Study Guide: Immune, Cardiovascular, and Blood Physiology

Lymphatic System

Organs of the Lymphatic System

The lymphatic system is composed of primary and secondary organs that play crucial roles in immune function and fluid balance.

• Primary organs: Sites where lymphocytes are produced and mature (e.g., bone marrow, thymus).

• Secondary organs: Sites where immune responses are initiated (e.g., lymph nodes, spleen, tonsils).

Example: The thymus is a primary organ where T cells mature, while lymph nodes are secondary organs where immune cells encounter antigens.

General Function of the Lymphatic System

The lymphatic system maintains fluid balance, absorbs dietary fats, and provides immune defense by transporting lymphocytes and filtering pathogens.

• Returns interstitial fluid to the bloodstream

• Transports dietary lipids

• Facilitates immune surveillance and response

Immune Response

1st Line of Defense: Physical and Chemical Barriers

The first line of defense consists of physical and chemical barriers that prevent pathogen entry.

• Skin: Acts as a physical barrier to block pathogens.

• Mucus: Traps microbes in respiratory and digestive tracts.

• Tears and Saliva: Contain enzymes (e.g., lysozyme) that destroy bacteria.

• Other secretions: Such as stomach acid, which kills ingested pathogens.

Example: Tears contain lysozyme, which breaks down bacterial cell walls.

Innate vs Adaptive Immunity

Immunity is divided into innate (nonspecific) and adaptive (specific) responses.

• Innate immunity: Immediate, nonspecific defense (e.g., barriers, phagocytes, inflammation).

• Adaptive immunity: Delayed, specific response involving lymphocytes (B and T cells) and memory formation.

2nd Line of Defense: Innate Immune Cells and Mechanisms

The second line of defense involves cellular and molecular mechanisms that target pathogens nonspecifically.

• White Blood Cells (WBCs): Phagocytes (e.g., neutrophils, macrophages) engulf and destroy pathogens.

• Interferons: Proteins that inhibit viral replication.

• Inflammation: Local response to injury or infection, increases blood flow and recruits immune cells.

• Fever: Systemic increase in body temperature to inhibit pathogens.

• Complement System: Plasma proteins that enhance phagocytosis and lyse pathogens.

• Phagocytosis: Engulfment and digestion of microbes by phagocytes.

• Antigen Presenting Cells (APCs): Present antigens to T cells (e.g., dendritic cells, macrophages).

• Natural Killer (NK) Cells: Destroy infected or abnormal cells without prior sensitization.

3rd Line of Defense: Adaptive Immunity

The third line of defense is characterized by specificity and memory, involving B and T lymphocytes.

• Humoral Immunity (B cells):

  • Plasma cells produce antibodies (five classes: IgG, IgA, IgM, IgE, IgD).

  • Memory B cells provide long-term immunity.

• Cell-mediated Immunity (T cells):

  • Cytotoxic T cells destroy infected cells.

  • Helper T cells activate other immune cells.

  • Regulatory T cells modulate immune response.

  • Memory T cells provide long-term protection.

• MHC I vs MHC II: MHC I presents antigens to cytotoxic T cells; MHC II presents to helper T cells.

• Immune Response to:

  • Allergies: Hypersensitivity reactions to harmless antigens.

  • Bacteria: Phagocytosis and antibody-mediated neutralization.

  • Viruses: Cytotoxic T cells and interferon response.

• NK Cells: Provide rapid response to virally infected cells and tumors.

Blood

Hemostasis

Hemostasis is the process that prevents blood loss after vessel injury.

• Vascular spasm: Immediate vasoconstriction to reduce blood flow.

• Platelet plug formation: Platelets adhere to exposed collagen and aggregate.

• Coagulation: Cascade of clotting factors leading to fibrin clot formation.

• Fibrinolysis: Breakdown and removal of the clot after healing.

Plasma Components

Plasma is the liquid portion of blood, containing water, proteins, and dissolved substances.

• Hormones: Chemical messengers (e.g., insulin, erythropoietin).

• Transferrin: Iron transport protein.

• Antibodies: Immunoglobulins produced by plasma cells.

• Ions: Electrolytes such as Na+, K+, Ca2+.

• Albumin: Maintains osmotic pressure.

• Fibrinogen: Precursor to fibrin in clotting.

• Water: Solvent for transport.

• Gases: Oxygen and carbon dioxide.

Hematopoiesis

Hematopoiesis is the formation of blood cells from hematopoietic stem cells in the bone marrow.

• Produces erythrocytes, leukocytes, and platelets.

• Regulated by cytokines (e.g., EPO for RBCs, TPO for platelets, CSF for WBCs).

• Myeloid and lymphoid lineages give rise to different cell types.

Red Blood Cells (RBCs)

RBCs transport oxygen and carbon dioxide and are essential for iron metabolism and homeostasis.

• Hemoglobin: Oxygen-carrying protein containing iron.

• Hematocrit: Percentage of blood volume occupied by RBCs.

• Iron metabolism: Involves absorption, transport (transferrin), storage (ferritin), and regulation (hepcidin, DMT1, ferroportin).

Cardiovascular System

Heart

The heart pumps blood through the circulatory system, maintaining pressure and flow.

• Cardiac Cycle: Sequence of events in one heartbeat, including systole and diastole.

• Blood flow: Follows a specific path through chambers and valves (AV and SL valves).

• Cardiac muscle structure: Specialized for rhythmic contraction and relaxation.

• Excitation-contraction coupling: Electrical signals trigger muscle contraction.

• ECG: Records electrical activity; P-wave (atrial depolarization), QRS complex (ventricular depolarization), T-wave (ventricular repolarization).

• Conduction system: SA node, AV node, AV bundle, bundle branches, Purkinje fibers coordinate heartbeat.

Blood Vessels

Blood vessels transport blood throughout the body and differ in structure and function.

• Types: Arteries (carry blood away from heart), veins (return blood to heart), capillaries (exchange vessels).

• Anatomical differences: Arteries have thicker walls, veins have valves, capillaries are thin for exchange.

Physical and Chemical Factors Influencing Blood Pressure

Blood pressure is regulated by multiple factors affecting vessel diameter, blood volume, and cardiac function.

• Resistance changes: Vasodilation decreases resistance; vasoconstriction increases resistance. Vessel length and blood volume also affect resistance.

• Pressure gradient: Drives blood flow from high to low pressure.

• Autonomic Nervous System (ANS): Sympathetic increases, parasympathetic decreases blood pressure.

• Baroreceptors: Detect pressure changes and adjust heart rate and vessel diameter.

• Chemoreceptors: Respond to changes in blood gases (O2, CO2).

• Stroke volume and cardiac output: Cardiac output = heart rate × stroke volume.

Equation:

$\text{Cardiac Output} = \text{Heart Rate} \times \text{Stroke Volume}$

$\text{Blood Pressure} = \text{Cardiac Output} \times \text{Total Peripheral Resistance}$

Summary Table: Blood Vessel Types

Type	Main Function	Key Features
Arteries	Carry blood away from heart	Thick, elastic walls
Capillaries	Exchange of gases, nutrients, wastes	Thin walls, single cell layer
Veins	Return blood to heart	Thinner walls, valves present