Unit 10 · Cardiovascular System
The Heart
10.1
Overview, Position and Coverings
Fig 3.65 Anterior surface of the heart. SVC, ascending aorta, arch of aorta, pulmonary trunk, left auricle, RCA, right atrium, right ventricle (sternocostal surface), small cardiac vein, IVC, inferior margin, apex, obtuse margin, left ventricle, anterior IV groove, great cardiac vein, anterior IV branch of LCA. Inset Fig 3.63: schematic of all 4 chambers and 4 valves.
Gray's Anatomy for Students 4e · Fig 3.65, p191
10.1.1 — The Pericardium
5.1 Definition
The pericardium is a fibroserous sac enclosing the heart and the roots of the great vessels, situated in the middle mediastinum. It consists of an outer fibrous layer and an inner serous layer, and functions to anchor the heart in position while allowing it to contract freely with minimal friction.
5.2 Location
Situated in the middle mediastinum, posterior to the sternum and costal cartilages, anterior to thoracic vertebrae T5–T8, and between the two pleural cavities.
5.3 Structure / Layers
The pericardium is organised into two distinct layers. The outer fibrous pericardium is a tough, inextensible connective tissue sac fused below to the central tendon of the diaphragm and blending above with the adventitia of the great vessels. The inner serous pericardium has two surfaces: the parietal layer (lines the inner surface of the fibrous pericardium) and the visceral layer — also called the epicardium — which is tightly adherent to the outer surface of the myocardium. Between these two serous layers lies the pericardial cavity, a potential space containing approximately 15–50 mL of lubricating serous fluid.
5.4 Blood & Nerve Supply
Supplied by the pericardiacophrenic arteries (branches of the internal thoracic arteries). Innervated by the phrenic nerve (C3–C5) — which explains why pericardial irritation produces pain referred to the shoulder tip.
🩺 5.6 Clinical — Cardiac Tamponade
When fluid accumulates in the pericardial cavity — from pericarditis (pericardial effusion) or trauma (haemopericardium) — the inextensible fibrous pericardium cannot expand. The mounting pressure compresses the ventricles, impeding filling. This is cardiac tamponade — a medical emergency. Classic signs: distended neck veins, muffled heart sounds, falling pulse pressure (Beck's Triad). Emergency treatment: pericardiocentesis — needle inserted into the 5th/6th intercostal space adjacent to the sternum, exploiting the cardiac notch in the left lung. [Netter's 5th §22 p158]
10.1.2 — Surface Projection & Valve Auscultation Areas
Fig 3.81 Cardiac auscultation. Insets show valve positions at S1 (mitral + tricuspid closure) and S2 (aortic + pulmonary closure). Ventricular pressure curve with ECG (P, QRS, T waves) and atrial contraction marker — exact timing of heart sounds within the cardiac cycle.
Gray's Anatomy for Students 4e · Fig 3.81, p209
5.3 Borders & Projection
Right border — formed by the right atrium; from the 3rd to the 6th costal cartilage approximately 1 cm right of the sternum.
Left border — formed mainly by the left ventricle; from the 2nd left intercostal space to the apex.
Superior border — level of the 2nd costal cartilages bilaterally; great vessels emerge here.
Inferior border — from the 6th right costal cartilage to the apex.
Apex — left 5th intercostal space, midclavicular line (~9 cm from midline); formed by the left ventricle; the site of the apex beat (point of maximum impulse).
Left border — formed mainly by the left ventricle; from the 2nd left intercostal space to the apex.
Superior border — level of the 2nd costal cartilages bilaterally; great vessels emerge here.
Inferior border — from the 6th right costal cartilage to the apex.
Apex — left 5th intercostal space, midclavicular line (~9 cm from midline); formed by the left ventricle; the site of the apex beat (point of maximum impulse).
🔖 Mnemonic — Valve Auscultation Areas
PV2L — Pulmonary valve heard over 2nd Left intercostal space
AV2R — Aortic valve heard over 2nd Right intercostal space
Tricuspid — lower left sternal edge (4th ICS) | Mitral — Apex (5th ICS MCL)
Tip: "All Patients Take Medicine" — Aortic, Pulmonary, Tricuspid, Mitral (right→left, top→bottom)
10.2
Internal Features of the Cardiac Chambers
Fig 3.69B MRI midthorax, all four chambers labeled: right ventricle (anterior, thin-walled), left ventricle (posterior, thick-walled), right atrium, left atrium, thoracic aorta. LV wall approximately 3× thicker than RV.
