What is the thin layer of hyaline cartilage that sits between the epiphysis and diaphysis in a growing bone called?

The thin layer of hyaline cartilage that sits between the epiphysis and diaphysis in a growing bone is called the "epiphyseal plate" or "growth plate". Here are the steps to understand this:

1. The bone structure: A long bone is divided into three parts - the epiphysis (end of the bone), diaphysis (shaft or middle of the bone), and metaphysis (the narrow portion between the epiphysis and diaphysis).

2. The role of cartilage: In a growing bone, there is a layer of cartilage in the metaphysis region. This cartilage is made up of a type called hyaline cartilage, which is the most common type of cartilage in the body.

3. The epiphyseal plate: This layer of hyaline cartilage is known as the epiphyseal plate, or growth plate. It is the area of growing tissue near the ends of the long bones in children and adolescents.

4. Function: The cells in the epiphyseal plate divide rapidly, which contributes to the bone's growth in length. Once the person has stopped growing, the epiphyseal plate becomes an epiphyseal line (a remnant of the growth plate), and no more growth in length occurs.

So, in summary, the thin layer of hyaline cartilage that sits between the epiphysis and diaphysis in a growing bone is called the epiphyseal plate.