Bone

Question 1

Functions of bone

Answer 1

• Haematopoiesis
• Lipid and mineral storage
• support
• protection

Question 2

Haematopoiesis

Answer 2

The formation of blood cells from haematopoietic stem cells found in the bone marrow

Question 3

Lipid and mineral storage

Answer 3

Bone is a reservoir holding adipose tissue within the bone marrow and calcium within the hydroxyapatite crystals

Question 4

Support

Answer 4

Bones form the framework and shape of the body

Question 5

Protection

Answer 5

Especially the axial skeleton which surrounds the major organs of the body

Question 6

Cellular components of bone (3 types of cells)

Answer 6

Osteoblasts- synthesize uncalcified/unmineralized extracellular matrix called osteoid. this will later become calcified/mineralized to form bone

Osteocytes- As the osteoid mineralizes, the osteoblasts become entombed bw lamellar in lacunae where they mature into osteocytes. They then monitor the minerals and proteins to regulate bone mass.

Osteoclasts- derived from monocytes and resorb bone by releasing H+ ions and lysosomal enzymes.

Balancing osteoblasts and osteoclasts activity is crucial in maintaining structural integrity. Plays a role in conditions such as osteoporosis

Question 7

Extracellular matrix of bone

Answer 7

ECM refers to the molecules that provide biochemical and structural support to the cells.

Bone ECM is highly specialized. Contains collagen and mineral salts (calcium hydroxyapatite crystals). These crystals associate with collagen fibers making bone hard and strong. This matrix is organized into numerous layers known as lamellae.

Question 8

Woven bone (primary bone)

Answer 8

Appears in embryonic development and fracture repair as it can be laid done rapidly.
Consists of osteoid (unmineralized ECM), with the collagen fibers arranged randomly. It is a temporary structure soon replaced by mature lamellar bone.

Question 9

Lamellar bone (secondary bone)

Answer 9

Bone of the adult skeleton. It consists of highly organized sheets of mineralized osteoid. This organized structure makes it stronger that woven bone.
Can be divided into two types: Compact bone and spongy bone

Question 10

Periosteum

Answer 10

External surface of bone. A layer of connective tissue.

Question 11

Endosteum

Answer 11

lines the cavities within the bone (such as the medullary canal, Volkmann’s canal and spongy bone spaces)

Question 12

Compact bone

Answer 12

Forms the outer shell of bone. In this type of bone, the lamellae are organized into concentric circles which surround a vertical Haversian canal (which transmits small neurovascular and lymphatic vessels). This entire structure is called an osteon and is the functional unit of bone.
The Haversian canals are connected by horizontal Volkmann’s canals. These contain small vessels that join together the arteries of the Haversian canals. Volkmann’s canals also transmit blood vessels from the periosteum.

Question 13

Spongy bone

Answer 13

Makes up the interior of most bones and is located deep to the compact bone. Contains many large spaces which gives a honeycombed appearance.
The lightness afforded to spongy bone is crucial in allowing the body to move. Compact bone is much heavier
Contains red and yellow bone marrow.

Question 14

Endochondral ossification

Answer 14

Where the hyaline cartilage is replaced by osteoblasts secreting osteoid. The femur is an example of a bone that undergoes this.

Question 15

Intramembranous ossification

Answer 15

where embryonic tissue is condensed into bone. This type of ossification forms flat bones such as the temporal bone and the scapula.

Question 16

Remodeling

Answer 16

Occurs b/c bone is living tissue.Process by which mature bone tissue is reabsorbed and new bone tissue is formed. It is carried out by the cellular components of bone.

Osteoclasts break down bone, nutrients are reabsorbed and osteoblasts lay down new osteoid.
Occurs primarily at sites of stress and damage, strengthening those areas.

Question 17

Osteogenesis imperfecta

Answer 17

Condition in which there is abnormal synthesis of collagen from the osteoblasts.
Features: fragile bones, bone deformities, and blue sclera.
It’s a rare genetic disease, with autosomal dominant genetic pattern
Bones are predisposed to fracture.

Question 18

Osteoporosis

Answer 18

Refers to a decrease in bone density, reducing its structural integrity. This is produced by osteoclast activity (bone reabsorption) outweighing osteoblast activity (bone production). Bones are fragile and at increased risk of fracture.
Three types:
-type 1: Postmenopausal osteoporosis
-type 2: Senile osteoporosis
-type 3: secondary osteoporosis
Risk factors: age, gender, diet (vit D and calcium), ethnicity, smoking and immobility.
Usually managed by bisphosphonates which are taken up by osteoclasts causing them to become inactive and undergo apoptosis.

Question 19

Type 1: postmenopausal osteoporosis

Answer 19

Develops in women after menopause due to decreased oestrogen production. Oestrogen protects against osteoporosis by increasing osteoblast and decreasing osteoclast activity.

Question 20

Type 2: Senile osteoporosis

Answer 20

Usually occurs above the age of 70

Question 21

Secondary osteoporosis

Answer 21

Where osteoporosis occurs due to co-existing disease. (Eg chronic renal failure.)

Question 22

Rickets

Answer 22

Vitamin D or calcium deficiency in children with growing bones. This means that the osteoid mineralizes poorly and remains pliable. The epiphyseal growth plates can the become distorted under the weight of the body, potentially leading to skeletal deformities.

Question 23

Osteomalacia

Answer 23

Vitamin D or calcium deficiency in adults with remodeling bones. Here the osteoid laid down by osteoblasts is poorly mineralized leading to increasingly weak bones, increasing their susceptibility to fracture.