Which Organ Receives Maximum Cardiac Output
The kidneys receive the maximum percentage of cardiac output at rest in healthy adults, receiving approximately 20-25% of total cardiac output despite representing only about 0.5% of body weight. 1
Resting Cardiac Output Distribution
The distribution of cardiac output among organs at rest follows a clear hierarchy based on metabolic demands and functional requirements:
Kidneys: The Dominant Recipient
- The kidneys receive approximately one-fifth (20%) of cardiac output at rest, which is disproportionately high relative to their small mass 1
- In quantitative studies, the kidneys received 12.95% of cardiac output in one animal model, though human values are typically higher at 20-25% 2
- This high renal blood flow is necessary for filtration function rather than metabolic oxygen demands, as evidenced by the kidneys' characteristically low oxygen extraction ratio 1
Other Major Organ Recipients
- Gastrointestinal tract and splanchnic circulation: Receives approximately 18-19% of cardiac output 2, 3
- Skeletal muscle at rest: Receives a modest percentage at rest, but this dramatically increases during exercise 4
- Brain: Receives approximately 1.1-1.13% of cardiac output, which remains relatively constant 2, 3
- Heart (coronary circulation): Receives approximately 2.7-3.04% of cardiac output 2, 3
- Liver via hepatic artery: Receives approximately 4.27-11.81% of cardiac output (note: total hepatic blood flow is higher when including portal venous flow) 2, 3
Important Physiological Context
Why Kidneys Receive Maximum Flow
- The high renal blood flow serves filtration rather than metabolic needs, as the kidneys have a characteristically low oxygen extraction ratio compared to other organs 1
- This creates regional variations in renal oxygenation that are prerequisites for kidney function, including concentration of urine and regulation of electrolytes 1
Internal Organs as a Group
- Internal organs collectively (brain, heart, kidneys, liver, and gastrointestinal tract) constitute only 8.25% of total body mass but receive 45-56% of resting cardiac output 2, 3
- This demonstrates the metabolically active nature of visceral organs compared to peripheral tissues 2
Dynamic Changes During Exercise
While the kidneys receive maximum cardiac output at rest, this distribution changes dramatically during exercise:
- During maximal exercise in healthy individuals, skeletal muscle can receive up to 85-90% of total cardiac output 4
- Cardiac output can increase 4- to 6-fold above basal levels during exercise 4
- Vasoconstriction occurs in most circulatory systems except exercising muscle, cerebral, and coronary circulations during maximal exercise 4
Common Pitfall to Avoid
Do not confuse absolute blood flow per unit weight with percentage of total cardiac output. While the kidneys receive the highest percentage of cardiac output at rest, organs like the brain may have higher blood flow per 100g of tissue weight. The question asks specifically about cardiac output distribution, where kidneys are the clear winner at rest 2, 1.