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Endocrine System Anatomy & Physiology

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  • Difference between endocrine and exocrine glands

    Endocrine glands are ductless and release hormones into surrounding tissue; exocrine glands have ducts and secrete non-hormonal substances like sweat and saliva.

  • Major endocrine glands and organs
    Includes pituitary, thyroid, parathyroid, adrenal, pineal, thymus glands, hypothalamus, pancreas, and gonads (testes and ovaries).
  • Circulating vs local hormones
    Circulating hormones travel through blood to distant targets; local hormones act near the site of secretion as autocrines or paracrines.
  • Chemical classification of hormones
    Hormones are either amino acid-based (amines, peptides, proteins) or steroids (derived from cholesterol).
  • Examples of eicosanoids and their roles
    Leukotrienes (inflammation, allergy) and prostaglandins (raise blood pressure, uterine contractions, blood clotting, pain). Act locally, not true hormones.
  • Five common cellular responses to hormone stimulus
    1) Alter membrane permeability, 2) Stimulate protein synthesis, 3) Activate/deactivate enzymes, 4) Induce secretion, 5) Stimulate mitosis.
  • Mechanism of action for water-soluble hormones
    Bind to plasma membrane receptors, activate G proteins, and use second messengers to mediate cellular response.
  • Mechanism of action for lipid-soluble hormones
    Diffuse through membrane, bind intracellular receptors, and directly activate gene transcription.
  • Three major stimuli regulating hormone release
    Humoral (blood ion/nutrient levels), neural (nerve fibers stimulate glands), and hormonal (hormones stimulate other glands).
  • Example of humoral stimulus
    Low blood calcium triggers parathyroid gland to release parathyroid hormone (PTH) to increase calcium levels.
  • Example of neural stimulus
    Sympathetic nervous system stimulates adrenal medulla to release epinephrine and norepinephrine during stress.
  • Example of hormonal stimulus
    Hypothalamus releases hormones that regulate anterior pituitary hormone secretion.
  • Factors influencing target cell activation
    Blood hormone levels, number of receptors on target cells, and receptor-hormone binding affinity.
  • Up-regulation vs down-regulation of hormone receptors
    Up-regulation increases receptor number in response to low hormone levels; down-regulation decreases receptors when hormone levels are high.
  • Types of hormone interactions at target cells
    Permissiveness, synergism, and antagonism describe how hormones influence each other's effects.
  • Anatomy of the pituitary gland
    Located in sella turcica; has anterior (glandular) and posterior (neural) lobes connected to hypothalamus.
  • Hormones released by posterior pituitary
    Oxytocin and antidiuretic hormone (ADH), synthesized in hypothalamus and stored in posterior pituitary.
  • Thyroid gland location and structure
    Butterfly-shaped gland anterior to trachea, inferior to larynx; largest pure endocrine gland.
  • Main thyroid hormones and their effects
    Thyroxine (T4) and triiodothyronine (T3) regulate basal metabolic rate, growth, nervous system development, and cardiovascular function.
  • Role of parathyroid hormone (PTH)
    Increases blood calcium by stimulating osteoclasts, enhancing kidney reabsorption, and promoting intestinal absorption via vitamin D activation.
  • Adrenal gland structure and zones
    Paired glands atop kidneys; cortex has zona glomerulosa (mineralocorticoids), zona fasciculata (glucocorticoids), zona reticularis (gonadocorticoids); medulla produces catecholamines.
  • Functions of adrenal cortex hormones
    Mineralocorticoids regulate sodium and potassium; glucocorticoids promote glucose production and stress resistance; gonadocorticoids influence sex characteristics.
  • Adrenal medulla hormones and effects
    Epinephrine and norepinephrine increase heart rate, blood pressure, and metabolic rate during fight-or-flight response.
  • Pancreas endocrine function
    Islets of Langerhans produce glucagon (raises blood glucose) and insulin (lowers blood glucose).
  • Glucagon's main action
    Stimulates liver to break down glycogen and produce glucose, raising blood glucose levels.
  • Insulin's main action
    Promotes glucose uptake by cells, glycogen formation, and lowers blood glucose levels.
  • Female gonadal hormones and roles
    Estrogens promote secondary sex characteristics and uterine cycle; progesterone maintains pregnancy and prepares mammary glands.
  • Male gonadal hormone and role
    Testosterone promotes reproductive system maturation, secondary sex characteristics, and libido.
  • Pineal gland function
    Secretes melatonin regulating circadian rhythms and may prevent early sexual maturation.