Cardiovascular Physiology and Blood Flow: Study Guide (Chapters 14 & 15)

Cardiovascular Physiology

Overview of the Cardiovascular System

The cardiovascular system is responsible for transporting blood throughout the body, delivering oxygen and nutrients, and removing waste products. It consists of the heart, blood vessels, and blood.

• Pulmonary circuit: Carries deoxygenated blood from the right side of the heart to the lungs and returns oxygenated blood to the left side.

• Systemic circuit: Distributes oxygenated blood from the left side of the heart to the rest of the body and returns deoxygenated blood to the right side.

• Pressure: Drives blood flow; generated by heart contraction and affected by vessel diameter, length, and blood volume.

• Volume: Changes in blood volume (e.g., hemorrhage, dehydration, transfusion) directly affect blood pressure.

• Vessel diameter: Regulated by smooth muscle contraction/relaxation; vasoconstriction increases pressure, vasodilation decreases it.

• Vessel length: Longer vessels increase resistance and decrease flow.

• Viscosity: Thicker blood (higher viscosity) increases resistance and decreases flow; affected by hematocrit.

Poiseuille’s Law and Blood Flow

Blood flow through vessels is governed by Poiseuille’s Law, which relates flow to pressure, vessel radius, length, and viscosity.

• Poiseuille’s Law:

$Q = \frac{\Delta P \cdot \pi \cdot r^4}{8 \cdot \eta \cdot L}$

• Q: Flow rate

• ΔP: Pressure difference

• r: Vessel radius

• η: Viscosity

• L: Vessel length

Flow is most sensitive to changes in vessel radius (to the fourth power).

Velocity, Flow, and Cross-sectional Area

Velocity of blood flow is inversely related to the total cross-sectional area of the vessels.

• Capillaries have the largest cross-sectional area and slowest velocity, allowing for exchange.

• Arteries have smaller cross-sectional area and faster velocity.

Heart Anatomy and Function

The heart is a muscular organ with four chambers: two atria and two ventricles. It is surrounded by the pericardium, which protects and anchors it.

• Pathway of deoxygenated blood: Vena cava → right atrium → right ventricle → pulmonary artery → lungs.

• Right side: Pulmonary circuit; Left side: Systemic circuit.

• Valves: AV valves (tricuspid, bicuspid/mitral) between atria and ventricles; semilunar valves (aortic, pulmonary) at base of heart.

• Chordae tendineae and papillary muscles: Prevent AV valve prolapse during contraction.

• Coronary arteries: Supply heart muscle with oxygenated blood.

Cardiac Muscle Structure and Function

Cardiac muscle differs from skeletal muscle in its structure and function.

• Spiral configuration: Allows efficient contraction and ejection of blood.

• Intercalated disks: Connect cardiac cells, allowing rapid electrical transmission.

• Autorhythmic (pacemaker) cells: Generate spontaneous action potentials.

• Contractile cells: Responsible for force generation.

Cardiac Action Potentials

Cardiac action potentials are essential for coordinated contraction. There are two types: pacemaker and contractile cell action potentials.

• Pacemaker cells: Located in SA node, AV node, Purkinje fibers.

• Contractile cells: Found in atria and ventricles.

• Four phases of contractile action potential: Rapid depolarization, initial repolarization, plateau, final repolarization.

• Plateau phase: Caused by Ca2+ influx; prevents tetanus, ensures proper filling and ejection.

• NCX antiporter: Exchanges Na+ and Ca2+; does not use ATP directly.

Cardiac Conduction Pathway

The cardiac conduction system ensures coordinated contraction.

• Pathway: SA node → AV node (AV node delay) → Bundle of His → Purkinje fibers → ventricles.

• SA node pace: ~70 bpm; AV node: ~50 bpm; Purkinje fibers: ~35 bpm.

• AV node delay: Allows atria to contract before ventricles.

Electrocardiogram (ECG)

An ECG records the electrical activity of the heart.

• Segments: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

• Heart rate calculation: Count QRS complexes per minute.

Cardiac Cycle and Heart Sounds

The cardiac cycle consists of five phases, corresponding to contraction and relaxation.

• "Lub" sound: Closure of AV valves.

• "Dub" sound: Closure of semilunar valves.

Frank-Starling Law and Cardiac Output

The Frank-Starling Law states that increased EDV leads to increased stroke volume due to greater stretch of cardiac muscle.

• Stroke volume calculation:

$SV = EDV - ESV$

• Cardiac output equation:

$CO = HR \times SV$

• Autonomic nervous system: Sympathetic increases heart rate and inotropy; parasympathetic decreases heart rate.

• Increasing EDV: Venous return via skeletal muscle pump, respiratory pump, and sympathetic venoconstriction.

