Chapter 6: The Skeletal System

Osteoporosis: Causes and Prevention

Osteoporosis is a condition characterized by decreased bone mass and increased risk of fractures. It is especially common in postmenopausal women due to decreased estrogen levels.

• Causes: Hormonal changes (notably menopause), insufficient calcium/vitamin D, sedentary lifestyle, genetics.

• Preventative Measures: Adequate calcium and vitamin D intake, regular weight-bearing exercise, medications (e.g., bisphosphonates), hormone replacement therapy (in some cases).

• Example: Postmenopausal women are at higher risk due to decreased estrogen, which normally helps maintain bone density.

Epiphyseal Plate and Hormonal Regulation

The epiphyseal plate (growth plate) is a region of cartilage in growing bones where new bone is produced, allowing for longitudinal growth.

• Hormones Affecting the Epiphyseal Plate:

  • Growth Hormone (GH): Stimulates overall bone growth.

  • Thyroid Hormone: Regulates bone growth and development.

  • Sex Hormones (Estrogen and Testosterone): Promote growth during puberty and eventually cause closure of the plate.

• Example: Early puberty can lead to early closure of the epiphyseal plate, resulting in shorter adult stature.

Functions of the Skeletal System

• Support: Provides structural framework for the body.

• Protection: Shields vital organs (e.g., skull protects the brain).

• Movement: Serves as levers for muscles to act upon.

• Mineral Storage: Stores calcium and phosphorus.

• Blood Cell Production: Houses red bone marrow for hematopoiesis.

• Triglyceride Storage: Yellow bone marrow stores fat.

Bone Cells: Osteoblasts vs. Osteoclasts

• Osteoblasts: Bone-forming cells; synthesize and secrete bone matrix.

• Osteoclasts: Bone-resorbing cells; break down bone tissue to release minerals.

• Comparison: Osteoblasts build bone, osteoclasts break it down.

Hormonal Regulation of Blood Calcium

• Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclast activity, increasing calcium reabsorption in kidneys, and activating vitamin D.

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts and promoting calcium deposition in bones.

Bone Types: Spongy vs. Compact Bone

• Spongy Bone: Contains trabeculae (lattice-like structures), found at ends of long bones and inside flat bones.

• Compact Bone: Dense, solid bone forming the outer layer of bones; provides strength.

• Example: The femur's shaft is mostly compact bone, while its ends contain spongy bone.

Chapter 9: Joints (Articulations)

Classification of Joints

Joints are classified both structurally and functionally.

• Structural Classification:

  • Fibrous Joints: Bones joined by dense connective tissue (e.g., sutures in the skull).

  • Cartilaginous Joints: Bones joined by cartilage (e.g., intervertebral discs).

  • Synovial Joints: Bones separated by a fluid-filled cavity (e.g., knee, shoulder).

• Functional Classification:

  • Synarthrosis: Immovable joints.

  • Amphiarthrosis: Slightly movable joints.

  • Diarthrosis: Freely movable joints (all synovial joints).

Joint Anatomy and Terminology

• Key Terms: Articular cartilage, joint capsule, synovial membrane, synovial fluid, ligaments, bursae, menisci.

• Example: The knee joint contains articular cartilage, a synovial cavity, and menisci for shock absorption.

Stability vs. Mobility in Joints

• Multiaxial Joints: Allow movement in multiple planes (e.g., shoulder, hip).

• Trade-off: Increased mobility leads to decreased stability, making these joints more susceptible to injury.

• Example: The shoulder joint is highly mobile but prone to dislocation.

Chapter 10: Muscle Tissue

Connective Tissue Wrappings

• Endomysium: Surrounds individual muscle fibers.

• Perimysium: Surrounds bundles of muscle fibers (fascicles).

• Epimysium: Surrounds the entire muscle.

• Fascicle: A bundle of muscle fibers within a muscle.

Rigor Mortis

• Definition: Stiffening of muscles after death due to lack of ATP, which prevents detachment of myosin from actin.

• Onset: Begins 2-6 hours after death, lasts up to 72 hours.

