Anatomy Terms Starting With T

Tendon is a dense regular connective tissue cord composed primarily of parallel type I collagen fibers that transmits contractile force from muscle to bone, enabling skeletal movement.

Tendon collagen fibers are arranged in a hierarchical structure: fibrils bundle into fibers, fibers into fascicles, and fascicles into the whole tendon, producing exceptional tensile strength along the force transmission axis. This tissue is poorly vascularized, which slows healing after injury; the Achilles tendon, the largest in the human body, can experience loads exceeding ten times body weight during running and ranks among the most commonly ruptured tendons in athletes. Low-level elasticity within the collagen network stores strain energy during loading and returns it during recoil, reducing the metabolic cost of repetitive movements such as walking and running.

Testis is the paired male gonadal organ that produces spermatozoa through spermatogenesis and secretes testosterone to maintain male secondary sex characteristics and reproductive function.

Each testis is divided into approximately 250 lobules containing seminiferous tubules where spermatogenesis occurs, supported by Sertoli cells that nurse developing sperm and by interstitial Leydig cells that secrete testosterone in response to luteinizing hormone. Positioning in the external scrotum maintains a temperature approximately 2 to 3 degrees Celsius below core body temperature, which spermatogenesis requires because elevated heat impairs sperm formation and motility. The blood-testis barrier, formed by tight junctions between adjacent Sertoli cells, isolates developing sperm from the systemic circulation and prevents immune recognition that would destroy these genetically distinct cells.

Thoracic Cavity is the chest space enclosed by the rib cage, sternum, thoracic vertebrae, and diaphragm that houses the lungs, heart, esophagus, trachea, and major blood vessels.

Separated from the abdominal cavity by the diaphragm, the thoracic cavity changes volume with each breath: diaphragm contraction and rib elevation increase volume, reducing intrathoracic pressure and driving air into the lungs. Penetrating injury to the thoracic wall can cause pneumothorax, which eliminates this pressure gradient and causes lung collapse. The mediastinum, the central compartment between the two pleural sacs, contains the heart, great vessels, thymus, trachea, esophagus, and major lymphatics, and shifts position with disease processes such as large pleural effusions or tension pneumothorax.

Thyroid Gland is a butterfly-shaped endocrine gland in the anterior neck that synthesizes and secretes triiodothyronine and thyroxine to regulate metabolic rate, growth, and development throughout the body.

Thyroid hormones are synthesized in follicular cells using iodine and the glycoprotein thyroglobulin stored in colloid-filled follicles, then released in response to thyroid-stimulating hormone from the anterior pituitary. Triiodothyronine, the biologically active form, binds nuclear receptors in virtually every cell to increase basal metabolic rate, thermogenesis, cardiac output, and protein synthesis. Parafollicular C cells scattered through the thyroid parenchyma produce calcitonin, which lowers blood calcium by inhibiting osteoclast activity, a function entirely separate from the follicular hormone axis.

Tibia is the larger, medial long bone of the lower leg that bears approximately 80 to 90 percent of body weight transmitted from the femur, forming the primary weight-bearing articulation at both the knee and ankle joints.

The flat tibial plateau articulates with the femoral condyles at the knee, while the distal tibia forms the medial malleolus and the main articular surface of the ankle mortise joint with the talus. Its anterior crest lies directly beneath the skin with minimal soft tissue coverage, making it highly vulnerable to direct impact and stress fractures from repetitive loading. Tibial shaft fractures are the most common open long bone fractures in adults and carry significant risk of compartment syndrome and delayed union because the periosteal blood supply is easily disrupted.

Trachea is the cartilaginous tube approximately 10 to 12 centimeters long and 2 centimeters in diameter that connects the larynx to the primary bronchi, conducting air between the upper airway and the lungs.

Sixteen to twenty C-shaped hyaline cartilage rings maintain tracheal patency during inspiration, while the posterior membranous wall, composed of smooth muscle and connective tissue, allows the esophagus to bulge anteriorly during swallowing. Pseudostratified ciliated columnar epithelium with interspersed goblet cells lines the lumen; cilia beat in coordinated waves to escalate a mucus blanket carrying trapped particles toward the pharynx for clearance. Tracheal intubation during general anesthesia bypasses upper airway humidification and filtration, requiring heated humidified gas delivery to prevent mucosal desiccation and ciliary dysfunction.