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Endocrine System and Hormonal Regulation - Anatomy & Physiology

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  • What is the primary function of the endocrine system?

    The endocrine system controls the body via hormones released into the bloodstream, regulating metabolic functions with prolonged effects.

  • Name the major endocrine glands and their locations.

    Pituitary: base of brain in sella turcica
    Thyroid: neck below larynx
    Parathyroid: posterior thyroid
    Adrenal: atop kidneys
    Pineal: epithalamus of brain

  • What are autocrine and paracrine signals?

    Autocrine: act on same cell that secretes them
    Paracrine: act on nearby cells
    Neither are hormones as they do not travel via bloodstream.

  • What are the two main chemical classes of hormones?

    Amino acid-based hormones: amines, peptides, proteins
    Steroid hormones: derived from cholesterol, including gonadal and adrenocortical hormones.

  • How do amino acid-based hormones typically exert their effects?

    They bind to plasma membrane receptors and use second messenger systems like cAMP to activate intracellular enzymes.

  • How do steroid hormones act on target cells?

    Steroid hormones enter cells and bind to intracellular receptors, directly activating gene transcription and protein synthesis.

  • List the cellular changes hormones can induce in target cells.

    Alter membrane permeability, stimulate protein synthesis, activate/deactivate enzymes, induce secretion, and stimulate mitosis.

  • Describe the simplified steps of amino acid-based hormone action using cAMP.

    1. Hormone binds receptor
    2. G protein activated
    3. Adenylate cyclase activated
    4. cAMP produced
    5. Protein kinases activated
    6. Cellular response occurs.

  • What determines target cell specificity for hormones?

    Presence of specific receptors on/in target cells, hormone blood levels, receptor number, and receptor affinity.

  • What is up-regulation and down-regulation of hormone receptors?

    Up-regulation: target cells increase receptor numbers
    Down-regulation: target cells decrease receptors, often due to high hormone levels.

  • How are steroid and thyroid hormones transported in the blood?

    They bind to plasma proteins (e.g., thyroxine-binding globulins) because they are hydrophobic and need carriers.

  • What are the three types of hormone interactions?

    Permissiveness: one hormone needs another to act
    Synergism: hormones have additive effects
    Antagonism: hormones oppose each other.

  • What stimuli control hormone release?

    Humoral: blood ion/nutrient levels
    Neural: nerve fibers stimulate release
    Hormonal: hormones stimulate other hormones.

  • Describe the hypothalamic-pituitary-thyroid hormone axis.

    Hypothalamus releases TRH → anterior pituitary releases TSH → thyroid gland releases T3 and T4 hormones.

  • What are the two lobes of the pituitary gland and their functions?

    Anterior (adenohypophysis): synthesizes and secretes hormones
    Posterior (neurohypophysis): stores and releases hypothalamic hormones ADH and oxytocin.

  • List the main hormones secreted by the anterior pituitary.

    GH, TSH, ACTH, FSH, LH, and Prolactin (PRL).

  • What is the role of Growth Hormone (GH)?

    Stimulates growth and repair, promotes protein synthesis, and encourages fat use for energy; effects mediated by IGFs.

  • What triggers and inhibits GH release?

    Stimulated by Growth Hormone-Releasing Hormone (GHRH); inhibited by Growth Hormone-Inhibiting Hormone (GHIH or somatostatin).

  • What is the function of thyroid hormones T3 and T4?

    Increase metabolic rate, heat production, regulate tissue growth, and support nervous system development.

  • How is thyroid hormone synthesized?

    Iodide is trapped and oxidized, attached to tyrosine on thyroglobulin forming MIT and DIT, which combine to form T3 and T4.

  • What is the role of parathyroid hormone (PTH)?

    Increases blood calcium by stimulating osteoclasts, enhancing kidney reabsorption of Ca2+, and increasing intestinal absorption.

  • What are the three layers of the adrenal cortex and their main hormones?

    Zona glomerulosa: mineralocorticoids (aldosterone)
    Zona fasciculata: glucocorticoids (cortisol)
    Zona reticularis: gonadocorticoids (androgens)

  • What is the main function of aldosterone?

    Maintains sodium balance by reducing sodium excretion and promoting potassium excretion, regulating blood volume and pressure.

  • What hormones are secreted by the adrenal medulla and their effects?

    Epinephrine and norepinephrine increase blood glucose, constrict blood vessels, increase heart rate, and redirect blood flow to vital organs.

  • What are the main endocrine functions of the pancreas?

    Alpha cells secrete glucagon to raise blood glucose; beta cells secrete insulin to lower blood glucose.

  • What are the cardinal signs of diabetes mellitus?

    Polyuria (excessive urination), polydipsia (excessive thirst), and polyphagia (excessive hunger).

  • What hormones do the gonads produce and their roles?

    Ovaries produce estrogens and progesterone for reproductive organ maturation and secondary sex characteristics; testes produce testosterone for male reproductive development and sperm production.

  • What is the function of the pineal gland and its hormone?

    Secretes melatonin, which regulates circadian rhythms and physiological processes with daily cycles.

  • What hormones are stored and released by the posterior pituitary?

    Antidiuretic hormone (ADH) regulates water balance; oxytocin stimulates uterine contractions and milk ejection.