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Skeletal system

This article provides an overview of the functions and anatomy of the skeletal system, including the axial and appendicular skeleton. It covers the support and protection of organs, movement, mineral storage, blood-cell formation, and bone classification. Additionally, it discusses the gross anatomy of bones, the structure of a typical long bone, and bone development and growth.

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Skeletal system

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  1. Skeletal system

  2. Axial Skeleton Support and protect organs of the head, neck, and trunk Skull Vertebral Column Thoracic cage Appendicular Skeleton Bones of limbs Bones that anchor limbs to axial skeleton Pectoral Girdle Pelvic girdle Skeleton

  3. Functions • 1. Support • A hard framework that supports the weight of the body and cradles its soft organs

  4. Functions • 2. Protection • Skull forms a protective case for the brain • Vertebrae surround spinal cord • Rib cage protect the organs of the thorax

  5. Functions • 3. Movement • Skeletal muscles attach to the bones by tendons and use the bones as levers to move the body and its parts. • The arrangement of bones and the structure of the joints determine the types of movement that are possible

  6. Functions • 4. Mineral Storage • Reservoir for minerals, especially calcium and phosphate • Stored minerals are released into the bloodstream as ions for distribution to all parts of the body as needed. • If body needs more, osteoclasts break down bone to release Ca into blood

  7. Osteoporosis: disorder caused by excessive loss of bone volume and mineral content *Bones easily fractured *Most common in light skinned females after menopause *Risk increases if decrease calcium intake, decrease exercise, and decrease estrogen *May be prevented if dietary intake of 800mg Ca before age 35, regular excercise

  8. Functions • 5. Blood-cell formation • Bones contain red and yellow bone marrow in the cavity of long bones, spongy bone, osteonic canals of compact bone. • In adults red marrow is found in spongy bone of ribs, sternum, vertebrae, pelvis and epiphyses of humerus and femur • Red marrow makes the blood cells (red, white, and platelets), and yellow marrow is a site of fat storage, with little or no role in blood-cell formation • With increase age, red marrow is replaced by yellow marrow.

  9. Classification of Bones • The shape of each bone fills a particular need • Bones are classified by their shape as long, short, flat or irregular

  10. 1. Long Bones • Long bones are longer than they are wide • Most bones in the limbs are long bones • named for elongated shape, not for overall size

  11. 2. Short Bones • Roughly cube shaped • Ex. Bones of wrist • Sesamoid bones are a special type of short bone that forms within a tendon (patella)

  12. 3. Flat Bones • Flat bones are thin, flattened, and usually curved. • Ex. Skull, ribs, sternum, and scapula

  13. 4. Irregular Bones • Various shapes that don’t fit into previous categories • Ex. Vertebrae and hip bones

  14. Gross Anatomy of Bones • Compact bone: almost every bone of the skeleton has a dense outer layer that looks smooth and solid to the naked eye. This external layer is compact bone. Composes the wall of the diaphysis • Internal to this is spongy bone (cancellous bone) a honeycomb of small needle like or flat pieces called trabeculae (little beams) Open spaces between the trabeculae are filled with red or yellow bone marrow Found in epiphysis, lightweight

  15. Structure of a Typical Long Bone • The tubular diaphysis or shaft forms the long axis of a long bone • The epiphyses are the ends of bones • Periosteum- covering of the bone, made of fibrous c.t.; place of attachment for ligaments and tendons, helps repair bone tissue • Medullary cavity- hollow chamber in the diaphysis; lined by the endosteum, filled with marrow (marrow cavity)

  16. Bone Structure • Matrix is dense and mostly calcium phosphate with some collagen fibers • -contains bones cells within pockets (lacunae) • 1. Osteocytes- mature bone cells which recycle calcium in the matrix and repair damaged bone • 2. osteoblasts- cells actively depositing bone matrix • 3. osteoclasts- cells actively removing bone matrix

  17. Functional Unit of Bone is the Osteon. • Osteocytes are arranged in concentric layers (lamellae) around a central canal which contains one or more blood vessels • Narrow passageways (canaliculi) extend between the lacunae and blood vessels to form a network for exchange of nutrients, gases, and wastes

  18. Bone Development and Growth • During development cartilage is replaced by bone (ossification) • 2 types: • Intramembranous ossification • Occurs in the deeper layers of the dermis (fibrous connective tissue) • Some skull bones, mandible, clavicle

  19. Endochondral ossification • Most bones form this way • Within cartilage • 1. cavities form within the cartilage • 2. blood vessels grow around the edges • 3. cartilage cells convert to osteoblasts & a layer of bone forms around the shaft

  20. Endochondral ossification • 4. blood vessels penetrate the central region & osteoblasts start producing spongy bone • 5. remodeling forms the marrow cavity & bone of the shaft becomes thicker & the cartilage near the epiphysis is replaced by bone

  21. Increasing the length of bone • 1. Osteoblasts from the diaphysis continually invade the cartilage of the epiphyses & ossify • 2. new cartilage is continually added to the epiphyses. This region is the epiphyseal plate. This causes the bone to lengthen.

