Chapter 6: The Skeletal System

Front 1

What are the functions of the skeletal system?

Back 1

- Framework

- Support

- Protection

- Movement - bones act like levers for muscles to use

- Hematopoiesis (formation of red blood cells)

- RBC's, WBC's, platelets

- Mineral Storage

Front 2

Cartilage

Back 2

- Made up of chondrocytes

- Has a flexible matrix

- Undergoes mitosis

- Is used as the tissue on which the embryonic skeleton develops

Front 3

Picture of cartilage types on the skeleton

Back 3

Front 4

What is bone classification based on?

Back 4

Location: - axial skeleton (skull, ribs, spine)

- Appendicular skeleton (long bones of upper and lower limbs, hips, hands, feet)

Bone shapes:

- Long bone (humerus, i.e.)

- Irregular bone (vertebra, i.e.)

- Flat bone (sternum, i.e.)

- Short bone (talus, tarsals, carpals, etc.)

Front 5

Bone structure - what is bone tissue and what are the types of bone cells?

Back 5

Bone tissue (Osseous tissue) is connective tissue

Types of Bone cells:

-Osteogenic stem cell

-Osteoblast

-Osteocyte

-Osteoclast

Front 6

Osteogenic stem cell (pic)

Back 6

Front 7

What cell is this a picture of? What is its function?

Back 7

Osteoblast

- matrix-synthesizing cell responsible for bone growth

- young cell that produces osteoid

Front 8

What cell is this a picture of? What is its function?

Back 8

Osteocyte

- mature bone cell that monitors and maintains the mineralized bone matrix

Front 9

What cell is this a picture of? What is its function?

Back 9

Osteoclast

- bone-resorbing cell

- breaks down the bone; important for bone remodeling

Front 10

What are the bone types? (textures)

Back 10

1) Compact bone (lamellar)

- dense outer layer

2) Spongy (cancellous) bone

- honeycomb of trabeculae

Front 11

spongy and compact bone picture

Back 11

Front 12

What are the different membranes of the bone?

Back 12

1) Periosteum

- a dense layer of vascular connective tissue enveloping the bones EXCEPT at the surfaces of the joints.

2) Endosteum

- a thin vascular membrane of connective tissue that lines the surface of the bony tissue that forms the medullary cavity of long bones

- AKA lines the hollow tube of a long bone

Front 13

What is the structure of short, flat, and irregular bones?

Back 13

- Consist of thin plates of periosteum covered compact bone

- spongy bone is sandwiched between the 2 layers of compact bone

- the layer of spongy bone is called "Diploe"

- the bone marrow is contained in between the trabecula cavities

Front 14

Structure of flat bone (PIC)

Back 14

Front 15

Endosteum and Periosteum pic

Back 15

Front 16

Structure of a long bone (PIC)

Back 16

Front 17

What is the Diaphysis?

Back 17

Diaphysis: the shaft of the bone (long bone)

- thick collar of compact bone on the periphery encircling spongy bone on the inside

- covered with periosteum

- Medullary cavity: hollow central part, filled with bone marrow

Front 18

What is the Epiphysis?

Back 18

Epiphysis: are the bone ends

- areaswhere the bone makes a joint

- Covered with articular cartilage

Front 19

Histology of compact bone (PIC)

Back 19

Front 20

Slide of compact bone tissue (PIC)

Back 20

Front 21

What gives bones the hard consistency and flexibility?

Back 21

Hard consistency - calcium

Flexibility - collagen

Front 22

What is the chemical composition of bone?

Back 22

Organic components: all the bone cells;

- Osteoid: ground substance and collagen fibers

Inorganic components: 65% bone mass

- hydroxyapatites (hydroxyapatite crystals)

- largely calcium phosphate salts

- contribute to the exceptional hardness of bones

Front 23

What is the process of bone formation called?

Back 23

Osteogenesis or Ossification

Depending on the particular stage of life it is described as:

- Bone formation

- Bone growth

- Bone remodeling

Front 24

What are the processes of bone formation in the developing embryo and fetus?

