Biology Anatomy

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Karen Dunbar Kareiva

Ivy Tech Community College

Chapter 6 Part A

Bones and Skeletal Tissue

Why This Matters

Understanding bone anatomy and the process of bone remodeling allows you to work effectively with patients with bone diseases such as osteoporosis

6.1 Skeletal Cartilages

The human skeleton initially consists of just cartilage, which is replaced by bone, except in areas requiring flexibility

Basic Structure, Types, and Locations

Skeletal cartilage: made of highly resilient, molded cartilage tissue that consists primarily of water

Contains no blood vessels or nerves

Perichondrium: layer of dense connective tissue surrounding cartilage like a girdle

Helps cartilage resist outward expansion

Contains blood vessels for nutrient delivery to cartilage

Cartilage is made up of chondrocytes, cells encased in small cavities (lacunae) within jelly-like extracellular matrix

Basic Structure, Types, and Locations (cont.)

Three types of cartilage:

Hyaline cartilage

Provides support, flexibility, and resilience

Most abundant type; contains collagen fibers only

Articular (joints), costal (ribs), respiratory (larynx), nasal cartilage (nose tip)

Elastic cartilage

Similar to hyaline cartilage, but contains elastic fibers

External ear and epiglottis

Fibrocartilage

Thick collagen fibers: has great tensile strength

Menisci of knee; vertebral discs

Epiglottis

Larynx

Cartilage in

external ear

Cartilages in

nose

Trachea

Cartilage in

intervertebral

disc

Respiratory

tube cartilages

in neck and thorax

Pubic symphysis

Meniscus (padlike

cartilage in

knee joint)

Cartilages

Articular cartilage

of a joint

Articular

cartilage

of a joint

Costal

cartilage

Thyroid

cartilage

Cricoid

cartilage

Lung

Axial skeleton

Appendicular skeleton

Bones of skeleton

Hyaline cartilages

Elastic cartilages

Fibrocartilages

Figure 6.1 The bones and cartilages of the human skeleton.

Epiglottis

Larynx

Cartilage in

external ear

Cartilages in

nose

Trachea

Cartilage in

intervertebral

disc

Respiratory

tube cartilages

in neck and thorax

Pubic symphysis

Meniscus (padlike

cartilage in

knee joint)

Cartilages

Articular cartilage

of a joint

Articular

cartilage

of a joint

Costal

cartilage

Thyroid

cartilage

Cricoid

cartilage

Lung

Axial skeleton

Appendicular skeleton

Bones of skeleton

Hyaline cartilages

Elastic cartilages

Fibrocartilages

Figure 6.1 The bones and cartilages of the human skeleton.

Figure 4.8i Connective tissues.

Cartilage: fibrocartilage

Description: Matrix similar to

but less firm than that in hyaline

cartilage; thick collagen fibers

predominate.

Function: Tensile strength

allows it to absorb compressive

shock.

Chondrocytes

in lacunae

Collagen

fiber

Location: Intervertebral discs;

pubic symphysis; discs of knee

joint.

Intervertebral

discs

Photomicrograph: Fibrocartilage of an

intervertebral disc (125×). Special staining

produced the blue color seen.

Growth of Cartilage

Cartilage grows in two ways:

Appositional growth

Cartilage-forming cells in perichondrium secrete matrix against external face of existing cartilage

New matrix laid down on surface of cartilage

Interstitial growth

Chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within

New matrix made within cartilage

Growth of Cartilage (cont.)

Calcification of cartilage occurs during normal bone growth in youth, but can also occur in old age

Hardened cartilage is not the same as bone

6.2 Functions of Bones

There are seven important functions of bones:

Support

For body and soft organs

Protection

Protect brain, spinal cord, and vital organs

Movement

Levers for muscle action

Mineral and growth factor storage

Calcium and phosphorus, and growth factors reservoir

6.2 Functions of Bones

Blood cell formation

Hematopoiesis occurs in red marrow cavities of certain bones

Triglyceride (fat) storage

Fat, used for an energy source, is stored in bone cavities

Hormone production

Osteocalcin secreted by bones helps to regulate insulin secretion, glucose levels, and metabolism

6.3 Classification of Bones

206 named bones in human skeleton

Divided into two groups based on location

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

6.3 Classification of Bones

Bones are also classified according to one of four shapes:

Long bones

Longer than they are wide

Limb bones

Short bones

Cube-shaped bones (in wrist and ankle)

Sesamoid bones form within tendons (example: patella)

Vary in size and number in different individuals

6.3 Classification of Bones

Flat bones

Thin, flat, slightly curved

Sternum, scapulae, ribs, most skull bones

Irregular bones

Complicated shapes

Vertebrae and hip 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)

6.4 Bone Structure

Bones are organs because they contain different types of tissues

Bone (osseous) tissue predominates, but a bone also has nervous tissue, cartilage, fibrous connective tissue, muscle cells, and epithelial cells in its blood vessels

Three levels of structure

Gross

Microscopic

Chemical

Gross Anatomy

Compact and spongy bone

Compact bone: dense outer layer on every bone that appears smooth and solid

Spongy bone: made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculae

Open spaces between trabeculae are filled with red or yellow bone marrow

Gross Anatomy (cont.)

