Bone Flashcards
Functions of bone
- Haematopoiesis
- Lipid and mineral storage
- support
- protection
Haematopoiesis
The formation of blood cells from haematopoietic stem cells found in the bone marrow
Lipid and mineral storage
Bone is a reservoir holding adipose tissue within the bone marrow and calcium within the hydroxyapatite crystals
Support
Bones form the framework and shape of the body
Protection
Especially the axial skeleton which surrounds the major organs of the body
Cellular components of bone (3 types of cells)
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
Extracellular matrix of bone
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.
Woven bone (primary bone)
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.
Lamellar bone (secondary bone)
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
Periosteum
External surface of bone. A layer of connective tissue.
Endosteum
lines the cavities within the bone (such as the medullary canal, Volkmann’s canal and spongy bone spaces)
Compact bone
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.
Spongy bone
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.
Endochondral ossification
Where the hyaline cartilage is replaced by osteoblasts secreting osteoid. The femur is an example of a bone that undergoes this.
Intramembranous ossification
where embryonic tissue is condensed into bone. This type of ossification forms flat bones such as the temporal bone and the scapula.
Remodeling
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.
Osteogenesis imperfecta
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.
Osteoporosis
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.
Type 1: postmenopausal osteoporosis
Develops in women after menopause due to decreased oestrogen production. Oestrogen protects against osteoporosis by increasing osteoblast and decreasing osteoclast activity.
Type 2: Senile osteoporosis
Usually occurs above the age of 70
Secondary osteoporosis
Where osteoporosis occurs due to co-existing disease. (Eg chronic renal failure.)
Rickets
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.
Osteomalacia
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.
