College Physics: Anatomy & Physiology 2E - Chapter 6: Bone Tissue and the Skeletal System

College Physics: Anatomy & Physiology 2E - Chapter 6: Bone Tissue and the Skeletal System

Bone Growth and Development

• Intramembranous Ossification

  • Defined as the process by which bone is formed directly from mesenchyme without prior cartilage modeling.
  • Example: Formation of flat bones of the skull.

• Endochondral Ossification

  • Described as the process whereby bone develops within hyaline cartilage.
  • Key points:
    • Cartilage undergoes calcification (death of cartilage).
    • Spongy bone develops first (most embryonic bone is spongy).
    • Compact bone develops on top of spongy bone.
    • Example: Long bones like the femur.
    • Sesamoid Bones: Bones that form within a tendon, such as the patella (kneecap).

Intramembranous Ossification Process

• Steps:
  1. Mesenchymal cell clustering: Mesenchymal cells group into clusters, leading to the formation of ossification centers.
  2. Osteoid secretion: Secreted osteoid traps osteoblasts, which later differentiate into osteocytes.
  3. Matrix and periosteum formation: The trabecular matrix of spongy bone and periosteum form around it.
  4. Compact bone development: Compact bone develops over the trabecular bone, and blood vessels condense into red marrow.

Endochondral Ossification Process

• Steps:
  1. Chondrocyte differentiation: Mesenchymal cells evolve into chondrocytes.
  2. Cartilage model formation: A cartilage model of the future bony skeleton and the surrounding perichondrium form.
  3. Vascular invasion: Capillaries penetrate the cartilage, changing the perichondrium into periosteum, allowing development of a periosteal collar and primary ossification center.
  4. Cartilage growth: Cartilage and chondrocytes proliferate at the ends of the bones.
  5. Secondary ossification centers: These centers develop. Cartilage remains in the epiphyseal (growth) plate and at the joint surfaces as articular cartilage.

Primary and Secondary Ossification Centers

• Primary Ossification Center:

  • Located in the diaphysis and appears before birth.
  • The medullary cavity is formed.
  • Bone diameter increases via the osteogenic (bone producing) periosteum.

• Secondary Ossification Centers:

  • Develop in the epiphyses after birth.
  • These centers strengthen the ends of bones for activities like walking.
  • The growth areas of a long bone keep a cartilage strip called the Epiphyseal Disc/Plate, allowing continued length growth.

Growth and Lengthening of Bone

• Growth Mechanism:
  • While cartilage growth at the epiphyseal disc exceeds bone growth, the bone continues to grow in length.
  • Once cartilage is depleted, longitudinal growth ceases; an Epiphyseal Line remains visible in the bone structure.

Bone Design and Stress

• Bone Anatomy and Stress Response:
  • The anatomy of bones is designed to endure specific types of stress, namely compression vs. tension.
  • Compression and tension are maximal at the external surfaces, where dense, strong compact bone is found.
  • These forces diminish in the interior, where weaker spongy bone resides, making bones optimized for their functional requirements.
  • Adequate stress from moderate exercise positively influences the strength of bones, ligaments, and tendons.

Types of Fractures

• Distinctions among several fracture types:
  • Closed Fracture: The skin remains intact.
  • Open Fracture: The fractured bone protrudes through the skin.
  • Transverse Fracture: A fracture that occurs straight across the bone.
  • Spiral Fracture: Caused by twisting forces, commonly seen in sports injuries.
  • Comminuted Fracture: The bone shatters into three or more fragments.
  • Impacted Fracture: Bones are driven into each other.
  • Greenstick Fracture: The bone breaks incompletely, analogous to a green twig.
  • Oblique Fracture: The fracture occurs at an angle across the bone.

Detailed Descriptions of Fracture Types

• Comminuted Fracture: The bone breaks into three or more pieces.
• Compression Fracture: The bone is crushed under pressure.
• Spiral Fracture: Twisting forces lead to a spiral break; prevalent in sports injuries.
• Epiphyseal Fracture: Separation of the epiphysis from the diaphysis at the growth plate, serious for growing children.
• Depressed Fracture: A portion of the bone is pressed inward.
• Greenstick Fracture: An incomplete break typical in children, where one side of the bone breaks while the other side bends.

Bone Repair Process

• Stages in Fracture Repair:
  1. Fracture Hematoma Formation: Blood vessels compromise, causing blood clot formation (hematoma).
  2. Callus Formation: Both internal and external calli emerge during healing.
  3. Cartilage Replacement: The cartilage in the calli is gradually replaced by trabecular bone.
  4. Remodeling: The bone is remodeled, restoring its original structure and function.

Synthesis of Vitamin D

• Sources of Vitamin D:

  • Vitamin D is acquired through sunlight, food, and supplements.
  • Sunlight exposure leads to its synthesis in the skin.
  • After absorption, vitamin D travels through the bloodstream to the liver, where it transforms into 25(OH)D (calcidiol).
  • In the kidneys, it converts into 1,25(OH)D2 (calcitriol), the active form.

• Physiological Role:

  • Essential for calcium absorption from the intestines.
  • Promotes calcium reabsorption in the kidneys.
  • Supports the rebuilding of bone tissue.

Graphical Representation of Age and Bone Mass

• Bone Density Trends:
  • Bone density reaches its peak around age 30.
  • Notably, women experience more rapid bone mass loss than men as they age.