Structure of short, irregular, and flat bones

Consist of thin plates of spongy bone (diploe) covered by compact bone

Compact bone sandwiched between connective tissue membranes

Periosteum covers outside of compact bone, and endosteum covers inside portion of compact bone

Bone marrow is scattered throughout spongy bone; no defined marrow cavity

Hyaline cartilage covers area of bone that is part of a movable joint

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

Gross Anatomy (cont.)

Structure of typical long bone

All long bones have a shaft (diaphysis), bone ends (epiphyses), and membranes

Diaphysis: tubular shaft that forms long axis of bone

Consists of compact bone surrounding central medullary cavity that is filled with yellow marrow in adults

Epiphyses: ends of long bones that consist of compact bone externally and spongy bone internally

Articular cartilage covers articular (joint) surfaces

Between diaphysis and epiphysis is epiphyseal line

Remnant of childhood epiphyseal plate where bone growth occurs

Figure 6.4a The structure of a long bone (humerus of arm).

Articular

cartilage

Proximal

epiphysis

Diaphysis

Distal

epiphysis

Spongy bone

Epiphyseal

line

Periosteum

Compact bone

Medullary

cavity (lined

by endosteum)

Figure 6.4b The structure of a long bone (humerus of arm).

Articular

cartilage

Compact

bone

Endosteum

Spongy

bone

Gross Anatomy (cont.)

Membranes: two types (periosteum and endosteum)

Periosteum: white, double-layered membrane that covers external surfaces except joints

Fibrous layer: outer layer consisting of dense irregular connective tissue consisting of Sharpey’s fibers that secure to bone matrix

Osteogenic layer: inner layer abutting bone and contains primitive osteogenic stem cells that gives rise to most all bone cells

Contains many nerve fibers and blood vessels that continue on to the shaft through nutrient foramen openings

Anchoring points for tendons and ligaments

Gross Anatomy (cont.)

Membranes (cont.)

Endosteum

Delicate connective tissue membrane covering internal bone surface

Covers trabeculae of spongy bone

Lines canals that pass through compact bone

Like periosteum, 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

artery

Gross Anatomy (cont.)

Hematopoietic tissue in bones

Red marrow is found within trabecular cavities of spongy bone and diploë of flat bones, such as sternum

In newborns, medullary cavities and all spongy bone contain red marrow

In adults, red marrow is located in heads of femur and humerus, but most active areas of hematopoiesis are flat bone diploë and some irregular bones (such as the hip bone)

Yellow marrow can convert to red, if person becomes anemic

Gross Anatomy (cont.)

Bone markings

Sites of muscle, ligament, and tendon attachment on external surfaces

Areas involved in joint formation or conduits for blood vessels and nerves

Gross Anatomy (cont.)

Bone markings (cont.)

Three types of markings:

Projection: outward bulge of bone

May be due to increased stress from muscle pull or is a modification for joints

Depression: bowl- or groove-like cut-out that can serve as passageways for vessels and nerves, or plays a role in joints

Opening: hole or canal in bone that serves as passageways for blood vessels and nerves

Table 6.1-1 Bone Markings

Table 6.1-2 Bone Markings (continued)

Microscopic Anatomy of Bone

Cells of bone tissue

Five major cell types, each of which is a specialized form of the same basic cell type

Osteogenic cells

Osteoblasts

Osteocytes

Bone-lining cells

Osteoclasts

Microscopic Anatomy of Bone (cont.)

Osteogenic cells

Also called osteoprogenitor cells

Mitotically active stem cells in periosteum and endosteum

When stimulated, they differentiate into osteoblasts or bone-lining cells

Some remain as osteogenic stem cells

Microscopic Anatomy of Bone (cont.)

Osteoblasts

Bone-forming cells that secrete unmineralized bone matrix called osteoid

Osteoid is made up of collagen and calcium-binding proteins

Collagen makes up 90% of bone protein

Osteoblasts are actively mitotic

Figure 6.5ab Comparison of different types of bone cells.

Osteogenic cell

Osteoblast

Stem cell

Matrix-synthesizing

cell responsible for

bone growth

Microscopic Anatomy of Bone (cont.)

Osteocytes

Mature bone cells in lacunae that no longer divide

Maintain bone matrix and act as stress or strain sensors

Respond to mechanical stimuli such as increased force on bone or weightlessness

Communicate information to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur

Microscopic Anatomy of Bone (cont.)

