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The Skeletal System Chapter 6 Anatomy and Physiology Mr. Knowles Liberty Senior High School
Question of the Day! Do bones remain the same? How do bones “know” when to stop growing? What happens when they don’t?
The Skeletal System! Our First System Cells (Osteocytes) Tissues (Osseous Tissue) Organs (Bones) Systems (Skeletal)
All C.T. have Three Parts 1. Specialized Cells 2. Extracellular Protein Fibers 3. The Fibers above and a ground substance (usually a liquid)- make up the Matrix that surrounds cells. (most of the volume of C.T.)
The Fibers Collagen Fibers- long, straight, unbranched, fibers of twisted protein; rope-like, very flexible, yet strong. (Tendons and Ligaments)
Bone (Osseous Tissue) G.S. = almost no liquid; collagen fibers + calcium salts (CaPO 4 and some CaCO 3) Strong and flexible properties. Lacunae in matrix contain osteocytes.
Bone (Osseous Tissue) Lacunae organized around a central canal (Haversian canal) which contains blood vessels. Diffusion cannot occur through calcium salts. Cytoplasm of osteocytes extend to central canal by canaliculi.
A Basic Pattern in Bone Tissue Lacunae with osteocytes arranged around and connected to a central canal by radiating canaliculi- Osteon Many osteons in one bone.
Bone (Osseous Tissue) Bone surfaces covered by periosteum- fibrous layer of C.T.; attachment for tendons and ligaments. Site of appositional growth of bone. Bone is constantly remodeled- grow thicker with stresses.
Anatomy of Bone (4 parts) 3. Marrow Cavity- core of bone with red and yellow marrow. 4. Metaphysis- area that connects the epiphysis and diaphysis. Contains the Epiphyseal plate- area of growth between epiphysis and diaphysis
Other Parts to Bone Periosteum- outermost layer of bone made of cells and fibers. Provides the point of attachment for tendons and ligaments on the outside. Route for vessels to enter the bone. Participates in bone growth and repair.
Other Parts of the Bone Endosteum- a layer of cells that lines marrow cavity; lines trabeculae of spongy bone and central canal of compact bone. Also site of bone growth.
Two Types of Osseous Tissue 1. Compact bone- dense bone, solid, more on surface of bone, shaft of bone. Function: osteons are all aligned;strengthen bone, the tissue of bone is parallel to stresses.
Two Types of Osseous Tissue 2. Spongy Bone- open network of trabeculae which are struts and plates in the interior of bone (matrix), light in weight; Function: has no osteons; withstand stress from a variety of directions, reduce the weight of the overall bone.
Bone Development Skeleton begins to develop at 6 weeks after conception, embryo is only 12 mm (0.5 in ) long. Bone growth continues through the age of 25 yrs. Bone is continuously remodeled or reshaped.
How do bones grow in humans? Can we see bone growth in a developing embryo?
The Players in Osteogenesis Ossification- formation of bone is a dynamic process. Osteoblasts- produce new bone matrix. Osteoclasts- produce acids and enzymes to release the stored minerals in the matrix. Osteocytes- mature bone cells that do not divide.
Bone Grows in Two Ways Intramembranous Ossification- bone forms from mesenchyme cells or fibrous connective tissue. Deep layers of the dermis. Endochondral Ossification- bone replaces a mold of cartilage.
Intramembranous Growth Step 1: Mesenchymal cells (stem cells) cluster at a site (ossification center) within the dermis (skin layers) and secrete bone matrix (collagen + Ca +2 ). These cells will become osteoblasts. Step 2: Bone grows outward in spicules which will become the struts of spongy bone. Vessels grow into area. Step 3: Osteoblasts at the outer edge become less active and become osteocytes.
Intramembranous Bones Dermal bones of the skull- parietal, occipital, etc, the mandible, the clavicle, and the scapula. Bones that are mostly spongy tissue are made by intramembranous ossification.
Osteogenesis Intramembranous ossification- bone growth within C.T. (mandible, parietal) see p. 181, 4th Ed., Martini) Want to see what happens when this growth is uncontrolled? Heterotopic Bone Formation, p. 50 of the A.M.
