Cardiovascular, Blood, and Respiratory Physiology: Mini-Textbook Study Guide

Cardiovascular Physiology

Heart Anatomy and Function

The heart is a muscular organ that acts as a pump to circulate blood throughout the body. Understanding its structure is essential for grasping its physiological functions.

• Atria: Upper chambers; receive blood from the body (right atrium, deoxygenated) and lungs (left atrium, oxygenated).

• Ventricles: Lower chambers; thick-walled, pump blood out to the lungs (right ventricle) and systemic circulation (left ventricle).

• Valves: Ensure unidirectional blood flow:

  • 2 Atrioventricular (AV) valves: Tricuspid (right), Bicuspid/Mitral (left)

  • 2 Semilunar valves: Pulmonary (right ventricle to pulmonary trunk), Aortic (left ventricle to aorta)

Pressure, Volume, Flow, and Resistance

Blood flow in the cardiovascular system is governed by pressure gradients and resistance.

• Pressure Gradient (ΔP): Drives blood flow from high to low pressure regions.

• Flow (F): Directly proportional to pressure gradient, inversely proportional to resistance: $F = \frac{\Delta P}{R}$

• Resistance (R): Opposes flow; increased by viscosity, vessel length, and decreased by vessel radius.

• Vessel Radius: Major determinant of resistance; small changes have large effects ($R \propto \frac{1}{r^4}$, see Poiseuille's Law).

• Flow Rate vs. Velocity: Flow rate is volume per time (Q), velocity is speed of movement (v). $v = \frac{Q}{A}$, where A is cross-sectional area.

Poiseuille’s Law

Describes the relationship between flow, pressure, and resistance in a tube:

• $R = \frac{8 \eta L}{\pi r^4}$ (where $\eta$ = viscosity, L = length, r = radius)

• Small changes in radius greatly affect resistance and thus flow.

Cardiac Muscle Cells

• Autorhythmic (Pacemaker) Cells: Generate electrical signals; do not contract; <2% of heart cells.

• Contractile Cells: Responsible for contraction and pressure generation; ~93% of heart muscle cells.

• Intercalated Disks: Specialized junctions between cardiac cells; contain desmosomes (anchoring) and gap junctions (electrical coupling).

Cardiac Muscle Contraction

1. Action potential travels along sarcolemma to T-tubules.

2. L-type Ca2+ channels open, allowing Ca2+ influx from ECF.

3. Ca2+ binds to ryanodine receptors (RyR) on sarcoplasmic reticulum, releasing more Ca2+ (calcium-induced calcium release).

4. Ca2+ binds to troponin, initiating contraction via the sliding filament mechanism.

5. Relaxation: Ca2+ is pumped back into SR (Ca2+-ATPase) and out of the cell via NCX (Na+/Ca2+ exchanger).

Action Potentials in Cardiac Cells

• Contractile Cells:

  • Resting membrane potential (RMP): -90 mV

  • Depolarization: Na+ influx

  • Plateau phase: Ca2+ influx balances K+ efflux

  • Repolarization: K+ efflux

  • Long refractory period prevents tetanus

• Autorhythmic Cells:

  • No true RMP; have pacemaker potential (~-60 mV)

  • IF channels allow Na+ influx and K+ efflux

  • Threshold: -40 mV; Ca2+ channels open for depolarization

  • Repolarization: K+ efflux

Comparison Table: Action Potentials

Cell Type	Resting Potential	Depolarization	Plateau	Refractory Period
Skeletal Muscle	-70 mV	Na+	No	Short
Cardiac Contractile	-90 mV	Na+	Yes (Ca2+)	Long
Cardiac Autorhythmic	No true RMP	Ca2+	No	Variable

Cardiac Conduction System

• SA Node: Main pacemaker, initiates atrial contraction

• AV Node: Delays impulse, allows ventricular filling

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

• Purkinje Fibers: Distribute impulse through ventricles, causing contraction

Electrocardiogram (ECG) Waves

• P wave: Atrial depolarization

• QRS complex: Ventricular depolarization (and atrial repolarization)

• T wave: Ventricular repolarization

• P-R interval: AV nodal delay

• T-P segment: Ventricular and atrial relaxation

Mechanical Events of the Cardiac Cycle

• Atrial Systole: Atria contract, AV valves open

• Ventricular Systole: Early: all valves closed (isovolumic contraction); Late: semilunar valves open, blood ejected

• Ventricular Diastole: Early: semilunar valves close, all valves closed (isovolumic relaxation); Late: AV valves open, ventricles fill

