178. Role of The Hypophysis (pituitary Gland): Physiology and Pathology

  1. Introduction: all endocrine receptors are dependent on stimulation by the hypophysis after birth. In the fetus, however, some endocrine glands partly or completely function without hypophyseal control
    1. HYPOPHYSECTOMY apparently does not affect fetal growth, which appears to be independent of growth hormone (in contrast to juvenile growth)
    2. ABLATION OF THE FETAL HYPOPHYSIS, experimentally, results in severe atrophy of the thyroid gland and adrenals, but only results in a slowing of gonadal function
  2. Neuroendocrine relations: hypothalamohypophyseal control
    1. IN THE FETUS: hypothalamic control seems less essential than in the adult. Only ACTH secretion appears to require nervous stimulation
    2. IN THE ADULT: all the tropic hormones of the anterior pituitary seem to be generally under hypothalamic nuclear control
      1. The neurosecretion material includes inhibitory and releasing factors
      2. Neurosecretion also includes oxytocin and vasopressin (antidiuretic, ADH) hormones of the posterior pituitary which originate in hypothalamic nuclei
  3. Gonadotropic hormones
    1. FOLLICLE-STIMULATING HORMONE (FSH): important in the development of the ovarian follicle as well as in spermatogenesis
    2. LUTEINIZING HORMONE (LH) influences testicular endocrine activity after the prenatal period, ovulation, and appearance of the ovarian corpus luteum. Synergistic with FSH
    3. PROLACTIN (LACTOGENIC) HORMONE: postpartum lactation in women. Important for the maintenance of progesterone secretion by the corpus luteum of pregnancy in the rat
    4. THYROTROPIC HORMONE (TSH) stimulates growth and function of the thyroid gland
    5. SOMATOTROPIC ORGROWTH HORMONE (STH) promotes body growth, fat metabolism, and inhibition of glucose utilization
    6. ADRENOCORTICOTROPIC HORMONE (ACTH): development of the fetal adrenal cortex and the primordium of the cortical zone of the definitive cortex
  4. The intermediate lobe produces the melanotropic hormone (MSH) or intermedin
    1. MSH STIMULATES PIGMENT MOVEMENT in the melanophores from cell body to cell processes. Seen in the retinal pigmented epithelium of the mammalian eye
  5. The pineal gland (epiphysis) and hypophyseal relations: its function is antagonistic to the gonadotropic cells of the pituitary in the fetus and in prepubertal children
    1. IF EXPERIMENTALLY DESTROYED or there is a destructive pineal tumor, there is precocious development of the sex organs and secondary sex characteristics
    2. THE ENDOCRINE ROLE of the pineal apparently stops at puberty. Its secretion, melatonin, however, may be involved in the timing of human adolescence
  6. Malformations of the hypophysis (pituitary gland)
    1. AGENESIS: appears to be the result of a disturbance of notochordal induction
    2. DOUBLING OF THE GLAND: produced experimentally by riboflavin deficiency, hypervitaminosis A, and some tranquilizers
    3. CRANIOPHARYNGIOMAS (Rathke's pouch tumor) constitute about 3-5% of intracranial neoplasms, are usually benign with effects due to pressure, are operable, and especially affect children. Seen intracranially with symptoms like anterior pituitary tumors
      1. Onset of symptoms is usually before the age of 15 years
      2. Usually form in front of the anterior pituitary lobe resulting in visual problems
      3. It is a heterogenous, intrasellar tumor, usually partly solid and partly cystic with keratinized areas and foci of necrosis. Cholesterol crystals and calcification are common. The latter are seen easily on x-rays

role of the hypophysis (pituitary gland): physiology and pathology: image #1