Anatomy

Endocrine Anatomy

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Endocrine Anatomy, Autocrine, Paracrine, Hormone

  • Definitions
  1. Cytokine
    1. See Cytokine
    2. Short-range, cell-released molecules that influence the same cell (Autocrine) or nearby cells (Paracrine)
  2. Autocrine Communication
    1. Cytokines that influence the same cell that released the molecule
  3. Paracrine Communication
    1. Cytokines that diffuse to influence nearby cells
  4. Endocrine Glands
    1. Glands that secrete hormonal agents that act systemically
    2. Contrast with exocrine glands (e.g. Salivary Glands) that secrete molecules locally into ducts
  5. Hormones
    1. Molecules secreted by endocrine organs, and carried by the vascular system to influence cells at distant sites
    2. Hormones may be proteins (e.g. TSH), amino acid derivatives (e.g. Thyroxine) or steroid rings (e.g. Progesterone)
  • Physiology
  • Hormonal Activity
  1. Polypeptides (e.g. Epinephrine)
    1. Bind cell surface receptors
    2. Receptor binding triggers G Protein (intermediate molecule) release
    3. G Proteins stimulate secondary messengers release (e.g. cAMP, cGMP)
  2. Steroid Hormones (e.g. Progesterone)
    1. Bind cytoplasmic receptors to form molecule complex
    2. Complex enters nucleus to influence protein transcription
  3. Amino Acid Derivatives (e.g. Thyroxine)
    1. Thyroxine enters cells and acts directly within nucleus to influence protein transcription
  1. Hypothalamus
    1. Corticotropin Releasing Hormone (CRH, CRF)
      1. Stimulates anterior pituitary release of Adrenocorticotropic Hormone (ACTH)
    2. Gonadotropin Releasing Hormone (GnRH, LHRH)
      1. Stimulates anterior pituitary release of Follicle Stimulating Hormone (FSH)
      2. Stimulates anterior pituitary release of Luteinizing Hormone (LH)
    3. Growth Hormone Releasing Hormone (GHRH)
      1. Stimulates anterior pituitary release of Growth Hormone
    4. Thyrotropin Releasing Hormone (TRH, TRF)
      1. Stimulates anterior pituitary release of Thyroid Stimulating Hormone (TSH)
      2. Stimulates anterior pituitary release of Prolactin
    5. Somatostatin
      1. Inhibits anterior pituitary release of Growth Hormone
      2. Inhibits anterior pituitary release of Thyroid Stimulating Hormone (TSH)
    6. Neurotransmitters
      1. Dopamine released from Hypothalamus inhibits anterior pituitary release of Prolactin
  2. Posterior Pituitary Gland (Hormones produced in the Hypothalamus, released from pituitary)
    1. Oxytocin
      1. Stimulates uterine contractions
      2. Stimulates milk let-down in Lactation
    2. Antidiuretic Hormone (ADH, Vasopressin)
      1. Increases renal water reaborption
  3. Anterior Pituitary Gland
    1. Prolactin
      1. Protein synthesized and secreted by Lactotrophs (acidophil cells) in the anterior pituitary
      2. Prolactin stimulates milk secretion into the Breast alveoli in pregnancy and Lactation
      3. Oxytocin stimulates myoepithelial cells to contract, expressing Breast Milk from the nipple
      4. Stimulated by Estrogen, vasoactive intestinal polypeptide (VIP), Thyroid Releasing Hormone (TRH)
      5. Inhibition by hypothalamic Dopamine (Prolactin Inhibiting Factor or PIF)
    2. Human Growth Hormone
      1. Polypeptide produced in the acidophil cells of the anterior pituitary
      2. Triggered by Hypoglycemia (or low amino acids) via hypothalamic release of GHRH
      3. Promotes bone and cartilage growth, protein synthesis, glycogen storage, Fatty Acid increase
    3. Adrenocorticotropic Hormone (ACTH)
      1. Polypeptide synthesized and secreted by Basophil cells in the anterior pituitary
      2. Stimulation (releasing factors) include Corticotropin Releasing Hormone (CRH) and stress
      3. Inhibition by negative feedback loops (Cortisol inhibits CRH and ACTH release)
      4. ACTH stimulates the Adrenal Cortex to release Cortisol (and to a lesser extent Aldosterone and androgens)
    4. Thyroid Stimulating Hormone (TSH)
      1. See Thyroid Physiology
      2. Thyroid Stimulating Hormone (TSH) is a glycoprotein synthesized in the Basophil cells of the anterior pituitary
      3. Stimulated by Thyroid Releasing Hormone (TRH)
      4. Inhibited by negative feedback from Thyroid Hormones (T4, T3)
      5. Thyroid Stimulating Hormone (TSH) promotes all aspects of Thyroid Hormone production
        1. Increases iodide uptake and incorporation of Iodine into Thyroglobulin
        2. Increases lysis into active Thyroid Hormones T4 and T3
    5. Follicle Stimulating Hormone (FSH)
      1. FSH is a glyoprotein secreted by Basophil cells in the anterior Pituitary Gland
      2. Stimulation (releasing factors) is by Hypothalamic Gonadotrophic Releasing Hormone (GnRH)
      3. Inhibited via negative feedback loop by Testosterone, Estrogens, Progesterone and inhibin
      4. FSH stimulates ovarian follicle growth (which secretes Estradiol) in women
      5. FSH stimulates spermatogenesis and sperm maturation within Sertoli Cells in men
    6. Luteinizing Hormone (LH)
      1. LH is a glycoprotein secreted by Basophil cells in the anterior Pituitary Gland
      2. Stimulation is by Hypothalamic Gonadotrophic Releasing Hormone (GnRH)
      3. Inhibited via negative feedback loop by Testosterone, Estrogens, Progesterone and inhibin
      4. LH stimulates ovarian follicles to ovulate and mature into a corpus luteum (produces Estrogen, Progesterone)
      5. LH stimulates Leydig Cells within Testes to produce Testosterone