Heart and Blood Vessels: Perfusion and Circulation — Study Notes
Perfusion: definition and importance
Perfusion is the delivery of blood per unit time, per gram of tissue.
Formal definition: with units typically mL·min⁻¹·g⁻¹.
Why it matters:
It determines whether cells receive enough oxygen and nutrients and can remove waste products.
Adequate perfusion is necessary for tissue function and survival.
If tissues don’t get enough oxygen/nutrients or can’t remove waste, cells die, organs fail, and ultimately life is threatened.
Practical implication: to achieve adequate perfusion, the heart must be healthy and the blood vessels must be open and capable of expanding/contracting to maintain proper blood pressure.
Arteries, Veins, and Capillaries: basic review and oxygenation nuances
Arteries carry blood away from the heart ("a for away").
Most arteries carry oxygenated blood, but not all; notably the pulmonary artery carries deoxygenated blood.
Veins carry blood toward the heart; not all veins carry deoxygenated blood (e.g., pulmonary veins carry oxygenated blood).
Color coding in models (red/blue) is not a universal rule for oxygenation status; what matters is the oxygen content of the blood.
In the lungs:
Alveoli are the sites of gas exchange.
Pulmonary capillaries drop off carbon dioxide and pick up oxygen, delivering oxygenated blood to the heart.
In the rest of the body:
Systemic vessels deliver oxygen and nutrients to tissues and pick up waste products.
The Heart: right vs left, chambers, and major vessels
The heart has two sides: right and left.
Right side pumps blood to the lungs (pulmonary circulation).
Left side pumps blood to the rest of the body (systemic circulation).
Four chambers:
Atria (plural) are the superior chambers; they receive blood.
Ventricles are the inferior chambers; they pump blood away from the heart.
Right atrium receives deoxygenated blood from the body via the superior and inferior vena cavae.
The left atrium receives oxygenated blood from the lungs via the pulmonary veins.
The heart’s valves ensure one-way blood flow and prevent regurgitation.
Detailed flow of blood through the heart (step-by-step path)
1) Blood returning to the heart enters the right atrium via the superior vena cava and the inferior vena cava (deoxygenated blood).
2) Blood moves from the right atrium to the right ventricle through the right atrioventricular valve (tricuspid valve).
3) The right ventricle contracts and blood is ejected through the pulmonary semilunar valve into the pulmonary trunk (leading to the lungs); this valve is between the right ventricle and the pulmonary trunk.
4) In the lungs, gas exchange occurs: carbon dioxide is released, oxygen is picked up; blood becomes oxygenated.
5) Oxygenated blood returns to the left atrium via the pulmonary veins.
6) Blood moves from the left atrium to the left ventricle through the left atrioventricular valve (mitral/bicuspid valve).
7) The left ventricle contracts and blood is ejected through the aortic semilunar valve into the aorta, delivering blood to the systemic circulation.
8) Systemic tissues receive oxygen and nutrients; waste products are collected; blood returns to the right heart via veins, starting the cycle again.
Quick notes on colors and vessels in diagrams:
The pulmonary trunk is depicted blue in some diagrams because it carries deoxygenated blood from the right ventricle to the lungs (it is an artery).
Veins returning to the heart from the lungs (pulmonary veins) are depicted red because they carry oxygenated blood.
In the rest of the body, arteries are typically shown red (oxygenated) and veins blue (deoxygenated), but this is a convention, not a universal rule.
The important distinction is the oxygen content, not the color itself.
Heart valves: structure, function, and mechanics
Two sets of valves:
Atrioventricular (AV) valves: right AV valve is the tricuspid; left AV valve is the mitral (bicuspid) valve.
Semilunar valves: pulmonary semilunar valve (between right ventricle and pulmonary trunk) and aortic semilunar valve (between left ventricle and aorta).
Function and timing:
AV valves close when the ventricles contract to prevent backflow into the atria.
Semilunar valves open during ventricular contraction to allow ejection into the pulmonary trunk and aorta.
