Overview of the Classification and Structure of Bones and Cartilages PDF

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Summary

The goal of the lecture is understand the classification and structure of bones and cartilages. Topics also discussed include --- the skeleton, cartilages of the skeleton, , bone classifications and bone markings, gross anatomy of the typical long bone, chemical composition of bone, microscopic stru...

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Overview of the Skeleton: Classification and structure of Bones and Cartilages 

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Skeleton o Supports and protects the body as an internal framework o Provides a system of layers with which the skeletal muscles work to move the body o The bones store lipids and many minerals  Calcium o Red marrow of bones provides a site for blood cell formation o Joints (articulations)  Bones that are connected o Skeleton is subdivided into two divisions:  Axial skeleton: Bones that lie around the body’s center of gravity  Appendicular Skeleton: Bones of the limbs, or appendages Cartilages of the Skeleton o Three types of cartilage found in the body:  Hyaline cartilage  Most common type found in the body  Articular cartilage: Cover the ends of most bones at movable joints  Costal cartilages: Connect the ribs to the sternum  Respiratory cartilages: Found in the larynx and other respiratory structures  Nasal cartilages: Support the external nose  Elastic cartilage  Found in the external ear and the epiglottis o Guardian of the airway  Fibrocartilage  Known for its flexibility  Provides strength and shock absorption  Interverbal discs: Pads located between the vertebrae  Menisci: Pads located in the knee joint  Pubic symphysis: Located where the hip bones join anteriorly o In embryos, the skeleton is predominantly made up of hyaline cartilage, but in adults, most of the cartilage has been replaced by more rigid bone. o Perichondrium: Cartilage contains no nerves or blood vessels and is surrounded by a covering of dense irregular connective tissue which acts to resist distortion of the cartilage. Bone Classification and Bone Markings o 206 bones of the adult skeleton are composed of two basic kinds of osseous tissue that differ in their texture  Compact bone: Dense and made up of organizational units called osteons  Spongy bone: Cancellous bone  Composed of small trabeculae (columns) of bone and lots of open space o Bones may be classified further on the basis of their gross anatomy into four groups:  Long: Much longer than they are wide, generally consisting of a shaft with heads at either end  Composed mostly of compact bone  Ex: femur and phalanges (singular: phalanx)  Short: Typically cube shaped  They contain more spongy bone than compact bone  Ex: tarsals and carpals  Flat: Generally thin, with two wafer-like layers of compact bone sandwiching a thicker layer of spongy bone between them.  “flat bone” implies a structure that is straight, many bones are curved

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o EX: bones of the cranium  Irregular bones: Bones that do not fall into one of the preceding categories  The vertebrae o Two other subcategories of bones:  Sesamoid bones: Special types of short bones formed within tendons  EX: Patella (kneecaps)  Sutural bones: Tiny bones between cranial bones o Bone markings  Casual observation of the bones will reveal that bone surfaces are not featureless smooth areas  Have an array of bumps, holes, and ridges  Reveal where bones form joints with other bones, where muscles, tendons, and ligaments were attached, and where blood vessels and nerves passed.  Two main categories  Projections that grow out from the bone and serve as sites of muscle attachment or help form joins  Depressions or openings in the bone that often serve as conduits for nerves and blood vessels  Bone Markings: Projections that are sites of muscles and ligament attachment:  Tuberosity: Large rounded projection; may be roughened  Crest: Narrow ridge of bone; usually prominent  Trochanter: Very large, blunt, irregularly shaped process (only examples are on the femur)  Line: Narrow ridge of the bone; less prominent than a crest  Tubercle: Small rounded projection or process  Epicondyle: Raised area on or above a condyle  Spine: Sharp, slender, often pointed projection  Process: Bony prominence  Bone Markings: Projections that help form joints  Head: Bony expansion carried on a narrow neck  Facet: Smooth, nearly flat articular surface  Condyle: Rounded articular projection  Ramus: Arm like bar of bone  Depressions and Openings: Passage of vessels and Nerves  Fissure: Narrow, slit-like opening  Foramen: Round-like or oval opening through a bone  Notch: Indentation at the edge of a structure  Depressions and Openings: Others  Meatus: Canal-like passageway  Sinus: Bone cavity filled with air and lined with mucous membrane  Fossa: Shallow basin-like depression in a bone, often serving as an articular surface. Gross Anatomy of the Typical Long Bone o Homeostatic imbalance  Longitudinal bone growth at epiphyseal plates (growth plate)  Follows a predictable sequence and provides a reliable indicator of the age of children exhibiting normal growth.  If problems of long-bone growth are suspected, X-ray films are taken to view the width of the growth plates  EX: pituitary dwarfism  An abnormally thin epiphyseal plate indicates growth retardation Chemical Composition of Bone o Bone is one of the hardest materials in the body. o Bone has a remarkable ability to resist tension and shear forces that continually act on it. o The hardness of bone is due to the inorganic calcium salts deposited in its ground substance.

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 Its flexibility comes from the organic elements of the matrix, particularly the collagen fibers. Microscopic Structure of Compact Bone o Spongy bone has a spiky, open-work appearance, resulting from the arrangement of the trabeculae  Compact bone appears to be dense and homogeneous on the outer surface. o Microscopic examination of compact bone reveals that it is riddled with passageways carrying blood vessels, nerves, and lymphatic vessels that provide the living bone cells with needed substances and a way to eliminate wastes. Ossification: Bone Formation and Growth in Length o Except for the collarbones, all bones of the body inferior to the skull form by the process of endochondral ossification  Uses hyaline cartilage as a model for bone formation. o Major events of this process:  Blood vessels invade the perichondrium covering the hyaline cartilage model and convert it to a periosteum  Osteoblasts at the inner surface of the periosteum secrete bone matrix around the hyaline cartilage model, forming a bone collar.  Cartilage in the shaft center calcifies and then hollows out, forming an internal cavity.  A periosteal bud (blood vessels, nerves, red marrow elements, osteoblasts, and osteoclasts) invade the cavity and forms spongy bone, which is removed by osteoclasts, producing the medullary cavity.  This process proceeds in both directions from the primary ossification center o As bones grow longer, the medullary cavity gets larger and longer.  Chondroblasts lay down new cartilage matrix on the epiphyseal face of the epiphyseal plate, and it is eroded away and replaced by bony spicules on the diaphyseal face.  This process continues until late adolescence when the entire epiphyseal plate is replaced by bone. o Growth in length of a long bone occurs at the epiphyseal plate  Resting zone  Proliferation zone: Cartilage cells undergo mitosis  Hypertrophic zone: Older cartilage cells enlarge  Calcification zone: Matrix becomes calcified; cartilage cells die; matrix begins deteriorating  Ossification zone: New bone is forming  Calcified cartilage spicule  Osseous tissue...