Unit 5: SKELETAL SYSTEM (a) NRSG231 Dr. Moattar Raza Rizvi Skeletal System: Contents Functions of the Skeletal System Fracture Structure of Bone Tissue Articulations & Joint Bone Development and Growth Divisions of the Skeleton Classification of Bones 1
Skeletal System: Introduction The human skeletal system consists of bones, cartilage, ligaments and tendons and accounts for about 20 of the body weight. Ligaments: Bone to Bone Attachment Tendons: Bone to Muscle Attachment What are the functions of the skeletal system? SUPPORT: Hard framework that supports and anchors the soft organs of the body. PROTECTION: Surrounds organs such as the brain and spinal cord. MOVEMENT: Allows for muscle attachment therefore the bones are used as levers. STORAGE: Minerals (calcium) and lipids (yellow marrow) are stored within bone material. BLOOD CELL FORMATION: The bone marrow (red) is responsible for blood cell production. 2
Division of the Skeletal System Axial skeleton Appendicular skeleton Skull Vertebral column Rib cage 80 bones Upper and Lower Limbs (appendages) Pectoral girdle Pelvic girdle 126 bones Division of the Skeletal System 3
Bone: Shape Long bones are longer than they are wide, have a definite shaft and two ends, and consist of all limb bones except patellas, carpals, and tarsals. Short bones are somewhat cube-shaped and include the carpals and tarsals. Flat bones are thin, flattened, often curved bones that include most skull bones, the sternum, scapulae, and ribs. Irregular bones have complicated shapes that do not fit in any other class, such as the vertebrae and coxae. Bone: Shape 4
Bone: Shape Which of the following bones is considered a sesamoid bone? Patella Structure of Typical Long Bone Long bones have a tubular bone shaft, consisting of a bone collar surrounding a hollow medullary cavity, which is filled with yellow bone marrow in adults. EPIPHYSES are at the ends of the bone, and consist of internal spongy bone covered by an outer layer of compact bone. The Epiphyseal Line is located between the epiphyses and diaphysis, and is a remnant of the epiphyseal plate. 5
Structure of Typical Long Bone Structure of Typical Long Bone DIAPHYSIS is the shaft of the bone which surrounds the medullary cavity. Composed of compact bone The dense connective tissue covering the outer surface of bone diaphyses is known as the: PERIOSTEUM. The internal surface of the bone is lined by a connective tissue membrane called the ENDOSTEUM. 6
Structure of Typical Long Bone Articular Cartilage covers the external surface of the epiphyses; made of hyaline cartilage; decreases friction at joint surfaces Medullary cavity: Cavity of the shaft; contains yellow marrow (mostly fat) in adults; contains red marrow (for blood cell formation) in infants Types of Bone cells There are three types of cells that contribute to bone homeostasis. Osteoblasts are bone-forming cell The organic component of bone matrix is produced by Osteoblasts Osteoclasts resorb or break down bone, and Osteocytes are mature bone cells. An equilibrium between osteoblasts and osteoclasts maintains bone tissue. 7
Bone Textures: Compact Bone There are two types of bone tissue: 1. Compact Bone 2. Spongy (Also called as Cancellous) Bone The names imply that the two types of differ in density, or how tightly the tissue is packed together. Bone Textures: Compact Bone Compact bone consists of closely packed osteons or haversian systems. The osteon consists of a central canal called the osteonic (haversian) canal, which is surrounded by concentric rings (lamellae) of matrix. Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae. Small channels (canaliculi) radiate from the lacunae to the osteonic (haversian) canal to provide passageways through the hard matrix. 8
Bone Textures: Compact and Spongy Bone Bone Textures: Compact Bone In compact bone, the haversian systems are packed tightly together to form what appears to be a solid mass. The osteonic canals contain blood vessels that are parallel to the long axis of the bone. These blood vessels interconnect, by way of perforating canals, with vessels on the surface of the bone. 9
Bone Textures: Compact and Spongy Bone Bone Textures: Spongy Bone Spongy (cancellous) bone is lighter and less dense than compact bone. Spongy bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow. The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply. 10
Chemical composition of Bone Cells, matrix of collagen fibers and ground substance (organic: 35%) Contribute to the flexibility and tensile strength The organic component of bone matrix is produced by: osteoblast Mineral crystals (inorganic: 65%) Primarily calcium phosphate Lie in and around the collagen fibrils in extracellular matrix Contribute to bone hardness Small amount of water Formation of Bony Skeleton The terms osteogenesis and ossification are often used synonymously to indicate the process of bone formation. 1. Intramembranous ossification forms membrane bone from fibrous connective tissue membranes, and results in the cranial bones and clavicles. 2. In endochondral ossification bone tissue replaces hyaline cartilage, forming all bones below the skull except for the clavicles. 11
Factors regulating bone growth Vitamin D: increases calcium from gut Parathyroid hormone (PTH): stimulates the breakdown of bone and the increase in blood calcium levels Calcitonin: decreases blood calcium (opposes PTH) Growth hormone & thyroid hormone: modulate bone growth Sex hormones: growth spurt at adolescense and closure of epiphyses Calcium regulation is negative feedback mechanism 12
