Download 2. Parenchymal Cells

II. THYRIOD GLAND
Anatomically consists from two lobes communicated by isthmus.
1. Capsule: the capsule of thyroid gland consists of a thin collagenous c.t. in all
animals except in large ruminants and swine. their septa extend into the substance of
the gland, subdividing it into lobules.
2. Parenchymal Cells: the parenchymal cells of the thyroid gland composed from
Follicular Cells in stimulating phase are (simple cuboidal epithelium with
microvilli) while in resting these epithelial cells are squamous & Parafollicular
Cells (clear cells) located at the periphery of the follicles which are source of calcitonin.
3. Connective tissue: consists of interfollicuar connective tissue of well vascular .
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Histo-Physiology: The iodide from blood stream is actively transported into follicular cells at
their basal aspect via iodide pumps. The iodide is oxidized by thyroid peroxidase on the
apical cells membrane and bound to tyrosine producing of thymoglobulin(colloid)which
rearranged to form tri iodothyronine (T3) and tetraiodothyronine or thyroxin (T4) which
stimulated protiens synthesis.
Release: the binding of TSH to receptors on the basal aspect of plasma membrane induce
follicular cells to become tall cuboidal cells to form psedopods on their apical cell mem. That
engulf and endocytose colloid –filling vesicle then T3&T4 are removed from thymoglobulin,
liberate into the cytosol and release at the basal aspect of follicular cells into perifollicular
capillaries.
The enlargement of thyroid gland is referred to hyper plastic goiter.
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III. PARATHYROID GLAND
This gland is presented adherent to thyroid gland. And separated from it by c.t.
capsule
•Capsule: consist from DICT as in thyroid gland in animals.
•Parenchymal cells:
1. Chief Cells: are numerous small cells with large nuclei composed of two types of
cells, dark and light acidophilic cytoplasmic that form cords these cells containing
glycogen granules with lipid droplets.
2. Oxyphils: are large very light acidophilic and much fewer in numbers than chief
cells.
3. Syncytial cells: are small and dark with dark nuclei with acidophilic cytoplasm.
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Histo-Physiology: the Parathyroid hormone (PTH) produce by chief cells is responsible
maintaining proper calcium ion balance, a drop in blood calcium concentration activated a feed
back mechanism that stimulated chief cell secretion PTH which stimulate osteioblast that
released osteoclast stimulating factors which followed by bone resorption, in kidneys the PTH
prevent urinary calcium loss, also control calcium uptake from intestine
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