Bones & The Skeleton Lecture 1

Cartilage: Skeletal Cartilage Made of some variety of cartilage tissue molded to fit it’s body and function Cartilage is mostly water (which is why it’s resilient-it can spring back into shape) There are three types: Hyaline Elastic And Fibro Cartilage

Hyaline Cartilage: Look like frosted glass Provide support with flexibility & resilience Most abundant Include: Articular Cartilage: cover ends of most bones at moveable joint sites Costal Cartilage: Connect ribs to Sternum Respiratory Cartilage: form the voice box & reinforce passageways Nasal Cartilage: support the external nose

Elastic Cartilage: Resemble Hyaline Cartilage but are more stretchy Can stand up to repeated bending Found in the ear & epiglottis

Fibrocartilage: Highly compressible with great tensile strength Consist of parallel rows of chondrocytes and alternating with collagen fibers Found in between the vertebrae, knee, & hip

Growth of Cartilage: Cartilage has a flexible matrix which accommodates mitosis Grows 2 ways Appositional Growth: cartilage forming cells secrete a matrix against the existing cartilage tissue. Growth from OUTSIDE Interstitial Growth: Chondrocytes divide and secrete a new matrix , expanding the cartilage from within Growth from INSIDE Typically cartilage growth ends when the skeleton stops growing. Cartilage and bone are two different tissues.

Functions Support: Provide a framework and cradles soft organs. Protection: Protect the skull, Heart, and vertebrae. Movement: Skeletal muscles attach to bone by tendons and bones act as levers to move the body. Mineral Growth/Storage: Bone is a reservoir for minerals (calcium & phosphate). These can be released into the bloodstream as needed. It also sores growth factors. Blood Cell Formation: Most blood cell formation (hematopoiesis) occurs in red marrow in certain bones. Triglyceride (Fat) Storage: This energy source is stored in yellow marrow in certain bones. Hormone Production: Bones produce Osteocalcin (helps to regulate bone formation & helps to protect against obesity or glucose intolerance).

Bone Classifications: Axial Skeleton: Forms the long axis of the body Includes the skull, vertebral column, and rib cage These bones protect, support, or carry other body parts.

Bone Classifications Appendicular Skeleton: Bones of the upper and lower limbs, & girdles (shoulder bones and hip bones) Help you move from place to place

Facts Bones come in many sizes and shapes The unique shape of the bones fulfill a particular need Ex. Femur withstands great pressure, and it’s hollow cylinder design provides maximum strength with minimum weight to accommodate our posture.

Classification Of Bones by Shape Long: Longer than they are wide Have a shaft plus two ends that are usually expanded All limb bones (except patella and wrist/ankle) Elongated shape NOT overall size Ex. finger bones=long bones Short: Roughly cube shaped Bones of the wrist and ankle Vary in number and size Sesamoid bone: short bone that form in a tendon- they act to alter the direction of pull for that tendon

Classification Of Bones by Shape Flat: Thin flattened bones Usually slightly curved Sternum, Scapula, ribs, and most skull bones Irregular: Have complicated shapes Vertebrae & Hip Bones

Bone Structure: Gross Anatomy Bone Textures: COMPACT BONE: A dense OUTER layer that looks smooth and solid SPONGEY BONE: next layer after compact bones. A matrix of small bone which are normally filled

Structure of Short, Irregular, & Flat Bones All of these bones consist thin plates of spongy bone covered by compact bone The plates are covered by connective tissue membranes They contain marrow but have no marrow cavity

Structure of Typical Long Bones: Usually have: a shaft, bone ends, and membranes Diaphysis (shaft): Forms the long axis of the bone Has a thick collar of compact bone surrounding the medullary cavity (marrow cavity) Epiphysis (bone ends): Boarder than the shaft Outer shell=compact bone, inside that=spongy bone Thin layer of articular (hyaline) cartilage covers the joint surface of each end—this cushions the opposing bone end during movement.

Structure of Typical Long Bones: Epiphysis (Bone ends): In adults: between diaphysis & epiphysis is an epiphyseal line—remnant of the plate (this is where your plate grew when you were younger) Membranes (Periosteum & Endosteum): Covers the outside (external) surface of all but the joint surfaces Outer layer= irregular connective tissue Inner layer= osteogenic cells that give rise to all bone except bone-destroying cells Supplied with nerve fibers and blood which pass through the shaft and enter the marrow cavities Collagen fibers attach & secure the periosteum to the bone

Structure of Typical Long Bones: Membranes Endosteum (within the bone) covers the internal bone

Cells of bone Tissue: Osteogenic Cells: active stem cells found in the membranes they can become osteoblasts or bone lining cells Osteoblasts: actively mitotic cells. They secrete an un-mineralized bone matrix of bone protein and calcium binding proteins. They can also play a role in matrix calcification Osteocytes: mature bone cells which monitor and maintain the bone matrix and act as stress sensors Bone Lining Cells: maintain the matrix and are found on the surface of bone Osteoclasts: located at bone reabsorption sites (breaking down)

Bone Formation Two Types: 1. Endochondral ossification: (endo=within, chondro=cartilage) a bone develops by replacing hyaline cartilage. The resulting bone is called a cartilage bone or endochondral bone. 2. Intramembranous Ossification: a bone develops from a fibrous membrane and the bone is called a membrane bone.

Endochondral Ossification

Intramembranous Ossification