Describe the microscopic structure of compact bone How does

Describe the microscopic structure of compact bone. How does the structure of compact bone differ from the structure of spongy bone? Identify the bones that comprise the axial skeleton. What are the primary function of red bone marrow and yellow bone marrow? In which bones is red bone marrow most abundant?

Solution

2.

Bone is a connective tissue containing matrix composed of calcium phosphate and other minerals. The osseous tissue is a single component of bone but also may contain other components like blood, bone marrow, cartilage, adipose tissue, nervous tissue and fibrous connective tissue. Therefore, bone is an organ composed of all these components.

A bone is composed of an outer shell of dense white osseous tissue called compact or dense bone. The shell encloses a space known as marrow cavity or medullary cavity containing bone marrow. At the end of the bone the osseous tissue is loosely arranged and is called spongy or cancellous bone. The long bone contains a shaft called diaphysis and an expanded head called epiphysis. An epiphyseal plate of hyaline cartilage separates the marrow cavities of epiphysis and diaphysis.

In cross section the compact bone appears with onion like concentric lamellae forming the layers of matrix around a central canal called harvesian or osteonic canal. In longitudinal section the osteon is a cylinder of tissue surrounding the central canal joined by transverse or diagonal passage is called perforating canal.

The spongy bone is made up of lattice of silvers of bone called spicules and trabeculae. The matrix is arranged in lamellae like those of compact bone but is not arranged in concentric layers and contains few osteons. In flat bones two layers of compact bone enclosed middle layer of spongy bone and appears as a sandwich like construction. In the skull the spongy layer is called dipole.

3.

The skeleton is divided into two regions known as axial skeleton and appendicular skeleton. The axial skeleton is the central supporting axis of the body. The axial skeleton includes the skull, vertebral column, ribs and sternum. The appendicular skeleton consists of the bones of upper limb, pectoral girdle and bones of lower limb and pelvic girdle.

4.

Bone marrow is the soft tissue within the marrow cavity of long bone. The spongy bone contains the medullary cavity known as red marrow in which the production of blood cells occurs. It is myeloid tissue and is described as hematopoietic or blood forming tissue. Various types of blood cells are produced here.

With the age the red bone marrow is replaced by fatty tissue called yellow bone marrow. The cavity in the bone shaft is filled with yellow marrow which stores the fat. In adults the red bone marrow is limited to organs like skull, vertebrae, sternum, ribs and part of pelvic gurdle and proximal heads of humerus and femur bones. Rest of the skeleton is replaced with yellow marrow. The yellow bone marrow does not produce blood cells but it may become red marrow under severe or chronic anemia condition.