Sarcoplasmic Reticulum (SR)

• Function: Stores and releases calcium ions, which are essential for muscle contraction.

Functional Units of Skeletal Muscle

• Sarcomere: The basic contractile unit of muscle, defined by Z-disks; contains actin and myosin filaments.

• T Tubules: Invaginations of the sarcolemma that transmit action potentials into the muscle fiber, ensuring coordinated contraction.

Properties of Muscle Tissue

• Excitability: Ability to respond to stimuli.

• Contractility: Ability to shorten and generate force.

• Extensibility: Ability to be stretched.

• Elasticity: Ability to return to original length after stretching.

Sarcomere Structure

• Z Disk: Defines the boundaries of a sarcomere.

• A Band: Contains thick filaments (myosin).

• I Band: Contains thin filaments (actin) only.

• H Zone: Central region of A band with only thick filaments.

Chapter 18: Blood and Hematology

White Blood Cell (WBC) Types and Functions

• Neutrophils: Phagocytize bacteria; first responders to infection.

• Lymphocytes: B cells produce antibodies; T cells destroy infected cells.

• Monocytes: Become macrophages; phagocytize pathogens and debris.

• Eosinophils: Combat parasitic infections; involved in allergic responses.

• Basophils: Release histamine; involved in inflammatory responses.

Erythropoietin Function

• Erythropoietin: Hormone produced by the kidneys that stimulates red blood cell production in the bone marrow.

Centrifugation and Hematocrit

• Centrifugation: Process of spinning blood to separate its components by density, allowing measurement of hematocrit (percentage of RBCs in blood).

Properties of Erythrocytes (Red Blood Cells)

• Biconcave Shape: Increases surface area for gas exchange.

• Lack of Organelles: Maximizes space for hemoglobin.

• Anaerobic Metabolism: RBCs generate ATP without using the oxygen they transport.

Anemias: Causes and Types

• Sickle Cell Anemia: Caused by abnormal hemoglobin, leading to sickle-shaped RBCs.

• Pernicious Anemia: Caused by vitamin B12 deficiency.

• Other Types: Iron-deficiency anemia, aplastic anemia, etc.

Hemoglobin Structure and Oxygen Transport

• Structure: Four polypeptide chains, each with a heme group containing iron.

• Oxygen Binding: Each hemoglobin molecule can carry up to four oxygen molecules.

Diapedesis

• Definition: The process by which WBCs move out of blood vessels into tissues ("foot" refers to the cell's movement).

Clotting Factors and Disorders

• Hemophilia: A condition resulting from lack of clotting factors, leading to excessive bleeding.

Chapter 19: The Heart and Circulation

Ventricular Wall Thickness

• Left Ventricle: Thicker wall than the right ventricle to pump blood throughout the systemic circulation (higher pressure).

• Right Ventricle: Thinner wall, pumps blood to the lungs (pulmonary circulation, lower pressure).

Pulmonary Circulation and Blood Flow

• Pulmonary Arteries: Carry deoxygenated blood from the right ventricle to the lungs.

• Pulmonary Veins: Carry oxygenated blood from the lungs to the left atrium.

• Blood Flow Sequence: Right atrium → right ventricle → pulmonary arteries → lungs → pulmonary veins → left atrium → left ventricle → aorta → body.

Heart Location and Anatomy

• Mediastinum: The central region of the thoracic cavity where the heart is located.

• Pericardial Cavity: The space between the parietal and visceral layers of the pericardium, containing lubricating fluid.

• Coronary Arteries: Blood vessels that supply the myocardium (heart muscle) with oxygenated blood.

Fetal Circulation: Foramen Ovale

• Foramen Ovale: An opening in the fetal heart that allows blood to bypass the lungs by flowing from the right atrium to the left atrium; closes after birth.

Oxygenation of Blood in the Heart

• Deoxygenated Blood: Found in the right atrium, right ventricle, and pulmonary arteries.

• Oxygenated Blood: Found in the left atrium, left ventricle, pulmonary veins, and systemic arteries.