Skeletal Tissue (Bone Remodeling, Bone Disorders, and Bone Repair)

What is Bone Remodeling

The constant bone deposit and bone resorption

What is Bone Remodeling Controlled by

Hormonal and mechanical stress

Ratio of Deposition-Resorption in a Healthy Adult

Deposition=Resorption (bone mass remains the same)

How Often is Bone Recycled/Replaced

5-7% bone mass recycled each week

Trabecular bone is replaced every 3-4 years

Cortical bone is replaced every 10 years

What is Calcium Required for

Nerve impulses, muscle contraction, blood clotting, mitosis

What is Hypocalcemia

Low calcium in the blood.

hyperexcitability (muscle spasms)

What is Hypercalcemia

High calcium in the blood.

Non-responsiveness (muscles and nerves)

Describe Bone Deposition

Accomplished by osteoblasts, calcium taken from bloodstream (deposited into bone)

When does Bone Deposit Occur

When bone is injured or requires more strength

Describe Bone Resorption

Accomplished by osteoclasts, lysosomal enzymes digest organic matrix, calcium enters bloodstream

Describe the Parathyroid Hormone

Responds to low blood calcium levels.

Stimulates osteoclasts and inhibits osteoblasts, increasing renal absorption of calcium from urine

Where is the Parathyroid Hormone Produced

Parathyroid glands

Describe Calcitonin

Responds to high blood calcium levels.

Stimulates osteoblasts activity and inhibits osteoclasts

Where is Calcitonin Produced

Thyroid gland

What is Calcitriol

Vitamin D, important for low blood calcium. Stimulates calcium absorption in the small intestine.

Describe Wolffs Law

Bone grows in response to the mechanical stresses placed on it

Vigorous Exercise =

Increased mechanical stress, thicker, stronger bones

What are Bone Spurs

Bony projections that develop in response to continuous stress

What Happens When Bones Experience Lack of Stress

Bone density decreases

What is Osteomalacia

Bones are poorly mineralized, soft, and weak bones

Cause: vitamin D deficiency, lack of dietary calcium

ex: rickets

What is Osteoporosis

Resorption exceeds deposit, normal matrix, but declining bone mass

Risk factors: postmenopausal women

treatment: calcium, vitamin D, weight-bearing exercise

What is Pagets Disease

Excessive haphazard bone deposit and resorption, a high ratio of spongy bone to compact bone

Cause: unknown (viral?)

treatment: calcitonin biphosphonates

What is a Fracture

A broken bone

In youth, usually results from trauma

In old age, it usually results from bone weakness

What are the 4 Parts of Bone Repair

Hematoma Formation

Fibrocartilaginous Callus Formation

Bony Callus Formation

Bone Remodeling

Describe Hematoma Formation

Bleeding at the sight of a fracture causes a hematoma, bone cells deprived of nutrition die, the area swells, inflames, and becomes painful

Describe Fibrocatilaginous Callus Formation

Capillaries invade the hematoma, followed by fibroblasts and osteoblasts, and phagocytic cells clear debris. Fibroblasts differentiate into chondroblasts and form a cartilage matrix

Describe Bony Callus Formation

Within a week, the fibrocartilaginous callus begins to be converted into bone. Trabeculae appear. Occurs for about 8 weeks

Describe Bone Remodeling

Starts with bony callus formation and continues for several months, and spongy bone becomes compact bone.