A&P Chapter 7: Skeletal Tissues

What are the two types of bone tissue?

• Cancellous (spongy) bone

• Compact bone

What are the four classifications of bones?

• Long bones

• Short bones

• Flat bones

• Irregular bones

What are the seven parts of a long bone

• Diaphysis

• Epiphysis

• Epiphyseal line or plate

• Medullary or marrow cavity

• Periosteum

• Endosteum

• Articular cartilage

What is the periosteum, and where is it located?

A tough connective tissue membrane that covers the outer surface of a bone, except at the joint surfaces, which are covered by articular cartilage.

What is the endosteum, and where is it located?

A thin membrane that lines the inner surfaces of a bone, including the medullary (marrow) cavity.

What dominates bone tissue?

The matrix.

What is the inorganic salt in the inorganic matrix of bone, and what is it made of?

Hydroxyapatite, which is calcium phosphate

What property does the inorganic matrix give bone?

Hardness.

What is the organic matrix of bone made of?

• Protein fibers (collagen)

• Glycoproteins

What property does the organic matrix give bone?

Flexibility.

What is another name for an osteon?

Haversian system

What does the osteon (Haversian system) permit?

• Delivery of nutrients

  • Removal of waste products

What are the five components of an osteon?

• Lamellae (lamella)

• Lacunae (lacuna)

• Canaliculi (canaliculus)

• Central or Haversian canal

  • Volkmann's or perforating canals

What is compact bone good at providing?

• Protection

• Support

What are the characteristics of spongy bone?

• Lightweight

• Provides tissue support

What forms the sponge-like appearance of cancellous bone?

Plates of bone called trabeculae.

How many osteons or central canals do trabeculae have?

Few.

How close is any osteocyte in trabeculae to a blood supply?

No osteocyte is far from the blood of the bone marrow.

What does cancellous bone provide?

Strength with little weight.

Along what do trabeculae develop?

Along the bone's lines of stress.

What do osteoblasts do?

They secrete matrix.

What do osteocytes do?

They maintain the matrix.

What are osteocytes, and where are they trapped?

Osteoblasts that are trapped in lacunae.

What is notable about the number of nuclei in an osteoclast?

They are multinucleated.

What do osteoclasts do to the matrix?

They dissolve the matrix.

What type of tissue is bone marrow?

Myeloid tissue.

Where is bone marrow located in long bones, and where is it located in spongy bone?

• Long bone: in the medullary cavity

• Spongy bone: among the trabeculae

What is bone marrow the site for?

The production of blood cells.

In adults, where is red marrow found?

• Vertebrae

• Ribs

• Sternum

• Pelvic girdle

  • Proximal heads of the femur and humerus

What is yellow marrow, and where is it found in adults?

Fatty marrow of the long bones in adults.

What is hemopoiesis (hematopoiesis)?

The formation of blood cells: red blood cells, white blood cells, and platelets.

What are the six functions of the skeletal system?

• Support

• Protection

• Movement

• Mineral storage

• Hemopoiesis (hematopoiesis)

• Homeostasis of calcium levels

How much of the body's calcium do bones store?

99% of the body's calcium.

What happens when calcium levels in the blood are decreased?

1. Parathyroid hormone is released

2. Osteoclasts are stimulated to increase bone resorption

3. Calcium is released into the blood

What happens when calcium levels in the blood are increased?

1. Calcitonin is released

2. Osteoblasts are stimulated to increase bone deposition

3. Calcium is removed from the blood

What are the two types of ossification in osteogenesis?

• Intramembranous ossification

• Endochondral ossification

Where does intramembranous ossification occur?

Within a connective tissue membrane.

What is apposition growth, and what does it do?

It adds bone tissue to the outer surface.

Where does endochondral ossification occur?

Within a cartilage model.

Which cells deposit bone in endochondral ossification?

Osteoblasts.

What types of growth occur in endochondral ossification, and what do they increase?

• Appositional and interstitial growth

• They increase diameter and length

Hodo most bones develop?

by endochondral ossification

Endochondral ossification, step 1
What forms in the shaft of the cartilage model, and what happens during this step?

Formation of the primary ossification center and marrow cavity in the shaft of the model.

• Bony collar developed by osteoblasts

• Chondrocytes swell and die

• Stem cells give rise to osteoblasts and osteoclasts

• Bone is laid down and the marrow cavity is created

Endochondral ossification, step 2
What forms in the ends of the bone during this step?

Secondary ossification centers and marrow cavities form in the ends of the bone.

Endochondral ossification, step 3
What cartilage remains after the ossification centers form, and what do the growth plates do?

