Lecture 5 Chapter 6: Bones and Skeletal Tissues Anatomy & Physiology I Lecture 5 Chapter 6: Bones and Skeletal Tissues

Human Skeleton Initially made up of cartilages and fibrous membranes before becoming bone. Remaining cartilage found where flexible skeletal tissue is needed

Skeletal Cartilage Hyaline cartilage Elastic cartilage Fibrocartilage Provides support, flexibility, and resilience Collagen fibers only Elastic cartilage Similar to hyaline cartilage, but contains elastic fibers Fibrocartilage Thick collagen fibers—has great tensile strength

Hyaline Cartilages Articular Costal Respiratory Nasal covers the ends of most bones at movable joints Costal connects ribs to sternum Respiratory form the skeleton of the larynx, reinforce respiratory passageway Nasal support the external nose

Figure 6.1 The bones and cartilages of the human skeleton. Epiglottis Thyroid cartilage Larynx Cartilage in external ear Cartilages in nose Cricoid cartilage Trachea Articular cartilage of a joint Lung Costal cartilage Cartilage in intervertebral disc 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 © 2013 Pearson Education, Inc.

Cartilage Growth??

Classification of Bones 206 named bones in skeleton Divided into two groups Axial skeleton Long axis of body Skull, vertebral column, rib cage Appendicular skeleton Bones of upper and lower limbs Girdles attaching limbs to axial skeleton

Figure 6.1 The bones and cartilages of the human skeleton. Epiglottis Thyroid cartilage Larynx Cartilage in external ear Cartilages in nose Cricoid cartilage Trachea Articular cartilage of a joint Lung Costal cartilage Cartilage in intervertebral disc 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 © 2013 Pearson Education, Inc.

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

Long Bones Longer than they are wide All bones but the patella, wrist and ankle

Short Bones Cube-shaped bones Sesamoid bones (within tendons) wrist and ankle Sesamoid bones (within tendons) Patella Vary in size and number in different individuals

Flat Bones Thin, flat, slightly curved Sternum, scapulae, ribs, most skull bones

Irregular Bones Complicated shapes Vertebrae, coxal bones

Figure 6.2 Classification of bones on the basis of shape. Flat bone (sternum) Long bone (humerus) Irregular bone (vertebra), right lateral view Short bone (talus) © 2013 Pearson Education, Inc.

Important Functions of Bones Support for body and soft organs Protection for brain, spinal cord, and vital organs Movement Levers for muscle action

Important Functions of Bones Mineral and growth factor storage Calcium and phosphorus, and growth factors reservoir Blood cell formation (Hematopoiesis) red marrow cavities of certain bones Triglyceride (fat) storage Energy source when needed

Important Functions of Bones Hormone production: Osteocalcin Regulates bone formation Protects against obesity, glucose intolerance, diabetes mellitus

Bones are Organs Contain different types of tissues Bone (osseous) tissue, nervous tissue, cartilage, fibrous connective tissue, muscle and epithelial cells in its blood vessels Three levels of structure Gross anatomy Microscopic Chemical

Gross Anatomy Bone textures Compact Spongy (cancellous or trabecular) Compact and spongy bone Compact Dense outer layer; smooth and solid Spongy (cancellous or trabecular) Honeycomb of flat pieces of bone deep to compact called trabeculae open spaces filled with red or yellow bone marrow

Spongy bone (diploë) Compact bone Trabeculae of spongy bone Figure 6.3 Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone. Spongy bone (diploë) Compact bone Trabeculae of spongy bone © 2013 Pearson Education, Inc.

Membranes of Bone Bones are covered inside and outside by connective tissue membranes Periosteum outside Endosteum inside

Figure 6.4a The structure of a long bone (humerus of arm). Articular cartilage Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Distal epiphysis © 2013 Pearson Education, Inc.

