Chapter 7 Bone Tissue

What is osteology?

The study of bones.

What is the skeletal system composed of?

Bones, cartilage, ligaments, and other connective tissues.

What are the six functions of the skeleton?

Support, movement, protection, electrolyte balance, acid-base balance, and blood formation

What type of tissue is bone?

Bone is osseous tissue.

What is mineralization and what is another name for it?

Mineralization is the hardening of bone, also known as calcification

What other tissue types are present in bone?

Cartilage, adipose tissue, blood, nervous tissue, fibrous connective tissue

Describe flat bones and give some examples.

Flat bones are thin and flat, providing protection and surface area for muscle attachment; examples include the skull, ribs, and sternum.

Describe long bones and give some examples.

Long bones are longer than they are wide, primarily involved in movement; examples include the femur, humerus, and tibia.

Describe short bones and give some examples.

Short bones are roughly cube-shaped and provide stability and support; examples include the carpals and tarsals.

Describe irregular bones and give some examples.

Irregular bones have complex shapes that do not fit into other categories; examples include the vertebrae and pelvis.

What is the general anatomy of bones observed in a _______ bone?

Long bone; compact bone

Describe the composition of a long bone.

A long bone consists of a diaphysis (shaft), epiphyses (ends), compact bone, cancellous (spongy) bone, and a medullary cavity.

What do the terms diaphysis and epiphysis refer to and what are their purposes?

Diaphysis refers to the shaft of a long bone that provides bone leverage; epiphysis refers to the ends of the bone that strengthens the joint and provides surface area for tendons and ligaments.

The joint surface where bones meet is covered with a layer of hyaline cartilage called the _______ cartilage, which enables a joint to move easily.

Articular cartilage

What are minute holes called that allow blood vessels to penetrate into the bone?

Nutrient foramina

What is the periosteum and what are its two layers?

The periosteum is a tough surface membrane covering the bone, consisting of an outer fibrous layer of collagen and an inner osteogenic layer of bone-forming cells.

Some collagen fibers of the outer later are continuous with _____ that bind muscle to bone

Tendons

Other collagen fibers of the outer later penetrate into the bone matrix as ___________ fibers

Perforating

Why is the osteogenic layer important?

It is responsible for the growth of bone and healing of fractures

A thin layer of reticular connective tissue called the ________ lines the internal marrow cavity, covers all surfaces of the spongy bone, and lines the canal system

Endosteum

In children and adolescents, an epiphyseal plate of _______ cartilage separates the marrow spaces of the epiphysis and diaphysis

Hyaline

What is the epiphyseal plate and what happens to the epiphyseal plate in adults?

A growth place; It becomes ossified and turns into an epiphyseal line.

Describe the sandwich-like arrangement of the cranium.

The cranium consists of an outer layer of compact bone, a middle layer of spongy bone (diploe), and an inner layer of compact bone.

What is diploe and how does it handle a moderate blow?

Diploe is the spongy bone between the layers of compact bone in flat bones, which helps absorb shock.

What covers both surfaces of a flat bone?

Periosteum.

What lines the marrow spaces of flat bones?

Endosteum.

What are osteogenic cells and where are they found?

Osteogenic cells are stem cells that develop from embryonic mesenchyme that are found in endosteum and inner periosteum

What are osteoblasts and where are they found?

Osteoblasts are bone-forming cells that synthesize organ matter and promote mineralization; they also secrete hormones that regulate bone metabolism

What hormone do osteoblasts secrete and what does it stimulate?

They secrete osteocalcin, which stimulates bone formation and regulates blood sugar, also triggers the body stress response

What are osteocytes?

Osteocytes are former osteoblasts that have become trapped in the bone matrix they deposited.

Define lacunae and canaliculi.

Lacunae are small cavities in bone tissue that house osteocytes, while canaliculi are microscopic channels that connect lacunae.

What do the slender, fingerlike cytoplasmic processes of osteocytes do?

They facilitate communication and nutrient exchange between neighboring osteocytes, reach out to nearest blood vessels, and contact osteoblasts on bone surface

What are neighboring osteocytes connected by?

