Bones and Skeletal Tissues Chapter 6 http://images5.fanpop.com/image/photos/26500000/-skeleton-dance-skeletons-26529088-725-544.png

Skeletal Cartilages Contain no blood vessels or nerves Perichondrium (dense irregular connective tissue girdle) contains blood vessels for nutrient delivery to cartilage Types Hyaline Elastic Fibrocartilage

Respiratory tube cartilages in neck and thorax Epiglottis Larynx Thyroid cartilage Cartilage in external ear Cartilages in nose Trachea Cricoid cartilage Lung Articular Cartilage of a joint Cartilage in Intervertebral disc Costal cartilage Respiratory tube cartilages in neck and thorax Pubic symphysis Bones of skeleton Axial skeleton Meniscus (padlike cartilage in knee joint) Appendicular skeleton Cartilages Articular cartilage of a joint Hyaline cartilages Elastic cartilages Fibrocartilages Figure 6.1

Growth of Cartilage Appositional Cells secrete matrix against the external face of existing cartilage Interstitial Chondrocytes divide and secrete new matrix, expanding cartilage from within http://www.vetmed.vt.edu/education/curriculum/vm8054/labs/Lab7/IMAGES/elastic%20cartilage%20WITH%20LABEL%20copy.jpg

Bones of the Skeleton Cartilage in Cartilages in external ear nose Articular Cartilage of a joint Cartilage in Intervertebral disc Costal cartilage Pubic symphysis Meniscus (padlike cartilage in knee joint) Articular cartilage of a joint Figure 6.1

Classification of Bones by Shape Long bones Short bones Flat bones Irregular bones

Functions of Bones Support Protection Movement Mineral & Growth Factor Storage Blood cell formation Triglyceride storage Hormone Production

Bone Structure Bones are organs! Multiple tissue types Bone (osseous) tissue, nervous tissue, cartilage, fibrous connective tissue, muscle and epithelial cells (in its blood vessels)

Bone Texture Compact Spongy (trabecular) Dense outer layer; smooth and solid Spongy (trabecular) Honeycomb of flat pieces of bone (trabeculae) deep to compact Space b/w trabeculae filled with red or yellow bone marrow

Structure of Short, Irregular, and Flat Bones Periosteum covered compact bone on the outside Endosteum covered spongy bone within diploë Bone marrow b/w the trabeculae Hyaline cartilage on articular surfaces

Structure of Typical Long Bone Diaphysis Tubular shaft forms long axis Compact bone surrounds medullary cavity Epiphyses (bone ends) Compact bone outside; spongy bone inside Articular cartilage covers articular surfaces Epiphyseal line b/w diaphysis and epiphysis Remnant of epiphyseal plate

Membranes of Bone Periosteum Outer fibrous layer Inner osteogenic layer Contains nerve fibers, nutrient blood vessels, and lymphatic vessels that enter the bone via nutrient foramina Secured to underlying bone by Sharpey’s fibers

Membranes of Bone Endosteum Delicate membrane on internal surfaces of bone Contains osteogenic cells

Hematopoietic Tissue (Red Marrow) Infants (long bones) Medullary cavities and spongy bone Adults (long bones) Little red marrow Red marrow in flat and some irregular bones is most active http://www.gla.ac.uk/ibls/US/fab/images/generic/bocompac.jpg

Bone Markings Projections, depressions, and holes Sites of attachment for muscles, ligaments, and tendons Joint surfaces Passageways for blood vessels and nerves

Bone Markings: Projections Sites of muscle and ligament attachment Tuberosity Crest Trochanter Line Tubercle Epicondyle Spine Process Projections that help to form joints Head Facet Condyle Ramus

Bone Markings: Depressions and Openings Passages for blood vessels and nerves Meatus Sinus Fossa Groove Fissure Foramen

Microscopic Anatomy of Bone

Microscopic Anatomy of Bone: Compact Bone Haversian system (or osteon) Lamellae Central (Haversian) canal

Microscopic Anatomy of Bone: Compact Bone Perforating (Volkmann’s) canals Lacunae Canaliculi

Microscopic Anatomy of Bone: Spongy Bone Trabeculae Align along lines of stress No osteons Irregularly arranged lamellae, osteocytes, and canaliculi Capillaries in endosteum supply nutrients

Chemical Composition of Bone Organic Bone cells Osteoid—organic bone matrix secreted by osteoblasts Ground substance, collagen fibers Inorganic Hydroxyapatites (mineral salts) 65% of bone by mass Mainly calcium phosphate crystals

Bone Development Ossification (osteogenesis): process of bone tissue formation Formation of bony skeleton Begins in 2nd month of development Postnatal bone growth Until early adulthood Bone remodeling and repair Lifelong

Types of Ossification Endochondral ossification Bone forms by replacing hyaline cartilage Majority of skeleton Intramembranous ossification Bone develops from fibrous membrane Bones called membrane bones Forms flat bones, e.g. clavicles and cranial bones

Endochondral Ossification Forms most all bones inferior to base of skull (except clavicles) Begins late in 2nd month of development Uses hyaline cartilage models Hyaline cartilage must be broken down before ossification

Childhood to adolescence Week 9 Month 3 Birth Childhood to adolescence Articular cartilage Secondary ossification center Spongy bone Epiphyseal blood vessel Area of deteriorating cartilage matrix Epiphyseal plate cartilage Hyaline cartilage Medullary cavity Spongy bone formation Bone collar Blood vessel of periosteal bud Primary ossification center 1 2 3 4 5 Figure 6.9

