CH 6- Skeletal System Fun Bone Facts When you were born you had over 300 bones. Now, you have 206 bones. Over half the body's bones are in the hands and feet. Not all bones are in connection with another bone. Your bones are not all solid- store water. The smallest bone in the body is the stirrup (stapes) in the ear measuring about 3 mm in length. The longest bone in the body is the femur. Functions of the Skeletal System Support: forms the structural framework for the body. Serves as a point of attachment either directly or indirectly for the soft tissues of the body. Protection: protects the vital organs of the body. Form bony boxes or cages around vital organs like the brain, heart and lungs. Assists in movement: serves as a point of attachment for skeletal muscles. When a skeletal muscle contracts, it will pull on a bone- generating movement. Where muscles attach to and pull on bones, bone landmarks are formed. Mineral homeostasis (balance): stores minerals such as calcium and phosphorus. If the levels of these minerals in the blood drop, they can be released from the bone into the bloodstream. Calcium is essential for bone strength as well as muscle contraction. Hemopoiesis: the production of blood cells. Includes red cells, white cells and platelets. Happens in the red bone marrow of bone. Lipid storage: stores lipids for further use. Stored in the bone marrow Types of Bones (shapes) Long bones: Longer than they are wide Found in the arms and the legs Function as levers to generate movement Amplify the movement of muscles- 1 inch of travel when a skeletal muscle contracts translates to much more gross body movement. Short bones: Square or cube shaped Found in the wrists and ankles Function to evenly transfer forces from the hands and feet to the arms and legs. As they receive a force, they shift, causing the force transfer to be even. Flat bones: Thin, flat and slightly curved (difficult to break) Found on the top of the skull and on the ribcage Function to protect Irregular bones: No set shape Found in the spine (vertebrae), face and girdles (shoulder and hip) Function in muscle attachment Sesamoid bones: Develop inside a tendon Found in the kneecap Function to protect the tendon of a muscle during movement Histology of Bone Tissue Classified as a connective tissue because it contains an abundant extracellular matrix that surrounds widely spaced cells. Composed of: 98% matrix 50% inorganic minerals (mainly Ca and P) 25% protein fibers (mainly collagen that allows the bone to bend a little before it breaks) 23% water Bone cells- 2% of bone tissue Osteogenic cells: unspecified stem cells that are found within developing bone As they mature, they will change in structure and function (differentiate) Osteoblasts: bone forming cells Differentiated osteogenic cells Responsible for removing minerals from the blood and placing them into the developing bone matrix (like brick layers). This walls them off from neighboring cells. Bone cells- 2% of bone tissue Osteocytes: mature bone cells Differentiated osteoblasts Maintain the matrix of an area of bone tissue Osteoclasts: Bone destroying cells Contain powerful digestive enzymes that can break down the matrix of bone tissue Releases minerals into the blood Helps with the healing process by smoothing edges of a fracture so the osteoblasts can fill in the gap. Types of Bone Tissue Compact bone tissue: forms the external layer of all bones. Function Provides strength and rigidity to the bone Helps bones resist force Structure Composed of smaller columns of bone matrix held together by more matrix (adds to its strength) Compact Bone Structure cont Osteons: the structural unit of compact bone (bone columns) Lamellae: Mineral rings of matrix of an osteon. Lacunae: spaces within the osteons that contain osteocytes. One osteocyte per lacuna which maintains the matrix around that lacuna. Canaliculi: the small spaces extending from the lacunae. Connect neighboring lacunae so the osteocytes can transfer materials (oxygen & nutrients) between one another. Perforating canals: horizontal canals that pass through compact bone. These run perpendicular to the osteon and let blood vessels and nerves travel transversely in bone. Haversian canals: vertical canals that pass through compact bone. These are at the center of every osteon and run parallel to the osteon. They allow blood vessels and nerves travel the length of the bone. Spongy Bone (Cancellous) Forms the internal structure of all bones and the ends of long bones. Structure: Hard and not solid (airy) Function: Increases the strength without increasing its weight. Trabeculae: an irregular lattice of thin columns of bone organized along stress lines within bone. Hollow spaces between trabeculae are filled with red bone marrow. These thin columns fracture fairly easily; however, when they