ENDOCRINE SYSTEM

• HORMONE

  • secretory product of endocrine cells and organs that passes into the circulatory system (bloodstream) for transport to target cells
  • Hormonal control mechanisms
  • Paracrine
  • Autocrine
  • Juxtacrine

  
• PITUITARY GLAND = HYPOTHALAMUS & PINEAL GLAND
• PITUITARY GLAND (HYPOPHYSIS)

  • lies below the brain in a small cavity on the sphenoid bone, the sella turcica
  • formed in the embryo partly from the developing brain and partly from the developing oral cavity 
  • pituitary actually consists of two gland:
  • posterior neurohypophysis
  • anterior adenohypophysis
• Week 3

  A) Diencephalon

  B) Hypophyseal pouch

  C) Stomodeum

  D) Neuroectoderm

  E) Neurohypophyseal bud

  F) Oral ectoderm

  G) Pharynx

  
• Late second month and fetal period

  A) Infundibulum

  B) Hypophyseal pouch

  C) Neurohypophyseal bud

  D) Pars tuberalis

  E) Pars intermedia

  F) Pars distalis

  G) Median eminence

  H) Pars nervosa

  
• Hypothalamus

  A) pituitary hormones

  B) MSH

  C) ADH and oxytocin

  
• HYPOPHYSIS

  
• HYPOPHYSIS

  
• ANTERIOR PITUITARY

  • Adenohypophysis
  • derived embryonically from the hypophyseal pouch
  • 3 parts
  • Pars distalis
  • Pars tuberalis
  • Pars Intermedia
• Pars distalis

  • cords of well-stained endocrine cells interspersed with fenestrated capillaries and supporting reticular connective tissue

  • chromophils and chromophobes

  
• chromophils

  
• Chromophils

  A) Somatotrophs

  B) Lactotrophs

  C) Corticotrophs

  D) Gonadotrophs

  E) Thyrotrophs

  
• pars tuberalis

  •smaller funnel-shaped region surrounding the infundibulum of the neurohypophysis

  • Most of the cells are gonadotrophs
• pars intermedia

  •thin zone of basophilic cells between the pars distalis and the pars nervosa of the neurohypophysis

  •Basophils

  •usually contains colloid-filled cysts

  
• Anterior pituitary

  A) Growth hormone

  B) Prolactin

  C) Adrenocorticotropic hormone

  D) Follicle-stimulating hormone

  E) Luteinizing hormone

  F) Thyrotropic hormone

  G) straight

  H) straight

  I) small

  J) 2

  K) 2

  L) 2

  
• POSTERIOR PITUITARY

  • Neurohypophysis 
  • consists of the pars nervosa and the infundibular stalk 
  • not an endocrine gland
  • a storage site for neurosecretions
  • Pituicytes

  
• Pituicytes

  • highly branched glial cells that resemble astrocytes

  •most abundant cell type in the posterior pituitary
• POSTERIOR PITUITARY

  • neurosecretory neurons whose cell bodies lie in the supraoptic nuclei and paraventricular nuclei of the hypothalamus
  • hormones accumulate in axonal dilations called neurosecretory bodies or Herring bodies

  A) Oxytocin

  B) Antidiuretic hormone

  C) 9

  D) 9

  E) arginine

  F) lysine

  
• HYPOTHALAMUS

  • located in the middle of the base of the brain, and it encapsulates the ventral portion of the third ventricle 
  • regulates pituitary gland activity
  • A feedback system regulates endocrine function at two levels:

  1. hormone production in the pituitary gland

  2. hypothalamic releasing hormone production in the hypothalamus.
• PINEAL GLAND

  • epiphysis cerebri
  • an endocrine or neuroendocrine gland that regulates daily body rhythm
  • Located at the posterior wall of the third ventricle near the center of the brain
  • flattened, pine cone-shaped structure
  • Pinealocytes are the chief cells of the pineal gland 
  • characterized by the presence of calcified concretions, called corpora arenacea or brain sand
  • melatonin

