Blood: Why Is Blood Red? How Much Blood Does A human Produce Per Day?

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As we all know blood is essential for living beings and it plays a vital role with lots of its functions. Sometimes we think about how blood runs in our body and why we need blood to live alive. The content of this article is to provide basic knowledge about blood and helps to understand it in an easier and simple way


Blood is a transport liquid that is pumped by the heart to all parts of your body. Blood has both types of tissue and fluid. It acts like tissue because of the collection of specialized cells to perform specific functions then cells from a liquid matrix called plasma, which helps to make blood a fluid. Blood flows throughout the body and transport essential or crucial substances (i.e. oxygen and nutrients) to the body cells. Blood helps to transfer carbon dioxide metabolic waste products away from the cell.  There is no replacement for blood and can’t be made or manufactured. Your blood is made up of liquid and solid. 

  • A liquid portion of the blood is called plasma and it is made up of water, salt, and proteins.
  • A solid portion of blood carries Red blood cells RBCs, white blood cells  WBCs, and platelets.

These solid and liquid parts of blood are named as components of blood.

Components of Blood

Blood is made up of four major components,these are

1. Plasma:

Plasma is a liquid part of blood and it appears light-yellowish in color. The Shelf life of plasma is about one year. In our whole blood, 55% is plasma and 45% are RBCs,  WBCs, and platelets.

Blood plasma contains 92% of water and approx 7-8% of vital proteins albumin, gamma globulin and antihemophilic factors and 1% of mineral salts, sugar, hormones, fats and vitamin.

Function of blood Plasma

  1. The main function of plasma is the removal of waste from cellular function and it may help to produce energy.
  2. Plasma helps to maintain body temperature by absorption and release of heat from the body.
  3. Blood plasma also helps to carry different components such as plasma in protein,  immunoglobulin, and electrolytes. 

i) Protein in plasma

The plasma protein carries two types of protein.

a) Albumin: It’s a major or vital protein for maintaining,  support, and balance of fluid which is known as on it I can pressure blood. The people who have low albumin results in swelling of feet, hands, and abdomen.

b) Fibrinogen: The function of fibrinogen helps to decrease or reduce bleeding and helps in blood clotting and also prevents blood loss.

ii)  Immunoglobulin

Blood plasma also contains gamma globulin (a type of immunoglobulin) which helps to fight against infection.

iii) Electrolytes

Electrolytes have the ability to conduct electricity whenever they dissolve in water. These electrolytes are sodium (Na), magnesium (Mg), potassium (K), and calcium (Ca). When you have decreased concentration in electrolyte, you may result in muscles, weakness, and seizures.

2. Red blood cells (RBCs) 

Red blood cells are also known as erythrocytes. The fully mature RBCs are smaller in size, rounded and biconcave in shape. RBCs cover a layer of the membrane which is composed of lipids and proteins. RBCs have a lack of nucleus and carry hemoglobin (which is red in color, iron-rich protein, and binds with oxygen).


  • The human body makes approx 119 million red blood cells per second.
  • Size of red blood cells is about 0.000007meter.
  • Human blood contains 44% of blood cells.
  • The average range of RBCs in humans is about 100-120 days.

The production of new RBCs also known as erythropoiesis because RBCs grown in bone marrow with different stages, these are

i) Hemocytoblast: From Hemocytoblast, potential cells in mesenchymal (a type of connective tissue),have capability to become erythrocytes.

ii) Normoblast: In between 2-5 days of development, the erythrocytes fully fill with hemoglobin, mitochondria and nucleus gradually disappear.

iii) Reticulocytes: The delayed stage of RBCs is named as Reticulocytes (fully matured cells).

Function of red blood cells:

  1. The main function of RBCs is to carry oxygen (from lungs to all body tissues)and also transfer carbon dioxide (waste products to the lungs where it is excreted).
  2. RBCs also help to maintain homeostasis (body temperature) to regulate the internal temperature of the body and also maintain body PH. 
  3. The biconcave shape of RBCs allows oxygen to interchange at a specific rate to cover the largest possible area. 

