Question

Explain how erythrocytes are recycled

Answer 1

1. How are erythrocytes recycled ?

Ans Erythrocytes are the red blood cells of the body which are biconcave in shape and without a nucleus. They are called red blood cells because they contain a pigment called hemoglobin that imparts redcolour to those cells. The two most important function of erythrocytes is to carry oxygen from lungs to different parts of the body and CO2 from tissues to lungs. The oxygen is transported by the pigment,  haemoglobin which is present in the R.B.C’s.

Erythrocytes Recycling

Erythrocytes are produced in bone marrow and then enter the blood circulation.

They circulate in blood for about 100-120 days after which they are recycled by macrophages. Therefore, the typical life span of erythrocytes is considered to be 120 days.

Like most of the cells in the body Erythrocytes also undergo aging and damage and hence are recycled by our own body They are damaged because during their circulation they collide with each other and are squeezed through walls of caplillaries.

About 25 trillion R.B.C’s are present in our body and about every second 2.5 million of these cell undergo recycling. The process of recycling occurs in spleen and lymphnodes by specialised white blood cells called macrophages that are present in them. Macrophages recycle about 90% of red blood cells and the remaining 10% are lysed in blood plasma, a process known as hemolysis. The reminants of lysed cells are engulfed by macrophages.

Step wise process of Erythocyte recycling:

• After circulating in the blood for 120 days, R.BC's age or are damaged and needs to be recycled.
• 90% of red blood cells are engulfed by phagocytic cells called macrophages that are present in spleen, liver and lymph nodes, where the recycling takes place.
• Once the macrophage engulfs red blood cell, it forms a vacuole which contain lysosomes.
• Lysosomes are digestive enzymes, so when fused with red blood cells, they start breaking them resulting in the release of components of red blood cells inside the macrophages.
• Since the red blood cells are anucleated they do not contain any specialised organelles all that they contain is hemoglobin protein. Therefore this protein is released upon digestion and undergoes recycling.
• The hemoglobin is made up of two components namely heme which contains iron atom and the globin group which is a protein made up of amino acids. Therefore when they undergo digestion heme is broken down into iron atoms and bilurubin and globin is broken down into amino acids.
• The iron atoms and amino acids can either stay back into phagocytic cells and used by them or they can enter blood plasma and travel back to bone marrow where they are reused for making more red blood cells.
• Amino acids can travel through the blood plasma by themselves but the iron needs a specialised carrier protein called transferin for its transport.
• The bilurubin which is produced from heme eventually exits into blood plasma and travels to the liver.
• The liver either transfers bilurubin to kidneys or it combines it with the bile that is excreted into the intestine where bile combines with reminants of whatever we ingest and eventually is excreted by the large intestine.