Chapter 6 Bones and skeletal tissues

Endochondral ossification

Manner of bone development that starts with a cartilage model of the future bone.

Intramembranous ossification

Manner of bone development whereby bone develops from a fibrous membrane.

Fibroblasts

Responsible for synthesis of the matrix of all types of connective tissue proper.

Chondroblasts

Responsible for synthesis of the matrix of all the types of cartilage.

Osteoblasts

Responsible for synthesis of the matrix of all types of oscular tissue and secrete osteoid to produce new bone.

Osteoclasts

Bone destroying cells.

Hydroxyapatite

Mineral salts such as calcium phosphate that account for the hardness in bone to resist compression.

Osteocytes

Mature bone cells that monitor and repair mature bone tissue.

Organic osteoid

Secreted by bone-forming cells and composed of proteoglycans, glycoproteins, and collagen.

Skeletal Cartilage

Made of some variety of cartilage tissue depending on its location and function.

Composition of Cartilage

Consists of primarily water and is very resilient, returning to its original shape after compression.

Nerves and Blood Vessels in Cartilage

Cartilage contains no nerves or blood vessels.

Perichondrium

A layer of dense irregular connective tissue that surrounds cartilage, acting as reinforcement and containing blood vessels.

Function of Perichondrium

Resists outward expansion when cartilage is compressed and nourishes cartilage cells.

Chondrocytes

Cells contained in all three types of cartilage, enclosed in lacunae.

Extracellular Matrix in Cartilage

Jellylike matrix that contains fibers.

Chondrocytes

Cells enclosed in lacunae found in all types of cartilage.

Hyaline Cartilage

Provides support with flexibility; most abundant skeletal cartilage with fine collagen fibers.

Articular cartilages

Type of hyaline cartilage found at joint points of connection.

Costal cartilages

Type of hyaline cartilage that connects the rib to the sternum.

Respiratory cartilages

Type of hyaline cartilage that forms the skeleton of the larynx.

Nasal cartilages

Type of hyaline cartilage that forms the external nose.

Elastic Cartilage

Resembles hyaline cartilage but contains more elastic fibers for repeated bending.

Fibrocartilages

Consist of parallel rows of chondrocytes alternating with thick collagen fibers.

Menisci

Podlike fibrocartilages found in sites subjected to pressure and stretch.

Intervertebral disks

Fibrocartilages located between vertebrae that provide support.

What is the primary difference between the matrix of bone and cartilage?

Bone has a hard matrix, while cartilage has a flexible matrix.

What are the two ways cartilage can grow?

Appositional growth and interstitial growth.

Describe appositional growth in cartilage.

In appositional growth, cartilage-forming cells in the perichondrium secrete new matrix against the external face of existing cartilage tissue.

How does interstitial growth occur in cartilage?

In interstitial growth, the lacunae-bound chondrocytes divide and secrete new matrix, expanding the cartilage from within.

Under what conditions can cartilage become calcified?

Cartilage can become calcified due to the deposit of calcium salts in youth and old age.

Does calcification of cartilage make it bone?

No, calcification does not make cartilage bone.

Support

Bones provide a framework that supports the body and cradles its soft organs.

Protection

The fused bones of the skull protect the brain and the rib cage helps protect the vital organs of the thorax.

Anchorage

Skeletal muscles attach to bones by tendons, allowing us to walk, grasp objects, and breathe.

Mineral Storage

Bone is a reservoir for minerals, most importantly calcium and phosphate, with deposits and withdrawals occurring.

Blood Cell Formation

Most blood cell formation or hematopoiesis occurs in the red marrow of certain bones.

Triglyceride (Fat storage)

Yellow bone marrow contains fat for a source of energy.

Hormone Production

Bones secrete osteocalcin, a hormone that helps to regulate insulin secretion, glucose homeostasis, and energy expenditure.

Axial Skeleton

Forms the long axis of the body and includes the bones of the skull, vertebral column, and rib cage.

Appendicular Skeleton

Consists of the bones of the upper and lower limbs and the girdles that attach the limbs to the axial skeleton.

Long Bones

Considerably longer than wide, with a shaft plus two ends; all limb bones are long except the patella and tarsals/carpals.

Short Bones

Roughly cube-shaped; examples include the bones of the wrist and ankles.

Sesamoid Bones

A special type of bone that forms in tendons and varies in size and number.

Flat Bones

Thin, flattened, and usually a bit curved; examples include the sternum, scapulae, ribs, and most cranial bones.

Irregular Bones

Have complicated shapes that fit none of the preceding classes; examples include the vertebrae and hip bones.

Compact Bone

The external layer of the bone.

Spongy Bone

The internal layer of the bone, also known as trabecular bone.

Gross Structure of Bones

Bones are organs that contain osseous tissue, nervous tissue, cartilage, muscle, and epithelial tissue.

Trabeculae

In living bones, trabeculae are filled with yellow or red bone marrow.

What are the main components of short irregular and flat bones?

