Endo 1

• Hormones


  Chemical messengers in the body (from the Greek term meaning "to spur on")
• Hormone


  A substance that acts at a site distant from its place of origin
• Feedback mechanism


  To maintain the constancy of chemical composition of extracellular and intracellular fluid
• Regulation: Hypothalamic-Pituitary-Target Organ Axis (HPT axis)

  1. Positive feedback mechanism (increase production)

  2. Negative feedback mechanism (decrease production)
• Positive feedback mechanism


  Increased in the product also increases the activity of the system and the production rate
• Negative feedback mechanism


  Increased in the product decreases the activity of the system and the production rate
• Endocrinology: H-P-T axis and specific hormones


  • Hypothalamus hormone: CRH
  • Pituitary hormones: ACTH, TSH, LH/FSH, GH
  • Target glands: Adrenal, Thyroid, Ovaries/Testes, Bone
  • Effector hormones: Glucocorticoid, Mineralocorticoid, Catecholamine, T3 & T4, Sex Steroid, Insulin-like Growth Factor
• Mechanism of hormone action

  1. Binding of hormone to a specific receptor molecule on the cell surface or cell interior

  2. Cell surface receptors: Hormone-Receptor Complex→ Cyclic AMP→ Interior enzyme phosphorylation→ Effects on biochemical process

  3. Internal receptors: Diffusion→ Steroid-receptor complex→ DNA→ Protein synthesis
• Types of hormone action

  • Autocrine
  • Paracrine
  • Intracrine
  • Endocrine
  • Juxtacrine
  • Exocrine
• Prohormone


  Biochemically inactive hormone
• Prohormone examples


  • Proinsulin- removal of C-peptide converts to Insulin
  • Parathormone
  • Vasopressin
• Hormone classification by structure

  • Protein or peptides
  • Steroid
  • Amines
  • Fatty acids
• Protein or peptide hormones

  • About two-thirds of the hormones are proteins or peptides
  • Water soluble, not bound to carrier protein, requires transport protein to get inside the cell, produce their effect on the outer surface of the cell
• Protein or peptide hormones

  • Glycoproteins: FSH, HCG, TSH, Erythropoietin
  • Polypeptides: ACTH, ADH, insulin, glucagon, somatostatin, PTH, calcitonin, Angiotensin, Gastrin
• Steroid hormones


  • Primarily involved in the regulation of sexual development and characteristics
  • Cholesterol as the basic molecule, not water soluble, bound to carrier protein, does not require transport protein to get inside the cell
• Steroid hormones


  • Cortisol, Progesterone, estrone, estradiol, testosterone, aldosterone
• Amine hormones


  Derived from an amino acid and are intermediary between steroid and protein hormones
• Amine hormones


  • Epinephrine, Norepinephrine, Thyroxine & Triiodothyronine
• Fatty acid hormones


  Class of hormones formed from arachidonic acid
• Fatty acid hormones


  • Prostaglandins
• Hormone transport proteins


  • Steroid and Thyroid hormone family have required transport proteins
  • Only free (unbound) fraction exhibits hormone activity
  • Changes in transport protein concentration affects the hormone activity
• Transport proteins and associated hormones

  • Cortisol Binding Protein (CBG) - Cortisol
  • Sex Hormone Binding Protein (SHBG) - Estradiol, Testosterone
  • Thyroid-Binding globulin (TBG) - T3, T4
  • Thyroxine-Binding Prealbumin - T4
  • Albumin - All hormones
• Hypothalamus


  • Also known as "Master Switchboard"
  • Portion of the brain located in the walls and floor of the third ventricles
  • Hormones produced by magnocellular neurons of the Supraoptic nuclei (ADH) and paraventricular nuclei (OXYTOCIN) but secreted by the Posterior Pituitary Gland
• Hypothalamic products


  • GnRH (Gonadotropin Releasing Hormone)
  • TRH (Thyrotropin RH)
  • CRH (Corticotropin RH)
  • GH-RH (Growth Hormone RH)
  • Somatostatin
• Pituitary gland


  • Also known as hypophysis; "Master Gland"
  • All pituitary hormones have circadian rhythm
• Anterior pituitary gland (Adenohypophysis)


  • Secretes Polypeptides & Glycoprotein hormones: prolactin, GH, Gonadotropins (FSH & LH), TSH, & ACTH
• Posterior pituitary gland (Neurohypophysis)

  • Releases and stores oxytocin & vasopressin but does not produce them
  • The release of the hormones occurs in response to serum osmolality or by suckling
• Anterior pituitary cell types and hormones

  • Somatotrophs - growth hormone
  • Lactotrophs or Mammotrophs - prolactin
  • Thyrotrophs - TSH
  • Gonadotrophs - LH & FSH
  • Corticotrophs - Proopiomelanocortin (POMC is cleaved within the pituitary to produce ACTH, B-endorphin, & B-lipotropin)
• Anterior pituitary hormones, target glands, and feedback hormones

  • Luteinizing Hormone (LH) - Gonad (tropic) - Progesterone
  • Follicle Stimulating Hormone (FSH) - Gonad (tropic) - Inhibin
  • Thyroid Stimulating Hormone (TSH) - Thyroid (tropic) - T3 & T4
  • Adrenocorticotropic Hormone (ACTH) - Adrenal (tropic) - Cortisol
  • Growth Hormone - Multiple (direct effector) - IGF-1
  • Prolactin - Breast (direct effector) - Unknown
• Hypothalamus


  Also known as "Master Switchboard", portion of the brain located in the walls and floor of the third ventricles
• Hypothalamus


  • Hormones produced by magnocellular neurons of the Supraoptic nuclei (ADH) and paraventricular nuclei (OXYTOCIN) but secreted by POSTERIOR PITUITARY GLAND
• Hypothalamic products


  • GnRH (Gonadotropin Releasing Hormone)
  • TRH (Thyrotropin RH)
  • CRH (Corticotropin RH)
  • GH-RH (Growth Hormone RH)
  • Somatostatin
• Pituitary Gland


  Also known as hypophysis; "Master Gland"
• All pituitary hormones have CIRCADIAN RHYTHM
• Anterior Pituitary Gland (Adenohypophysis)


  Also known as "True endocrine gland", secretes Polypeptides & Glycoprotein hormones such as prolactin, GH, Gonadotropins (FSH & LH), TSH, & ACTH
• Posterior Pituitary Gland (Neurohypophysis)

  Releases and stores oxytocin & vasopressin but does not produce them, release occurs in response to serum osmolality or by suckling
• Anterior Pituitary Cell Types and Hormones

  • SOMATOTROPHS - growth hormone
  • LACTOTROPHS or MAMMOTROPHS - prolactin
  • THYROTROPHS - TSH
  • GONADOTROPHS - LH & FSH
  • CORTICOTROPHS - Proopiomelanocortin (POMC is cleaved within the pituitary to produce ACTH, B-endorphin, & B-lipotropin)
• Anterior Pituitary Hormones


  • Luteinizing Hormone (LH)
  • Follicle Stimulating Hormone (FSH)
  • Thyroid Stimulating Hormone (TSH)
  • Adrenocorticotropic Hormone (ACTH)
  • Growth Hormone
  • Prolactin
• Anterior Pituitary Hormones


  LH, FSH, TSH are tropic (their actions are specific for another endocrine gland), Growth Hormone and Prolactin are direct effectors (act directly on peripheral tissue)
• TSH, FSH, LH as well as hCG share a common alpha chain subunits