Chapter 5: The Skeletal System

Functions of the Skeleton

The human skeleton provides the framework for the body and serves several vital functions:

• Support: Provides structural support for the entire body.

• Protection: Shields vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Acts as levers for muscles to pull on, enabling movement.

• Mineral Storage: Stores minerals such as calcium and phosphorus.

• Blood Cell Production: Houses bone marrow, which produces blood cells (hematopoiesis).

• Energy Storage: Yellow bone marrow stores fat as an energy reserve.

Types of Bone: Gross and Microscopic

• Gross Types:

  • Compact Bone: Dense, forms the outer layer of bones; provides strength.

  • Spongy Bone (Cancellous): Porous, found at the ends of long bones and inside flat bones; contains red marrow.

• Microscopic Structure:

  • Osteon (Haversian System): The structural unit of compact bone, consisting of concentric rings (lamellae) around a central canal.

  • Lamellae: Layers of bone matrix.

  • Lacunae: Small spaces housing osteocytes (bone cells).

  • Canaliculi: Tiny channels connecting lacunae for nutrient/waste exchange.

Living and Nonliving Components of Bone

• Living: Osteocytes (mature bone cells), osteoblasts (bone-forming cells), osteoclasts (bone-resorbing cells).

• Nonliving: Extracellular matrix composed of collagen fibers (flexibility) and mineral salts, mainly hydroxyapatite (strength).

Bone Development and Growth

• Embryonic Development: Bones initially form from cartilage (hyaline cartilage model) or fibrous membranes.

• Ossification: Process of bone formation; primary ossification centers develop in the diaphysis (shaft), secondary in the epiphyses (ends).

• Growth: Bones grow in length at the epiphyseal (growth) plates until adulthood, when these plates ossify under hormonal control.

• Hormonal Regulation: Growth hormone, thyroid hormones, sex hormones (estrogen, testosterone) regulate growth and closure of growth plates.

Bone Remodeling

• Continuous Process: Bone is constantly broken down (resorption by osteoclasts) and rebuilt (formation by osteoblasts).

• Hormonal Control:

  • Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclasts.

  • Calcitonin: Lowers blood calcium by stimulating osteoblasts.

  • Estrogen: Inhibits bone resorption; loss after menopause increases osteoporosis risk.

Divisions of the Skeleton

• Axial Skeleton: Skull, vertebral column, rib cage, sternum.

• Appendicular Skeleton: Limbs, pectoral (shoulder) girdle, pelvic (hip) girdle.

Skull and Hyoid Bone

• Cranial Bones: Enclose the brain (e.g., frontal, parietal, occipital).

• Facial Bones: Form the face (e.g., maxilla, mandible, zygomatic).

• Hyoid Bone: Unique; does not articulate with other bones; supports the tongue.

Vertebral Column and Ribs

• Regions: Cervical (7), thoracic (12), lumbar (5), sacrum, coccyx.

• Intervertebral Discs: Cartilaginous pads between vertebrae for cushioning.

• Ribs: 12 pairs; true ribs (1-7) attach directly to sternum, false ribs (8-12) do not, floating ribs (11-12) have no anterior attachment.

Pectoral and Pelvic Girdles

• Pectoral Girdle: Clavicle and scapula; attaches upper limbs to trunk.

• Pelvic Girdle: Hip bones (ilium, ischium, pubis); supports lower limbs.

Joints and Movement

• Types of Joints:

  • Fibrous: Immovable (e.g., sutures of skull).

  • Cartilaginous: Slightly movable (e.g., intervertebral discs).

  • Synovial: Freely movable (e.g., knee, shoulder); contain synovial fluid.

• Parts of Synovial Joints: Articular cartilage, joint capsule, synovial membrane, ligaments.

• Knee Joint: Includes menisci, cruciate ligaments, patella.

• Types of Movement: Flexion, extension, adduction, abduction, rotation, circumduction, supination, pronation.

Chapter 6: The Muscular System

Characteristics and Types of Muscle Tissue

• Excitability: Responds to stimuli.

• Contractility: Can shorten to produce force.

• Extensibility: Can be stretched.

• Elasticity: Returns to original length after stretching.