Structure of Long Bone Diaphysis Epiphyses Between is epiphyseal line Tubular shaft forms long axis Compact bone surrounding medullary cavity Epiphyses Bone ends External compact bone; internal spongy bone Between is epiphyseal line Remnant of childhood bone growth at epiphyseal plate

Periosteum Membrane White, double-layered membrane that covers external surfaces except joint surfaces Many nerve fibers and blood vessels Outer fibrous layer of dense irregular connective tissue secure to bone matrix Inner layer abuts contains osteogenic cells gives rise to bone cells Anchoring points for tendons and ligaments

Endosteum Membrane Delicate connective tissue membrane covering internal bone surface Covers trabeculae of spongy bone Lines canals that pass through compact bone Contains osteogenic cells that can differentiate into other bone cells

Figure 6.4c The structure of a long bone (humerus of arm). Endosteum Yellow bone marrow Compact bone Periosteum Perforating (Sharpey’s) fibers Nutrient arteries © 2013 Pearson Education, Inc.

Marrow Yellow Red hollow interior of long made up of fat cells can convert itself into red bone marrow Red within trabecular cavities of spongy bone hematopoietic tissue

Bone Markings Sites of muscle, ligament, and tendon attachment on external surfaces Joint surfaces Conduits for blood vessels and nerves Three types Projections Depressions Openings

Bone Markings Projections Depressions and openings Most indicate stresses created by muscle pull or joint modifications Depressions and openings Usually allow nerves and blood vessels to pass

Table 6.1 Bone Markings (1 of 2) Familiarize yourself with these terms. You will see them again when identifying bones © 2013 Pearson Education, Inc.

Table 6.1 Bone Markings (2 of 2) © 2013 Pearson Education, Inc.

Cells of Bone Tissue Five major cell types Each specialized form of same basic cell type Osteogenic cells Osteoblasts Osteocytes Bone lining cells Osteoclasts

Osteogenic Cells Also called osteoprogenitor cells Mitotically active stem cells in periosteum and endosteum When stimulated differentiate into osteoblasts or bone lining cells Some persist as osteogenic cells

Osteoblasts Bone-forming cells Secrete unmineralized bone matrix or osteoid Includes collagen and calcium-binding proteins Collagen = 90% of bone protein Actively mitotic

Osteocytes Mature bone cells in lacunae Monitor and maintain bone matrix Act as stress or strain sensors Respond to and communicate mechanical stimuli to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur

Bone Lining Cells Flat cells on bone surfaces believed to help maintain matrix On external bone surface called periosteal cells Lining internal surfaces called endosteal cells

Osteoclasts Derived from hematopoietic stem cells that become macrophages Giant, multinucleate cells for bone resorption

Compact Bone Also called lamellar bone Withstands stress – resist twisting Osteon or Haversian system Structural unit of compact bone Elongated cylinder parallel to long axis of bone Hollow tubes of bone matrix called lamellae Collagen fibers in adjacent rings run in different directions

Artery with capillaries Structures in the Vein central canal Figure 6.6 A single osteon. Artery with capillaries Structures in the central canal Vein Nerve fiber Lamellae Collagen fibers run in different directions Twisting force © 2013 Pearson Education, Inc.

Figure 6.7 Microscopic anatomy of compact bone. Spongy bone Central (Haversian) canal Perforating (Volkmann’s) canal Endosteum lining bony canals and covering trabeculae Osteon (Haversian system) Circumferential lamellae Perforating (Sharpey’s) fibers Lamellae Periosteal blood vessel Periosteum Nerve Vein Lamellae Artery Central canal Canaliculi Osteocyte in a lacuna Lacunae Interstitial lamella Lacuna (with osteocyte) © 2013 Pearson Education, Inc.

Canals and canaliculi Central (Haversian) canal runs through core of osteon Contains blood vessels and nerve fibers Lacunae—small cavities that contain osteocytes Canaliculi—hairlike canals that connect lacunae to each other and central canal

Interstitial and Circumferential Lamellae Interstitial lamellae Incomplete lamellae not part of complete osteon Fill gaps between forming osteons Remnants of osteons cut by bone remodeling Circumferential lamellae Just deep to periosteum Superficial to endosteum Extend around entire surface of diaphysis Resist twisting of long bone

Making up the Osteoid Osteoid—1/3 of organic bone matrix secreted by osteoblasts Made of ground substance (proteoglycans and glycoproteins) Collagen fibers Contributes to structure; provides tensile strength and flexibility

