Red Blood Cells(RBCs) |Composition, Functions, Disorders

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  • Post last modified:December 15, 2023
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  • Post category:Zoology

Red blood cells are fluid connective tissue. Fluid connective tissue are also called as haemopoietic tissue and consists of blood and lymph. Blood is composed of blood cells and plasma. Blood cells are also called as corpuscles which are of 3-types- RBCs, WBCs and plateletes(or thrombocytes). The plasma constitutes about  55% and blood corpuscles about 45% of total blood volumn.

red blood cells

Blood plasma is pale yellow liquid consisting 90% water and 10% organic and inorganic substances.It consists of various kinds of proteins molecules like fibrinogens, albumins and globulins. Fibrinogen is essential for blood clotting. Albumin helps in maintaining osmotic balance of the blood by grasping water molecules. And globulin contains antibodies for developing body immunity. Inorganic compounds mostly include salts of carbonates, bicarbonates, chlorides, sodium, potassium, magnesium, iron etc.

Plasma also contains hormones like insulin and testosteron. It also contains glucose, amino acids, fatty acids, vitamins etc due to transportation of digested food materials inside body. It also function as transportation of respiratory gases (i.e O2 and CO2).

Composition of RBCs-Erythrocytes

Out of total blood volumn, Red blood cells(i.e RBCs) occupies 40-45%. It is composed of outer cell membrane(or plasma membrane), cytoplasma and with or without nucleus. Cell membrane is made up protein-lipid layer and is semipermeable from where oxygen molecules gets diffused from lungs.

Cytoplasma of erythrocytes contains an important iron containing compound-haemoglobin. Haemoglobin is made up of two complex parts – iron and protein. Iron is indigestible while protein-globin is digestible part in haemoglobin. It imparts red coloration to the blood and main function is to carry oxygen diffused from lungs to every tissues of the body.


It is metalloprotein compound found in cytoplasm of RBCs. It is mostly found in every vertebrates performing aerobic respiration. The metal part is iron while protein part is globin(not globulin). Oxygen molecules combines with haemoglobin to form oxyhaemoglobin. Oxyhaemoglobin breaks up into oxygen and haemoglobin, releasing oxygen into cells and tissues.

Shape and structure of RBCs in different group of animals

In mammals – Red blood cells are small, biconcave and having “no nucleus”(i.e anucleated) in mammals. It undergoes different adaptations for increasing maximum efficiency of the cells.

In early stage it has nucleus but as maturity gains, nucleus get lost . After maturity, it also begins to loose most of the cells organells to provide maximun space for haemoglobin. It has depression in center making a disk shape structure. These adaptations makes mammalian RBCs to accormodate for maximum haemoglobin and overall speeding the transportation of red blood cells inside the capillaries.

In birds, reptiles, frog and fish – It is oval and nucleated. In this group of animals, RBCs do not loss nucleus and persists through out life.

Life span of erythrocytes

Red blood cells have life span of 120 days. After functionless, it is destroyed in liver by the phagocytes called kupffer cells and also in spleen. The turn over of these cells are short and very rapid. In one second time period, about 20 millions old cells get destroyed and new ones are formed. Red blood cells are made in bone marrow of  vertebrates, ribs, and pelvis of adult. In embryo mostly liver and least in spleen, are the sites for formation of erythrocytes. The process of formation of RBCs is called as erythropoiesis.

Functions and importancen of red blood cells

The pigment present in blood is haemoglobin which imparts red color to RBCs making blood red. WBCs lacks pigments and are colourless.

The important function of haemoglobin is transportation of respiratory gases(i.e O2 and CO2). Oxygen combines with haemoglobin during diffusion from lungs and form oxyhaemoglobin. It is then transported to cells and tissues where it releases oxygen molecule returning again into haemoglobin. The released oxygen takes part in cellular respiration from where energy is released.

The presence of Rh factor present on the cell memrane of RBCs plays an key role in determining different blood groups. It hepls in blood trsansfusion. Many of the diseases and blood related diseases requires blood during its surgery or recovery. It is also used as transfusion under the name “packed red blood cells”(i.e PRBC).

Red Blood Cells Disorders

Anemia– It is a disease caused due to low count or low efficiency of corpuscles or its haemoglobin to transport oxygen molecules to the tissues. There are different types to anemia. Some of them are:

Pernicious anemia– It is a type of anemia where there is less amount of haemoglobin. Haemoglobins is produced with the help of vitamin B12 In pernicious anemia, body lacks intrinsic factors to absorb vitamin B12 from the diet resulting in the low formation of haemoglobin and causing the disease.

Sickle cell anemia– It is a genetic disease and are transferable from parents to offsprings. The haemoglobin became abnormal resulting in the low oxygen carrying capacity. In this disease, red blood cells appears as sickle shape structure so called as sickle cell anemia.

Iron deficiency anemia– It is a common type of anemia. It is clear from it’s name i.e it occurs due to deficiency of iron(Fe) during the formation of its derivative-haemoglobin. When diet lacks iron or there is inability of the body to absorb iron from diet, it resulting in iron deficiency anemia.

Aplastic anemia– It occurs due to inability of bone marrow to produe RBCs.

Polycythemia– It is the term used when there is increased number of blood cells. It may result in several abnormal symptoms and deficiencies.

Frequently asked questions (FAQs)

How many grams of haemoglobin are present in 100ml of blood?

In 100ml of blood, 12-20 grams of haemoglobin is present. This ranges varies according to different age group people and their health conditions.

How many ml of oxygen is carried by 1gm of haemoglobin?

1 gram of haemoglobin has an capacity of carrying 1.34ml oxygen.

Why do people living in higher altitude have red cheeks?

As altitude increases, density of oxygen decreases. Haemoglobin are oxygen carrying agent found inside RBCs. To maintain proper oxygen need for body, more nos. of haemoglobin are needed to overcome less availability of oxygen in the environment. As the need of haemoglobin increases, nos. of RBCs also increases which results in red coloration to the cheeks of people living in himalayas.