• Cartilage remains as articular cartilage and epiphyseal (growth) plates

• Growth plates provide for increase in length of bone during childhood and adolescence

• Growth plates disappear when growth stops

Where do bones grow in length?

At the epiphyseal plate.

How do bones grow in diameter, and what does each cell type do?

Bones grow in diameter by the combined action of osteoclasts and osteoblasts.

• Osteoclasts enlarge the diameter of the medullary cavity

• Osteoblasts from the periosteum build new bone around the outside of the bone

In the early to middle years, how does bone formation compare with bone destruction?

Bone formation = bone destruction.

What is remodeling activity important for?

Homeostasis of blood calcium levels.

When does remodeling occur?

Throughout life.

What is epiphyseal growth, and what happens during it?

• Growth in the cartilage surrounding the epiphysis

• Cartilage is replaced by bone

• Bone is remodeled

What happens at the epiphyseal plate during growth in length?

• Cartilage grows in the epiphyseal plate

• Cartilage is replaced by bone

• Bone is remodeled

• Bone is resorbed

What is the epiphyseal line?

The line seen in adult bone that marks where the epiphyseal plate was, after growth stops.

What does a fracture do to the blood vessels, and what does that start?

• A fracture tears and destroys blood vessels that carry nutrients to osteocytes

• Vascular damage initiates the repair sequence

What is a callus?

A specialized repair tissue that binds the broken ends of the fracture together.

What does rapidly growing callus tissue do?

It effectively collars the broken ends and stabilizes the fracture so healing can proceed.

How long does fracture healing normally take?

Normally 8 to 12 weeks, and longer in the elderly.

Fracture healing, stage 1 of 4
What happens in this stage?

Stage 1 = fracture hematoma.

• A clot forms

  • Then osteogenic cells form granulation tissue

Fracture healing, stage 2 of 4
What happens in this stage?

Stage 2 = soft callus.

• Fibroblasts produce fibers and fibrocartilage

Fracture healing, stage 3 of 4
What happens in this stage, and how long does it take?

Stage 3 = hard callus.

• Osteoblasts produce a bony collar in 6 weeks

Fracture healing, stage 4 of 4
What happens in this stage, and how long does it take?

Stage 4 = remodeling, in 3 to 4 months.

• Spongy bone is replaced by compact bone

What does a deficiency of vitamin A do to bone?

It retards bone development.

What does a deficiency of vitamin C do to bone?

It results in fragile bones.

What conditions result from a deficiency of vitamin D?

• Rickets

• Osteomalacia

What does insufficient growth hormone cause?

Dwarfism

What conditions does excessive growth hormone cause?

• Gigantism

• Acromegaly

What does insufficient thyroid hormone do to bone growth?

It delays bone growth.

What do sex hormones do to bone?

• They promote bone formation

• They stimulate ossification of the epiphyseal plates

What does physical stress do to bone?

It stimulates bone remodeling.

What type of joint is a synovial joint, and what is its other name?

A freely movable joint, also called a diarthrosis (plural: diarthroses).

What are the seven structures of a synovial joint?

• Joint capsule

• Synovial membrane

• Articular cartilage

• Joint cavity

• Menisci

• Ligaments

• Bursae

Synovial joint, joint capsule
What type of tissue makes up the joint capsule?

Dense regular connective tissue.

What does the inner synovial membrane of the joint capsule secrete?

Synovial fluid.

What does synovial fluid do?

• Lubricates and nourishes the articular cartilages

• Absorbs shock during compression of the joint

What type of cartilage is articular cartilage, and what does it cover?

Hyaline cartilage that covers the articular surfaces.

What does articular cartilage prevent?

Bone-to-bone contact during compression of the joint.

What is the joint cavity, and what does it allow?

The space between 2 bones, which allows movement of the bones.

What do the ligaments of a synovial joint do?

• Connect bone to bone

• Strengthen and reinforce the capsule

What is the purpose of the synovial fluid-filled structures, and what are the two types?

They reduce friction.

• Bursae

• Tendon sheaths

What are bursae, and where are they located?

Sacs outside most synovial joints where ligaments, muscles, tendons, and/or bones rub.

What are tendon sheaths?

Elongated bursae around tendons.

Where are tendon sheaths particularly found, and why?

In confined areas, such as the wrist and ankle, where tendons rub each other.

What happens to bones in osteoporosis?

• Bones lose mass

• They become increasingly brittle

• They become subject to fractures

In which group is osteoporosis more prevalent, and what type is it called?

Women, where it is postmenopausal osteoporosis.

When do men develop osteoporosis, and what type is it called?

Later in life, where it is senile osteoporosis.