Cardiovascular Anatomy and Blood Flow — Study Guide
Course: HyNote study pack on cardiovascular anatomy and blood flow, written for nursing and anatomy students preparing for course exams and clinical check-offs. Public references: OpenStax Anatomy and Physiology 2e, chapters 18 and 19 (CC BY), and the 2017 ACC/AHA blood pressure categories. Worked calculations are checked. Ranges follow those sources.
Style: exam-first. The heart is walked chamber by chamber in blood-flow order, then compressed into the rules, mnemonics, and calculation formulas exams are built from. Three original cases walk the bedside logic. All scenarios are fictional and educational.
Notation: RA/LA = right and left atrium; RV/LV = right and left ventricle; SVC/IVC = superior and inferior vena cava. CO = cardiac output; SV = stroke volume; EDV/ESV = end-diastolic and end-systolic volume; EF = ejection fraction; SBP/DBP = systolic and diastolic blood pressure; MAP = mean arterial pressure.
PART 1 — THE BLOOD FLOW PATH (THE MAP EXAMS TEST)
1.1 The complete circuit, in order
Deoxygenated blood returns from the body: SVC (head, neck, and arms) and IVC (abdomen, pelvis, and legs) → RA → tricuspid valve → RV → pulmonary valve → pulmonary artery → lungs (gas exchange: CO2 out, O2 in) → pulmonary veins → LA → mitral valve → LV → aortic valve → aorta → the body.
Count SVC and IVC as one return station, and stop at the aorta. That is 13 stations: (1) SVC/IVC, (2) RA, (3) tricuspid, (4) RV, (5) pulmonary valve, (6) pulmonary artery, (7) lungs, (8) pulmonary veins, (9) LA, (10) mitral, (11) LV, (12) aortic valve, (13) aorta. The body is the destination, not a fourteenth station. Exams test any segment of this path. Cardiac venous blood also returns to the RA through the coronary sinus; that side path is not one of the 13.
1.2 The two pumps in one heart
The right heart is the pulmonary pump: a short, low-resistance loop to the lungs. Pulmonary artery pressure is about 25/10 mm Hg. The left heart is the systemic pump: a long, high-resistance loop to the body. Aortic pressure is about 120/80 mm Hg. Those figures are arterial pressures, not the pressure inside the atria. Right atrial pressure is only a few mm Hg, and left ventricular diastolic pressure is low, not 80. The LV wall is about 2 to 3 times thicker than the RV — the resistance difference made visible.
1.3 Oxygenated vs deoxygenated: which vessel carries what
After birth, the pulmonary arteries are the only arteries carrying deoxygenated blood (away from the heart to the lungs), and the pulmonary veins are the only veins carrying oxygenated blood (back from the lungs to the heart). Before birth the umbilical arteries carry deoxygenated blood and the umbilical vein carries oxygenated blood, so this "only" rule is postnatal. Rule: arteries carry blood AWAY from the heart; veins carry it TOWARD — oxygen content is a different question.
1.4 The four valves and their heart sounds
- Tricuspid: RA to RV (right AV valve).
- Pulmonary (semilunar): RV to pulmonary artery.
- Mitral (bicuspid): LA to LV (left AV valve).
- Aortic (semilunar): LV to aorta.
S1 ("lub") = AV valves closing (tricuspid + mitral) at the start of systole. S2 ("dub") = semilunar valves closing (aortic + pulmonary) at the start of diastole.
1.5 Part 1 checklist
PART 2 — THE CONDUCTION SYSTEM
2.1 The pacemaker hierarchy
Rates below are inherent rates with no nervous or endocrine input, from OpenStax 19.2. SA node (right atrium): the primary pacemaker, about 80-100 beats per minute. At rest, vagal tone usually slows this to a sinus rhythm of 60-100. AV node: the backup, 40-60 per minute. If the AV node is also blocked, the bundle of His fires at about 30-40 per minute, the bundle branches at about 20-30, and the Purkinje fibers at about 15-20. Slower down the line. His is faster than Purkinje, so they are not one 20-40 rate. And 60-100 is the resting sinus range, not the SA node's inherent rate.
2.2 The pathway in order
SA node → internodal pathways → AV node (the electrical gate — delays the impulse about 0.10 seconds, so the atria finish filling the ventricles) → bundle of His → right and left bundle branches → Purkinje fibers → ventricular contraction from apex upward.
2.3 The ECG basics that follow from the pathway
P wave = atrial depolarization. The SA node starts the impulse, but its own firing is not the P wave; the P wave is the impulse spreading across the atria. QRS complex = ventricular depolarization (through His-Purkinje). Depolarization is electrical; contraction follows it and is not the same event. T wave = ventricular repolarization. The PR interval runs from the start of the P wave to the start of the QRS (normal 0.12-0.20 seconds). It includes atrial conduction plus the AV node delay of about 0.10 seconds. It is not the AV delay alone.
2.4 Part 2 checklist
PART 3 — CARDIAC OUTPUT AND THE NUMBERS
3.1 The master formula
CO = HR × SV. At HR 70 and SV 70 mL: CO = 4,900 mL/min ≈ 5 L/min — the usual resting teaching value.
