Chapter 4: Skeletal

Skeletal

Osseous tissue is made of what type of tissue?

Connective

Functions of bones

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

outer covering consisting of fibrous CT and a layer of bone-forming cells, attaches to cartilage.

Periosteum

Dense layer of osseous tissue that makes up the outer portion of a bone.

Compact bone

porous bone often found at ends of long bones and within flat bones. Always surrounded by compact bone

spongy bone

 inner compartment that contains bone marrow

Marrow cavity

soft tissue composed of adipose tissue (YELLOW MARROW) and/or  RED MARROW (HEMATOPOIETIC TISSUE that is responsible for blood cell formation). Red marrow decreases with age

Bone marrow

Yellow marrow tissue

adipose

Red marrow tissue

Hematopoietic

thin layer of reticular CT that lines the marrow cavity. Also contains OSTEOGENIC cells

endosteum

main shaft of a bone where many muscles attach

Diaphysis

end of a bone that articulates with other bones to form  a joint

Epiphysis

layer of hyaline cartilage that separates the epiphysis from the diaphysis. In children and adolescents, this is the zone of dividing cells that allows bones to grow longer (a.k.a, “growth plate”).

Epiphyseal plate or line

Perforating holes that allow blood vessels to enter the bone and transport nutrients and waste

Nutrient Foramina

Since bone is connective tissue, it contains

cells, fiber, ground substance

undifferentiated cells that will mature and become osteoblasts. Found in endosteum and periosteum

Osteogenic cells

undifferentiated cells that will mature and become osteoblasts. Found in endosteum and periosteum

Osteoblasts

These are “retired” osteoblasts that live in LACUNAE

* Communicate via GAP JUNCTIONS
* Can “sense” mechanical stress
* Small ability to deposit or resorb bone

Osteocytes

large multi-nucleated cells whose job is to dissolve bone. Similar origin as macrophages (blood derived)

Osteoclasts

 non-cellular, ground substance of osseous tissue

bone matrix

Bone cell types

Osteogenetic cells, osteoblasts, osteocytes, osteoclasts

Bone matrix is made of

Organic protein matter and inorganic matter

Organic protein matter is mainly made of

collagen

organic protein matter makes up ___ of the bone matrix

1/3

inorganic matter makes up ___ of the bone matrix

2/3

Inorganic matter of the bone matrix is made of

Hydroxyapatite and calcium carbonate

2 or more structural componants are called

a composite

inorganic matter gives bones

strength and rigidity

organic matter gives bones

flexibility

brittle bones

osteogenesis

too soft

osteomalcia or rickets

central canal surrounded by circular layers of bone matrix

Osteon

 circular layers of bone matrix surrounding a central canal

lamellae

runs the length of a bone and contain blood vessels and nerves

Haversian canal

 cavities which contain osteocytes

Lacunae

 tiny ducts between lacunae and allow osteocytes to communicate via gap junctions

Canaliculi

allows communication between central canals and/or nutrient foramina

Volkman’s Canal

a meshwork of thin rods and plates of osseous tissue (TRABECULAE)

spongy bone

Types of bone marrow

Red and yellow

Red marrow is found in what parts of the body?

pelvis, skull, ribs, heads of femur and humerus

Red bone marrow does what with age?

disappears

Yellow bone marrow is found in

Adipose tissue

Red marrow turns into

yellow marrow

Red bone marrow function

blood formation

Red marrow is what type of tissue?

Hematopoietic

Where the lacunae of the cartilage grow larger and become calcified (hardened)

Primary ossification center

Blood vessels enter the primary ossification center, then

 osteoblasts convert hyaline cartilage to osseous tissue, chondrocytes proliferate

convert hyaline cartilage to osseous tissue

osteoblasts

secondary ossification centers

blood vessels invade the epiphyses of the bone creating

secondary ossification centers eventually hollow out into

secondary marrow cavities

secondary marrow cavities fill with

spongy bone

Epiphyseal Plate is between

primary and secondary marrow cavities

this is on the surface of the ends of you bones

articular cartilage

How does bone grow with endochondrial ossification?

