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Introduction of Endocrinology, endocrine and endocrine hormones
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- 2. INTRODUCTION • All thephysiological activities of the body are regulated by two major systems: 1. Nervous system 2. Endocrine system. • These two systems interact with one another and regulate the body functions. Endocrine system functions by secreting some chemical substances called hormones.
- 3. CELL-TO-CELL SIGNALING • Cell-to-cellsignaling refers to the transfer of information from one cell to another. It is also called cell signaling or intercellular communication. The cells of the body communicate with each other through some chemical substances called chemical messengers.
- 4. CHEMICAL MESSENGERS • Chemicalmessengers are the substances involved in cell signaling. These messengers are mainly secreted from endocrine glands. Some chemical messengers are secreted by nerve endings and the cells of several other tissues also. • All these chemical messengers carry the message (signal) from the signaling cells (controlling cells) to the target cells. The messenger substances may be the hormones or hormonelike substances.
- 5. Classification of ChemicalMessengers • Generally the chemical messengers are classified into two types: 1. Classical hormones secreted by endocrine glands 2. Local hormones secreted from other tissues. However, recently chemical messengers are classified into four types: 1. Endocrine messengers 2. Paracrine messengers 3. Autocrine messengers 4. Neurocrine messengers.
- 6. Types • 1. EndocrineMessengers • Endocrine messengers are the classical hormones. A hormone is defined as a chemical messenger, synthesized by endocrine glands and transported by blood to the target organs or tissues (site of action). Examples are growth hormone and insulin. • 2. Paracrine Messengers • Paracrine messengers are the chemical messengers, which diffuse from the control cells to the target cells through the interstitial fluid. Some of these substances directly enter the neighboring target cells through gap junctions. Such substances are also called juxtacrine messengers or local hormones. Examples are prostaglandins and histamine
- 8. • 3. AutocrineMessengers • Autocrine messengers are the chemical messengers that control the source cells which secrete them. So, these messengers are also called intracellular chemical mediators. Examples are leukotrienes. • 4. Neurocrine or Neural Messengers • Neurocrine or neural messengers are neurotransmitters and neurohormones. • Neurotransmitter - Neurotransmitter is an endogenous signaling molecule that carries information form one nerve cell to another nerve cell or muscle or another tissue. Examples are acetylcholine and dopamine.
- 10. Neurohormone • Neurohormone isa chemical substance that is released by the nerve cell directly into the blood and transported to the distant target cells. Examples are oxytocin, antidiuretic hormone and hypothalamic releasing hormones. • Some of the chemical mediators act as more than one type of chemical messengers. For example, noradrenaline and dopamine function as classical hormones as well as neurotransmitters. Similarly, histamine acts as neurotransmitter and paracrine messenger.
- 11. ENDOCRINE GLANDS • Endocrinologyis the study of the endocrine system in the human body. Endocrine glands are the glands which synthesize and release the classical hormones into the blood. Endocrine glands are also called ductless glands because the hormones secreted by them are released directly into blood without any duct. Endocrine glands are distinct from exocrine glands which release their secretions through ducts. • Endocrine glands play an important role in homeostasis and control of various other activities in the body through their hormones. Hormones are transported by blood to target organs or tissues in different parts of the body, where the actions are executed.
- 14. CHEMISTRY OF HORMONES •Hormones are chemical messengers, synthesized by endocrine glands. Based on chemical nature, hormones are classified into three types: 1. Steroid hormones 2. Protein hormones 3. Derivatives of the amino acid called tyrosine.
- 15. STEROID HORMONES • Steroidhormones are the hormones synthesized from cholesterol or its derivatives. Steroid hormones are secreted by adrenal cortex, gonads and placenta. PROTEIN HORMONES • Protein hormones are large or small peptides. Protein hormones are secreted by pituitary gland, parathyroid glands, pancreas and placenta. TYROSINE DERIVATIVES • Two types of hormones, namely thyroid hormones and adrenal medullary hormones are derived from the amino acid tyrosine.
- 17. Pituitary Gland • Pituitarygland or hypophysis is a small endocrine gland with a diameter of 1 cm and weight of 0.5 to 1 g. It is situated in a depression called ‘sella turcica’, present in the sphenoid bone at the base of skull. It is connected with the hypothalamus by the pituitary stalk or hypophyseal stalk. DIVISIONS OF PITUITARY GLAND • Pituitary gland is divided into two divisions: 1. Anterior pituitary or adenohypophysis 2. Posterior pituitary or neurohypophysis. • Both the divisions are situated close to each other. Still both are entirely different in their development, structure and function. Between the two divisions, there is a small and relatively avascular structure called pars intermedia. Actually, it forms a part of anterior pituitary.