Gap junctions that allowing the passage of nutrients, wastes, and chemical signals

What do osteocytes do in terms of bone matrix?

Some osteocytes absorb bone matrix while others deposit it, maintaining homeostasis of both bone density and blood concentrations of calcium and phosphate ions

What does it mean that osteocytes are strain sensors?

A load is applied to bone, producing flow in the extracellular fluid of lacunae and canaliculi; also stimulates cilia, secretes signals that regulate bone remodeling

What are osteoclasts?

Osteoclasts are bone-dissolving cells found on the bone surface

What do osteoclasts develop from?

Bone marrow stem cells that give rise to blood cells; thus, they have an independent origin from osteogenic cells, osteoblasts, and osteocytes

What is the ruffled border of osteoclasts for?

It increases the surface area and efficiency for bone resorption.

What are pits where osteoclasts reside called?

Resorption bays

What are the two processes involved in bone remodeling?

Osteogenesis and osteolysis

What constitutes the matrix of osseous tissue?

About one-third organic matter and two-thirds inorganic matter.

What does the organic matter in bone include?

Collagen fibers and protein-carbohydrate complexes

What is the inorganic matter in bone mostly made up of?

Hydroxyapatite crystals.

What class of materials does bone belong to?

A composite material, combining a ceramic (inorganic) and a polymer (organic).

What happens to bones deficient in calcium salts?

They become flexible and can bend easily.

What does the protein component of bone provide?

It provides tensile strength; without it, bones would be brittle.

How does the ratio of minerals to collagen vary?

It varies in different parts of the skeleton in response to tension and compression

What are the onion-like concentric structures in compact bone called?

Lamellae arranged around a central canal and connected to each other by canaliculi

What is an osteon?

The structural unit of compact bone, consisting of a central canal surrounded by concentric lamellae.

Describe perforating (Volkmann) canals.

They are channels that connect the blood supply and nerves from periosteum into central canal

How are collagen fibers arranged in the bone matrix?

They are helical arrangements in a screw-like (corkscrew) formation that enhances bone strength

How do nutrients and waste enter and leave bone?

Cytoplasmic processes of osteocytes that maintains a two-way form between the central canal and the outermost cells of osteon

What are circumferential lamellae?

Inner and outermost boundaries of dense bone that run parallel to bone, providing structural support.

What are interstitial lamellae?

Remnants of old osteons found between newer osteons with irregular regions

Spongy bone consists of a lattice of delicate slivers of bone called spicules and thins plates called ________; the term spongy refers to its appearance, not its hardness

Trabeculae

Spongy bone is covered with ______, and permeated by spaces filled with bone marrow

Endosteum

Central canals are not needed, why is this?

No osteocyte is very far from marrow

Spongy bone imparts _______ while adding a minimum of weight; its trabeculae are arranged alone the bone's lines of stress

Strength

Bone marrow is a general term for soft tissues that occupies he marrow cavity of a long bone, the spaces in spongy bone, and larger central canals; the two kinds are _____ marrow and _____ marrow

Red marrow; yellow marrow.

What does red bone marrow fill?

The marrow cavity

Red marrow is often termed ___________ tissue because it produces blood cells, but it is actually composed of multiple tissues and acts as an organ unto itself.

Hematopoietic

What happens to most red marrow in adults?

It turns into fatty yellow marrow.

What does yellow marrow no longer produces ________, although in cases of severe of chronic anemia it can do what?

Blood; it transforms back into red marrow and resumes hematopoietic function

Where is red marrow limited to in adults?

The axial skeleton and proximal ends of the humerus and femur.

What is osteogenesis?

The process of bone formation.

What are the two methods of bone development?

Intramembranous ossification and endochondral ossification.

What bones does intramembranous ossification produce?

Flat bones of the skull, clavicles, and some facial bones.

What are the four stages of intramembranous ossification?

1. Deposition of osteoid tissue into embryonic mesenchyme, 2. Calcification of osteoid tissue and entrapment of osteocytes, 3. Honeycomb of spongy bone with developing periosteum, 4. Filling of space to form compact bone at surfaces, leaving spongy bone in middle

What is endochondral ossification?

