Ch25 Endocrine


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Ch25 Endocrine

  1. 1. The Endocrine System Chapter 25
  2. 2. The Endocrine System <ul><li>A system of ductless glands that secrete hormones (‘messenger’) molecules </li></ul><ul><li>- secrete hormones directly into the blood or lymph </li></ul><ul><li>- hormones trigger physiological changes in target cells </li></ul><ul><li>Controls and integrates the functions of other body systems </li></ul><ul><li>- closely interacts with the nervous system </li></ul><ul><li>Endrocrinology </li></ul><ul><li>- the study of hormones and endocrine glands </li></ul>
  3. 3. <ul><li>Nervous System </li></ul><ul><li>Controls homeostsis rapidly </li></ul><ul><li>Anatomically continuous: </li></ul><ul><li>nerve impluse conducted along axons from one neuron to the next </li></ul><ul><li>Neurotransmitters (NTs) </li></ul><ul><li>Brief effect (muscle contraction) </li></ul><ul><li>Endocrine System </li></ul><ul><li>Controls growth and metabolism slowly </li></ul><ul><li>Scattered: </li></ul><ul><li>messenger molecules released into the EC space will immediately enter adjacent capillaries </li></ul><ul><li>Hormones (‘to excite’) </li></ul><ul><li>Longer lasting effect with feedback loops </li></ul>Together these systems interact to coordinate and integrate activity of our cells
  4. 4. Endocrine Organs <ul><li>Series of ductless glands </li></ul><ul><li>- small and scattered throughout the body </li></ul><ul><li>- some may be both endocrine and exocrine </li></ul><ul><li>‘ Pure’ endocrine glands </li></ul><ul><li>- pituitary, pineal, thyroid, parathyroid, and adrenal </li></ul><ul><li>Organs containing endocrine cells </li></ul><ul><li>- pancreas, thymus, gonads, and hypothalamus </li></ul><ul><li>Most endocrine cells are of epithelial origin </li></ul><ul><li>- others include hormone-secreting neurons, muscle cells, and fibroblast-like cells </li></ul><ul><li>Highly vascularized – blood and lymph vessels </li></ul>
  5. 5. Location of the Major Endocrine Glands <ul><li>Endocrine cells also </li></ul><ul><li>occur in the heart, </li></ul><ul><li>alimentary canal, </li></ul><ul><li>kidney, skin, placenta, </li></ul><ul><li>and elsewhere </li></ul>Fig 25.1
  6. 6. Endocrine System Overview <ul><li>Endocrine glands may be stimulated by the nervous system or chemical changes in the body </li></ul><ul><li>- respond by secreting hormones into the circulation </li></ul><ul><li>Hormones travel through the bloodstream but affect only specific tissues called target tissues </li></ul><ul><li>Hormones secreted by cells regulate the metabolic function of other cells in the body </li></ul><ul><li>- effects result from pre-programmed responses of target cells </li></ul>
  7. 7. Endocrine Functions <ul><li>Regulation of: </li></ul><ul><li>- Internal environment (adjust fluid/volume ratio): aldosterone </li></ul><ul><li>- Metabolism and energy balance: thyroid hormones </li></ul><ul><li>- Cardiac and smooth muscle contraction: epinephrine and norepinephrine </li></ul><ul><li>- Immune system: cytokines </li></ul><ul><li>- Glandular secretions: hypothalamus and pituitary hormones </li></ul><ul><li>Maintainance and assistance of: </li></ul><ul><li>- Homeostasis despite disruptions: pancreatic hormones </li></ul><ul><li>- Growth and development: growth hormones </li></ul><ul><li>- Reproduction: hormones that influence oogenesis and spermatogenesis </li></ul>
  8. 8. Classes of Hormones <ul><li>The body produces many different kinds of hormones with distinct chemical structures </li></ul><ul><li>Two broad molecular categories: </li></ul><ul><li>1. Amino acid-based hormones - modified amino acids (amines), peptides (short chains of amino acids), and proteins (long chains of amino acids) </li></ul><ul><li>2. Steroid hormones - lipid molecules derived from cholesterol </li></ul>
