1 / 94

Chapter 7

Chapter 7. The Endocrine System. About this Chapter. Expand on integration of chemical and nervous coordination Form and function of key endocrine glands Classification, structure and synthesis of hormones Pathways of nervous to endocrine regulation How target cells/tissues are impacted

rebeccafreeman
Download Presentation

Chapter 7

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 7 The Endocrine System

  2. About this Chapter • Expand on integration of chemical and nervous coordination • Form and function of key endocrine glands • Classification, structure and synthesis of hormones • Pathways of nervous to endocrine regulation • How target cells/tissues are impacted • Some pathologies of the endocrine system

  3. Summary of the Endocrine System Figure 7-2-1: ANATOMY SUMMARY: Hormones

  4. Summary of the Endocrine System Figure 7-2-2: ANATOMY SUMMARY: Hormones

  5. Summary of the Endocrine System Figure 7-2-3: ANATOMY SUMMARY: Hormones

  6. Mechanism of Hormone Action • Hormones produce one or more of the following cellular changes in target cells • Alter plasma membrane permeability • Stimulate protein synthesis • Activate or deactivate enzyme systems • Induce secretory activity • Stimulate mitosis

  7. Chemical Regulating Systems: Overview • Pheromones: organism to organism communication • Hormones: cell to cell communication molecules • Made in gland(s) or cells • Transported by blood • Distant target tissue receptors • Activates physiological response

  8. Protein and Polypeptide Hormones: Synthesis and Release Figure 7-3: Peptide hormone synthesis, packaging, and release

  9. Hormones • Three types • Proteins • Glycoproteins • Small peptides • Large proteins • Lipids • Cholesterol derivatives • Eicosanoids • Amino acid derivatives (Amine Hormones)

  10. Protein and Polypeptide Hormone Receptors • Surface receptor • Hormone binds • Transduction • Enzyme activation • Open channels • Second messenger systems • Synthesis Figure 7-5: Membrane receptors for peptide hormones

  11. Amine Hormone Structures and Functions • Made of 1-2 amino acids, derived from tyrosine or tryptophan • Receptors • Surface • Intracellular • Small size, OH group • Benzine ring • Examples • Thyroxin • Epinephrine

  12. Amine Hormone Structures and Functions Figure 7-8: Tyrosine-derived amine hormones

  13. Steroid Hormones: Structure and Action • From cholesterol, lipophilic, enter target cell, • Cytoplasmic or nuclear receptors (mostly) • Activate DNA for protein synthesis • Slower acting, longer half-life • Examples: cortisol, estrogen & testosterone

  14. Steroid Hormones • Steroid hormones and thyroid hormone diffuse easily into their target cells • Once inside, they bind and activate a specific intracellular receptor • The hormone-receptor complex travels to the nucleus and binds a DNA-associated receptor protein • This interaction prompts DNA transcription to produce mRNA • The mRNA is translated into proteins, which bring about a cellular effect

  15. Steroid Hormones: Structure and Action Figure 7-7: Steroid hormone action

  16. Steroid Hormones: Structure and Action Figure 7-6: Steroid hormones are derived from cholesterol

  17. Target Cell Specificity • Hormones circulate to all tissues but only activate cells referred to as target cells • Target cells must have specific receptors to which the hormone binds • These receptors may be intracellular or located on the plasma membrane

  18. Target Cell Activation • Target cell activation depends on three factors • Blood levels of the hormone • Relative number of receptors on the target cell • The affinity of those receptors for the hormone • Up-regulation – target cells form more receptors in response to the hormone • Down-regulation – target cells lose receptors in response to the hormone

  19. Hormone Concentrations in the Blood • Hormones circulate in the blood in two forms – free or bound • Steroids and thyroid hormone are attached to plasma proteins • All others are unencumbered

  20. Hormone Concentrations in the Blood • Concentrations of circulating hormone reflect: • Rate of release • Speed of inactivation and removal from the body • Hormones are removed from the blood by: • Degrading enzymes • The kidneys • Liver enzyme systems

  21. Control of Hormone Release • Blood levels of hormones: • Are controlled by negative feedback systems • Vary only within a narrow desirable range • Hormones are synthesized and released in response to humoral, neural, and hormonal stimuli

  22. Endocrine Reflex Pathways: Overview • Stimulus • Afferent signal • Integration • Efferent signal (the hormone) • Physiological action • Negative feedback

  23. Multiple Stimuli for Hormone Release: Nervous & Endocrine • Stimuli • Stretch • Glucose • Insulin levels • Reflex • Lower blood glucose • Reduces stimulus • Reduces insulin release

  24. Endocrine Reflex Pathways: Overview Figure 7-9: Hormones may have multiple stimuli for their release

  25. Neurohormones: secreted into the Blood by Neurons • Adrenal Medulla–catecholamines • Hypothalamus to: • Anterior pituitary • Trophic Hs • Growth H. • Prolactin • Posterior pituitary • Vasopressin • Oxytocin

  26. Neurohormones: secreted into the Blood by Neurons Figure 7-12: Synthesis, storage, and release of posterior pituitary hormones

  27. Pituitary-Hypothalamic Relationships: Posterior Lobe • The posterior lobe is a downgrowth of hypothalamic neural tissue • Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract) • Nuclei of the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH) • These hormones are transported to the posterior pituitary

