Endocrine System - Hormones, Growth & Reproduction PDF

Endocrine System – Hormones, Growth and Reproduction Part 1 - 2 Dr Pallav Sengupta Assistant Professor, Physiology www.gmu.ac.ae COLL...

Endocrine System – Hormones, Growth and Reproduction Part 1 - 2 Dr Pallav Sengupta Assistant Professor, Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Learning objectives On completion of this unit, the student will be able to: Discuss general functions of the endocrine system in the human body; Classify hormones by their chemical makeup; Describe the endocrine functions of the hypothalamus and pituitary; Discuss the hormone functions of the pancreas and adrenal glands; Describe the hormone functions of the thyroid and parathyroid glands; Discuss the hormones produced by reproductive organs; Describe other hormone sources and other chemical messengers used in control of homeostasis; and Discuss various disorders of the endocrine system.  Endocrine system Collection of specialized cells, tissues, and glands - produce and secrete circulating chemical messenger molecules -- hormones. Hormones are secreted by endocrine glands Endocrine ductless organs that secrete their products into interstitial fluid, lymph, and blood gland Exocrine secrete products such as mucus, sweat, tears, and digestive fluids into ducts that empty into glands the appropriate sites. Overview: Endocrine System Characteristics of Endocrine System Hormones of the endocrine system reach nearly every living cell. Each hormone acts only on certain cells. Endocrine control tends to be slower than nervous system control. The endocrine and nervous systems can interact with each other Classification of Hormones STEROID structurally related to cholesterol - lipid soluble. Hormones NON-STEROID structurally related to proteins - lipid insoluble Mechanism of steroid hormone action on a target cell. be able to inside If small it will go amino acid) receptors (steroid + inside cell.  Mechanism of nonsteroid hormone action on a target cell fat le + protein) on surface of cell. second , third receptors.  The Hypothalamus > - releasing hormones The hypothalamus - homeostatic control center. It is an important link between the nervous system and the endocrine system. It receives neural input about certain internal environmental conditions such as water and solute balance, temperature, and carbohydrate metabolism. (not pituitary gland is under hypothalamus. physically from "-rh"releasing hormone comes Functions: hypothalamus. Monitors and controls the hormone secretions of the pituitary gland Synthesizes releasing hormones in cell bodies of neurons Hormones are transported down the axon and stored in the nerve endings Hormones are released in pulses circadian rytumn > -. Integrates functions that maintain chemical and temperature homeostasis Functions with the limbic system  The Pituitary Gland trophic vs. local hormone Master gland which is located directly beneath it and connected to it by a thin stalk of tissue - most hormones secreted distantly located (trophic hormones) major The anterior pituitary (or adenohypophysis) is a lobe of the gland that regulates several physiological processes including stress, growth, reproduction, and lactation. > - MSH The intermediate lobe synthesizes and secretes melanocyte-stimulating 2 hormones only hormone. ADH helps concentrated - Oxytocin-Chibita milk. urine prod. (vasoprocine major The posterior pituitary (or neurohypophysis) is a lobe of the gland that is functionally connected to the hypothalamus by the median eminence via a small tube called the pituitary stalk (also called the infundibular stalk or the infundibulum).  Hypothalamic Releasing Hormones hormones. > trophic Seven releasing hormones are made in the hypothalamus - & go to pituitary snotamu – Thyrotropin-releasing hormone (TRH) Samee – Corticotropin-releasing hormone (CRH) – Gonadotropin-releasing hormone (GnRH) – Growth hormone-releasing hormone (GHRH) – Growth hormone-release inhibiting hormone (GHIH) – Prolactin-releasing factor (PRF) – Prolactin-inhibiting hormone (PIH) Hypothalamus Releasing Hormones: Secretion Is influenced by emotions Can be influenced by the metabolic state of the individual Delivered to the anterior pituitary via the hypothalamic-hypophyseal portal system Usually initiates a three-hormone sequence A ‘global’ view of Hypothalamic Pituitary Functions Releasing