Chapter 6: & Skeletal Tissue I. Skeletal A. Basic Structure, Types and Location 1. Skeletal are made from cartilage, surrounded by a layer of dense irregular connective tissue called

2. is most abundant and includes: articular, costal, respiratory and nasal cartilage

3. Elastic Cartilages are most flexible and are located in the external ear and the epiglottis of the larnyx

4. is located in the areas where large amounts of pressure are exerted or stretch occurs ( knees and intervertbral discs)

B. Growth of Cartilage 1. Appositional growth results in outward expansion due to the production of cartilage matrix on the outer face of the tissue

2. Interstitial growth is the results in the expansion from within the cartilage matrix due to the division of the lacunae bound II. Classification of A. Divisions of the skeleton 1. Axial: Includes the rib cage and vertebral column, 2. Appendicular: Includes the bones of the upper limb, lower limb and the girdles that attach them to the axial skeleton B. Shape 1. Long bones are longer than they are wide, have a definite shaft two ends and consist of all the limb bones except the patella, carpals and tarsals 2. Short bones are somewhat cube shaped and include the the carpals, tarsals and patellas 3. Flat bones are thin, flattened, and often curve that include skull bones, sternum, scapulae and ribs 4. Irregular bones have complicated shapes the do not fit into any other class such as the vertebrae and coxae

III. Function of Bones A. Support B. Protection for the soft organs C. Movements D. Nutrient storage E. Produce hormones IV: Bone Structure A. Gross Anatomy 1. Bones have projections, depressions and openings on the surface that function as sites for muscle, ligament and tendon attachment, serves as surfaces and opening for the passage of blood vessels

2. Bone Textures a. Spongy bone: Internal structure of the bone, looks like honeycomb, needle like or flat pieces called trabeculae b. The bones dense out layer the is classified as compact and appears solid and smooth c. Compact bone: Internal structure of the bone, looks like honeycomb, needle like or flat pieces called trabeculae d. The bones dense outer layer the is classified as compact and appears solid and smooth

3. Structure of short, irregular and flat bones a. Compact bone on outside and spongy bone on the inside, houses

4. Structure of Typical a. Have a tubular (shaft), consisting of a bone collar surrounding a hollow with is filled with yellow marrow in adults b. Epiphysises are the ends of the bone and consist of internal spongy bone covered by an outer layer of compact bone and articular cartilage c. Epiphyseal line is locacted between the epiphysises and diaphysis which is a remnant of the , the hyaline cartilage that provides lengthwise growth of the bone d. The covers the bone and is the location of the osteogenic cells (external surface) e. The internal surface of the bone is lined with connective tissue called endosteumand is the location of osteogenic cells in the bone.

5. Location of Hematopoietic Tissue in Bones a. Red marrow is located in the trabecular cavities of the spongy bone in long bones and in the diploe of flat bones 1. Red marrow is found only in inmature bone 2. Yellow marrow in found in MATURE bone

b. In long bones, red marrow is found in all medullary cavities and all areas of spongy bone in infants, distribution is restricted to the proximal epiphyses of the humerus and femur in adults

B. Microscopic Anatomy 1. Bone tissue contains 5 types of cells: bone stem cells (osteogenic), (secrete bone matrix), & bone lining cells (monitor and maintain bone matrix) and ()

2. Compact unit of bone structure is the (Haversian System), a series of concentric tubes or bone matrix (lamellae) surrounding central and serves as a passageway for blood vessels and nerves

a. Perforating (Volkman’s) canal lie at right angles to the long axis of the bone and connect the blood and nerve supply of periosteum to the centeral canal and medullary cavitiy b. Lacunae, small holes housing the osteocytes, are junctions of the lamellae and are connected to each other and the central canal via a series of hair like channels called canaliculi.

