Chapter 6- Bone Tissue

6 important functions of the skeletal system

1. Provide support by acting as a structural framework and a point of attachment for tendons and ligaments

2. Protect the internal organs (brain, chest, etc.)

3. Assist body movements (in conjunction with muscles)

4. Store and release salts of calcium and phosphorus

5. Participate in blood cell production (hemopoiesis)

6. Store triglycerides in adipose cells of yellow marrow

dynamic tissue

always remodeling (building up or breaking down)

vascularized

blood supply

Compact bone

-Protection and support

- It forms the dialysis of long bones, and the external layer of all bones

Spongy bone

-Light weight and provides tissue support

-It forms much of the epiphysis and the internal cavity of long bones

Diaphysis

Shaft of the long bone

Articular cartilage

Thin layer of hyaline cartilage covering the epiphysis of long bones

Location of articular cartilage

articular joint surface where two bones move against each other

Purpose of articular cartilage

protection

Periosteum

A tough outer sheath of dense, irregular connective tissue and an inner osteogenic (bone stem cells) layer

-Attached to the bone by Sharpey's fibers

Sharpeys fibers

Like velco

-stick to the bone

Purpose of periosteum

Fracture repair and as attachment points for tendons and ligaments

Diaphysis

The shaft of body of a long bone

Epiphyses

Form the distal and proximal ends of the long bone

Metaphyses

The areas where the epiphyses and diaphysis join

Medullary cavity

A space within the diaphysis of long bones that contains fatty yellow bone marrows in adults

Endosteum

membrane that lines the medullary cavity

Organic constituents

Collagen fibers provide flexibility and tensile strength

Inorganic hydroxyapatite crystals

Mineral salts

Osteogenic cell

Develops into an osteoblast

Osteoblast

Forms bone extracelluar matric

Osteocyte

Maintains bone tissue

Osteoclast

Functions in resorption, the breakdown of bone extracellular matrix

Osteons

The circle thing in compact bone

Concentric lamellae

rings of calcified matrix

Interstitial lamellae

Between osteons are left over fragments of older osteons

Outer circumferential lamellae

Encircle the bone beneath the periosteum

Inner circumferential lamellae

Encircle the medullary cavity

Lacunae

Small spaces between the lamellae which house osteocytes that nourish the mature bone tissue from the blood circulating through the trabeculae

Canaliculi

Small chancels filled with extravellular fluid connecting the lacunae

Central canal

Blood and lymphstic vessels are found here

Perforating (Volkmann's) canals

allow tranist of these vessels to the outer cortex of the bone

Spongy bone lacks

Osteons

Trabeculae

lamellae are arranged in a lattice of thin columns

Purpose of spongy bone

-trabeculae support and protect red bone marrow

-are oriented along lines of stress (to help resist stresses without breaking)

Interior of long bones is made up

primarily of spongy bone

-lessens overall bone weight

Periosteal arteries

Accompanied by nerves- enter the diaphysis through Volkmann's canal.

Nutrient artery

Enters the center of the diaphysis though a nutrient foramen

Nutrient veins

exit through the nutrient foramen

Ossification (osteogenesis)

the process of bone formation

Ossification occurs in these 4 situations

-During embryological and fetal development

-Growth of bones until adulthood

-Remodeling of bone (throughout life)

-Repair of fractures

Intra-membranous ossification

produces spongy bone.

-subsequently be remodeled to form compact bone

-Flat bones of the skull, mandible and clavicle

Endochondral ossification

A process whereby cartilage is replaced by bone

Forms both compact and spongy bone

-The method used in the formation of most bones, especially long bones

-Replacement of cartilage by bone

-One primary and two secondary centers of growth

What is intra-membranous ossification formed from?

