Unit 2 Study Guide: The Heart, Blood Vessels, Lymphatic System, and Immunity

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Chapter 19: The Heart

Location and Structure of the Heart

The heart is a muscular organ located in the mediastinum of the thoracic cavity. It is surrounded by protective membranes called the pericardium.

Pericardial Layers: Parietal pericardium (outer layer), visceral pericardium (inner layer, also called epicardium).
Function: Protects and anchors the heart, reduces friction during heartbeats.

Histology of the Heart Wall

The heart wall consists of three layers, each with distinct functions and structures.

Epicardium: Outer layer, provides protection.
Myocardium: Middle, muscular layer responsible for contraction.
Endocardium: Inner layer, lines the chambers and valves.

Anatomy of the Heart: Chambers, Valves, and Vessels

The heart contains four chambers and several valves that regulate blood flow.

Chambers: Right atrium, right ventricle, left atrium, left ventricle.
Valves: Tricuspid, pulmonary, mitral (bicuspid), aortic.
Associated Vessels: Superior/inferior vena cava, pulmonary arteries/veins, aorta.

Pathway of Blood Flow Through the Heart

Blood flows through the heart in a specific sequence, ensuring oxygenation and circulation.

Right atrium → right ventricle → pulmonary arteries → lungs (oxygenation) → pulmonary veins → left atrium → left ventricle → aorta → body.
Oxygenation: Blood is oxygen-poor in the right side, oxygen-rich in the left side.

Heart Valves: Location, Structure, and Function

Valves prevent backflow and ensure unidirectional blood flow.

Tricuspid Valve: Between right atrium and ventricle.
Pulmonary Valve: Between right ventricle and pulmonary artery.
Mitral Valve: Between left atrium and ventricle.
Aortic Valve: Between left ventricle and aorta.
Heart Sounds: Produced by valve closure ("lub-dub").

Heart Murmurs

Abnormal heart sounds caused by turbulent blood flow, often due to valve defects.

Example: Mitral valve prolapse causing a systolic murmur.

Cardiac vs. Skeletal Muscle Structure

Cardiac muscle has unique features compared to skeletal muscle.

Intercalated Discs: Specialized connections for synchronized contraction.
Striations: Both have striations, but cardiac muscle is branched.
Autorhythmicity: Cardiac muscle can contract without neural input.

Innervation of the Heart

The heart is innervated by both sympathetic and parasympathetic neurons.

Sympathetic: Increases heart rate and force.
Parasympathetic: Decreases heart rate.
Clinical Note: Severing all nerves would result in loss of regulation but the heart may continue to beat due to intrinsic pacemaker cells.

Regulation of Contraction

Cardiac muscle contraction is regulated by electrical impulses and calcium ion dynamics.

Comparison: Cardiac muscle contracts involuntarily; skeletal muscle contracts voluntarily.
Intercalated Discs: Allow rapid transmission of action potentials.

Cardiac Conduction System

The conduction system coordinates heartbeats.

Components: SA node, AV node, bundle of His, bundle branches, Purkinje fibers.
Function: Initiates and distributes electrical impulses.
Which Chamber Contracts First: Atria contract before ventricles due to SA node location.

Cardiac Cycle and EKG

The cardiac cycle includes all events in one heartbeat, represented on an EKG.

Phases: Systole (contraction), diastole (relaxation).
EKG Waves: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

Cardiac Output, Stroke Volume, Heart Rate

These parameters determine the amount of blood pumped by the heart.

Cardiac Output (CO): Volume of blood pumped per minute.
Stroke Volume (SV): Volume of blood pumped per beat.
Heart Rate (HR): Beats per minute.
Relationship:

Factors Affecting CO: Preload, afterload, contractility, heart rate.

Chapter 20: Blood Vessels

Histology and Function of Blood Vessels

Arteries, veins, and capillaries have distinct structures and functions.

Arteries: Thick muscular walls, carry blood away from the heart.
Veins: Thinner walls, valves to prevent backflow, carry blood to the heart.
Capillaries: Thin walls for exchange of gases and nutrients.