Gray's Anatomy for Students 4e · Fig 3.69B, p195
Fig 3.64 Base (posterior surface) of the heart. Labels: arch of aorta, left pulmonary artery, left superior/inferior pulmonary veins, left atrium, coronary sinus, left ventricle, apex, right ventricle, IVC, sulcus terminalis, right atrium, right pulmonary veins, SVC.
Gray's Anatomy for Students 4e · Fig 3.64, p190
10.2.1 — Right Atrium — Inlets & Outlet ★
5.1 Definition
The right atrium is the thin-walled, posterosuperior chamber of the right heart, receiving deoxygenated blood from the systemic venous circulation and delivering it to the right ventricle via the right atrioventricular orifice.
5.3 Three Inlets & One Outlet
Three inlets:
- Orifice of the superior vena cava — returns deoxygenated blood from the upper half of the body (head, neck, upper limbs)
- Orifice of the inferior vena cava — returns deoxygenated blood from the lower half of the body (trunk, lower limbs, abdominal viscera)
- Orifice of the coronary sinus — returns venous blood from the myocardium (cardiac muscle) itself
5.3 Internal Features
The crista terminalis (muscular ridge) divides the right atrium into a smooth-walled posterior part (sinus venarum — where the venae cavae open) and a rough anterior part bearing pectinate muscles. The interatrial septum bears the fossa ovalis — the remnant of the fetal foramen ovale.
🩺 Clinical — Atrial Septal Defect
The fossa ovalis is the commonest site of atrial septal defect (ASD). A patent foramen ovale (PFO) persists in ~25–30% of adults and can allow paradoxical emboli (venous clots crossing to the arterial circulation), causing cryptogenic stroke.
📝 Exam Q&A — Right Atrium
Q: Write down the names of the inlets and outlet of the right atrium.
The right atrium has three inlets: (1) the orifice of the superior vena cava — returns blood from the upper half of the body; (2) the orifice of the inferior vena cava — returns blood from the lower half of the body; (3) the orifice of the coronary sinus — returns blood from the cardiac muscle. One outlet: the right atrioventricular orifice.
[2008 Final Exam Q1 — Model Answers]
10.2.2 — Right Ventricle ★
5.1 Definition
The right ventricle is the anterosuperior chamber of the right heart, receiving deoxygenated blood from the right atrium and pumping it through the pulmonary orifice into the pulmonary trunk for oxygenation in the lungs.
5.3 Two Parts
Inflowing part (sinus): rough-walled, bears trabeculae carneae. Contains the septomarginal trabecula (moderator band) — a muscular band extending from the interventricular septum to the base of the anterior papillary muscle, conducting the right bundle branch of the AV bundle. Inlet: tricuspid valve (3 cusps: anterior, posterior, septal).
Outflowing part (conus arteriosus / infundibulum): smooth-walled, cone-shaped, directs blood upward to the pulmonary orifice, guarded by the pulmonary valve (3 semilunar cusps: anterior, right, left).
Outflowing part (conus arteriosus / infundibulum): smooth-walled, cone-shaped, directs blood upward to the pulmonary orifice, guarded by the pulmonary valve (3 semilunar cusps: anterior, right, left).
10.2.3 — Tricuspid Complex ★★★
Fig 3.76 Cardiac skeleton with atria removed, superior view. All 4 fibrous rings: aortic ring (Lt/Rt/Post cusps), pulmonary ring (Ant/Lt/Rt cusps), left AV ring (mitral: Ant/Post), right AV ring (tricuspid: Ant/Septal/Post). Left + right fibrous trigones. Atrioventricular bundle pierces the skeleton at the right fibrous trigone.
Gray's Anatomy for Students 4e · Fig 3.76, p203
Anterior view of the aortic valve (Fig 3.75). Labels: 3 semilunar cusps (right, posterior/noncoronary, left), aortic sinuses (each sinus faces a cusp), lunule (free edge thickening), nodule (central thickening), opening for right coronary artery, right coronary artery, left coronary artery. Key: RCA opens from right aortic sinus; LCA from left aortic sinus; posterior sinus = noncoronary.
