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The Endocrine System

The Endocrine System. CHAPTER 10. Nervous vs. Endocrine. Both systems are different, but are also alike for the following reasons: Rely on the release of chemicals that bind to specific receptors on target cells Share various chemical messengers

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The Endocrine System

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  1. The Endocrine System CHAPTER 10

  2. Nervous vs. Endocrine • Both systems are different, but are also alike for the following reasons: • Rely on the release of chemicals that bind to specific receptors on target cells • Share various chemical messengers • E.g. norepinephrine, epinephrine are called hormones when released into the bloodstream and are neurotransmitters when released across synapses. • Primarily regulated by feedback mechanisms • Coordinate and regulate activities of other cells, tissues, organs, and systems and maintain homeostasis

  3. Overview • Endocrine cells– glandular secretory cells that release their secretions into the extracellular fluid • Hormones – chemical messengers that are released in one tissue and transported by the bloodstream to reach target cells in other tissues.

  4. Overview – Control of Endocrine Activity • Communication with other cells and tissues involves releasing chemicals into the extracellular fluid. • Communication over greater distances is handled by the nervous and endocrine systems.

  5. Overview – The Structure of Hormones • 3 groups, depending on the chemical structure: 1. Amino acid derivatives – relatively small molecules • Includes epinephrine, norepinephrine, thyroid hormones and melatonin. 2. Peptide hormones – consist of chains of amino acids • ADH, oxytocin, growth hormone, prolactin 3. Lipid derivatives – steroids and eicosanoids. • Steroid hormones: derived from cholesterol and are released from reproductive organs and the adrenal glands. • Eicosanoids: fatty acid-based compounds derived from the 20-C fatty acid arachidonic acid. Includes prostaglandins. • Prostaglandins coordinate local cellular activity and affect enzymatic processes in extra-cellular fluids

  6. Overview – The Mechanisms of Hormonal Action • Hormones alter cellular operations by changing following qualities of important enzymes and structural proteins of various target cells: • Identity • Activity • Location • Quantity • The target cell’s sensitivity is determined by the presence or absence of a specific receptor • Can be on or under the cell membrane

  7. Overview – Secretion and Distribution of Hormones • A freely-circulating hormone remains functional for anywhere from 2-60 minutes. They are inactivated* when: • 1. they diffuse out of the bloodstream and bind to receptors on target cells • 2. they are absorbed and broken down by certain liver or kidney cells • 3. they are broken down by enzymes in the plasma or interstitial fluids. *They can remain active, however, if they are assisted by special transport proteins.

  8. Overview – Control of Endocrine Activity • Endocrine activity (hormonal secretion) is controlled by at least 3negative feedback mechanisms. These are the result from liquids, hormones, and neurotransmitters: • Humoral stimuli: changes in the composition of extracellular fluid. E.g. blood calcium levels. • Hormonal stimuli: changes in the levels of circulating hormones. • Neural stimulation: result of an arriving neurotransmitter at a neuroglandular junction.

  9. The Hypothalamus’ Control • This is a primary link between the nervous and endocrine systems. • The highest level of endocrine regulation. • Coordinating centers in the hypothalamus regulate the activities of the nervous and endocrine systems in 3 ways: 1. Secretes regulatory hormones: • Releasing hormones (RH) STIMULATE PRODUCTION in the APG • Inhibiting hormones (IH) PREVENT PRODUCTION in the PPG 2. Acts as an endocrine organ by making ADH & oxytocin 3. Contains ANS centers that control the endocrine cells of adrenal medullae through sympathetic innervation.

  10. The Hypothalamus’ Pituitary Gland • AKA: HYPOPHYSIS • And it sits at the bottom of the infundibulum. • Seriously. • APG: Anterior Pituitary Gland • RH – Releasing hormones • IH – Inhibiting hormones • Hormones released by the APG control other endocrine glands • PPG: PosteriorPituitary Gland • Releases ADH and oxytocin • 9 total different hormones produced.

  11. APG • Instead of a normal capillary structure, these appear as veins. • The linking vessels between the hypothalamus and the APG are called portal vessels. • The entire system is called a portal system. • The portal system ensures all the blood entering the portal vessels reach certain target proteins before returning to general circulation. • Portal systems are named after their destinations, so this particular network is called the hypophyseal portal system. • The HPS releases either RHs, IHs, or a combo of both. • RHs released at the hypothalamus are transported directly to the APG via the HPS.

  12. APG • Produces 7 hormones: • TSH (also called thyrotropin) – to the thyroids • ACTH – to the adrenal gland • FSH – to the reproductive organs (more to the testes) • LH – to the reproductive organs (more to the ovaries) • PRL – to the breasts • GH – to the liver • MSH – to the melanocytes

  13. PPG • Posterior pituitary gland. • Releases 2 hormones: • ADH • oxytocin

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