Blood Flow Pathways

Blood circulates through arteries, capillaries, and veins in a closed circuit.

Arterial Path: Heart → arteries → arterioles → capillaries.
Venous Path: Capillaries → venules → veins → heart.
Portal Systems: Blood passes through two capillary beds before returning to the heart (e.g., hepatic portal system).

Blood Pressure Changes and Physiology

Blood pressure varies throughout the circulatory system.

Systolic Pressure: Pressure during ventricular contraction.
Diastolic Pressure: Pressure during ventricular relaxation.
Mean Arterial Pressure (MAP): Average pressure in arteries.
Equation:

Factors Affecting Blood Pressure: Cardiac output, blood volume, resistance.

Blood Pressure Regulation

Blood pressure is regulated by neural, hormonal, and renal mechanisms.

Baroreceptors: Detect changes in pressure.
Hormones: ADH, aldosterone, epinephrine.
Conditions: Hypertension (high BP), Hypotension (low BP).

Major Circulatory Pathways

Systemic, pulmonary, and coronary circuits transport blood throughout the body.

Systemic Circuit: Delivers oxygen-rich blood to tissues.
Pulmonary Circuit: Exchanges CO2 for O2 in lungs.
Coronary Circuit: Supplies heart muscle itself.

Chapter 21: The Lymphatic System

Components and Functions of the Lymphatic System

The lymphatic system returns excess fluid to the bloodstream and provides immune defense.

Components: Lymph, lymphatic vessels, lymph nodes, thymus, spleen, tonsils, appendix.
Main Functions: Fluid balance, fat absorption, immune response.

Specific Functions of Lymphatic Organs

Lymph Capillaries and Vessels: Collect and transport lymph.
Thymus: Site of T cell maturation.
Lymph Nodes: Filter lymph, house immune cells.
Tonsils: Protect against inhaled/ingested pathogens.
Spleen: Filters blood, removes old RBCs, immune surveillance.
Appendix: May play a role in gut immunity.

Lymphatic vs. Blood Vessels

Lymphatic vessels are similar to veins but carry lymph, not blood, and have more valves.

Lymph: Contains water, proteins, lymphocytes.
Valves: Prevent backflow, ensure one-way movement.

Chapter 21: Immunity

Innate Immunity

Innate immunity provides immediate, non-specific defense against pathogens.

Barriers: Skin, mucous membranes.
Antimicrobial Proteins: Interferons, complement.
Cells: Natural killer cells, phagocytes.
Responses: Inflammation, fever.

Adaptive (Specific) Immunity

Adaptive immunity targets specific pathogens and provides long-term protection.

Key Terms: Pathogen (disease-causing agent), Antigen (molecule recognized by immune system), Antibody (protein that binds antigen).
Cell-Mediated Immunity: T cells attack infected cells.
Antibody-Mediated Immunity: B cells produce antibodies.

Development and Activation of Lymphocytes

Development: T cells mature in thymus, B cells in bone marrow.
Activation: Involves antigen recognition, proliferation, and differentiation.
Clonal Selection: Only lymphocytes specific to an antigen are activated.

Functions of Immune Cells

Helper T Cells: Activate other immune cells.
Cytotoxic T Cells: Destroy infected cells.
Memory T Cells: Provide long-term immunity.
Plasma B Cells: Produce antibodies.
Memory B Cells: Rapid response upon re-exposure.

Antibody Structure and Function

Antibodies are Y-shaped proteins that bind antigens and mediate immune responses.

Mechanisms: Neutralization, immobilization, agglutination, complement activation, opsonization.

Types of Immunity

Passive Immunity: Antibodies acquired from another source (e.g., maternal antibodies).
Active Immunity: Antibodies produced by the individual's own immune system.
Immunological Memory: Ability to respond more rapidly and effectively to previously encountered pathogens.
Primary vs. Secondary Response: Secondary response is faster and stronger due to memory cells.