The Skeletal System Skeletal System Notes Standard SAP
- Slides: 36
The Skeletal System
Skeletal System Notes • Standard SAP 2 b. Explain how the skeletal structures provide support and protection for tissues EQ: How do bones and the skeletal system function to help the body maintain homeostasis?
The Skeletal System • Parts of the skeletal system – Bones (skeleton) – Joints – Cartilages – Ligaments • Divided into two divisions – Axial skeleton – Appendicular skeleton
Functions of Bones • • • Support of the body Protection of soft organs Movement due to attached skeletal muscles Storage of minerals and fats Blood cell formation
Bones of the Human Body • The adult skeleton has 206 bones • Two basic types of bone tissue – Compact bone • Homogeneous – Spongy bone • Small needle-like pieces of bone • Many open spaces Figure 5. 2 b
Classification of Bones on the Basis of Shape Figure 5. 1
Classification of Bones • Long bones – Typically 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 mostly spongy bone • Examples: Carpals, tarsals
Classification of Bones • Flat bones – Thin and flattened – Usually curved – Thin layers of compact bone around a layer of spongy bone • Examples: Skull, ribs, sternum
Classification of Bones • Irregular bones – Irregular shape – Do not fit into other bone classification categories • Example: Vertebrae and hip
Classification of Bones on the Basis of Shape Figure 5. 1
Gross Anatomy of a Long Bone • Diaphysis – Shaft – Composed of compact bone • Epiphysis – Ends of the bone – Composed mostly of spongy bone Figure 5. 2 a
Structures of a Long Bone • Periosteum – Outside covering of the diaphysis – Fibrous connective tissue membrane • Sharpey’s fibers – Secure periosteum to underlying bone • Arteries – Supply bone cells with nutrients Figure 5. 2 c
Structures of a Long Bone • Articular cartilage – Covers the external surface of the epiphyses – Made of hyaline cartilage – Decreases friction at joint surfaces Figure 5. 2 a
Structures of a Long Bone • Medullary cavity – Cavity of the shaft – Contains yellow marrow (mostly fat) in adults – Contains red marrow (for blood cell formation) in infants Figure 5. 2 a
Bone Markings • Sites of attachments for muscles, tendons, and ligaments • Categories of bone markings – Projections and processes – grow out from the bone surface – Depressions or cavities – indentations
Summary • • 3 -2 -1 3 facts that you learned 2 things that you found interesting 1 question that you have
Microscopic Anatomy of Bone • Standard SAP 2 b. Explain how the skeletal structures provide support and protection for tissues • EQ: How does the microscopic structure of bones contribute to the functions of bones?
Microscopic Anatomy of Compact Bone • Osteon (Haversian System) – A unit of bone • Central (Haversian) canal – Opening in the center of an osteon – Carries blood vessels and nerves • Perforating (Volkman’s) canal – Canal perpendicular to the central canal – Carries blood vessels and nerves
Microscopic Anatomy of Compact Bone Figure 5. 3
Microscopic Anatomy of Compact Bone • Lacunae – Cavities containing bone cells (osteocytes) – Arranged in concentric rings • Lamellae – Rings around the central canal – Sites of lacunae Detail of Figure 5. 3
Microscopic Anatomy of Compact Bone • Canaliculi – Tiny canals – Radiate from the central canal to lacunae – Form a transport system – Supply O 2 and nutrients to osteocytes.
Microscopic Anatomy of Spongy Bone • Does not contain osteons • Consists of units called trabeculae – Irregular latticework of thin columns of bone tissue • Spaces between trabeculae filled with red marrow – In hip bones, ribs, sternum, backbone, ends of long bones.
Trabeculae structure
Summarizer • Describe the difference between compact bone and spongy bone in terms of gross and microscopic anatomy.
Types of Bone Cells • Osteogenic Cells – Unspecialized stem cells – Only bone cells that undergo cell division • Osteocytes – Mature bone cells • Osteoblasts – Bone-forming cells • Osteoclasts – Bone-destroying cells – Break down bone matrix for remodeling and release of calcium
Bone Formation • Ossification – the process by which bones form • Bone growth occurs in 4 situations: – Initial formation in an embryo/ fetus – Growth during infancy, childhood, and adolescence until adulthood – Remodeling – replacing old tissue with new – Repair after a fracture
Initial Bone Formation • Skeleton begins as mesenchyme – embryonic connnective tissue that forms all other tissues • 2 methods of bone formation – Intramembranous ossification • Bone forms in mesenchyme in sheet like layers – Endochondral ossification • Bone forms in hyaline cartilage made from mesenchyme
Intramembranous ossification • Simpler method • Forms flat bones of skull and mandible • Steps: 1. Ossification center develops – site where bone will be made • Osteoblasts secrete extracellular matrix of bone 2. Calcification – calcium and other mineral salts are deposited to harden the extracellular matrix
3. Trabeculae form as the extracellular matrix hardens to form spongy bone 4. Periosteum develops from mesenchyme around the outside of bone - a layer of compact bone replaces surface layers of spongy bone
Endochondral Ossification
Bone Growth in Length • Occurs at epiphyseal plate • New cartilage cells (chondrocytes) added to epiphyseal side of the plate • Old chondrocytes on diaphyseal side turn into bone tissue • Diaphyseal side increases in length
Bone Growth in Thickness • Osteoblasts add bone tissue to the outside • Osteoclasts break down bone on the inside • Medullary cavity enlarges as bone thickness increases
Bone Remodeling • Ongoing process of replacing old bone tissue with new • Bone resporption – removal of minerals and collagen fibers by osteoclasts • Bone deposition - addition of minerals and collagen fibers to bone by osteoblasts
Bone Fractures
Bone Fracture Repair • 1. phagocytes remove dead bone tissue • 2. chonroblasts (cartilage forming cells) form cartilage at the fracture site • 3. fibrocartilage converted to spongy bone • 4. bone remodeling occurs -> osteoclasts absorb dead bone, spongy bone converted to compact bone • Takes longer to heal because calcium is deposited gradually
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