Lec1 Introduction to Endocrinology PDF

College of Medicine Dr. Firas Al-Masoody Second stage Endocrinology Lecture 1 Introduction to Endocrinology Learning objectives: 1. Define key terms: hormone, target organ (tissue), endocrine, neuroendocrine, paracrine, autocrine,...

College of Medicine Dr. Firas Al-Masoody Second stage Endocrinology Lecture 1 Introduction to Endocrinology Learning objectives: 1. Define key terms: hormone, target organ (tissue), endocrine, neuroendocrine, paracrine, autocrine, cytokines, and adipokines. 2. Discuss the difference between endocrine and exocrine glands. 3. Explain the role of hormones in coordinating body functions. 4. Identify the major functions of hormones. 5. Describe the properties of hormones. 6. Recognize the different chemical classes of hormones. 7. Analyze the factors that influence the magnitude of a hormonal response. Introduction Hormone: the Greek root, hormon, means sets in motion “execute or arouse" - ⑤ A hormone is defined as a chemical substance, synthesized by a specific organ(s) or tissue, and usually secreted into the blood stream, and has specific regulatory effect on a target cell or organ. Target organ “tissue”: Organ or tissue specifically affected by the action of a hormone. The target organ must have specific receptors for hormones. Figure below shows the anatomical loci of the major endocrine glands and endocrine tissues of the body, except for the placenta, which is an additional source of the sex hormones. The multiple hormone systems play a key role in regulating - almost all body functions, including metabolism, growth and development, water and - - & electrolyte - balance, reproduction, - and behavior. mood/ For example, without growth hormone, a person - would have very short stature. - Without thyroxine and triiodothyronine from the -- - - thyroid gland, almost all the chemical reactions of - the body would become sluggish, and the person - would become sluggish as well. - Without insulin from the pancreas, the body’s cells - could use - little of the food carbohydrates for e energy. And without the sex hormones, sexual - - development and sexual functions would be absent. - 1 M Difference between exocrine and endocrine glands - Two principal types of glands exist: exocrine and endocrine. The key difference between the two · types is that exocrine glands secrete substances into a ductal system to an epithelial surface, - while endocrine glands secrete products directly into the bloodstream. COORDINATION OF BODY FUNCTIONS BY CHEMICAL MESSENGERS The multiple activities of the cells, tissues, and organs of the body are coordinated by the interplay of several types of chemical messenger systems: 1. Neurotransmitters are released by axon terminals of neurons into the synaptic - junctions and act locally to control nerve cell functions 2. Endocrine hormones are released by glands or specialized cells into the circulating blood and influence the function of target cells at another location in the body. E.g. - FSH and LH, secreted by the anterior pituitary, and act on the ovaries and testes. - - - 3. Neuroendocrine hormones are secreted by neurons into the circulating blood and - influence the function of target cells at another location in the body. E.g. antidiuretic - - hormone (ADH) and oxytocin, secreted from the nerve endings into the systemic - circulation and act on target tissues. 2  4. Paracrines hormones are secreted by cells into the extracellular fluid and affect neighboring target cells of a different type in the same tissue. E.g. estrogen produced in the ovaries are crucial for the maturation of ovarian follicles. 5. Autocrines are secreted by cells into the extracellular fluid and affect the function of the same cells that produced them. E.g. IGF-1 produced mainly in the liver and acts as - endocrine (as well as paracrine and autocrine). & gu 6. Cytokines are peptides secreted by cells into the extracellular fluid and can function as autocrine, paracrine, or endocrine hormones. Examples of cytokines include the interleukins and other lymphokines that are secreted by helper cells and act on other g & - cells of the immune system. Cytokine hormones (e.g., leptin) produced by adipocytes & are sometimes called adipokines. - MCQg The function of the nervous system, endocrine system and other chemical messenger system are coordinated with one another to maintain homeostasis. & For example, A significant decrease in the circulating blood volume is sensed by: - baroreceptors, the cardiac atria, the kidney, and the brain. - - - - To restore blood volume, the sympathetic nervous system, a neurohormone from the posterior pituitary gland (ADH) and hormones from the cardiac atria and ventricles, the adrenal medulla, the adrenal cortex, and the kidneys act on target cells in blood vessels and kidneys. 