A process where bone develops by replacing hyaline cartilage.

What are the six stages of endochondral ossification?

1. Early cartilage model, 2. Formation of primary ossification center, bony collar, and periosteum, 3. Vascular invasion, formation of primary marrow cavity, and appearance of secondary ossification center, 4. Bone at birth, with enlarged primary cavity and appearance of secondary marrow cavity in on epiphysis, 5. Bone of child, with epiphyseal plate at distal end, 6. Adult bone with a single marrow cavity and closed epiphyseal plate

What does the epiphyseal plate consist of?

Hyaline cartilage in the middle, with a transitional zone on each side

What is the transitional zone facing the marrow cavity called?

Metaphyses

Cartilage converts to bone in a five-stage process.

1. Zone of reserve cartilage, 2. Zone of cell proliferation, 3. Zone of cell hypertrophy, 4. Zone of calcification, 5. Zone of bone deposition

The growth of cartilage from within the metaphyses is called ________ growth; _______ can result from a failure of cartilage to grow in the long bones

Interstitial; dwarfism

What happens when all the cartilage is depleted?

Growth stops and the epiphyseal plate becomes an epiphyseal line.

What is appositional growth?

The process of bones growing in diameter and thickness; it deposits new tissue at the surface

Appositional growth is similar to intramembranous ossification; how so?

Osteoblasts in periosteum deposit osteoid tissue on bone surface, calcify it, and become osteocytes

They lay down matrix in layers parallel to the surface, not in cylindrical osteons; this process produces ________________ lamellae.

Circumferential

What happens to the marrow cavity as a bone increases in diameter?

It widens

Bones are continually remodeled throughout life by the ______ of old bone and _______ of new, replacing about _____ of skeletal tissue per year

Absorption; deposition; 10%

What does Wolff's law of bone state?

Architecture of bone is determined by mechanical stresses placed on it, then adapts to withstand them

Bone remodeling results from the action of what?

Osteoblasts and osteoclasts

What is mineral deposition?

A crystallization process where calcium and phosphate ions are taken from blood plasma and deposited in bone tissue, mainly as crystals and hydroxyapatite

How does mineral deposition happen?

Osteoblasts lays down collagen fibers in the osteon, then the fibers become encrusted with minerals tat harden the bone matrix; the first few hydroxyapatite act ass seed crystals that attract more calcium and phosphate

What is ectopic ossification?

The abnormal calcification of bone in non-skeletal tissues.

What is arteriosclerosis?

The thickening and hardening of arterial walls (calcification)

What is a calculus?

A calcified mass in an otherwise soft organ

What is mineral resorption?

The process of dissolving bone tissue to release minerals into the bloodstream.

How does mineral resorption happen?

It releases minerals into the blood, carried out by osteoclasts, pump hydrogen to extracellular fluid, hydrochloric acid dissolve bone materials

What does calcitonin do?

It lowers blood calcium levels by inhibiting osteoclast activity and stimulating osteoblasts

What does parathyroid hormone do?

It increases blood calcium by stimulating osteoclast population and bone resorption; also promotes calcium reabsorption by kidneys, promotes calcitriol synthesis, and inhibits osteoblasts (bone deposition)

What causes a stress fracture?

Repeated stress or overuse of a bone, or abnormal trauma to bone

What is a pathologic fracture and what is it due to?

A fracture that occurs in a bone weakened by disease.

What are the four stages of fracture healing, and how long do they take to heal?

1. Hematoma formation; 2. Soft callus formation; 3. Bony callus formation; 4. Bone remodeling; it takes 8-12 weeks

What does treatment of fractures involve?

Reducing the alignment of broken bones and immobilizing the bone during healing.

How are bone fragments manipulated in closed reduction?

They are realigned without surgical intervention.

What happens to the bone in an open reduction?

Surgical intervention is used to realign the bone fragments.

What does a cast do?

It immobilizes the bone to allow for proper healing.

What is the most common bone disorder?

Osteoporosis.