Gray's Anatomy for Students 4e · Fig 3.75, p201
5.1 Definition
The tricuspid complex is the collective term for the four structural components that together prevent backflow of blood from the right ventricle into the right atrium during ventricular systole.
5.3 Four Components
- Right atrioventricular fibrous ring — the annular fibrous skeleton anchoring the valve cusps.
- Tricuspid valve cusps — three cusps (anterior, posterior, septal) projecting into the ventricular lumen. Their free edges face downward into the ventricle.
- Chordae tendineae — strong tendinous cords attaching the free edges and ventricular surfaces of the cusps to the papillary muscles. They prevent the cusps from inverting into the atrium during systole.
- Papillary muscles — three cone-shaped muscular projections (anterior, posterior, septal) arising from the ventricular wall. They contract simultaneously with the ventricle, maintaining chordae tension throughout systole.
5.5 Function / Mechanism
During ventricular systole, rising ventricular pressure forces the tricuspid cusps upward toward the atrioventricular orifice. Simultaneously, the papillary muscles contract and pull the chordae tendineae taut — preventing the cusps from prolapsing into the right atrium. The cusps meet at their free edges, sealing the orifice. Blood is thereby directed exclusively toward the pulmonary orifice.
🩺 Clinical — Tricuspid Regurgitation
When the tricuspid complex fails — from right ventricular dilation stretching the annulus, or rheumatic disease — blood leaks back into the right atrium during systole. This raises right atrial and venous pressure, causing: raised jugular venous pressure (JVP), peripheral oedema, hepatomegaly, and ascites — the classic signs of right heart failure.
📝 Exam Q&A — Tricuspid Complex
Q: Define the tricuspid complex.
The tricuspid complex comprises: (1) the right atrioventricular fibrous ring, (2) the tricuspid valve cusps (anterior, posterior, septal), (3) the chordae tendineae, and (4) the papillary muscles. Together, these structures prevent backflow of blood from the right ventricle into the right atrium during ventricular contraction.
[2019/2020 Final Paper Section I Q6; 2008 Final model answers]
10.2.4 — Left Atrium
5.1 Definition
The left atrium is the posterosuperior chamber of the left heart, receiving oxygenated blood from the four pulmonary veins and delivering it to the left ventricle via the left atrioventricular orifice.
5.3 Four Inlets & One Outlet
Four inlets: the four pulmonary veins — two right (superior and inferior) and two left (superior and inferior) — enter the posterior wall, returning oxygenated blood from the lungs.
One outlet: the left atrioventricular orifice — guarded by the bicuspid (mitral) valve; leads blood into the left ventricle.
One outlet: the left atrioventricular orifice — guarded by the bicuspid (mitral) valve; leads blood into the left ventricle.
📝 Exam Q&A
Q: Write down the inlets and outlet of the left atrium.
The left atrium receives four inlets — the orifices of four pulmonary veins (two right, two left). Its one outlet is the left atrioventricular orifice, guarded by the bicuspid (mitral) valve, leading into the left ventricle.
[2008 Review Q1]
10.2.5 — Left Ventricle ★
Fig 3.74 Internal view of the left ventricle. Labels: arch of aorta (outflow), mitral valve anterior cusp, chordae tendineae, anterior papillary muscle, posterior papillary muscle, trabeculae carneae, mitral valve posterior cusp, left atrium, pulmonary arteries, pulmonary veins, coronary sinus.
Gray's Anatomy for Students 4e · Fig 3.74, p201
5.1 Definition
The left ventricle is the posteroinferior chamber of the left heart that receives oxygenated blood from the left atrium and pumps it into the aorta for systemic distribution. Its wall is approximately three times as thick as the right ventricle, reflecting the much higher pressures it must generate.
5.3 Structure
Inflowing part: rough-walled with trabeculae carneae. Inlet guarded by the bicuspid (mitral) valve — two cusps (anterior and posterior).
