Chapter 7: Bone Tissue

Question 1

What is the fundamental reason osteoporosis result in bone loss?

Answer 1

• 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.

Question 2

what is secondary ossification centers?

Answer 2

Secondary Ossification Center - area of ossification that appears after the primary ossification center has already appeared

• most appear during the postnatal and adolescent years.
• Most bones have multiple secondary ossification center.
• In long bones the secondary centres appear in the epiphyses.

Question 3

Describe the process of intramembranous ossification and provide examples of bone that develop by this process.

Answer 3

• It produces the flat bones of the skull and most of the clavicle.
• The Process
• Mesenchyme condenses into soft sheet of tissue permeated with blood vessels. Mesenchymal cells line up along blood vessels, become osteoblasts, and secrete a soft collagenous osteoid tissue (pre-bone) in the direction away from the vessel. Osteoid tissue resembles bone but isn’t calcified yet.
• Calcium phosphate and other minerals crystallize on the collagen fibers of the osteoid tissue and harden the matrix. Osteoblasts get pushed down narrow spaces, trapping them and hardening their matrix becoming osteocytes.
• Spongy bone becomes a honeycomb of slender calcified trabeculae.
• Osteoblasts beneath the periosteum fill in the spaces between the trabeculae and overall thicken the bone.

Question 4

Describe the gross and microscopic anatomy of a long bone such as the femur (structures, tissue, cells and connective sheaths)

Answer 4

• The principal features of a long bone are the diaphysis and epiphysis. The diaphysis provides leverage and the epiphysis is enlarged to strengthen the joint and provide added surface area for the attachment of tendons and ligaments.
• The joint surface, where one bone meets another, is covered with a layer of hyaline cartilage called the articular cartilage. Together with a lubricating fluid secreted between the bones, the cartilages enables a joint to move far more easily than it would if one bone rubbed directly against the other.
• Blood vessels penetrate into the bone through minute holes called nutrient foramina.
• The bone is covered with the periosteum, a sheath. It has a tough, outer fibrous layer of collagen and an inner osteogenic layer of bone-forming cells.
• The endosteum lines the internal marrow cavity and covers honeycomb surfaces of the spongy bone and lines the canal system.

Question 5

provide specific examples of bones that develop by endochondral ossification

Answer 5

Ex. Most bones; vertebrae, ribs, sternum, scapula, bones of the limbs

Question 6

Distinguish between the two types of bone marrow

Answer 6

1. Red bone marrow (myeloid tissue) Hemopoietic tissue- tissue that produces blood cells
2. Yellow bone marrow most of the red marrow turns into this. It doesn’t produce blood anymore.

Question 7

Describe the process of endochondral bone development

Answer 7

Question 8

Describe the fibers and ground substance of bone matrix.

Answer 8

• MATRIX: Connective tissue matrix is composed of: ground substance and fibers.
• Ground substance
• In ordinary connective tissue, the ground substance consists of water stabilized by glycosaminoglycans, proteoglycans, and glycoproteins.
• In bone the ground substance includes minerals.
• In blood, the ground substance is fluid (plasma).
• Fibers
• The principal fiber type is collagen – the most abundant protein in the body – which confers tensile strength with flexibility.
• Elastic fibers confer resiliency.

Question 9

Describe and provide examples of the 4 classes of bone based on shape.

Answer 9

1. Flat bones- most cranial bones; ex. sternum, hip bones
2. Long bones- most important for movement; ex. arm & leg bones
3. Short bones- ex. carpal/tarsal bones, patella
4. Irregular bones- ex. vertebra and 3 tiny middle-ear bones

Question 10

Where is the parathyroid hormone produced and why is it important to plasma [Ca] regulation?

Answer 10

• It’s secreted by the parathyroid glands which adhere to the posterior surface of the thyroid gland.
• They release when calcium levels are low.

Question 11

Describe 4 functions of the skeletal system.

Answer 11

1. Movement
2. Electrolyte balance- the skeleton stores calcium and phosphate ions and releases them into the tissue fluid according to the body’s needs.
3. Acid-base balance- bone tissue buffers the blood against excessive pH changes by absorbing/releasing alkaline phodphate and carbonate salts
4. Blood formation- red bone marrow is the major producer of blood cells, including cells of the immune system

Question 12

What is primary ossification center?

Answer 12

• Primary Ossification Center- first area of a bone to start ossifying. It usually appears during prenatal development in the central part of each developing bone.
  
  • In long bones- the primary centers occur in the diaphysis/shaft
  • irregular bones- the primary centers occur usually in the body of the bone. some irregular bones such as the coxa (hip) and vertebrae have multiple primary centers.
  • Most bones have only one primary center (e.g. all long bones)

Question 13

Describe the process of endochondral long bone growth

Answer 13

• Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created.
• Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral ossification.