  9. 9. Basic Hormone Action <ul><li>Hormones circulate throughout the body in BVs </li></ul><ul><li>- leave the bloodstream at capillaries encountering all body tissues </li></ul><ul><li>- influences only specific tissue cells or target cells </li></ul><ul><li>- same hormone can have different effects on different target cells </li></ul><ul><li>- similar molecular structures can have very different functions </li></ul><ul><li>Cells have receptors on their surface that bind only specific types of hormones </li></ul><ul><li>- receptor binding initiates a response/reaction </li></ul><ul><li>- hormones are just molecular triggers and do not carry any coded information </li></ul>
  10. 10. Control of Hormone Secretion <ul><li>Secretion is triggered by three major types of stimuli: humoral, neural, and hormonal stimuli </li></ul><ul><li>Humoral (‘body fluids’) - simplest of endocrine control mechanisms </li></ul><ul><li>- secretion is in direct response to changing critical ion or nutrient levels in the blood </li></ul><ul><li>- parathyroid monitors calcium: responds to decline be secreting hormone to reverse decline </li></ul><ul><li>Neural </li></ul><ul><li>- a few glands secrete their hormones in response to stimuli by the nervous system to induce physiological changes </li></ul><ul><li>- sympathetic nerve fibers stimulate cells in the adrenal medulla </li></ul><ul><li>- induces release of epinephrine and norepinephrine </li></ul>
  11. 11. Control of Hormone Secretion <ul><li>Hormonal </li></ul><ul><li>- many endocrine glands secrete their hormones in response to hormonal stimuli received from other endocrine glands </li></ul><ul><li>- certain hormones signal secretion of other hormones </li></ul><ul><li>- the hypothalamus secretes hormones  stimulates the pituitary  stimulates other glands (the thyroid, adrenal cortex, and the gonads) </li></ul><ul><li>Note: the hypothalamus is called the master gland </li></ul><ul><li>- controls many functions of the endocrine system, through hormonal and other mechanisms </li></ul>
  12. 12. Control of Hormone Release: 3 Mechanisms Fig 25.2
  13. 13. Control of Hormone Secretion <ul><li>Always controlled by feedback loops </li></ul><ul><li>- ensures that hormone concentrations stay within a narrow ‘desirable’ range in the blood </li></ul><ul><li>Negative feedback loop: </li></ul><ul><li>- Hormonal blood concentration declines below a minimum set point more hormone is secreted </li></ul><ul><li>- Blood concentration exceeds a maximum set point hormone production is halted </li></ul><ul><li>Positive feedback loop: </li></ul><ul><li>- as blood concentrations of a certain hormone increase the response of the effector organ stimulates further secretion </li></ul><ul><li>- progression of labor in childbirth by oxytocin </li></ul>
  14. 14. The Pituitary Gland (Hypophysis) <ul><li>The pituitary gland (hypophysis - undergrowth): </li></ul><ul><li>- secretes 9 major hormone </li></ul><ul><li>- sits in the hypophyseal fossa of the sella turcica </li></ul><ul><li>- resembles a golf club: the gland forms the head of the club, and the stalk, called the infundibulum (funnel), forms the shaft </li></ul><ul><li>- the infundibulum connects superiorly to the hypothalamus </li></ul><ul><li>2 basic divisions of the pituitary gland: </li></ul><ul><li>- Anterior adenohypophysis (adeno = glandular) </li></ul><ul><li>- Posterior neurohypophysis (neuro = neural) </li></ul><ul><li>Blood supply: 2 branches of the internal carotid artery </li></ul><ul><li>- superior hypophyseal artery supplies the adenohypophysis </li></ul><ul><li>- inferior hypophyseal artery supplies the pars nervosa </li></ul>
  15. 15. The Pituitary Gland Figure 25.3a–c
