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Essentials of Human Anatomy The Skeletal System 1 Bone • Bones are organs • Bones are composed of all tissue types. • Their primary component is osseous connective tissue. • The matrix is sturdy and rigid due to calcification (also called mineralization). Function of Bones • Support: form the framework that supports the body and cradles soft organs • Protection: provide a protective case for the brain, spinal cord, and vital organs • Movement: provide levers for muscles • Mineral storage: reservoir for minerals, especially calcium and phosphorus • Blood cell formation: hematopoiesis occurs within the marrow cavities of bones • Energy storage (fat in yellow marrow) Support and Protection • Bones provide structural support and serve as a framework for the entire body. • Bones protect many delicate tissues and organs from injury and trauma. Movement • Muscles attach to the bones of the skeleton –Contract and pull on bone –Functions as a series of levers. Storage of Mineral and Energy Reserves • More than 90% of the body’s reserves of the minerals calcium and phosphate are stored and released by bone. Hematopoiesis Blood Cell Formation • Blood cell production in red bone marrow – located in some spongy bone. • Red bone marrow contains stem cells – form all of the blood cell types. Changes in the Human Skeleton • In embryos, the skeleton is primarily hyaline cartilage • During development, much of this cartilage is replaced by bone • Cartilage remains in isolated areas Bridge Parts of the nose of ribs Joints Classification of Bones on the Basis of Shape Classification of Bones Long bones • Generally longer than wide. • Have a shaft with heads at both ends. • Contain mostly compact bone • Examples: Femur, humerus Classification of Bones Short bones • Generally cube-shape • Contain more spongy bone than compact • Examples: Carpals, tarsals Classification of Bones Flat bones • Thin and flattened like pancackes. • Usually curved • They have two thin layers of compact bone sandwiching a layer of spongy bone • Examples: Skull, ribs, sternum Classification of Bones Irregular bones • Do not fit into other bone classification categories • Irregular shape • Example: Vertebrae The Histologic Types: • Compact bone ( cortical) • Spongy bone ( cancellous) Compact Bone: • Haversian system, or osteon – the structural unit of compact bone – Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen – Haversian, or central canal – central channel containing blood vessels and nerves – Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal Compact Bone • Osteocytes – mature bone cells • Lacunae – small cavities in bone that contain osteocytes • Canaliculi – hairlike canals that connect lacunae to each other and the central canal Compact Bone: Spongy (cancellous) Bone • Does not contain osteons. • trabeculae surrounding red marrow spaces Cell Types of Bone 3 types of cells in bone tissue • Osteoblasts: – Form matrix & collagen fibers but can’t divide • Osteocytes: – Mature cells that no longer secrete matrix • Osteoclasts: – Huge cells from fused monocytes (WBC) – Function in bone resorption at surfaces such as endosteum SKLETAL SYSTEM • It is divided into two parts : Axial Appendicular Bone Structure - External Cartilage protection for joints Bone Structure - External Epiphyses Expanded ends of long bones Exterior is compact bone, and the interior is spongy bone Epiphyse Joint surface is covered with articular (hyaline) cartilage location of red bone marrow Epiphyseal line separates the diaphysis from the epiphyses Bone Structure - External Diaphysis Tubular shaft that forms the axis of long bones Composed of compact bone that surrounds the medullary cavity Yellow bone marrow (fat) is contained in the medullary cavity Diaphysis Bone Membranes • Periosteum – double-layered protective membrane – Outer fibrous layer • dense regular connective tissue – Inner osteogenic layer • composed of osteoblasts and osteoclasts • Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina • Secured to underlying bone by Sharpey’s fibers • Endosteum – delicate membrane covering internal surfaces of bone Blood and Nerve Supply of Bone • Periosteal arteries – Supply periosteum • Nutrient arteries – Enter through nutrient foramen – Supplies compact bone of diaphysis & red marrow • Metaphyseal & epiphyseal aa – Supply red marrow & bone tissue of epiphyses Skeletal system includes Axial division – Skull and associated bones