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The Endocrine System - Anatomy & Physiology

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  • Difference between endocrine and exocrine glands
    Endocrine glands produce hormones released into the blood and are ductless. Exocrine glands produce non-hormonal substances like sweat and have ducts to carry secretions to membrane surfaces.
  • Three types of chemical messengers
    Hormones travel long distances in blood or lymph. Autocrines affect the same cells that secrete them. Paracrines affect nearby cells locally.
  • Two main classes of hormones by chemical composition
    1. Amino acid–based hormones (water soluble) including peptides and proteins. 2. Steroid hormones (lipid soluble) synthesized from cholesterol.
  • How do hormones affect target cells?
    Hormones alter cell activity by changing membrane permeability, stimulating enzyme synthesis, activating/deactivating enzymes, inducing secretion, or stimulating mitosis.
  • Mechanism of action for water-soluble hormones
    Bind to plasma membrane receptors, activate G protein, which activates adenylate cyclase to convert ATP to cAMP, a second messenger that activates protein kinases.
  • Mechanism of action for lipid-soluble hormones
    Diffuse into target cells, bind intracellular receptors, receptor-hormone complex enters nucleus, binds DNA, initiates transcription and protein synthesis.
  • Three stimuli that control hormone release
    1. Humoral stimulus: changes in blood levels of ions/nutrients. 2. Neural stimulus: nerve fibers stimulate hormone release. 3. Hormonal stimulus: hormones stimulate other endocrine glands.
  • What is up-regulation and down-regulation of hormone receptors?
    Up-regulation: target cells form more receptors when hormone levels are low. Down-regulation: prolonged exposure to hormone decreases receptor numbers, reducing sensitivity.
  • Types of hormone interactions at target cells
    Permissiveness: one hormone needs another to have full effect. Synergism: combined hormones have greater effect. Antagonism: one hormone opposes another.
  • Role of the hypothalamus in pituitary relationships
    Hypothalamic neurons synthesize ADH and oxytocin transported to posterior pituitary for storage and release; hypothalamus also secretes releasing/inhibiting hormones to anterior pituitary.
  • Negative vs positive feedback in hormone regulation
    Negative feedback reduces original stimulus by hormone action. Positive feedback enhances the original stimulus, e.g., oxytocin during labor.
  • Function of oxytocin
    Stimulates uterine contractions during labor and milk ejection; promotes affection and well-being feelings.
  • Function of antidiuretic hormone (ADH)
    Reduces urine production and increases urine concentration by promoting water reabsorption in kidneys.
  • Hormones secreted by the anterior pituitary
    Growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL).
  • Steps in thyroid hormone synthesis
    Follicular cells produce thyroglobulin; iodide is oxidized to iodine; iodine attaches to thyroglobulin forming MIT and DIT; MIT and DIT combine to form T3 and T4 hormones.
  • Parathyroid hormone (PTH) functions
    Increases blood calcium by activating osteoclasts, enhancing kidney calcium reabsorption, and promoting vitamin D activation for intestinal calcium absorption.
  • Zones and hormones of the adrenal cortex
    Zona glomerulosa produces mineralocorticoids (aldosterone), zona fasciculata produces glucocorticoids (cortisol), zona reticularis produces gonadocorticoids (androgens).
  • How aldosterone regulates blood pressure
    Stimulated by low blood pressure or high potassium, aldosterone increases sodium retention and potassium excretion in kidneys, raising blood volume and pressure.
  • Metabolic effects of cortisol
    Promotes gluconeogenesis, glycogenolysis, fat mobilization, and protein catabolism to increase blood glucose and fuel availability.
  • Short-term stress response hormones and effects
    Sympathetic stimulation causes adrenal medulla to release epinephrine and norepinephrine, increasing heart rate, vasoconstriction, bronchodilation, and blood glucose.
  • Long-term stress response (HPA axis)
    Hypothalamus releases CRH → anterior pituitary releases ACTH → adrenal cortex releases cortisol and aldosterone, sustaining stress response and increasing blood glucose and volume.
  • Pancreas endocrine functions
    Pancreatic islets contain alpha cells producing glucagon and beta cells producing insulin to regulate blood glucose levels.
  • Insulin effects on target tissues
    Promotes glycogenesis, lipogenesis, protein synthesis, and glucose uptake in most body cells; inhibits glycogenolysis and gluconeogenesis.
  • Glucagon effects when blood glucose is low
    Stimulates glycogenolysis, gluconeogenesis, and glucose release from the liver to raise blood glucose levels.
  • Role of the thymus in the endocrine system
    Releases thymic hormones that act as paracrines to facilitate T lymphocyte development for immune function.