Shaimaa Munther ENDOCRINE SYSTEM The Endocrine system Overview Two major regulatory systems make important contributions to homeostasis The nervous system and The endocrine system In order to maintain relatively constant conditions in the internal environment of the body each of the ID: 999126
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1. LEC1 Shaimaa MuntherENDOCRINE SYSTEM
2. The Endocrine systemOverview Two major regulatory systems make important contributions to homeostasis:The nervous system and The endocrine system. In order to maintain relatively constant conditions in the internal environment of the body, each of these systems influences the activity of all the other organ systems.
3. Body functions are regulated by 2 systems:
4. The Endocrine systemThe nervous system coordinates fast, precise responses, such as muscle contraction. Electrical impulses generated by this system are very rapid and of short duration (milliseconds).The endocrine system regulates metabolic activity within the cells of organs and tissues. In contrast to the nervous system, this system coordinates activities that require longer duration (hours, days) rather than speed. Examples of such activities include growth; long-term regulation of blood pressure; and coordination of menstrual cycles in females.
5. Endocrine glands are groups of cells that produce specific chemicals, called hormones, having well defined effects on body functions. Endocrine glands also, called ductless glands since their secretion is not conveyed along ducts but pass directly into blood and lymphatic vessels. Endocrine glands
6. HormonesHormones are mediators secreted From endocrine glands, which are ductless structures , released directly into the blood.They are then transported by the circulation to the tissues. The blood carries the hormones to target cells that contain specific protein receptors for the hormones, thus can respond in a specific fashion to them.
7. 1) A specific chemical substance2) Secreted by ductless gland3) In a catalytic amount (very small amounts), 4) Transported by the blood (directly or through lymphatics), To a specific target cells (which have a specific hormone receptors), 5) Where it produces: physiologic, morphologic and biochemical responses General Features of Hormones
8. Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells. A target cell responds to a hormone because it bears receptors for the hormone. Hormones affect the metabolism of their target organs and thus regulate total body metabolism, growth and reproduction. Target Cells
9. Blood vesselsEndocrine glandBiological effectReceptorTarget cell
10. Biochemical Classification of HormonesHormones are classified into three biochemical categories Steroids hormones Proteins& polypeptides hormones Aminoacids derived hormones
11. Properties of Steroid hormonesSteroid hormones are produced by the adrenal cortex, testes, ovaries, and placenta.Synthesized from cholesterol, Thus these hormones are lipid soluble (lipophilic); therefore, they cross cell membranes readily and bind to receptors found intracellularly. ( link to cell DNA & activating specific genes to initiate protein synthesis)Their lipid solubility renders them insoluble in blood, thus these hormones are transported in the blood bound to proteins.Steroid hormones are not typically preformed and stored for future use within the endocrine gland. Steroid hormones are absorbed easily by the gastrointestinal tract and therefore may be administered orally.
12. Steroid Hormones
13. Properties of Protein& Polypeptide HormonesThese hormones are preformed and stored for future use in membrane-bound secretory granules, When needed, they are released by exocytosis. Protein/peptide hormones are water soluble, circulate in the blood predominantly in an unbound form, and thus tend to have short half-lives. Because these hormones are unable to cross the cell membranes of their target tissues, they bind to receptors on the membrane surface and activating 2nd messenger which regulate other enzymes.Protein/peptide hormones cannot be administered orally because they would be digested in the gastrointestinal tract. Instead, they are usually administered by injection (e.g., insulin).Because small peptides are able to cross through mucus membranes, they may be given sublingually or intranasal. For example, Miacalcin ® , the synthetic form of the hormone calcitonin, is prepared in the form of a nasal spray.
14. Protein Hormones
15. PEPTIDE HORMONESHYPOTHALAMICPITUITARYPANREATICPARATHYROIDGIKIDNEYLIVERHEART
16. Properties of Aminoacid Derived HormonesThese are hormones derived from the amino acids tyrosine and tryptophan. They include the hormones secreted by the adrenal medulla, thyroid, e.g. catecholamines.The thyroid hormones tend to be biologically similar to the steroid hormones, They are mainly insoluble in the blood and are transported predominantly (> 99%) bound to proteins. As such, these hormones have longer half-lives (triiodothyronine, T3, = 24 h; thyroxine, T4 , = 7 days). Furthermore, thyroid hormones cross cell membranes to bind with intracellular receptors and may be administered orally (e.g., synthryoid). In contrast to steroid hormones, however, thyroid hormones have the unique property of being stored extracellularly in the thyroid gland as part of the thyroglobulin molecule.
