This is a common question that many people have about human blood. At a glance, blood drawn from a vein often appears dark red. However, there are times when blood may take on a yellowish hue. So why does this happen? Read on to learn more about the color of blood and what causes it to appear yellow at times.
What gives blood its red color?
Blood appears red because of the millions of red blood cells that travel through the circulatory system. Red blood cells contain a protein called hemoglobin that helps carry oxygen from the lungs to tissues and organs throughout the body. Hemoglobin contains iron, which gives it a red color. This pigment is what makes blood appear red.
When does blood look yellow?
There are a few instances when blood may take on a yellowish color:
- Plasma – This is the liquid portion of blood that suspends the blood cells. Plasma makes up about 55% of blood volume. Plasma contains proteins, glucose, clotting factors, hormones, and minerals. On its own, plasma has a yellowish color due to proteins within it.
- Jaundice – This condition causes a yellow discoloration of the skin and eyes. It’s the result of a buildup of bilirubin, a yellowish waste material. An overabundance of bilirubin causes the blood to take on a yellowish hue.
- Bruising – When blood pools and clots under the skin after an injury, it can cause bruising. Over time as the bruise heals, it may turn yellow or green.
- Dietary supplements – Some supplements like vitamin B12 and folic acid can give urine or other bodily fluids a yellow/orange color that may be noticeable.
What is the medical term for yellowing of the skin?
The medical term for yellowing of the skin and eyes is known as jaundice or icterus. This yellowish discoloration indicates an excess of bilirubin in the bloodstream. Bilirubin is a pigment produced when old red blood cells break down in the liver. Normally, the liver filters out bilirubin and it exits the body in stool. But when the liver is damaged or diseased, bilirubin can build up and leak into the blood, causing yellowing of the skin and eyes. Some common causes of jaundice include:
- Hepatitis – Liver inflammation from viral infection
- Gallstones – Blockage of bile ducts
- Cirrhosis – Scarring of the liver
- Cancer – Spread of cancer to the liver
- Hemolytic anemia – Excessive breakdown of red blood cells
Jaundice itself is not a disease, but rather a sign of an underlying problem with the liver, gallbladder, or blood. Seeking medical treatment for jaundice is important to identify and manage the underlying condition causing it.
What are the three main types of human blood cells?
Human blood contains three main types of cells:
- Red blood cells – Also called erythrocytes, these cells are by far the most numerous cell type in blood. Red blood cells are shaped like biconcave disks which gives them a large surface area to transport oxygen and carbon dioxide. They contain hemoglobin which carries oxygen from the lungs to the tissues.
- White blood cells – Also called leukocytes, white cells are part of the immune system and defend the body against infection. There are several types of white blood cells including lymphocytes, neutrophils, eosinophils, monocytes, and basophils. They destroy pathogens and produce antibodies.
- Platelets – Platelets, or thrombocytes, are small colorless cell fragments that help form blood clots and control bleeding. They stick together to plug wounds and prevent blood loss.
In addition to these three major types of cells, blood plasma acts as the suspension medium. Plasma makes up about 55% of total blood volume.
What are the normal hematocrit levels for females and males?
Hematocrit is a measurement of the percentage of blood volume made up by red blood cells. Normal hematocrit levels are:
- Female: 36% – 48%
- Male: 40% – 52%
Hematocrit levels outside the normal range can indicate certain medical conditions:
- Low hematocrit (anemia) – Can result from blood loss, destruction of red blood cells, or lack of production
- High hematocrit (polycythemia) – Can result from lung disease, dehydration, cancer, or heart disease
How are red blood cells made?
Red blood cells are continuously produced in the bone marrow through a process called erythropoiesis. There are several steps involved:
- Hematopoietic stem cells in the bone marrow divide and mature into red blood cell precursors called erythrocytes.
- The immature erythrocytes lose their nucleus and organelles to become reticulocytes.
- Reticulocytes enter the bloodstream where they mature into fully-functional red blood cells over 1-2 days.
- A protein called erythropoietin (EPO) regulates red blood cell production by stimulating growth and differentiation of erythrocytes.
- Mature red blood cells circulate for about 120 days before dying off and being filtered out of the blood by the spleen and liver.
Problems with any part of erythropoiesis can lead to abnormal red blood cell counts. Anemia results when red blood cell production is too low, while polycythemia is caused by overproduction of red cells.
