What is Systemic Circulation?
Systemic circulation is the large loop that carries oxygenated blood from the left side of the heart to every organ and tissue in the body, then returns deoxygenated blood to the right atrium. It is a high-pressure, high-resistance circuit.
Systemic circulation carries oxygenated blood from the left ventricle through the aorta to the body's tissues, where oxygen and nutrients are exchanged, then returns deoxygenated blood via the venae cavae to the right atrium.
- 1.Left ventricle — Pumps oxygenated blood into the aorta at high pressure (about 120 mmHg)
- 2.Arteries & arterioles — Distribute blood to organs, regulating pressure and flow
- 3.Systemic capillaries — Exchange oxygen, nutrients and waste with body tissues
- 4.Venules & veins — Collect deoxygenated blood in a low-pressure return system
- 5.Venae cavae — Superior and inferior vena cava empty into the right atrium
Step-by-step worked examples
Aortic pressure is about 120/80 mmHg, while pulmonary artery pressure is only about 25/8 mmHg. Why must systemic pressure be so much higher?
Systemic circulation must push blood through the entire body, including distant tissues like the feet and hands This long distance and high resistance requires a much stronger driving pressure The left ventricle's thick myocardium generates this higher pressure
Blood in the aorta has oxygen saturation of about 98%; blood returning in the vena cava has about 75%. What caused the drop?
Oxygenated blood leaves the left ventricle at about 98% saturation As blood passes through systemic capillaries, tissues extract oxygen for metabolism Deoxygenated blood returns via the venae cavae at roughly 75% saturation
During exercise, systemic blood flow to skeletal muscle can increase from about 1 L/min to about 20 L/min. What causes this increase?
Arterioles supplying active muscle dilate (vasodilation) in response to metabolic demand This lowers resistance and increases local blood flow Cardiac output also rises via increased heart rate and stroke volume to support the shift
Flashcards
Quick quiz
Q1.Systemic circulation begins in which heart chamber?
Q2.Where does gas and nutrient exchange occur in systemic circulation?
Q3.Systemic circulation ends when deoxygenated blood enters the:
Q4.Why is aortic pressure (about 120/80 mmHg) much higher than pulmonary artery pressure (about 25/8 mmHg)?
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Common mistakes
Systemic circulation and pulmonary circulation are the same pathway. — Correct: They are two separate loops: systemic (heart to body to heart) and pulmonary (heart to lungs to heart).
All veins carry deoxygenated blood. — Correct: Most systemic veins do, but pulmonary veins are an exception — they carry oxygenated blood.
Systemic circulation is a low-pressure system. — Correct: It's a high-pressure system (about 120/80 mmHg) because it must reach the entire body.
Exchange of oxygen and nutrients happens in the arteries. — Correct: Exchange happens in the capillaries, not the arteries, which mainly transport blood.
FAQ
What is systemic circulation?
The pathway that carries oxygenated blood from the left ventricle to the body's tissues and returns deoxygenated blood to the right atrium.
What is the systemic circulation pathway in order?
Left ventricle → aorta → arteries → arterioles → capillaries → venules → veins → venae cavae → right atrium.
What are examples of systemic circulation disorders?
Hypertension, atherosclerosis, and peripheral artery disease are common examples affecting systemic circulation.
How is systemic circulation different from pulmonary circulation?
Systemic circulation is a long, high-pressure loop supplying the whole body; pulmonary circulation is a short, low-pressure loop to the lungs.