Thyroid
• Fibrous capsule surrounds the gland, sends septa inside dividing the gland into
lobules. Each lobule contains follicles of various sizes separated by connective
tissue containing numerous capillaries.
• Follicles are filled with eosinophilic homogenous material called colloid
(iodinated thyroglobulin).
Folliclelined by follicular cellsresting on a basement membrane, Cells vary in shape
depending on the activity of the gland normally they are cuboidal in shape.
When inactive, the cells are flat squamous type with abundant colloid,
When highly active, the cells are columnar with scanty colloid,
• Parafollicular cells or C cells are located between the follicular cells and basement
membrane or in between the follicles-pale staining with eccentric nuclei.
• Hormones produced:
Follicular cells secrete triiodothyronine (T3) and tetra-lodothyronine
(T4/ thyroxin). T3 is more active than T4. These hormones influence the
metabolic rate of cells.
Parafollicular cells secrete thyrocalcitonin which regulates calcium
metabolism by lowering the blood calcium levels.
Parathyroid gland:
Connective tissue capsule send septa which divide the gland into lobules.
Each lobule contains cords/clusters of cells separated by numerous sinusoids
• Two types of cells:
1. Chief cells or principal cells--more numerous, small round cells with clear
cytoplasm.
2. Oxyphil cells-lew in number, large cells with eosinophilic cytoplast
Appear at the time of puberty.
• Hormones produced:
Chief cells produce parathyroid hormone (parathormone)-which increase
the blood calcium levels.
Oxyphil cells-function not known.
Suprarenal Gland
• Connective tissue capsule surrounds the gland. Divided into outer cortex and inner medulla
• Cortex-three layers depending on arrangement of cells:
1. Zona glomerulosa -outermost layer, outer 1/5th. Polyhedral cells arranged in the form of inverted U-shape.
2. Zona fasciculata-middle 3/5th. Polyhedral cells are arranged in the form of straight columns separated by sinusoids. Cells contain lipids which give a spongy appearance
to cells.
3. Zona reticularis-inner 1/5th. Cells arranged in the form of network of branching and anastomosing cords, separated by capillaries.
• Medulla-large chromaffin cells in groups separated by sinusoids.
• Hormones produced:
Zona glomerulosa---mineralocorticoid called aldosterone--for electrolyte and water balance
Zona fasciculata-glucocorticoids called cortisone and cortisol—for carbohydrate and protein metabolism.
Zona reticularis-sex hormones estrogen and androgens,
Medulla-catecholamine-adrenaline and noradrenaline.
Pituitary Gland
• It has two parts-adenohypophysis and neurohypophysis.
• Adenohypophysis/pars anterior-made of clusters of cells separated by sinusoids.
-Two cell types-chromophobes and chromophils
-Chromophobes do not take up stain and appear pale.
-Chromophils have granules in their cytoplasm. Depending on the staining two types:
-Acidophils which take up acidic stain and appear eosinophilic
-Basophils which take up basic stain and appear basophilic.
Pars intermedia has colloid filled vesicles.
• Neurohypophysis/pars posterior
-Madeof unmyelinated nerve fibers, cell bodies of which are located in the paraventricular and supraoptic nuclei of hypothalamus.
-Terminal parts of axons are called Herring bodies which contain the hormones produced by the hypothalamus.
-Supporting cells called pituicytes are present in between the nerve fibers.
• Hormones produced:
Acidophils:Somatotrophs-growth hormone; mammotrophs-prolactin.
Basophils: Corticotrophs adrenocorticotropic hormone ; thyrotrophs--thyroid stimulating
hormone; gonadotrophs-follicle stimulating hormone and luteinizing hormone (female)/interstitial cell stimulating hormone (male).
Pars intermedia-melanocytes stimulating hormone.
Pars posterior-stores vasopressin/antidiuretic hormone and oxytocin.