3.2 Stroke volume: three determinants
SV = EDV − ESV (what filled the ventricle minus what remains). At EDV 120 and ESV 50: SV = 70 mL.
- Preload: the stretch before contraction (venous return, EDV). Frank-Starling law: more stretch → stronger contraction, up to a point.
- Contractility: the force of contraction (sympathetic stimulation, inotropes).
- Afterload: the resistance the LV pumps against (systemic vascular resistance is the usual proxy; hypertension increases it).
3.3 Ejection fraction
EF = SV / EDV × 100. With SV 70 and EDV 120: EF = 58%. A common teaching normal is 55-70%. Heart failure with reduced ejection fraction (HFrEF, the systolic pattern) is an EF of 40% or below. An EF of 41-49% is mildly reduced: not normal, and not the ≤40% cutoff. EF alone does not diagnose the clinical syndrome of heart failure.
3.4 Mean arterial pressure
MAP ≈ (SBP + 2 × DBP) / 3 at usual heart rates; marked tachycardia shortens diastole and makes this approximation less accurate. At 120/80: MAP = (120 + 160) / 3 = 93 mm Hg. Organ perfusion is usually taught as unsafe when MAP falls below about 60-65 mm Hg. The common clinical target is 65 or higher.
3.5 Blood pressure categories (2017 ACC/AHA)
If systolic and diastolic fall in different rows, use the higher category. A single reading can be categorized, but hypertension diagnosis normally uses the average of at least two properly taken readings on at least two occasions unless urgent treatment is required.
| Category | SBP | DBP |
|---|
| Normal | Below 120 | and below 80 |
| Elevated | 120-129 | and below 80 |
| Stage 1 hypertension | 130-139 | or 80-89 |
| Stage 2 hypertension | 140 or higher | or 90 or higher |
| Severe hypertension | Above 180 | and/or above 120; repeat promptly and assess symptoms |
| Hypertensive emergency | Usually above 180 | and/or above 120 with acute target-organ injury or concerning symptoms |
3.6 Part 3 checklist
PART 4 — CORONARY CIRCULATION
4.1 The heart feeds itself in diastole
Coronary arteries branch off the aorta just above the aortic valve: the left coronary artery divides into the LAD and the circumflex, and the right coronary artery is separate. Left ventricular coronary flow happens mainly during DIASTOLE. In systole the coronary ostia remain open, but contracting myocardium compresses intramural vessels—especially in the thick LV—and reduces flow. In diastole the myocardium relaxes, compression falls, and aortic diastolic pressure drives blood through the coronary ostia. The right coronary is less dependent on diastole because right ventricular wall tension is lower. Extreme tachycardia still shortens diastole and can cut left coronary filling while cardiac work rises.
4.2 The named vessels and their territories
LAD: anterior wall and the anterior septum (the "widow maker" — a proximal LAD occlusion is the classic large anterior MI). Circumflex: lateral wall. In the common right-dominant pattern (most people), the right coronary supplies the inferior wall and usually the AV node. The SA node artery comes from the right coronary in about 60% of people and from the circumflex in the rest. An inferior MI can cause bradycardia and heart block, but that is the usual pattern, not a rule for every heart.
4.3 Part 4 checklist
PART 5 — BLOOD COMPOSITION
5.1 What blood is made of
Plasma is about 55% in a typical teaching sample (OpenStax: about 53% in males and 59% in females, because hematocrit differs): water, proteins (albumin — the oncotic pressure keeper; clotting factors; antibodies). Formed elements are mostly RBCs, about 45% (erythrocytes — hemoglobin, oxygen transport, live up to 120 days), plus a buffy coat of WBCs (leukocytes — immunity) and platelets (thrombocytes — clotting fragments) that is normally under 1%.
5.2 Hemoglobin numbers (OpenStax)
Normal Hgb: male 13-18 g/dL, female 12-16 g/dL. Hematocrit: male 42-52% (mean 47), female 37-47% (mean 41). Each gram of hemoglobin carries about 1.34 mL of oxygen, the usual oxygen-binding constant.
5.3 Part 5 checklist
PART 6 — THREE ORIGINAL CASES
6.1 Case 1 — the heart failure readout
A patient has EDV 130 mL, ESV 80 mL, HR 90. SV = 130 − 80 = 50 mL. CO = 90 × 50 = 4,500 mL/min = 4.5 L/min. EF = 50/130 = 38%, which is at or below the 40% line for heart failure with reduced ejection fraction. A low EF supports that pattern; the clinical syndrome also needs symptoms and the rest of the assessment. Nursing: monitor daily weights, restrict sodium, watch for crackles and edema, medications per prescription (ACE inhibitor, beta blocker, diuretic).
6.2 Case 2 — the hypertension category
A patient's BP is 148/92. Stage 2 is SBP 140 or higher OR DBP 90 or higher. Here both qualify, so the category is Stage 2 either way. Nursing: verify technique and recheck; outside an emergency, diagnosis uses averaged readings from at least two measurements on at least two occasions, supported by home or ambulatory monitoring when appropriate; provide lifestyle counseling (sodium, exercise, weight), medications per prescription, teach home monitoring.