• Types:

  • Skeletal Muscle: Voluntary, striated, attached to bones.

  • Cardiac Muscle: Involuntary, striated, found in heart.

  • Smooth Muscle: Involuntary, non-striated, found in walls of organs.

Organization of Skeletal Muscle

• Synergistic Muscles: Work together for movement.

• Antagonistic Muscles: Oppose each other's action.

• Tendon: Connects muscle to bone.

• Origin: Fixed attachment point.

• Insertion: Movable attachment point.

• Hierarchy: Whole muscle → fascicle → muscle fiber (cell) → myofibril → myofilament (actin, myosin).

• Connective Tissue Sheaths: Epimysium (around muscle), perimysium (around fascicle), endomysium (around fiber).

Sarcomere and Muscle Contraction

• Sarcomere: Functional unit; bordered by Z lines; contains actin (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Myosin heads bind to actin, pulling filaments past each other, shortening the sarcomere.

• Role of ATP: Provides energy for myosin head movement and detachment.

• Role of Calcium: Binds to troponin, causing tropomyosin to move and expose binding sites on actin.

• Calcium Storage: Sarcoplasmic reticulum; released via T-tubules during stimulation.

Neuromuscular Junction and Motor Units

• Neuromuscular Junction: Synapse between motor neuron and muscle fiber.

• Acetylcholine: Neurotransmitter that initiates muscle contraction.

• Motor Unit: One motor neuron and all the muscle fibers it innervates.

Chapter 7: Blood

Functions and Composition of Blood

• Functions: Transport (gases, nutrients, wastes), regulation (pH, temperature), protection (immune response, clotting).

• Composition:

  • Plasma: 55% of blood; water, proteins, nutrients, hormones.

  • Formed Elements: 45%; erythrocytes (RBCs), leukocytes (WBCs), platelets (thrombocytes).

Origin and Types of Formed Elements

• Origin: All formed elements arise from hematopoietic stem cells in red bone marrow.

• Categories:

  • Platelets: Cell fragments for clotting.

  • Erythrocytes: Red blood cells; carry oxygen via hemoglobin.

  • Leukocytes: White blood cells; immune defense. Types include neutrophils, eosinophils, basophils, lymphocytes, monocytes.

Red Blood Cells (RBCs)

• Function: Transport oxygen and carbon dioxide.

• Features: Biconcave, no nucleus, filled with hemoglobin.

• Life Span: ~120 days; destroyed in spleen and liver.

• Erythropoietin: Hormone from kidneys stimulating RBC production.

• Recycling: Iron and amino acids reused; heme converted to bilirubin.

Leukocytes (WBCs)

• Function: Defend against pathogens.

• Types:

  • Granulocytes: Neutrophils, eosinophils, basophils.

  • Agranulocytes: Lymphocytes, monocytes.

Platelets

• Function: Blood clotting (hemostasis).

• Features: Fragments of megakaryocytes.

Blood Disorders

• Anemia: Low RBCs or hemoglobin; causes include iron deficiency, sickle-cell disease.

• Leukemia: Cancer of WBCs; treated with chemotherapy, bone marrow transplant.

Blood Types and Transfusion

• ABO System: Based on presence of A and B antigens.

• Rh Factor: Positive or negative based on D antigen.

• Agglutination: Clumping of RBCs due to antibody-antigen reaction.

• Hemolytic Disease of the Newborn: Occurs if Rh- mother has Rh+ baby; prevented by RhoGAM.

Hemostasis and Clotting

• Three Steps: Vascular spasm, platelet plug formation, coagulation.

• Clotting Cascade: Prothrombin activator converts prothrombin to thrombin; thrombin converts fibrinogen to fibrin.

Chapter 8: The Cardiovascular System

Components and Functions

• Components: Heart, blood vessels, blood.

• Functions: Transport, regulation, protection.

Pathway of Blood and Blood Vessels

• Order: Heart → arteries → arterioles → capillaries → venules → veins → heart.

• Oxygenation: Arteries usually carry oxygen-rich blood (except pulmonary arteries); veins usually carry oxygen-poor blood (except pulmonary veins).

Structure and Types of Blood Vessels

• Lumen: Central cavity of vessel.

