endocrine system

• Endocrine system


  System of glands that secrete hormones directly into the bloodstream to regulate the body's metabolism and other functions
• Contents of the endocrine system

  • Definition of endocrine system
  • Hormones definition and role
  • Types of hormones
  • Chemical classes of hormones
  • Endocrine glands (pituitary, thyroid, parathyroid, adrenal, pancreas, ovaries, testes, pineal)
• Nervous system

  Transmits nerve impulses using neurotransmitters
• Endocrine system


  Transmits signals using hormones
• Hormone


  A mediator molecule that is released in one part of the body but regulates the activity of cells in other parts of the body
• Hormone secretion and action

  1. Secretory cells release hormones into interstitial fluid

  2. Hormones diffuse into blood capillaries

  3. Hormones circulate in bloodstream

  4. Hormones bind to receptors on or in target cells

  5. Hormone-receptor complex alters gene expression and cell activity
• Hormones


  • Most hormones are required in very small amounts, so circulating levels are usually low
  • Dependent on the cardiovascular system for distribution
• Endocrine glands

  • Pituitary
  • Thyroid
  • Parathyroid
  • Adrenal
  • Pineal
  • Hypothalamus
  • Thymus
  • Pancreas
  • Ovaries
  • Testes
  • Kidneys
  • Stomach
  • Liver
  • Small intestines
  • Skin
  • Heart
  • Adipose tissues
  • Placenta
• Hormone receptors


  • Only target cells for a given hormone have receptors that bind and recognize that hormone
  • Receptor number can increase (up-regulation) or decrease (down-regulation) based on hormone levels
• Hormone receptor blocking


  • RU486 (Mifepristone) binds to progesterone receptors, preventing hormone action and inducing abortion
• Circulating hormones


  Secreted by cells, pass into interstitial fluid and bloodstream, linger in blood and exert effects for minutes to hours, inactivated by liver and excreted by kidneys
• Local hormones

  • Secreted without entering bloodstream, usually inactivated quickly
  • Paracrine: act on neighboring cells
  • Autocrine: act on the same cells that secreted them
• Local hormones

  • Interleukin 2 (activates nearby immune cells and self)
  • Nitric oxide (relaxes nearby smooth muscle in blood vessels)
• Chemical classes of hormones

  • Lipid soluble (steroid, thyroid)
  • Water soluble (amine, peptide, protein, eicosanoid)
• Mechanism of lipid-soluble hormone action

  1. Diffuse to blood and interstitial fluid

  2. Enter target cell membrane

  3. Bind to and activate receptors in cytosol or nucleus

  4. Hormone-receptor complex alters gene expression

  5. New mRNA and proteins synthesized

  6. Alter cell activity and response
• Water-soluble hormones


  Cannot diffuse through lipid bilayer, bind to receptors on target cell surface
• Steroid and thyroid hormones are effective when taken orally, but peptide and protein hormones like insulin are not effective orally because they are destroyed by digestive enzymes
• Pituitary gland


  Master endocrine gland that secretes several hormones and controls other endocrine glands, located in the sella turcica of the sphenoid bone, influenced by the hypothalamus
• Anterior pituitary hormones

  • Growth hormone
  • Thyroid stimulating hormone
  • Follicle stimulating hormone
  • Luteinizing hormone
  • Prolactin
  • Adrenocorticotropic hormone
  • Melanocyte stimulating hormone
• Posterior pituitary


  Does not synthesize hormones but stores and releases oxytocin and antidiuretic hormone (vasopressin)
• Excess human growth hormone can have a diabetogenic effect, causing hyperglycemia and potentially leading to beta-cell burnout and diabetes mellitus
• Oxytocin


  Regulates blood pressure, contracts uterine smooth muscle, stimulates milk ejection in response to suckling
• Synthetic oxytocin (Pitocin) is used to induce labor, increase uterine tone, and control hemorrhage after childbirth
• Excess secretion of human growth hormone

  May cause beta-cell burnout, a greatly decreased capacity of pancreatic beta cells to synthesize and secrete insulin
• Excess secretion of human growth hormone

  May have a diabetogenic effect, causing diabetes mellitus (lack of insulin activity)
• Posterior pituitary gland


  Also known as neurohypophysis, composed of neural tissues, does not synthesize hormones but stores and releases 2 hormones
• Posterior pituitary gland


  • Consists of axons and axon terminals of more than 10,000 hypothalamic neurosecretory cells
• Oxytocin


  Hormone released by the posterior pituitary gland, targets arterioles, uterus, and breast, actions include blood pressure regulation, contraction of smooth muscle in walls of uterus, and stimulation of milk ejection after birth in response to the mechanical stimulus provided by a suckling infant
• Synthetic oxytocin (Pitocin) is given to induce labor, to increase uterine tone, and control hemorrhage just after giving birth
• Years before oxytocin was discovered, it was common practice in midwifery to let a first-born twin nurse at the mother's breast to speed the birth of the second child. This practice stimulates the release of oxytocin.
• Even after a single birth, nursing promotes expulsion of the placenta (afterbirth) and helps the uterus regain its smaller size
• Antidiuretic hormone (ADH)


  Also known as vasopressin, substance that decreases urine production from 1-2L to 20L/day, targets the kidney, acts to reabsorb water, conserve body water, decrease water loss through perspiration, and raise blood pressure by constricting arterioles
• Alcohol inhibits secretion of ADH
• Hyperpituitarism

  Overproduction of pituitary hormones: GH, ACTH and antidiuretic hormone
• Acromegaly in adults


  • Enlargement of hands and feet, coarsed facial features with furrowed brows, oligomenorrhea or amenorrhea in women, paresthesias of hands, CTS, sweating, headaches, impotence in men, diabetes mellitus, hypertension, joint pains, osteoarthritis
• Gigantism in children


  • Characterized by disproportionately long limbs
• Hypopituitarism


  Causes include pituitary adenoma, craniopharyngioma, ischemic necrosis occurring during late stage of pregnancy, Sheehan's syndrome (pituitary failure due to severe post-partum hemorrhage leading to decrease in FSH and LH)
• Signs and symptoms of hypopituitarism

  • Amenorrhea, regression of secondary sexual characteristics, infertility, dilutional hyponatremia (decrease sodium), diabetes insipidus, short stature, hypothyroidism, glucocorticoid deficiency
• Diabetes insipidus


  Excretion of large amount of dilute urine, caused by failure to synthesize or release vasopressin (pituitary diabetes insipidus) or deficiency of vasopressin receptors in the renal collecting ducts (renal/nephrogenic diabetes insipidus)
• Thyroid gland


  • Located inferior to the larynx, composed of right and left lateral lobes connected by an isthmus, normal mass 30g/1oz, made up of thyroid follicles (follicular cells)