  16. 16. The Adenohypophysis <ul><li>Hormone release is controlled by the hypothalamus </li></ul><ul><li>- stimulated and inhibited by releasing and inhibiting hormones </li></ul><ul><li>3 subdivisions: pars distalis, pars intermedia, pars tuberalis </li></ul><ul><li>- pars distalis the largest division has 5 different endocrine cell types </li></ul><ul><li>- secrete protein hormones, have many secretory granules and a well-developed RER and Golgi apparatus </li></ul><ul><li>Somatotropic cells </li></ul><ul><li>- secrete growth hormone (GH) </li></ul><ul><li>Mammotropic cells </li></ul><ul><li>- secrete prolactin (PRL) </li></ul>
  17. 17. Pars Distalis Endocrine Cells <ul><li>Thyrotropic cells </li></ul><ul><li>- secrete thyroid-stimulating hormone (TSH) </li></ul><ul><li>Corticotropic cells </li></ul><ul><li>- secrete adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH) </li></ul><ul><li>Gonadotropic cells </li></ul><ul><li>- secrete follicle-stimulating hormone (FSH), luteinizing hormone (LH) </li></ul><ul><li>Tropic (‘changing’) hormones – TSH, ACTH, FSH, LH </li></ul><ul><li>- regulate secretion of hormones by other endocrine glands </li></ul><ul><li>- GH, PRL, and MSH act directly on nonendocrine target tissues </li></ul><ul><li>5 cell types group into 3 categories when stained: acidophils, basophils, chromophobes </li></ul>
  18. 18. <ul><li>GH or somatotropin - stimulates growth of body tissues, especially in muscle and skeleton </li></ul><ul><li>TSH - stimulates the thyroid to produce and release T4 and T3 (influences metabolism) </li></ul><ul><li>PRL – initiates and maintains milk production (lactation) by mammary glands in the breasts </li></ul><ul><li>ACTH – influences production and secretion of hormones by the adrenal cortex (helps us deal with stress) </li></ul><ul><li>MSH - stimulates melanocytes of the epidermis to produce more melanin, thus darkening the skin </li></ul><ul><li>FSH - stimulates ova maturation and estrogen production in ovaries and sperm production in the testes </li></ul><ul><li>LH or ICSH – stimulates ovulation and progesterone secretion in ovaries and testosterone secretion in the testes </li></ul>
  19. 19. Hypothalamic Control of Hormone Secretion from the Adenohypophysis <ul><li>The hypothalamus have neurons that produce and release hormones much like NTs are released </li></ul><ul><li>- secretes releasing factors to release hormones </li></ul><ul><li>- secretes inhibiting hormones to turn off hormone secretion </li></ul><ul><li>- travels through the hypophyseal portal system into the anterior pituitary to stimulate its hormone secretion </li></ul><ul><li>- the hypophysial portal system involves two beds of capillaries connected by a vein </li></ul><ul><li>- allows a high level of hormone concentration within a small region </li></ul><ul><li>- designed so that the hormones released by the hypothalamus travel directly to the anterior pituitary </li></ul><ul><li>- in turn the anterior pituitary releases hormones into systemic circulation </li></ul>
  20. 20. Hypothalamic Control of Hormone Secretion from the Adenohypophysis Fig 25.4
  21. 21. The Neurohypophysis <ul><li>Stores and releases hormones produced by the hypothalamus </li></ul><ul><li>- structurally part of the brain </li></ul><ul><li>- composed of nervous tissue (unmyelinated axons and neuroglial cells) </li></ul><ul><li>Hormones made in the neuron cell bodies, transported along the axons, and stored in dilated axon terminals ( Herring bodies ) – secrete 2 hormones </li></ul><ul><li>- antidiuretic hormone (ADH) or vasopressin (‘vessel constrictor’): targets the kidney to resorb more water from the urine and return it to the blood </li></ul><ul><li>- secretes oxytocin induces contractions of smooth muscle of reproductive organs </li></ul>
