Cardiovascular and Lymphatic Systems: Study Guide for A&P II

The Cardiovascular System

Heart Physiology

The heart's physiology involves electrical conduction, ionic mechanisms, and mechanical events that coordinate its function as a pump. Understanding these processes is essential for grasping how the heart maintains circulation.

• Conduction System of the Heart: The heart's electrical system includes the Sinoatrial (SA) node, Atrioventricular (AV) node, AV bundle (Bundle of His), right and left bundle branches, and Purkinje fibers. The SA node initiates the heartbeat, and impulses travel through the system to coordinate contraction.

• Pacemaker Potential: The SA node generates spontaneous depolarizations due to slow Na+ influx, followed by Ca2+ entry and K+ exit. This pacemaker potential ensures rhythmic contractions.

• Intrinsic Rates of Autorhythmic Cells: Different cells (SA node, AV node, Purkinje fibers) have varying intrinsic rates. If the SA node fails, other cells can take over as pacemakers, though at slower rates.

• Cardiac Contractile Cell Action Potential: The action potential includes rapid depolarization (Na+ influx), a plateau phase (Ca2+ influx balances K+ efflux), and repolarization (K+ efflux). The plateau phase prevents tetanus and ensures proper contraction.

• Excitation-Contraction Coupling: Depolarization triggers Ca2+ release, which binds to troponin, allowing actin-myosin interaction and contraction.

• EKG Recording: An EKG shows the heart's electrical activity. The P wave represents atrial depolarization, the QRS complex ventricular depolarization, and the T wave ventricular repolarization.

• Mechanical Events of the Cardiac Cycle: Includes atrial systole, ventricular systole, and diastole. Valve positions and pressure gradients change to direct blood flow.

• Heart Sounds: The first sound ("lub") is due to AV valve closure; the second sound ("dub") is due to semilunar valve closure.

Cardiac Output

• Definitions: Cardiac output (CO) is the volume of blood pumped per minute. Stroke volume (SV) is the volume per beat. Heart rate (HR) is beats per minute.

• Relationship: $CO = SV \times HR$

• Manipulation: CO can be increased by raising HR or SV, such as during exercise.

• Regulation: Factors affecting SV include preload, contractility, and afterload. Factors affecting HR include autonomic nervous system activity, hormones, and fitness.

Blood Vessels

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

• Types of Blood Vessels: Arteries (high pressure, thick walls), arterioles (regulate flow), capillaries (exchange), venules (collect blood), veins (low pressure, thin walls).

• Specific Circulations: Pulmonary (lungs), systemic (body), coronary (heart), cerebral arterial circle (Circle of Willis), hepatic portal system (liver), fetal circulation.

Flow, Pressure, and Resistance

• Definitions: Flow (F) is the volume per time. Blood pressure (\Delta P) is the force per area. Resistance (R or PR) opposes flow.

• Relationship: $F = \frac{\Delta P}{R}$

• Sources of Resistance: Vessel diameter (most important), vessel length, blood viscosity.

Elastic vs. Muscular Arteries

• Elastic arteries: Large, near the heart, stretch and recoil to maintain pressure.

• Muscular arteries: Distribute blood, more smooth muscle, regulate flow.

Systemic Arterial Pressure

• Systolic pressure: Peak during ventricular contraction.

• Diastolic pressure: Lowest during relaxation.

• Pulse pressure: $\text{Pulse Pressure} = \text{Systolic} - \text{Diastolic}$

• Mean arterial pressure (MAP): $\text{MAP} = \text{Diastolic} + \frac{1}{3}(\text{Pulse Pressure})$

Capillaries

• Types: Continuous (tight junctions), fenestrated (pores), sinusoidal (large gaps).

• Features: Thin walls, intercellular clefts, fenestrations, high cross-sectional area, low velocity.

• Regulation: Precapillary sphincters control flow; bypass via metarterioles.

Movement of Materials

• Diffusion: Movement of solutes down concentration gradients.

