Key Takeaways
- The heart has 4 chambers: right atrium, right ventricle, left atrium, left ventricle; the left ventricle is the thickest
- Blood flow: body → vena cava → RA → RV → pulmonary artery → lungs → pulmonary veins → LA → LV → aorta → body
- Arteries carry blood AWAY from the heart (thick walls, high pressure); veins carry blood TO the heart (thinner walls, valves)
- The cardiac conduction system: SA node → AV node → Bundle of His → bundle branches → Purkinje fibers
- Normal adult blood pressure is below 120/80 mmHg; hypertension is 130/80 or higher
- The respiratory system consists of upper (nose, pharynx, larynx) and lower (trachea, bronchi, lungs, alveoli) airways
- Gas exchange occurs in the alveoli by diffusion — O2 enters the blood, CO2 exits into the alveoli
- Breathing is controlled by the medulla oblongata and is primarily driven by CO2 levels in the blood
Cardiovascular & Respiratory Systems
The cardiovascular and respiratory systems work together to deliver oxygen to every cell in the body and remove carbon dioxide. Dysfunction of either system is life-threatening.
The Heart
The heart is a muscular pump about the size of a fist, located in the mediastinum (center of the chest, slightly left).
Four Chambers
| Chamber | Function | Receives From | Sends To |
|---|---|---|---|
| Right Atrium (RA) | Receives deoxygenated blood | Superior/inferior vena cava | Right ventricle |
| Right Ventricle (RV) | Pumps blood to lungs | Right atrium | Pulmonary arteries |
| Left Atrium (LA) | Receives oxygenated blood | Pulmonary veins | Left ventricle |
| Left Ventricle (LV) | Pumps blood to body | Left atrium | Aorta |
The left ventricle has the thickest walls because it must generate enough pressure to pump blood throughout the entire body.
Four Heart Valves
| Valve | Location | Function |
|---|---|---|
| Tricuspid | Between RA and RV | Prevents backflow to RA |
| Pulmonary (pulmonic) | Between RV and pulmonary artery | Prevents backflow to RV |
| Mitral (bicuspid) | Between LA and LV | Prevents backflow to LA |
| Aortic | Between LV and aorta | Prevents backflow to LV |
Blood Flow Pathway
Deoxygenated blood: Body → Vena Cava → RA → Tricuspid Valve → RV → Pulmonary Valve → Pulmonary Arteries → Lungs
Oxygenated blood: Lungs → Pulmonary Veins → LA → Mitral Valve → LV → Aortic Valve → Aorta → Body
Cardiac Conduction System
The heart's electrical system controls the heartbeat:
- SA node (sinoatrial) — "pacemaker" in the right atrium, sets the rate (~60-100 bpm)
- AV node (atrioventricular) — delays the signal briefly to allow atrial emptying
- Bundle of His — conducts signal from atria to ventricles
- Bundle branches (left and right) — carry signal down the interventricular septum
- Purkinje fibers — distribute signal throughout the ventricles, triggering contraction
Blood Vessels
| Vessel | Function | Wall Thickness | Pressure |
|---|---|---|---|
| Arteries | Carry blood AWAY from heart | Thick, muscular | High |
| Arterioles | Small arteries, regulate blood flow | Moderate | Moderate |
| Capillaries | Gas/nutrient exchange | One cell thick | Low |
| Venules | Small veins, collect blood | Thin | Low |
| Veins | Carry blood TO the heart | Thin, contain valves | Low |
Key exception: Pulmonary arteries carry DEoxygenated blood; pulmonary veins carry oxygenated blood.
Blood Pressure
- Systolic (top number): Pressure during ventricular contraction
- Diastolic (bottom number): Pressure during ventricular relaxation
- Normal adult: < 120/80 mmHg
- Hypertension (Stage 1): 130-139 / 80-89 mmHg
- Hypertension (Stage 2): ≥ 140/90 mmHg
Cardiac Output
Cardiac output (CO) is the volume of blood pumped by the heart per minute:
CO = Stroke Volume (SV) x Heart Rate (HR)
| Term | Definition | Normal Value |
|---|---|---|
| Stroke volume | Blood ejected per heartbeat | ~70 mL/beat |
| Heart rate | Beats per minute | 60-100 bpm |
| Cardiac output | Volume per minute | ~5 L/min (70 mL x 72 bpm) |
Factors that increase cardiac output:
- Exercise, fever, anxiety, anemia, pregnancy
- Sympathetic nervous system activation (epinephrine)
Factors that decrease cardiac output:
- Heart failure, myocardial infarction, bradycardia
- Parasympathetic nervous system activation (vagus nerve)
Clinical significance: Adequate cardiac output ensures sufficient oxygen delivery to all tissues. Heart failure occurs when the heart cannot pump enough blood to meet the body's metabolic demands.
