The body's delivery network — transporting oxygen, nutrients, and waste to and from every cell, 24 hours a day.
Connection Quiz ↓The circulatory and respiratory systems are inseparable partners. Blood travels from the heart to the lungs via pulmonary circulation to pick up oxygen and drop off CO₂. Without the respiratory system loading oxygen into red blood cells, the circulatory system would be delivering empty packages.
After the small intestine breaks down food, blood vessels lining the intestinal wall absorb glucose, amino acids, and fatty acids directly into the bloodstream and carry them to every cell in the body.
The excretory system removes waste from the blood in three ways: the kidneys filter liquid waste (urea → urine), the large intestine expels solid waste while returning absorbed water to the bloodstream, and the lungs expel gaseous CO₂ with every exhale.
Red bone marrow inside the femur and sternum manufactures all blood cells — red cells to carry oxygen and white cells to fight infection. Without the skeletal system, the circulatory system could not maintain its cellular supply.
The circulatory system is the immune system's highway network. White blood cells and antibodies travel through blood vessels to infection sites anywhere in the body. Lymph nodes filter pathogens out of the blood before they can spread.