Erythrocytes: Life Span, Formation of Red Blood Cells, Physiological Factors influencing RBC number, Hemoglobin (Hb), Recycling RBC, and Blood Groups
Erythrocytes (Red Blood Cells =RBC)
• Red blood cells are biconcave discs devoid of cytoplasmic organelles and a nucleus. Haemoglobin is a crimson protein that they have. Their primary role is to transfer gases, primarily oxygen but also some carbon dioxide.
Human erythrocytes have a diameter of 7.5 µm, a core thickness of 0.8 µm, and a rim thickness of 2.6 µm. Their biconcave shape enhances their surface area for gas exchange, while the middle portion’s thinness permits quick gas entry and departure.
• The cells’ flexibility allows them to pass via small capillaries. For women, the normal blood erythrocyte concentration is between 3.9 and 5.5 million per microliter, while for men, it is between 4.1-6 million per microliter. RBC in a biconcave form
Life Span and Formation of Red Blood Cells
• Red bone marrow, found in flat, uneven bones and the ends of long bones, produces erythrocytes.
• They go through several developmental phases before entering the bloodstream.
• They have a lifespan of roughly 120 days when in circulation.
• The process known as erythropoiesis, which produces red blood cells from stem cells, takes roughly seven days.
• The immature cells enter the bloodstream as reticulocytes and develop into erythrocytes for one to two days. They lose their nucleus during this period, making it impossible for them to divide.
• The synthesis of erythrocytes depends on the hormone erythropoietin as well as elements like iron, folic acid, and vitamin B12.
• The hormone erythropoietin, a glycoprotein generated in the kidneys, promotes the creation of globin, the protein component of haemoglobin, increases the discharge of reticulocytes into the bloodstream, and promotes the maturation of reticulocytes into mature red blood cells.
Physiological Factors influencing RBC number
• The RBC count is higher in children than in adults, and it is quite high during birth (8–10 million mm).
• During excitement, the RBC count rises at high elevations and in warm weather.
• During pregnancy, women’s red blood cell counts are often low. Low altitude is associated with a decrease in RBC count.
Haemoglobin (Hb)
• The most crucial component of red blood cells is haemoglobin. It is in charge of moving CO2 from tissues back to the lungs and oxygen from the lungs to the tissues.
• A normal adult male weighs 13–18 g/100 ml, and a normal adult female weighs 11.5–16.5 g/100 ml.
• Hemoglobin molecules are big and intricate. They consist of globin and heme.
• Porphyrin and iron (in ferrous form) make up heme.
• Globin is a polypeptide protein with two alpha and two beta chains.
• The alpha and beta chains of globin bind the four units of heme that make up each unit of Hb.
• One molecule of O2 can join with each unit of heme. 4 molecules of O2 can therefore be carried by one Hb molecule.
• Each red blood cell can carry more than a billion O2 molecules because it contains roughly 280 million Hb molecules.
• Oxyhemoglobin is haemoglobin, and deoxyhemoglobin is haemoglobin without oxygen.
Types of Normal Hb
• Fetal haemoglobin Hb F (α2 and γ2): Appears in the fetus in the final seven months of its uterine development. And, at six months of birth, replaced by adult haemoglobin.
• Adult Hb (Hb A) is composed of: – HbA (α2 β2) 95% Hb A2 (α2 δ2) 1.5–3% Minimal concentrations of Hb F (α2 γ2)
Recycling RBC
• The components of erythrocytes (Hb) are broken down (to heme and globin) toward the end of their life cycle and repurposed to create new erythrocytes.
• Transferrin protein transports the iron liberated from heme into the circulation and subsequently to different tissues (liver, bone marrow).
• Bilirubin, a yellow pigment, is created from porphyrin that is liberated from heme.
• Bilirubin in its unconjugated state is insoluble. Liver cells absorb it, convert it to a soluble form (conjugated form), and then expel it as bile.
• Bacteria in the large intestine convert conjugated bilirubin to stercobilinogen, which is then transformed into stercobilin, which gives faeces their brown hue.
• Some urobilinogen, which is stercobilinogen that has been exposed to air, is taken into circulation and expelled as urobilin.
Blood Groups
• Lipids and proteins make up the erythrocytes’ plasma membrane.
• There are several other kinds of proteins, such as the Rh (D) factor, which determines a person’s blood group, and the A and B proteins (antigens).
• People develop antibodies to these antigens, but not to their particular antigen.
• Red blood cells belonging to blood group A contain the type A antigen. They have type B antibodies in their serum.
• Red blood cells belonging to blood type B contain the B antigen. They have type A antibodies in their serum.
• Individuals with blood group AB possess both type A and type B antigens. Both type A and type B antibodies are absent from them.
• Blood group O individuals lack both A and B. Both type A and type B antibodies are present.
• The antigen, known as Rh factor or rhesus factor, is present in the cell membrane of RBCs in around 85% of individuals.