The thyroid, or thyroid, gland consists of two connected lobes and is an endocrine gland in the neck. A thin band of tissue known as the thyroid isthmus connects the lower two thirds of the lobe. The thyroid is situated under the Adam apple on the front of the arm. The spherical thyroid follicle lined with folliculate cells and, at times, parafollicular cells which surround a lumen containing a colloid is the microscopic function unit of the thyroid gland. Two hormones – triiodothyronine and thyroxine – and the peptide hormone, calcitonin – are released in the thyroid gland. In calcium homeostasis, calcitonin plays a role. Thyroid stimulatory hormone that is secreted from the anterior pituitary gland is regulated for secretion of the two thyroid hormones. TSH is regulated by the hypothalamus-generated thyrotropin releasing hormone.
During prophase I, the homologous chromosomes condense and become visible as the x shape we know, pair up to form a tetrad, and exchange genetic material by crossing over.