  22. 22. The Neurohypophysis <ul><li>When the neurons </li></ul><ul><li>fire, they release </li></ul><ul><li>stored hormones </li></ul><ul><li>into a capillary bed </li></ul><ul><li>in the pars nervosa </li></ul><ul><li>for distribution </li></ul>Fig 25.5
  23. 23. Table 25.1
  24. 24. The Thyroid Gland <ul><li>Largest pure endocrine gland </li></ul><ul><li>- located in the anterior neck </li></ul><ul><li>Internally, is composed of hollow follicles </li></ul><ul><li>- separated by areolar CT rich in capillaries </li></ul><ul><li>- walls are formed of cuboidal or squamous epithelial cells (follicular cells) </li></ul><ul><li>- lying within the epithelium are parafollicular (C) cells </li></ul><ul><li>- central lumen filled with colloid (‘gluelike’) consisting of thyroglobulin (protein precursor to thyroid hormone) </li></ul><ul><li>Produces 2 hormones: amino-based and protein </li></ul><ul><li>- Thyroid hormone (TH): thyroxine (T 3 ); tri-iodothyronine (T 4 ) </li></ul><ul><li>- Calcitonin: lowers blood levels of Ca 2+ , mostly during childhood </li></ul>
  25. 25. The Thyroid Gland <ul><li>T4 and T3, consists of 2 amino acids and iodine </li></ul><ul><li>Main function is to increase metabolic rate </li></ul>Fig 25.6
  26. 26. Histology of the Thyroid Gland <ul><li>Follicle cells continuously synthesize thyroglobulin and secrete it into the follicle lumen for iodination and storage </li></ul><ul><li>TSH (pituitary gland) signals the follicle cells to release TH </li></ul>Fig 25.6
  27. 27. The Parathyroid Glands <ul><li>Lie on the posterior surface of the thyroid gland surrounded by CT capsules (number varies) </li></ul><ul><li>Contains thick branching cords composed of 2 types of endocrine cells </li></ul><ul><li>- small abundant chief cells and rare larger oxyphil cells </li></ul><ul><li>Chief cells produce a small protein hormone, PTH </li></ul><ul><li>- PTH increases calcium levels and is essential to life: </li></ul><ul><li>1) stimulates osteoclasts to release calcium from bones </li></ul><ul><li>2) decreases secretion of calcium by the kidney </li></ul><ul><li>3) activates vit D, which stimulates uptake of Ca by the intestine </li></ul>
  28. 28. The Parathyroid Glands <ul><li>Posterior view of the pharynx a </li></ul><ul><li>and trachea showing the location </li></ul><ul><li>of the parathyroid glands on the </li></ul><ul><li>posterior aspect of the thyroid </li></ul>Fig 25.7
  29. 29. Histology of the Parathyroid Gland <ul><li>The function of oxyphil (‘acid-loving’) cells is unknown </li></ul><ul><li>PTH is essential to life - low Ca 2+ levels lead to lethal neuromuscular disorders </li></ul><ul><li>What is the antagonist of PTH? </li></ul>Fig 25.7
  30. 30. The Adrenal (Suprarenal) Glands <ul><li>Paired pyramidal organs on the superior surface of the kidneys – highly vascularized </li></ul><ul><li>3 groups of 60 small suprarenal arteries supply each gland </li></ul><ul><li>- the superior suprarenal arteries from the inferior phrenic artery; </li></ul><ul><li>- middle suprarenal arteries from the aorta; </li></ul><ul><li>- inferior suprarenal arteries from the renal artery </li></ul><ul><li>Veins </li></ul><ul><li>- left suprarenal vein drains into the renal vein and the right suprarenal vein drains into the inferior vena cava </li></ul>
  31. 31. <ul><li>Nerve supply is almost entirely sympathetic fibers </li></ul><ul><li>2 endocrine glands in one - internal and external: </li></ul><ul><li>- Adrenal medulla: a cluster of neurons derived from the neural crest, acts as part of the sympathetic NS </li></ul><ul><li>- Adrenal cortex: bulk of the adrenal gland derived from mesoderm </li></ul>The Adrenal (Suprarenal) Glands