hormones Three Methods of Hypothalamic Control over the Endocrine System  Hypothalamic Control of the Anterior Pituitary Hormonal control mechanism Hypothalamic neurons synthesize releasing and inhibiting peptide hormones. These are transported to axon endings in the median eminence where they are secreted into the hypothalamo-hypophyseal portal system to reach receptors that regulate the secretions of anterior pituitary hormones  How does the neuroendocrine axis work? either target starts or stops secreting. Hypothalamic parvicellular neurons synthesize release- or release-inhibiting “factors” or “hormones” (peptides) Packaged in secretory granules, transported in axons to nerve terminal storage sites On demand, neurons depolarize, prompting frequency- dependent exocytosis into the median eminence capillaries of the pituitary portal vessels Transported as “hormones” to the anterior pituitary where they exit to the extracellular space Attach to specific G-protein coupled receptors on target cells, triggering exocytosis of appropriate “hormones” that seek their peripheral glandular targets Hypothalamic Releasing Hormones and Respective Anterior Pituitary Trophic Hormones HYPOTHALAMIC HORMONE EFFECTS ON THE ANTERIOR PITUITARY Thyrotropin-releasing hormone (TRH) Stimulates release of TSH (thyrotropin) and Prolactin Corticotropin-releasing hormone Stimulates release of ACTH (CRH) (corticotropin) Gonadrotropin-releasing Stimulates release of FSH and hormone (GnRH) LH (gonadotropins) Growth hormone-releasing hormone Stimulates release of growth (GHRH) hormone Growth hormone-inhibiting hormone Inhibits release of growth (GHIH) hormone Prolactin-inhibiting hormone (PIH) Stimulates release of prolactin Prolactin-inhibiting hormone (PIH) Inhibits release of prolactin  Anterior Pituitary Trophic Hormones and Their Actions gonodotrophins  Disorders of Pituitory gland GH may be secreted in excess or there can be deficiency of GH with different clinical manifestations GH abnormalities can occur both in children and adults Excess of GH: Giantism in children and Acromegaly in adults Deficiency of GH: Dwarfism in children – Rare in adults dwarfism thyroid pituariy idwig no change.  in adults Differences Between Acromegaly and Gigantism - Acromegaly Giantism Nature Excess of GH in adults when Excess of GH in children when epiphysis are closed epiphysis are ununited Major action Increase in the size of short Over growth of the long bones of and flat bones especially the limbs especially lower limb extremities Size of skull and lower jaw Prominent skull, fore head Over growth of long bones especially and overgrowth of lower jaw of lower limb Size of the Viscera Enlarged liver and heart No relative increase in size Muscle mass Increase in muscle mass Increase in bone mass Metabolic role Promotion of proteogenesis- Promotion of GIT absorption of Lipolysis and hyperglycemia Ca++ Proteogenesis, Lipolysis and Hyperglycemia Hypogonadism Absent Present usually  Thyroid and Parathyroid Gland ↑ blood calcium. calcitonin - metabolism Thyroid gland - below the larynx at the front of the trachea, and consists of two lobes The two main hormones produced by the thyroid gland - thyroxine and calcitonin. calcium ↑ blood calcium The four small parathyroid glands are embedded in the back of the thyroid. The parathyroid glands produce parathyroid hormone. Help to regulate calcium balance & role in controlling metabolism.  Thyroid Gland Produces two very similar hormones called thyroxine (T4) and triiodothyronine (T3). Thyroxine concentration increases, the basal metabolic rate (BMR) also increases. Decreasing the blood concentration of thyroxine reduces energy utilization and BMR.  Thyroid Gland Disorders Goitre- A goitre, or goiter, is a swelling in the neck resulting from an enlarged thyroid gland. The main cause is iodine deficiency Hypothroidism- Deficiency of secretion of thyroid hormones In children lack of thyroid hormones leads to stunted growth and mental retardation In adults it leads to lack of energy, dry skin and weight gain Hyperthyroidism- Increased secretion of thyroid hormone. Nervousness, irregular heart rate and weight loss The most common form of hyperthyroidism is Graves’ disease  Parathyroid hormone (PTH) Controls blood calcium levels Parathyroid hormone (PTH) : Removes calcium and phosphate from bone, Increases absorption of calcium by the digestive tract, Causes the kidneys to retain calcium and excrete phosphate.  