Notes on Cardiovascular Circulation: Pulmonary, Systemic, and Coronary
Coronary Circulation
Purpose: Supply oxygen and nutrients to the heart muscle (myocardium) so the heart can contract effectively without ischemia. The heart is a muscle that also needs oxygen and needs to remove CO₂; coronary circulation ensures continuous flow.
Key vessels on anterior view:
Right coronary artery (RCA): shown on the right side of the heart.
Left coronary artery (LCA): visible on the left side; gives off branches.
Major coronary branches:
From the right coronary artery (RCA):
Posterior interventricular artery (also called the posterior descending artery, PDA) – runs between the ventricles on the posterior side.
Marginal arteries – run along the right ventricle.
Atrioventricular nodal branch – supplies the AV node (important for conduction system).
Posterior septal artery – runs along the posterior portion of the septum.
From the left coronary artery (LCA):
Anterior interventricular branch (left anterior descending, LAD) – runs in the anterior interventricular groove and supplies the anterior wall.
Branches into the anterior septal artery.
Circumflex artery – wraps around the left side of the heart (around the outside).
Gives rise to anterior and posterior ventricular branches (supplies the ventricles).
Left vs. right dominance and supply:
The LAD and circumflex branches supply most of the left ventricle, which is the largest tissue mass in the heart and has the greatest oxygen demand.
Blood flow generation for coronary arteries:
Blood flows from the aortic sinus into the coronary arteries when the aortic valve is closed (diastole).
During systole (ventricular contraction), the aortic valve is open and coronary flow is reduced; diastole provides the main perfusion.
Cardiac tissue blood supply sequence:
Coronary arteries originate at the aortic sinuses just above the aortic valves.
After leaving the aorta, they give off branches (RCA and LCA and their sub-branches) to both ventricles and atria.
Blood then drains via the cardiac veins, which run parallel to arteries, into the coronary sinus, and finally into the right atrium.
Venous drainage:
Cardiac veins collect deoxygenated blood from the myocardium.
Veins drain into the coronary sinus, which empties into the right atrium, similar to how the superior and inferior vena cavae drain systemic blood into the right atrium.
Circulation overview (two circuits):
Systemic circulation = blood flow from the left ventricle through the body’s vessels and back to the right atrium; excludes gas exchange in the lungs.
Pulmonary circulation = deoxygenated blood from the right heart to the lungs for gas exchange and back to the left atrium; includes pulmonary arteries, lungs, and pulmonary veins.
Pulmonary Circulation and Gas Exchange
Pathway:
Deoxygenated blood reaches the right atrium from the systemic veins via the superior and inferior vena cavae.
Blood moves from the right atrium to the right ventricle.
From the right ventricle, blood travels through the pulmonary trunk into the left and right pulmonary arteries toward the lungs.
In the lungs, arteries branch into arterioles and capillaries surrounding alveoli where gas exchange occurs.
CO₂ is released from the blood and exhaled; O₂ is taken up by the blood.
Oxygenated blood returns to the left atrium via the pulmonary veins.
Blood then moves to the left ventricle and is distributed systemically via the aorta.
Pulmonary veins are red in diagrams because they carry oxygenated blood.
Gas exchange organ focus: lungs only; arteries bring deoxygenated blood to lungs, veins return oxygenated blood to the heart.
Systemic Circulation (General Pathways)
Definition: Blood flows from the left ventricle through systemic arteries to all body tissues and returns to the right atrium via veins.
Major venous drainage (overview):
Head, neck, and upper limbs drain into the superior vena cava (SVC).
Thoracic organs drain directly into the SVC.
Lower limbs and abdomen drain into the inferior vena cava (IVC).
Systemic arteries – general pattern:
Aorta is the main artery emerging from the left ventricle.
Aorta branches into the arch and then the descending aorta.
Major regional arteries are named by region they serve (head/neck, upper limbs, abdomen, pelvis, legs).
Major Arteries (Systemic) by Region
Aortic arch and proximal branches:
Brachiocephalic artery (only on the right side) branches into:
Right subclavian artery
Right common carotid artery
Left common carotid artery (direct branch from the arch)
Left subclavian artery (direct branch from the arch)
Head and neck region branches (from the arch via the common carotid and associated branches):
Carotid arteries supply the head and neck and extend to the eyes.
Vertebral arteries (ascending through the cervical vertebrae) contribute to brain circulation.
Facial, maxillary, occipital, and thyroid arteries are branches encountered in this region.
Upper limb arteries:
Axillary artery (under the clavicle) – continuation from the subclavian artery.
Brachial artery – continues down the upper arm.
Forearm arteries: radial (lateral) and ulnar (medial).
Hand arteries: palmar and digital arteries.
Lower limb arteries:
External iliac artery leads to the femoral artery in the thigh.
Femoral artery becomes the popliteal artery at the knee.
Tibial and fibular (peroneal) arteries extend into the lower leg and foot.
Abdominal branch terminology (named by region):
Gastric (stomach), celiac (foregut), splenic (spleen), renal (kidney), hepatic (liver), suprarenal (adrenal), mesenteric (gut), gonadal (gonads).
These branches arise from the abdominal aorta as it descends.