Bone-lining cells

Flat cells on bone surfaces believed to also help maintain matrix (along with osteocytes)

On external bone surface, lining cells are called periosteal cells

On internal surfaces, they are called endosteal cells

Microscopic Anatomy of Bone (cont.)

Osteoclasts

Derived from same hematopoietic stem cells that become macrophages

Giant, multinucleate cells function in bone resorption (breakdown of bone)

When active, cells are located in depressions called resorption bays

Cells have ruffled borders that serve to increase surface area for enzyme degradation of bone

Also helps seal off area from surrounding matrix

Figure 6.5cd Comparison of different types of bone cells.

Bone-resorbing cell

Osteoclast

Osteocyte

Mature bone cell that

monitors and maintains

the mineralized

bone matrix

Microscopic Anatomy of Bone (cont.)

Compact bone

Also called lamellar bone

Consists of:

Osteon (Haversian system)

Canals and canaliculi

Interstitial and circumferential lamellae

Microscopic Anatomy of Bone (cont.)

Osteon (Haversian system)

An osteon is the structural unit of compact bone

Consists of an elongated cylinder that runs parallel to long axis of bone

Acts as tiny weight-bearing pillars

An osteon cylinder consists of several rings of bone matrix called lamellae

Lamellae contain collagen fibers that run in different directions in adjacent rings

Withstands stress and resist twisting

Bone salts are found between collagen fibers

Figure 6.6 A single osteon.

Artery with

capillaries

Structures

in the

central

canal

Vein

Lamellae

Collagen

fibers

run in

different

directions

Twisting

force

Nerve fiber

Microscopic Anatomy of Bone (cont.)

Canals and canaliculi

Central (Haversian) canal runs through core of osteon

Contains blood vessels and nerve fibers

Perforating (Volkmann’s) canals: canals lined with endosteum that occur at right angles to central canal

Connect blood vessels and nerves of periosteum, medullary cavity, and central canal

Microscopic Anatomy of Bone (cont.)

Canals and canaliculi (cont.)

Lacunae: small cavities that contain osteocytes

Canaliculi: hairlike canals that connect lacunae to each other and to central canal

Osteoblasts that secrete bone matrix maintain contact with each other and osteocytes via cell projections with gap junctions

When matrix hardens and cells are trapped the canaliculi form

Allow communication between all osteocytes of osteon and permit nutrients and wastes to be relayed from one cell to another

Microscopic Anatomy of Bone (cont.)

Interstitial and circumferential lamellae

Interstitial lamellae

Lamellae that are not part of osteon

Some fill gaps between forming osteons; others are remnants of osteons cut by bone remodeling

Circumferential lamellae

Just deep to periosteum, but superficial to endosteum, these layers of lamellae extend around entire surface of diaphysis

Help long bone to resist twisting

Compact

bone

Spongy bone

Perforating

(Volkmann’s) canal

Central

(Haversian) canal

Endosteum lining bony canals

and covering trabeculae

Osteon

(Haversian system)

Circumferential

lamellae

Perforating (Sharpey’s) fibers

Lamellae

Periosteal blood vessel

Nerve

Lamellae

Canaliculi

Lacuna (with osteocyte)

Interstitial lamella

Periosteum

Vein

Artery

Osteocyte

in a lacuna

Lacunae

Central

canal

Figure 6.7 Microscopic anatomy of compact bone.

Microscopic Anatomy of Bone (cont.)

Spongy bone

Appears poorly organized but is actually organized along lines of stress to help bone resist any stress

Trabeculae, like cables on a suspension bridge, confer strength to bone

No osteons are present, but trabeculae do contain irregularly arranged lamellae and osteocytes interconnected by canaliculi

Capillaries in endosteum supply nutrients

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

Chemical Composition of Bone

Bone is made up of both organic and inorganic components

Organic components

Includes osteogenic cells, osteoblasts, osteocytes, bone-lining cells, osteoclasts, and osteoid

Osteoid, which makes up one-third of organic bone matrix, is secreted by osteoblasts

Consists of ground substance and collagen fibers, which contribute to high tensile strength and flexibility of bone

Chemical Composition of Bone (cont.)

Organic components (cont.)

Resilience of bone is due to sacrificial bonds in or between collagen molecules that stretch and break to dissipate energy and prevent fractures

If no additional trauma, bonds re-form

Inorganic components

Hydroxyapatites (mineral salts)

Makeup 65% of bone by mass

Consist mainly of tiny calcium phosphate crystals in and around collagen fibers

Responsible for hardness and resistance to compression

Chemical Composition of Bone (cont.)

Inorganic components (cont.)

Bone is half as strong as steel in resisting compression and as strong as steel in resisting tension

Lasts long after death because of mineral composition

Can reveal information about ancient people