- 19. HORMONES SECRETED BYANTERIOR PITUITARY • Six hormones are secreted by the anterior pituitary: 1. Growth hormone (GH) or somatotropic hormone (STH) 2. Thyroid-stimulating hormone (TSH) or thyrotropic hormone 3. Adrenocorticotropic hormone (ACTH) 4. Follicle-stimulating hormone (FSH) 5. Luteinizing hormone (LH) in females or interstitial cell- stimulating hormone (ICSH) in males 6. Prolactin. Recently, the hormone β-lipotropin is found to be secreted by anterior pituitary.
- 20. • Tropic Hormones •First five hormones of anterior pituitary stimulate the other endocrine glands. Growth hormone also stimulates the secretory activity of liver and other tissues. Therefore, these five hormones are called tropic hormones. • Prolactin is concerned with milk secretion. • Gonadotropic Hormones • Follicle-stimulating hormone and the luteinizing hormone are together called gonadotropic hormones or gonadotropins because of their action on gonads.
- 21. HORMONES OF POSTERIORPITUITARY • Posterior pituitary hormones are: 1. Antidiuretic hormone (ADH) or vasopressin • 2. Oxytocin.
- 22. Key Hormones inEnergy Metabolism and Nutrient Utilization • Key Hormones in Energy Metabolism and Nutrient Utilization • 1. Insulin • Source: Pancreatic β-cells • Role: Anabolic hormone (energy storage) • Functions: • Promotes glucose uptake into muscle and adipose tissue. • Stimulates glycogen synthesis in liver and muscle. • Enhances lipid synthesis (lipogenesis) and inhibits fat breakdown (lipolysis). • Promotes protein synthesis and reduces protein breakdown.
- 23. • 2. Glucagon •Source: Pancreatic α-cells • Role: Catabolic hormone (energy release) • Functions: • Stimulates glycogenolysis (breakdown of glycogen) in the liver. • Promotes gluconeogenesis (formation of glucose from non-carbohydrates). • Increases lipolysis in adipose tissue.
- 24. • 3. Epinephrine& Norepinephrine (Catecholamines) • Source: Adrenal medulla • Role: “Fight-or-flight” response; rapid mobilization of energy • Functions: • Stimulate glycogen breakdown in liver and muscle. • Enhance lipolysis in adipose tissue. • Increase glucose release into the bloodstream.
- 25. • 4. Cortisol(Glucocorticoid) • Source: Adrenal cortex • Role: Long-term stress adaptation, catabolic • Functions: • Stimulates gluconeogenesis in the liver. • Promotes protein catabolism in muscle. • Enhances lipolysis, though also promotes fat deposition in certain areas. • Maintains glucose availability during stress or fasting.
- 26. • 5. GrowthHormone (GH) • Source: Pituitary gland • Role: Growth and energy mobilization • Functions: • Stimulates lipolysis (fat breakdown) for energy. • Reduces glucose uptake in tissues (anti-insulin effect). • Promotes protein synthesis for growth and repair.
- 27. • 6. ThyroidHormones (T3, T4) • Source: Thyroid gland • Role: Regulate basal metabolic rate (BMR) • Functions: • Increase oxygen consumption and heat production. • Stimulate carbohydrate metabolism (glycolysis and gluconeogenesis). • Enhance lipid mobilization and fatty acid oxidation. • Support protein turnover.
- 28. • 7. Leptin& Ghrelin (Appetite Regulation) • Leptin (adipose tissue): Suppresses appetite, promotes energy expenditure. • Ghrelin (stomach): Stimulates hunger and promotes energy intake.
- 29. • Integration ofHormonal Action • Fed state (after eating): Insulin dominates → glucose uptake, glycogen and fat storage, protein synthesis. • Fasting state: Glucagon, cortisol, and GH dominate → glucose production, fat and protein breakdown for energy. • Stress/Exercise: Epinephrine and norepinephrine provide quick energy by mobilizing glycogen and fat stores. • Basal metabolism: Thyroid hormones maintain energy expenditure and regulate overall nutrient utilization.
- 30. Major Endocrine Glandsand Their Hormones • Continue..