Endocrine

• What is the function of the endocrine system?

  Secretes hormones that regulate processes such as growth, reproduction, and metabolism by body cells
• What are some regulating factors?

  hormones , local factors
• What are the characteristics of an endocrine gland?

  No ducts , local secretion (blood vessels)
• What are the chemical composition of hormones?

  Peptides , amino acids and lipids
• What is the morphology of endocrine cells?

  Peptides/amino acid hormones: Polyhedral cells , close to capillaries , RER, golgi , secretion granules

  
  

  Lipids: polyhedral cells , close to capillaries , SER , lipid droplets , mitochondria
• How are endocrine cells irrigated?

  Fenestrated capillaries , sinusoidal capillaries
• What are the characteristics of the pineal gland?

  Located at the posterior wall of third ventricle close to brain centre , small
• What are the cells in the pineal gland?

  Pinealocytes (secreting cells , associated in clumbs , large nuclei with nucleolus and lipid droplets) and glial cells
• What is brain sand?

  Calcified concretions (crystals) , precipitation of phosphates and carbonates in carrier proteins
• What are the functions of pinealocytes?

  Secrete melatonin which help regulate circadian rhythms (melatonin is inhibited by light) and inhibits gonadal activity
• What are the characteristics of the thyroid?

  Synthesize: T3 , T4 and calcitonin

  
  

  Functions: maintain basal metabolism , stimulate growth , regulate body heat , stimulate cell differentiation , regulate calcium metabolism
• What are the structures in the thyroid?

  Foillicles: follicular cells + parafollicular cells , simple epithelium (cube when active)

  
  

  Colloid: eosynophil , PAS+ , storage of thyroglobulin
• What is the structure of the follicular cells?

  Microvilli , RER , golgi , lisosomes , colloid droplets
• What is hiperthyroidism?

  Abnormal stimulating autoantibodies , enlarged thyroid , increased metabolic rate
• What is hipothyroidism?

  Congenital anomalies , iodine deficiency
• What are the characteristics of the C/parafollicular cells?

  Basal localization , big round nucleus , pale stain , endocrine granules (TEM)

  
  

  Secrete calcitonin
• How do C cells control calcium levels?

  There is an increase in Ca and so increase of calcitonin secretion which increase calcium in bone , decreases calcium reabsorption in kidney and inhibits osteoclast activity leading to a decrease of Ca in blood
• What are the cells in the parathyroid gland?

  Oxyphil cells (no secretory function, big and round) , principal cells (parathyroid hormone)
• How does the parathyroid maintain ca equilibrium?

  decrease in blood

  increases PTH which stimulate ca reabsorption in kidney and efflux of ca from bone. Kidney stimulates active vitamin D production leading to absorption in intestine leading to increase levels in blood
• What are the characteristics of the suprarenal gland?

  produce steroids , capsule , cortex , medulla , vein collect hormones
• What are the layers in the suprarenal cortex?

  Zona glomerulosa: grouped cells , glomerules , small rounded or columnar cells , few lipid droplets , SER

  
  

  Zona fasiculata: Cells in cords , biggest part , polyhedric cells , abundant lipid droplets , highly developed SER and golgi

  
  

  Zona reticularis: Anastomosing cords , dark cells , few lipid droplets
• What is the mechanism of aldosterone and cortisol activity?

  Aldosterone: ZOna glomerulosa , target distal convolutes tubules and collecting tubes , water reabsorption , triggered by renin

  
  

  Cortisol: Zona fasciculata , immunosupressor , anti inflammatory , increases glucose and fatty acids in blood , peak in the morning , long term stress response
• What are the structures in the suprarenal. medulla?

  Neuroectodermic origin from neural crest , modified sympathetic ganglion without axons , very irrigated
• What is the function of chromaffin cells?

  Catecholamines secretion , epinephrine and norepinephrine , immediate stress response
• What is the structure of norepinephrine and epinephrine cells?

  norepinephrine: Big vesicles , dense granules

  
  

  epinephrine: Small vesicles , less dense
• What are the characteristics of the hypophysis?

  Base of the brain , bound to hypothalamus , on stella turcica
• What is the structure of the hypophysis?

  posterior lobe (neurohypophysis) and anterior lobe (adenohypophysis)
• What is the structure of the adenohypophysis and neurohypophysis?

  Adenohypophysis: Glandular epithelial tissue

  
  

  Neurohypophysis: Neural secretor tissue
• How is the hypophysis irrigated?

  Adenohypophysis

  1)Superior hypophyseal artery

  2)primary capillary plexus

  3)Hypophyseal portal veins

  4)Secondary capillary plexus (sinusoids)

  5) Hypophyseal

  
  

  
  

  Neurohypophysis

  1)inferior hypophyseal arteries

  2) capillary plexus

  3) Hypophyseal veins
• What is the structure of the adenohypophysis?

  Pars distalis: Surrounded by dense CT , groups of endocrine cells , fenestrated sinusoids , network of reticular fibers
• What are the cells located in the adenohypophysis?

  Chromophils: Basophils , acidophils

  chromophobes (lightly stained)
• What are the functions of the chromophils?

  Acidophils:

  SOmatotrope - GH, somatotropin

  Lactotrope - prolactin

  
  

  Basophils:

  Thyrotrope - TSH

  Gonadotrope - gonadotropins (LH , FSH)

  Corticotrope- corticotropin
• What does somatotropin do?

  Stimulated IGF which induces growth
• What does prolactin do?

  Pregnancy and lactation , hypertrophy and hyperplasia , enlarged hypophysis.

  
  

  More prolactin secreted at night and after feed , suppresses ovulation
• What do corticotrope cells do?

  Produce a precursor of ACTH -> proopiomelanocortin (effects: metabolic changes , immune suppression , anti inflammatory)

  cleaved in several fragments , stimulates suprarenal glands
• What do the gonadotropes do?

  FSH: follicule maturation in ovaries and stimulates seminiferous epithelium in testes

  
  

  LH: Triggers ovulation and corpus luteum development , stimulates testosterone secreting cells
• What does TSH do?

  stimulates the thyroid to release T3 and T4
• How is the adenohypophysis regulated?

  1) synthesis of regulation factors in the neurons

  2) Transport to infundibulum

  3) Secretion to primary capillary plexus

  4) transport through hypophyseal portal veins

  5) regulation factors arrive to adenohypophysis through secondary capillary plexus

  6) Hormones are released to blood stream through secondary capillary network

  
  

  1) release hormones/factors

  2) inhibiting hormones
• What is the negative feedback loop of the adenohypophysis?

  Hypothalamus releases TRH which stimulates hyphophysis to release TSH which then stimulates target organ which releases specific hormone which inhibits T3 and T4
• What are the cells in the neurohypophysis?

  Magnocellualr secretory cells , pituicytes (supporting role with blood vessles , sinusoinds and axons) , herring bodies (accumulation of neurohormones , close to capillaries , rich in mitochondria)