They consist of thin plates of spongy bone covered by compact bone.

What covers the compact bone in short irregular and flat bones?

The compact bone is covered by periosteum and endosteum.

Do short irregular and flat bones have a well-defined marrow cavity?

No, they contain bone marrow between their trabecula but no well-defined marrow cavity.

How is flat bone structured?

Flat bone is arranged in a stiffened sandwich: Compact Bone—> Spongy bone—-> Compact Bone.

What is the diaphysis of a long bone?

A tubular diaphysis or shaft that forms the long axis of the bone.

What does the medullary cavity contain?

The medullary cavity contains yellow bone marrow.

What are the epiphyses of a long bone?

The epiphyses are the bone ends, with an outer shell of compact bone and an interior of spongy bone.

What is the epiphyseal plate?

A disc of hyaline cartilage that grows during childhood and lengthens the bone, commonly called the growth plate.

What covers the external surface of the entire bone?

The periosteum covers the external surface, except for the joint surfaces.

What is the outer layer of the periosteum made of?

The outer layer of the periosteum is made of dense irregular connective tissue.

What is the function of the periosteum?

It provides anchoring points for tendons and joints and is supplied with nerve fibers and blood vessels.

What does the endosteum cover?

The endosteum covers internal bone surfaces and lines the canals that pass through compact bone.

How are bones vascularized compared to cartilage?

Bones are well vascularized, unlike cartilage.

What are the primary vessels serving the diaphysis?

The nutrient artery and nutrient vein.

What is red marrow?

Blood-forming tissue found in spongy bone and the medullary cavity.

Where is red marrow typically found in adults?

In the trabeculae of spongy bones in flat bones of the skull, sternum, ribs, clavicles, scapulae, hip bones, vertebrae, and the heads of the femur and humerus.

What are bone markings?

Features that provide information on how a bone is attached to the body.

What do projections on bones indicate?

They are sites of muscle and ligament attachments.

What do depressions and openings on bones accommodate?

They accommodate blood vessels and nerves.

What do surfrace bone markings accomadate

Help form joints

Major cell types in bone tissue

Osteoprogenitor cells, osteoblasts, osteocytes, bone lining cells, and osteoclasts.

Osteoprogenitor cells

Stem cells found in the periosteum and endosteum that differentiate into osteoblasts when stimulated.

Osteoblasts

Bone forming cells that secrete the bone matrix, which consists of collagen and calcium binding proteins.

Shape of osteoblasts

Cube-shaped when depositing bone; become flattened when inactive; become osteocytes when surrounded by matrix.

Osteocytes

Cells that maintain and monitor the bone matrix, acting as sensors and communicating with osteoblasts and osteoclasts.

Bone lining cells

Flat cells found on bone surfaces where bone remodeling is not occurring.

Osteoclasts

Multinucleate cells located at sites of bone resorption, lying in shallow depressions they carve out.

Ruffle of osteoclasts

Distinctive structure that makes contact with the bone when actively resorbing bone.

Microscopic anatomy of compact bone

Compact bone has openings and canals that serve as conduits for nerves and blood.

Osteon

The structural unit of compact bone, functioning as tiny elongated cylindrical weight-bearing pillars.

Composition of osteons

Each osteon is a group of hollow tubes of bone matrix, similar to tree trunks.

Lamella

Each matrix tube in an osteon.

Collagen fibers in lamella

Run in a single direction in particular lamella, while adjacent lamella run in the opposite direction.

Function of collagen fibers in osteons

Help resist twisting.

What is the central canal in an osteon called?

The Haversian canal

What do perforating canals connect?

They connect the blood and nerve supply of the medullary cavity to the central canals.

What lines the perforating canals?

Endosteum

What are canaliculi?

Hairlike canals that radiate from the lacunae connecting osteocytes to each other and the central canal.

What do interstitial lamellae represent?

Incomplete lamellae found between complete osteons.

What do circumferential lamellae do?

They extend around the entire circumference of the diaphysis and resist twisting of the bone.

What is the role of trabecular bone?

It helps the bone resist stress.

What is the composition of osteoid?

It is made up of ground substance and collagen fibers, constituting 1/3 of the bone matrix.

What are the organic components of bone?

Osteoprogenitor cells, osteoblasts, osteocytes, bone lining cells, osteoclasts, and osteoid.

What do sacrificial bonds in collagen molecules do?

They stretch and break easily on impact, dissipating energy to prevent fractures.

What are the inorganic components of bone?

Inorganic hydroxyapatites or mineral salts, primarily large calcium phosphates around collagen fibers.

What are the two types of ossification?

Intramembranous ossification and endochondral ossification.

What is ossification?

The process of bone tissue formation.

How does endochondral ossification occur?

Bone develops by replacing hyaline cartilage, resulting in endochondral bone.

What is formed through intramembranous ossification?

Bone develops from fibrous membrane, resulting in membranous bone.

Which bones form by endochondral ossification?

All bones below the base of the skull, except for the clavicle.