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Organs Thyroid (Cross Section)

Connective Tissue

Connective Tissue helps hold our body together, supports other tissues and even transports substances. Connective tissue is found in between other tissues everywhere in the body, including the nervous system. In the central nervous system, the three outer membranes (the meninges) that envelop the brain and spinal cord are composed of connective tissue. They support and protect the body. Connective tissue has a wide variety of functions that depend on the types of cells and the different classes of fibers involved. Loose and dense irregular connective tissue, formed mainly by fibroblasts and collagen fibers, have an important role in providing a medium for oxygen and nutrients to diffuse from capillaries to cells, and carbon dioxide and waste substances to diffuse from cells back into circulation. They also allow organs to resist stretching and tearing forces.      Source


Follicular Cells

These (also called thyroid epithelial cells or thyrocytes) are cells in the thyroid gland that are responsible for the production and secretion of thyroid hormones thyroxine (T4) and triiodothyronine (T3). The thyroid epithelial cells take up iodine and amino acids from the blood circulation on the basolateral side, synthesize thyroglobulin and thyroperoxidase from amino acids and secrete these into the thyroid follicles together with iodine. The thyroid epithelial cells can subsequently take up iodinated thyroglobulin from the follicles by endocytosis, extract thyroid hormones from it with the help of proteases and subsequently release thyroid hormones to the blood. These thyroid hormones are transported throughout the body where they control metabolism (which is the conversion of oxygen and carbohydrates to energy). Every cell in the body depends upon thyroid hormones for regulation of their metabolism. The normal thyroid gland produces about 80% T4 and about 20% T3, however, T3 is about four times as potent as T4.


Thyroid Follicle

The small, spheric, vesicular components of the thyroid gland lined with epithelium and containing colloid in varying amounts; the colloid serves for storage of the thyroid hormone precursor, thyroglobulin. Follicles are filled with colloid, a proteinaceous depot of thyroid hormone precursor.       Source  


Parafollicular Cells

Parafollicular cells (also called C cells) are neuroendocrine cells in the thyroid which primary function is to secrete calcitonin. They are located adjacent to the thyroid follicles and reside in the connective tissue. These cells are large and have a pale stain compared with the follicular cells or colloid. In teleost and avian species these cells occupy a structure outside the thyroid gland named the ultimobranchial body. Parafollicular cells secrete calcitonin, a hormone that participates in the regulation of calcium metabolism. It is important in fish and rodents, but its relevance in humans has not been demonstrated. Calcitonin lowers blood levels of calcium by inhibiting the resorption of bone by osteoclasts, and its secretion is increased proportionally with the concentration of calcium. Parafollicular cells are also known to secrete in smaller quantities several neuroendocrine peptides such as serotonin, somatostatin or CGRP. They may also have a role in regulating thyroid hormones production locally, as they express thyrotropin-releasing hormone.


Interlobular Connective Tissue

The lymphatic drainage of the thyroid gland runs in the interlobular connective tissue and then communicates with a network of lymphatic vessels. The lymphatic vessels communicate with the tracheal plexus, and pass to prelaryngeal nodes above the thyroid isthmus, and to pretracheal and paratracheal nodes. Some may drain into brachiocephalic nodes. Laterally the gland drains into deep cervical nodes. Some lymph may drain directly, without nodes, to the thoracic duct.       Source



Thyroglobulin is stored within the gland in follicles as the main component of a substance called the thyroid colloid. Thyroid follicles are small spherical groupings of cells that play the main role in thyroid function. They consist of a rim that has a rich blood supply, nerve and lymphatic presence, that surrounds a core of colloid that consists mostly of thyroid hormone precursor proteins called thyroglobulin, an iodinated glycoprotein.      Source


Blood Vessels

The blood vessels are part of the circulatory system and function to transport blood throughout the body. Blood is carried through the body via blood vessels. An artery is a blood vessel that carries blood away from the heart, where it branches into ever-smaller vessels. Eventually, the smallest arteries, vessels called arterioles, further branch into tiny capillaries, where nutrients and wastes are exchanged, and then combine with other vessels that exit capillaries to form venules, small blood vessels that carry blood to a vein, a larger blood vessel that returns blood to the heart.       Source