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Main page | Structure | Departments | Department of Histology and Embryology | Materials for students | Modul 2 | HYPOPHYSIS. HYPOTHALAMUS. PINEAL GLAND.

HYPOPHYSIS. HYPOTHALAMUS. PINEAL GLAND.
HYPOPHYSIS.
It has pars distalis, pars intermedia, pars nervosa and median eminence. Pars distalis and pars intermedia belong to Adenohypophysis. Parenchymal cells here are EPITHELIAL endocrine cells.
Pars nervosa and median eminence belong to Neurohypophysis. Parenchymal cells here are glia -like cells (NERVOUS tissue).
  1. Pars distalis is composed of: A) epithelial cords (parenchymal endocrine cells),
B) sinusoidal capillaries of secondary capillary plexus.
  1. Endocrine epithelial cells are classified on: CHROMOPHILS (well-staining) and Chromophobs (bad- staining). CHROMOPHILS include 2 groops: A) Basophils, B) Acidophils.
  2. Basophils include 3 types of endocrine cells: A) Corticotrophs, B) Thyrotrophs,
C) Gonadotrophs. Corticotrophs secrete ACTH (adrenocorticotropic hormone). It stimulates zona fasciculata cells of suprarenal cortex. Thyrotrophs secrete TSH (thyroid stimulating hormone). It stimulates follicular cells of thyroid gland. Gonadotrophs secrete 2 hormones: FSH (follicle stimulating hormone), LH (luteinizing hormone). FSH stimulates maturation of follicles in ovary. LH stimulates ovulation.
  1. Acidophils include 2 types of endocrine cells: A) Somatotrophs and B) Mammotrophs.
Somatotrophs secrete STH (or GH) -Somatotropic hormone (or growth hormone). It stimulates elongation of long bones. Mammotrophs secrete hormone prolactin. It stimulates milk synthesis in mammary gland.
  1. Pars nervosa is composed of: A) glial-like cells – named pituicytes. It form parenchyme. It do NOT have proper endocrine function. B) axonic terminals (Herring bodies). It belong to neurosecretory cells of anterior hypothalamic nuclei. C) fenestrated capillaries. Axonic termini form synapses with these capillaries.
  2. Function of pars nervosa: axonic terminals through synapses release to peripheral blood 2 hormones: A) ADH (antidiuretic hormone), or VASOPRESSIN, B) OXYTOCIN. BUT:site of these hormones synthesis is SON and PVN of anterior hypothalamus. ADH stimulates water reabsorbtion in renal tubules, hence prevents diabetes insipidus. Vasopressin consricts arterioles, hence increases blood pressure. OXYTOCIN stimulates contraction of uterine myometrium during labor and milk ejection.
  3. Embryonic origin for endocrine epithelial cells of pars distalis – is oral ectoderm, named Rathkes pouch. For pituicytes is – neural tube.
HYPOTHALAMUS.
Anterior hypothalamus is composed of nervous tissue cells, named neurosecretory cells (or secretory neurons). It form 2 magnocellular nuclei: A) SON, or SUPRAOPTIC nucleus, B) PVN, or PARAVENTRICULAR nucleus. SON synthetises hormone ADH. PVN synthetises oxytocin. Both nuclei send its axons to pars nervosa. Axonic terminals form synapses with fenestrated capillaries. ADH prevents diabetes insipidus.
Medial hypothalamus is composed of neurosecretory cells also. It form parvicellular nuclei, for example arquate nucleus. Axons of these nuclei terminate in median eminence and form synapses with primary capillary plexus. Through synapses termini secrete RELEASING HORMONES (ACTH-RH, GH-RH) to primary capillaries. It move to portal vein. Vein enters into pars distalis and branches on secondary capillaries. Portal blood brings RELEASING HORMONES (RHs) to CHROMOPHILS of pars distalis. These hormones stimulate function of chromophils.
PORTAL SYSTEM includes: A) superior hypophiseal artery – B) primary capillary plexus –
C) portal vein - D) secondary (sinusoidal) capillaries.
PINEAL GLAND.
It is composed of capsule, connective tissue septa, incomplete lobules. Parenchymal cells in lobules are: A) pinealocytes (belong to neurosecretory cells), B) interstitial cells.Pinealocytes secrete hormone
melatonin and other hormones, that inhibit abnormal fast development of reproductive system.
Составитель – доцент В.В. Бондаренко.
 
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