Bone Repair Fractures are breaks in bones, and are classified by: 1. The position of the bone ends after fracture, 2. Completeness of break, 3. Orientation of the break relative to the long axis of the bone, and 4. Whether the bone ends penetrate the skin. Repair of fractures involves four major stages: 1. Hematoma formation, 2. Fibrocartilaginous callus formation, 3. Bony callus formation, and 4. Remodeling of the bony callus. Bone Repair The callus that forms around a bone fracture is comprised of fibrocartilage tissue. 13
Joints (articulations) Where two or more bones meet Functions: movement, hold skeleton together Classified by structure (or function): 1. Fibrous (synarthroses): immovable joint 2. Cartilaginous (amphiarthroses): slightly movable 3. Synovial (diarthroses): freely movable No movement Located: Fibrous Joints Sutures: bones of skull held together by connective tissue fibers Between teeth & jaws 14
Fibrous Joints Cartilaginous Joints Bones united by cartilage Located: Epiphyseal plates Rib & sternum Pubic symphysis 15
Cartilaginous Joints Synovial Joints Bones separated by fluid-containing joint cavity Synovial fluid reduces friction between cartilages Menisci: The thickened fibrocartilage cartilage "cushions" found in the knee and vertebral joints that absorb compression reduces friction Bursa: fibrous, saclike structures that are lined by a synovial membrane containing synovial fluid, occur where bones, ligaments, tendons, muscles, skin rub together 16
Lateral & Medial Meniscus Torn medial meniscus 17
Bursa fluid-filled sac that cushions between bones & tendons/muscles Types of Synovial Joints 1. Plane wrist 2. Hinge elbow, ankle, fingers 3. Pivot ulna/radius 4. Condyloid (ellipsoidal) wrist, knuckle 5. Saddle thumb 6. Ball-and-socket shoulder, hip 18
Types of Synovial Joints The structure of a synovial joint These type of joints, also known as Freely Moveable joints, are surrounded by a Capsule. This capsule has an internal lining, called a Synovial Membrane. The membrane secretes a fluid called Synovial Fluid which helps to produce Friction Free Movement. Synovial fluid: - is found within the joint; - It lubricates the joint; - It allows friction free movement. Synovial membrane: - is a layer on the inside of the capsule; - it secretes the synovial fluid. 19
The structure of a synovial joint Ligaments: - are bands of tough, fibrous tissue; - they vary in shape and size; - they hold bones together at the joints; - they limit the range of movement; - they prevent dislocation; - there are joint capsules which surround the joint. Hyaline cartilage: - has a hard, tough, slippery layer; - it covers the head of bones forming the joint; - it protects the bone; - reduces friction within the joint. Cartilage Embryo More prevalent than in adult Skeleton initially mostly cartilage Bone replaces cartilage in fetal and childhood periods 20
Skeletal Cartilage is connective tissue Cells called chondrocytes Abundant extracellular matrix Fibers: collagen & elastin Jellylike ground substance of complex sugar molecules 60-80% water (responsible for the resilience) No nerves or vessels (hyaline cartilage) Skeletal Cartilages Skeletal cartilages are made from cartilage, surrounded by a layer of dense irregular connective tissue called the perichondrium. Hyaline cartilage is the most abundant skeletal cartilage, and includes the articular, costal, respiratory, and nasal cartilages. Elastic cartilages are more flexible than hyaline, and are located only in the external ear and the epiglottis of the larynx. Fibrocartilage is located in areas that must withstand a great deal of pressure or stretch, such as the cartilages of the knee and the intervertebral discs. 21
Locations of the different kinds of cartilage Growth of Cartilage Appositional growth results in outward expansion due to the production of cartilage matrix on the outside of the tissue. Interstitial growth results in expansion from within the cartilage matrix due to division of lacunae-bound chondrocytes and secretion of matrix. 22
Common Types of Fractures Common Types of Fractures 23
Common Types of Fractures Terms (Examples) chondro refers to cartilage chondrocyte endochondral perichondrium osteo refers to bone osteogenesis osteocyte periostium blast refers to precursor cell or one that produces something osteoblast cyte refers to cell osteocyte 24
Main objective of Unit 2 Skeletal system: At the end of this unit, you should be able to answer the following? 1. Define tendon and ligament? 2. Write different functions of skeletal system? 3. Explain the division of the skeletal system? 4. Give the classification of bones based on shape and their location? 5. Write the different types and function of bone cells? 6. What is the main difference between compact and spongy bone? Compact bone consists of closely packed osteons or haversian systems. Spongy (cancellous) bone is lighter and less dense than compact bone 7. Give the chemical composition of bones? hydroxyapatite, a mineral salt that is largely calcium phosphate, which accounts for the hardness and compression resistance of bone. 8. Write the difference between two types of ossification? 9. What are the four major stages in the repair of fracture? 10. Give the names and location of different types of cartilages found in human? 11. Write the types of joints and their location? 12. Give the names of different types of synovial joints? 13. Define comminuted and greenstick fracture? 25