Semilunar valves close after contraction when the pressure falls and blood starts to attempt backflow into the ventricles; the cusps fill and prevent regurgitation.
Chordae tendineae (tendinous cords) and papillary muscles:
Chordae tendineae attach to the AV valve leaflets and anchor them to the ventricular wall.
They prevent AV valve cusps from being pushed back into the atria when the ventricles contract, acting like tethers to keep the valve closed in the proper direction.
Visual/analogies used:
Umbrella analogy: valves function like doors that open and close in response to pressure, with chordae tendineae acting like cords to prevent the valves from flapping backward.
Clinical relevance:
Murmurs can occur when valve closure is imperfect, resulting in regurgitation and abnormal heart sounds.
Murmurs are often discussed in clinical labs and lectures when valve function is impaired or abnormal.
Pulmonary vs. systemic circulation: overview
Pulmonary circulation:
Pathway: right heart → lungs → left heart.
Deoxygenated blood leaves the right ventricle via the pulmonary trunk/arteries to the lungs, gas exchange occurs, and oxygenated blood returns to the left atrium via the pulmonary veins.
Systemic circulation:
Pathway: left heart → systemic tissues → right heart.
Oxygenated blood leaves the left ventricle via the aorta to the muscles, bones, organs, etc.; deoxygenated blood returns to the right atrium via the vena cavae.
This division is a useful way to understand how the heart handles gas exchange and tissue perfusion separately.
Internal anatomy: key structures and the memorization approach
For lecture and lab, you should know the structures through which blood passes during a typical cycle.
A simplified memorandum (as described in the slide) starts with the right atrium and follows the path through the heart valves, chambers, and into the great vessels:
Right atrium → via superior/inferior vena cava (deoxygenated blood) → through the tricuspid valve → right ventricle → via pulmonary semilunar valve → pulmonary trunk → to lungs (gas exchange) → returns via pulmonary veins to the left atrium → through the mitral/bicuspid valve → left ventricle → via the aortic semilunar valve → aorta → systemic circulation → back via veins to the right heart.
Color-coded arrows in diagrams often indicate the oxygenation status along the pathway: the orangey-red arrows typically signify oxygenated blood, while the bluish arrows indicate deoxygenated blood.
Remember: the naming of valves reflects the vessel they open into, e.g., pulmonary semilunar valve opens into the pulmonary trunk; mitral/bicuspid valve opens into the left ventricle.
The right side of the heart pumps to the lungs; the left side pumps to the rest of the body.
Practical takeaways and connections
Perfusion is essential for tissue viability; failure leads to organ failure and death if unchecked.
The heart and vessels must work in concert: healthy myocardium, open/compliant vessels, and proper valve function to maintain adequate BP and perfusion.
Valve mechanics are tightly linked to the cardiac cycle: contraction and relaxation phases coordinate with valve opening/closing to ensure one-way flow and prevent regurgitation.
Common clinical relevance: valve disorders can cause murmurs; understanding the anatomy and flow helps interpret those sounds.
Foundational links: this material ties into gas exchange (pulmonary capillaries), systemic tissue perfusion, and the regulatory logic of cardiovascular physiology (pressure, flow, resistance).
Quick review: key terms to remember
Perfusion:
Atria (plural) vs Atrium (singular)
Ventricles
Superior vena cava, Inferior vena cava
Pulmonary trunk; Pulmonary arteries; Pulmonary veins
Aorta
Atrioventricular valves: tricuspid (right), mitral/bicuspid (left)
Semilunar valves: pulmonary semilunar valve, aortic semilunar valve
Chordae tendineae
Papillary muscles
Pulmonary circulation vs Systemic circulation
Murmur and regurgitation
Contextual reminder mentioned in class
The Wednesday-to-Labor Day note appears in the transcript as a contextual aside; the core content above remains focused on perfusion, heart anatomy, and the flow of blood through the heart and vessels.