Final answer:
Epiphyseal plate closure ends the lengthwise growth of long bones. Hormones regulate the proliferation of chondrocytes that contribute to longitudinal growth. Once chondrocytes stop dividing, bone replaces the cartilage, leading to the formation of the epiphyseal line.
Step-by-step explanation:
The longitudinal growth of long bones is halted when the epiphyseal plates harden. This process, known as epiphyseal plate closure, occurs typically around the age of 18 in females and 21 in males. The transition from growth to closure involves the cessation of chondrocyte proliferation - these are the cartilage cells responsible for new growth at the plate.
During the bone growth phase, on the epiphyseal side of the epiphyseal plate, chondrocytes divide and help the bone to lengthen. As these chondrocytes age, they move towards the diaphysis, where they eventually calcify. The cartilage is then replaced by bone, resulting in the bone's lengthening. Eventually, the entire epiphyseal plate is replaced by bone, leaving behind an epiphyseal line, signifying that the bone is no longer growing in length.