Abdominal Aorta and Its Branches
Abdominal branches (examples listed, not exhaustive):
Celiac trunk: gastric (stomach), hepatic (liver), splenic (spleen)
Superior mesenteric artery (gut)
Renal arteries (kidneys)
Gonadal arteries (gonads)
Inferior mesenteric artery (distal gut)
Concept: branch patterns reflect major organ regions supplied by the abdominal viscera.
Head, Neck, and Thoracic Vessels (Further Details)
Branches from the aortic arch and its proximal vessels:
Right side: brachiocephalic trunk → right subclavian and right common carotid
Left side: left common carotid and left subclavian arise directly from the arch
Additional head/neck arteries encountered in imaging include:
Vertebral artery (posterior circulation to the brain)
Facial and maxillary arteries (facial/anterior face regions)
Occipital artery (posterior scalp region)
Visualizing the arms:
From axillary to brachial to radial and ulnar arteries; hand arteries include palmar and digital arteries.
Visualizing the legs:
From femoral to popliteal to tibial and fibular arteries; continuation to the foot.
Systemic Veins (Venous Return)
General pathway: venous blood returns to the heart via progressively larger venous channels (venules → veins).
Major drainage concepts:
Veins mirror arteries in naming and branches; valveless or minimally valved in many regions, enabling one-way flow aided by skeletal muscle pumps.
Venous drainage from head, neck, upper extremities, and thoracic organs drains into the superior vena cava (SVC).
Venous drainage from the lower extremities and abdomen drains into the inferior vena cava (IVC).
Brain and thoracic venous drainage:
Veins draining the brain and thoracic organs contribute to systemic venous return via the SVC.
Intercostal veins provide venous drainage around the ribs.
Cardiac Conduction-Related Vascular Considerations
Sinoatrial (SA) node location: located in the right atrium; its blood supply is from branches of the coronary arteries (noted as part of conduction system considerations).
Atrioventricular (AV) node and nodal supply: supplied in part by the AV nodal artery (branch from the RCA(s) or LCA depending on dominance).
Clinical relevance: compromised coronary flow can affect conduction and rhythm because the SA/AV nodes rely on adequate coronary perfusion.
Arteriovenous Anastomoses (Shunts) and Thermoregulation
Definition: arteriovenous anastomoses (AV shunts) are connections between arteries and veins that bypass capillaries in some regions.
Common regions: skin of face, palms, and other exposed areas.
Function: permit rapid heat loss by allowing blood to flow directly from arteries to veins, bypassing capillary beds which normally regulate heat exchange.
Practical implication: elevated AV shunt activity helps cool the body on hot days; visible in skin perfusion patterns during thermoregulation.
Summary of Key Concepts and Connections
Three interconnected circulations:
Pulmonary circulation enables gas exchange in the lungs.
Systemic circulation supplies the entire body with oxygenated blood and returns deoxygenated blood to the heart.
Coronary circulation specifically nourishes the heart muscle itself to maintain contractile function.
Blood vessel organization mirrors body anatomy:
Major arteries originate from the aorta or its arch, then branch regionally to supply specific organs and limbs.
Veins follow the venous return pathways back to the heart, with naming and drainage patterns often mirroring the arteries.
The heart’s own blood supply is primarily via the two coronary arteries (right and left), with multiple branches that nourish different regions of the myocardium, especially the left ventricle.
Gas exchange and circulation cycle ensure continuous oxygen delivery and carbon dioxide removal to maintain cellular respiration across all tissues.
The conduction system (SA node, AV node) is intimately linked to coronary perfusion, underlining the clinical importance of maintaining adequate coronary blood flow.
References to Diagrams and Pathways (as described in the lecture visuals)
Anterior view of heart showing RCA, left coronary artery, aorta and vena cavae.
Posterior view highlighting descending aorta, inferior vena cava, pulmonary veins, and pulmonary arteries.
Flowchart: aortic sinus → ascending aorta → right and left coronary arteries → branch networks (RCA to marginal and posterior interventricular; LCA to LAD and circumflex) → myocardium → coronary veins → coronary sinus → right atrium.
Diagram of the dual circulations (systemic and pulmonary) illustrating gas exchange in the lungs and return to the left heart.
Images of systemic arteries and their branches (aorta, brachiocephalic trunk, carotids, subclavians, axillary, brachial, radial, ulnar, palmar, digital; iliac, femoral, popliteal, tibial, fibular).
Vein anatomy showing drainage patterns into the superior and inferior vena cava and intercostal/brain venous pathways.
Key Terms to Memorize
Coronary arteries: right coronary artery (RCA), left coronary artery (LCA), posterior interventricular artery (PDA), marginal arteries, anterior interventricular artery (LAD), circumflex artery, anterior and posterior ventricular branches, AV nodal artery, posterior septal artery.
Aortic sinuses, aortic arch, brachiocephalic trunk, common carotid arteries, subclavian arteries, axillary, brachial, radial, ulnar, palmar, digital arteries.
Abdominal branches: gastric, celiac, splenic, hepatic, renal, suprarenal, mesenteric, gonadal.
Veins: superior vena cava, inferior vena cava, coronary sinus, intercostal veins.
AV (arteriovenous) anastomoses and thermoregulation implications.
Note: The above notes consolidate the content from the transcript into a structured set of study notes with clear sections on coronary, pulmonary, systemic circulations, and major vessels, including flow directions, anatomical branches, and functional implications for physiology and medicine.