  32. 32. The Adrenal Medulla <ul><li>Part of the autonomic nervous system (Ch 15) </li></ul><ul><li>Chromaffin (‘affinity for chromium’) cells </li></ul><ul><li>- arranged in spherical clusters with some branching cords </li></ul><ul><li>- modified ganglionic sympathetic neurons </li></ul><ul><li>- secrete catecholamines: the amine hormones epinephrine and norepinephrine </li></ul><ul><li>- active in the ‘fight, flight, and fright’ (fight or flight) response </li></ul><ul><li>- hormones stored in secretory vesicles </li></ul>
  33. 33. The Adrenal Cortex <ul><li>Secretes a variety of corticosteroid hormones </li></ul><ul><li>- all are lipid-based steroids </li></ul><ul><li>Cortex is composed of 3 layers or zones: </li></ul><ul><li>- Zona glomerulosa (‘ball of yarn’): cell clusters </li></ul><ul><li>- Zona fasciculata: cells arranged in bundles </li></ul><ul><li>- Zona reticularis (‘network’): cells arranged in a branching network </li></ul>
  34. 34. The Adrenal Gland Figure 25.8a, b
  35. 35. Adrenal Corticosteroids <ul><li>2 main classes: mineralocorticoid & glucocorticoid </li></ul><ul><li>Main mineralocorticoid is aldosterone </li></ul><ul><li>- secreted by the zona glomerulosa </li></ul><ul><li>- in response to a decline in blood volume or BP </li></ul><ul><li>- prompts kidney to resorb more sodium into the blood; water passively follows, increasing blood volume </li></ul>
  36. 36. <ul><li>Glucocorticoids: cortisol is the main type </li></ul><ul><li>- secreted by zona fasciculata and zona reticularis </li></ul><ul><li>- helps the body deal with stressful situations by keeping glucose levels high to support the brain </li></ul><ul><li>- body cells switch to fats and amino acids as energy sources </li></ul><ul><li>- high amounts depress the inflammatory response </li></ul>Adrenal Corticosteroids
  37. 37. Adrenal Corticosteroids <ul><li>Hormonal pathway of stress: </li></ul><ul><li>- hypothalamus sends corticotropin-releasing hormone (CRH) </li></ul><ul><li>to the adenohypophysis, which secretes ACTH </li></ul><ul><li>- ATCH travels to the adrenal cortex to signal glucocorticoid secretions </li></ul><ul><li>- the sympathetic NS can also stimulate glucocorticoid secretions </li></ul>
  38. 38. <ul><li>Zona reticularis secretes an androgen hormone, dehydroepiandrosterone (DHEA) </li></ul><ul><li>- DHEA is converted to testosterone and estrogens in peripheral tissues </li></ul><ul><li>- proposed beneficial effects include counteracting stress, boosting immunity, and mood </li></ul>Adrenal Corticosteroids
  39. 39. Structure of Steroid-Secreting Cells <ul><li>Steroid-secreting cells have distinctive features </li></ul><ul><li>- abundant SER and no secretory granules </li></ul><ul><li>- mitochondria have unusual cristae shaped like tubes </li></ul><ul><li>- lipid droplets are abundant in cytoplasm (lipids = raw material of steroids) </li></ul><ul><li>Characterize cells of the adrenal cortex </li></ul><ul><li>- also testicular and ovarian cells which secrete steroid sex hormones: the interstitial cells, theca folliculi cells, and cells of the corpus luteum </li></ul>
  40. 40. Interstitial cell in the testis Fig 25.9
  41. 41. The Pineal Gland <ul><li>Small, pine cone shaped structure at the end of a short stalk on the roof of the diencephalon </li></ul><ul><li>Pinealocytes are arranged in both spherical clusters and branching cords </li></ul><ul><li>- star-shaped cells with long, branching cell process </li></ul><ul><li>- dense particles of calcium lie between the cell clusters, forming the ‘pineal sand’ (which is radiopaque) </li></ul><ul><li>- in Xrays used as a landmark to identify brain structures </li></ul><ul><li>- secretes melatonin: a hormone that regulates circadian rhythms (hypothalamus responds to a lack of visual input) </li></ul>
  42. 42. The Pineal Gland
