CHAPTER 6-1 Bone connective tissue

“Objectives ” 1.Functions of the skeletal system 2.Classification of bones based on shape 3.General features of bone 4.Bone cells and matrix of bone 5.Compact and spongy bone 6.Bone marrow 7.Bone development 8.Overview of bone growth and remodeling

Bone Skeletal system Defined: Includes all of the bones of the human body (total of 206), and their associated cartilages and joints. Functions: 1.Support – supporting framework for body 2.Protection – protects vital organs (brain and thoracic cavity) 3.Movement / levers- allows movement and flexion as well as levers for different movements 4.Mineral storage- calcium and phosphate 5.Hematopoiesis- principal site for blood cell formation in red marrow of flat bones (e.g. sacrum, sternum, etc.) 6.Electrolyte balance of calcium and phosphorus 7.Acid/Base balance buffers the blood calcium phosphate 8.Detoxification by absorbing heavy minerals

Bone Two types: Compact and Spongy Compact bone consists of osteons (Haversian systems) osteocytes in lacunae and lamellae. Spongy bone is characterized by trabeculae surrounded by spaces filled with red bone marrow.

Compact Bone

Bone Two types: a) Compact b) Spongy

Classification based on the “shape” Long bones – bones that are longer than they are wide Ex. Femur, tibia, fibula, ulna and humerus Short bones – bones that are shaped like a cube; there is also a special class of short bones called sesamoid bones. Ex. Tarsal, carpal, and patella. Flat bones – bones that are thin and flat. Ex.Scapula, skull, ribs, and sternum. Irregular bones – bones that do not fit in any of the prior categories because they have irregular shapes. Ex. Vertebrae and hip bones.

Classification based on shapes

Bone markings and landmarks

“GROSS” structure of a typical bone Articular cartilage: Consists of Hyaline cartilage covering the end of the bone surface where it articulates with another bone, (e.g. femur and tibia, humerus and scapula). Fibrocartilage makes up the menisci of the knee joints. Epiphyses: The end of the bone. One at each end of long bones. Epiphyseal line: Remnant of the cartilaginous “growth plate” or epiphyseal plate.

Typical bone structure

Bone structure Periosteum: Tough outer connective tissue covering on bone. Consists of 2 layers; outside is dense irregular CT and deeper layer lined with osteoblast and osteoclast cells. It is richly supplied by blood vessels and nerves and secured to bone by Sharpey’s fibers. Endosteum: connective tissue covering on inside of bone cavities. Is osteogenic in that it contains osteoblasts and osteoclasts.

Typical bone structure

Bone structure continued Diaphysis: The shaft of the bone between the two epiphyses. Contains the medullary cavity and is filled with yellow marrow in adults. Sharpey’s fibers: Bundles of collagenous fibers that tightly attach the periosteum to bony matrix.

Types of Bones cells Bone is formed and metabolized by specific cells and is in constant state of remodeling. Osteoclasts: Bone destroying cells “C” means chewing 2.Osteoblasts: Bone generating cells “B” means building 3.Osteocytes: Mature bone cells, spider shaped and maintain bone tissue

Bone Cells

Bone matrix The matrix of bone is made up of organic and inorganic matter. The organic portion is composed of collagen fibers and various proteoglycans, glycosaminoglycans and glycoproteins. The collagen fibers form the framework of the matrix of bones and allows for elasticity and flexibility.

Bone matrix The majority of the matrix of bone is composed of inorganic crystals called hydroxyapatite and are composed of calcium phosphate and calcium carbonate. Hydroxyapatite forms a cement-like material that gives bone its hardness and strength. The combination of collagen and hydroxyapatite allows bone to be strong and hard, yet somewhat flexible and elastic.

Compact bone terms Osteon/Haversian System: structural unit of compact bone. Oriented parallel to shaft and forming a group of hollow tubes through which an artery, vein and nerve pass into and through bone. Lacunae: small cavities (halo’s) containing osteocytes Osteocyte: true bone cell, spider shaped and found in lacunae at the junctions of the lamellae Lamellae: layers of the matrix with each layer of collagen fibers going in opposite direction to the adjacent layer.

Compact bone terms Lamellae may be concentric (forming rings like a tree) or circumferential (encircling the entire bone structure). Canaliculi: Hair like canals that connect each lacunae and in turn connect to the central canal. Remove wastes and bring nutrients into osteocytes Volkman’s canal/perforating canal: Canals running perpendicular to the Haversian canals, but connecting to them. They bring in the artery, vein and nerves to the bone structure.

Compact bone structure

Spongy Bone Spongy bone composes the inner portion of the bone lining the marrow cavity. It contains trabeculae and spicules giving it a honeycomb appearance. Although it looks poorly organized it is designed to withstand the specific stresses put on each bone because of their trabeculae. Trabeculae are tiny bone struts or plates that form very strong support structure for the spongy bones. Trabeculae are irregularly arranged and contain lamellae and osteocytes, but contain no osteons as they receive nutrients from the marrow tissue.

Spongy bone histology

Flat bone structure

Bone marrow Yellow marrow is found in medullary cavity of long bones and is not hematopoietic in adults. Yellow marrow replaces red marrow as we mature and is made up mainly of fat. Red marrow is found in the axial skeleton, the pectoral and pelvic girdles, and in the epiphyses of the femur and humerus. Red marrow is very hematopoietically active.