Top videos
By 5 weeks' gestational age, the wolffian (ie, mesonephric) and the müllerian (ie, paramesonephric) ducts have formed from intermediate mesoderm. In the absence of testosterone and müllerian inhibitory substance, the mesonephric ducts regress and the paramesonephric ducts continue to form the female reproductive structures with fusion of the distal portions of the paramesonephric ducts to give rise to the uterine fundus, the cervix, and the upper vagina. These developmental changes are genetically controlled in large part by a series of complex transcriptional signaling pathways including Wnt signaling, Hox genes, and many others. In a female fetus, the wolffian duct disappears except for nonfunctional vestiges. The müllerian duct is lined by a columnar epithelium. This includes the entire cervix and upper vagina to the vaginal plate (ie, sinovaginal bulb). Through a process of squamous metaplasia, the vagina and a variable portion of the ectocervix become covered with squamous epithelium. This process is complete by the fifth month of pregnancy.
The temporomandibular joint (TMJ), located just in front of the lower part of the ear, allows the lower jaw to move. The TMJ is a ball-and-socket joint, just like the hip or shoulder. When the mouth opens wide, the ball (called the condyle) comes out of the socket and moves forward, going back into place when the mouth closes. TMJ becomes dislocated when the condyle moves too far and gets stuck in front of a bony prominence called the articular eminence. The condyle can't move back into place. This happens most often when the ligaments that normally keep the condyle in place are somewhat loose, allowing the condyle to move beyond the articular eminence. The surrounding muscles often go into spasm and hold the condyle in the dislocated position.
This video, Rheumatoid arthritis is a chronic inflammatory disorder that can affect more than just your joints. In some people, the condition also can damage a wide variety of body systems, including the skin, eyes, lungs, heart and blood vessels. An autoimmune disorder, rheumatoid arthritis occurs when your immune system mistakenly attacks your own body's tissues. Unlike the wear-and-tear damage of osteoarthritis, rheumatoid arthritis affects the lining of your joints, causing a painful swelling that can eventually result in bone erosion and joint deformity. The inflammation associated with rheumatoid arthritis is what can damage other parts of the body as well. While new types of medications have improved treatment options dramatically, severe rheumatoid arthritis can still cause physical disabilities.