Chapter 6: Bone Tissue

Osteocytes

Mature bone cells Main cells of bone tissue Maintain bone's daily metabolism, such as the exchange of nutrients and wastes with the blood Do not undergo cell division

Nutrient artery

Passes through the nutrient foramen along with the nutrient vein.

Nutrient vein

Passes through the nutrient forament along with the nutrient artery.

Location of red bone marrow

Spongy bone tissue of the epiphyses and metaphysis

Spongy vs compact bone

Spongy: 1. light, reducing overall weight of the bone. 2. Trabeculae support and protect red bone marrow Compact: heavy

Bone deposition

The addition of minerals and coolagen fibers to bone by osteoblasts. Results in the formation of bone ECMatrix

Trabeculae

The arrangement of lamellae in an irregular lattice of thin columns - contains lacunae that contain osteocytes - canaliculi radiate outward from the lacunae - arranged along lines of stress

Resorption

The breakdown of bone extracellular matrix. Part of the normal development, growth, maintenance and repair of bone

Fracture hematoma

The clot formed around the site of a fracture as blood leaks from the torn ends of the vessels.

Osteoarthritis

The degeneration of articular cartilage such that the bony ends touch - the resulting friction of bone against bone worsens the condition. - usually associated with the elderly.

Bone remodeling

The ongoing replacement of old bone tissue by new bone tissue, involving bone resorption and bone deposition.

Calcification

The process in bone tissue development where mineral salts crystallize and tissue hardens

Calcification steps

The process requires the presence of collagen fibers. Mineral salts first begin to crystallize in the microscopic spaces between collagen fibers. After the spaces are filled mineral crystals accumulate around the collagen fibers.

Bone resorption

The removal of minerals and collagen fibers from bone by osteoclasts Results in the destruction of bone ECMatrix

Ossification centre

The site of a cluster of cells that differentiate (in bone formation)

Osteogenic cells

Unspecialized stem cells derived from mesenchyme, the tissue from which all connective tissues are formed. Only bone cells to undergo cell division - the resulting cells becoming osteoblasts Found along the inner portion of the periosteum, the endosteum and in the canals within bone that contain blood vessels.

Last bone to stop growing

Clavicle

Interstitial growth

Growth in length (of cartilage) via continual cell division of chondrocytes accompanied by further secretion of the cartilage ECMatrix

Functions: Skeletal - Assistance in movement

Most skeletal muscles attach to bones; when they contract, they pull on bones to produce movement.

Functions of periosteum

- enables bone to grow in thickness - protects the bone - assists in fracture repair - helps nourish bone tissue - serves as an attachment point for ligaments and tendons.

Bone Growth: In length

-Activity of the epiphyseal plate is the only way that the diaphysis can increase in length -As bone grows, new chondrocytes are formed on the epiphyseal side of the plate, which old chondrocytes are replaced by bone; thickness remains constant while bone on the diaphyseal side increases in length. -Epiphyseal cartliage stops dividing, bone replaces all cartilage.

Steps of endochondral ossification

1. Development of the cartilage model 2. Growth of the cartilage model. 3. Development of the primary ossification centre 4. Development of the medullary (marrow) cavity 5. Development of the secondary ossification centres 6. Formation of the articular cartilage and the epiphyseal plate.

Steps of intramembranous ossification

1. Development of the ossification centre 2. Calcification 3. Formation of trabeculae 4. Development of the periosteum

Two methods of bone formation

1. Intramembranous ossification 2. Endochondral ossification

4 types of bone cells

1. Osteogenic cells 2. Osteoblasts 3. Osteocytes 4. Osteoclasts

Functions of bone tissue/skeletal system

1. Supports soft tissue and provides attachment for skeletal muscles 2. Protects internal organs 3. Assists in movement along with skeletal muscles. 4. Stores and releases minerals 5. Contains red bone marrow, which produces blood cells 6. Contains yellow bone marrow, which stores trigycerides (fats)

Extracellular matrix in bone tissue

25% water 25% collagen fibers 50% crystallized mineral salts

Compact bone tissue

80% of the skeleton - contains few spaces - is the strongest form of bone tissue - found beneath the periosteum of all bones and makes up the bulk of the diaphyses of long bones - provides protection and support and resists the stresses produced by weight and movement.