Outflowing part (aortic vestibule): smooth-walled. Leads to the aortic orifice guarded by the aortic valve (three semilunar cusps: posterior, right, left). Above the aortic valve cusps, the aortic wall bulges outward to form the aortic sinuses (sinuses of Valsalva) — the right and left aortic sinuses give rise to the right and left coronary arteries respectively.
Outflowing part (aortic vestibule): smooth-walled. Leads to the aortic orifice guarded by the aortic valve (three semilunar cusps: posterior, right, left). Above the aortic valve cusps, the aortic wall bulges outward to form the aortic sinuses (sinuses of Valsalva) — the right and left aortic sinuses give rise to the right and left coronary arteries respectively.
10.2.6 — Bicuspid (Mitral) Complex ★★
5.1 Definition
The bicuspid complex is the set of four structural components guarding the left atrioventricular orifice that together prevent backflow of blood from the left ventricle into the left atrium during ventricular systole.
- Left atrioventricular fibrous ring — the structural anchor for the bicuspid valve cusps.
- Bicuspid valve cusps — two cusps (anterior and posterior). The mitral valve is the most frequently diseased heart valve.
- Chordae tendineae — tether the free edges of the cusps to the papillary muscles below, preventing inversion into the left atrium.
- Papillary muscles — anterior and posterior; contract simultaneously with the left ventricle to maintain chordae tension throughout systole.
🩺 Clinical — Mitral Valve Disease
The mitral valve is the most frequently diseased heart valve — particularly in rheumatic heart disease and infective endocarditis. Mitral regurgitation allows backflow into the left atrium, producing a high-pitched pansystolic murmur loudest at the apex. Longstanding mitral regurgitation leads to left atrial enlargement, pulmonary hypertension, and eventually left ventricular failure. [Netter's 5th §22 p172]
📝 Exam Q&A — Bicuspid Complex
Q: Describe the bicuspid complex.
The bicuspid complex consists of: (1) the left atrioventricular fibrous ring, (2) the bicuspid (mitral) valve cusps — anterior and posterior, (3) the chordae tendineae, and (4) the papillary muscles. Its function is to prevent backflow of blood from the left ventricle into the left atrium during ventricular contraction.
[2008 Final Exam model answers]
Q: Write down the names of the inlet and outlet of the left ventricle.
Inlet — the left atrioventricular orifice (bicuspid/mitral valve). Outlet — the aortic orifice (aortic valve).
[2008 Review]
10.3
Conduction System of the Heart ★★★
Conduction system of the heart (Fig 3.83). A — Right chambers: sinu-atrial (SA) node (near SVC junction), atrioventricular (AV) node (interatrial septum), atrioventricular bundle (Bundle of His), right bundle branch running in septomarginal trabecula, septomarginal trabecula, anterior papillary muscle, IVC. B — Left chambers: left bundle branch spreading over LV wall, anterior/posterior papillary muscles, left atrium, right pulmonary veins.
Gray's Anatomy for Students 4e · Fig 3.83, p212
10.3.1 — Overview of the Conduction System ★★★
5.1 Definition
The cardiac conduction system is a network of specialised myocardial fibres that spontaneously generates and coordinates electrical impulses, ensuring the sequential, rhythmic contraction of the atria followed by the ventricles at an appropriate rate.
5.3 Five Components — In Order of Impulse Propagation
- Sinoatrial node (SA node) — in the wall of the right atrium, near the opening of the superior vena cava. The pacemaker of the heart — spontaneously depolarises at 60–100/min, initiating each cardiac cycle.
- Internodal tracts — three pathways (anterior, middle, posterior) conducting the impulse through the atrial walls to the AV node, causing atrial contraction en route.
- Atrioventricular node (AV node) — in the interatrial septum near the opening of the coronary sinus. Introduces a brief delay (~0.1 seconds) — allowing atrial contraction to complete and ventricular filling to occur before ventricular systole begins.
- Atrioventricular bundle (Bundle of His) with right and left bundle branches — passes from the AV node into the interventricular septum; the right bundle branch runs within the septomarginal trabecula (moderator band) to the right ventricular wall; the left bundle branch passes through the septum to the left ventricular wall.