What causes high hemoglobin levels?
Hemoglobin is the protein in red blood cells that carries oxygen. A high hemoglobin level indicates an abnormally increased number of red cells or excess hemoglobin in the cells. Some possible causes include:
- Dehydration – When the plasma volume is reduced, the concentration of hemoglobin rises.
- Lung disease – Conditions like emphysema and pulmonary fibrosis can cause overproduction of red blood cells and hemoglobin.
- Tumors – Blood cell tumors like polycythemia vera and erythrocytosis lead to excessive red cell counts.
- Smoking – Carbon monoxide from smoking stimulates hemoglobin production.
- Living at high altitudes – The body adapts by producing more red blood cells and hemoglobin.
- Kidney disease – Damaged kidneys release too much erythropoietin hormone.
- Congenital heart disease – Abnormal heart structure can increase hemoglobin levels.
Mildly elevated hemoglobin is usually not concerning. But levels above 18 g/dL in men and 16 g/dL in women require medical evaluation to determine the cause.
What are the four main blood types?
The four main blood types are based on the presence or absence of antigens on the red blood cell surface. The types are:
- A – Has A antigens on red cells with anti-B antibodies in the plasma.
- B – Has B antigens with anti-A antibodies.
- AB – Has both A and B antigens, but no antibodies.
- O – Has neither A nor B antigens, but both anti-A and anti-B antibodies.
A person’s blood type is inherited from their parents. Type O is the most common, while AB is the rarest. Blood banks categorize blood into these four main types so transfusions can be matched between donor and recipient blood.
What happens if you get the wrong blood type?
Getting an incompatible blood type during transfusion can trigger a harmful immune response. Here’s what happens if the blood types don’t match up:
- Type A gets Type B – The anti-B antibodies will attack the Type B red blood cells causing agglutination (clumping) and hemolysis (rupturing).
- Type B gets Type A – Anti-A antibodies attack Type A cells.
- Type AB gets Type O – Anti-A and anti-B antibodies react with the transfused blood.
- Type O gets Type A/B/AB – Anti-A and/or anti-B antibodies respond accordingly.
This immune reaction can lead to life-threatening complications such as kidney failure, shock, and death in severe cases. That’s why pre-transfusion testing is vital to ensure blood group compatibility.
Do different blood types have different characteristics?
While all human blood is made up of basically the same components, some research has suggested links between blood type and certain traits or health risks:
Blood Type | Associated Characteristics |
---|---|
Type O |
|
Type A |
|
Type B |
|
Type AB |
|
However, larger studies are still needed to confirm these associations. Many experts believe diet, lifestyle, family history, and environment play much bigger roles in disease risk and behavior than blood type alone.
How does blood clotting work?
Blood clotting, also called coagulation, is a complex process that prevents excessive bleeding when a blood vessel is damaged. Here is a basic overview of how it works:
- When injury damages a blood vessel wall, platelets rush to the site of damage and stick together to form a temporary plug.
- Nearby proteins called clotting factors respond in a cascading chain reaction that activates more clotting factors.
- Thrombin, a key enzyme, is generated and converts fibrinogen to fibrin threads that strengthen the platelet plug.
- The resulting clot stops bleeding and allows the blood vessel wall to repair.
- Once healing takes place, the clot naturally dissolves and blood flow is restored.
This process is carefully regulated to ensure clots form only at sites of injury. However, clotting disorders can lead to abnormal bleeding or clotting throughout the body.
What is the liquid part of blood called?
The liquid portion of blood is called plasma. Plasma is comprised of:
- Water – About 92%
- Proteins – Albumins, clotting factors, immunoglobulins
- Nutrients – Glucose, fats, vitamins, minerals
- Hormones
- Gases – Oxygen, carbon dioxide
- Waste products – Urea, uric acid
- Electrolytes – Sodium, potassium, chloride
Plasma suspends the blood cells and transports nutrients, hormones, clotting factors, and other vital substances to tissues throughout the body. The normal percentage of blood volume made up of plasma is roughly 55%.
Conclusion
While blood may often appear red, there are instances in which it can take on a yellowish color. This is most often seen in the plasma, as well as in conditions like jaundice, bruising, and dietary changes. The multitude of cells and proteins in blood contribute to its main roles – transporting oxygen, fighting infections, and preventing blood loss. Understanding the basic components and functions of this life-sustaining fluid remains an essential part of medicine.