Chapter 6

Name the tissues and organs that compose the skeletal system.

• Bone - osseous tissue forming whole bone + vessels + nerves

• Cartilage - embryonic forerunner of most bones and covering of many joint surfaces

• Ligaments - hold bone to bone at joint

  • Note: tendons - attach muscles to bone 

State several functions of the skeletal system.

• Support

• Movement

• Protection of delicate organs

• Blood formation in red bone marrow

Distinguish between bone as a tissue and as an organ.

• Osseous tissue is connective tissue with the matrix hardened by mineralization

Describe the general features of a long bone.

• Compact and spongy bone tissue

• Two epiphysis (heads) at the ends of diaphysis (shaft)

• Marrow (medullary) cavity

• Epiphyseal line: remnant of growth plate

• Periosteum covering

• Nutrient foramina

• Endosteum lining

• Articular cartilage: smooths joints

List and describe the cells, fibers, and ground substance of bone tissue.

• Osteogenic (osteoprogenitor) cells - osteoblast/osteocyte stem cells

• Osteoblasts - bone forming cells that become…

• Osteocytes - mature bone cells that sit in lacunae

• Osteoclasts - Derived from the fusion of multiple stem cells; Bone-dissolving macrophages (phagocytic cells)

State the functional importance of each constituent of bone tissue.

• Bone is a composite material—a combination of a ceramic and a polymer

• Hydroxyapatite and other minerals are the ceramic and collagen (protein) is the polymer

• Ceramic portion allows the bone to support body weight without sagging

• Rickets is a disease caused by mineral deficiency and resulting in soft, deformed bones

• Polymer (protein) gives some flexibility

• Osteogenesis imperfecta (brittle bone disease) results from a defect in collagen deposition

Compare the histology of the two types of bone tissue.

• Compact bone

  • Osteon - basic unit

  • Contains concentric lamellae (round circles like a dart bullseye board) with the central (Haversian) canal in center

  • Central canal contains vessels, nerves, lymphatics for compact bone

  • Perforating canals - Vessels, nerves, lymphatics shared with other osteons

  • Circumferential lamellae - Circles/fills-in around the most superficial part of compact bone

  • Lacunae - Small open space where osteocytes reside

  • Canaliculi - Small canals for sharing of nutrients among osteocytes in the lacunae

• Spongy (cancellous) bone

  • Trabeculae - thin plates of bones

  • Spicules - rods and spines of bone

  • Porous appearance

  • Spaces filled with red bone marrow

  • Lightweight but strong

Distinguish between two types of bone marrow.

• Red bone marrow (myeloid tissue)

  • Hematopoietic tissue (blood forming tissue) - both red and white blood cells are made here

• Yellow marrow

  • Mainly fat

Describe two mechanisms of bone formation.

• Ossification (osteogenesis) - bone formation

  • Begins with mesenchyme (an embryonic connective tissue)

• 2 methods of ossification:

  • Intramembranous

    • Produces flat bones of skull and most of clavicle

    • Bone develops in a fibrous sheet resembling the dermis in the fetus

  • Endochondral

    • Most bones develop this way

    • Bone develops from hyaline cartilage model in the fetus

Explain how a child grows in height.

• Changes in the growth plates in the long bones of their arms and legs via endochondral ossification

Explain how mature bone continues to grow and remodel itself.

• Ossification happens through appositional growth

• Appositional growth - growth in diameter and thickness

• Intramembranous ossification at surface

  • Osteoblasts in periosteum deposit matrix

  • Once matrix hardens, cells become osteocytes

  • Circumferential lamellae are formed

• Osteoclasts widen medullary cavity

Name and describe selected types of fractures.

• Stress fracture

  • Caused by abnormal trauma

• Pathological fracture

  • Occurs in bone weakened by a disease such as osteoporosis

Explain how a fracture is repaired.

• Closed reduction

  • Non surgical manipulation of fragments

• Open reduction

  • Surgical setting involving plates, screws, or pins

• Cast (fiberglass)

• Healing in 8-12 weeks

Discuss the causes and effects of osteoporosis.

• Causes

  • Decrease in estrogen in women at the time of menopause and a decrease in testosterone in men as they age

  • Confined to a bed due to a prolonged illness (mostly affects bones in children)

  • Having certain medical conditions that cause increased inflammation in the body

• Effects

  • Bone lose mass and become subject to pathological fractures

  • Bones become weak and brittle — so brittle that a fall or even mild stresses such as bending over or coughing can cause a fracture