Your circulatory system delivers oxygen, nutrients, hormones, and other essential substances to cells throughout your body. It also carries carbon dioxide to the lungs and transports other waste products to organs that process or remove them.

Circulation contributes to much more than transportation. It helps distribute heat, maintain fluid balance, support immune activity, and deliver platelets and other substances needed for healing. Every organ depends on an adequate blood supply, which is why impaired circulation can affect many seemingly unrelated parts of the body.

The circulatory system includes the heart, blood, and an extensive network of arteries, veins, and capillaries. Each component has a different role, but they function as one continuously connected system.

Blood follows two connected circuits. In pulmonary circulation, blood that is low in oxygen travels from the right side of the heart to the lungs. There, it releases carbon dioxide and receives oxygen. The oxygen-rich blood then returns to the left side of the heart.

In systemic circulation, the left side of the heart pumps that oxygen-rich blood through the aorta and into progressively smaller arteries. The blood eventually reaches capillaries, where oxygen and nutrients pass into surrounding tissues and waste products enter the bloodstream.

Veins then carry the returning blood through progressively larger vessels until it reaches the right side of the heart. The entire sequence repeats continuously.

Arteries carry blood away from the heart. Their muscular, elastic walls help them withstand the pressure created when the heart contracts. Most arteries carry oxygen-rich blood, although the pulmonary arteries carry blood that is low in oxygen from the heart to the lungs.

Veins carry blood back toward the heart. Because blood pressure is lower in veins, many veins contain one-way valves that help prevent blood from flowing backward. Movement of nearby muscles also helps push venous blood toward the heart, particularly from the legs.

Capillaries are microscopic vessels connecting the smallest arteries with the smallest veins. Their extremely thin walls allow oxygen, nutrients, fluid, and waste products to move between the blood and body tissues.

The heart and lungs operate as a coordinated system. The right side of the heart receives blood returning from the body and pumps it to the lungs. Inside the lungs, blood passes through tiny capillaries surrounding the air sacs. Carbon dioxide moves out of the blood to be exhaled, while oxygen from inhaled air enters the blood.

This oxygen-rich blood returns to the left side of the heart. The heart then pumps it into the arteries so oxygen can be delivered throughout the body.

If the heart cannot pump effectively, or the lungs cannot transfer enough oxygen into the blood, organs and muscles may receive less oxygen than they need. This can contribute to fatigue, shortness of breath, reduced exercise tolerance, or other symptoms.

Arteries distribute blood from the heart to the rest of the body. The aorta, the body’s largest artery, receives blood directly from the left side of the heart. It branches into progressively smaller arteries that supply particular organs and regions.

Most arteries carry oxygen-rich blood. The principal exception is the pulmonary arteries, which carry oxygen-poor blood from the heart to the lungs. Arteries also help regulate blood flow by widening or narrowing in response to changing demands. During physical activity, for example, blood vessels supplying active muscles can widen so that more oxygenated blood reaches those tissues.

Different arteries supply different areas, so the consequences of impaired blood flow depend partly on which artery is affected.

A common cause is atherosclerosis, a gradual buildup of plaque within the arterial wall. Plaque contains cholesterol, fat, calcium, cellular debris, and other substances. As it accumulates, the artery may become narrower and less flexible, reducing the amount of blood that can pass through it.

High blood pressure, smoking, diabetes, elevated cholesterol, chronic kidney disease, aging, and family history can increase the risk of arterial damage. A blood clot can also suddenly obstruct an already narrowed artery or form after a plaque ruptures.

Not every narrowing produces immediate symptoms. Arterial disease may develop over many years before blood flow becomes restricted enough to cause a noticeable problem.

Symptoms depend on the location and severity of the narrowing. Reduced blood flow to the heart may cause chest pressure or discomfort. Reduced blood flow to the brain can contribute to a transient ischemic attack or stroke. A sudden interruption of blood flow may cause abrupt weakness, difficulty speaking, vision changes, severe pain, or loss of function and requires emergency care.

