Categories: Heart Health

How do Venous and Arterial blood differ?

The heart is a pump that is constantly delivering purified or oxygenated blood from the left chambers of the heart (left side from the person’s perspective), to millions of cells all over the body, through a large network of blood vessels called arteries. At the same time, impure blood created by the metabolism happening in these cells is collected through a large network of blood vessels called veins and sent to the right chambers of heart, and in turn to the lungs, for purification or oxygenation. Such a mechanism is called a double circulation system.

The only exception to this rule, are the pulmonary artery and pulmonary vein. The pulmonary artery delivers impure blood to the lungs for purification while the purified blood from the lungs is sent to the heart through the pulmonary vein.

Interestingly, there are several differences between arterial and venous blood. These differences matter to pathologists who conduct diagnostic tests and other types of doctors too, during various treatments meted out to patients. It’s also useful for the common man to be aware of these differences.

Differences between arterial and venous blood

Difference	Arterial Blood	Venous Blood
Location	As explained above, arterial blood is oxygenated or purified blood that flows in lungs, pulmonary vein, left chambers of the heart, and vast network of arteries all over the body.	In contrast, venous blood is the deoxygenated or impure blood that has passed through all parts of the body except lungs, and is found in the vast network of veins all over the body, right chambers of the heart, and pulmonary artery.
Direction of Flow	Arterial blood always flows away from the heart	While venous blood flows towards the heart.
Driving Force	While the pumping action or pumping pressure of the heart is what delivers or drives flow of arterial blood	The pressure of the venous blood is generally 5-8 mm Hg at the right atrium, and rarely needs to be measured.
Blood Pressure	Both arterial and venous blood has pressure in them which is required to sustain the flow. BP in the arterial blood in healthy conditions is 120/80 mm Hg, and this is what a doctor measures using a sphygmomanometer or BP-measuring instrument.	The pressure of the venous blood is generally 5-8 mm Hg at the right atrium, and rarely needs to be measured.
Partial Pressure of Oxygen	The partial pressure of oxygen, denoted as PaO2, is a measure of oxygen pressure in the blood. It indicates how efficiently oxygen is able to move from the lungs to the arterial blood. Illness of any kind tends to alter this factor. At sea level and with good health of the person, partial pressure of oxygen in the arteries is good enough to satisfy the oxygen requirements of the entire body. This value is generally 100 mm Hg.	Venous blood in contrast has lesser PaO2 as most of the oxygen has been delivered to the body cells. This value is generally 30-40 mm Hg. A person with very good health and fitness has better oxygen intake, at sea levels, so this figure can be higher in him/her.
Color of the blood	This is the only physical marker that differentiates these 2 types of blood. Arterial blood is a bright-red color as the hemoglobin present in it has received plenty of oxygen.	In contrast, hemoglobin in the venous blood has lost a lot of oxygen, so venous blood is dark-red, almost blackish in colour. Good health and ill-health can also alter these colours slightly.
Constitution	Other than oxygen, arterial blood is rich in vitamins, amino acids, minerals and glucose, absorbed from food or medication being given for one or more conditions.	In contrast, the venous blood is low in the above constituents as these have already been delivered to the body cells. Instead, its rich in metabolic wastes collected from the body, such as urea and bicarbonate. In the lungs, the bicarbonate is converted to carbon di-oxide and expelled out of the lungs during exhalation.
pH Value	Arterial blood generally has a pH of 7.4 in normal health conditions of the person.	In comparison, venous blood has a lower pH.
Temperature	Arterial blood is around 37 degrees Celsius or 98.6 degree Fahrenheit in a healthy person.	In comparison, venous blood has a lower temperature.
Medicinal utility	Arterial blood is collected generally to evaluate arterial blood gases (ABG). This is a measure of oxygen and carbon di-oxide content in them. This can indicate efficiency of lung function and presence of any lung condition.	Venous blood is what is generally drawn for all routine, laboratory, diagnostic, blood-tests. The reference ranges shown in blood-test reports are based on venous blood.
Method of extraction	Arterial blood samples are obtained directly from the artery, generally the radial artery, by a doctor, nurse or paramedic who is trained to do this and is aware of complications that come from not doing it right. Arterial blood can also be obtained using vascular access devices (VADs) such as a femoral arterial line or catheter that are inserted into an artery.	Venous blood is drawn by directly puncturing a vein, most often located in the antecubital area of the arm (near the elbow), or the top posterior portion of the hand. Sometimes, VADs such as a central venous pressure line or an IV start may also be used.

Kauvery Hospital is globally known for its multidisciplinary services at all its Centers of Excellence, and for its comprehensive, Avant-Grade technology, especially in diagnostics and remedial care in heart diseases, transplantation, vascular and neurosciences medicine. Located in the heart of Trichy (Tennur, Royal Road and Alexandria Road (Cantonment), Chennai, Hosur, Salem, Tirunelveli and Bengaluru, the hospital also renders adult and pediatric trauma care.

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Updated on 22^nd Jan 2024