The normal range of RBCs count is,

  • Red cell normal range signifies the number of RBCs in a volume of blood. The normal range of RBCs in men is about 4.7 to 6.1 million cells/ul (microliter) and in women, the normal range is approx 4.2 to 5.4 million cells/ul.

What is polycythemia?

Polycythemia is a condition of red blood count that increases its normal range. The People who have a high level of RBCs might increase the level of hematocrit and hemoglobin.

  • Hematocrit: Polycythemia is reported when the level of hematocrit is >48% in women and >52% in men.
  • Hemoglobin: Polycythemia is considered when hemoglobin levels are >16.5g/dL and >18.5 g/dL in men.

What Is Anemia?

Anemia is a condition that refers to a low number of RBCs. The people who have low levels of RBCs have low hemoglobin or hematocrit. Hemoglobin is the protein that carries oxygen to deliver throughout the body.

Cause of Anemia: Common cause of anemia is,

  • Due to blood loss
  • Due to a decrease in red blood cell production
  • Due to the destruction of red blood cells

3. White blood cells (WBCs) 

The stem cells in the bone marrow are responsible for producing WBCs and the bone marrow stores about 80-90% WBCs. WBCs are also known as leukocytes whenever an infection occurs in your body, then suddenly, WBCs release to fight against the infection.

Types of white blood cells

Basically WBCs have divided into three categories,

1. Granulocytes:

Granulocytes are types of WBCs that have small granules and thus, granules contain a protein. Granules are further subdivided into three types.

a) Basophil: The Basophil represents less than 1% of WBCs in your body. The Basophil increases whenever any allergic reaction occurs in the body.

b) Eosinophil: Eosinophil is responsible for fighting against infection, which is caused by parasites and also responsible for protecting the immune system if any inflammatory response occurs in the body.

c) Neutrophil: Neutrophils represent vital parts of WBCs in your body. These are responsible for acting as scavengers (resembles animals who eat dead plants), which helps to protect from bacteria and fungi.

2. Lymphocytes

Lymphocytes are also types of WBCs and subdivided into three categories.

a)  B-Cells: B-Cells are responsible for producing or making antibodies to protect the immune system. B-Cells are also known as B-lymphocytes.

b) T-Cells: T-Cells help to recognize and eliminate infection cells. These cells are also known as T-lymphocytes.

c) Natural killer cells: Natural killer cells are responsible for destroying and killing viral cells, cancer cells from the body. 

3. Monocytes

Manicures are cells which make around 2-8% of WBCs in your body. These cells are responsible for fighting against chronic infection. 

Do you know normal range of WBCs:

  • In newborn WBCs are range in 13,00-38,000
  • In two weeks to adult infants, WBCs are range in 5,000-20,000
  • In adult WBCs are range in size is 4,500-11,000 
  • In pregnant woman WBCs are range in size is 5,800-13,200 

What is Leukocytes?

A low level of WBCs is a decreased number of white blood cells known as leukocytes in your blood and a low level of WBCs is considered as leukopenia.

When you have a decreased level of white blood cells, your immune system is suppressed. A low level of WBC count is caused by a variety of diseases, disorders, and conditions and certain medications.

Elevated white blood cells

A high level of WBCs count is not because of any specific disease in itself, but it can show due to underlying problems. For example, infection, stress, inflammation, trauma, and allergy. A high level of white blood cells requires further investigation.

4. Platelets

Platelets also named as thrombocytes and small in size. The platelets are colorless cells in blood fragment.platelets also make bone marrow. It helps to form clots and prevent bleeding. The process of clotting is known as adhesion. 

Platelets start to connect with each other and form a plug named as oxygenation. If once the clot is formed in your blood vessels, the clotting factor (coagulation) rapid flow is activated and also adds fibrin to the plug to unite it together. 

Platelets count:

  • The lower range of platelets is <150,000 per microlitre
  • The normal range of platelets is 150,000-450,000 per microlitre
  • Elevated range of platelets is >500,000-1,000,000 per microlitre

How blood travels in your body?

The heart pumps the blood with each heartbeat throughout bodies and transfers oxygen to every cell.  After transportation of oxygen, the blood comes back to the heart then the heart sends blood to the lungs to carry more oxygen. This process Continuously repeated over and over again. 