- Subendocardial plexus of Purkinje fibres — terminal network of large, rapidly-conducting fibres spreading from the bundle branches throughout both ventricular walls. Their rapid conduction ensures near-simultaneous ventricular depolarisation, producing a single powerful coordinated contraction. [Gray's 4e Ch3 p188]
🔖 Failsafe Pacemaker Hierarchy
SA node (60–100/min) → AV node (40–60/min) → Purkinje fibres (30–40/min)
Each level becomes the pacemaker if the one above it fails. At Purkinje rate (30–40/min) the patient is haemodynamically compromised → requires an implanted cardiac pacemaker.
📝 Exam Q&A — Conduction System
Q: What is the normal pacemaker? Write out the composition of the conduction system of the heart.
The normal pacemaker is the sinoatrial (SA) node, located in the wall of the right atrium near the superior vena cava orifice. The conduction system comprises: (1) SA node, (2) internodal tracts, (3) atrioventricular (AV) node, (4) the atrioventricular bundle (Bundle of His) with its right and left bundle branches, and (5) the subendocardial plexus of Purkinje fibres.
[2008 Final Paper Q5; TMU Review Notes]
Q: Why is the AV node delay clinically important?
The AV node introduces a ~0.1-second delay that allows the atria to finish contracting and the ventricles to fill completely before ventricular contraction begins — maximising stroke volume and cardiac output.
10.4
Coronary Circulation ★★★
Fig 3.78A Anterior view, right-dominant coronary pattern. RCA: sinu-atrial nodal branch, right marginal branch, posterior IV branch (PDA). LCA: circumflex branch, left marginal branch, anterior IV branch (LAD), diagonal branch. Both arteries originate from their respective aortic sinuses.
Gray's Anatomy for Students 4e · Fig 3.78A, p205
Fig 3.79 Left-dominant coronary pattern. LCA: circumflex branch (dominant, gives posterior IV), left marginal branch, anterior IV branch (LAD), diagonal branch. RCA: right marginal branch only (non-dominant). In left-dominant pattern, circumflex supplies posterior IV sulcus and posterior LV.
Gray's Anatomy for Students 4e · Fig 3.79, p206
10.4.1 — Coronary Arteries ★★★
5.1 Definition
The coronary arteries are the first branches of the aorta, arising from the aortic sinuses (sinuses of Valsalva) immediately above the aortic valve cusps, and supplying the entire myocardium with oxygenated blood.
5.3 Origins & Main Branches
| Vessel | Origin | Main Branches | Territory Supplied |
|---|---|---|---|
| Right Coronary Artery (RCA) | Right aortic sinus | Posterior interventricular branch (posterior descending artery); Posterior branch of left ventricle; SA nodal branch; AV nodal branch | Right atrium, right ventricle, posterior septum, posterior left ventricle, SA node (60%), AV node (80–90%) |
| Left Coronary Artery (LCA) | Left aortic sinus | Anterior interventricular branch (LAD); Circumflex branch | Anterior walls of both ventricles, anterior 2/3 of interventricular septum (LAD); left atrium, posterior left ventricle (circumflex) |
5.5 Function / Key Mechanism
Unlike other organs, the myocardium receives its blood supply predominantly during diastole — because during systole, ventricular contraction compresses the intramural coronary vessels. Therefore, a fast heart rate (shortened diastole) reduces coronary perfusion time and can precipitate ischaemia in diseased vessels.
🩺 Clinical — Coronary Artery Disease & Referred Pain
The left anterior descending artery (LAD) — the "widow maker" — supplies the largest amount of ventricular muscle. Its occlusion causes a large anterior myocardial infarction with high mortality. In CABG surgery, the internal thoracic artery or saphenous vein is grafted to bypass the occlusion, restoring distal perfusion. [Netter's 5th §22 p158]
Cardiac ischaemic pain is referred to the left pectoral region and medial left arm because visceral afferent fibres from the heart enter spinal cord segments T1–T4/T5 on the left — the same segments receiving somatic sensory input from the chest wall and arm. The brain misinterprets the cardiac signal as coming from the arm.
📝 Exam Q&A — Coronary Arteries
Q: Write out the origin and main branches of the arteries supplying the heart.
The right coronary artery (RCA) arises from the right aortic sinus and gives two main branches: the posterior interventricular branch and the posterior branch of the left ventricle. The left coronary artery (LCA) arises from the left aortic sinus and gives two main branches: the anterior interventricular branch (LAD) and the circumflex branch.
