All You Need To Know About Human Blood

Human Blood

Blood is a combination of plasma (watery liquid) and cells that float in it. It is a specialized bodily fluid that supplies essential substances and nutrients, such as sugar, oxygen, and hormones to our cells, and carries waste away from those cells, this waste is eventually flushed out of the body in urine, faeces, sweat, and lungs (carbon dioxide). Blood also contains clotting agents.

Plasma constitutes 55% of blood fluid in humans and other vertebrates (animals with a backbone, spinal column).

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Apart from water, plasma also contains:

  • Blood cells
  • Carbon dioxide
  • Glucose (sugar)
  • Hormones
  • Proteins

Types of blood cells:

Red blood cells – also known as RBCs or erythrocytes. They are shaped like slightly indented, flattened disks. These are the most abundant cells and contain haemoglobin (Hb or Hgb). Haemoglobin is a protein which contains iron; it transports oxygen from the lungs to body tissues and cells. 97% of a human’s red blood cell’s dry content is protein. Each RBC has a lifespan of about 4 months; at the end of their lives, they are degraded by the spleen and the Kupffer cells in the liver. The body continuously replaces the ones that (9)

White blood cells (leukocytes) – these are the cells of our immune system; they defend the body against infections and foreign materials. Lymphocytes and granulocytes (types of white blood cells) can move in and out of the bloodstream to reach affected areas of tissue. White blood cells will also fight abnormal cells, such as cancer cells. There are normally between 4×1010 white blood cells in one litre of blood (making up about 1% of total blood) in a healthy individual.

Platelets (thrombocytes) – are involved in the clotting (coagulation) of blood. When we bleed the platelets clump together to help form a clot. If exposed to air the platelets break down and release fibrinogen into the bloodstream, this sets off a series of reactions which results in the clotting of blood in, for example on a skin wound. A scab is formed. When haemoglobin is oxygenated human blood is bright red. The heart pumps blood around the body through blood vessels. Oxygen-laden arterial blood is carried from the lungs to the rest of the body, and carbon dioxide laden blood (venous blood) is returned to the lungs where the carbon dioxide is exhaled. Carbon dioxide is a waste product produced by cells during metabolism.

What is haematology?

Haematology is the diagnosis, treatment and prevention of blood and bone marrow diseases, as well as immunologic, blood clotting (hemostatic) and vascular systems. A doctor who is specialized in haematology is called a haematologist.

download (11)Functions of blood

  • It supplies oxygen to cells and tissues.
  • It supplies essential nutrients to cells, such as amino acids, fatty acids, and glucose.
  • It removes carbon dioxide, urea and lactic acid (waste products)
  • Its white blood cells have antibodies which defend us from infection and foreign bodies.
  • It has specialized cells, such as platelets, which help the blood to clot (coagulate) when we are bleeding.
  • It transports hormones – chemicals released by a cell in one part of the body that sends out messages that affect cells elsewhere in the body.
  • It regulates our acidity (pH) levels.
  • It regulates our body temperature. When the weather is very warm or during strenuous exercise there will be increased blood flow to the surface, resulting in warmer skin and faster heat loss. When environmental temperatures drop, blood flow focuses more on the important organs deep inside the body.
  • It also has hydraulic functions – when a human is sexually aroused, engorgement (filling the area with blood) will result in a male erection and swelling of the female’s clitoris.

Blood cells are produced in the bone marrow White cells, red cells and platelets are made in the bone marrow – a jellylike substance that fills the cavities of bones. Bone marrow consists of fat, blood, and special cells (stem cells) that turn into the various kinds of blood cells. The main areas of bone marrow involved in the formation of blood cells are in the vertebrae, ribs, sternum, skull and hips.

There are two types of marrow, red marrow and yellow marrow. Most of our red and white blood cells, as well as platelets are made in the red marrow.

Blood cells in babies and very young children are made in the bone marrow of most of the bones in the body. As we get older, some of the bone marrow converts to the yellow marrow, and just the bones that make up the spine (vertebrae), ribs, pelvis, skull and sternum contain red marrow. If a human experiences severe blood loss, the body is able to convert yellow marrow back to red marrow as it tries to boost blood cell production.

Blood groupsdownload (1)

Humans can have one of four main blood groups, either RhD positive or negative:

Group A – RhD negative or positive
Antigens are found on the surface of blood cells. Anti-B antibodies are found in the plasma.

Group B – RhD negative or positive
B antigens are found on the surface of blood cells. Anti-A antibodies are found in the plasma.

Group AB – RhD negative or positive
A and B antigens are found on the surface of blood cells. There are no antibodies are found in the plasma.

