The Skeletal System

1. The Skeletal System Chapter 6 pgs 176-201

2. Skeletal Cartilages • Basic Structure, Types, and Locations: • Skeletal Cartilages- made from cartilage, surrounded by a layer of dense irregular connective tissue called the perichondrium • Hyaline cartilage- most abundant and includes the articular, costal, respiratory, and nasal cartilages

3. Skeletal Cartilages • Basic Structure, Types, and Locations: • Elastic cartilages- more flexible than hyaline and are located only in the external ear and the epiglottis of the larynx. • Fibrocartilage- located in areas that must withstand a great deal of pressure or stretch • Knee • Intervertebral discs

4. Figure 6.1 pg 177

5. Skeletal Cartilages • 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

6. Classification of Bones • Two main division of the skeleton: • Axial Skeleton- Skull, vertebral column, and the rib cage • Appendicular Skeleton- Bones of the upper and lower limbs, and the girdles that attach them to the axial skeleton http://www.besthealth.com/besthealth/bodyguide/reftext/images/Axial_AppendicularSkel.jpg`

7. Classification of Bones: Bone Shape • Long Bone • Longer than they are wide • Have a definite shaft and two ends • Consist of all limb bones except patellas, carpals, and tarsals. • Short Bone • Somewhat cube-shaped • Include the carpals and tarsals http://www.ganfyd.org/images/4/48/Carpal.PNG http://www.arthursclipart.org/medical/skeletal/long%20bone%20structure.gif

8. Classification of Bones: Bone Shape • Sesamoid Bone • Special type of short bone that form in a tendon • Example: Patella (knee cap) http://www.healthhype.com/wp-content/uploads/kneecap.jpg

9. Classification of Bones: Bone Shape • Flat Bone • Thin, flattened, and often curved bones • Include most of the skull bones, the sternum, scapula, and ribs. • Irregular Bone • Have complicated shapes that do not fit into any other class • Vertebrae • Hip http://www.arthursclipart.org/medical/skeletal/page_04.htm

10. Figure 6.2

11. Functions of Bone • Support • Supports soft tissues and provides points of attachment for most skeletal muscles • Protection • Provides protection for the body’s vital organs • Cranial bones protect the brain • Vertebrae protect the spinal cord • Ribcage protects the heart and lungs

12. Functions of Bone • Movement • Muscles are attached to bones, therefore when muscles contract they cause bones to move • Mineral Storage • Stores minerals such as calcium and phosphate • Blood Cell Formation • Most blood cell formation, or hematopoiesis, occurs in the marrow cavities of certain bones

13. Bone Structure:Gross Anatomy • Bone Markings • Projections- grow outward from the bone surface, are sites of muscle and ligament attachment, and help form joints • Depressions and Openings- Allows blood vessels and nerves to pass and indent the bone • Types of bone markings are listed in Table 6.1 on page 179 http://classes.mst.edu/ide120/lessons/composite/materials/examples/bone_2.gif http://www.labtechindia.net/product/Biology/bl42.jpg

14. Bone Structure:Gross Anatomy • Bone Textures • Compact Bone- Dense outer layer that looks smooth and solid to the naked eye • Spongy Bone- Internal layer that is a honeycomb of small needle-like or flat pieces called trabeculae http://www.gla.ac.uk/ibls/US/fab/tutorial/generic/bone2.html

15. Bone Structure:Gross Anatomy • Structure of a typical long bone • Tubular bone shaft, called the diaphysis, consists of compact bone that surrounds 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. http://www.teachpe.com/images/anatomy/bone_structure.jpg

16. Bone Structure:Gross Anatomy • Structure of a typical long bone • Epiphyseal line- located between the diaphysis and each epiphysis, and is a remnant of the epiphysealplate, which is a disc of hyaline cartilage that grows during childhood to lengthen the bone • Periosteum- covers the external surface of the bone • Endosteum- A connective tissue membrane that lines the internal surface of the bone