Pancreas Both an endocrine gland (secreting hormones into the blood) and an exocrine gland (secreting enzymes, fluids, and ions into the digestive tract to aid in digestion). Endocrine cells - located in small clusters scattered throughout the pancreas called the islets of Langerhans Pancreatic islets contain three types of cells and produce 3 hormones secrete glucagon - raises Alpha cells blood sugar. secrete insulin- lowers Beta cells blood sugar. Delta cells secrete somatostatin.  Disorders of Pancreas Diabetes Type 1 diabetes - failure of pancreas to produce enough insulin - insulin-dependent diabetes - an autoimmune disorder in which the person’s own immune system attacks the insulin-producing cells in the pancreas. Type 2 diabetes (non-insulin-dependent diabetes)— cells fail to respond adequately to insulin even when it is present. Type 2 diabetes may have a genetic component, but lifestyle factors are thought to be the major determinants.  Adrenal Glands Two adrenal glands, each weighs about 4 gm lie at the superior poles of the two kidneys. Each gland is composed of two distinct parts: adrenal medulla (20%) and adrenal cortex (80%) Adrenal Cortex is related to corticoids: Glucocorticoids and Mineralocorticoids Adrenal Medulla is related functionally to sympathetic nervous system and secretes epinephrine and norepinephrine in response to sympathetic stimulation  Adrenal Cortex Zones of Adrenal gland 1) Zona glomerulosa  Outer 15% of the adrenal cortex  secrete aldosterone (mineralocorticoid)  (aldosterone synthase) mainly controlled by : a) Renin- Angiotensin system b) Plasma potassium level 2) Zona faciculata Middle 75 % of the adrenal cortex Secretes Cortisol and Corticosterone; (glucocorticoids) small amounts of adrenal androgens and estrogen  controlled by: hypothalamic-pituitary axis via ACTH 3) Zona reticularis Deep layer of the cortex secretes the adrenal androgens: dehydroepiandrosterone and androstenedione small amounts of estrogens and glucocorticoids controlled by : ACTH & cortical androgen-stimulating hormone  Adrenal Medulla Produces the nonsteroid hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) and dopamine Opioid peptides (encephalin) & adrenomedullin Play roles in metabolism and controlling blood pressure and heart activity. Other sources of NE and Dopamine Most of circulating NE come from noradrenergic Nerve ending & about ⅟₂ of circulating dopamine are from sympathetic ganglia. catacolomices  Disorders of Adrenal Gland Addison’s disease: Too little cortisol and aldosterone Lack of cortisol lowers blood glucose levels, and lack of aldosterone lowers blood sodium. chronic symptoms of fatigue, weakness, abdominal pain, weight loss, and a characteristic “bronzed” skin color. vs. > - SATH Cushing disease Cushing’s syndrome: Too much cortisol The symptoms of Cushing’s syndrome are due to the exaggerated effects of too much cortisol, including (1) excessive production of glucose from glycogen and protein (2) retention of too much salt and water.  Reproductive Hormones Reproduction is regulated by:  Gonadotrophins (FSH and LH) released by pituitary gland  Sex hormones released by the gonads (ovaries in females and testes in males) Action of gonadotrophins Regulate the function of the gonads Causes the gonads to mature during puberty and release sex hormones FSH stimulates egg and sperm production LH stimulates ovulation  Reproductive Hormones Action of gonadal hormones Androgens are primarily testosterone- the male sex hormone Testosterone regulate the development and function of male reproductive system During puberty they cause the appearance of male secondary sexual characteristics Estrogen and progesterone cause the development of female secondary sexual characteristics, regulate the menstrual cycle, prepare and maintain the uterus during pregnancy  Regulation of Reproductive Hormones In Female In Male Endocrine functions of the heart, the digestive system, and the kidneys  Learning Resources Johnson D Michael.,Human Biology, 8th edition.Pearson education limited 2017.ISBN: 978-1-292-16627-8 endocrine > - ductless (slower system be no electricity) exocrine > - duct Hormones Steroid (limited supply) from adrenal cortex & testes + ovaries) Derivatives AA (limited) Come from thyroid gland (T> Tn) adrenal mecula Peprides (numerous Proteins