In the legs, peripheral artery disease may cause aching, cramping, heaviness, or weakness during walking that improves with rest. Other possible signs include one foot being colder than the other, color changes, weak pulses, loss of leg hair, or wounds that heal slowly.

Some people have significant arterial disease without classic symptoms, so risk factors and medical evaluation also matter.

Protecting your arteries involves reducing the conditions that injure blood vessels or accelerate plaque buildup. Important measures include avoiding smoking, remaining physically active, and managing blood pressure, blood sugar, and cholesterol. Nutrition, sleep, weight management, and taking prescribed medications correctly may also contribute to vascular health.

Regular medical care is particularly important if you have diabetes, kidney disease, high blood pressure, elevated cholesterol, a history of smoking, or known vascular disease. These conditions can affect arteries before symptoms become obvious.

Lifestyle changes can reduce risk, but they do not reliably tell you whether an artery is already narrowed. Persistent or concerning symptoms should be evaluated rather than managed solely through self-care.

The upper number is the systolic pressure. It measures the pressure in your arteries when the heart contracts and pumps blood forward. The lower number is the diastolic pressure. It measures the pressure remaining in the arteries while the heart relaxes and fills between beats.

Both numbers provide useful information. A high systolic reading may indicate that the arteries are experiencing excessive pressure during each heartbeat. An elevated diastolic reading means that pressure remains high even while the heart is resting between contractions.

Blood-pressure categories are based on the relationship between the two numbers, but your clinician may also consider your age, symptoms, health conditions, medications, and pattern of readings over time.

Blood pressure is not fixed. It generally falls during sleep and rises when you awaken and become active. Exercise, pain, emotional stress, caffeine, illness, a full bladder, conversation, and recent meals can temporarily affect a reading. Some medications and supplements can raise or lower it as well.

Measurement conditions also matter. An incorrectly sized cuff, unsupported arm, crossed legs, talking, or failing to rest before the measurement can produce a misleading result.

Because normal variation occurs, one unusual reading does not always establish a problem. Repeated readings taken under similar conditions provide a more useful picture of your usual blood pressure.

High blood pressure repeatedly exposes arterial walls to greater force. Over time, this can damage the vessel lining, contribute to arterial stiffness, and make plaque buildup more likely. The heart may also have to work harder to move blood through the body.

The effects can extend beyond the arteries and heart. Persistent hypertension can damage small blood vessels in the brain, kidneys, and eyes and increase the risk of heart attack, stroke, heart failure, kidney disease, and vision loss.

High blood pressure often causes no obvious symptoms. Feeling well does not necessarily mean that your blood pressure is within a healthy range, which is why measurement and long-term monitoring are important.

Some people naturally have lower blood pressure without symptoms or health consequences. Low blood pressure becomes more concerning when it reduces blood flow to the brain or other organs or represents a significant change from someone’s usual level.

Possible causes include dehydration, blood loss, infection, heart problems, hormonal disorders, prolonged bed rest, and medications used for blood pressure or other conditions. Standing suddenly can also cause a temporary drop known as orthostatic hypotension.

Symptoms may include dizziness, weakness, blurred vision, confusion, nausea, or fainting. Sudden or symptomatic low blood pressure should be evaluated, particularly when accompanied by chest discomfort, shortness of breath, bleeding, severe illness, or loss of consciousness.

The legs and feet are relatively far from the heart, and blood returning from them must move upward against gravity. Walking and other leg movements help by contracting the calf muscles and pushing blood through the veins toward the heart. Long periods of immobility reduce this muscular assistance and may allow blood and fluid to collect in the lower legs.

The arteries supplying the legs may also become narrowed by plaque. Because the muscles require more oxygen during walking, reduced arterial flow may become noticeable first during activity.

Diabetes can further complicate the picture by affecting large arteries, small blood vessels, nerves, and healing. A person may therefore have significant foot problems without experiencing the pain that would ordinarily serve as a warning.

Arterial problems reduce the delivery of oxygen-rich blood to the legs and feet. Possible signs include pain or cramping during walking, unusual coldness, pale or bluish skin, weak pulses, loss of leg hair, and wounds that heal slowly. Severe arterial obstruction may cause pain even at rest.