6.3 Case 3 — the tachycardia and coronary filling
A patient with a rapid arrhythmia runs HR 180 sustained. Diastole shortens with each beat. Left ventricular coronary flow is greatest in diastole because myocardial compression falls while aortic pressure continues to drive flow through patent coronary ostia, so tachycardia can reduce perfusion while cardiac work rises. The patient develops chest pain. Nursing: assess rhythm, notify the provider, prepare for rhythm treatment per protocol, monitor BP and symptoms continuously.
PART 7 — EXAM PATTERNS AND TRAPS
7.1 The five question patterns
- Order the blood flow path (any segment).
- Valve-to-sound matching: S1 = AV valves, S2 = semilunar valves.
- Compute CO, EF, or MAP from given numbers.
- ECG wave to event matching (P, QRS, T) — electrical events, not contraction.
- Vessel oxygen-content questions (pulmonary arteries are deoxygenated after birth).
7.2 Traps that cost points
- Saying the pulmonary artery carries oxygenated blood — arteries carry blood away; oxygen content varies.
- Calling the pulmonary vessels the only oxygen exceptions in every circulation — that is the postnatal rule. Umbilical vessels are the fetal exceptions.
- Putting the tricuspid on the left side — tricuspid is right, mitral is left.
- Reading S2 as AV valves closing — S2 is semilunar.
- Saying the heart valves open so the coronaries can fill — the aortic valve closes in diastole.
- Using SV/ESV instead of SV/EDV for EF.
- Calling 60-100 the SA node's inherent rate — that is the resting sinus range. Inherent SA rate is about 80-100, and Purkinje fibers are about 15-20, slower than the bundle of His (about 30-40).
- Equating the PR interval with AV node delay — the PR interval also includes atrial conduction. The AV delay itself is about 0.10 seconds.
- Reading the P wave as "the SA node firing," or the QRS as contraction.
- Confusing preload (stretch before contraction) with afterload (resistance against contraction).
- Treating an EF of 46% as normal because it is not below 40%. 46% is mildly reduced.
| Item | Value |
|---|
| CO = HR × SV | 70 × 70 = 4,900 mL/min ≈ 5 L/min |
| SV = EDV − ESV | 120 − 50 = 70 mL |
| EF = SV / EDV × 100 | 70 / 120 = 58% (teaching normal 55-70%; HFrEF is ≤40%; 41-49% is mildly reduced) |
| MAP = (SBP + 2 × DBP) / 3 | (120 + 160) / 3 = 93 mm Hg (perfusion concern below about 60-65; target often ≥65) |
| SA node inherent rate | About 80-100/min |
| Resting sinus rhythm | 60-100/min (vagal tone slows the SA node) |
| AV node rate | 40-60/min |
| Bundle of His | About 30-40/min |
| Purkinje rate | About 15-20/min |
| AV node delay | About 0.10 seconds |
| PR interval | 0.12-0.20 seconds (start of P to start of QRS) |
| Pulmonary artery pressure | About 25/10 mm Hg |
| Aortic pressure | About 120/80 mm Hg |
| Normal Hgb (OpenStax) | Male 13-18, female 12-16 g/dL |
| Normal Hct (OpenStax) | Male 42-52% (mean 47), female 37-47% (mean 41) |
| Plasma / RBCs | About 55% / 45% in a typical sample |
| LV wall vs RV | About 2-3 times thicker |
Mnemonic: "Try Pulling My Aorta" = Tricuspid, Pulmonary, Mitral, Aortic — the valves in blood-flow order.
APPENDIX B — TRAP LIST
- After birth: pulmonary arteries = deoxygenated; pulmonary veins = oxygenated. Fetal umbilical vessels are the other pair.
- Tricuspid on the right, mitral on the left.
- S1 = AV valves (lub); S2 = semilunar (dub).
- Left ventricular coronary flow is greatest in diastole because myocardial compression is relieved; the coronary ostia remain open during systole.
- EF = SV / EDV (not ESV). ≤40% is HFrEF; 41-49% is mildly reduced.
- SA node is the pacemaker (inherent about 80-100). Resting sinus rhythm of 60-100 is vagal slowing, not the inherent rate.
- AV node delay is about 0.10 seconds. The PR interval (0.12-0.20 seconds) is longer because it also includes atrial conduction.
- P wave = atrial depolarization, not the SA node spike. QRS = ventricular depolarization, not contraction.
- Preload = stretch before contraction (venous return); afterload = resistance against contraction.
- 25/10 and 120/80 are pulmonary artery and aortic pressures, not atrial pressures.
- MAP below about 60-65 means organ perfusion is at risk.
These are original HyNote study notes for nursing and anatomy students. They summarize public educational references and all cases are fictional. They are not official materials of any nursing organization, they are not exam questions, and they are not clinical advice. Following the content plan, qualified clinical review is recommended before wider promotion.
