1003 - Endocrine Histology Flashcards
What is the difference between endocrine and exocrine glands?
While exocrine glands have discrete secretory units and ducts, both lined by cuboidal cells, endocrine glands are organised clusters of secretory epithelial cells that synthesise release hormones directly into the interstitium and then bloodstream - no ducts. They have a rich capillary network, and all cells have dense core granules on EM.
Describe the broad appearance of the pituitary gland under light microscopy.
Anterior pituitary is glandular, with dark pink staining (1). Posterior is nervous tissue (2), lighter staining and contiguous with the infindibulum (3).
What are the three cell types of the anterior pituitary? What does each secrete?
Acidophils (70%) - dark pink staining, secrete growth hormone and prolactin. Basophils (30%) - light purple staining, secrete ACTH (adrenocorticotrophic hormone), thyrotrophic hormone, gonadotrophic hormones. Chromophobes (few) - pale staining with few cytoplasmic granules - may be resting or degranulated cells. You can use immunohistochemical staining to tell which hormone is in which cell.
What are Herring bodies?
Dark-purple staining ‘storage centres’ near the axon terminals of posterior pituitary cells - store hormones prior to release.
What are the two cell types in the posterior pituitary?
Non myelinated axons (contain ADH and oxytocin) arise from hypothalamic neurosecretory cells.
Pituicytes - seen as nuclei, supporting glial cells.
What does a pituitary tumour look like under light microscopy?
Like normal pituitary tissue, but only one cell type.
What does the thyroid look like under low power light mycroscopy?
Circular follicles - structures filled with uniformly pink staining colloid. Colloid contains thyroglobulin, with T3 and T4 molecules attached. Thyroid is unique in storying the hormone outside the cell, in the colloid.
What does the thyroid look like under high power light microscopy?
Each follicle (1) lined by a layer of thyroid epithelial cells (3). Parafollicular cells exist in the interstitial spaces between the follicles (4).
Describe the macroscopic appearance of the thyroid.
Butterfly shaped, found in front of the upper trachea. Weighs around 20 grams, and produces T3 and T4 thyroid hormones, and calcitonin.
Which thyroid areas produce what hormone?
Follicles produce thyroid hormones T3 and T4 - these regulate basal metabolic rate and are important in growth and maturation. Parafollicular cells produce calcitonin. This regulates blood calcium levels in conjunction with parathyroid hormone. It lowers blood calcium levels by inhibiting osteoclastic resorption of bone, and is invisible without specific IHC staining.
Describe the macroscopic appearance of the parathyroid glands.
4 glands, located on posterior aspect of the thyroid, at each end of the butterfly wings. Approx 3x6mm, weighing 0.2-0.3g.
Describe the parathyroid under light microscopy
Low power - Endocrine epithelial and adipose cells. 2 types of endocrine epithelial cells - Chief cells and Oxyphilic cells.
Describe chief cells
Most common parathyroid cell type, with a round, central nucleus and homogenous cytoplasm. They are arranged in cords or places, are surrounded by capillaries, and secrete parathyroid hormone.
Describe oxyphil cells
Present as groups or ‘nests’ of cells. Larger than chief cells, with eosinphilic cytoplasm (darker staining). Are a feature of aging, with an unknown function and lots of mitochondria.
What are the clinical features of a parathyroid adenoma?
Parathyroid hormone raises blood calcium from bones, increased dietary absorption, and decreased urine calcium excretion. Presents with moans, groans, bones and stones. Psychological upsets, abdominal discomfort, aching bones and kidney stones (lots of calcium in blood stream).
Describe the 3 layers of the adrenal cortex under light microscopy.
Zona Glomerulosa - Ovoid clusters of cells, secretes aldosterone. Zona Fasciculata - Radially arranged cords of cells (looks regular), rich in lipid droplets, secretes cortisol. Zona Reticularis - Irregular arrangement of cords of cells. Secretes androgens and glucocorticoids. All layers are composed of epithelium.
Describe the adrenal medulla under light microscopy
Large nuclei with basophilic (light purple) granular cytoplasm, with no lipid in cytoplasm. Secretes adrenaline, noradrenaline.
Describe the pancreas under light microscopy
Extensive small, dense clusters of acinar cells (2 - exocrine) with occasional larger clusters of lighter-staining islets of Langerhans (1 - produce glucagon, insulin, somatostatin). 1 million islets per pancreas.