Group O – RhD negative or positive
There are no antigens are found on the surface of blood cells. Both Anti-B and Anti-A antibodies are found in the plasma.

Another protein, an antigen, may be found on some red blood cells – called Rh factor. Blood cells that have Rh factor are RhD positive, those that don’t are RhD negative. According to the National Health Service (NHS), UK, 85% of the British population is Rh positive.

When someone receives a blood transfusion, the medical team has to make sure it is a compatible blood group.

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Who Discovered the blood groups??

The ABO blood group system is widely credited to have been discovered by the Austrian scientist Karl Landsteiner, who identified the O, A, and B blood types in 1900. Landsteiner originally described the O blood type as type “C”, and in parts of Europe, it is rendered as “0” (zero), signifying the lack of A or B antigen. Landsteiner was awarded the Nobel Prize in Physiology or Medicine in 1930 for his work. Alfred von Decastello and Adriano Sturli discovered the fourth type, AB, in 1902.

Universal recipient and Universal Donor:-

  • In addition to the ABO system, the Rh blood group system can affect transfusion compatibility. An individual is either positive or negative for the Rh factor; this is denoted by a ‘+’ or ‘−’ after their ABO type.
  • Those with Rh-positive blood can safely receive both Rh-positive and Rh-negative blood, but those with Rh-negative blood should only receive Rh-negative blood.
  • Rh-negative blood is used in emergencies when there is no time to test a person’s Rh type. Because of this, the AB+ blood type is referred to as the “universal recipient”, as there are neither Anti-B or Anti-A antibodies in its plasma, and can receive both Rh-positive and Rh-negative blood.
  • Similarly, the O− blood type is called the “universal donor”; since its red blood cells have no A or B antigens and are Rh-negative, no other blood type will reject it.

imagesWorld Blood Donor Day: June 14

The Theme of 2016 Blood Donor day is “Blood connects us all”

Amount of Blood in Human Body:-

  • Most sources state the volume of blood in an average human adult, who is between 150 to 160 pounds(68-70 kg), as between 4.7 and 5 liters, although the more recent sources state the volume of blood in an average adult as 4.7 liters, which is composed of plasma and several kinds of cells.
  • Blood accounts for 7% of the human body weight, with an average density of approximately 1060 kg/m3, very close to pure water’s density of 1000 kg/m3.

Blood Donation Process:-

  • It is always good to plan blood donation in advance. Consult your doctor before donating blood if there are any health issues or concerns. It is always good to have healthy diet weeks before the donation.
  • On the day of donation, make sure you are well hydrated so keep drinking plenty of fluids.
  • One should wear comfortable clothes during the donation process.
  • In case you are undergoing any treatment or medication, it is advisable to inform the blood bank/clinic/hospital where you are donating blood.

The entire process takes about one hour and 15 minutes; the actual donation of a pint of whole blood unit takes eight to 10 minutes.

Health Benefits of Blood Donation:-download

  • Balance Iron Levels in Your Blood
  • Better Blood Flow
  • It reduces the risk of heart attacks and even cancer
  • It burns 650 calories for every point given
  • Blood donation is beneficial in reducing the risk of heart and liver ailments caused by the iron overload in the body.
  • New Blood Cells to maintain good health

What is Plasma Donation??

  • Generally, plasma donors must be 18 years of age and weigh at least 110 pounds (50kg). Donating plasma is similar to giving blood. A needle is placed into a vein in your arm.
  • Plasma is collected through a process call plasmapheresis and is conducted in cycles that may take up to an hour. Whole blood is drawn.
  • The plasma is separated from the red blood cells and other cellular components.
  • These are returned to your body with a sterile saline solution to help the body replace the plasma removed from the whole blood.
  • Your first donation will take approximately 2 hours. Return visits on average take about 90 minutes.

Nearly 500 different types of proteins have been found in human blood plasma. Approximately 150 of these may be used for diagnosing disease or manufacturing therapies.

Why Human Blood is Red??

  • Each haemoglobin protein is made up subunits called hemes, which are what give blood its red colour. More specifically, the hemes can bind iron molecules, and these iron molecules bind oxygen.
  • The blood cells are red because of the interaction between iron and oxygen.

images (1)How to donate blood??

There are so many websites which are looking forward to donors. You can click on these link,,‎,, and register as a donor.

Indian Red Cross Society has launched an app to address problems associated with blood shortage in India. This Blood Banking App is part of a larger digital blood banking initiative that has been rolled out by Red Cross Society in association with J Walter Thompson.

The app is currently being tested in Bengaluru and later on, it will be used in other parts of the country and rest of the world.

The blood you donate gives someone another chance at life. One day that someone may be a close relative, a friend, a loved one—or even you.