Sacrificial Bonds Resilience of bone due to sacrificial bonds in or between collagen molecules Stretch and break easily on impact to dissipate energy and prevent fracture If no addition trauma, bonds re-form

Inorganic Components Hydroxyapatites (mineral salts) 65% of bone by mass Mainly of tiny calcium phosphate crystals in and around collagen fibers Responsible for hardness and resistance to compression

Bone Summary Half as strong as steel in resisting compression As strong as steel in resisting tension Last long after death because of mineral composition Reveal information about ancient people Can display growth arrest lines Horizontal lines on bones Proof of illness - when bones stop growing so nutrients can help fight disease

Bone Development Ossification (osteogenesis) Postnatal bone growth 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

Two Types of Ossification Endochondral ossification Bone forms by replacing hyaline cartilage Bones called cartilage (endochondral) bones Forms most of skeleton Intramembranous ossification Bone develops from fibrous membrane Bones called membrane bones Forms flat bones (clavicles and cranial bones) Why do you think using collagen first is a better idea than calcified bone?

Endochondral ossification Primary ossification center in center of shaft Blood vessel infiltration Bone collar forms around diaphysis of cartilage model Central cartilage in diaphysis calcifies, then develops cavities Periosteal bud invades cavities Diaphysis elongates & medullary cavity forms Epiphyses ossify

Figure 6.8 Endochondral ossification in a long bone. Slide 1 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 Spongy bone formation Medullary cavity Bone collar Blood vessel of periosteal bud Primary ossification center Bone collar forms around the diaphysis of the hyaline cartilage model. 1 Cartilage in the center of the diaphysis calcifies and then develops cavities. 2 The periosteal bud invades the internal cavities and spongy bone forms. 3 The diaphysis elongates and a medullary cavity forms. Secondary ossification centers appear in the epiphyses. 4 The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages. 5 © 2013 Pearson Education, Inc.

Intramembrane Ossification Forms frontal, parietal, occipital, temporal bones, 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. Slide 2 Mesenchymal cell Collagen fibril Ossification center Osteoid Osteoblast 1 Ossification centers appear in the fibrous connective tissue membrane. • Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center that produces the first trabeculae of spongy bone. © 2013 Pearson Education, Inc.

Figure 6.9 Intramembranous ossification. Slide 3 Osteoblast Osteoid Osteocyte Newly calcified bone matrix 2 Osteoid is secreted within the fibrous membrane and calcifies. • Osteoblasts begin to secrete osteoid, which calcifies in a few days. • Trapped osteoblasts become osteocytes. © 2013 Pearson Education, Inc.

Figure 6.9 Intramembranous ossification. Slide 4 Mesenchyme condensing to form the periosteum Trabeculae of woven bone Blood vessel 3 Woven bone and periosteum form. • Accumulating osteoid is laid down between embryonic blood vessels in a manner that results in a network (instead of concentric lamellae) of trabeculae called woven bone. • Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum. © 2013 Pearson Education, Inc.

Figure 6.9 Intramembranous ossification. Slide 5 Fibrous periosteum Osteoblast Plate of compact bone Diploë (spongy bone) cavities contain red marrow 4 Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. • Trabeculae just deep to the periosteum thicken. Mature lamellar bone replaces them, forming compact bone plates. • Spongy bone (diploë), consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow. © 2013 Pearson Education, Inc.

Bone Growth Interstitial (longitudinal) growth Appositional growth Increase in length of long bones Appositional growth Increase in bone thickness

Interstitial (longitudinal) growth Requires presence of epiphyseal cartilage Epiphyseal plate maintains constant thickness Rate of cartilage growth on one side balanced by bone replacement on other Concurrent remodeling of epiphyseal ends to maintain proportion

Figure 6.11 Long bone growth and remodeling during youth. Bone remodeling Articular cartilage Cartilage grows here. Bone replaces cartilage here. Epiphyseal plate Bone that was here has been resorbed. Cartilage grows here. Appositional growth adds bone here. Bone replaces cartilage here. Bone that was here has been resorbed. © 2013 Pearson Education, Inc.