[2008 Final Paper Q6; TMU Review Notes p28]
Q: The left coronary artery arises from: [MCQ — 2019/2020 Paper Q13]
Answer: B — the left aortic sinus. (Not the right aortic sinus, not the coronary sinus, not the orifice of the pulmonary trunk.)
[2019/2020 Final Paper MCQ Q13]
Summary — Four Cardiac Chambers at a Glance
| Chamber | Inlets | Outlet | Key Internal Feature | Exam Note |
|---|---|---|---|---|
| Right Atrium | SVC orifice IVC orifice Coronary sinus orifice |
Right AV orifice (tricuspid valve) | Fossa ovalis; crista terminalis; pectinate muscles | 3 inlets = most tested |
| Right Ventricle | Right AV orifice (tricuspid) | Pulmonary orifice (pulmonary valve) | Septomarginal trabecula (moderator band); conus arteriosus | Moderator band = right bundle branch |
| Left Atrium | 4 pulmonary vein orifices | Left AV orifice (bicuspid/mitral valve) | Smooth posterior wall; left auricle | 4 pulmonary veins = always tested |
| Left Ventricle | Left AV orifice (bicuspid/mitral) | Aortic orifice (aortic valve) | Thickest wall; aortic vestibule; aortic sinuses → coronary arteries | Thickest wall = 3× right ventricle |
📋
Past Paper Questions — Exact Questions, Model Answers & Reasons
2019/2020 Final
Define · 3'
Section I Q6 — Define the tricuspid complex.
✅ Model Answer
The tricuspid complex refers to the four structural components that together prevent backflow of blood from the right ventricle into the right atrium during ventricular systole. These are: (1) the right atrioventricular fibrous ring, (2) the tricuspid valve — consisting of three cusps: anterior, posterior, and septal, (3) the chordae tendineae, and (4) the papillary muscles.
💡 Why this answer is correct
TMU defines a "complex" as the entire functional unit — not just the valve cusps. The 4 components work as a single integrated mechanism: the fibrous ring anchors, cusps seal, chordae prevent prolapse, and papillary muscles maintain chordae tension during contraction. All 4 must be named for full marks.
🔑 Key marking points
① "4 components" must be stated or implied ② All 3 cusp names (ant, post, septal) — or "three cusps" as minimum ③ Chordae tendineae (correct spelling) ④ Papillary muscles ⑤ Function stated: "prevent backflow from RV to RA during systole"
2008 Final
Long Q1
Please write down the names of the inlet and outlet of the right atrium.
✅ Model Answer (from 2008 model answer sheet)
Inlets (3): (1) the orifice of the superior vena cava — returns deoxygenated blood from the upper half of the body; (2) the orifice of the inferior vena cava — returns deoxygenated blood from the lower half of the body; (3) the orifice of the coronary sinus — returns venous blood from the myocardium itself. Outlet (1): the right atrioventricular orifice.
💡 Reason
The right atrium is the collecting chamber for all systemic venous return. The 3-inlet pattern is unique to the RA (compared with LA's 4 pulmonary veins). The coronary sinus is frequently omitted — it is essential. The outlet is the AV orifice, not the tricuspid valve (the valve guards the orifice — they are distinct terms).
① 3 inlets named ② "Coronary sinus" must appear — most commonly missed ③ Outlet = "right atrioventricular orifice" (not just "tricuspid valve")
2008 Final
Long Q2
Please write down the names of the inlet and outlet of the left ventricle.
✅ Model Answer
Inlet: the left atrioventricular orifice, guarded by the bicuspid (mitral) valve — receives oxygenated blood from the left atrium. Outlet: the aortic orifice, guarded by the aortic valve — opens into the ascending aorta to distribute blood to the systemic circulation.
💡 Reason
The LV has exactly 1 inlet and 1 outlet — simpler than the atria. The key distinction is naming the orifice (the opening) and noting the valve that guards it. Both terms should appear in the answer.
① Inlet = "left AV orifice" (or "left atrioventricular orifice") ② "bicuspid/mitral valve" ③ Outlet = "aortic orifice" ④ "aortic valve"
2008 Final
Long Q3
Please write down the names of valves of the right ventricle.
