Lec. No.3 Dr. Wahda Kharofa Bone

Objectives: To give information about: Bone, functions. What is periosteum & endosteum? Bone components. Bone cells. Types of bones. Compact & spongy bone.

Bone Bones are rigid organs that form part of the endoskeleton of vertebrates. They are primary structural framework for support and protection of the organs of the body, including the brain and spinal cord and the structures within the thoracic cavity, namely lungs and heart.organsendoskeleton vertebrates

Functions: Bones have main functions: Protection — Bones can serve to protect internal organs, such as the skull protecting the brain or the ribs protecting the heart and lungs.skullbrain ribsheartlungs Shape — Bones provide a frame to keep the body supported. Movement — Bones, skeletal muscles, tendons, ligaments and joints.skeletal musclestendons ligamentsjoints Sound transduction — Bones are important in the mechanical aspect of overshadowed hearing.hearing Blood production. Mineral storage — Bones act as reserves of minerals important for the body, most calcium and phosphorus.calcium phosphorus

Periosteum and endosteum: Periosteum: Each bone is surrounded by fibrous sheath called “periosteum”, It consists of two layers, the outer layer is dense fibrous connective tissue and contained blood vessels, the inner layer is composed of more loosely arranged connective tissue contains numerous spindle shaped cells called esteogenic cells which on stimulation becomes activated and gives osteoblasts. Endosteum: It has same comments as periosteum, but it is thinner and doesn’t have two layers, it lines the marrow cavities.

Bone Components: Inorganic Component: The inorganic portion of bone responsible for its rigidity, which constitutes about 65% of its dry weight, is composed mainly of calcium and phosphorus, along with other components including bicarbonate, citrate, magnesium, sodium, and potassium. Organic Component: The organic component of bone matrix, contains 35% of the dry weight of bone, include type I collagen, and sulfated glycoaminoglycans-namely, chondroitin sulfate and keratan sulfate, and several glycoproteins also are present in the bone.

Bone cells: There are four types of cells in the bone: Osteogenic cells: there are drived from mesenchymal cells, they are found in the inner portion of periosteum and endosteum. There are two types of osteogenic cells are recognized one type (preosteoblast) which gives rise to osteoblast and the other type (preosteoclast) which gives rise to osteoclast. Osteogenic cells are elongated have pale nuclei.

Bone cells: Osteoblasts cells (Bone forming cells): they are cubical in shape, with rounded nucleus; they are closely packed cells like simple epithelial cells. They lie on the surface of the bone;. Osteoblasts responsible for secreting of organic part of bone, they secret alkaline phosphates which cause liberation of calcium from the blood to the bone, so the cell builds the bone matrix.

Bone cells: Osteocytes cells, when osteoblasts secret the bone matrix they become surrounded completely by this matrix they called ostocytes which occupy space called lacunae. Osteocytes have fine cytoplasming processes extend from some distance into the canaliculi (which are an extension from lacunae), these canaliculi help in the exchange of metabolites between the blood stream and the osteocytes.

Bone cells: Osteoclasts (Bone destroyers): They are giant multinucleated cells lie in space called “Howship’s lacunae”. The cytoplasm is foamy, the surface of these cells irregular. They secrete acid phosphates which cause dissolving of the bone and libration of calcium from the bone and libration of calcium from the matrix to the blood.

Types of bones: There are five types of bones in the human body: long, short, flat, irregular and sesamoid bone. Long bones are characterized by a shaft, the diaphysis, that is much greater in length than width. They are comprised mostly of compact bone and lesser amounts of marrow, which is located within the medullary cavity, and spongy bone. Most bones of the limbs, including those of the fingers and toes, are long bones. Long bonesdiaphysiscompact bonemarrowmedullary cavityspongy bonelimbsfingerstoes

Short bones are roughly cube-shaped, and have only a thin layer of compact bone surrounding a spongy interior. The bones of the wrist and ankle are short bones. Short bonescube Flat bones are thin and generally curved, with two parallel layers of compact bones sandwiching a layer of spongy bone. Most of the bones of the skull are flat bones, as is the sternum. Flat bones skullsternum Irregular bones consist of thin layers of compact bone surrounding a spongy interior. The bones of the spine and hips are irregular bones. Irregular bonesspinehips Sesamoid bones are bones embedded in tendons. Examples of sesamoid bones are the patella and the pisiform. Sesamoid bonespisiform

Compact and Spongy bone: There are two basic structural types of bone, compact and spongy. Compact bone forms the outer shell of all bone and also the shafts in long bones. Compact or cortical bone, is made up many rod-like units called osteons or Haversian systems which run longitudinally within the bone. Haversian systems have a central Haversian canal which carries blood and lymphatic vessels and nerve branches, the canal is surrounded by rings a concentric lamellae of calcified bone matrix.. The lamellae contain dark spots, these are the lacuni (holes) where osteocytes. The perforating canals Volkman’s canal which pierce the bone from its outer and inner surface and become continuous with the central canals and not lined by concentric lamallae.

Compact and Spongy bone: Spongy bone it is called spongy because, contains less bone material & large number of space called spicules or trabeculae & between them lies a spaces filled with marrow. It is covered with periosteum & lined with endosteum. The trabeculae are formed of bone matrix which contain bone cells (osteocytes) arranged at the periphery of the trabeculae, the osteoclasts lie in the Howship lacunae at the periphery of the trabeculae.

Difference Between Compact and Spongy BoneDifference Between Compact and Spongy Bone: Our bones are the primary skeletal structure that support the muscles and adds shape to the body. There are some important differences between compact and spongy bone as follows: Compact and spongy bones are the two main types of osseous tissues. Compact bone is also called cortical bone while spongy bone is also called cancellous bone. Compact bones are made of osteons while spongy bones are made of trabeculae. Compact bones are heavy while spongy bones are light. Compact bones fill the outer layer of most of the bones while spongy bones fill the inner layer of the bones.