Histology Mentor

Endocrine System Questions 102-109

102. Question - Diagram and name the two major divisions of the pituitary gland. Indicate and name their subdivisions.

103. Question - Illustrate the hypophyseal portal system and explain its role in the regulation of the adenohypophysis.

Factors synthesized by the nerve cells in the tuberal nuclei (tuber cinereum of the median eminence) are released from axon terminals in the infundibular stalk. The factors are picked up by capillaries that join to form veins that drain through sinusoids in the adenohypophysis. These factors regulate the secretion of hormones by the cells of the adenohypophysis. The releasing and inhibiting factors are specific for the hormone that they regulate. For example TSH releasing factor stimulates the secretion of TSH by thyrotrophs.

104. Question - Explain with a diagram the structure and function of the pars nervosa. What cells are found in the pars nervosa?

The pars nervosa is an extension of nerve fibers from the hypothalamus. Axons from the paraventricular and supraoptic nuclei pass through the median eminence and infundibular stalk to terminate in the infundibular process. Secretion granules containing oxytocin and antidiuretic hormone (ADH) accumulate in and are secreted from enlarged axon terminations called Herring bodies. Glial cells, called pituicytes, support these axons.

105. Question - Describe and indicate the function of the cells found in the pars distalis.

There are two classes of epithelial cells in the pars distalis. Their classification depends upon the amount and staining qualities of their cytoplasm - chromophobes (50%) and chromophils (50%). Chromophobes are small with few secretion granules. They are thought to be resting chromophils. There are two classes of chromophils, acidophils (35%) and basophils (15%).

Somatotrophs (growth hormone) and lactotrophs (prolactin) are acidophils.

Basophils produce (nemonic B-FLAT)

Follicle stimulating hormone (FSH) -gonadotrophs
Luteinizing hormone (LH) or, in the male, LH is called interstitial cell stimulating hormone (ICSH) - gonadotrophs
Adrenocorticotropic hormone (ACTH) - corticotrophs
Thyroid stimulating hormone (TSH)-thyrotrophs

Their cytoplasmic staining qualities depend upon the products stored in their secretion granules. Basophils have basophilic secretion granules and acidophils have acidophilic secretion granules.

106. Question - Diagram a thyroid follicle identifying two types of endocrine cells. Explain how each type functions.

Thyroid follicular cells synthesize and secrete into the follicle lumen colloid, an eosinophilic, glycoprotein called thyroglobulin. This protein contains the modified and iodinated amino acids, triiodothyronine (T3) and tetraiodothyronine (T4). To release these biologically active amino acids into the circulation the follicular cells phagocytose and digest the colloid. Parafollicular cells (also called C cells) are found among the follicular cells but they are derived from neural crest rather than pharyngeal pouch endoderm. These cells synthesize and store in secretion granules the polypeptide hormone, calcitonin. When calcium levels are high the hormone, that inhibits osteoclasts, is released through the basal lamina by exocytosis.

107. Question - Show with a diagram the structure of the adrenal gland. Include its blood supply and course through the gland.

Superior, middle and inferior suprarenal arteries form a plexus in the capsule of the adrenal gland. From this plexus blood passes either through sinusoids in the cortex and then into the medulla or it follows arterioles straight through the cortex to supply the medulla. The medullary vein that has a heavy coat of longitudinal smooth muscle drains the gland.

108. Question - Describe the structure and function of the cells that comprise the parathyroid gland. Explain the function and regulation of each region of the adrenal gland.

The parathyroid gland consists of small cells, called chief cells, that have few secretion granules. They produce a polypeptide hormone called parathormone that acts on kidneys and bone to elevate the blood calcium level. At puberty a second cell type appears, the oxyphil cell. This is a large eosinophilic cell with abundant mitochondria but its function is obscure. In children each of the 4 parathyroid glands is a small compact mass of cells but with age fat accumulates within the gland.

The outer layer of the adrenal cortex, the zona glomerulosa, produces aldosterone that conserves sodium under the regulation of angiotensin II. The zona fasciculata and zona reticularis produce glucocorticoids and sex steroids under the regulation of ACTH. Sympathetic preganglionic fibers directly regulate the secretion of epinephrine and norepinephrine from the medullary chromaffin cells.

109. Question - Describe the cytology of the cells that are found in each region of the adrenal gland.

All steroid-producing cells are characterized by their high content of smooth endoplasmic reticulum and accumulations of lipid droplets that are rich in cholesterol. Instead of storing the lipid soluble hormones, which can diffuse through membranes, they store precursors. When stimulated to produce more hormone the reserves of lipids are depleted. Both smooth endoplasmic reticulum and mitochondria cooperate in the synthesis of steroid hormones. In the zona glomerulosa the mitochondria have typical shelf-like cristae but in the fasciculata and reticularis they have tubular cristae.

The adrenal medullary (chromaffin) cells are of two types. One secretes epinephrine the other norepinephrine. Both of them store the catecholamine in a complex with protein (chromogranin) in secretion granules that are released by exocytosis when stimulated by preganglionic sympathetic axons.

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