BONE TISSUEA. PHYSIOLOGY: FUNCTIONS OF BONEList, then briefly describe, the six basic functions of bone tissue and the skeletal system.Support -- Bone provides a framework for the body by supporting soft tissues and providing points of attachment or most of the skeletal muscles.Protection -- Bones protect many internal organs from injury very well, such as the brain and spinal cord. In addition, the heart, lungs, and reproductive organs are given some degree of protection.Movement -- Most skeletal muscles attach to bones. When the muscles contract, they pull on bones to activate lever systems, and move-ment is produced.Mineral homeostasis -- Bone tissue stores a number of minerals, particularly calcium and phosphorus. Under control of the endocrine system, bone releases the minerals into the blood or stores the minerals in bone matrix to maintain critical mineral balances.Blood cell production -- In all bones of the infant and certain bones of the adult, a connective tissue known as red marrow produces blood cells by the process of hematopoiesis.Storage of energy -- In some bones, yellow bone marrow stores lipids, creating an important energy reserve for the body.B. ANATOMY: STRUCTURE OF BONEIdentify each of the following parts of a long bone:Diaphysis -- The diaphysis of a long bone is its shaft or long main portion.Epiphysis -- The epiphysis of a long bone is its end. The two ends together are called the epiphyses. Each epiphysis is covered with articular cartilage.Metaphysis -- The metaphysis of a long bone is the region of mature bones where the diaphysis meets the epiphysis43Epiphyseal plate -- In a growing bone, the epiphyseal plate is formed of hyaline cartilage divided into four zones of cells. Under the influence of growth hormone, the plate continues to grow, giving length to the bone. When bone growth exceeds cartilage growth, beginning at puberty, the epiphyseal plate is slowly lost. Growth of long bones stops when the cartilage is completely gone.Identify each of the following parts of a long bone:Articular cartilage -- Articular cartilage is a thin layer of hyaline cartilage covering the articular surfaces of the epiphysis at a joint.Medullary cavity -- The medullary (marrow) cavity is the space within the bone containing either red or yellow bone marrow. Red bone marrow consists of blood precursors while yellow marrow consists of adipose tissue.Periosteum -- The periosteum is the double-layered connective tissue surrounding the bone except where the articular cartilage is present. It is divided into an outer fibrous layer and an inner osteogenic layer.Fibrous periosteum -- The outer fibrous layer of the periosteum is composed of dense irregular connective tissue containing blood vessels, lymphatics, and nerves that pass into the bone.Osteogenic periosteum -- The inner osteogenic layer of the periosteum contains elastic fibers and various bone cell types, particularly osteoprogenitor cells, that give rise to newosteoblasts when stimulated.Periosteal functions -- The periosteum functions in bone growth, repair, and nutrition. In addition, it provides attachment points for skeletal muscles.Endosteum -- The endosteum is a single layer of osteoprogenitor cells lining the medullary cavity.Compare spongy bone with compact bone.Spongy bone consists of lamellae (layers) of bone matrix arranged in an irregular latticework of thin plates of bone called trabeculae. The spaces between the trabeculae are a part of the medullary cavity ofthe bone.44Compact bone contains very few spaces. The layers of bone matrix are packed together tightly, forming osteons (Haversian systems). It forms the external layer of all bones, providing protection and support and helps the long bone resist the stress of weight applied to them.C. HISTOLOGY OF BONEIdentify the following cells:Osteoprogenitor cells -- Osteoprogenitor cells are immature quiescent cells lining the bone surfaces. When stimulated, they enter mitosis,giving rise to a new cell type called the osteoblast.Osteoblast -- Osteoblasts, once differentiated, lose their mitotic ability, andbegin producing new bone matrix in a process known as osteogenesis.Osteocytes -- Osteocytes are mature bone cells completely embedded in bone matrix, are incapable of mitosis, and probably do not secrete new matrix. Their role in bone homeostasis is poorly understood.Osteoclasts -- Osteoclasts reside scattered along the endosteal surfaces. They function in a process known as bone resorption, the destruction of bone matrix. This process is required for normal bone function.Unlike the other connective tissues, the matrix of bone contains an abundance ofmineral salts embedded into an homogeneous frame work of extracellular materials. Identify the three main components of bone matrix and briefly describe the process of ossification (mineralization or calcification).1. Tricalcium phosphate (hydroxyapatite--50% of total matrix)2. Ground substance (25% of total matrix is water)3. Collagen fibers (25% of total matrix)The predominant mineral salt is tricalcium phosphate (hydroxyapatite) (50% of total mineral) (there is also calcium carbonate, magnesium hydroxide, fluoride, and sulfate). As these salts are deposited into the framework of ground substance and collagen fibers, they crystallize and the tissue hardens or ossifies.45Although the hardness of the bone depends upon the crystallized mineral salts, without the collagen the matrix would be very brittle (ex: an egg shell). Why? Collagen fibers provide pliability and tensile strength to resist being stretched or torn apart. The mineral salts are crystallized onto the collagen fibers, giving bone its hardness.Did you ever see the experiment in which a chicken bone is placed into vinegar for a few weeks? When the bone was pulled from the vinegar, it could be bent and twisted, even tied into a knot. Why? Because the acetic acid in the vinegar dissolved the mineral salts from the bone, leaving only the collagen framework.We tend to think of bone as a solid mass of calcified matrix, but it is instead riddled with microscopic spaces through which blood vessels pass and fluids percolate.Define each of the following:Volkmann’s canal -- A Volkmann’s canal is a minute passageway by means of which blood vessels and nerves from the periosteum of a bone penetrate into compact bone.Haversian canal -- An Haversian (central) canal is a circular channel running longitudinally in the center of an