Auditory ossicles Hyoid bones – Vertebral column – Thorax (Thoracic cage ) – Ribs sternum Appendicular division - Pectoral girdle - Pelvic girdle The Adult Skull skull is formed of two sets of bones:- cranium is encloses and protects the fragile brain tissues. = 8 bones: frontal, occipital, 2 temporals, 2 parietals, sphenoid and ethmoid facial bones holed the eyes in an anterior position and allow the facial muscles to show our feelings. = 14 bones: nasals, maxillae, zygomatics, mandible, lacrimals, palatines, inferior nasal conchae, vomer. Bones of the Cranium Frontal View Frontal Frontal View Parietal Frontal View Temporal Frontal View Nasal Frontal View Vomer Frontal View Zygoma Frontal View Maxilla Frontal View Mandible Frontal View Frontal Parietal Temporal Nasal Vomer Zygoma Maxilla Mandible Frontal View Lateral View Frontal Lateral View Parietal Lateral View Temporal Lateral View Nasal Lateral View Zygoma Lateral View Maxilla Lateral View Mandible Lateral View Sphenoid Lateral View Occipital Lateral View Mastoid Process Lateral View External Auditory Meatus Lateral View Parietal Frontal Sphenoid Temporal Occipital Mastoid Process Nasal Zygoma Maxilla Mandible External Auditory Meatus Lateral View Fetal skull • The skull of a newborn differs from an adult one: – – – – – – The infant’s face is very tiny compared to the cranium. The whole skull is large compared to infant’s body length The adult skull represents only 1/8th of the total body length, whereas that of new born infant is 1/4th as long as its entire body. The fetal skull has fibrous cartilage area between the cranial bones. These membranous area are called fontanels, which allow the fetal skull to be compressed during birth and allow the infant’s brain to be grow. The fontanels usually closes by age 20-22 months. Fetal skull Adult Vertebral Column Formed from 33 bones in the adult Divided into five major regions Cervical vertebrae 7 vertebrae of the neck region Thoracic vertebrae 12 vertebrae of the thoracic region Lumbar vertebrae 5 vertebrae of the lower back Sacrum Inferior to lumbar vertebrae Articulates with coxal bones Coccyx Most inferior region of the vertebral column Intervertebral disks The single vertebrae are separated by pads of elastic cartilage intervertebral disks Cushion vertebrae and absorb shocks. Have a high water content (about 90%) and are compressible. General Structure of Vertebrae Cervical Vertebrae • Atlas – 1st; supports head • Axis – 2nd; dens pivots to turn head • transverse foramina • bifid spinous processes • vertebral prominens – useful landmark Thoracic Vertebrae long spinous processes Rib facets Lumbar Vertebrae large bodies thick, short spinous processes Sacrum five fused vertebrae median sacral crest posterior sacral foramina posterior wall of pelvic cavity sacral promontory Coccyx Tailbone Four fused vertebrae Thorax Often called the thoracic cage. Components of the thorax Sternum– anteriorly Ribs – laterally Thoracic vertebrae – posteriorly Protects thoracic organs (heart, lungs, and major blood vessels). The Thorax Sternum Breast bone is typical flat bone and the result of fusion of three bones. Manubrium – superior section Body – bulk of sternum Xiphoid process – inferior end of sternum Attached to the 1st seven pairs of ribs. Ribs The 12 pairs of ribs form the wall of the thoracic cage. All ribs attach to vertebral column posteriorly True ribs - superior seven pairs of ribs Attach directly to sternum by costal cartilage False ribs – inferior five pairs of ribs Have cartilages attachment to the sternum that are indirect or are not attached at all. Ribs 11–12 are known as floating ribs The Thoracic cage Ribs Ribs APPENDICULAR SKELETON • It is formed of : Pectoral girdle Pelvic girdle Bones of the upper and lower limbs. PECTORAL GIRDLE • It is formed of : • CLAVICLE which holds the arm away from the thorax. • SCAPULA (WING). Clavical Scapula UPPER LIMB • ARM :Humerus • FORE ARM: Radius & Ulna. • Long bones They are formed of Epiphysis on each end. Diaphysis a tubular shaft. It is covered externally by the periosteum. HAND • WRIST : Carpal bones. • PALM : Metacarpal bones. • FINGERS : Phalanges. • They are examples of short bones. PELVIC GIRDLE • Formed of the two HIP bones. • Each hip bone is formed of three parts : ILium. Ischium. Pubis. • The hip bones and the sacrum form the bony pelvis. LOWER LIMB • THIGH : Femur. • LEG : Tibia & Fibula. • Also Patella bone FOOT • TARSUS : Tarsal bones. • Metatarsals. • Phalanges.