Endocrinology

• Hypothalamus


  Produces TRH, CRF, GnRH, others
• Anterior Pituitary


  Produces TSH, ACTH, FSH, LH, Prolactin, GH
• Posterior Pituitary


  Produces Vasopressin, Oxytocin
• Adrenal Medulla


  Produces Epinephrine, Norepinephrine
• Adrenal Cortex


  Produces Cortisol, 11-deoxycortisol, Aldosterone
• Thyroid


  Produces T3, T4, Calcitonin
• Parathyroid


  Produces Parathyroid hormone (PTH)
• Pancreas


  Produces Insulin, Glucagon, Somatostatin
• Ovaries


  Produce Estrogens, Progesterone
• Testes


  Produce Testosterone, other androgens
• Characteristics of Hormones


  • Each hormone is produced by a specific tissue (gland)
  • Released directly from the tissue into the bloodstream and carried to the specific site of action
  • Acts at a specific site or sites (target cells) to induce certain characteristics biochemical changes
• Structural Classes of Hormones

  • Steroid Hormones
  • Protein Hormones
  • Amine Hormones
• Steroid Hormones


  • Site of Production: Adrenal glands, gonads, and placenta
  • Chemical Component: Cholesterol
  • Product and Storage: Synthesized as needed, not stored
  • Soluble to: Lipid
  • Carrier: Protein
• Protein Hormones


  • Site of Production: Anterior pituitary, placenta, and parathyroid glands
  • Chemical Component: Protein
  • Product and Storage: Synthesized, then stored in cell as secretory granules until needed
  • Soluble to: Water
  • Carrier: Do not need protein
• Amine Hormones


  • Site of Production: Thyroid and adrenal glands
  • Chemical Component: Amino acids
  • Product and Storage: Synthesized, then stored in the cells as secretory granules until needed
  • Soluble to: Water
  • Carrier: Require a carrier protein and others do not
• Glycoproteins


  Composed of two polypeptide chains containing carbohydrate. Alpha chains are the same in all. Beta chains determine specificity.
• Pituitary Hormones


  • Luteinizing Hormone (LH)
  • Follicle-stimulating hormone (FSH)
  • Thyroid-stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
  • Growth hormone (GH; aka somatotropin)
  • Prolactin
  • Oxytocin
  • Vasopressin (Antidiuretic hormone)
• Luteinizing Hormone (LH)


  • Target Gland: Gonad (tropic)
  • Action: Maturation of follicles, ovulation, production of estrogen, progesterone, testosterone
  • Regulation: Regulated by GnRH from hypothalamus
• Follicle-stimulating hormone (FSH)


  • Target Gland: Gonad (tropic)
  • Action: Sperm and egg production
  • Regulation: Regulated by gonadotropin-releasing hormone (GnRH) from hypothalamus
• Thyroid-stimulating hormone (TSH)


  • Target Gland: Thyroid (tropic)
  • Action: Production of T3 and T4 by thyroid
  • Regulation: Thyrotropin-releasing hormone (TRH) from hypothalamus
• Adrenocorticotropic hormone (ACTH)


  • Target Gland: Adrenal (tropic)
  • Action: Production of adrenocortical hormones by adrenal cortex
  • Regulation: Regulated by corticotropin-releasing hormone (CRH) from hypothalamus
• Growth hormone (GH; aka somatotropin)


  • Target Gland: Multiple (direct effector)
  • Action: Allows an individual to transition from a fed state to a fasting state, ↑ protein synthesis in skeletal muscle and other tissues, Antagonizes the effects of insulin
  • Regulation: Regulated by growth-hormone releasing hormone (GHRH) & somatostatin from hypothalamus
• Prolactin


  • Target Gland: Breasts (direct effector)
  • Action: Lactation
  • Regulation: Regulated by prolactin-releasing factor (PRF) & prolactin inhibiting factor (PIF) from hypothalamus
• Oxytocin


