In immunology, an antigen (Ag) is any structural substance that serves as a target for the receptors of an adaptive immune response, TCR or BCR or its secreted form antibody.he term originally described a structural molecule that binds specifically to an antibody. It expanded to refer to any molecule or a linear molecular fragment that can be recognized by highly variable antigen receptors (B-cell receptor or T-cell receptor) of the adaptive immune system.
Definition. A navicular fracture is a fracture of the navicular bone of the foot, a bone on the top of the midfoot. Athletes are particularly susceptible to fractures of the navicular bone.(There is also a navicular bone in the wrist.).A navicular fracture can be caused by a fall, severe twist, or direct trauma to the navicular bone. It can also be caused by repeated stress to the foot, creating a fracture not due to any acute trauma (a stress fracture).efinition. A navicular fracture is a fracture of the navicular bone of the foot, a bone on the top of the midfoot. Athletes are particularly susceptible to fractures of the navicular bone.
From Wikipedia, the free encyclopedia. A scaphoid fracture, a fracture of the scaphoid bone also known as the carpal navicular, is the most common type of carpal bone fracture. Scaphoid fractures usually cause pain at the base of the thumb accompanied by swelling in the same area.herefore, people with tenderness over the scaphoid (those who exhibit pain to pressure in the anatomic snuff box) are often casted for 7â10 days at which point a second set of X-rays is taken. If there was a hairline fracture, healing will now be apparent. Even then a fracture may not be apparent.