Endochondral Ossification Endo means inside; -chondros means cartilage. Bone tissue gradually replaces a cartilage model or mold for the bone. Most bones form this way; all of the appendicular (limb) skeletal bones.
Endochondral Growth Step 1: Cartilage forms a mold and the chondrocytes grow very large in the center of the mold. Lacunae expand and the matrix thins to struts. Chondrocytes die. Step 2: Blood vessels grow into the shaft of cartilage; cells of the perichondrium become osteoblasts. The perichondrium now becomes the periosteum.
Endochondral Growth Step 3: Blood supply increases; fibroblasts migrate to the center and become osteoblasts. They start to make spongy bone- Primary Center of Ossification. Step 4: As bone enlarges, osteoclasts appear and erode the trabeculae in the center- creates the marrow cavity.
Endochondral Ossification Osteoblasts of the diaphysis and chrondrocytes of epiphysis continue to grow; elongate bone. Epiphyseal Plate is the interface between the two. At puberty, the osteoblasts overcome chondrocytes; the plate becomes more narrow- epiphyseal line.
Lengthening Bones- Hyaline chondrocytes die and leave calcified struts. Blood vessels grow at edges and perichondrial cells become osteoblasts. Osteoclasts- create a marrow cavity by dissolving struts
Bone Growth Intramembranous Occurs in a layer between dermis (dermal bones). Mesenchymal (stem) cells osteoblasts. Spongy Bone. Skull bones, mandible, scapula, clavicle. Endochondral Fills in a cartilage mold in a center of ossification. Fibroblasts osteoblasts in the center of mold. Osteoclasts form a marrow cavity. Compact Bone. Most other bones; long bones.
Basic Multicellular Unit (BMU) A group of wandering cells that constantly reform or remodel bone. Many BMU move throughout the bone’s center and surface. Specific sequence of 5 events or steps.
5 Steps to Bone Formation 1.Osteoclast Recruitment- osteoclasts arrive at the site of repair or reformation. 2.Resorption- osteoclasts resorb or release the Ca +2 from the matrix. This forms a cavity in the area (2 weeks). 3.Osteoid Formation- osteoclasts self- destruct and attract osteoblasts to the area. The osteoblasts secrete new collagen and Ca +2 into the cavity.
5 Steps to Bone Formation 4.Mineralization- the new osseous tissue begins to mineralize; Ca +2 fills the cavity. 5.Quiescence- the last osteoblasts develop into osteocytes and remain quiet in the bone tissue. They have long cell processes that can detect mechanical stresses.
Diseases of Bone Growth Gigantism – overproduction of growth hormone before puberty, growth plates still open; pituitary tumor. Acromegaly – overproduction of growth hormone after puberty, growth plates closed but abnormal growth of cartilage and small bones. Marfan’s Syndrome – defect in fibrillin, a protein of C. T. matrix; excessive cartilage at plates that is weak; blood vessels are not as elastic; genetic.
Diseases of Bone Growth Achondroplasia – “a’ without, “chondro” cartilage, “plasia” formation – cartilage within the epiphyseal plates grow extremely slow; affects appendicular skeleton more than axial skeleton.
The Skeletal System Anatomy and Physiology Chapters 7 and 8 Mr. Knowles Liberty Senior High School
The Skeletal System How many bones do women and men have? 206 bones in humans
Two Divisions: Axial Skeleton- bones of skull, vertebral column, ribs, and sternum- 80 bones Appendicular Skeleton- bones of limbs (appendages), pectoral and pelvic girdles;attach the limbs to the trunk of the body.
Functions of the Skeletal System 1. Support- framework, 2. Storage of Minerals- Ca 3 (PO 4 ) 2, and CaCO 3 3. Storage of Lipids- yellow marrow.
Functions of the Skeletal System 4. Blood cell production- red marrow makes erythrocytes, leukocytes, and others. 5. Protection- protect vital organs. Ex. Ribs. 6. Leverage- change magnitude and direction of forces.
Your Assignment Finish the handouts over the tissues of bone. Identify all bones and structures listed in the outline (Refer to Table 6-2 on p. 192). Classify these bones into the six major types of bones.
What can we learn about a person’s life from their bones? G. B. Dyson (2000). The Aleutian Kayak. Scientific American (April) 84-91.