Back 24

1) Endochondral ossification

- Cartilage model - long bones made this way

2) Membranous ossification

- Membranous tissue - flat bones

- Both begin around 2nd month of gestation*

Front 25

What are the steps to Endochondral Ossification? (How are long bones made?)

Back 25

1) Bone collar forms around diaphysis of the hyaline cartilage model

2) Cartilage in center of the diaphysis calcifies and develops cavities

3) The periosteal bud invades the internal cavities and spongy bone forms

4) The diaphysis elongates and a medullary cavity forms. Secondary ossification centers appear in the epiphyses (at birth)
5) The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages (childhood to adolescence)

Front 26

Endochondral ossification (PIC)

Back 26

Front 27

What are the steps of Intramembranous Ossification?

Back 27

1) Ossification centers appears in the fibrous connective tissue membrane

2) Osteoid is secreted w/in the fibrous membrane and calcifies

3) Woven bone and periosteum form

4) Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears

Front 28

Which type of ossification is this?

What is occurring?

Back 28

Endochondral ossification

- bone collar is forming around the diaphysis of the hyaline cartilage model

Front 29

Which type of ossification is this?

What is occurring?

Back 29

Endochondral ossification

- cartilage in the center of the diaphysis calcifies and then develops cavities

Front 30

Which type of ossification is this?

What is occurring?

Back 30

Endochondral ossification

- the periosteal bud is invading the internal cavities and spongy bone forms

Front 31

Which type of ossification is this?

What is occurring?

Back 31

Endochondral ossification

- the diaphysis elongates and a medullary cavity forms. Secondary ossification centers appear in the epiphyses

Front 32

Which type of ossification is this?

What is occurring?

Back 32

Endochondral ossification

- The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages

Front 33

Which type of ossification is this?

What is occurring?

Back 33

Intramembranous ossification

Ossification centers appear in the fibrous connective tissue membrane

- selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center that produces the first trabeculae of spongy bone

Front 34

Which type of ossification is this?

What is occurring?

Back 34

Intramembranous ossification

Osteoid is secreted within the fibrous membrane and calcifies

- Osteoblasts begin to secrete osteoid, which calcifies in a few days.

- trapped osteoblasts become osteocytes

Front 35

Which type of ossification is this?

What is occurring?

Back 35

Intramembranous ossification

Woven bone and periosteum form

- Accumulating osteoid is laid down between embryonic blood vessels in a manner that results in a network (instead of concentric lamellae) of trabeculae called woven bone.

- Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum

Front 36

Which type of ossification is this?

What is occurring?

Back 36

Intramembranous ossification

Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears

- trabeculae just deep to the periosteum thicken. Mature lamellar bone replaces them, forming compact bone plates.

- Spongy bone (diploe), consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow

Front 37

What are facts about postnatal bone growth?

Back 37

1) Growth in length is obtained by interstitial bone growth of the epiphyseal plates cartilage

2) Bone cells replace cartilage

3) Growth in thickness occurs by Appositional bone growth

Front 38

Bone growth picture/diagram

Back 38

Front 39

What is bone growth in width called and how does it occur?

Back 39

Appositional bone growth

- osteoblasts on the external bone surface lay osteoid and cause an increase in the bone diameter

Front 40

Appositional bone growth pic

Back 40

Front 41

What is bone remodeling?

Back 41

Bone remodeling: the ongoing bone deposition and bone resorption

- in healthy adults, bone mass remains the same

- it is coupled and coordinated by "packets" of adjacent osteoblasts and osteoclasts called "remodeling units"

Front 42

What controls bone remodeling?

Back 42

growth hormone (HGH)

thyroid hormone

parathyroid hormone

sex hormones

calcium

vitamin D

Front 43

Picture comparing bone growth and bone remodeling

Back 43

Front 44

What are the hormonal controls of bone remodeling?

Back 44

Normal blood calcium level: 9-11mg/100ml blood

Daily calcium reqt (birth-10yr): 400-800mg

(adult) : 1200-1500mg

Key hormones involved: parathyroid & calcitonin

Front 45

How do the hormonal controls of blood calcium work?

