Endocrine System

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Endocrine System

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Objectives

• How do the thyroid follicular epithelial cells
  synthesize thyroglobulin and release thyroxine?
• Function of parafollicular cells.
• Cells and function of parathyroid gland.
• Describe the structure and function of pituitary
  gland.
• The structure and function of adrenal gland.

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Overview

• Pituitary gland
• Thyroid gland
• Parathyroid gland
• Adrenal gland

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Features of the endocrine system
1?typically arranged as cords or clusters 2?no
ducts 3?numerous Cap.
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Hormone Synthesis

• 1.Protein and peptide hormone
• Cytology is similar to serous cells of exocrine
  glands
• But are not oriented towards the lumen
• RER, Golgi
• 2. steroid hormones
• Abundant smooth ER
• Numerous mitochondria with tubular cristae
• Cytoplasmic lipid droplets

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ultrastructure
Secreted G.
SER
Golgi complex
lipid
Mito.
RER
Lysosome
Protein hormone
Steroid hormone
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Thyroid gland

• Two lobes connected by an isthmus
• Capsule DCT
• FolliclesLCT with cap.

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Thyroid follicles

• normally cuboidal but become columnar when
  stimulated and squamous when inactive
• Colloid-iodinated thyroglobulin
• RER, mitochondria and numerous lysosomes
• Function synthesize and store thyroid hormones

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Synthesis/Storage/Secretion of TH

• Synthesis of thyroglobulin (TG) from tyrosine
• Glycosylated by Golgi complex,
• Secreted into the lumen and iodinated
• TSH stimulates endocytosis of iodinated TG by
  follicular cells
• Lysosomes fuse with the endosomes
• Proteases cleave off the iodinated residues to
  form T4 (90) and T3 (10)
• T3 and T4 diffuse into the fenestrated
  capillaries

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Function of thyroid hormones

• Regulate basal metabolic
• Influence body growth and development of the
  nervous system during fetal
• Hypothyroidism fail to produce enough thyroid
  hormone
• Hyperthyroidism excessive thyroid hormone

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Parafollicular cells

• Btw the follicular cells and basal lamina
• Pale staining, c (clear) cell
• Lots of small secretory granules that contain
  calcitonin

• A polypeptide hormone
• Lower blood calcium levels

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Parathyroid glands

• Overview
• Four small glands
• Posterior surface
• Capsule
• Parenchyma
• Chief cell
• parathyroid hormone (PTH)
• Oxyphil cells
• function is not known

Raise blood calcium levels
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Adrenal gland

• Overview
• At the superior pole of each kidney
• Embryonic sources
• cortex-mesoderm
• medulla-neural crest

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Adrenal cortex

• Zona Glomerulosa
• in cords or clusters,a few small lipid droplets.
• Mineralcorticoids--aldosterone
• Zona Fasciculata
• Columns of cells,spongiocytes with many lipid
• droplets
• Glucocorticoids
• Zona Reticularis
• In anastomosing cords
• Androgens and small amount of glucocorticoids

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Adrenal medulla

• Chromaffin cells,large polyhedral cells
• Arranged in irregular cords
• Postganglionic sympathetic neurons
• adrenaline and noradrenaline

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Blood Supply of the Adrenal Glands

• Capsular arteries branch to form two types of
  arterial blood flow
• A supply that branches to form cortical
  fenestrated capillaries
• Dont branch in the cortex,but branches in
  medulla to form a fenestrated capillary network
• Both drain into small venules and then into
  medullary veins

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Hypophysis (Pituitary gland)
General Features
Pea-sized Sits in the sella turcica Compound
gland Attaches to the hypothalamus by the
pituitary stalk (infundibulum) Two Lobes (1)
adenohypophysis (2) neurohypophysis
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Development of the 2 Pituitary Components

• Anterior pituitary Glandular epithelial tissue
  that derives from oral ectoderm (Rathkes pouch)
• Posterior pituitary Neuroendocrine tissue that
  derives from a down growth of the diencephalon
  (neural ectoderm) retains its neural connections

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Pituitary gland
Adenohypophysis Pars distalis Pars intermedia
Pars tuberalis Neurohypophysis Pars
nervosa Infundibulum
adenohypophysis
neurohypophysis
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Pars Distalis

• Previously identified on the basis of affinity
  of their granules for acidic or basic dyes
• Distinct Cell Types (3)
• 1. Basophils blue granules
• 2. Acidophils pink granules
• 3. Chromophils no obvious
  granules

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Pars Distalis Hormone secretion
(ICSH)
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(No Transcript)
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Pars Intermedia

• Colloid-containing cysts
• Basophilic cells
• Melanocyte-stimulating hormone (MSH)
• Pars Tuberalis
• Cells arranged in cords
• May secrete FSH and LH, but has not
• been confirmed

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Neurohypophysis

• Unmyelinated nerve fibers
• Pituicytes
• Cap.
• accumulated neurosecretory
• granules (Herring bodies)
• Oxytocin
• Antidiuretic hormone(ADH)
• Supraoptic
• Paraventricular nuclei

Herring body
Cap.
Pituicyte
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Vascularization of the pituitary gland

• 1.Arterial supply
• Superior and inferior
• hypophyseal arteries
• 2.Hypophyseal portal system
• Primary cap. plexus
• store hypothalamic hormones
• Drained by hypophyseal portal veins
• Secondary cap. plexus

No direct artery in the pars distalis
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Pineal Gland

• Its secretions vary with the light and dark
  cycles of the Melatonin (at night)
• Serotonin (during the day) and melatonin (at
  night)

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Endocrine Glands
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• Single choice
• 1.Parafollicular cells in thyroid gland are able
  to produce
• A. rennin B.
  erythropoietin
• C. thyroxine D. calcitonin
• E. Prostaglandin
• 2. The epithelial cells in parathyroid gland are
  of two types
• A. chief cells and parietal cells
• B. follicular cells and parietal cells
• C. chief cells and oxyphil cells
• D. follicular cells and oxyphil cells
• E. alpha cells and beta cells
• 3.Which one of the following hormones lowers
  blood calcium levels by inhibiting bone
  resorption?
• A.Calcitonin
• B. adrenaline
• C.Parathyroid hormone
• D.T3
• E.Prolactin

(D)
(C)
(A)
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The End of Endocrine System