Respiratory System
Upper Respiratory Tract
- Nose/Nasal cavity — warms, humidifies, filters air
- Pharynx — shared airway and food passage
- Larynx — voice box, contains vocal cords and epiglottis
Lower Respiratory Tract
- Trachea — windpipe, supported by C-shaped cartilage rings
- Bronchi — left and right main bronchi branch from trachea
- Bronchioles — smaller airways, no cartilage
- Alveoli — tiny air sacs where gas exchange occurs (~300 million)
Gas Exchange
Gas exchange occurs in the alveoli through diffusion:
- O2 moves from alveoli (high concentration) → blood (low concentration)
- CO2 moves from blood (high concentration) → alveoli (low concentration)
Mechanics of Breathing
| Phase | Diaphragm | Pressure | Air Flow |
|---|---|---|---|
| Inhalation | Contracts (flattens) | Intrathoracic pressure decreases | Air rushes IN |
| Exhalation | Relaxes (domes up) | Intrathoracic pressure increases | Air pushed OUT |
Breathing is controlled by the medulla oblongata in the brainstem, primarily driven by CO2 levels in the blood (not O2 levels). High CO2 stimulates increased respiratory rate.
Lung Volumes
| Volume | Definition | Normal Adult Value |
|---|---|---|
| Tidal volume (TV) | Air in a normal breath | ~500 mL |
| Inspiratory reserve | Extra air that can be inhaled beyond tidal | ~3,100 mL |
| Expiratory reserve | Extra air that can be exhaled beyond tidal | ~1,200 mL |
| Residual volume | Air remaining after maximal exhalation | ~1,200 mL |
| Vital capacity | Maximum air exhaled after maximum inhalation (TV + IRV + ERV) | ~4,800 mL |
| Total lung capacity | All air the lungs can hold | ~6,000 mL |
Vital Signs — Normal Adult Ranges
| Vital Sign | Normal Range | Abnormal Terms |
|---|---|---|
| Heart rate | 60-100 bpm | Tachycardia (>100), Bradycardia (<60) |
| Respiratory rate | 12-20 breaths/min | Tachypnea (>20), Bradypnea (<12), Apnea (0) |
| Blood pressure | <120/80 mmHg | Hypertension (≥130/80), Hypotension (<90/60) |
| Temperature | 97.8-99.1°F (36.5-37.3°C) | Hypothermia (<95°F), Fever (>100.4°F / 38°C) |
| Oxygen saturation (SpO2) | 95-100% | Hypoxemia (<90%) |
Blood Types — Clinical Significance
Blood type compatibility is critical for safe transfusions:
Transfusion reactions occur when the recipient's antibodies attack donor red blood cells:
- Type A blood has Anti-B antibodies → reacts against Type B blood
- Type B blood has Anti-A antibodies → reacts against Type A blood
- Type O blood has both Anti-A and Anti-B → reacts against A, B, and AB
- Type AB blood has NO antibodies → does not react against any type
In emergencies when blood type is unknown, Type O negative packed RBCs are given because they lack all major antigens.
Cardiac Output
Cardiac output (CO) is the volume of blood pumped by the heart per minute:
CO = Heart Rate (HR) x Stroke Volume (SV)
- Stroke volume = amount of blood ejected per heartbeat (~70 mL)
- Normal cardiac output = 70 bpm x 70 mL = ~4,900 mL/min (~5 L/min)
- Cardiac output must match the body's metabolic demands
- During exercise, both HR and SV increase, raising CO to 15-25 L/min
Factors that affect cardiac output:
- Preload — amount of blood filling the ventricles (more stretch = stronger contraction)
- Afterload — resistance the heart must pump against (higher BP = more work)
- Contractility — strength of ventricular contraction
Blood Vessel Anatomy — Detailed
| Layer | Name | Description |
|---|---|---|
| Inner | Tunica intima | Smooth endothelium; in direct contact with blood |
| Middle | Tunica media | Smooth muscle and elastic tissue; controls vessel diameter |
| Outer | Tunica adventitia | Connective tissue; provides structural support |
Arteriosclerosis = hardening and thickening of arterial walls Atherosclerosis = plaque buildup inside arteries (a type of arteriosclerosis)
- Risk factors: high cholesterol, hypertension, smoking, diabetes, obesity
- Can lead to heart attack (MI), stroke (CVA), or peripheral vascular disease
Which chamber of the heart has the thickest wall?
What is the "pacemaker" of the heart called?
Pulmonary arteries are unique because they:
Arrange the cardiac conduction pathway in the correct order.
Arrange the items in the correct order
Gas exchange in the lungs occurs primarily by which process?
Breathing is primarily controlled by the _____ oblongata in the brainstem.
Type your answer below