  43. 43. The Pancreas <ul><li>Located in the posterior abdominal wall </li></ul><ul><li>Contains endocrine and exocrine cells </li></ul><ul><li>Exocrine acinar cells, form most of the gland </li></ul><ul><li>- secrete digestive enzymes into the small intestine </li></ul><ul><li>Endocrine cells are contained in spherical bodies </li></ul><ul><li>- pancreatic islets or islets of Langerhans </li></ul><ul><li>- about 1 million scattered among the exocrine acini </li></ul>
  44. 44. <ul><li>Main endocrine cell types: </li></ul><ul><li>- Alpha cells ( α cells): secrete glucagon signals liver to release glucose from glycogen; raises blood sugar </li></ul><ul><li>- Beta cells ( β cells): secrete insulin signals most body cells to take up glucose from the blood; promotes glucose storage as glycogen in liver; lowers blood sugar </li></ul>The Pancreas
  45. 45. Figure 25.10 A Pancreatic Islet
  46. 46. The Thymus <ul><li>Located in the lower neck and anterior thorax </li></ul><ul><li>Important immune organ </li></ul><ul><li>Site at which T-lymphocytes arise from lymphocyte-precursor cells </li></ul><ul><li>- transformation stimulated by thymic hormones, secreted by the thymus epithelial reticular cells </li></ul><ul><li>Thymic hormones – a family of peptide molecules, including thymopoietin and thymosin </li></ul>
  47. 48. The Gonads <ul><li>Main sources of sex hormone – testes and ovaries </li></ul><ul><li>Male testes </li></ul><ul><li>- interstitial cells secrete androgens (primarily testosterone) </li></ul><ul><li>- promotes the formation of sperm </li></ul><ul><li>- maintains secondary sex characteristics </li></ul>
  48. 49. <ul><li>Female ovaries </li></ul><ul><li>- androgens secreted by the theca folliculi directly converted into estrogens by the follicular granulosa cells & progesterone </li></ul><ul><li>- estrogens and progesterone secreted by the corpus luteum </li></ul><ul><li>- estrogens maintain reproductive organs and secondary sex characteristics </li></ul><ul><li>- progesterone signals uterus to prepare for pregnancy </li></ul>The Gonads
  49. 50. <ul><li>Endocrine cells occur within </li></ul><ul><li>The heart - the atria contains atrial natriuretic peptide (ANP) </li></ul><ul><li>- hormone that stimulates the kidneys to produce more urine containing salt </li></ul><ul><li>- getting rid of the excess fluid and salt reduces excess blood volume and salt levels; reduces blood pressure </li></ul><ul><li>The GI tract has scattered enteroendocrine cells </li></ul><ul><li>- release amino acid/peptide hormones chemically similar to neurotransmitters </li></ul><ul><li>- affect functions related to regulating digestion, blood chemistry, and blood flow </li></ul>Other Endocrine Structures
  50. 51. Other Endocrine Structures <ul><li>The placenta is produced when conception occurs </li></ul><ul><li>- secretes hormones that prevent the uterus from getting rid of the nutrient layer to which it is attached </li></ul><ul><li>- produces other steroid protein hormones: estrogen, progesterone, corticotropin-releasing hormone, and human chorionic gonadotropin </li></ul>
  51. 52. <ul><li>The kidneys </li></ul><ul><li>- cells of the juxtaglomerular apparatus (JGA) secrete rennin which regulates blood pressure </li></ul><ul><li>- endothelial cells and interstitial CT secrete erythropoietin which stimulates erythrocyte production </li></ul><ul><li>The skin </li></ul><ul><li>- when exposed to UV rays produces a steroid hormone precursor to vitamin D essential for calcium metabolism </li></ul>Other Endocrine Structures
  52. 53. Pituitary Disorders <ul><li>Gigantism </li></ul><ul><li>- hypersecretion of GH in children </li></ul><ul><li>Acromegaly </li></ul><ul><li>- hypersecretion in adults causes </li></ul><ul><li>Pituitary dwarfism </li></ul><ul><li>- hyposecretion of GH </li></ul><ul><li>Diabetes insipidus </li></ul><ul><li>- pars nervosa does not make enough ADH </li></ul>
