Study Notes on Bones and Skeletal Tissues

Diaphysis

The long shaft of a bone.

Epiphysis

The end part of a long bone, initially growing separately from the shaft.

Epiphyseal Plate

A plate of cartilage where bone growth occurs in childhood, allowing for the increase in length of the bone.

Metacarpal Bone

One of the long bones in the hand.

Bone Remodeling Regulation (Continuous Process)

Regulated by genetic factors, negative feedback hormonal loop for Ca^{2+} homeostasis, and mechanical/gravitational forces.

Functions of Calcium in the Body

Nerve impulse transmission, muscle contraction, blood coagulation, secretion by glands and nerve cells, cell division.

Parathyroid Hormone (PTH)

Secreted by parathyroid glands; functions to increase calcium levels in the blood by promoting calcium release from bone.

Calcitonin

Produced by parafollicular cells of the thyroid gland; can temporarily lower blood calcium levels in high doses.

Negative Feedback Hormonal Loop for Calcium Homeostasis

Falling blood calcium stimulates PTH release -> PTH promotes osteoclast activity -> Calcium released into bloodstream -> Increased blood calcium stops PTH release.

Hyperexcitability (Calcium Fluctuation)

A consequence of low blood calcium levels, leading to severe neuromuscular problems.

Nonresponsiveness (Calcium Fluctuation)

A consequence of high blood calcium levels, leading to severe neuromuscular problems.

Hypercalcemia

Sustained high blood calcium levels, which can lead to deposits of calcium salts in blood vessels and kidneys.

Wolff's Law

States that bones grow or remodel in response to the demands placed on them.

Nondisplaced Fracture

A type of fracture where bone ends retain normal alignment.

Displaced Fracture

A type of fracture where bone ends are out of alignment.

Complete Fracture

A fracture that goes all the way through the bone.

Incomplete Fracture

A fracture that does not extend through the bone.

Open (Compound) Fracture

A fracture where the skin is penetrated by the broken bone.

Closed (Simple) Fracture

A fracture where there is no skin penetration.

Greenstick Fracture

One side of the bone is broken while the other is bent; common in children.

Impacted Fracture

Broken ends of the bone are jammed into each other.

Comminuted Fracture

The bone is splintered into multiple pieces; common in the elderly.

Spiral Fracture

Twisting forces cause the break; frequent in skiing accidents.

Transverse Fracture

The break occurs straight across the bone.

Oblique Fracture

The break occurs at an angle across the bone.

Fracture Treatment: Reduction

Realignment of broken bone ends, either closed (manipulation by physician) or open (surgical pins or wires).

Fracture Treatment: Immobilization

Achieved through casting or traction to ensure healing.

Stage 1 of Bone Repair

Formation of Hematoma: Torn blood vessels lead to hemorrhage and a clot forming, causing swelling, pain, and inflammation.

Stage 2 of Bone Repair

Fibrocartilaginous Callus Formation: Capillaries grow, phagocytic cells clear debris, fibroblasts secrete collagen to form a callus of cartilage matrix and spongy bone.

Stage 3 of Bone Repair

Bony Callus Formation: Within one week, new trabeculae appear, converting the fibrocartilaginous callus to a bony (hard) callus of spongy bone.

Stage 4 of Bone Repair

Bone Remodeling: Begins during callus formation, removing excess material from diaphysis exterior and medullary cavity, reconstructing shaft walls.

Osteomalacia

Characterized by poorly mineralized bones due to inadequate calcium salts, leading to soft, weak bones and discomfort when bearing weight.

Rickets

A pediatric form of osteomalacia, leading to bowed legs and other deformities with enlarged and abnormally long ends; primarily caused by Vitamin D deficiency.

Osteoporosis

A group of conditions where bone resorption outpaces deposition, leading to significant bone density loss, particularly affecting spongy bone in the spine and neck of the femur.

Osteoporosis Risk Factors

Aging, postmenopausal women, petite body form, insufficient exercise, deficit of calcium and vitamin D, poor dietary protein, smoking, hyperthyroidism, diabetes, and certain medications.

Osteoporosis Treatment (Traditional)

Calcium and Vitamin D supplements, weight-bearing exercises, hormone replacement therapy (controversial).

Osteoporosis Treatment (New Pharmacological)

Bisphosphonates, selective estrogen receptor modulators (SERMs), statins, and Denosumab (a monoclonal antibody).

Paget's Disease

Involves excessive and chaotic bone deposits and resorption, creating poorly constructed bone structure (pagetic bone) with a high ratio of spongy to compact bone and diminished mineralization. Commonly affects spine, pelvis, femur, skull, rarely before age 40. Treatment includes calcitonin and bisphosphonates.