Long bone

A bone that has greater length than width

Arrangement along lines of stress

A characteristic that helps bones resist stresses and transfer force without breaking.

Osteoporosis

A condition of porous bones - bone resorption outpaces bone deposition. - in large part due to depletion of calcium from the body - more calcium is lost in urine, feces and sweat than is absorbed from the diet.

Nutrient foramen

A hole in compact bone near the centre of the diaphysis through which a large nutrient artery and a large nutrient vein pass.

Epiphyseal plate

A layer of hyaline cartilage in the metaphysis of a growing bone that consists of four zones.

Epiphyseal plate

A layer of hyaline cartilage that allows the diaphysis of the bone to grow in length.

Osteomyelitis

An infection of bone characterized by high fever, sweating, chillds, pain and nausea, pus formation, edema and warmth over the affected bone and rigid overlying muscles. Often caused by bacteria, often Staph aureus

Fracture

Any break in a bone

Intramembranous ossification

Bone forms directly within mesenchyme arranged in sheetlike layers that resemble membranes - simpler of the two - flat bones of skull and mandible formed this way - think of fontanelle hardening as classic example

Endochondral ossification

Bone forms within hyaline cartilage that develops from mesenchyme. aka THE REPLACEMENT OF CARTILAGE BY BONE - most of the bones in the body formed this way - more complicated than intramembranous ossification

Blood and nerve supple of bone

Bone is richly supplied with blood. Blood vessels pass into bones from the periosteum.

Functions: Skeletal - Mineral homeostasis

Bone tissue stores several minerals, esp. calcium and phosphorus, which contribute to the strength of bone. On demand, bone releases minerals into the blood to maintain critical mineral balances (homeostasis) and to distribute the minerals to other parts of the body.

Osteoblasts

Bone-building cells Synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue Initiate calcification As osteoblasts surround themselves with extracellular matrix, they become trapped in their own secretions and become osteocytes. Do not undergo cell division

Hydroxyapatite

Calcium phosphate + Calcium hydroxide = crystals of hydroxyapatite (in bone tissue) As the crystals form, they combine with other mineral salts. As these mineral salts are deposited in the framework formed by the collagen fibers of the extracellular matrix, they crystallize and the tissue hardens.

Bone/osseous tissue

Contains an abundant extracellular matrix that surrounds widely separated cells.

7 structures of a long bone

DEMAPME 1. Diaphysis - shaft/body. Long, cylindrical. 2. Epiphyses - distal and proximal ends of the bone. 3. Metaphyses - region where diaphysis meets epiphysis 4. Articular cartilage - thin layer of hyaline cartilage covering the part of the epiphysis where the bones forms a joint with another bone. Reduces friction, absorbs shock. 5. Periosteum - tough sheath of dense irregular connective tissue that surrounds bone surface. Enables bone to grow in thickness. 6. Medullary cavity - the space within the diaphysis that contains fatty yellow bone marrow in adults 7. Endosteum - thin membrane that lines the medullary cavity. Contains a single layer of bone-forming cells and a small amount of connective tissue

Bone's flexibility

Depends on its collagen fibers

Bone's hardness

Depends on the crystallized inorganic mineral salts

4 zones of the epiphyseal plate

Diaphysis ---------------------- Zone of calcified cartilage Zone of hypertrophic cartilage Zone of proliferating cartilage Zone of resting cartilage ---------------------- Epiphyseal side

Spongy bone tissue

Does not contain osteons - 'Spongy' refers only to appearance, not texture -Consists of trabeculae - Makes up most of the bone tissue of short, flat and irregularly shaped bones. - Forms most of the epiphyses of long bones and the narrow rim around the medullary cavity of the diaphysis of long bones

Bone growth: In length. Summary.

Due to cell division in the epiphyseal plate, resulting in growth on the diaphysis in length.

Bone growth: In thickness. Summary.

Due to the addition of new bone tissue by periosteal osteoblasts around the outer surface of the bone. Called: appositional growth

Calcitriol

Formation of this is stimulated by PTH - the active form of Vit D - a hormone that promotes absorption of calcium of foods in the gastrointestinal tract into the blood.

