ENDOCRINOLOGY

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ENDOCRINOLOGY
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Endocrine Glands

• Ductless glands
• Produce highly active chemical regulators-hormones
  
• Hormones excreted into bloodstream and carried to
  target organs

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Functional Types of Hormones

• Releasing Factors
• From hypothalmus
• Stimulate secretion of tropic hormones of
  anterior pituitary
• Tropic Hormones stimulate growth and activity of
  other endocrine glands
• Nontropic (effector) hormones exert action on
  non-endocrine tissue

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Control and Regulation of Hormones

• Primary control in hypothalmus
• Acted on by CNS or stress
• Secretes releasing factors which stimulate
  anterior pituitary to secrete tropic hormones
• Also secretes ADH and oxytocin (stored and
  released by posterior pituitary)

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• Anterior pituitary
• master gland- secretes tropic hormones
• Also secretes Growth hormone, an effector
  hormones
• Effector hormones exert feedback inhibition on
  hypothalamus or the anterior pituitary

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THYROID HORMONES

• Thyroid
• Small gland wrapped around trachea
• Secretes hormones that regulate metabolic rate
  and oxygen consumption
• Also secretes calcitonin, a hormone that aid in
  calcium metabolism

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• Thryotropin releasing hormone (TRH) made and
  released by hypothalmus
• TRH stimulating synthesis and secretion of
  thyroid stimulating hormone (TSH) by anterior
  pituitary.
• TSH stimulates synthesis and secretion of T3 and
  T4 by thyroid.

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Circulating thyroid hormones

• T3 (triiodothyronine) and T4 (thyroxine)
  iodinated derivatives of tyrosine
• Poorly soluble in plasma- transported in blood by
  thyroid-binding globulins (TBG) or albumin
• gt99 is bound to these proteins, lt1 is free-
  free portion is active

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Hyperthyroidism

• Symptoms sweating, palpitations, insomnia,
  tremors, anxiety, exophthalmos
• Most common cause-Graves disease
• Autoimmune disorder - antibodies to TSH
  receptors
• Elevated T4 confirms diagnosis
• May need to measure free T4 if abnormalities in
  thyroid binding globulins.

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• If T4 levels are normal, may need to also measure
  T3 to rule out T3 thyrotoxicosis

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Hypothyroidism

• Symptoms dry skin, coarse/dry hair, swelling of
  eyes, constipation, lack of energy
• Decreased T4 in most cases
• Elevated TSH to confirm diagnosis
• Neonatal Hypothyroidism cretinism

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Parathyroid Hormone (PTH)

• Also called parathryin
• Synthesized by parathyroid gland
• Key hormone in regulating calcium ion metabolism
• Acts on bone, kidney, GI tract to reabsorb or
  conserve calcium ions
• Reduces urinary excretion of calcium
• Increases bone resorption (release of calcium
  from bone
• Increases synthesis of active form of Vitamin D-
  stimulates intestinal reabsorption of calcium

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• Hyperparathyroidism- causes hypercalcemia (other
  cause of hypercalcemia is malignancy)
• Symptoms
• Bone pain, osteoporosis
• Kidney stones, flank pain, polyuria
• Anorexia, constipation, vomiting
• Anxiety, depression, fatigue

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Anterior Pituitary Hormones

• Growth Hormone (GH) or Somatropin
• Release stimulated by growth hormone releasing
  factor suppressed by somatostatin
• Promotes protein synthesis- stimulates bone
  growth
• Decreased dwarfism
• Increased Giantism
• Diurnal variation highest around midnight

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• Gonadotropins (FSH and LH)
• Induce growth of gonads
• Induce secretion of gonadal hormones
• Necessary for production of ova and development
  of sperm
• Surge in LH is basis of home ovulation kits

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• Prolactin
• Initiates and maintains lactation
• Useful in diagnosis, management, and follow-up of
  prolactinomas
• Galactorrhea
• Infertility

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Posterior Pituitary Hormones

• ADH (vasopressin)
• Increases reabsorption of water by renal tubules
• Decreased levels in diabetes insipidus
• Oxytocin
• Contraction of smooth muscle
• Used to induce labor
• No medical reason to measure blood levels

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Adrenal Cortex Hormones

• Corticosteroids (Cortisol)
• Metabolism of proteins, carbohydrates, lipids
• Diurnal variation, highest in morning
• Diagnosis of adrenalcortical disorders, such as
  Cushings (increase) and Addisons disease
  (decrease)
• Often measure cortisol metabolites in urine
  (17-ketogenic steroids and 17-hydroxysteroids)

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• Testosterone
• Aldosterone increases sodium reabsorption in
  renal tubules

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Female Sex Hormones

• Ovarian Hormones Estrogens
• Most potent is estradiol
• Menstrual difficulties (with FSH and LH) to
  differentiate ovarian from pituitary causes
• Estriol-no hormonal activity
• Produced in 3rd trimester of pregnancy
• Gives indication of fetal well-being
• Sudden drop indicates fetal-placental distress

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• Placental hormones
• Human Chorionic Gonadotroping (HCG)
• Stimulates corpus luteum to produce progesterone
  and prevent menstruation
• Produced by placenta shortly after implantation
  of fertilized egg
• Pregnancy tests
• Greatly influenced in hydatidiform moles
• Increased in males with testicular cancer

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Male Sex Hormones

• Testosterone
• Development of secondary sexual characteristics
• Increased may indicated premature puberty in
  males or masculinity in females (virulism and
  hirsuitism)
• Decreased in hypogonadism and some cases of
  infertility

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Adrenal Medulla Hormones

• Epinephrine and Norepinephrine
• Called catecholamines
• Measured along with their metabolite
  vanillymandelic acid (VMA) when
• Unexpected hypertension rule out
  pheochromocytoma
• Detect neuroblastoma in children