Chapter 7- Skeletal System: Bone Structure And Function

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Spongy bone

Back 1

One type of osseous tissue inside of bones that resembles a sponge or a honeycomb with spaces containing bone marrow or fat.
Found in ends of long bones. Function: produce red blood cells

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Compact bone

Back 2

Another type of osseous tissue inside bones that is very dense. Function: support, protect organs, provide levers for movement, and store calcium.

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Function of Bone

Back 3

Support, protection, movement, produce red blood cells (hematopoiesis), storage (mostly calcium)

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3 Types of Cartilage, Functions, and Locations

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1. Elastic- Function: springy and flexible, tolerate bending. Location: Ear, epiglottis, eustachian tube (connects middle ear with throat)

2. Fibrocartilage/fibrous- Function: resists compression and tension. Location: menisci in knees, intervertebral discs, pubic symphysis

3. Hyaline- Function: resist repetitive stress, most abundant. Location: in articular cartilage, trachea, bronchi, larynx, connects ribs to the sternum, nose, embryonic skeleton

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4 types of bone

Back 5

flat, irregular, long, and short

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Basic Structural Components of Long Bones

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Epiphysis (ends)

Diaphysis (body)

Medullary cavity (center)

Periosteum (outer layer)

Endosteum (inner layer)

Articular cartilge (on epiphysis)

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2 Types of Bone Marrow, Functions, Locations

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1. Red- Function: produces red blood cells, white blood cells and platelets. Location: Epiphysis (ends of bones)

2. Yellow- Function: Produces fat, cartilage, and bone. Location: Medullary cavity.

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Bone Marrow Transplants

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Red bone marrow transplants can occur between matched donor and recipient. Done by injecting harvested cells into bloodstream of recipient.

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4 Types of Bone Cells and Functions

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1. Osteocytes: lies within the substance of fully formed bone

2. Osteoblasts: bone-forming cells

3. Osteoclasts: bone-reabsorbing/shaping cells

4. Osteoprogenitor cells: cells that aid in repair of fractures, produce osteoblasts.

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Bone Matrix Formation

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Formation begins with secretion of osteoid and calcification. Process requires Vitamin D for calcium to form GI. Requires Vitamin C for collagen.

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Osteitis deformens

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Disruption between osteoclasts and osteoblasts functions. Excessive bone reabsorption/bone disruption effected by excessive bone deposition.

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Bone Reabsorption

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Proteolytic enzymes released from lysosomes wihtin osteoclasts. Calcium and phosphate dissolved by HCl. May occur when blood calcium levels are low.

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Components of Osteon

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Central canal, caniliculi, calunae, lamellae, perforating (Volkmann's) canals

Function:basic functional and structural unit of mature compact bone

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Structure of Hyaline Cartilage

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Chondroblasts-cells that form matrix

Chondrocytes-mature cells

No calcium present in matrix.

Blood supply in mature tissue is avascular (lack of blood vessels)

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Interstitial Growth

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within internal regions of cartilage (inside cartilage)

1. Chondrocyte in lacuna exhibits mitotic activity (gets ready to divide)

2. Two cells (now called chondroblasts) produced by mitosis from chondrocyte

3. Each cell makes new matrix and begins to separate from neighbor. Cells now called chondrocytes.

4. Cartilage continues to grow interally.

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Appositional Growth

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on cartilage outside edge

1. Mitotic activity in stem cells in perichondrium (cells on outside of cartilage getting ready to divide)

2. New cells formed. Chondroblasts produce new matrix.

3. Chondroblasts then push apart and become chondrocytes. Chondrocytes continue to produce more matrix at the periphery (make more cells on outside).

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2 Effects of Aging on Bones

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1. Decreased tensile strength (reduced rate of protein synthesis, amount of inorganic material increases, brittle bones that break easily)

2. Bone loss of calcium & other materials

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Determination of Age from Skeleton

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Determine age at death by the oldest complete union (all aspects of epiphysis are united to rest of bone) and the youngest open center (no bony fusion or union between the epiphysis and other bone end).

Age of skeleton = older than older than oldest union but younger than youngest open center.

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Osteopenia

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Osteoblast activity declining; osteoclast activity at previous levels.

Vertebrae, jaw bones, epiphyses losing large amount of mass.

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Osteoporosis

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Reduced bone mass sufficient to compromise normal function.

Occurs in significant percentage of older women.

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Bone Formation

Back 21

Ossification.

2 types: Intramembranous ossification and endochondral ossification

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Intramembranous Ossification

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Bones formed = flat bones of skull & some facial bones, central part of clavicle

Steps:

1. Ossification centers (osteoprogenitor and osteoblasts)

2. Calcification of osteoid (entrapped become osteocytes)

3. Woven bone & periosteum (primary bone)

4. Lamellar bone (secondary bone)

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Endochondral Ossification

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Bones formed = bones of upper and lower limbs, pelvis, vertebrae, ends of clavicle

Steps:

1. Begins with hyaline cartilage model

2. Cartilage calcifies and periosteal bone collar develops

3. Primary ossification center forms

4. Secondary ossification center forms in epiphyses (hyaline cart. calcifies and degenerates, blood vessels and osteoprogenitor cells enter)

5. Bone replaces cartilage (not articular or epiphyseal plates)

6. Epiphyseal plates ossify and form lines

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Bone Remodeling

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The continual process of bone deposition and resportion.
Varies in different bones and different parts of same bones (ex = distal part of femur replaced 4-6 months, while diaphysis of femur never completely replaced over lifetime).

Mechanical stress- needed for normal bone remodeling. Causes osteoblasts to increase synthesis of osteoids, which increases bone strength and bone mass.

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Hormones that influence bone growth

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Growth hormone (stimulates liver to produce somatomedian)

Thyroid hormone (influences metabolic rate of bone cells, regulates normal activity at epiphyseal plates)
Somatomedian (stimulates growth of cartilage in epiphyseal plate)
Estrogen & testosterone (increase rate of cartilage and bone formation in epiphyseal plates)
Glucocorticoids (high amounts will increase bone loss, impare growth at ep. plate)
Serotonin (helps rate and regulation of normal bone remodeling)

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Regulating Blood Calcium Levels

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Essential. Calcium required for initiating muscle contraction, exocytosis of molecules from cells, stimulation of heart, blood clotting.

2 primary hormones that regulate blood calcium: Calcitriol & Parathyroid

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Activation of Vitamin D to Calcitriol

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1. UV light converts a molecule in blood to vitamin D3

2. Vitamin D3 circulates through body (converted to calcidiol by liver enzymes)

3. Calcidiol circulates in blood (converted to calictriol by kidney, more parathyroid hormone [PTH] present = more calictriol formed)

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Calcitriol + PTH Function Together to Regulate Blood Calcium Levels

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PTH secreted in and released by parathyroid glands in response to low blood calcium levels.

Calcitriol formed more readily in presence of PTH.

Both increase blood calcium levels by increasing osteoclast activity and resorbing bone matrix to release calcium from bone. Also work on kidney to excrete less calcium in urine.

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Calcitonin

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Aids in regulating blood calcium levels (not as important as PTH and calcitriol).

Inhibits osteoclast acitivity to prevent calcium to be released from bone into blood, stimulates kindeys to increase loss of calcium in urine.

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Types of Fractures

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1. Stress: think break caused by increased physical activity or experiencing repetitive loads

2. Simple: crack/break in bone, but no separation

3. Compound: complete break and separation in bone

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4 Steps Fractures Heal

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1. Fracture hematoma forms from clotted blood.

2. Fibrocartilaginous callus forms

3. Hard (bony) callus forms

4. Bone is remolded