Calcium Homeostasis Mechanisms

• Regulatory Pathways:
  • The body employs two primary pathways for calcium homeostasis: one activates when blood calcium levels drop, while the other counteracts when levels are elevated.

Hormonal Control of Blood Calcium Levels

• Calcitonin:

  • A hormone released from the thyroid gland in response to elevated blood calcium levels (hypercalcemia).
  • It lowers blood calcium levels by facilitating calcium deposition into bones.

• Parathyroid Hormone (PTH):

  • A hormone produced by the parathyroid glands activated when blood calcium levels are low (hypocalcemia).
  • It elevates blood calcium levels by prompting the breakdown of bone via osteoclasts, releasing calcium.

Bone Disorders

• Osteoporosis:

  • Characterized by a decrease in bone mass; it occurs when bone resorption surpasses bone deposition, commonly observed in post-menopausal women.

  • Osteomalacia vs. Rickets:

  • Osteomalacia: Occurs in adults when bones are inadequately mineralized.

  • Rickets: A childhood condition linked to inadequate bone mineralization, frequently due to vitamin D deficiency resulting from insufficient sunlight exposure. This vitamin is vital for the right absorption of calcium.

  • Osteosarcoma: A type of bone cancer.

Disorders of the Appendicular Skeleton

• Acromegaly:

  • Abnormally high growth hormone (GH) production from the pituitary gland leads to excessive skeletal growth; severe complications arise if untreated, potentially resulting in premature death.
  • Examples: Known cases include the wrestler “Andre the Giant” and character “Lurch” from The Addams Family.

• Pituitary Dwarfism:

  • Occurs due to insufficient GH production by the pituitary gland, resulting in small stature with normalized body proportions.

Axial and Appendicular Skeleton Overview

• Axial Skeleton:

  • Forms the body's central axis consisting of the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton:

  • Comprises the pectoral and pelvic girdles, limb bones, and bones of the hands and feet.

Pectoral Girdle Composition

• The pectoral girdle, also known as the shoulder girdle:
  • Composed of two scapulae and two clavicles.

Anatomy of the Scapula and Clavicle

• Clavicle Features:
  • Composed of an acromial end and sternal end.
  • Scapula Features:
    • Notable landmarks include the acromion, suprascapular notch, supra-spinous fossa, spine of scapula, infra-spinous fossa, coracoid process, and glenoid fossa.

Upper Limb Structure

• The upper limb consists of the arm, forearm, and hand:
  • Humerus: Main arm bone.
  • Radius and Ulna: Bones of the forearm; the radius is lateral to the ulna.
  • Hand Composition: Made up of carpals (wrist bones), metacarpals (palm), and phalanges (finger bones).

Humerus Anatomy

• Key features of the humerus include the head, greater tubercle, intertubercular sulcus, capitulum, coronoid fossa, medial and lateral epicondyles, and the olecranon fossa.

Radius and Ulna Structure

• Features of the radius include:
  • Styloid process, interosseous border, and radial tuberosity.
• Features of the ulna include:
  • Olecranon process, trochelar notch, and coronoid process.

Hand and Wrist Bones

• Phalanges composition:
  • Individual phalanges labeled as proximal, middle, and distal, from thumb (I) to pinky (V).
• Carpals in the wrist include names such as:
  1. Trapezium
  2. Trapezoid
  3. Capitate
  4. Hamate
  5. Scaphoid
  6. Lunate
  7. Triquetrum
  8. Pisiform

Pelvic Girdle Structure

• Composition:
  • Consists of paired hip bones (ossa coxae).
  • Each os coxae is formed from the fusion of ilium, ischium, and pubic bones.
  • The pubic bones connect at the anterior via the pubic symphysis (fibrocartilage).
  • The sacrum connects posteriorly with the two ossa coxae.

Anatomy of the Pelvic Girdle

• The bony pelvis includes structures formed by ossa coxae, sacrum, and coccyx.
• Pelvic Brim: Defined as the set of structures including the sacral promontory, arcuate lines of the ilium, and superior pubic area.
• Distinction between false pelvis (superior region) and true pelvis (inferior region).
• The pubic arch forms a characteristic inverted “V” shape at the anterior portion.
• Female Pelvis Adaptation: Broader with features promoting childbirth—larger subpubic angle, rounder pelvic brim, wider lesser pelvic cavity.

Comparison of Male and Female Pelvis

• The female pelvis is notably suited for childbirth, with adaptations that include dimensions favoring a wider pelvic cavity compared to the male pelvis.

Lower Limb Structure

• The lower limb consists of the thigh, leg, and foot:
  • Femur: The thigh bone that articulates with the acetabulum of the os coxae.
  • Tibia and Fibula: Bones of the leg; the fibula is lateral to the tibia.
  • Patella: Known as the kneecap.
  • Foot Composition: Made up of tarsals (ankle and heel), metatarsals (arch and sole), and phalanges (toe bones).

Anatomy of the Femur

• Noteworthy features of the femur include:
  • Greater and lesser trochanters, lateral and medial condyles, head, and neck.

Tibia and Fibula Anatomy

• The tibia features the medial malleolus, while the fibula includes the lateral malleolus and interosseous border.

Tarsals in the Foot

• Notable tarsal names include:
  1. Calcaneus
  2. Talus
  3. Navicular
  4. Medial cuneiform
  5. Intermediate cuneiform
  6. Lateral cuneiform
  7. Cuboid.

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