6. BONE TISSUE AND HOMEOSTASIS

6. THE SKELETAL SYSTEM: BONE TISSUE 

BONE TISSUE AND HOMEOSTASIS 

• Bone tissue is continuously growing, remodeling, and repairing itself. 
• It contributes to homeostasis of the body 

1. by providing support, 
2. protection,
3. the production of blood cells, 
4. and the storage of minerals and triglycerides. 

A bone is composed of several different tissues working together: 

• bone or osseous tissue, 
• cartilage, 
• dense connective tissues, 
• epithelium, 
• adipose tissue, and 
• nervous tissue. 

• For this reason, each individual bone in your body is considered an organ. 

Bone tissue,

•  a complex and dynamic living tissue,
• continually engages in a process called remodeling—the construction of new bone tissue and breaking down of old bone tissue. 

The entire framework of

• bones 
• and their cartilages, 
• along with ligaments and tendons, 

             - constitutes the skeletal system.

 The study of bone structure and the treatment of bone disorders
is called osteology 

• osteo- bone; -logy study of). 

6. FUNCTIONS OF BONE AND THE SKELETAL SYSTEM

• Bone tissue makes up about 18% of the weight of the human body. 

The skeletal system performs several basic functions:

1. Support. 


The skeleton serves as the structural framework for the body 

• by supporting soft tissues 
• and providing attachment points for the tendons of most skeletal muscles.

2. Protection. 

• The skeleton protects the most important internal organs from injury. 

For example, 

• cranial bones protect the brain, 
• vertebrae (backbones) protect the spinal cord, 
• and the rib cage protects the heart and lungs.

3. Assistance in movement. 

• Most skeletal muscles attach to bones; 
• when they contract, they pull on bones to produce movement.

4. Mineral homeostasis (storage and release). 

• Bone tissue stores several minerals, especially calcium and phosphorus,which contribute to the strength of bone. 
• Bone tissue stores about 99% of the body’s calcium. 
• On demand, bone releases minerals into the blood to maintain critical mineral balances (homeostasis) and to distribute the minerals to other parts of the body.

5. Blood cell production. 

• Within certain bones, a connective tissue called red bone marrow produces red blood cells, white blood cells, and platelets, a process called hemopoiesis ( hemo- blood; poiesis- making). 

Red bone marrow consists of 

• developing blood cells, 
• adipocytes, 
• fibroblasts,
• and macrophages within a network of reticular fibers.

It is present in 

• developing bones of the fetus 
• and in some adult bones, such as 
• the hip bones,
•  ribs, 
• breastbone, 
• vertebrae (backbones),
• skull, 
• and ends of the bones of the arm and thigh. 

6. Triglyceride storage. 

Yellow bone marrow consists mainly of 

• adipose cells, which store triglycerides. 

• The stored triglycerides are a potential chemical energy reserve. 
• In a newborn, all bone marrow is red and is involved in hemopoiesis. 
• With increasing age, much of the bone marrow changes from red to yellow.