  53. 54. A Closer Look Potential Uses for Growth Hormone
  54. 55. Disorders of the Pancreas <ul><li>Diabetes Mellitus </li></ul><ul><li>- caused by insufficient secretion of insulin </li></ul><ul><li>- or resistance of body cells to the effects of insulin </li></ul><ul><li>Type 1 diabetes </li></ul><ul><li>- develop suddenly, usually before age 15 </li></ul><ul><li>- T cell-mediated autoimmune response destroys β cells </li></ul>
  55. 56. Diabetes Mellitus <ul><li>Type 2 diabetes </li></ul><ul><li>- Adult onset </li></ul><ul><li>- Usually occurs after age 40 </li></ul><ul><li>- Cells have lowered sensitivity to insulin </li></ul><ul><li>- Controlled by dietary changes and regular exercise </li></ul>
  56. 57. Disorders of the Thyroid Gland <ul><li>Grave’s Disease </li></ul><ul><li>- most common type of hyperthyroidism </li></ul><ul><li>- immune system makes abnormal antibodies </li></ul><ul><li>- stimulates the oversecretion of TH by follicle cells </li></ul><ul><li>- leads to nervousness, weight loss, sweating, and rapid heart rate </li></ul><ul><li>Myxedema </li></ul><ul><li>- adult hypothyroidism </li></ul><ul><li>- antibodies attack and destroy thyroid tissue </li></ul><ul><li>- common symptoms include low metabolic rate and weight gain </li></ul>
  57. 58. Disorders of the Thyroid Gland <ul><li>Endemic goiter </li></ul><ul><li>- due to lack of iodine in the diet </li></ul><ul><li>Cretinism </li></ul><ul><li>- hypothyroidism in children </li></ul><ul><li>- short, disproportionate body, thick tongue and mental retardation </li></ul>
  58. 59. Thyroid Disorders Figure 25.11
  59. 60. Disorders of the Adrenal Cortex <ul><li>Cushing’s syndrome </li></ul><ul><li>- caused by hypersecretion of glucocorticoid hormones usually due to a pituitary tumor </li></ul><ul><li>Addison’s disease </li></ul><ul><li>- hyposecretory disorder of the adrenal cortex </li></ul><ul><li>- deficiencies of both mineralocorticoids and glucocorticoids </li></ul>
  60. 61. Thyroid Disorders Figure 25.12
  61. 62. The Endocrine System Throughout Life <ul><li>Endocrine organs operate effectively until old age </li></ul><ul><li>Adenohypophysis </li></ul><ul><li>- increase in CT and lipofuscin </li></ul><ul><li>- decrease in vascularization and number of hormone-secreting cells </li></ul><ul><li>Adrenal cortex </li></ul><ul><li>- normal rates of glucocorticoid secretion continue </li></ul><ul><li>Adrenal medulla </li></ul><ul><li>- no age-related changes in catecholamines </li></ul>
  62. 63. <ul><li>Pituitary gland – dual origin </li></ul><ul><li>- adenohypophysis originates from the roof of the mouth </li></ul><ul><li>- neurohypophysis grows inferiorly from the floor of the brain </li></ul><ul><li>Thyroid hormones </li></ul><ul><li>- decrease slightly with age </li></ul><ul><li>Parathyroid glands </li></ul><ul><li>- little change with aging </li></ul><ul><li>GH, DHEA, and the sex hormones </li></ul><ul><li>- marked drops in secretion with age </li></ul>The Endocrine System Throughout Life
  63. 64. Embryological Origin of Endocrine Organs <ul><li>Thyroid gland </li></ul><ul><li>- forms from a thickening of endoderm on the floor of the pharynx </li></ul><ul><li>Parathyroids and the thymus gland </li></ul><ul><li>- from endoderm lining the pharyngeal pouches </li></ul><ul><li>Pineal gland </li></ul><ul><li>- originates from ependymal cells </li></ul><ul><li>Adrenal gland – dual origin gland </li></ul><ul><li>- adrenal medulla from neural crest cells of nearby sympathetic trunk ganglis </li></ul><ul><li>- adrenal cortex from mesoderm lining the coelom </li></ul>
  64. 65. Embryonic Development Figure 25.13
  65. 66. Figure 25.b–d