypothalamus.  Hormones, sensory information that enters the central nervous system, and emotions, in turn, influence the activity of the hypothalamus  Pituitary gland  or hypophysis secretes 9 major hormones that regulate: ◦ numerous body functions and ◦ the secretory activity of several other endocrine glands.  1. Pituitary Gland Structure  roughly 1cm in diameter, weighs 0.5–1.0g,  rests in the sella turcica of the sphenoid bone  located inferior to the hypothalamus  connected to it by a stalk of tissue called the infundibulum  divided functionally into two parts: ◦ posterior pituitary, or neurohypophysis ◦ anterior pituitary, or adenohypophysis Posterior Pituitary  Also called the Neurohypophysis because it is continuous with the brain  formed during embryonic development from an outgrowth of the inferior part of the brain in the area of the hypothalamus  the outgrowth of the brain forms the infundibulum,  the distal end of the infundibulum enlarges to form the posterior pituitary.  secretions of the posterior pituitary are considered neurohormones because it is an extension of the nervous system Anterior Pituitary  or Adenohypophysis  arises as an out pocketing of the roof of the embryonic oral cavity called the pituitary diverticulum or Rathke’s pouch,  which grows toward the posterior pituitary.  as it nears the posterior pituitary, the pituitary diverticulum loses its connection with the oral cavity and becomes the anterior pituitary  The anterior pituitary is subdivided into three areas with indistinct boundaries: ◦ the pars tuberalis, ◦ the pars distalis, ◦ the pars intermedia  The hormones secreted from the anterior pituitary, in contrast to those from the posterior pituitary, are not neurohormones Relationship of the Pituitary to the Brain  Portal vessels are blood vessels that begin and end in a capillary network.  hypothalamohypophysial portal system extends from a part of the hypothalamus to the anterior pituitary.  The primary capillary network in the hypothalamus is supplied with blood from arteries that deliver blood to the hypothalamus.  From the primary capillary network, the hypothalamohypophysial portal vessels carry blood to a secondary capillary network in the anterior pituitary.  Veins from the secondary capillary network eventually merge with the general circulation.  Neurohormones, produced and secreted by neurons of the hypothalamus,  enter the primary capillary network and are carried to the secondary capillary network.  Then neurohormones leave the blood and act on cells of the anterior pituitary.  act either as; ◦ releasing hormones, increasing the secretion of anterior pituitary hormones, or ◦ inhibiting hormones, decreasing the secretion of anterior pituitary hormones.  In response to the releasing hormones, ◦ anterior pituitary cells secrete hormones that enter the secondary capillary network and are carried by the general circulation to their target tissues  Thus, the hypothalamohypophysial portal system provides a means by which the hypothalamus, using neurohormones as chemical signals, ◦ regulates the secretory activity of the anterior pituitary Hypothalamic neurohormones  Growth hormone-releasing hormone (GHRH)  a small peptide that stimulates the secretion of growth hormone from the anterior pituitary gland  Growth hormone-inhibiting hormone (GHIH), also called somatostatin,  a small peptide that inhibits growth hormone secretion.  Thyroid-releasing hormone (TRH) a small peptide that stimulates the secretion of thyroid- stimulating hormone from the anterior pituitary gland.  Corticotropin-releasing hormone (CRH) ◦ a peptide that stimulates adrenocorticotropic hormone from the anterior pituitary gland.  Gonadotropin-releasing hormone (GnRH) ◦ a small peptide that stimulates luteinizing hormone and ◦ follicle-stimulating hormone from the anterior pituitary gland.  