Our circulatory system is made up of blood vessels that transfer blood away and towards the heart. Generally, two types of blood vessels carry blood throughout your bodies.

1. Arteries: The function of arteries PS to transfer oxygenated blood (which acquire oxygen from lungs) from the heart to the rest of your body.

2. Veins: The function of veins is to carry deoxygenated blood (blood which comes back to hear you and lungs) for getting more oxygen to send again to your body. 

What is the density of blood? 

Density is measured as mass per unit volume. As you know, the blood is liquid tissue and it is composed of 55% of plasma fluid and 45‰ of cells. 

  • 92% of blood plasma is made up of water and the remaining 8% is our protein, ions, and metabolites.
  • The density of plasma is about 1025 kg/m3
  • The density of cell which circulates in the blood is about 1125 kg/m3
  • It means the density of whole blood for the human body is approx 1060kg/m3.

Remember, the density of blood changes with the posture of your body.

The venous density is higher when people are in standing position rather than in sitting.

Why is blood red? 

The color of the blood is red because it is made up of cells and these cells are red in color named RBCs.  But for your clear concept, you must understand and study on a molecular level. In RBCs, pretend is present, which is known as hemoglobin (hemoglobin is a protein that forms complex molecules with iron and transport oxygen). Every single hemoglobin is made up of submits called hemes and this heme is responsible for red color if blood.

In other words, whenever a gene binds with iron molecules and this molecule of iron binds with oxygen, the blood cells become red in color because of interactivity between iron and oxygen.

Why do your veins look blue?

The chemical seems specific to your eyes and it is based on the wavelength of light they reflect. When hemoglobin binds with oxygen, it may absorb blue-green light into your eyes and appears red. That’s the reason blood turns into a bright red color when it binds with oxygen and iron. 

When it’s connected without oxygen, the blood is darker red in color but sometimes blood looks blue in your skin.

Mostly you have heard that blood is blue in veins when it leads back to kings (with lack of oxygen) but it’s wrong. The color of blood in human beings is never blue but in actuality, the blue color of the vein is only an optical illusion (images recognize different than its really rare).

The blue light is not penetrated into tissues, rather than red light penetrated. If the blood vessels are deep enough, then you see more blue than red reflected lights because blood partially absorbs red wavelengths.

The blue color of blood only seems in animals. For example,  horseshoe crabs and blood depends on chemicals known as hemocyanin (contains copper atoms) to carry oxygen, and mostly purple color of blood also present in animals. It is due to different molecules that carry oxygen, preferably hemoglobin use. 

How much blood is present in your body?

  1. NewBorns: Newborn babies having about 70-75ml of blood per kg according to their body weight. Let suppose, if the weight of a newborn is 8-pounds, so they have approximately 270ml (0.07 gallon) of blood per kg.
  2. In infants/children: The infants of 80-pounds have about 75-80ml (0.7 gallons) of blood per kg.
  3. In adults: The adult’s weight is about 150-180 pounds, they have approx 4,500- 5,700 ml or 4.5-5.5 liter or (1.2-1.5 gallons) of blood per kg.
  4. In pregnant women: In pregnant women, for supporting the babies who are growing in the mother’s embryo, they have 30-50% more blood volume and 0.3-0.4 additional gallons of blood in the body.

How much blood does a human produce per day?

As we all know, the human body makes approximately two-millions RBCs per second, and stem cells of bone marrow produce RBCs and these stem cells are responsible for creating other cells. Different components of blood take different amounts of time to replace. However, it only takes 24 hours to replace the lost plasma. But it takes longer to make more RNCs (about 4-6 weeks).

The hemoglobin carries iron, whenever the person donates blood, so iron is lost. It may take about 6-12 weeks to come back to its normal range.


Blood is the liquid type fluid in your body which maintains life. A living being cannot survive without blood because blood supports all of your bodily functions. Blood carries oxygen, vitamins, and minerals, which is essential to our body.

When your blood is in a good and healthy condition, it helps to fight against infections.

The circulation of the blood all over the body helps to keep us warm while at the same time it also works as a cooling mechanism for sensitive areas (such as the brain, to keep it from overheating).
The main function of blood is to regulate, balance the body mechanism.