Mesenchymal cells- without going through a cartilage stage

Step 1 of intra-membranous ossification

Development of ossification center: osteoblasts secrete organic extracellular matrix

Step 2 of intra-membranous ossification

Calcification: calcium and other mineral salts are deposited and extracellular matrix calcifies (hardens)

Step 3 of intra-membranous ossification

Formation of trabeculae: extracellular matrix develops into trabeculae that fuse to form spongy bone

Step 4 of intra-membranous ossification

Development of the periosteum: mesenchyme at the periphery of the bone develops into the periosteum

Stage 1 of endochondral ossification

Development of cartilage model: mesencymal cells develop into chondroblasts, which form the cartilage model

Stage 2 of endochondral ossification

Growth of cartilage model: growth occurs by cell division of chondrocytes

Stage 3 of endochondral ossification

Development of primary ossification center: in this region of the diaphysis, bone tissue replaced most of the cartliage

Stage 4 of endochondral ossification

Development of the medullary (marrow) cavity: bone breakdown by osteoclasts forms the medullary cavity

Stage 5 of endochondral ossification

Development of secondart ossifcation centers: these occur in the epiphyses of the bone

Stage 6 of endochondral ossification

Formation of articular cartilage and epiphyseal plate: both structures consist of hyaline cartilage

epiphyseal growth plate

the epiphysis of long bones contains hyaline cartilage and forms this

When is ossifcation contributing to bone length usually complete by?

18-21 years of age

Human Growth Hormone (HGH)

Anabolic hormone.

-Stimulate bone growth, muscle growth, loss of fat and increase glucose output in the liver

Normal bone metabolism depends on several factors

1. Minerals

2. Vitamins

3. Hormones

Minerals

Essential component

-Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling

Vitamins

necessary for normal bone metabolism

Vitamin A

Stimulates activity of osteoblasts

Vitamin C

Needed for synthesis of collagen

Vitamin D

Essential to health bones because it promotes the absorption of calcium from foods in the gastrointestinal tract into the blood

Vitamins K and B12

Needed for synthesis of bone proteins

Growth hormone (GH)

secrete by the anterior lobe of the piturary gland; promtes general growth of all body tissue, including bone, mainly by stimulating production of insulin-like growth factors

Sex hormones

(estrogen and testosterone) cause a dramatic effect on bone growth, such as the sudden "growth spurt" that occurs during the teenage years.

The sex hormones also promote widening of the pelvis in the female skeleton.

They are (especially estrogen) also responsible for closing the epiphyseal plates at the end of puberty.

Parathyroid hormone (PTH)

Secreted by the parathyroid glands, promotes bone resorption by osteoclats, enhances recovery of calcium ions from urine; promotes formation of the active form of vitamin D

Calcitonin (CT)

Secreted by the thyroid gland; inhibits bone resorption by osteoclasts

Insulin

Secreted by the pancreas; promotes normal bone growth by increasing the synthesis of bone protein

Thyroid hormone

Secreted by thyroid gland; promote normal bone growth by stimulating osteoblasts

Fracture

break in the bone

Green stick fracture

like breaking a green twig- it cracked by not all the way through

-named by anatomical appearance

Impacted fracture

the distal part is shoved up into the proximal part

-named by anatomical appearance

Comminuted fracture

Bone is crushed or broken into pieces at the site of the impact

-named by anatomical appearance

Open (compound) fracture

One or bone boths are "open" to the outside.

-named by anatomical appearance

Closed (simple) fracture

One of both bones are closed, where the bone remains in the skin

Pathological fracture

chronis disease like osteoporsis or cancer weakens the bone

Compression fracture

Produced by extreme forced such as in trauma

Stress fracture

Produced from repeated strenuous activities such as running

Colles' fracture

fracture of the distal radius where the distal fragment is displaced posteriorly

Pott's fracture

fracture of the distal fibula with injury to the distal tibial articulation

The three phases of Fracture and repair of bone

1. The reactive phase

2. The reparative phase

3. Bone remodeling phase

The reactive phase

an early inflammatory phase which occurs 6-8 hours after injury, is the formation of a fracture hematoma as a result of blood vessels breaking in the periosteum and in osteons.

The reparative phase

involves the formation of a callus (takes a few weeks, to as many as six months).

Phagocytes remove cellular debris and fibroblasts deposit collagen to form a fibro- cartilaginous callus first which is followed by the second step of osteoblasts forming a bonycallus of spongy bone.

Bone remodeling phase

takes several months

Spongy bone is replaced by compact bone.

The fracture line disappears, but evidence of the break remains.

Two principal effects of aging on bone tissue

1. Loss of bone mass

2. Brittleness

Osteoporosis

a condition where bone resorption outpaces bone deposition.

Often due to depletion of calcium from the body or inadequate intake