Back 45

Negative feedback mechanism, primarily controlled by parathyroid hormone (PTH)

1) drop in blood calcium level

2) Parathyroid glands release PTH

3) PTH stimulates osteoclasts to degrade bone matrix and release calcium

4) rise in blood calcium

Front 46

Hormonal controls of blood calcium (diagram)

Back 46

Front 47

How do bones respond to mechanical stress?

Back 47

Wolff's Law: a bone grows or remodels in response to forces or demands placed upon it

Front 48

What are some observations that support Wolff's Law?

Back 48

1) Handedness (right or left) results in bone of dominant arm being thicker and stronger

2) Curved bones are thickest where they are most likely to buckle

3) Trabeculae form along lines of stress

4) Large, bony projections occur where heavy, active muscles attach

Front 49

What factors aside from mechanical stress affect bone growth?

Back 49

1) Growth hormone

2) Thyroid hormones

3) Testosterone and estrogens

Front 50

What is the role of vitamins in bone formation?

Back 50

Vitamin A - important in growth and bone health

Vitamin C - help collagen synthesis

Vitamin D - helps body absorb calcium

Front 51

What are some examples of bone diseases?

Back 51

- Rickets

- Osteomalacia

- Osteoporosis

Front 52

What is Rickets disease?

Back 52

- A nutritional disorder that can develop from lack of vitamin D, calcium, or phosphate

- Rickets leads to poor functioning of a bone’s growth plate (growing edge), softened and weakened bones, stunted growth, and, in severe cases, skeletal deformities.

Front 53

What is Osteomalacia?

Back 53

- a softening of the bones usually due to lack of vitamin D

- soft bones are more likely to bow or fracture

Front 54

What is osteoporosis?

Back 54

- a medical condition in which the bones become brittle and fragile from loss of tissue, typically as a result of hormonal changes, or deficiency of calcium or vitamin D

Front 55

How are fractures described?

Back 55

1) Location

2) External appearance

3) nature of the break

Front 56

What are bone fractures classified due to?

Back 56

1) Position of bone ends after fracture

- aligned, non-aligned

2) Completeness of break

- complete, incomplete, multiple breaks

3) Orientation of break to long axis of bone

4) Whether or not bone ends penetrate skin

- open or closed

Front 57

What are the main stages in the healing of fractures?

Back 57

1) Hematoma formation

2) Fibro cartilaginous callus formation (soft callus)

3) Hard callus formation

4) Bone remodeling

Front 58

How does hematoma formation occur?

Back 58

1) Blood vessels are broken

2) Blood escapes

3) Blood collects

4) Swelling occurs

Front 59

What is occurring here?

Back 59

This is the healing after a fracture

- the fibrocartilaginous callus is forming

(soft callus formation)

Front 60

What is occurring here?

Back 60

Healing process after a fracture

- hematoma formation

Front 61

What is occurring here?

Back 61

Healing process after a fracture

- hard callus formation

Front 62

The healing of a fracture (picture)

Back 62

Front 63

What are common types of fractures?

Back 63

1) Comminuted

2) Compression

3) Spiral

4) Epiphyseal

5) Depressed

6) Greenstick

Front 64

What is a comminuted fracture?

Back 64

- bone fragments into 3 or more pieces

- more common in older persons whose bones are more brittle

Front 65

What is a compression fracture?

Back 65

- bone is crushed

- common in porous bones subjected to extreme trauma, such as in a fall

(vertebra for example)

Front 66

What is a spiral fracture?

Back 66

- Ragged break occurs when excessive twisting forces are applied to a bone

- common sports fracture

Front 67

What is an epiphyseal fracture?

Back 67

- Epiphysis separates from the diaphysis along the epiphyseal plate

- tends to occur where cartilage cells are dying and calcification of the matrix is occurring

Front 68

What is a Depressed fracture?

Back 68

- broken bone portion is pressed inward

- typical of skull fracture

Front 69

What is a greenstick fracture?

Back 69

- bone breaks incompletely similar to how a green twig would break

- common in children whose bones have relatively more organic matrix and are more flexible than the bones in adults