  22. Increasing the length of bone • 3. at puberty, the onset of hormones stimulates bone growth. Osteoblasts produce bone faster than the cartilage can keep up. The epiphyseal plate narrows and disappears. The epiphyseal line is all that remains. THE BONE STOPS GROWING

  23. Axial Skeleton • Bones of the skull, thoracic cage, & vertebral column

  24. The skull (22 bones) Cranium • Occipital bone: posterior & inferior surfaces • Frontal bone: forms forehead & roof orbits • Parietal bones (2): superior & lateral surfaces • Temporal bones (2): lateral & inferior • Sphenoid bone: extends from one side, behind the eyes, and to the other side • Ethmoid bone: forms part of the orbital wall, floor of cranium, roof of nasal cavity, & nasal septum

  25. Face • Maxillae (2): forms upper jaw • Palatine bones (2): form posterior of hard palate (roof of mouth) • Nasal bones (2): extend from bridge of nose to nares • Vomer: inferior portion of nasal septum • Inferior nasal conchae (2): scroll like bone in nasal cavity • Zygomatic bones (2): Cheek bones • Lacrimal bones (2): smallest; in the medial portion of each orbit • Mandible: lower jaw

  26. Vertebrae (24) Cervical vertebrae (7) Neck; C1-C7 Thoracic (12) vertebrae Midback; articulates with the ribs; T1--T12 Lumbar (5) vertebrae Lowerback; L1-L5 Sacrum 5 bones fused into 1 Coccyx 4 bones fused into 1 Vertebral Column (26 bones)

  27. Vertebra anatomy • 1. body-supports weight • 2. vertebral foramen- opening for spinal cord • 3. transverse process- site of muscle attachment; may articulate with ribs. • 4. spinous process- posterior projection (what you feel) • 5. superior & inferior articular processes where vertebrae articulate with one another • Intervertebral discs- discs of fibrocartilage which help absorb shock

  28. Thoracic Cage • Ribs (costae) 12 pairs • 1-7 Vertebrosternal (true) ribs connected to vertebrae & sternum • 8-12 (false ribs) • 8-10 Vertebrochondral ribs connected to vertebrae, ribs fused together to connect to sternum • 11-12 vertebral ribs (floating ribs) connected to vertebrae only

  29. Sternum (breast bone) • Manubrium-articulates with clavicles & 1st ribs • Body- ribs attach here • Xiphoid process- diaphragm and abdominal muscle attach here

  30. Appendicular Skeleton • 126 bones • 1. Pectoral girdle (shoulder girdle) • Connect arms to trunk of body • A. clavicle (2) (collarbone) s-shaped bones; articulate with manubrium of sternum • B. scapula (2) (shoulder blade) triangular bones; articulate with the humerus

  31. 2. humerus (2) • Extends from the scapula to the elbow • 3. Ulna (2) • Bone of forearm (medial) • Forms the point of the elbow • 4. Radius (2) • Bone of forearm (lateral) • 5. Carpals (16) • Bones of the wrist (capitate, hamate, lunate, pisiform, scaphoid, trapezium, trapezoid, triqetrum)

  32. 6. Metacarpals (10) • Bones of the hand • 7. phalanges (56) • Bones of the fingers, thumbs, and toes • 2bones in each thumb and great toe

  33. 8. Pelvic girdle • Connect the legs to the axial skeleton • A. coxa (2) (hip bone) a fusion of 3 bones • 1. ilium- large flared bones • 2. ischium- inferior & posterior; the body weight is on this when seated • 3. pubis- inferior & anterior; the two pubic bones articulate at the pubic symphysis (a pad of fibrocartilage

  34. b. differences between male and female pelvis • 1. women- enlarged pelvic outlet; less curvature of the sacrum & coccyx; low pelvis; pubic arch greater than 100° • 2. men- opposite of above; pubic arch 90° or less

  35. 9. femur (2) • Bones of thigh • Longest and heaviest bones of the body • 10. Patella (2) • Bones of the knee • 11.tibia (2) • Large medial bone of the lower leg (shin) • 12. fibula (2) • Slender lateral bone of the lower leg

  36. 13. tarsals (14) • Bones of the ankle • A. talus -2nd largest foot bone; articulates with the tibia • B. calcaneus- heel bone; largest bone of the foot • 14. metatarsals (10) • Bones of feet

  37. JOINTS:  WHERE TWO BONES MEET • JOINTS, OR PLACES WHERE TWO BONES COME TOGETHER, PERMIT THE BONES TO MOVE WITHOUT DAMAGING EACH OTHER. • Joints are responsible for keeping bones far enough apart so they do not rub against each other as they move.  At the same time, joints hold the bones in place.

  38. THE CLASSIFICATION OF JOINTS IS BASED ON THE AMOUNT OF MOVEMENT POSSIBLE: •     A.  SYNARTHROSIS IS AN IMMOVABLE JOINT; THEY ARE OFTEN CALLED FIXED JOINTS, AND ALLOW NO MOVEMENT BETWEEN BONES.  These joints are interlocked and held together by Connective Tissue, or they are fused together.  The places where the bones of the SKULL meet (SUTURES) are examples of immovable joints.

  39.     B. AMPHIARTHROSIS IS A SLIGHTLY MOVABLE JOINT. (SEMI MOVABLE JOINTS)  These joints permit a small amount of movement.  These bones are farther apart from each other than immovable joint bones. The joints between the two bones of the lower leg (TIBIA and FIBULA) and the joints of the vertebrae are examples of slightly movable joints.

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