Stroke Volume and Cardiac Output

• Stroke Volume (SV): Volume ejected per beat: $SV = EDV - ESV$ (e.g., 135 mL - 65 mL = 70 mL)

• Cardiac Output (CO): Volume ejected per minute: $CO = SV \times HR$ (e.g., 70 mL × 70 bpm = 4900 mL/min)

Autonomic Control of Heart Rate

• Parasympathetic: Decreases HR (hyperpolarizes SA node, opens K+ channels, closes Ca2+ channels)

• Sympathetic: Increases HR (opens Ca2+ and Na+ channels)

Factors Influencing Stroke Volume

• Preload: Volume of blood at start of contraction (EDV); length-tension relationship

• Frank-Starling Law: SV is directly related to EDV; the heart pumps all blood returned to it

• Inotropic Effects: Affect contractility; positive inotropes increase, negative decrease contractility

• Venous Return: Enhanced by skeletal muscle pump, respiratory pump, and sympathetic innervation

Blood Flow and Transport

Blood Vessel Anatomy

• Arteries: Carry blood away from heart; thick, elastic walls; pressure reservoir

• Arterioles: Smaller arteries; thick tunica media; control mean arterial pressure (MAP)

• Metarterioles: Connect arterioles to capillaries; have precapillary sphincters

• Capillaries: Smallest, thinnest; site of exchange; only endothelium

• Venules: Small veins; can exchange some substances

• Veins: Return blood to heart; thin walls, large lumens; volume reservoir

Specialized Structures

• Precapillary Sphincters: Regulate blood flow into capillaries

• Pericytes: Support capillaries, regulate exchange

Blood Pressure Concepts

• Systolic Pressure: Peak arterial pressure during ventricular systole (e.g., 120 mmHg)

• Diastolic Pressure: Minimum arterial pressure during ventricular diastole (e.g., 80 mmHg)

• Pulse Pressure: Systolic - Diastolic (e.g., 40 mmHg)

• Mean Arterial Pressure (MAP): $MAP = DP + \frac{1}{3}(SP - DP)$; normal 70-110 mmHg

• Factors Affecting MAP: Cardiac output, peripheral resistance, blood volume

Regulation of Blood Pressure

• Compensation for Increased Blood Volume: Cardiovascular (decrease CO, HR, SV, vasodilation) and renal (increase urine output)

• Myogenic Autoregulation: Vascular smooth muscle adjusts its own contraction

• Active Hyperemia: Increased blood flow due to increased metabolism

• Reactive Hyperemia: Increased flow after occlusion is removed

• Sympathetic Control: Norepinephrine maintains arteriolar tone (vasoconstriction)

Baroreceptor Reflex

• Baroreceptors in carotid arteries and aorta sense pressure changes, send signals to medulla oblongata

• Increased BP: increased baroreceptor firing, decreased sympathetic, increased parasympathetic output

• Results: vasodilation, decreased HR and contractility, decreased BP

Capillary Exchange

• Types of Capillaries:

  • Continuous: least permeable (skin, muscle)

  • Fenestrated: more permeable (kidney, intestine)

  • Sinusoids: most permeable (liver, spleen, bone marrow)

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

• Colloid Osmotic Pressure: Due to plasma proteins; draws fluid into capillaries

• Bulk Flow: Net movement depends on balance of hydrostatic and osmotic pressures

Lymphatic System

• Drains excess tissue fluid (lymph), cleans lymph, absorbs and transports lipids (via lacteals)

• Edema: Swelling due to excess interstitial fluid; caused by increased MAP, decreased osmotic pressure, or increased capillary permeability

Blood

Plasma and Plasma Proteins

• Plasma: Mostly water; transports hydrophilic molecules and some gases

• Plasma Proteins:

  • Albumins: Most abundant; create osmotic pressure

  • Globulins: Antibodies; immune function

  • Fibrinogen: Clotting

  • Transferrin: Iron transport

Blood Cells

• Erythrocytes (RBCs): Gas transport

• Thrombocytes (Platelets): Clotting

• Leukocytes (WBCs): Immunity

  • Granulocytes: Neutrophils (first defense), Eosinophils (anti-parasite, allergy), Basophils

  • Agranulocytes: Monocytes (macrophages), Lymphocytes (T and B cells)

Hematopoiesis and Cytokines

• Hematopoiesis: Formation of blood cells in bone marrow

• Cytokines:

  • Erythropoietin: increases RBCs (from kidneys)