17. Figure 6.3 page 180

18. Bone Structure:Gross Anatomy • Structure of Short, Flat, and Irregular Bones • Consist of thin plates of periosteum-covered compact bone on the outside and endosteum-covered spongy bone inside Figure 6.4 page 181

19. Bone Structure:Gross Anatomy • Location of Red Marrow • Found within the spongy bone in flat bones and in the epiphyses of long bones. • Found in all flat bones, epiphyses, and medullary cavities of infants • In adults, distribution is restricted to flat bones and the proximal epiphyses of the humerus and femur http://www.besthealth.com/besthealth/bodyguide/reftext/images/Marrow.jpg

20. Bone Structure:Microscopic Anatomy of Bone • Osteon- Structural unit of compact bone. Also called the Haversian system. • Consists of concentric tubes of bone matrix (lamellae) surrounding a central Haversian canal that serves as a passageway for blood vessels and nerves.

21. Bone Structure:Microscopic Anatomy of Bone • Volkmann’s canals lie at right angles to the long axis of the bone, and connect the blood and nerve supply of the periosteum to those in the central canals and the medullary cavity. • Osteocytes (mature bone cells) occupy lacunae at the junctions of the lamellae. • Canaliculi connect the lacunae to each other and to the central canal.

22. Bone Structure:Microscopic Anatomy of Bone • Interstitial lamellae lie between intact osteons, filling the spaces inbetween. • Circumferential lamellae are located beneath the periosteum, which extends around the entire circumference of the bone. • Spongy bone lacks osteons but has trabeculae that align along lines of stress, which contain irregular lamellae.

23. Figure 6.6 page 183

24. Bone Structure:Chemical Composition of Bone • Organic components: • Cells (osteoblasts, osteocytes, and osteoclasts) • Osteiod (ground substance and collagen fibers) • Contribute to the flexibility and tensile strength of bone • Inorganic components: • Make up 65% of bone by mass • Consists of hydroxapatites, or mineral salts, that accounts for the hardness and compression resistance of bone.

25. Bone Development:Formation of the Bony Skeleton • Ossification and osteogenesis: • Process of bone formation • Membrane Bone (cranial bones and the clavicles) • When bone develops from a fibrous membrane • Cartilage bone (forms all bones below skull except for clavicles) • When bone develops by replacing hyaline cartilage

26. Bone Development:Postnatal Bone Growth • Growth in length of long bones: • Cartilage cells undergo mitosis which pushes the epiphyses away from the diaphysis, causing the long bone to lengthen Figure 6.9 page 186

27. Bone Development:Postnatal Bone Growth • Hormonal Regulation • Growth hormone stimulates epiphyseal plate activity during infancy and childhood • At puberty, testosterone and estrogen promote a growth spurt, but ultimately initiate the closure of the epiphyseal plate

28. Bone Homeostasis: Remodeling and Repair • Fractures: Breaks in Bones • Classified by: • Position of the bone ends after fracture • Completeness of the break • Orientation of the break relative to the long axis of the bone • Whether the bone ends penetrate the skin

29. Bone Homeostasis: Remodeling and Repair • Fracture Repair: Four major stages • Hematoma Formation • Fibrocartilaginous callus formation • Bony callus formation • Remodeling of the bony callus

30. Homeostatic Imbalances of Bone: Osteoporosis • Group of disorders in which the rate of bone removal exceeds the rate of formation. • Bones have reduced bone mass and become more porous and lighter, increasing the likelihood of fractures • Older women are more vulnerable, due to the decline in estrogen after menopause

31. Homeostatic Imbalances of Bone: Osteoporosis • Other factors that contribute: a petite body form, insufficient exercise of immobility, a diet poor in calcium and vitamin D, smoking, and certain hormone-related conditions. Figure 6.15 page 193

32. Developmental Aspects of Bones • At birth, most bones are well formed, except for the epiphyses. • Throughout childhood, bone growth exceeds bone resorption • In young adults, these processes are in balance • In old age, resorption exceeds formation