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ZOOLOGY — DSE 1A ENDOCRINOLOGY AND REPRODUCTON, , UNIT -I, HUMAN ENDOCRINE SYSTEM, , , , , , , , , , The endocrine system is a network of glands and organs located throughout the body. It’s similar to, the nervous system in that it plays a vital role in controlling and regulating many of the body’s functions., However, while the nervous system uses nerve impulses and neurotransmitters for communication,, , the endocrine system uses chemical messengers called hormones., , Hormones are special chemical messengers constantly present in circulation. The organ/tissue on, which the hormone acts is known as target organ. The study of hormones secreted by specialized, , glands that are ductless is known as endocrine glands., , Hormones are conventionally defined as organic substances, produced in small amounts by specific, tissues (of endocrine glands), secreted into the blood stream to control the metabolic and biological, , activities in the target cells., , ROLE OF ENDOCRINE GLANDS:, , 1. Endocrine glands release hormones into the bloodstream. This lets the hormones travel to cells, , in other parts of the body., , 2. The endocrine hormones help control mood, growth and development, the way our organs, , work, metabolism, and reproduction., , 3. The endocrine system regulates quantity of hormone is released. This can depend on levels of, , hormones already in the blood, or on levels of other substances in the blood, like calcium., , , , LEO ANTHONY, T. / BGS FIRST GRADE COLLEGE, MYSURU-23 / 2021-22, , OCULNIEU WILET COLNOC

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ZOOLOGY — DSE 1A ENDOCRINOLOGY AND REPRODUCTON, , CONCEPTS OF AUTOCRINE, PARACRINE, AND ENDOCRINE SECRETIONS:, , AUTOCRINE:, @%~,, ee e, Autocrines are chemical signals produced by the cell and influences the —s, activity of the cell itself. Autocrine action, , An example of an autocrine agent is the cytokine interleukin-1 in monocytes. When interleukin-1 is, , produced in response to external stimuli, it can bind to cell-surface receptors on the same cell that, , produced it., , , , PARACRINE:, a, Paracrines are chemical signals produced by a cell and diffuse ¥ _, ., e o, in the surrounding area and act on the cells in the vicinity, Paracrine action Nearby cell, , without entering circulation., , Somatostatin which regulates the secretion of insulin and glucagon in pancreas is a classic example, , for paracrine., , ENDOCRINE:, , In endocrine signaling, the signaling molecules (hormones) are secreted by specialized endocrine, , cells and carried through the circulation to act on target cells at distant body sites., , A classic example is provided by the steroid hormone oestrogen, which is produced by the ovary and, stimulates development and maintenance of the female reproductive system and secondary sex, , characteristics., , , , e*, o> a, -* Circulation, Endocrine action Distant cell, , , , LEO ANTHONY, T. / BGS FIRST GRADE COLLEGE, MYSURU-23 / 2021-22, , OCULNIEU WILET COLNOC

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ZOOLOGY — DSE 1A ENDOCRINOLOGY AND REPRODUCTON, , TYPES OF HORMONES:, , Hormones can be categorised into three distinct groups according to their chemical composition., The three types of hormones are steroid hormones, peptide hormones and amino acid derivatives., The different types of hormones will have different mechanisms of action due to their distinct chemical, , properties, STEROID HORMONES:, , 1. Steroid hormones are lipophilic (fat-loving) — meaning they can freely diffuse across the, , plasma membrane of a cell., , 2. They bind to receptors in either the cytoplasm or nucleus of the target cell, to form an active, receptor-hormone complex., , 3. This activated complex will move into the nucleus and bind directly to DNA, acting as a, transcription factor for gene expression., , 4. Examples of steroid hormones include those produced by the gonads (i.e., oestrogen,, , progesterone and testosterone)., , CYTOPLASM, , steroid, receptor, , Hormone-receptor complex, , , , , , LEO ANTHONY, T. / BGS FIRST GRADE COLLEGE, MYSURU-23 / 2021-22, , OCULNIEU WILET COLNOC

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ZOOLOGY — DSE 1A ENDOCRINOLOGY AND REPRODUCTON, , PEPTIDE HORMONES:, , 1. Peptide hormones are hydrophilic and lipophobic (fat-hating) — meaning they cannot freely, cross the plasma membrane., , 2. They bind to receptors on the surface of the cell, which are typically coupled to internally, anchored proteins (e.g. G proteins)., , 3. The receptor complex activates a series of intracellular molecules called second messengers,, which initiate cell activity., , 4. This process is called signal transduction, because the external signal (hormone) is transduced, via internal intermediaries., , 5. Examples of second messengers include cyclic AMP (cAMP), Calcium ions (Ca**), Nitric, oxide (NO) and protein kinases. The use of second messengers enables the amplification of, the initial signal (as more molecules are activated)., , 6. Peptide hormones include insulin, glucagon, leptin, ADH and oxytocin., , CYTOPLASM, , Signal Transduction, , Number of molecules activated, , , , , , LEO ANTHONY, T. / BGS FIRST GRADE COLLEGE, MYSURU-23 / 2021-22, , OCULNIEU WILET COLNOC

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ZOOLOGY - DSE 1A ENDOCRINOLOGY AND REPRODUCTON, , AMINE HORMONES:, , 1. Amine hormones are derived from the amino acid tyrosine and include adrenaline, thyroxin, and triiodothyronine., , 2. Amine hormones do not all share identical properties and have properties common to both, , peptide and steroid hormones., , SUMMARY OF DIFFERENT CLASSES OF HORMONES:, , Steroid Amino acid derivative, , Synthesised as prohormones,, ey Tn rt ey requiring further processing, (e.g. cleavage) to activate, , ene Stored in vesicles Released immediately Stored before release, e (regulatory secretion) (constitutive secretion) (storage mechanism varies), Pa Most are polar and water soluble, | Generally non-polar and require Some are polar (adrenaline),, i can travel freely in the blood carrier proteins to travel in blood others must be protein-bound, , Synthesised in a series of Synthesised from the, reactions from cholesterol amino acid tyrosine, , Bind receptors on cell membrane Adrenaline acts on membrane, f Bind to intracellular receptors to, totale) cele) and transduce signal via the use change gene expression directly receptors, while thyroid hormones, of second messenger systems Bes P act directly on nuclear receptors, , Often fast onset transient changes Alterations in gene expression; Adrenaline functions like peptides,, in protein activity, though gene slower onset but longer duration thyroid hormones function ina, expression changes can occur than peptide hormones similar manner to steroids, , ene Insulin, glucagon, prolactin, ACTH, | Cortisol, aldosterone, estrogen, Adrenaline, thyroxin,, gastrin parathyroid hormone progesterone, testosterone triiodothyronine, , , , ROLE OF HORMONES IN HOMEOSTASIS:, , Homeostasis is the regulation of the internal conditions within cells and whole organisms such as, temperature, water, and sugar levels. Hormones are responsible for key homeostatic processes, , including Control of blood glucose levels and Control of blood pressure., , , , LEO ANTHONY, T. / BGS FIRST GRADE COLLEGE, MYSURU-23 / 2021-22, , OCULNIEU WILET COLNOC