Prolactin-releasing hormone (PRH) and prolactin-inhibiting hormone (PIH) ◦ regulate the secretion of prolactin  Anterior Pituitary Hormones  master gland  secretes 6 tropic (or trophic) hormones A. Thyroid Stimulating Hormone (TSH) ◦ stimulate development and secretions from thyroid gland B. Adrenocorticotropic Hormone (ACTH) ◦ normal growth and development of adrenal cortex C. Follicle Stimulating Hormone (FSH) ◦ in women: stimulates follicle development to ovulation ◦ in men: stimulates development of seminiferous tubules and sperm cells D. Leutinizing Hormone (LH)  in women:  final maturation of follicle  stimulates formation of corpus luteum (a temorary endocrine gland of pregnancy) ◦ promotes secretion of progesterone  in men:  stimulates interstitial cells to secrete hormone = testosterone in addition to tropic hormones, Ant Pit also secretes some other (nontropic) hormones: E. Growth Hormone (GH)  promotes growth of bone and soft tissue  stimulate protein synthesis  amount of GH secreted decreases with age Hypersecretion of GH  during childhood lead to giantism  during adulthood lead to acromegaly enlargement esp of bones of hands, feet, jaws and cheeks Hyposecretion of GH  during childhood lead to dwarfism F. Prolactin (PRL; = Lactogenic Hormone)  affects female: ◦ induces breast development during pregnancy ◦ initiates milk secretion after childbirth  prolactin release is stimulated by suckling no significant functions in males Posterior Pituitary Gland  hormones released by direct nervous stimulation of posterior pituitary 1. Antidiuretic Hormone (ADH, =vasopressin)  ADH is released whenever receptors indicate dehydration ◦ i.e. decreases urine output hence conserves water 2. Oxytocin  stimulates contraction of uterine muscles during labour  causes milk ejection into ducts as result of nursing infant Pituitary Gland hormone summary  the pituitary gland, or hypophysis  Neurohypophysis (posterior lobe) ◦ ADH ◦ Oxytocin  Adenohypophysis (anterior lobe) ◦ ACTH —adrenocorticotropic hormone ◦ TSH —thyroid-stimulating hormone ◦ GH —growth hormone ◦ PRL —prolactin ◦ FSH —follicle-stimulating hormone ◦ LH —luteinizing hormone 2.Thyroid Gland  the largest endocrine gland in adults  Sits on thyroid cartilage of larynx  Butterfly-like appearance  Consists 2 main lobes connected by the isthmus  Controls metabolism  Involved in calcium homeostasis  Calcitonin Thyroid hormones A. Thyroxine (T4) and Triiodothyronine (T3)  activated by TSH from Ant Pituitary  contain Iodine atoms.  inadequate iodine in diet leads to goitre  thyroid hormones help to regulate metabolism in all cells by: ◦ increases metabolic rate & ATP production ◦ increase oxygen consumption and blood O₂ levels Cont… ◦ promotes maturation and development of the nervous system ◦ increases protein synthesis ◦ help maintain normal reproductive function  many environmental stimuli can inhibit secretions of this gland: ◦ cold temp, ◦ physical stressors, ◦ noxious stimuli Hypersecretion of Thyroid Hormones  Graves disease  up to 30% increase in Metabolic Rate increased appetite, weight loss, nervous irritability Hyposecretion of Thyroid Hormones  During growing years; ◦ cretinism, low metabolic rate, ◦ retarded growth and sexual development, often mentally retarded  As adult; ◦ Myxedema, ◦ loss of mental and physical vigor, ◦ weight gain, thickened skin. B. Calcitonin  decreases blood Ca²+  promoting bone deposition by inhibiting osteoclasts and stimulating osteoblasts  its effects are significant only in children,  negligible effect in adults Hyposecretion of Calcitonin  can cause rickets in children (but usually due to Ca²+ or Vit D deficiency) 3. Parathyroid Glands  small round bodies attached to the posterior surfaces of the thyroid gland usually 4 or 5, but varies a. Parathyroid Hormone (PTH)  helps maintain homeostasis of blood calcium  antagonist to calcitonin  raises blood Ca²+ levels: ◦ promotes Ca²+ absorption by kidney tubules and intestine ◦ stimulates osteoclasts to dissolve bone, since bone contains both calcium and phosphorus this releases both into blood  Calcium homeostasis is important in: ◦ neuromuscular function, ◦ blood clotting, ◦ synapses, ◦ to activate certain enzymes, ◦ affects cell membrane permeability  NB: surgical removal of thyroid gland requires PTH hormone replacement therapy if all parathyroids are removed at the time 4. Pancreas  both an exocrine and endocrine gland  exocrine 98% of mass of pancreas: ◦ secretes digestive enzymes  endocrine