Length

Bone elongation steps:

1. Chondrocytes of the hyaline cartilage in the epiphyseal plate grow larger and multiply

2. As cartilage layer expands, the cartilage at the upper and lower edges of the epiphyseal plate becomes ossified

3. Process of expansion/ossification at the metaphysis repeats over and over, thereby extending the length of the bon

Growing pains are

the epiphyseal plate expanding faster than the periosteum muscle covering

Hyaline Cartilage is precursor to

osseous bone tissue

The widening and thickening of bone is called

appositional growth

appositional growth

A thin layer of osteoblasts (the bone forming cells) resides on the inner surface of the periosteum. As the osteoblasts lay down more and more osseous tissue, making the bone thicker and wider, osteoclasts come behind from inside the marrow cavity and dissolve some of that bone allowing the marrow cavity to grow as well

Appositional growth results in

production of circumferential lamellae

How many bones to infants have?

270

soft spaces between the skull in infants are called

fontanelles

Fontanelles grow together, now called

cranial sutures

Fontanelles allow

brain to grow fast than body

Mandible is two seperate bones fused along midline, ossified cartilage is called the

mandibular symphysis

Pelvis consists of

2 ox coxae

1 os coxae

fused pubis, ilium, ischium

Everyday bone remodeling repairs

microfractures

Forces that develop bone features

pulling and compression

Pulling forces stimulate

osteoblast activity

Contractile forces stimulate

osteoclast activity

Bone remodeling is important for

mineral release and absorption into bloodstream

Bone remodeling maintains what chemical levels?

calcium and phosphate

Wolff’s Law

bone architecture is determined by mechanical stresses placed on it

Bones increase in density when

mechanical stress is placed on them

Stress lines

trabeculae of spongy bone will increase in density and orient themselves to accommodate increased mechanical stress

When does bone remodeling happen?

Throughout life

Osteoblasts __ bone matrix

synthesizes

Osteoclasts __ bone matrix

dissolve

Creating more bone is called

bone deposition

Removing bone tissue is called

bone resorption

Osteoclast dissolve, increasing what levels

Ca2+

What secretions help break down osseous tissue?

HCl and collagenase

Bone repairs in

8-12 weeks

Blood clot =

Hematoma

Fracture Repair Steps

Hematoma formation and granulation, soft callus formation, hard callus formation, remodeling.

Bone and blood vessels are severed, blood clots around site.

Fibroblasts, osteogenic cells, and blood vessels invade the area creating a soft mass of tissue called GRANULATION TISSUE

Hematoma formation and granulation

Fibroblasts deposit collagen that creates a fibrous patch around the fracture

Soft Callus formation

Osteoblasts lay down a collar of new bone surrounding the fracture called a HARD CALLUS.

The hard callus is the body’s version of a cast that keeps the pieces of bone properly aligned during healing.

At this point the fracture is still fragile and can be re-broken quite easily.

Hard Callus formation

Remodeling

 process by which the broken pieces of bone are remodeled and gaps between bone pieces are filled.

Osteoclasts remove small fragments of broken bone and smooth jagged edges.

Osteoblasts enter and lay down a layer of spongy bone to close any gaps (prevents bones from shortening after a fracture)

Spongy bone transitions to compact bone and fracture site is often nearly undetectable

Fibroblasts, osteogenic cells, and blood vessels invade the area creating a soft mass of

Granulation tissue

 fibrous patch around the fracture is a

soft callus

osteoblasts lay down collar of new bone called

hard callus

Osteoporosis

Disease in which bones become less dense, very brittle and susceptible to fracture

Osteoporosis literally means

porous bones

What is decreased in Osteoporosis?

Bone mineral density

This is affected most when you have osteoporosis

spongy bone

Risk factors for osteoporosis

Females, Asian or Caucasian, low estrogen levels, poor diet, smoking, sedentary lifestyle, taking glucocorticoids.

Treatments for osteoporosis

Activity, resistance training, diet, supplements, medications to inhibit osteoclast activity,

abnormal bone formation due to lack of Vitamin D, calcitriol, or calcium/phosphate. Weight bearing bones such as the femur often bow in/out due to softness of bone

Rickets