Cartilage cells undergo mitosis. Figure 6.10 Growth in length of a long bone occurs at the epiphyseal plate. Resting zone 1 Proliferation zone Cartilage cells undergo mitosis. 2 Hypertrophic zone Older cartilage cells enlarge. 3 Calcification zone Matrix calcifies; cartilage cells die; matrix begins deteriorating; blood vessels invade cavity. Calcified cartilage spicule Osteoblast depositing bone matrix Osseous tissue (bone) covering cartilage spicules 4 Ossification zone New bone forms. © 2013 Pearson Education, Inc.

Appositional Growth Allows lengthening bone to widen Occurs throughout life Osteoblasts beneath periosteum secrete bone matrix on external bone Osteoclasts remove bone on endosteal surface Usually more building up than breaking down Thicker, stronger bone but not too heavy

Figure 6.11 Long bone growth and remodeling during youth. Bone remodeling Articular cartilage Cartilage grows here. Bone replaces cartilage here. Epiphyseal plate Bone that was here has been resorbed. Cartilage grows here. Appositional growth adds bone here. Bone replaces cartilage here. Bone that was here has been resorbed. © 2013 Pearson Education, Inc.

Hormone Regulation of Bone Growth Growth hormone Most important in stimulating epiphyseal plate activity in infancy and childhood Thyroid hormone Modulates activity of growth hormone Ensures proper proportions Testosterone (males) and estrogens (females) at puberty Promote adolescent growth spurts End growth by inducing epiphyseal plate closure

Bone Homeostasis Recycle 5-7% of bone mass each week Spongy bone replaced ~ every 3-4 years Compact bone replaced ~ every 10 years Older bone becomes more brittle Calcium salts crystallize Fractures more easily Consists of bone remodeling and bone repair

Figure 6.11 Long bone growth and remodeling during youth. Bone remodeling Articular cartilage Cartilage grows here. Bone replaces cartilage here. Epiphyseal plate Bone that was here has been resorbed. Cartilage grows here. Appositional growth adds bone here. Bone replaces cartilage here. Bone that was here has been resorbed. © 2013 Pearson Education, Inc.

Control of Remodeling Occurs continuously but regulated by genetic factors and two control loops Negative feedback hormonal loop for Ca2+ homeostasis Controls blood Ca2+ levels; Not bone integrity Responses to mechanical and gravitational forces

Calcium Functions in 1200 – 1400 grams of calcium in body Nerve impulse transmission Muscle contraction Blood coagulation 1200 – 1400 grams of calcium in body 99% as bone minerals Amount in blood tightly regulated (9-11 mg/dl) Intestinal absorption from diet

Hormones for Calcium Parathyroid hormone (PTH) Produced by parathyroid glands Removes calcium from bone regardless of bone integrity Acts to control blood Ca2+ levels, not bone integrity

Response to Mechanical Stress Bones reflect stresses they encounter Long bones thickest midway along diaphysis where bending stresses greatest Bones stressed when weight bears on them or muscles pull on them Usually off center so tends to bend bones Bending compresses on one side; stretches on other

Wolff’s Law Bones grow or remodel in response to demands placed on it Explains Handedness (right or left handed) results in thicker and stronger bone of that upper limb Curved bones thickest where most likely to buckle Trabeculae form trusses along lines of stress Large, bony projections occur where heavy, active muscles attach

Figure 6.13 Bone anatomy and bending stress. Load here (body weight) Head of femur Tension here Compression here Point of no stress © 2013 Pearson Education, Inc.

Figure 6.14 Vigorous exercise can strengthen bone. Cross- sectional dimension of the humerus Added bone matrix counteracts added stress Serving arm Nonserving arm © 2013 Pearson Education, Inc.

End Result Hormonal controls determine whether and when remodeling occurs to changing blood calcium levels Mechanical stress determines where remodeling occurs

Lab Today Lab Exercise 9 You can start on exercise 10 Labs 10 and 11 are long and detailed Will take you a long time to memorize and understand these two labs Having more than 1 lab period to cover them is adviced