17. PLASMA CONCENTRATION OF HORMONESUsually their level is very lawDepends on rate of secretionSome subjected to negative feedbackSome act with neuroendocrine reflexes Some subjected to diurnal rhythms
18. Some hormones act only locally, e.g.:1- Paracrine hormones, which diffuse for a short distance through the interstitial space to affect neighbouring cells. 2- Autocrine hormones, which act on the same cells. 3- Juxtacrine, whereby one cell interact with specific receptor on juxta-posed cells. Example: PGs, histamine, serotonin, bradykinin, epinephrine, acetylcholine, endorphins, encephalins, GIT hormones. Local Hormones
19. Functional classification of hormonesHormones are classified into two functional categories:Trophic hormonesNontrophic hormones
20. Trophic HormoneActs on another endocrine gland to stimulate secretion of its hormone. For example, thyrotropin, or thyroid-stimulating hormone (TSH), stimulates the secretion of thyroid hormones.Adrenocorticotropin, or adrenocorticotropic hormone (ACTH), stimulates the adrenal cortex to secrete the hormone cortisol.Gonadotropins releasing hormones ( Follicle stimulating hormone FSH & Lutilizing hormone LH)Growth hormone GHTrophic hormones are produced by the pituitary gland.The pituitary gland is sometimes referred to as the “master gland” because its hormones regulate the activity of other endocrine glands.
21. Hypothalamic Regulation of Hormonal Functions In humans, coordination of endocrine signaling relies heavily on a region of the brain called the hypothalamus. The hypothalamus receives information from nerves throughout the body and, in response, initiates endocrine signaling appropriate to environmental conditions.Signals from the hypothalamus travel to the pituitary gland, a gland located at the base of the hypothalamus. Roughly the size and shape of a lima bean. The pituitary has discrete posterior (neurohypophysis) and anterior parts ( adenohypophysis ), or lobes, which are actually two fused glands that perform very different functions.
22. Relation to the Pituitary GlandThere are neural connections between the hypothalamus and the posterior lobe of the pituitary gland and vascular connections between the hypothalamus and the anterior lobe.Some specialized neurons, particularly in the hypothalamus secrete chemical messengers into the blood rather than into a narrow synaptic cleft. In these cases, the chemical that the neurons secrete is sometimes called a neurohormoneExamples of this link:Within the hypothalamic neurosecretory cells: Some neurons delivered substances through hypothalamo-hypophyseal portal vessels to the anterior pituitary to regulate its secretions, these called regulating hormones.Other hypothalamic neurons send their axons to the posterior pituitary, where they release neurosecretory products ( NT ) directly into the blood stream.
23. Neuro-endocrine systemHypothalamic neurosecretory cells
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25. Virtually all organs of the body exhibit endocrine functionHormone Secreting Tissues I-Endocrine glandsII- Organs with endocrine functions1- Hypothalamus2- Pituitary gland3- Thyroid gland. 4- Parathyroid glands 5- Arenal glands6- Endocrine portion of the pancreas7- Primary sex organs: testes and ovaries 8- Thymus gland9- Pineal gland1- Heart 2- Kidney 3- Liver 4- Skin5- GIT6- Placenta
26. Hormone secreting glands of the endocrine system
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29. Pituitary Hormones
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35. Figure 1 : Typical motor neuron with a myelinated axon.A motor neuron is comprised of a cell body (soma) with a nucleus, several processes called dendrites, and a long fibrous axon that originates from the axon hillock. The first portion of the axon is called the initial segment. A myelin sheath forms from Schwann cells and surrounds the axon except at its ending and at the nodes of Ranvier. Terminal buttons (boutons) are located at the terminal endings.
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