A&P Unit 2: Bone Function, Classification, and Long Bone Formation

What are the five functions of bone?

1. Support Movement

2. Protection

3. Calcium Storage

4. Calcium Homeostasis

5. Blood Cell Production

How do bones support movement?

they act as levers when muscles span a joint and contract

What are the five functions of bone?

1. Support Movement

2. Protection

3. Calcium Storage

4. Calcium Homeostasis

5. Blood Cell Production

How do bones support movement?

they act as levers when muscles span a joint and contract

How do bones provide protection?

they surround and shield vital organs from injury and trauma, such as the skull protecting the brain and the ribcage safeguarding the heart and lungs.

What are the two types of marrow in bones?

red marrow and yellow marrow

Yellow Marrow

• found in the center of a bone

• stores fat

Red Marrow

• surrounds yellow bone marrow

• responsible for hematopoiesis

Hematopoiesis

blood cell production

Bones are classified according to their shape. What are a few examples of different bone classifications?

• Flat Bones

• Long Bones

• Irregular Bones

• Short Bones

• Sesamoid Bones

Long Bone

A bone that is larger in length than width

The ____ and ____ line bones inside and out!

periosteum; endosteum

Periosteum

forms the outer surface of the bone

Endosteum

lines the medullary cavity

Osteoblast

forms bone matrix

Osteocyte

the primary cell found in mature bone, and is responsible for maintaining bone tissue

Osteogenic Cell

bone stem cells that differentiate into osteoblasts, which are responsible for building new bone tissue

Osteoclast

responsible for breaking down and reabsorbing bone cells

Flat Bone

• spongey bone with compact bone on top and bottom

• protects internal organs

Where is spongey bone found?

the interior of bones

Describe the characteristics of spongey bone.

it is a less dense, porous type of bone

Why is spongey bone important?

it provides a balance between strength and lightness, making it more suited for metabolic functions and facilitation the production of blood cells (hematopoiesis)

What does spongey bone lack?

the highly organized osteons found in compact bone

What occurs in the spaces found in the lattice-like structure of spongey bone?

blood cell production

Are osteocytes found in spongey bone?

yes

What is another name for compact bone?

cortical bone

What does compact bone do? Why is that important?

it forms the dense outer layer of bones, which makes it very strong and suitable for weight bearing and protection

What is the primary structural unit of compact bone?

osteon

What does an osteon consist of?

concentric rings of bone tissue surrounding a central canal called the Haversian canal

The Haversian Canal

• a canal that contains blood vessels, nerves, and connective tissue

• this network supplies and nourishes bone tissue

What surrounds the Haversian Canal?

concentric lamellae

Lamellae

layers of mineralized extracellular matrix (mainly collagen), where bone cells are located

Where are osteocytes found?

in lacunae

Lacunae

small spaces between the lamellae

______ are tiny channels that connect osteocytes to the Haversian Canal, allowing for nutrient and waste exchange between cells.

Canaliculi

What is compact bone highly resistant to?

bending and twisting forces

Osteogenesis

the formation of bone

What are the two ways in which bone develops in the human fetus and infant?

• intramembranous ossification

• endochondral ossification

How do osteoblasts become osteocytes?

Osteoblasts become osteocytes by embedding themselves within the calcified matrix they create, eventually maturing and maintaining the bone tissue

What does Intramembranous Ossification produce?

flat bones, such as those in the skull and clavicle.

Intramembranous Ossification thickens…

long bones throughout life

Describe the steps of Intramembranous Ossification.

1. Mesenchymal cells begin to cluster and differentiate into osteoblasts

2. The osteoblasts secrete an un-calcified bone matrix called the osteoid, which hardens and traps the osteoblasts within it

3. The osteoblasts then differentiate into osteocytes

4. The osteoid develops around blood vessels, forming thin columns and plates of bone called trabeculae

5. The trabeculae will eventually form spongey bone

6. The periosteum forms around the bone and the compact bone develops superficial to the trabecular bone

What does Endochondral Ossification produce?

long bones

What are the six steps of Endochondral Ossification

1. Mesenchymal cells differentiate into chondrocytes

2. The cartilage model of the future bony skeleton and the perichondrium form

3. Capillaries penetrate cartilage. Perichondrium transforms into periosteum. Periosteal collar develops. Primary ossification center develops.

4. Cartilage and chondrocytes continue to grow at ends of the bone

5. Secondary ossification centers develop

6. Cartilage remains at the epiphyseal plate and at joint surfaces as articular cartilage

What is the epiphyseal plate responsible for?

longitudinal bone growth

What happens at the epiphyseal plate?

cartilage grows within the epiphseal plate, and then is replaced with bone

Describe the composition of the epiphyseal plate.

it has typical hyaline cartilage in the middle with transition zones on each side where cartilage is replaced by bone

What is the Metaphysis?

The region of long bones between the epiphysis and the diaphysis, where active growth occurs.

Bone elongation is a result of ____ growth within the epiphyseal plate

cartilage

When do epiphyses close?

when cartilage is gone

Longitudinal growth occurs from ____ a bone.

within

Appositional growth

bone widening and thickening

Appositional growth occurs at bone _______.

surfaces

Describe the process of appositional growth in terms of intramembranous ossification

1. Osteoblasts of inner periosteum deposits osteoid tissue and becomes trapped as tissue calcifies

2. They lay down matrix in layers parallel to the surface

   • forms circumferential lamellae

   • osteoclasts of endosteum enlarge marrow cavity

At what age does endochondral ossification, longittudinal bone growth, stop?

by late teens to early 20s

When endochondrial ossification stops, what three things happen?

1. the gap between epiphyses and diaphysis close

2. primary and secondary marrow cavities unite into a single cavity

3. bone can no longer grow in length

As the bone matures, the epiphyseal plate transitions into an ____ ____.

epiphyseal line

Wolff’s Law

the body conforms and adapts in the directions and intensities it is habitually subjected to

Bone remodeling and growth occur in response to ____ ____.

mechanical stress

What gender loses bone mass more rapidly after the age of 30?

women

What other factors affect bone growth?

• hormones

• vitamins

• growth factors

Bone growth is especially rapid in puberty and adolescence due to the presence of what hormones?

surges in growth hormone, estrogen, and testosterone

What affect does steroids have on adolescents?

it causes premature closure of the epiphyseal plate, and results in abnormally short adult stature