Colles

Fracture of the distal end of the lateral forearm bone (radius) in which the distal fragment is displaced posteriorly.

Pott

Fracture of the distal end of the lateral leg bone (fibula), with serious injury of the distal tibial articulation.

Parathyroid hormone (PTH)

Hormone secreted by parathyroid glands. - increases blood Ca2+ level -operates via a negative feedback system - stimulates formation of calcitriol, which also increases blood Ca2+ level.

Calcitonin (CT)

Hormone secreted from the thyroid gland - decreases Ca2+ level - inhibits activity of osteoclasts, sppeds blood Ca2+ uptake by bone, accelerates Ca2+ deposition into bones. Net result: promotes bone formation and decreases blood Ca2+ level.

Osteoclasts

Huge cells derived from the fusion of as many as 50 monocytes and are concentrated in the endeosteum - Has a ruffled border one the side of the cell that faces the bone surface - Here, the cell releases lysosomal enzymes and acids that digest the protein and mineral components of the underlying bone matrix - Help regulate blood calcium levels.

Functions: Skeletal - Blood cell production

In a process called HOMEOPOIESIS, red bone marrow produces red blood cells, white blood cells and platelets

'Blasts'

In any tissue, this type of cell secretes extracellular matrix

Location of yellow bone marrow

Medullary cavity of the diaphysis

Perichondrium

Membrane that develops around cartilage model at the beginning of endochondral ossification

Primary ossification centre

Region where bone tissue will replace most of the cartilage

Osteon/Haversian System

Repeating units within compact bone tissue. - consists of a central canal, with concentrically arranged lamellae, lacunae, osteocytes and canaliculi - arranged along lines of stress

Central/Haversian canals

Run longitudinally through bone

Concentric lamellae

Situated around central canals - rings of calcified extracellular matrix, much like rings of a tree trunk.

Functions: Skeletal - Protection

Skeleton protects the most important internal organs from injury ex: - cranial bones protect the brain - vertebrae protect the spinal cord - rib cage protects the heart and lungs

Functions: Skeletal - Support

Skeleton serves as a structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles.

Canaliculi

Small channels filled with extracellular fluid that radiate in all directions from the lacunea

Lacunae

Small spaces between the lamellae, containing osteocytes.

Bone's role in calcium homeostasis

To help buffer the blood Ca2+ level, releasing Ca2+ into blood plasma (using osteoclasts) when the level decreases, and absorbing Ca2+ (using osteoblasts) when the level rises. Process is regulated by hormones. Most important: PTH: parathyroid hormone

Functions: Skeletal - Triglyceride storage

Yellow bone marrow consists mainly of adipose cells, which store triglycerides <-- These are a potential chemical energy reserve.

Comminuted

bone is splintered, crushed, or broken into pieces at the site of impact, and smaller bone fragments lie between the two main fragments.

Open (Compound)

broken ends of the bone protrude through the skin.

Epiphyses

distal and proximal ends of the bone.

Closed (Simple)

fracture does not break the skin.

Impacted

one end of the fractured bone is forcefully driven into the interior of the other.

Greenstick

partial fracture in which one side of the bone is broken and the other side bends; occurs only in children, whose bones are not fully ossified and contain more organic material than inorganic material.

Metaphyses

region where diaphysis meets epiphysis

Medullary cavity

the space within the diaphysis that contains fatty yellow bone marrow in adults

Articular cartilage

thin layer of hyaline cartilage covering the part of the epiphysis where the bones forms a joint with another bone. Reduces friction, absorbs shock.

Endosteum

thin membrane that lines the medullary cavity. Contains a single layer of bone-forming cells and a small amount of connective tissue

Periosteum

tough sheath of dense irregular connective tissue that surrounds bone surface. Enables bone to grow in thickness.

Appositional growth

Growth in thickness (of cartilage) via the addition of more extracellular matrix material to the periphery of the model by new chondroblasts that develop from the perichondrium.

Diaphysis

shaft/body. Long, cylindrical.

Ossification

aka osteogenesis The process by which bone forms