Intramembranous Ossification Forms cranial bones of the skull and clavicles Begins within fibrous connective tissue membranes formed by mesenchymal cells Ossification centers appear Osteoid is secreted Woven bone and periosteum form Lamellar bone replaces woven bone & red marrow appears

Figure 6.9 Intramembranous ossification. Mesenchymal cell Osteoblast Osteoid Collagen fibril Ossification center Osteocyte Newly calcified bone matrix Osteoid Osteoblast 1 Ossification centers appear in the fibrous connective tissue membrane. 2 Osteoid is secreted within the fibrous membrane and calcifies. Fibrous periosteum Mesenchyme condensing to form the periosteum Osteoblast Plate of compact bone Trabeculae of woven bone Diploë (spongy bone) cavities contain red marrow Blood vessel 3 Woven bone and periosteum form. 4 Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. Figure 6.9 Intramembranous ossification.

Postnatal Bone Growth Interstitial growth: Appositional growth:  length of long bones Appositional growth:  thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces

Interstitial (Longitudinal) Growth Epiphyseal plate cartilage organizes into 5 important functional zones: Resting (quiescent) zone Proliferation (growth) Hypertrophic Calcification Ossification (osteogenic)

Cartilage cells undergo mitosis. Resting zone Proliferation zone Cartilage cells undergo mitosis. 1 Hypertrophic zone Older cartilage cells enlarge. 2 Calcification zone Matrix becomes calcified; cartilage cells die; matrix begins deteriorating. 3 Calcified cartilage spicule Osteoblast depositing bone matrix Ossification zone New bone formation is occurring. Osseous tissue (bone) covering cartilage spicules 4 Figure 6.10

Appositional Growth Growth in Width Osteoblasts active in periosteum Osteoclasts active in the endosteum Building > Breaking down = thicker stronger bone

Bone growth Bone remodeling Articular cartilage Cartilage grows here. Epiphyseal plate Cartilage is replaced by bone here. Bone is resorbed here. Cartilage grows here. Bone is added by appositional growth here. Cartilage is replaced by bone here. Bone is resorbed here. Figure 6.11

Hormonal Regulation of Bone Growth Growth hormone Thyroid hormone Testosterone and Estrogen http://2.bp.blogspot.com/-FrC7iCwLqDk/Tb8hrWvYXnI/AAAAAAAAOOg/i-l4zBWZI5Q/s1600/2008_01_17_pb%252520kids%252520growth.jpg

Bone Remodeling Bone is constantly being “recycled” Occurs @ surface of periosteum and endosteum Deposit Injury or needed strength, requires good diet Osteoid seam and Calcification front Resorption Osteoclasts secrete: lysosomal enzymes, acids Dissolved matrix is transcytosed

Control of Remodeling What controls continual remodeling of bone? Hormonal mechanisms that maintain calcium homeostasis in the blood Mechanical and gravitational forces http://tutor4physics.com/workliftbox.gif

Hormonal Control of Blood Ca2+ Most calcium in the body is in the bones Less that 1.5g in blood – tightly regulated narrow range Calcium is necessary for Transmission of nerve impulses Muscle contraction Blood coagulation Secretion by glands and nerve cells Cell division

Stimulus Thyroid gland Osteoclasts Parathyroid degrade bone glands Calcium homeostasis of blood: 9–11 mg/100 ml BALANCE BALANCE Stimulus Falling blood Ca2+ levels Thyroid gland Osteoclasts degrade bone matrix and release Ca2+ into blood. Parathyroid glands Parathyroid glands release parathyroid hormone (PTH). PTH Figure 6.12

Hormonal Control of Blood Ca2+ May be affected to a lesser extent by calcitonin  Blood Ca2+ levels  Parafollicular cells of thyroid release calcitonin Osteoblasts deposit calcium salts  Blood Ca2+ levels

Response to Mechanical Stress Wolff’s law: A bone grows or remodels in response to forces or demands placed upon it

Hormones and Mechanical Stress when remodeling occurs As a response to what??? Mechanical Stress Where the remodeling occurs

Classification of Bone Fractures Bone fractures may be classified by four “either/or” classifications Position of bone ends after fracture: Nondisplaced or Displaced Completeness of the break Complete or Incomplete Orientation of the break to the long axis of the bone: Linear or transverse Whether or not the bone ends penetrate the skin Compound (open) or Simple (closed)

Common Types of Fractures In addition to the previous classification, all fractures can be described in terms of Location External appearance Nature of the break http://www.schultzlegalgroup.com/images/Bone-Fracture-Injury-Lawyer.jpg

Table 6.2

Table 6.2

Table 6.2

Fracture Healing Hematoma forms Fibrocartilaginous callus forms

Fracture Healing Bony callus formation Bone remodeling

Homeostatic Imbalances Osteomalacia and Rickets Calcium salts not deposited Rickets (childhood disease) causes bowed legs and other bone deformities Cause: vitamin D deficiency or insufficient dietary calcium http://upload.wikimedia.org/wikipedia/commons/thumb/a/a9/XrayRicketsLegssmall.jpg/230px-XrayRicketsLegssmall.jpg

Homeostatic Imbalances Osteoporosis Loss of bone mass Spongy bone of spine and neck of femur become most susceptible to fracture Risk factors Lack of estrogen, calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus; smoking

Developmental Aspects of Bones Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms At birth, most long bones are well ossified (except epiphyses)

Developmental Aspects of Bones Nearly all bones completely ossified by age 25 Bone mass decreases with age beginning in 4th decade Rate of loss determined by genetics and environmental factors In old age, bone resorption predominates