Hypothalamic and Pituitary Function

• Pituitary - (derived from both Latin and Greek) literally means to “spit mucus,”
• Without pituitary there is a cessation of growth
• Hypophysis - undergrowth
• Three distinct parts of the pituitary: Anterior, Intermediate, and Posterior
• Pituitary function can be detected between the seventh and ninth weeks of gestation.
• 1. lactotrophs - (prolactin-secreting cells)
  2. somatotrophs - (growth hormone [GH]-secreting cells)
  3. thyrotrophs - (thyroid-stimulating hormone [TSH]-secreting cells)
  4. corticotrophs - (adrenocorticotropin hormone [ACTH]-secreting cells)
  5. gonadotrophs - (luteinizing hormone [LH], and follicle-stimulating hormone [FSH]-secreting cells)
• All anterior pituitary hormones are secreted in a pulsatile fashion.
• With ACTH, the trough of secretion is between 11:00 pm and 3:00 am, and the peak occurs on awakening or around 6:00 to 9:00 am.
• Pineal Gland - Attached to the midbrain; Its secretions are controlled by nerve stimuli, and secretes melatonin
• LH - Gonad (tropic); Dimeric glycoprotein; Sex steroids (E2T)

  FSH - Gonad (tropic); Dimeric glycoprotein; Inhibin

  TSH - Thyroid (tropic); Dimeric glycoprotein; Thyroid hormones (T3/T4)

  ACTH - Adrenal (Tropic); Single peptide derived from POMC; Cortisol

  Growth hormone - Multiple (direct); Single peptide; IGF-1

  Prolactin - Breast (director effector); Single peptide; Unknown
• Growth hormone or Somatotropin - Release of somatotropin from the pituitary is stimulated by the hypothalamic peptide growth hormone-releasing hormone (GHRH)
• 1. Ghrelin: hunger hormone - nutrient sensing
  2. Human Placental Lactogen - mammary gland
• Growth hormone is considered as amphibolic hormone because it influences anabolic and catabolic process.
• IGF - 1 (Insulin-like Growth Factor 1) is produced in the liver.

  • IGF-1 is increased in patients with acromegaly.
• Macimorelin Acetate Stimulation Test

  • It is considered as a secondary confirmatory in

  GHD.
• GHD types

  1. Idiopathic GHD - Most common cause in children; In children with pituitary dwarfism, normal proportions are retained and show no intellectual abnormalities
  2. Pituitary adenoma - Most common etiology of the adult-onset GHD
• GHD - Gold Standard: Insulin Tolerance Test (ITT)
• FSH and LH - important markers in the diagnosis of fertility and menstrual cycle disorders
• Hypogonadotropic hypogonadism (also known as 2° hypogonadism): Low FSH and LH

  ✔ Decrease in testicular production and synthesis of testosterone: Deficiency of FSH and LH
• Gonadotropin-Releasing Hormone (GnRH) Stimulation Test

  ➔ It is the gold standard test in identifying central precocious puberty (CPP) and premature activation of the hypothalamic-pituitary-gonadal axis (HPGA) in cases with clinical signs and symptoms of early puberty
• Thyroid-Stimulating Hormone (TSH)

  • Aka thyrotropin
  • Main stimulus for the uptake of iodide by the thyroid gland - Acts to increase the number of follicular cells
• Adrenocorticotropic Hormone (ACTH)

  • It is a single-chain peptide without disulfide bonds.
  • It is produced in response to low serum cortisol - regulator of adrenal androgen synthesis.
• Prolactin

  • Prolactin is structurally related to GH and human placental lactogen.
  • Considered a stress hormone, it has vital functions in relationship to reproduction.
• Dopamine - is the only neuroendocrine signal that inhibits

  prolactin and is now considered to be the elusive PIF.
• Hyperprolactinemia - may also be seen in renal failure an

  polycystic ovary syndrome.
• Hypopituitarism

  ➔ Complete loss of function is termed panhypopituitarism.

  ➔ There also may be a loss of only a single pituitary hormone, which

  is referred to as a monotropic hormone deficiency.
• The posterior pituitary is an extension of the forebrain and represents the storage region for arginine vasopressin (AVP) and oxytocin
• Oxytocin - has a critical role in lactation and plays a major role in labor and parturition (childbirth)
• Contraction of the gravid uterus at term "fergusson reflex"
• Diabetes Insipidus (DI)

  ➔ It is characterized by the deficiency of AVP which results in severe polyuria (2 2.5 liters of urine/day).
• Hypotonic Urine

  ✓ It is a urine sample with an osmolality of <300 mOsm/Kg.
• MAJOR TYPES OF DIABETES INSIPIDUS

  1. True Diabetes Insipidus (Hypothalamic/Neurogenic/Cranial/Central Diabetes Insipidus)
  2. Nephrogenic Diabetes Insipidus

  OTHER

  1. Primary Polydipsia (Psychogenic Polydipsia/Dipsogenie DI)
  2. Gestation Diabetes Insipidus
• Copeptin

  ➔ It is a 39-amino-acid C-terminal segment of pre-pro-arginine vasopressin.