3. Spongy bone lacks but has trabeculae that align along lines of stress, which contain irregular lamellae and osteocytes connected with the canaliculi

C. Chemical Composition

1. Organic components of the bone include cells and (ground substance and collagen fibers), which contribute to the flexibility and tensile strength of the bone

2. Inorganic components make up 65% of the bone by mass and consist of hydroxyapatites, mineral salts (largely calcium phosphates), that account for the hardness and compression resistance of bones

V. Bone Development A. Formation of Bony Skeleton (embryonic development) 1. In endochrondral , bone tissue replaces hyaline cartilage, forming all bones below the skull except for the clavicles a. Initially, osteoblasts secrete osteoid, creating a bone collar around the diaphysis of the hyaling cartilage model b. Cartilage in the center of the diaphysis calcifies and deteriorates forming cavities c. The periosteal bud invades the internal cavities and spongy pne forms around the remaining fragments of hyaline cartilage d. The diaphysis elongates as the cartilage in the continues to lengthen and a medullary cavity forms through the action of osteoclasts within the center of the diaphysis e. The epiphyses ossify shortly after birth through the development of secondary ossification centers

1. Itramembranous ossification forms membrane bone from fibrous connective tissue membranes and result in the cranial bones and clavical B. Postnatal Bone Growth 1. Growth in length of long bones occurs at the ossification zone through the rapid division of the upper cells in the columns of chondrocytes, calcification and deterioration of cartilage at the bottom of the columns and subsequent replacement of bone tissue

2. Growth is width or thickness occurs through appositional growth due to deposition of bone matrix by osteoblasts beneath the periosteum 3. Hormonal Regulation of bone growth a. During infancy and childhood, the most important stimulus of epiphyseal plate activity is the growth hormone from the anterior pituitary gland whose effects are modulated by thyroid hormone b. At puberty, testosterone and estrogen promote a growth spurt, ultimately resulting in the closure of the epiphyseal plate

VI. Bone Homeostasis: Remodeling & Repair A. 1. In adult skeletons, done deposit and resorption occur beneath the periosteum and

2. Is balanced bone deposit and resorption

3. Control of Remodeling a. Hormonal control is mostly used to maintain blood calcium homeostasis and balances activity of parathyroid hormone and calcitonin b. In response to mechanical stress and gravity, bone grows or remodels in what that allow it to withstand the stresses it experiences B. Bone Repair 1. Fractures or breaks in bones are classified by: a. The position of the bones ends after the fracture b. Completeness of the break c. Whether the bone penetrates the skin 2. The repair of fractures involves 4 stages a. Formation of Hematoma b. Fibrocartilagous callus formation (about a week after damage) c. Bony callus formation d. Remodeling of the bony callus (takes months)

VII: Homeostatic Imbalance A. Osteomalacia and Rickets 1. Osteomalacia is a disorder in adults in which the bone is inadequately mineralized resulting in soft bones

2. Rickets is the inadequate mineralization of bones in children caused by insufficient calcium in the diet or by Vitamin D deficiency

B. Osteoporosis 1. A group of disorders in adults by which the rate of bone resorption exceeds rate of formation (decays faster than replaced) 2. Bones have normal matrix but the mass is reduced and bones become more porous and lighter (fracture easier) 3. Elderly women are more vulnerable due to the decline of estrogen hormone caused by menopause 4. Contributing factors are: Petite stature, lack of exercise, poor calcium and Vitamin D diet, and smoking C. Paget’s Disease 1. Excessive bone deposition and resorption

2. Results in abnormally high amounts of spongy bone

3. Localized condition (varies in location), deformation of affected bone is common VIII. Developmental Aspects of Bone A. Bones begin with the embryonic mesenchyme cells, ossification occurs at precise times. Most long bones have primary ossification centers 12 weeks after conception

B. At birth most bones are well ossified except for the epiphyses which are secondary points

C. Throughout childhood bone growth exceeds resorption (bone gain), young adult equal process, old age resorption exceeds formation (bone loss)