  • Target Gland: Breasts and uterus (direct effector)
  • Action: Critical role in lactation, Major role in labor and parturition
  • Produced in hypothalamus, stored in posterior pituitary
• Vasopressin (Antidiuretic hormone)


  • Target Gland: Kidneys (direct effector)
  • Action: Regulation of renal free water excretion
  • Produced in hypothalamus, stored in posterior pituitary, Release stimulated by ↑osmolality, ↓blood volume or blood pressure
• Thyroid Gland


  • Located near the larynx; two lobes connected by a thin piece of tissue
  • Exerts significant control over the rate of metabolism in humans
  • Hormones produced: T3, T4, calcitonin
  • Stimulated by TSH (from the anterior pituitary) to produce and secrete T3, T4
  • Functional unit: thyroid follicle, Comprised of follicular cells surrounding a central colloid, Colloid contains thyroglobulin, which is rich in tyrosine (the amino acid that forms the backbone for the thyroid hormone molecules)
• Thyroid Hormone Production


  1. Thyroglobulin

  2. Monoiodotyrosine + diiodotyrosine = T3 (3, 5, 3'-triiodothyronine)

  3. Diiodotyrosine + diiodotyrosine = T4 (3, 5, 3', 5'- tetraiodothyronine)

  4. T3 is more potent (T4 is converted to T3 suggesting that T3 is more important)
• Thyroid Hormone Binding Proteins

  • Thyroxine – binding globulin (TBG) (70-75 %): Major transport protein for T3 and T4, T4: 0.03-0.05 % is unbound (almost completely bound to proteins), T3: 0.5 % free (weaker attachment to proteins)
  • Thyroxine- binding prealbumin (TBPA) (10-25 %)
  • Serum albumin (10 %)
• Thyroid Tests


  • T3
  • T4
  • THBR
  • FT4
  • FT3
  • FT4 Index
  • FT3 Index
  • TSH
• Laboratory Values in Hyperthyroidism

  T4: ↑, T3: ↑, TSH: ↓, TRH: ↓, T3 Uptake: ↑
• Laboratory Values in Hypothyroidism

  T4: ↓, T3: ↓, TSH: ↑, TRH: ↑, T3 Uptake: ↓
• Types of Hypothyroidism


  • Cretinism
  • Hashimoto's thyroiditis
  • Subclinical hypothyroidism
• Grave's Disease


  Most common cause of hyperthyroidism, Autoantibody (IgG) stimulates TSH receptor → increased synthesis and release of thyroid hormones, Clinical features: Hyperthyroidism, Diffuse goiter, Exophthalmos, Pretibial myxedema
• Adrenal Cortex


  • Composed of three layers; each secretes predominantly one class of hormones: Zona glomerulosa (mineralocorticoids), Zona fasciculata (glucocorticoids), Zona reticularis (androgens)
  • Cortical hormones are derived from cholesterol
• Classes of Steroid Hormones

  • Mineralocorticoids
  • Glucocorticoids
  • Sex steroids
• Mineralocorticoids


  Hormone: Aldosterone, Major Tissue of Origin: Adrenal cortex
• Glucocorticoids


  Hormones: Cortisol, Cortisone, 11-deoxycortisol, Major Tissue of Origin: Adrenal cortex
• Sex Steroids


  • Androgens: Testosterone, Major Tissue of Origin: Testes, ovaries, adrenal cortex
  • Estrogens: Estradiol, Estriol, Estrone, Major Tissue of Origin: Ovaries, placenta, adrenal cortex
  • Progesterone, Major Tissue of Origin: Adrenal cortex, ovary
• Steroidogenesis


  All adrenal steroids are derived by sequential enzymatic conversion of a common substrate, cholesterol.
• Steroid Transport Proteins


  • Albumin: Non-specific; carries many steroids
  • Cortisol-binding globulin: Cortisol and derivatives; progesterone
  • Sex hormone-binding globulin: Testosterone and estradiol