Comprehensive Study Guide: Cardiovascular, Blood, and Respiratory Physiology

Cardiovascular Physiology

Anatomy and Physiology of the Heart

The heart is a muscular organ responsible for pumping blood throughout the body. Understanding its anatomy is essential for grasping its physiological functions.

• Chambers: Right and left atria (receive blood), right and left ventricles (pump blood out).

• Valves: Atrioventricular (tricuspid and mitral) and semilunar (pulmonary and aortic) valves ensure unidirectional flow.

• Major vessels: Superior/inferior vena cava, pulmonary arteries/veins, aorta.

Pressure, Volume, Flow, and Resistance

Blood flow in the cardiovascular system is governed by physical principles involving pressure gradients, resistance, and vessel properties.

• Pressure Gradient: Blood flows from areas of higher pressure to lower pressure. The greater the gradient, the higher the flow.

• Distance: Pressure decreases with distance due to friction.

• Resistance: Flow is inversely proportional to resistance. Higher resistance means lower flow.

• Viscosity: Increased blood viscosity increases resistance and decreases flow.

• Vessel Radius: Resistance is inversely proportional to the fourth power of the vessel radius. Small changes in radius have large effects on resistance and flow.

• Vasoconstriction: Decreases vessel radius, increases resistance, decreases flow.

• Vasodilation: Increases vessel radius, decreases resistance, increases flow.

• Flow Rate vs. Velocity: Flow rate is the volume of blood passing a point per unit time; velocity is the speed of blood movement. Velocity = Flow rate / Cross-sectional area.

Poiseuille’s Law: Describes the relationship between flow, pressure, radius, length, and viscosity:

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

Where $Q$ is flow, $\Delta P$ is pressure difference, $r$ is radius, $\eta$ is viscosity, and $l$ is length.

Cardiac Muscle Cells: Autorhythmic vs. Contractile

• Autorhythmic Cells: Generate action potentials spontaneously; set the heart rate (e.g., SA node).

• Contractile Cells: Make up most of the myocardium; responsible for contraction and pumping blood.

Cardiac Muscle Contraction and Action Potentials

• Steps of Contraction: Depolarization (Na+ influx), plateau (Ca2+ influx), repolarization (K+ efflux).

• Plateau Phase: Prolongs action potential, prevents tetanus.

• Refractory Period: Longer in cardiac muscle than skeletal muscle, ensuring rhythmic contractions.

Action Potentials in Autorhythmic Cells

• Pacemaker Potential: Gradual depolarization due to funny channels (If) and Ca2+ influx.

• Threshold: When reached, rapid depolarization occurs.

• Repolarization: K+ efflux restores resting potential.

Comparison Table: Action Potentials

Cell Type	Resting Potential	Depolarization	Plateau	Refractory Period
Skeletal Muscle	-70 mV	Na+ influx	Absent	Short
Cardiac Contractile	-90 mV	Na+ influx	Present (Ca2+)	Long
Cardiac Autorhythmic	Unstable	Ca2+ influx	Absent	Variable

Cardiac Conduction System

• SA Node: Pacemaker, initiates impulse.

• AV Node: Delays impulse, allows atrial contraction.

• AV Bundle (Bundle of His): Conducts impulse to ventricles.

• Bundle Branches and Purkinje Fibers: Distribute impulse throughout ventricles.

Electrocardiogram (ECG) Waves

• P wave: Atrial depolarization.

• QRS complex: Ventricular depolarization (and atrial repolarization).

• T wave: Ventricular repolarization.

Mechanical Events of the Cardiac Cycle

• Atrial Systole: Atria contract, push blood into ventricles.

• Ventricular Systole: Ventricles contract, AV valves close (first heart sound), semilunar valves open.

• Isovolumic Contraction/Relaxation: All valves closed, volume constant.

• Diastole: Chambers relax, fill with blood.

• Valve Operation: Open/close in response to pressure changes.

Stroke Volume and Cardiac Output

• Stroke Volume (SV): Volume of blood ejected per beat. $SV = EDV - ESV$

• Cardiac Output (CO): Volume of blood pumped per minute. $CO = SV \times HR$

Autonomic Nervous System (ANS) Control of Heart Rate

• Sympathetic Stimulation: Increases heart rate and contractility.

• Parasympathetic Stimulation: Decreases heart rate.

Factors Influencing Stroke Volume

• Preload: Degree of stretch (length-tension relationship).

• Frank-Starling Law: Increased venous return increases stroke volume.

• Inotropic Effects: Substances that alter contractility (e.g., catecholamines).

• Venous Return: Affected by skeletal muscle pump, respiratory pump, and blood volume.

Blood Flow and Transport

Anatomy of Blood Vessels

• Types: Arteries, arterioles, capillaries, venules, veins.

• Structure: Arteries have thick muscular walls; veins have thinner walls and valves; capillaries are thin for exchange.

Specialized Vessels and Cells

• Metarterioles: Short vessels connecting arterioles to capillaries; regulate flow.

• Precapillary Sphincters: Control blood entry into capillaries.

• Pericytes: Support capillary walls, regulate permeability.

Blood Pressure and Its Regulation

• Systolic Pressure: Peak pressure during ventricular contraction.

• Diastolic Pressure: Lowest pressure during ventricular relaxation.

• Pulse Pressure: Difference between systolic and diastolic pressures.