  28. Major Endocrine Organs: Pituitary (Hypophysis) Figure 16.5

  29. The Posterior Pituitary and Hypothalamic Hormones • Posterior pituitary – made of axons of hypothalamic neurons, stores antidiuretic hormone (ADH) and oxytocin • ADH and oxytocin are synthesized in the hypothalamus • ADH influences water balance • Oxytocin stimulates smooth muscle contraction in breasts and uterus • Both use PIP-calcium second-messenger mechanism

  30. Oxytocin • Oxytocin is a strong stimulant of uterine contraction • Regulated by a positive feedback mechanism to oxytocin in the blood • This leads to increased intensity of uterine contractions, ending in birth • Oxytocin triggers milk ejection (“letdown” reflex) in women producing milk

  31. Oxytocin • Synthetic and natural oxytocic drugs are used to induce or hasten labor • Plays a role in sexual arousal and satisfaction in males and nonlactating females

  32. Antidiuretic Hormone (ADH) • ADH helps to avoid dehydration or water overload • Prevents urine formation • Osmoreceptors monitor the solute concentration of the blood • With high solutes, ADH is synthesized and released, thus preserving water • With low solutes, ADH is not released, thus causing water loss from the body • Alcohol inhibits ADH release and causes copious urine output

  33. Pituitary-Hypothalamic Relationships: Anterior Lobe • The anterior lobe of the pituitary is an outpocketing of the oral mucosa • There is no direct neural contact with the hypothalamus

  34. Endocrine Control: Three Levels of Integration Figure 7-13: Hormones of the hypothalamic-anterior pituitary pathway

  35. Adenohypophyseal Hormones • The six hormones of the adenohypophysis: • Are abbreviated as GH, TSH, ACTH, FSH, LH, and PRL • Regulate the activity of other endocrine glands • In addition, pro-opiomelanocortin (POMC): • Has been isolated from the pituitary • Is enzymatically split into ACTH, beta endorphin, and several Melanocyte Stimulating Hormones and Lipotropins

  36. Diagram of the POMC Gene • Pro-opiomelanocortin (POMC) is a precursor polypeptide with 241 amino acid residues. POMC is synthesized from the 285-amino-acid-long polypeptide precursor pre-pro-opiomelanocortin (pre-POMC), by the removal of a 44-amino-acid-long signal peptide sequence during translation.

  37. Activity of the Adenohypophysis • The hypothalamus sends a chemical stimulus to the anterior pituitary • Releasing hormones stimulate the synthesis and release of hormones • Inhibiting hormones shut off the synthesis and release of hormones

  38. Activity of the Anterior Pituitary (Adenophypophysis) • The tropic hormones that are released are: • Thyroid-stimulating hormone (TSH), Thyrotropin • Adrenocorticotropic hormone (ACTH), Corticotropin • Follicle-stimulating hormone (FSH), a Gonadotropin • Luteinizing hormone (LH), a Gonadotropin • Growth Hormone (GH), Somatotropin

  39. Endocrine Control: Three Levels of Integration • Hypothalamic stimulation–from CNS • Pituitary stimulation–from hypothalamic trophic Hs • Endocrine gland stimulation–from pituitary trophic Hs

  40. Negative Feedback Controls: Long & Short Loop Reflexes Figure 7-14: Negative feedback loops in the hypothalamicanterior pituitary pathway

  41. Negative Feedback Controls: Long & Short Loop Reflexes Figure 7-15: Control pathway for cortisol secretion

  42. Thyroid Gland • The largest endocrine gland, located in the anterior neck, consists of two lateral lobes connected by a median tissue mass called the isthmus • Composed of follicles that produce the glycoprotein thyroglobulin • Colloid (thyroglobulin + iodine) fills the lumen of the follicles and is the precursor of thyroid hormone • Other endocrine cells, the parafollicular cells, produce the hormone calcitonin

  43. Thyroid Gland Figure 16.7

  44. Thyroid Hormone • Thyroid hormone – the body’s major metabolic hormone • Consists of two closely related iodine-containing compounds • T4 – thyroxine; has two tyrosine molecules plus four bound iodine atoms • T3 – triiodothyronine; has two tyrosines with three bound iodine atoms

  45. Effects of Thyroid Hormone • TH is concerned with: • Glucose oxidation • Increasing metabolic rate • Heat production • TH plays a role in: • Maintaining blood pressure • Regulating tissue growth • Developing skeletal and nervous systems • Maturation and reproductive capabilities

  46. Synthesis of Thyroid Hormone • Thyroglobulin is synthesized and discharged into the lumen • Iodides (I–) are actively taken into the cell, oxidized to iodine (I2), and released into the lumen • Iodine attaches to tyrosine, mediated by peroxidase enzymes, forming T1 (monoiodotyrosine, or MIT), and T2 (diiodotyrosine, or DIT) • Iodinated tyrosines link together to form T3 and T4 • Colloid is then endocytosed and combined with a lysosome, where T3 and T4 are cleaved and diffuse into the bloodstream

  47. Synthesis of Thyroid Hormone Figure 16.8

  48. Transport and Regulation of TH • T4 and T3 bind to thyroxine-binding globulins (TBGs) produced by the liver • Both bind to target receptors, but T3 is ten times more active than T4 • Peripheral tissues convert T4 to T3 • Mechanisms of activity are similar to steroids • Regulation is by negative feedback • Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback

More Related