Endo 2

• Prostaglandins

  • Powerful substances found in a wide variety of body tissues
  • Produced in a tissue and diffuse only a short distance to act on cells in that tissue
  • Several class include: PGA, PGE, and PGF
  • Influence many body functions, including respiration, blood pressure, gastrointestinal secretions, and reproduction
• Pituitary (Hypophysis) Gland

  • Location: Diencephalon
  • Pituitary gland: Two-lobed organ that secrets important hormones
• Adenohypophysis (True gland)

  • Anterior lobe; made of glandular tissue
  • Synthesizes and secrets a number of hormones
• Neurohypophysis (Storage area)

  • Posterior lobe; made of neural tissue
  • Receives, stores, and releases hormones from the hypothalamus
• Six hormones of the anterior pituitary

  
  

  1. Growth hormone (GH)
  2. Prolactin (PRL)
  3. Thyroid-stimulating hormone (TSH)
  4. Adrenocorticotropic hormone (ACTH)
  5. Follicle-stimulating hormone (FSH)
  6. Luteinizing hormone (LH)
• Anterior Pituitary

  • Trophic effects:

  1. High blood [hormone] causes target organ to hypertrophy.
  2. Low blood [hormone] causes target organ to atrophy.
• TSH: Stimulates growth of the thyroid gland; also stimulates it to secrete thyroid hormone
• ACTH: Stimulates growth of the adrenal cortex and stimulates it to secrete glucocorticoids (mainly cortisol)
• FSH

  • Initiates growth of ovarian follicles each month in the ovary and stimulates one or more follicles to develop to the stage of maturity and ovulation
  • Stimulates estrogen secretion by developing follicles
  • Stimulates sperm production in the male
• LH

  • Acts with FSH to stimulate estrogen secretion and follicle growth to maturity
  • Causes ovulation
  • Causes luteinization of the ruptured follicle and stimulates progesterone secretion by corpus luteum
  • Causes interstitial cells in the testes to secrete testosterone in the male
• GH

  • Stimulates growth by accelerating protein anabolism
  • Accelerates fat catabolism and slows glucose catabolism
  • By slowing glucose catabolism, tends to increase blood glucose to higher than normal level (hyperglycemia)
• PRL: Stimulates breast development during pregnancy and secretion of milk after the delivery of the baby
• Hypothalamic Control of the Anterior Pituitary

  • Hormonal control rather than neural
  • Hypothalamus neurons synthesize releasing and inhibiting hormones
  • Hormones are transported to axon endings of median eminence
  • Hormones secreted into the hypothalamo-hypophyseal portal system regulate the secretions of the anterior pituitary
• Hypothalamic Control of Posterior Pituitary

  • Hypothalamus neuron cell bodies produce:

  1. ADH: supraoptic nuclei
  2. Oxytocin: paraventricular nuclei.

  • Transported along the hypothalamo-hypophyseal tract
  • Stored in posterior pituitary
  • Release controlled by neuroendocrine reflexes.
• Physiology of posterior Pituitary gland

  • Posterior pituitary hormones

  1. ADH also known as Vasopressin
  2. Oxytocin

  • These hormones are synthesized in the neuron cell bodies in the hypothalamus and packed in secretory vesicles with neurophysin (carrier protein)
  • Does not synthesize hormones
  • Consists of axon terminals of hypothalamic neurons
• Hypothalamic-Pituitary Relationships: Posterior Lobe

  • The posterior lobe is a down growth of hypothalamic neural tissue
  • Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract)
• Secretions of the posterior pituitary are controlled by nervous signals from hypothalamus
• Synthesis of ADH

  •  ADH synthesized in the cell bodies of hypothalamic neurons(supraoptic nucleus)
  • ADH is stored in the posterior pituitary
• Two types of receptors for ADH

  1. V1: Mediate vasoconstriction
  2. V2: Located in the principle cells in distal convoluted tubule and collecting ducts in the kidneys
• The most important function of ADH is to conserve body water by reducing urine output
• Osmotic pressure:

  • Osmoreceptors in the hypothalamus

  1. ↑Osmotic pressure = ↑ADH secretion
  2. ↓Osmotic pressure = ↓ADH secretion
• Blood volume

  • Baroreceptor  in carotid artery and aortic arch, and Stretch receptors in left atrium

  1. ↑Blood pressure = ↓ADH secretion
  2. ↓Blood pressure = ↑ADH secretion
• Synthesis of Oxytocin

  • Oxytocin is synthesized in the cell bodies of hypothalamic neurons(paraventricular nucleus)
  • Oxytocin is stored in the posterior pituitary
• Function of oxytocin

  • Stimulates the pregnant uterus to contract
  • May initiate labor
  • Causes glandular cells of the breast to release milk into ducts
  • Enhances social bonding
• Hypothalamus

  • Actual production of ADH and oxytocin occurs in the hypothalamus
  • After production in the hypothalamus, hormones pass along axons into the pituitary gland
  • The secretion and release of posterior pituitary hormones is controlled by nervous stimulation
  • The hypothalamus controls many body functions related to homeostasis (temperature, appetite, and thirst)