Graves' Disease Symptoms Quiz

Overview of the Endocrine System

• The endocrine system consists of glands that produce and secrete hormones that regulate various bodily functions
• The endocrine system works closely with the nervous system to maintain homeostasis

Comparison of the Nervous and Endocrine Systems

• Both systems can have similar effects on target cells (e.g. Norepinephrine and glucagon both cause glycogen hydrolysis in liver)
• The two systems can regulate each other (e.g. neurotransmitters can affect glands, and hormones can affect neurons)
• Neuroendocrine cells share characteristics with both systems (e.g. neuron-like cells that secrete oxytocin into blood)

Chemical Classes of Hormones

• Lipid-soluble hormones (e.g. progesterone, estrogen, testosterone, cortisol, and thyroxine)
  • Nonpolar and lipophilic
  • Need carrier protein in the blood
  • Can diffuse across target cell membrane
  • Their receptors are in the cytosol or nucleus
• Water-soluble hormones (e.g. peptides and catecholamines)
  • Polar and hydrophilic
  • Dissolve in the blood without help of carrier protein
  • Cannot diffuse across target cell membrane
  • Utilize G-protein coupled receptors

Pituitary Gland

• Embryonic development: derived from Rathke's pouch
• Posterior pituitary anatomy: consists of axons from the hypothalamus
• Anterior pituitary anatomy: consists of endocrine cells
• Histology of the pituitary gland: consists of chromophobes, acidophils, and basophils
• Posterior pituitary hormones:
  • Antidiuretic hormone (vasopressin): decreases urine production, stimulates thirst, constricts blood vessels
  • Oxytocin: causes uterine contraction, milk ejection, and emotional bonding
• Anterior pituitary hormones:
  • Thyrotropin-releasing hormone (TRH): promotes secretion of thyroid-stimulating hormone (TSH) and prolactin (PRL)
  • Corticotropin-releasing hormone (CRH): promotes secretion of adrenocorticotropic hormone (ACTH)
  • Gonadotropin-releasing hormone (GnRH): promotes secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
  • Growth hormone–releasing hormone (GHRH): promotes secretion of growth hormone (GH)
  • Prolactin-inhibiting hormone (PIH): inhibits secretion of prolactin (PRL)
  • Somatostatin: inhibits secretion of growth hormone (GH) and thyroid-stimulating hormone (TSH)

Thyroid Gland

• Anatomy: consists of follicular cells and parafollicular cells
• Thyroid hormone synthesis:
  • Follicular cells absorb iodide (I−) ions from blood and oxidize them to a reactive form
  • The cells also synthesize the large protein thyroglobulin (Tg) and store it in follicle lumen
  • Iodine (one or two atoms) is added to tyrosines within Tg
  • When two tyrosines within Tg meet, they link to each other forming forerunners of T3 (three iodines) and T4 (four iodines)
• Effects of thyroxine:
  • Increases metabolic rate and protein synthesis in targets
  • Stimulates synthesis of sodium-potassium pumps in neurons
  • Calorigenic: generates heat, raises temperature
  • Stimulates increased amino acid and glucose uptake
  • Increases number of cellular respiration enzymes within mitochondria
  • Fosters energy (ATP) production
• Thyroid-pituitary axis:
  • Hyperthyroidism: results from excessive production of TH (increased metabolic rate, weight loss, hyperactivity, heat intolerance)
  • Hypothyroidism: results from decreased production of TH (low metabolic rate, lethargy, cold intolerance, weight gain)
• Goiter: enlargement of thyroid visually (can be caused by hyperthyroidism or hypothyroidism)

Adrenal Glands

• Zona glomerulosa: thin, outer cortical layer (mineralocorticoids synthesized here help regulate electrolyte concentration in body fluids)
• Zona fasciculata: middle, largest layer (glucocorticoids synthesized here)
• Zona reticularis: innermost region of cortex (secrete minor amounts of sex hormones)
• Regulation and action of cortisol:
  • Hormone variables that influence blood levels of cortisol
  • Clinical view: stress response
• Addison's disease: form of adrenal insufficiency develops when adrenal glands fail (chronic shortage of glucocorticoids and sometimes mineralocorticoids)
• Cushing syndrome: chronic exposure to excessive glucocorticoid hormones