Venous problems interfere with the return of blood to the heart. They are more likely to produce leg heaviness, aching, visible veins, swelling, and skin discoloration around the ankles. Symptoms may worsen after prolonged sitting or standing and improve when the legs are elevated.

These patterns are helpful but not definitive. A person can have both arterial and venous disease, and similar symptoms can arise from nerve, joint, muscle, lymphatic, or medication-related problems.

Peripheral artery disease, commonly called PAD, develops when arteries carrying blood to the limbs become narrowed or blocked. Atherosclerosis is the most common cause. PAD most often affects the legs, although other arteries outside the heart and brain can also be involved.

A classic symptom is aching, cramping, heaviness, or weakness that begins during walking and improves after several minutes of rest. However, many people with PAD do not have this classic pattern. Some have mild or unusual symptoms, while others report no symptoms at all.

Smoking, diabetes, high blood pressure, abnormal cholesterol levels, kidney disease, older age, and a history of cardiovascular disease increase the likelihood of PAD.

A leg that suddenly becomes painful, swollen, red, or warm may contain a blood clot and needs prompt medical evaluation. Sudden chest pain, unexplained shortness of breath, coughing blood, fainting, or a rapid heartbeat could indicate that a clot has reached the lungs and requires emergency care.

Sudden severe leg pain accompanied by coldness, paleness, numbness, weakness, or loss of a pulse can indicate an abrupt loss of arterial blood flow. This is also an emergency.

Nonhealing sores, darkening skin, drainage, signs of infection, or increasing pain should not be ignored, particularly in someone with diabetes or known vascular disease. Early assessment may prevent tissue damage and more serious complications.

Regular physical activity helps the heart pump efficiently, supports healthy blood pressure, and encourages blood to return from the legs. Activity also assists with blood-sugar regulation, cholesterol management, muscle function, and weight maintenance.

Avoiding tobacco is especially important because smoking damages blood-vessel walls, promotes plaque buildup, and increases the risk of blood clots. Sleep and stress management may also influence blood pressure, metabolism, and the choices you make throughout the day.

No single habit must be performed perfectly. Circulatory protection comes from the cumulative effect of repeated choices combined with appropriate medical care.

Movement affects both arterial and venous circulation. During activity, working muscles require more oxygen, and blood vessels adjust to meet that demand. Contraction of the calf and leg muscles also helps push venous blood upward toward the heart.

Exercise sessions are valuable, but they do not eliminate the effects of remaining motionless for much of the day. Breaking up long periods of sitting or standing with brief movement gives the muscles and blood vessels repeated opportunities to work.

The appropriate type and intensity of activity depend on your health and physical capacity. New chest discomfort, unusual shortness of breath, faintness, or leg pain with activity should be medically evaluated rather than treated simply by exercising harder.

A dietary pattern that supports healthy blood pressure, blood sugar, and cholesterol can help protect the heart and blood vessels. Vegetables, fruits, legumes, whole grains, nuts, and other minimally processed foods can contribute useful fiber and nutrients. The appropriate balance will vary with a person’s medical needs, kidney function, medications, and ability to tolerate particular foods.

Products advertised as “circulation boosters” may produce temporary sensations without correcting a narrowed artery, weakened vein valve, blood clot, or heart problem. Some supplements may also interact with blood-pressure medicines, anticoagulants, or other treatments.

Nutrition can support circulatory health, but it should not be used to explain away persistent symptoms or replace necessary evaluation.

Blood pressure, blood sugar, cholesterol, kidney function, and smoking history help clinicians estimate cardiovascular risk. A physical examination may include checking pulses, comparing temperature and color between limbs, examining the skin and feet, and listening to the heart and blood vessels.

When symptoms or risk factors suggest a problem, additional testing may be appropriate. Depending on the concern, this could include an ankle-brachial index, ultrasound, heart testing, blood tests, or vascular imaging.

Not everyone needs every test. The purpose of screening is to identify meaningful risks early enough to address them, not to accumulate tests without a clear reason. Changes in symptoms, function, or healing should be reported even when previous results were normal.