Exam Overview

  • Test consists solely of word questions; no images included.
  • Students must bring a Scantron and a pencil.

Content Coverage

  • Cancer Related Questions

    • A couple of questions on cancer, specifically skin cancer and burns.

  • Skeletal System

    • Questions about the skeletal system will be included in Exam Three, but not on the upcoming Tuesday's test.

Osteogenic Cells

  • Definition: Osteogenic cells are stem cells that divide and generate new bone cells known as osteoblasts.
    • Some textbooks refer to them as osteoprogenitor cells.

Osteoblasts

  • Definition: Immature cells that produce new bone tissue.
    • Functions include:
    • Growth of bones.
    • Repair of bones.
    • Involved in bone remodeling.
  • Upon becoming trapped in the matrix they create, they mature into osteocytes.

Osteocytes

  • Definition: Mature bone cells derived from osteoblasts.
    • Function as the maintenance cells of bone tissue.

Osteoclasts

  • Definition: Cells responsible for the breakdown of bone tissue.
    • Involved in:
    • Bone growth.
    • Bone repair.
    • Bone remodeling.

Bone Tissue Composition

  • Compact Bone vs Spongy Bone

    • Compact Bone: Dense and solid.
    • Spongy Bone: Lattice-like structure resembling a sponge.

  • Osteons

    • Definition: Structural units of compact bone, similar to tree trunks.
    • Composed of:
    • Central Canal: Contains blood vessels, nerves, and lymphatic vessels.
    • Lamellae: Concentric rings of bone tissue containing calcium crystals and collagen fibers.
    • Lacunae: Tiny cavities where osteocytes reside.
      • Osteocytes are interconnected via gap junctions and arm-like extensions.
    • Canaliculi: Tiny canals that connect neighboring lacunae.
      • Meaning: In Latin, canaliculi translates to "tiny canals".

Bone Matrix

  • Definition: The extracellular material surrounding bone cells, composed of collagen fibers and calcium crystals.
    • Function of collagen: Provides flexibility and tensile strength, preventing bones from stretching.
    • Function of calcium: Provides hardness to bones and resists compression.

Bone Growth

  • Importance of Hormones: Bone growth occurs during development and is stimulated by various hormones:

    • Human Growth Hormone (hGH): Secreted by the pituitary gland, primarily stimulates bone growth.
    • Estrogen and Testosterone: Contribute to bone growth during puberty.

  • Growth in Length: Occurs at the epiphyseal plates in long bones through the following mechanism:

    • Division of chondrocytes at the epiphyseal plate, leading to growth in length.
    • Osteoblasts replace old cartilage with new bone tissue.

  • Growth in Width: Occurs through periosteal growth where osteoblasts add bone on the external surface while osteoclasts resorb bone inside, allowing the medullary cavity to expand.

Growth Plate Closure

  • Epiphyseal Plate Closure: Triggers an end to height increase, influenced by levels of estrogen or testosterone.
    • Anabolic steroids can cause earlier closure of epiphyseal plates, stunting growth.

Dwarfism Conditions

  • Pituitary Dwarfism: Lack of hGH due to insufficient production by the pituitary gland, affecting all bones.

  • Achondroplasia: Genetic condition resulting from poor responsiveness of epiphyseal plates to hGH, primarily affecting long bones, leading to short limbs but normal head and torso size.

    • Treatment for pituitary dwarfism is hGH therapy, leading to typical growth patterns when administered early.

Height Estimation Techniques

  • Average height predictions based on parental heights and influences of genetics and environment (nutrition and diseases).

  • Adult Height Influences: Testosterone promotes larger bones and muscle mass compared to estrogen.

Impact of HGH in Adults

  • Adult administration of hGH can lead to increased width of bones and organ growth but does not increase height once plates have closed.
    • Potential for muscle growth and healing enhancement.

Gigantism and Acromegaly

  • Gigantism: Occurs when excessive hGH is produced during childhood, often due to pituitary tumors. Results in substantially increased height.
  • Acromegaly: Develops after growth plate closure, where excess hGH causes enlargements of extremities and organs.

Examples of Gigantism

  • Famous Cases: Reference to record-holders and individuals with gigantism, including their medical backgrounds, common in professional athletes.

Conclusion of Lecture

  • Acknowledgment of the importance of differentiating between terms and conditions related to growth, particularly in a clinical or educational context.