3 Another example, the adrenal medullae and the pituitary gland secrete their hormones primarily in response to neural stimuli. The neuroendocrine cells, located in the hypothalamus, have axons that terminate in the posterior pituitary gland and median eminence and secrete several neurohormones, including ADH, oxytocin, and hypophysiotropic hormones, which control the secretion of anterior pituitary hormones. Comparison Between Nervous System and Endocrine System XePinePhnee and Nervous system Endocrine system ❑ Wired ❑ Wireless norepinephrem ❑ Rapid ❑ Slow second5 ❑ Brief duration ❑ Long duration * growth Hormony ↑ 91 j22's - - ❑ Close anatomical proximity ❑ Specific receptors on distant action"I - - -organs Functions of Hormones 1. Control of Reproduction Youad Hormone Regulation of menstrual cycle, ovulation, pregnancy, lactation, and spermatogenesis. 2. Regulation of Growth and development third Hormone Stimulation of Growth in children and adolescents, sexual differentiation, secondary sexual characteristics, growth velocity). · 3. Maintenance of internal balance “homeostasis” Maintaining extracellular fluid volume, blood pressure, regulation of plasma ions e.g. Calcium. third insulin glucagon , , 4. Control of metabolism Regulation of blood glucose levels (insulin and glucagon 5. Regulation of the Immune System cytosine chortisole , 6. Energy flux Lipton Energy storage, distribution, and consumption of calories, heat production. 7. Control of Behavior- Regulation of mood, sleep, food and water intake, sexual behavior. - 8. Regulation of the cardiovascular system ateral mortic Peptid , epinphrien morepine , 9. Mineral and electrolytes balance. ADH others Panathird , , , Caligum. 4  Qu Properties of Hormones % 1. Hormones may be secreted by one gland (such as thyroid hormones) or by more than one gland (estrogen is produced by the ovary and placenta). 2. Some endocrine hormones affect many types of cells of the body (e.g. growth hormone & thyroxine), while other hormones affect a specific target tissue (e.g. For ACTH example, adrenocorticotropic hormone from the anterior pituitary gland specifically McQ - stimulates the adrenal cortex) - 3. Hormones act on a very specific receptor (Lock & Key) 4. Most hormones are released from their glands in short bursts (pulses) except thyroid - - hormones. Cortisol - or sex hormones 5. Hormones produce their physiological effect by a very low concentration in blood. 6. Each of the different hormones has its own characteristic onset and duration of - action, some hormones, such as norepinephrine and epinephrine, are secreted within & seconds after the gland is stimulated and may develop full action within another few seconds to minutes; the actions of other hormones, such as thyroxine or growth - hormone, may require months for full effect. I - Chemical Structure of Hormones 1. Polypeptides and Proteins Hormones: most hormones in the body belong to this most & Body type. Example, hormones secreted by the anterior & posterior pituitary gland, the - pancreas (insulin and glucagon), parathyroid gland (parathyroid hormone), and endoplacin many others. Peptide Hormones are Stored in Secretory Vesicles Until Needed. 2. Steroids Hormones: Secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and - progesterone), the testes (testosterone), and the placenta (estrogen and progesterone). Steroid Hormones Are Usually Synthesized from Cholesterol and Are Not Stored. 3. Amine Hormones (derivatives of the amino acid tyrosine): Secreted by the thyroid gland (Thyroxine & triiodothyronine), and the adrenal medullae - (epinephrine & norepinephrine). 5  Package &9.25 %* Hormone& - Golgi uppentS. Properties of Different Chemical Classes of Hormones Hormone characteristic Peptide Hormones Steroid Hormones BroWater soluble Yes No Need a carrier protein No Yes Stored in secretory vesicles Yes, secreted by No, secreted by diffusion prior to secretion exocytosis Site of receptor at target cell Plasma membrane Intracellular Mechanism of action Mainly Second Mainly altered gene expression messenger - I b >/ Speed and duration of action Usually fast onset but Usually, slow onset but long-lasting response short-acting response The amines have variable characteristics: Catecholamines act like peptide H., while uc & e thyroid H. act like steroid H. Transport of Hormones in the Blood Water-soluble hormones (peptides and catecholamines) – dissolved in the plasma, diffusion from capillaries ⇉ interstitial fluid ⇉ target cells. Lipid soluble (steroid hormones and thyroid hormones) – circulate in the blood & - mainly bound to plasma proteins (