Final answer:
The third layer in the context of longitudinal bone growth refers to the zone of maturation and hypertrophy in the epiphyseal plate where chondrocytes mature and assist in lengthening the bone. Cartilage, consisting largely of a matrix where chondrocytes are embedded in lacunae, is characterized by the presence of chondroitin sulfates and proteoglycans.
Step-by-step explanation:
The third layer referred to in the question is likely part of the process of longitudinal bone growth, which involves the maturation and hypertrophy of chondrocytes. These cells are crucial in the development of cartilage and bone. Chondrocytes are found within the cartilage matrix in spaces called lacunae and are responsible for the secretion of the matrix and fibers of the cartilage. During the growth of long bones, these chondrocytes are organized in columns in a layer called the zone of maturation and hypertrophy within the epiphyseal plate, which is responsible for the bones' lengthening.
Cartilage is a type of connective tissue that is avascular, meaning it does not have blood vessels. Nutrients must diffuse through the large amount of ground substance matrix to reach the chondrocytes. This characteristic is a factor contributing to the slow healing of cartilaginous tissues. The distinctive appearance of cartilage is mainly due to chondroitin sulfates, which bind with ground substance proteins to form proteoglycans.