rebuild themselves, they are stronger and re-oriented to resist future force. The Anatomy of a Bone The long bone is used as the example when studying the anatomy of bone because all features are easily identifiable. The features are: Diaphysis: the shaft of a long bone. Functions to provide the strength to the bone because it contains a thick layer of compact bone and a thin layer of spongy bone. Epiphyses (es is plural; is is singular): the ends of a long bone. Function to form a joint and are rounded to allow joint formation. These are mainly composed of spongy bone. Proximal epiphysis: The end of the long bone that is closest to the trunk of the body. Distal epiphysis: The end of the long bone furthest from the trunk of the body. Metaphyses: the regions found between the epiphyses and the diaphysis of a long bone. Function depends on the age of the bone. Epiphyseal plate: the name given to the metaphyses in a developing bone. Made entirely of hyaline cartilage and allows for the lengthwise growth of bone. Called the growth plate and is not visible on x-rays. Epiphyseal line: the name given to the metaphyses in a mature bone. Once this is formed, bone growth stops because the raw material (cartilage) has been converted to bone. Articular cartilage: a thin layer of hyaline cartilage found covering the ends of bones (epiphyses) forming a joint. Functions as a shock absorber to protect the ends of bones. As we age, the cartilage breaks down and wears away. Periosteum: a thin layer of dense irregular connective tissue that covers all surfaces of a bone not covered by articular cartilage. Functions to protect blood vessels and nerves and is a point of attachment for muscle tendons. Because it is dense irregular, the collagen fibers running in different directions can resist any force from muscle contraction. Medullary cavity: a hollow space found within the diaphysis of a long bone. Function depends on the age of the bone (either contains red or yellow bone marrow. Red bone marrow: Produces blood cells (hemopoiesis) Fills the medullary cavity of younger individuals because they are growing and have a higher metabolic need (need more oxygen so need more red blood cells). Yellow bone marrow: Energy reserve (stores fat) Found in the medullary cavity of most adult bones Endosteum: a thin layer of fibrous connective tissue found lining the medullary cavity that holds the bone marrow in place. Nutrient foramen: small openings found throughout compact bone that allow blood vessels and nerves to enter the bone tissue. Anatomy of a Long Bone Bone Formation Ossification: the process responsible for converting connective tissue into bone. There are two different types of ossification that occur in the body: Intramembranous ossification: the formation of bones from fibrous connective tissue (mesenchyme). Occurs in flat bones like the skull The tissue is arranged in sheets called ossification centers and the process starts at the center of the sheet and works it way outwards. Begins before birth and doesnt finish until mid- teens The reason for a babys soft spot Bone Formation Endochondral ossification: the formation of bones from hyaline cartilage. Forms all bones except flat bones. Begins before birth in the center of the diaphysis (primary ossification center). Continues shortly after birth in the epiphyses (secondary ossification center). The growing regions meet at the epiphyseal plate, forcing the bone to grow lengthwise. Bone Surface Markings Depressions and openings: Fissure: Narrow slit between adjacent parts of bones through which blood vessels or nerves pass Foramen: Opening through which blood vessels, nerves or ligaments pass Fossa: Shallow depression Sulcus: Furrow along a bone surface that accomodates blood vessels, nerves or tendons. Meatus: Tube-like opening Fissure Foramen Fossa Sulcus Meatus Bone Surface Markings Processes that form joints: Condyle: Large, round protuberance with a smooth articular surface at the end of bone Facet: Smooth, flat, slightly concave or convex articular surface Head: Usually rounded articular projection supported by a constricted portion (neck) of the bone Condyle Facet Head Processes that form points of attachment for connective tissues: Crest: Prominent ridge or elongated projection Epicondyle: Typically roughened projection above a condyle Line: Long narrow ridge or border that is less prominent than a crest Spinous process: Sharp, slender projection Trochanter: Large projection Tuberosity: Variable sized projection that is rough and bumpy Tubercle: Variable sized rounded projection Crest Epicondyle Line Spinous Process Trochanter Femur Tuberosity Tubercle Bone Surface Markings Practice A.Fissure B.Foramen C.Fossa D.Sulcus E.Meatus F.Condyle G.Facet H.Head I.Crest J. Epicondyle K. Line L. Spinous process M. Trochanter N. Tuberosity O. Tubercle