• Bulk Flow: Movement of fluid driven by pressure differences.

Bulk Flow and Capillary Fluid Dynamics

• Definitions:

  • Capillary hydrostatic pressure: Pressure exerted by blood against capillary walls.

  • Capillary osmotic pressure: Pressure due to plasma proteins drawing water in.

  • Interstitial fluid hydrostatic pressure: Pressure in tissue fluid.

  • Interstitial fluid osmotic pressure: Pressure due to proteins in tissue fluid.

  • Net filtration pressure (NFP): Determines direction of fluid movement.

• Calculation: $\text{NFP} = (\text{Capillary hydrostatic pressure} + \text{Interstitial fluid osmotic pressure}) - (\text{Capillary osmotic pressure} + \text{Interstitial fluid hydrostatic pressure})$

• Filtration vs. Reabsorption: Filtration occurs at arterial end; reabsorption at venous end.

• Lymphatic System: Returns excess fluid to blood, preventing edema.

Veins and Venous Return

• Veins: Act as blood reservoirs due to their capacity and compliance.

• Venous Return: Affected by skeletal muscle contraction, respiratory pump, and venous valves.

MAP, CO, and PR

• Relationship: $\text{MAP} = CO \times PR$

• Regulation: CO and PR are adjusted via neural, hormonal, and local mechanisms.

Control of MAP

• Short-term: Neural and hormonal control (baroreceptors, chemoreceptors).

• Long-term: Renal regulation of blood volume.

Tissue Perfusion

• Perfusion: Blood flow to tissues varies by need.

• Autoregulation: Local control adjusts flow.

• Extrinsic Regulation: Nervous and hormonal control.

The Lymphatic System and Immunity

Major Functions of the Lymphatic System

The lymphatic system maintains fluid balance, absorbs fats, and provides immune defense.

• Fluid balance: Returns excess interstitial fluid to the bloodstream.

• Fat absorption: Absorbs fats from the digestive tract via lacteals.

• Immune defense: Houses lymphocytes and filters pathogens.

Plasma, Interstitial Fluid, and Lymph

• Plasma: Fluid component of blood.

• Interstitial fluid: Fluid between cells.

• Lymph: Fluid in lymphatic vessels, derived from interstitial fluid.

Lymph Vessels

• Structure: Thin-walled, valved vessels that transport lymph.

• Function: Collect and return fluid to the circulatory system.

Lymphoid Tissue and Organs

• Lymphocytes: Immune cells (B and T cells).

• Reticular tissue: Network supporting lymphocytes.

• Lymph nodes: Filter lymph, house immune cells.

• Spleen: Filters blood, recycles RBCs, immune surveillance.

• Tonsils: Protect against inhaled/ingested pathogens.

• MALT: Mucosa-associated lymphoid tissue in mucous membranes.

Structure of a Lymph Node

• Cortex: Contains follicles with germinal centers.

• Medulla: Contains medullary cords and sinuses.

• Afferent and efferent vessels: Lymph enters via afferent, exits via efferent.

Thymus

• Structure: Bi-lobed organ in the mediastinum.

• Function: Site of T cell maturation.

Functions of the Immune System

• Defense: Protects against pathogens.

• Homeostasis: Removes dead/damaged cells.

• Surveillance: Detects and eliminates abnormal cells.

Blood Vessel Type	Histology	Function	Pressure (mm Hg)
Arteries	Thick, elastic walls	Carry blood away from heart	High (80-120)
Arterioles	Small, muscular	Regulate flow to capillaries	Moderate (30-80)
Capillaries	Single layer endothelium	Exchange of materials	Low (20-40)
Venules	Thin walls	Collect blood from capillaries	Very low (10-20)
Veins	Thin, less elastic	Return blood to heart	Lowest (<10)

Example: During exercise, cardiac output increases to supply muscles with more oxygen, and blood flow is redirected from digestive organs to skeletal muscle.

Additional info: Academic context was added to expand brief objectives into full explanations, including definitions, formulas, and examples for clarity and completeness.