• Calcium pump/ATPase: Enhances contractility and relaxation.

• Sympathetic activity: Increases heart rate, contractility, and venous return.

Key Terminology

• Atria, Ventricles, Hydrostatic pressure, Aorta, Arteries, Arterioles, Capillaries, Venules, Veins, Vena cava, Pericardium, Tricuspid valve, Bicuspid valve, Chordae tendineae, Papillary muscles, Autorhythmic cells, Intercalated disks, NCX antiporter, Purkinje fibers, Sinoatrial (SA) node, Atrioventricular (AV) node, Electrocardiogram (ECG), Systole, Diastole, Stroke volume, Cardiac output, End-diastolic volume (EDV), End-systolic volume (ESV), Inotropy, Afterload, Ejection fraction

Blood Flow and Control of Blood Pressure

Blood Vessel Structure and Function

Blood vessels are classified by their structure and function.

• Arteries: Pressure reservoir; thick elastic and smooth muscle layers.

• Veins: Volume reservoir; thinner walls, less muscle, more compliant.

• Arterioles: Primary site for regulation of blood flow; mainly smooth muscle.

• Capillaries: Exchange vessels; only endothelium.

Vessel Type	Endothelium	Elastic Tissue	Smooth Muscle	Fibrous Tissue	Primary Purpose
Artery	Yes	High	High	Moderate	Pressure reservoir
Vein	Yes	Low	Low	Moderate	Volume reservoir
Arteriole	Yes	None	High	Low	Flow regulation
Capillary	Yes	None	None	None	Exchange

Blood Pressure Calculations

Blood pressure is measured and calculated using several methods.

• Pulse pressure:

$PP = Systolic\ Pressure - Diastolic\ Pressure$

• Mean arterial pressure (MAP):

$MAP = Diastolic\ Pressure + \frac{1}{3} (Systolic\ Pressure - Diastolic\ Pressure)$

• Sphygmomanometry: Measures blood pressure using a cuff; Korotkoff sounds indicate systolic and diastolic pressures.

Regulation of Blood Pressure

Blood pressure is regulated by cardiac output and resistance in arterioles.

• MAP equation:

$MAP \propto CO \times R_{arterioles}$

$MAP \propto CO \times TPR$

• Factors affecting MAP: Blood volume, cardiac output, resistance, distribution of blood.

• Shock: Inadequate blood flow; types include hypovolemic, cardiogenic, distributive.

• High blood pressure responses: Cardiovascular system reduces cardiac output; kidneys excrete excess fluid.

Vascular Regulation

Blood flow is redirected by manipulating arterioles.

• Myogenic autoregulation: Smooth muscle responds to stretch by contracting.

• Chemical mediators: Vasoconstriction (e.g., norepinephrine, angiotensin II); vasodilation (e.g., nitric oxide, histamine).

• Active hyperemia: Increased blood flow to active tissues.

• Reactive hyperemia: Increased flow after occlusion.

Baroreflex and Blood Distribution

The baroreflex maintains blood pressure homeostasis.

• Baroreceptors: Located in carotid and aortic arteries; detect pressure changes.

• Effectors: Heart and blood vessels.

• Orthostatic hypotension: Drop in blood pressure upon standing.

Blood Velocity and Exchange

Blood velocity is fastest in arteries, slowest in capillaries due to cross-sectional area.

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

• Filtration: Outward movement; occurs at arterial end of capillaries.

• Absorption: Inward movement; occurs at venous end.

• Colloid/oncotic pressure: Osmotic pressure due to plasma proteins; opposes filtration.

• Lymph vessels: Return excess filtered fluid to circulation.

Cardiovascular Disease and Atherosclerosis

Atherosclerosis is the buildup of plaques in arteries, leading to hypertension and cardiovascular disease.

• High-density lipoproteins (HDL): "Good" cholesterol; removes cholesterol from arteries.

• Low-density lipoproteins (LDL): "Bad" cholesterol; deposits cholesterol in arteries.

• Hypertension: Chronic high blood pressure; increases risk of heart disease.

Key Terminology

• Endothelium, Angiogenesis, Pulse pressure, Sphygmomanometry, Myogenic autoregulation, Active hyperemia, Reactive hyperemia, Nitric oxide, Histamine, Hyperemia, Baroreflex, Orthostatic hypotension, Bulk flow, Filtration, Absorption, Colloid/oncotic pressure, Edema, Cardiovascular disease, Atherosclerosis, High-density lipoproteins, Low-density lipoproteins, Hypertension

Example:

During exercise, active hyperemia increases blood flow to skeletal muscles, while vasoconstriction reduces flow to less active organs.

Additional info: Academic context was added to expand brief points into full explanations, and a table was inferred for vessel structure and function.