• Mean Arterial Pressure (MAP): Average pressure driving blood flow. $MAP = \text{Diastolic} + \frac{1}{3}(\text{Systolic} - \text{Diastolic})$

• MAP Influences: Cardiac output, peripheral resistance, blood volume.

Compensation Mechanisms for Blood Volume Changes

• Renal adjustments, hormonal responses, and vascular changes help restore normal blood pressure.

Autoregulation and Hyperemia

• Myogenic Autoregulation: Vessels constrict/dilate in response to pressure changes.

• Active Hyperemia: Increased blood flow due to increased metabolic activity.

• Reactive Hyperemia: Increased flow after a period of occlusion.

Sympathetic Control and Baroreceptor Reflex

• Sympathetic Stimulation: Causes vasoconstriction via norepinephrine.

• Baroreceptor Reflex: Senses changes in blood pressure, adjusts heart rate and vessel diameter to maintain homeostasis.

Capillary Exchange

• Types of Capillaries: Continuous, fenestrated, sinusoidal (vary in permeability).

• Velocity: Slowest in capillaries due to large cross-sectional area.

• Exchange Methods: Diffusion, transcytosis, bulk flow (filtration and absorption).

• Colloid Osmotic Pressure: Pulls fluid into capillaries; opposes filtration.

Lymphatic System and Edema

• Functions: Returns excess fluid to circulation, absorbs fats, immune defense.

• Edema: Swelling due to excess interstitial fluid.

• Disruptions: Increased capillary pressure, decreased plasma proteins, lymphatic obstruction.

Blood

Plasma Components and Functions

• Plasma: Water, ions, proteins (albumin, globulins, fibrinogen), nutrients, wastes.

• Plasma Proteins: Maintain osmotic pressure, transport, immunity, clotting.

Blood Cells and Their Functions

• Erythrocytes (RBCs): Oxygen transport.

• Leukocytes (WBCs): Immune defense (neutrophils, lymphocytes, monocytes, eosinophils, basophils).

• Thrombocytes (Platelets): Blood clotting.

Hematopoiesis and Cytokines

• Hematopoiesis: Formation of blood cells in bone marrow.

• Cytokines: Erythropoietin (RBCs), thrombopoietin (platelets), colony-stimulating factors (WBCs).

Complete Blood Count (CBC)

• CBC: Laboratory test measuring blood cell types and concentrations; used to assess health status.

Hemoglobin Metabolism

• Breakdown: RBCs destroyed in spleen; hemoglobin split into heme (converted to bilirubin) and globin (recycled).

Hemostasis

• Steps: Vasoconstriction, platelet plug formation, coagulation (clotting).

Mechanics of Breathing

Anatomy of the Respiratory System

• Bronchial Tree: Trachea, bronchi, bronchioles, alveoli.

• Lungs: Right (3 lobes), left (2 lobes).

Functions of the Respiratory System

• Gas exchange, pH regulation, protection, vocalization.

Pleural Sac and Alveolar Cells

• Pleural Sac: Reduces friction, creates pressure gradient.

• Alveolar Cells: Type I (gas exchange), Type II (produce surfactant).

Respiratory Membrane and Pulmonary Circulation

• Respiratory Membrane: Alveolar epithelium, capillary endothelium, fused basement membrane.

• Pulmonary Circulation: Right ventricle → pulmonary arteries → lungs → pulmonary veins → left atrium.

Mucociliary Escalator

• Cilia move mucus and trapped particles out of the airways.

Gas Laws in Respiration

• Dalton’s Law: Total pressure = sum of partial pressures of gases.

• Partial Pressure: Pressure exerted by a single gas in a mixture.

• Boyle’s Law: $P_1 V_1 = P_2 V_2$; pressure and volume are inversely related.

Lung Volumes and Capacities

• TV (Tidal Volume): Air in/out during normal breath.

• IRV (Inspiratory Reserve Volume): Extra air inhaled after normal inspiration.

• ERV (Expiratory Reserve Volume): Extra air exhaled after normal expiration.

• RV (Residual Volume): Air remaining after maximal exhalation.

• IC (Inspiratory Capacity): TV + IRV.

• FRC (Functional Residual Capacity): ERV + RV.

• TLC (Total Lung Capacity): TV + IRV + ERV + RV.

• VC (Vital Capacity): TV + IRV + ERV.

Pressure Changes During Breathing

• Inspiration: Thoracic volume increases, pressure decreases, air flows in.

• Expiration: Thoracic volume decreases, pressure increases, air flows out.

Surfactant and Airway Resistance

• Surfactant: Reduces surface tension, prevents alveolar collapse.

• Airway Resistance: Affected by airway diameter, lung volume, and smooth muscle tone.

Alveolar Ventilation

• Total air entering airways ≠ fresh air reaching alveoli due to dead space.

Gas Exchange and Transport

Hypoxia and Hypercapnia

• Hypoxia: Low oxygen levels.

• Hypercapnia: High carbon dioxide levels.

Variables Affecting Gas Exchange

• Oxygen, carbon dioxide, and pH are monitored to avoid hypoxia and hypercapnia.

Factors Affecting Gas Diffusion Rate

• Surface Area: More area increases diffusion.

• Concentration Gradient: Greater gradient increases diffusion.

• Barrier Permeability: More permeable = faster diffusion.

• Diffusion Distance: Shorter distance = faster diffusion.