• Endothelium: Inner lining of vessels.

• Arteries: Thick walls, high pressure, carry blood away from heart.

• Veins: Thinner walls, lower pressure, valves prevent backflow, carry blood to heart.

• Capillaries: Thin walls for exchange of substances.

Mechanisms for Blood Return

• Valves: Prevent backflow in veins.

• Muscle Contraction: Skeletal muscle pump aids venous return.

• Respiratory Pump: Changes in thoracic pressure during breathing help move blood.

Lymphatic System

• Function: Returns excess tissue fluid to bloodstream, immune defense.

Heart Structure and Function

• Layers: Pericardium (outer), myocardium (muscle), endocardium (inner).

• Chambers: Right/left atria (upper), right/left ventricles (lower).

• Valves: Right AV (tricuspid), left AV (bicuspid/mitral), pulmonary and aortic semilunar valves.

• Septum: Divides right and left sides.

• Heart Sounds: "Lub" (AV valves close), "dup" (semilunar valves close).

Blood Flow Through the Heart

• Right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body.

Circuits of the Heart

• Pulmonary Circuit: Right side pumps to lungs.

• Systemic Circuit: Left side pumps to body.

• Coronary Circulation: Supplies heart muscle itself.

Cardiac Cycle

• Systole: Contraction phase; blood ejected.

• Diastole: Relaxation phase; chambers fill.

Cardiac Conduction System

• SA Node: Pacemaker; initiates heartbeat.

• AV Node: Delays impulse.

• Bundle of His, Purkinje Fibers: Spread impulse through ventricles.

Electrocardiogram (ECG/EKG)

• P Wave: Atrial depolarization.

• QRS Complex: Ventricular depolarization.

• T Wave: Ventricular repolarization.

Blood Pressure

• Definition: Force of blood against vessel walls.

• Sphygmomanometer: Device to measure blood pressure.

• Systolic: Pressure during contraction.

• Diastolic: Pressure during relaxation.

• Pressure Gradient: Highest in aorta, lowest in veins.

Chapter 9: The Immune System and Mechanisms of Defense

Key Terms

• Pathogen: Disease-causing organism.

• Antigen: Substance that triggers immune response.

• Cancer Cells: Abnormal cells with uncontrolled growth.

Three Lines of Defense

• First Line (Non-specific): Physical and chemical barriers (skin, mucous membranes, secretions).

• Second Line (Non-specific): Internal defenses (phagocytes, NK cells, inflammation, fever, complement, interferons).

• Third Line (Specific): Adaptive immunity (lymphocytes, antibodies, memory).

First Line Components

• Skin, mucous membranes, tears, saliva, stomach acid.

Second Line Components

• Phagocytes: Engulf pathogens.

• Natural Killer (NK) Cells: Destroy infected/cancerous cells.

• Interferons: Proteins that inhibit viral replication.

• Complement: Proteins that enhance immune response.

• Pyrogens: Cause fever.

• Inflammation: Redness, heat, swelling, pain; caused by histamine.

Third Line: Adaptive Immunity

• MHC (Major Histocompatibility Complex): Cell surface proteins for self-recognition.

• Lymphocytes: B cells (produce antibodies), T cells (cell-mediated immunity).

• Effector Cells: Act immediately against antigen.

• Memory Cells: Provide long-term immunity.

• Antibodies: Proteins that bind antigens; classes include IgG, IgM, IgA, IgE, IgD.

Primary vs Secondary Immune Response

• Primary: First exposure; slower, less intense.

• Secondary: Subsequent exposure; faster, stronger due to memory cells.

Active and Passive Immunity

• Active: Body produces its own antibodies (natural: infection; artificial: vaccination).

• Passive: Antibodies from another source (natural: mother to baby; artificial: injection of antibodies).

T Lymphocytes

• Helper T Cells: Activate B and cytotoxic T cells.

• Cytotoxic T Cells: Destroy infected cells.

• Memory T Cells: Provide long-term immunity.

Immune Disorders

• Autoimmune Disease: Immune system attacks self (e.g., lupus, rheumatoid arthritis).

• Allergy: Overreaction to harmless antigen (allergen); first exposure sensitizes, second triggers reaction.