  
• ADRENAL GLANDS

  • paired organs lying near the superior poles of the kidneys, embedded in the perirenal adipose tissue
  • Flattened structures with a half-moon shape 
  • two concentric regions
  • yellowish adrenal cortex 
  • reddish-brown central adrenal medulla

  
• ADRENAL CORTEX

  • features of steroid-secreting cells: acidophilic cytoplasm rich in lipid droplets, with central nuclei
  • three concentric zones
  • Zona glomerulosa
  • zona fasciculata
  • zona reticularis

  
• Zona glomerulosa

  • immediately inside the capsule
  • consists of closely packed, rounded or arched cords of columnar or pyramidal cells with many capillaries 
  • Mineralocorticoids > ALDOSTERONE
• zona fasciculata

  • consists of long cords of large polyhedral cells, one or two cells thick, separated by fenestrated sinusoidal capillaries
  • filled with lipid droplets and appear vacuolated
  • Glucocorticoids > CORTISOL
• zona reticularis

  • consists of smaller cells in a network orinegulat

  cords interspersed with wide capillaries more heavily stained than those of the other zones because they contain fewer lipid droplets and more lipofuscin pigment

  • Weak androgens > Dehydroepiandrosterone (DHEA)

  
• ADRENAL MEDULLA

  • composed of large, pale-staining polyhedral cells arranged in cords or clumps and supported by a reticular fiber network
  • chromaffin cells
  • Medullary parenchymal cells & arise from neural crest cells
  • Modified sympathetic postganglionic neurons, lacking axons and dendrites and specialized as secretory cells
  • Catecholamines > either epinephrine or norepinephrine
• THYROID AND PARATHYROID GLAND

  
• THYROID GLAND

  • located anterior and inferior to the larynx, consists of two lobes united by an isthmus
  •  from the foregut endoderm near the base of the developing tongue
  • synthesizes the thyroid hormones thyroxine (tetra-iodothyronine or T4) and triiodothyronine (T3)
• THYROID FOLLICLE

  • the structural and functional unit of the thyroid gland.
  • roughly spherical cystlike compartment
  • Walls formed by follicular epithelium

  Simple cuboidal epithelium

  • contain a gel-like mass called colloid
  • contains the large glycoprotein thyroglobulin
  • Follicular epithelium contains two types of cells:
  • follicular cells
  • parafollicular cells
• Follicular cells 

  • principal cells
  • responsible for production of the thyroid hormones T4 and T3.
  • exhibit a slightly basophilic basal cytoplasm with spherical nuclei containing one or more prominent nucleoli
• parafollicular cells

  • C cell
  • located in the periphery of the follicular epithelium and lie within the follicle basal lamina
  • calcitonin
• THYROID FOLLICLE

  
• PARATHYROID GLANDS

  • four small ovoid masses located on the back of the thyroid gland, usually embedded in the larger gland's capsule
  • A sparse reticular stroma supports dense elongated clusters of secretory cells
  • principal (chief) cells
  • oxophil cells
• principal (chief) cells

  • small polygonal cells with round nuclei and pale-staining, slightly acidophilic cytoplasm
  • endocrine cells of the parathyroid glands 
  • parathyroid hormone (PTH)
• PARATHYROID GLANDS

  
• PARATHYROID GLANDS

  
• PANCREATIC ISLETS

  • compact spherical or ovoid masses of endocrine cells embedded within the acinar exocrine tissue of the pancreas
  • very thin reticular capsule surrounds each islet 
  • epithelial outgrowths from endoderm of the developing gut
  • polygonal or rounded, smaller, and more lightly stained than the surrounding acinar cells, arranged in cords separated by fenestrated capillaries

  
• a or A cells

  • glucagon and are usually located peripherally.
• ß or B cells

  • insulin are the most numerous, and are located centrally.
• 6 or D cells

  • somatostatin, are scattered and much less abundant