SN1
SHORT NOTE
5M
★ High-yield
Describe the coronary circulation with its branches and peculiarities.
Origin and Course
The coronary arteries are the first branches of the ascending aorta, arising from the aortic sinuses of Valsalva just above the aortic valve cusps.
| Artery | Origin | Course |
|---|---|---|
| Right coronary | Anterior aortic sinus | In the right atrioventricular groove, round the inferior border |
| Left coronary | Left posterior aortic sinus | Short trunk between the pulmonary trunk and the left auricle, then divides |
Branches and Territories
| Branch | Parent | Supplies |
|---|---|---|
| Anterior interventricular (LAD) | Left | Anterior two-thirds of the interventricular septum, anterior wall of the left ventricle, apex |
| Circumflex | Left | Left atrium and the posterolateral left ventricle |
| Left marginal | Circumflex | Left border |
| Right marginal | Right | Right ventricle |
| Posterior interventricular | Right in 70% | Posterior third of the septum; determines dominance |
| SA nodal artery | Right in 60% | SA node |
| AV nodal artery | Right in 80% | AV node |
Venous Drainage
- Coronary sinus (60%) — lies in the posterior atrioventricular groove and opens into the right atrium, guarded by the valve of Thebesius. Tributaries: great, middle and small cardiac veins, and the oblique vein of Marshall
- Anterior cardiac veins — drain the right ventricle directly into the right atrium
- Venae cordis minimae (Thebesian veins) — drain directly into the chambers
Peculiarities of the Coronary Circulation
- They are functional end arteries — anastomoses exist but are inadequate for sudden occlusion
- Filling occurs in diastole, because systolic compression obstructs the intramural vessels; so tachycardia, by shortening diastole, reduces coronary flow
- Extraction of oxygen is nearly maximal at rest (about 70%), so increased demand can be met only by increased flow
- Flow is regulated chiefly by local metabolites, especially adenosine
Applied Aspects
- Angina pectoris — reversible ischaemia; pain is referred to the retrosternal area, left arm, jaw and epigastrium via T1–T5
- Myocardial infarction — LAD occlusion gives anterior infarction (leads V1–V4); right coronary occlusion gives inferior infarction (II, III, aVF), often with bradycardia and heart block because the AV node is involved
- Coronary artery bypass grafting uses the internal thoracic artery (best patency) and the reversed great saphenous vein
- Angioplasty and stenting are performed through the radial or femoral artery
- Gradual stenosis permits collateral development, which is why a slowly occluding vessel may cause less damage than a sudden embolus
All questions in Thorax
- Q1Define the mediastinum and describe its divisions with their contents. Add a note on the structures at the level of the sternal angle. ★
- Q2Describe the chambers of the heart, its conducting system and its blood supply. Add a note on the surface marking of the valves. ★
- Q3Describe the lungs with their lobes, fissures and root. Explain bronchopulmonary segments and add a note on the pleura. ★
- Q4Describe the diaphragm under origin, openings, nerve supply and actions. Add a note on its applied anatomy. ★
- Q5Describe the intercostal space with its muscles, vessels and nerves. Add a note on the thoracic cage and applied aspects. ★
- SN1Describe the coronary circulation with its branches and peculiarities. ★
- SN2Describe the pericardium with its layers and sinuses. Add a note on cardiac tamponade. ★
- SN3Describe the course and distribution of the phrenic nerve. Explain the referred pain to the shoulder. ★
- SN4Describe the azygos system of veins and its clinical importance. ★
- SN5Describe the course and drainage of the thoracic duct. Add a note on chylothorax. ★
- SN6Describe the formation, course and relations of the superior vena cava. Add a note on SVC obstruction. ★
- SN7Describe the breast with its lymphatic drainage. Add a note on the surface anatomy of the thorax.