Basic Endocrinology

• Hormone - A chemical substance that sends a message to another cell in the body
• Endocrine - Secreted in one location and released into blood circulation

  • Binds to a specific receptor to elicit physiological response
• Paracrine - Secreted in endocrine cells and released into interstitial space

  • Binds to a specific receptor in adjacent cell and affects its function
• Autocrine - Secreted in endocrine cells and sometimes released into interstitial space

  • Binds to a specific receptor on cell of origin resulting to self-regulation of its function
• Juxtacrine - Secreted in endocrine cells and remains in that same cellular space in relation to plasma membrane

  • Acts on immediately adjacent cell by direct cell-to-cell contact
• Intracrine - Secreted in endocrine cells and functions inside the origin of synthesis
• Exocrine - Secreted in endocrine cells and released into lumen and GIT
• Neurocrine - Secreted in neurons and released into extracellular space

  • Binds to a receptor in nearby cell and affects its function
• Neuroendocrine - Secreted in neurons and released from nerve endings

  • Interacts with receptors of cells at distant site
• Hydrophilic - Amine, Peptides, and Proteins

  Hydrophobic - Lipid hormones or steroids
• Epinephrine is from tyrosine

  Melatonin is from tryptophan
• Peptide - considered to be an unbroken chain of amino acids of 50 or less )eg. oxytocin and vasopressin
• Protein - large number of amino acid residues in any length greater than 50 amino acids (ACTH, calcitonin, insulin, glucagon)
• Glycoprotein hormones are conjugated proteins bound to carbohydrates, which include galactose, mannose, or fructose

  **follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH)
• Steroid hormones - are all derived from a lipid, typically cholesterol
• Fatty Acids - made up of small fatty acid derivatives of arachidonic acid
• Alcohol increases the degradation of testosterone
• Predominant organs for eliminating hormones: kidneys and liver
• Common processes in the body that regulate hormone secretion are called feedback mechanisms, also known as feedback loops
• Long FM: thyroid and hypothalamus

  Short FM: thyroid and pituitary gland

  Ultrashort FM: pituitary and hypothalamus
• The zeitgeber (time giver) refers to the process of entraining or synchronizing these external cues into the function of internal biologic clocks. These circadian rhythms, or the diurnal variations, are typified by ACTH and TSH secretion
• 1. Circadian rhythms: Biological rhythms (endogenously generated) with a period close to 24 hours
  2. Diurnal rhythms: A circadian rhythm that is synchronized with the day/night cycle
  3. Ultradian rhythms: Biological rhythms (e.g., feeding cycles) with a much shorter period (i.e., much higher frequency) compared to a circadian rhythm
  4. Infradian rhythms: Biological rhythms with a cycle that lasts longer than 24 hours (e.g., the human menstrual cycle)
• ACE inhibitors - hypertension to decrease the activity of angiotensin converting enzyme and subsequently decrease the amount of angiotensin, which is formed from the conversion of angiotensinogen

  Methimazole: hyperthyroidism

  Corticosteroids: Exogenous corticosteroids will act just like the endogenous cortisol on the receptors in the body and usually increase the glucose concentrations in the plasma

  Psychotropic drugs: antidepressants and SIADH
• Growth hormone - Body growth, basal metabolic functions, and acute phase stress reactant
• ACTH - Regulates cortisol and androgen production
• TSH - Tropic hormone to regulate T4 production
• FSH - Women: Initiate follicular maturation and estrogen production; Men: Spermatogenesis
• LH - Women: Initiation of ovulation; Men: Activate testicular testosterone production
• Prolactin - Lactation
• ADH - Activation of ADH-sensitive water pores in the collecting duct to regulate osmolarity
• Calcitonin - Inhibits osteoclastic breakdown
• PTH - Prohormone to calcitonin
• PTH - Increases circulating calcium ions, by promoting Ca2+ absorption in the intestines, promotes Ca2+ reabsorption and blocks PO4- reabsorption
• Insulin - Drops plasma glucose levels by binding directly to insulin receptors on cell surfaces to allow glucose entry into cells through GLUT4 channels
• Glucagon - Increases glycogenolysis and gluconeogenesis by binding to G-coupled protein receptors throughout the body
• Gastrin - Induces HCl secretion from parietal cells in the stomach
• Secretin - Induce HCl secretion from parietal cells and bicarbonate release from the pancreas
• B-hCG - Stimulates the corpus luteum in the ovary to produce progesterone to maintain pregnancy
• Cortisol - Immune response, stress response, and glucose homeostasis
• Aldosterone - Increase sodium absorption in the distal tubules and proximal