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Gross Anatomy Long Bone
Basic Structure
Superior view Transverse section,
diaphysis of an immature long bone
Terminology Periosteum - fibrous connective
tissue covering the bone, it contains blood vessels and nerves and serves as an attachment site for ligaments and tendons
Compact bone – higher density bone, contains a larger percentage of mineral salts. The amount of compact bone varies depending on the individual and the particular stresses placed on the bone
Terminology Spongy / cancellous bone– found at
the ends (epiphyses) of long bones and in the flat bones. Lower density bone, offers more flexibility. Contains red marrow.
Marrow cavity – found in the center of the diaphysis (shaft). In a developing skeleton the marrow is red, as the skeleton matures the marrow in the cavity changes to yellow marrow.
Note : Red marrow is found in the the epiphysis of mature long bones (within the cancellous bone) and in flat bones
The Function of Bone Marrow
Red marrow is the site of blood cell formation (red blood cells, platelets and white blood cells)
Found mainly in flat bones, but also in the epiphyses of the long bones
Yellow marrow is found in the marrow cavities of long bones
Chiefly adipose tissue, yellow bone marrow is a storage site for fat (energy)
Yellow marrow can change to red marrow in times of need
Take a closer look…
Bone Formation & Remodelling Ossification – the process by which new
bone is produced Osteoblasts – bone forming cells (secrete
protein matrix called osteoid)Osteoid – gelatin-like substance, initial step
in bone formation Osteoclast – bone-resorbing cells (remove
old bone by releasing acids and enzymes)
**Note – bone is continually remodelled (created, destroyed, created etc.)
Bone formation Compact bone begins as cartilage
Cartilage is a specialized connective tissue composed of collagen and several other fibres
Cancellous bone begins as a fibrous membrane, and development proceeds as in compact bone
Osteoblasts deposit osteoid into the cartilage or fibrous membrane, minerals are then slowly deposited into the osteoid as cartilage / fibrous membrane converts to bone
Osteoclasts work to remodel the bones as they form
Bone formation Compact bone formation occurs at
ossification centers:Long bones have one in the middle
and one at either endShort bones have a single ossification
center near the middle Cancellous bone formation occurs
at ossification centers in the fibrous membrane (roughly in the middle of the bone)
Ossification centers (growth plates)
Compact bone formation As a person ages, and bone growth ceases
the ossification centers gradually change to epiphyseal plates
Adult or child??
Infant skeleton all blue areas represent cartilage
Bone Remodelling
Bones remodelling occurs in two phases:
1. Osteoclasts remove old bone by releasing acids and enzymes
2. Osteoblasts deposit new tissue by secreting osteoid thus allowing for mineral deposit, and eventually new bone growth
Bone Remodelling
During early years (age 0 – 35) remodelling is most active bone deposit heavily outweighs bone resorption
Remodelling declines by around age 35 and by around age 40, the process reverses (resorption outpaces deposit)
Resultloss of 5 to 10% of bone mass each decade after age 40
Bone Remodelling
What can you do??? Nothing…and something Bone resoprtion will outpace bone
deposit, but ensuring you have strong, healthy bones when you are younger will keep your bones healthier as you age
What’s the big deal about calcium?? The bones store 99% of the body’s
calcium, a vital ion in many cellular functions
If your calcium intake is not high enough, your body will signal your bones to release calcium (via osteoclast action)
Calcium balance
Rising blood Ca2+ levels trigger the thyroid to release calcitonin
Calcitonin stimulates calcium salt deposit in bone
Calcium balance
Falling blood Ca2+ levels signal the parathyroid glands to release PTH
PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood