PL1 Physiolgyy of Pituitary Hormones

• Hypothalamic and pituitary hormones

  Hormones produced by the hypothalamus and pituitary gland

  
• Pituitary gland

  • Consists of two distinct portions: anterior (adenohypophysis) and posterior (neurohypophysis)

  
• Hormones secreted by the anterior pituitary

  • Growth hormone (GH)
  • Adrenocorticotropin hormone (ACTH)
  • Thyroid-stimulating hormone (TSH)
  • Prolactin
  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
• Growth hormone (GH)

  Affects protein formation, cell multiplication and differentiation
• Adrenocorticotropin hormone (ACTH)

  Acts on adrenal cortex to secrete cortisol and aldosterone
• Thyroid-stimulating hormone (TSH)

  Causes the thyroid gland to secrete thyroxin (T4) and triiodothyronine (T3)
• Prolactin

  Promotes mammary gland development and milk production
• Follicle-stimulating hormone (FSH)

  Promotes growth of follicles before ovulation and formation of sperm in testes
• Luteinizing hormone (LH)

  Causes ovulation and secretion of female sex hormones by ovaries and testosterone by testes
• Posterior pituitary

  • Secretes two hormones: antidiuretic hormone (ADH/vasopressin) and oxytocin
• Antidiuretic hormone (ADH/vasopressin)

  Controls water secretion into urine, thus controlling concentration of water in body fluids
• Oxytocin


  Helps in the delivery of the baby and release of milk from the breast
• Second messengers

  cAMP, Ca2+ and Calmodulin, Phosphatidylinositol
• Control of pituitary secretion (part 1)

  1. Pain, powerful depressing or exciting thought from CNS, olfactory stimuli, concentrations of nutrients, electrolytes, water & various hormones in blood excite or inhibit various portions of hypothalamus

  2. Hypothalamus collects this information and controls secretions of pituitary hormones
• Control of pituitary secretion (part 2)

  1. Posterior pituitary: Nerve signal from hypothalamus

  2. Anterior pituitary: Hormones from hypothalamus known as hypothalamus releasing & inhibitory hormones, absorbed into Hypothalamic-hypophysial portal vessels and carried to anterior pituitary

  
• Hypothalamus releasing and inhibitory hormones

  • Thyrotropin-releasing hormone (TRH)
  • Corticotropin-releasing hormone (CRH)
  • Growth hormone releasing hormone (GHRH)
  • Growth hormone inhibitory hormone (GHIH)
  • Gonadotropin-releasing hormone (GnRH)
  • Prolactin inhibitory hormone (PIH)
• Function of hypothalamus releasing and inhibitory hormones

  Control secretion of anterior pituitary hormones
• Anterior pituitary hormones

  • TSH
  • ACTH
  • Cortisol
  • Aldosterone
  • Estrogen
  • Growth hormone
• Growth hormone

  • Effects on all or almost all tissues of the body
  • Metabolic effects: increases rate of protein synthesis, fat mobilization from adipose tissue, rate of glucose utilization
• Regulation of growth hormone

  1. GHRH from hypothalamus stimulates release of GH

  2. IGF-1 acts as negative feedback inhibiting GHRH and stimulating somatostatin
• Function of nerve signal from hypothalamus

  Control secretion of posterior pituitary hormones
• Antidiuretic hormone (ADH/vasopressin)

  Causes antidiuresis by increasing permeability of collecting ducts and tubules, conserving body water
• Oxytocin

  Causes contraction of pregnant uterus and contraction of myoepithelial cells in breast to help deliver milk
• Acromegaly is caused by overproduction of GH in the adult, leading to enlargement of bones in the face, fingers and toes
• GH action is opposite to insulin function, known as "diabetogenic" leading to diabetes mellitus
• Too much GH can lead to giantism, while insufficient GH results in pituitary dwarfism
• Prolactinoma

  A noncancerous pituitary tumor that produces excess prolactin, leading to galactorrhea
• Cushing's syndrome

  Caused by excess cortisol, leading to high blood pressure, upper body obesity, thin arms and legs, moon face, and other metabolic changes
• Cushing's syndrome causes high blood pressure


  Due to increased circulating cortisol and aldosterone
• calcitonin produced by

  TSH
• cAMP causes

  most of the intracellular action

  ACTH, TCH, LH, FSH, ADH & most hypothalamic releasing hormone
• anterior pituitary hormone

  1. CRH -> ACTH -> adrenal gland -> cortisol
  2. TRH -> TSH -> thyroid gland -> T3 & T4
  3. GnRH -> LH & FSH -> testis & ovaries
  4. dopamine -> inhibit PRL
  5. GHRH -> GH -> liver -> chondrocytes & IGF-1
• increase rate of protein synthesis by GH is

  • enhances AA transport through cell membrane
  • Enhances RNA translation
  • increase nuclear transcription of DNA to form RNA
  • decrease catabolism of protein and amino acids
• increase Fat mobilization for energy by GH

  • increase conc of fat in the blood
  • fatty acid -> acetyl-CoA
  • -> fat is used for energy in preference of carbohydrates and protein
• Carbohydrate Metabolism by GH

  • decrease use of glucose for energy
  • Enhancement of glycogen deposition in cells
  • decrease uptake of glucose by the cells &  blood glucose – “pituitary diabetes”
  • increase secretion of Insulin (diabetogenic effect)
• regulation of GH

  1. hypothalamus secrete GH & somatostatin
  2. GH stimulates pituitary gland -> release GH -> liver -> produce IGF-1 -> bone
  3. somatostatin (use for negative feedback mechanism) inhibit pituitary gland -> no GH
• GHRH

  1. increase level of cAMP
  2. have short & long term
  3. short term = Ca into the cell -> release of GH
  4. long term = increase transcription in nucleus by the gene -> new GH synthesis
• paraventricular nuclei

  release oxytoxin
• supraoptic nuclei release

  ADH
• regulation of ADH


  ***