✅ Model Answer
The right ventricle has two valves: (1) The right atrioventricular orifice is guarded by the tricuspid valve — it is the inlet valve, with three cusps: anterior, posterior, and septal. (2) The pulmonary orifice is guarded by the pulmonary valve — it is the outlet valve, with three semilunar cusps: anterior, right, and left.
💡 Reason
Every ventricle has exactly 2 valves — one inlet (AV valve) and one outlet (semilunar valve). The RV uses an AV-type valve (tricuspid, with tendinous apparatus) at inlet and a semilunar valve (pulmonary, no chordae) at outlet. Knowing which type of valve is at which orifice is fundamental.
① Two valves named ② Tricuspid = inlet, pulmonary = outlet ③ Cusp names not essential but gain marks
2008 Final
Long Q5
Please write down the conduction system of the heart. What is the normal pacemaker?
✅ Model Answer
The normal pacemaker is the sinoatrial (SA) node. The conduction system consists of five components: (1) the sinoatrial node — located in the wall of the right atrium near the opening of the superior vena cava; (2) the internodal tracts; (3) the atrioventricular (AV) node — located in the interatrial septum near the orifice of the coronary sinus; (4) the atrioventricular bundle (Bundle of His) with its right and left bundle branches — the right branch runs within the septomarginal trabecula (moderator band); (5) the subendocardial plexus of Purkinje fibres.
💡 Reason
The conduction system must be listed in the correct order of impulse propagation — it is a sequence, not a list. The SA node is the pacemaker because it has the highest intrinsic rate (60–100/min). The AV node introduces a mandatory delay. The moderator band is clinically notable because damage to it disrupts RV conduction.
① 5 components in order ② SA node = pacemaker + location (RA near SVC) ③ AV node location (interatrial septum near coronary sinus) ④ Moderator band = R bundle branch ⑤ Purkinje fibres named
2008 Final
Long Q6
What are the arteries of the heart? Where do they arise from? Please write down their main branches.
✅ Model Answer (from 2008 model answer sheet)
The heart is supplied by two coronary arteries. (1) The right coronary artery (RCA) arises from the right aortic sinus. Its main branches are: the posterior interventricular branch and the posterior branch of the left ventricle. (2) The left coronary artery (LCA) arises from the left aortic sinus. Its main branches are: the anterior interventricular branch (left anterior descending, LAD) and the circumflex branch.
💡 Reason
The coronary arteries are the first branches of the aorta, arising from the aortic sinuses (sinuses of Valsalva) just above the aortic valve cusps. Stating the aortic sinus (not just "aorta") is the precision TMU expects. The question asks three things — name, origin, branches — all three must be answered.
① Two arteries named (RCA + LCA) ② RCA from right aortic sinus; LCA from left aortic sinus ③ RCA branches: posterior IV + posterior LV ④ LCA branches: anterior IV (LAD) + circumflex
2019/2020 Final
MCQ Q13 · 1'
The left coronary artery arises from: A. Right aortic sinus B. Left aortic sinus C. Coronary sinus D. Orifice of the coronary sinus E. Orifice of the pulmonary trunk
✅ Answer: B — Left aortic sinus
The left coronary artery arises from the left aortic sinus (sinus of Valsalva) immediately above the left cusp of the aortic valve. It then divides into its two main branches: the anterior interventricular branch (LAD) and the circumflex branch.
💡 Why the distractors are wrong
A (right aortic sinus) — this is the origin of the right coronary artery, not the left. C (coronary sinus) — the coronary sinus is a venous channel draining into the right atrium; it has nothing to do with arterial supply. D (orifice of coronary sinus) — same as above, venous structure. E (pulmonary trunk orifice) — the pulmonary trunk carries deoxygenated blood to the lungs; no coronary arteries arise from it.
Classic MCQ trap: confusing "coronary sinus" (venous, drains into RA) with "aortic sinus / sinus of Valsalva" (arterial, above aortic valve). Always distinguish arterial (aortic sinus) from venous (coronary sinus).
📚 Full Question Bank — Unit 10 Heart
50 sample MCQs · 30 Define questions · 10 Essay questions — all with model answers & reasons