Endocrinology

• Endocrine system

  Network of ductless glands that secrete hormones directly into the blood
• Endocrine system

  • It is considered to be the regulatory hormone of the body
  • It is regulated by means of control of hormone synthesis rather than by degradation
• Hormones

  Chemical signals produced by specialized cells, secreted into the blood stream and carried to a target tissue
• Hormones

  • Play an important role in the growth and development of an individual
  • Regulated by metabolic activity either positive or negative feedback mechanism
• Major function of hormones

  To maintain the constancy of chemical composition of extracellular and intracellular fluids, and control metabolism, growth, fertility and responses to stress
• Positive feedback mechanism


  A system in which an increase in the product results to elevation of the activity of the system and the production rate
• Negative feedback mechanism


  A system in which an increased in the product results to decreased activity of the system and the production
• Types of hormone secretion

  • Endocrine
  • Paracrine
  • Autocrine
  • Juxtracrine
  • Intracrine
  • Exocrine
  • Neurocrine
  • Neuroendocrine
• Peptide and protein hormones

  • Synthesized and stored within the cell in the form of secretory granules and are cleaved as needed
  • Cannot cross the cell membrane due to their large molecular size and thus produce the effects on the outer surface of the cells
  • They are water soluble and not bound to carrier protein
• Steroid hormones


  • Lipid molecules that have cholesterol as a common precursor
  • Produced by adrenal glands, ovaries, testes, and placenta
  • Water insoluble (hydrophobic) and circulate bound to a carrier protein
• Examples of steroid hormones

  • Aldosterone
  • Cortisol
  • Estradiol
  • Progesterone
  • Testosterone
  • Activated vitamin D
• Amine hormones


  Derived from an amino acid and they are intermediary between steroid and protein hormones
• Examples of amine hormones

  • Epinephrine
  • Norepinephrine
  • Triiodothyronine
  • Thyroxine
• Hypothalamus


  • Portion of the brain located in the walls and floor of the third ventricle
  • Above the pituitary gland, and is connected to the posterior pituitary by the infundibulum (pituitary stalk)
  • The link between the nervous system and the endocrine system
• Anterior pituitary


  • Largest portion of the gland
  • The "true endocrine gland"
  • Regulates the released and production of hormones such as prolactin, growth hormone, gonadotropins (FSH and LH), TSH and ACTH
  • Hormones secreted by the anterior lobe are either peptides or glycoproteins
• Intermediate lobe


  Little functional capacity
• Posterior pituitary


  For storage and release of oxytocin and vasopressin
• Five types of cells in anterior pituitary

  • Somatotrophs
  • Lactotrophs or Mammotrophs
  • Thyrotrophs
  • Gonadotrophs
  • Corticotrophs
• Growth hormone (somatotropin)


  • Most abundant of all pituitary hormone
  • Controlled by GH-RH (the amount of release) and somatostatin (governs the frequency and duration of secretory pulse)
  • Structurally similar to prolactin and human placental lactogen
  • Secretion is erratic and occurs in short bursts
  • Overall metabolic effect is to metabolize fat stores while conserving glucose
• Major stimuli for growth hormone

  • Deep sleep (markedly increased GH)
  • Stress
  • Fasting
  • High protein diet
• Pharmacologic stimuli for growth hormone

  • Sex steroids
  • Apomorphine
  • Levodopa
• GH suppressors


  • Glucocorticoids
  • Elevated fatty acids
• Conditions with increased GH

  • Acromegaly
  • Gigantism
  • Chronic malnutrition
  • Renal disease
  • Cirrhosis and sepsis
• Conditions with decreased GH

  • Hyperglycemia
  • Obesity and hypothyroidism
• GH deficiency (GHD)

  • Idiopathic Growth Hormone Deficiency is the most common cause in children
  • In children with pituitary dwarfism, normal proportions are retained and show no intellectual abnormalities
  • Pituitary Adenoma is the most common etiology in adult-onset GH deficiency
• Acromegaly


  Due to overproduction of GH (>50 ng/ml or 2210 pmol)
• Diagnostic tests for GH deficiency

  • Screening test: Physical Activity Test (Exercise Test)
  • Confirmatory test: Insulin tolerance test (gold standard) or Arginine stimulation test
  • Interpretation: failure of GH to rise >5ng/ml (adults) and >10 ng/ml (child) in all the test is confirmed of GH deficiency
• Diagnostic tests for acromegaly

  • Screening test: somatomedin C or insulin-like growth factor 1 (IGF-1)
  • IGF-1 is produced in the liver
• Pituitary Adenoma


  The most common etiology in adult-onset GH deficiency
• Patient preparation for GH Deficiency test

  Complete rest 30 minutes before blood collection
• Specimen requirement for GH Deficiency test

  Preferably fasting serum
• Screening test for GH Deficiency

  Physical Activity Test (Exercise Test)
• Result of Physical Activity Test

  Elevated serum GH
• Confirmatory test for GH Deficiency

  1. Insulin tolerance test-gold standard

  2. Arginine stimulation test-2nd confirmatory test
• Procedure for GH Deficiency test

  24 hour or night time monitoring of GH
• Interpretation of GH Deficiency test

  Failure of GH to rise >5ng/ml (adults) and >10 ng/ml (child) in all the test is confirmed of GH deficiency
• GHD in childhood


  Defined by failure of serum GH to reach defined levels when at least two different pharmacologic stimuli are used
• Screening test for Acromegaly


  Somatomedin C or insulin-like growth factor 1 (IGF-1)
• IGF-1


  Produced in the liver, increased in patients with acromegaly, low in GHD
• Confirmatory test for Acromegaly

  Glucose Suppression Test - OGTT (75g glucose)