  • Thrombopoietin: increases platelets

  • Colony-stimulating factors: regulate WBC production

Complete Blood Count (CBC)

• Blood test measuring numbers of each cell type

• Most common cell: erythrocyte; most common WBC: neutrophil; least common: basophil

Hemoglobin Metabolism

• RBCs last ~120 days; precursors are reticulocytes

• Iron absorbed in gut, transported by transferrin to bone marrow/liver

• Old RBCs removed by spleen; iron recycled or stored as ferritin; heme converted to bilirubin (excreted in bile, urine, feces)

Hemostasis

1. Vasoconstriction

2. Platelet plug formation (activated by exposed collagen)

3. Coagulation cascade (fibrinogen to fibrin, stabilizes clot)

Mechanics of Breathing

Respiratory Anatomy

• Pathway: Nasal cavity → Pharynx → Larynx → Trachea → Bronchi (primary, secondary, tertiary) → Bronchioles → Alveoli

• Bronchi: Cartilage support; bronchioles lack cartilage, surrounded by smooth muscle

• Bronchoconstriction: Decreases radius/flow (parasympathetic); Bronchodilation: increases flow (sympathetic)

Functions of the Respiratory System

• Gas exchange (O2 in, CO2 out)

• pH balance (via CO2 regulation)

• Protection (mucociliary escalator)

• Vocalization

Pleural Membranes

• Parietal pleura: Lines thoracic cavity

• Visceral pleura: Covers lungs

• Serous fluid: Reduces friction

Alveolar Cells and Respiratory Membrane

• Type I: Squamous, gas exchange

• Type II: Cuboidal, secrete surfactant

• Alveolar macrophages: Immunity

• Respiratory membrane: Type I cell, basement membrane, capillary endothelium

Pulmonary Circulation

• Right ventricle → Pulmonary trunk → Pulmonary arteries → Capillaries → Pulmonary veins → Left atrium

Mucociliary Escalator

• Mucus (traps particles), cilia (move mucus), saline (separates cilia from mucus)

• NKCC and CFTR channels regulate saline production

Gas Laws

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

• Partial Pressure: $P_{gas} = \text{fraction of gas} \times \text{total pressure}$

• Boyle’s Law: $P_1V_1 = P_2V_2$; pressure inversely proportional to volume

Lung Volumes and Capacities

Volume/Capacity	Definition
TV (Tidal Volume)	Normal inhale/exhale
IRV (Inspiratory Reserve Volume)	Maximal forced inhale
ERV (Expiratory Reserve Volume)	Maximal forced exhale
RV (Residual Volume)	Air remaining after forced exhale
IC (Inspiratory Capacity)	TV + IRV
FRC (Functional Residual Capacity)	ERV + RV
VC (Vital Capacity)	TV + IRV + ERV
TLC (Total Lung Capacity)	TV + IRV + ERV + RV

Pressure Changes During Breathing

• Intrapleural pressure decreases during inhalation, increases during exhalation

• Alveolar pressure fluctuates above/below atmospheric pressure to drive airflow

Surfactant

• Secreted by Type II alveolar cells; reduces surface tension, prevents alveolar collapse

Airway Resistance

• Inversely proportional to radius; bronchoconstriction increases resistance, bronchodilation decreases it

Ventilation

• Total Pulmonary Ventilation: $TV \times \text{breathing rate}$

• Alveolar Ventilation: $(TV - \text{dead space}) \times \text{breathing rate}$

Gas Exchange and Transport

Hypoxia and Hypercapnia

• Hypoxia: Low O2 levels

• Hypercapnia: High CO2 levels

Regulation of Gas Exchange

• Sensors respond to O2, CO2, and pH (H+) to maintain homeostasis

Partial Pressures in Circulation

• Pulmonary capillaries: O2 low, CO2 high

• Alveoli: O2 high, CO2 low

• Systemic capillaries: O2 high, CO2 low

• Tissues: O2 low, CO2 high

Factors Affecting Gas Diffusion Rate

• Surface Area: Decreased in emphysema

• Concentration Gradient: Decreased in asthma

• Barrier Permeability: Decreased in fibrotic lung disease

• Diffusion Distance: Increased in pulmonary edema

• General Formula: $\text{Diffusion Rate} \propto \text{Surface Area} \times \text{Concentration Gradient} \times \text{Barrier Permeability}$

Additional info: Some explanations and definitions have been expanded for clarity and completeness, and tables have been reconstructed based on standard physiology knowledge.