Human Anatomy and Physiology : Haemopoietic System: Blood PDF Notes
Blood is a liquid connective in the body and runs through the blood vessels for the transport of oxygen, nutrients, hormones, and waste products.
Composition of blood: Blood contains fluid called plasma in which blood cells are suspended. Blood contains 55% of plasma and 45% of blood cell.
Blood cells contains
- R.B.C (red blood cells)
- W.B.C (white blood cells)
Composition of plasma
- Plasma proteins-7-8%
- Organic substances
- Inorganic substances
Functions of blood
- It transports oxygen to cells.
- It contains nutrient to cells.
- It transports hormones to the cels.
- It protects the cell or body from infection.
- It participates in the clothing of blood.
- It maintains the hody temperature
- It transports waste products from the cell to excretory organs known as kidney
Blood cells have a relatively short life span and must be continuously replaced with new cells from precursors developing during hemopoiesis [Greek word haima (blood) + poiesis (a making)] in the early embryo these blood cells arise in the yolk sac moesoderm.
mesoderm. In the second trimester, hemopoiesis (also called hematopoiesis) occurs primarily in the developing liver, with the spleen playing a minor role. Skeletal elements begin to ossify and bone marrow develops in their medullary cavities, so that in the third trimester marrow of specific bones becomes the major hemopoietic organ.
The formation of red blood cells is known as erythropoiesis. It involves the following step
- The very first step in erythropoiesis involves division of pluripotent stem cells to yield multipotent myeloid proginator cells.
- These cells, in the presence of growth factors develop into erythrocyte colony- forming cells or units.
- In the next step, erythropoietin (EPO) along with the other growth factors, promote the production of precursor cells, known as proerythroblasts or pronormoblasts.
- Proerythroblasts or pronormoblasts give rise to smaller daughter cells by going through a series of cell divisions. The cell divisions occur sequentially to produce basophilic erythroblasts (or early normoblasts) first, followed by polychromatic erythroblasts (or intermediate normoblasts), and the orthochromatic erythroblasts forlato narmohlasts
- Lastly, the cells become reticulocytes as their nuclel are lost. These reticulocytes are set free into the circulation and they mature into erythrocytes in a day or two.
- Formation of white blood cells is known as leucopoiesis. All the different kinds of WBCs are obtained from the haematopoletic stem cells in the bone marrow.
- The myelob lasts and monoblasts, originating from the granulocytes and monocyte colony-forming cells are the specific precursor cells of neutrophils and monocytes, respectively.
- The eosinophils and basophils, originate from the eosinophil and basophil colony- forming cells, respectively. Lymphocytes, similar to other WBCs develop in the bone marrow stem cells.
- Lymphoblasts are progenitor cells of lymphocytes, which undergo a series of cell divisions to form smaller prolymphocytes. These cells further mature into lymphocytes.
- Ahemocytoblast gives rise to a common myeloid progenitor cell (CMP).
- The CMP gives rise to CFU-Meg (or CFU-Mega, the colony forming unit that leads to the formation of megakaryocytes).
- The CFU-Meg develops into a megakaryoblast.
- The megakaryoblast develops into a promegakaryocyte.
- The promegakaryocyte develops into a megakaryocyte.
- The megakaryocyte is a mature cellular element in the blood responsible for the production of platelets (or thrombocytes).
- The process in which the promegakaryocyte differentiates into a mature megakaryocyte is called megakaryopoiesis.
- Thrombopoietin is the hormone that stimulates megakaryopoiesis. The hormone is produced by the liver and the kidney, and encoded by the THPO gene.
5.3 Characteristic and function of blood
5.3.1 Red blood cells (Erythrocyte)
RBCs are small, circular, disc-shaped cells suspended in the bloodplasma. These transport oxygen and hemoglobin throughout the body.
- All the cells in groups, appear as red in colour and thus blood becomes red-coloured.
- RBCs are produced in the red bone marrow. This process called erythropoiesis.Total lifespan of RBCs is 120 days.
- Haemoglobin is a complex protein of high molecular weight. It consists of a protein material called globin and non-protein material called ‘hem’. The hem contains iron which gives red colour to the haemoglobin.
- Normal values of RBCs:
(i) In adult → 5 million/mm³ of blood.
(ii) In male →→ 4.5 to 5.9 million/mm³ of blood.
(iii) In female →→ 4.1 to 5.1 million/mm³ of blood.
Functions of RBCs/Erythrocytes
(i) It transports the gases such as O₂ and CO, in the form ofoxyhaemoglobin and carboxyhaemoglobin.
(ii) It maintains acid-base balance by buffering action of hemoglobin.
(iii) RBCs help to maintain viscosity of blood.
(iv) RBCs maintain iron balance of the body.
(v) Various pigments are derived from the hemoglobinafter disintegration of RBCs, e.g. bilirubin, biliverdin.
5.3.2 White blood cells (leukocytes)
The WBCs are colorless cells having, irregular shaped largenucleus which supports the immune system. The normal count of leukocytes is 6000 to 10,000/mm³ of blood. There are several different types of white blood cells:
- A) Agranulocytes:They constitute about 25%.These are mononuclear cells and do not show presence of granules in their cytoplasm.
- Monocytes: These are large cells with large nucleus. Thennucleus is convoluted kidney-shaped.
- Function: They gives phagocytic action; engulf and digest debris, including bacteria
- Lymphocytes:These are produced in the lymph glands hencecalled lymphocytes.
(i) Small lymphocytes: The thin rim is present around nucleus and is stained by basic stains.
(ii) Large lymphocytes: The nucleus is oval, rounded orkidney-shaped and is stained by basic stains.
- Function: Including T cells and B cells, they are responsible for the development of immunity against foreign substances such as microorganisms, viruses and tumours.
- B) Granulocytes:They constitute about 75%. These contain granules in the cytoplasm, hence called granulocytes.
- Neutrophils:The granules of these cells are stained by neutral dye. The nucleus is many lobed.
- Function: They ingest the microbes and destroy it by phagocytosis.
- Eosinophil:The granules of these cells are stained by red acidic dye called eosin. The nucleus is many lobed.
- Function: Phagocytosis. Play a role in the inflammatory response, and help fight some parasites.
- Basophils:The granules of these cells are stained by basic dye. The nucleus is usually oval or slightly kidney-shaped.
- Function: They are responsible for destruction of products of antigen-antibody reactions.
5.3.3 Platelets (thrombocytes)
The blood platelets are the smallest cells of the blood cells, averaging about 2 to 4 μm in diameter. It formed in the bone marrow; the abundant granular cytoplasm of the megakaryocyte divides into many small segments that break off and are released as platelets into the circulating blood. After about 10 days in the circulation, platelets are removed and destroyed. Like the red cells, they lack a nucleus and are incapable of cell division (mitosis), but they have a more complex metabolism and internal structure.
Functions of Platelets (thrombocytes)
The function of the platelets is related to hemostasis, the prevention and control of bleeding. It contribute substances essential for the normal coagulation of the blood, and theycause the shrinking, or retraction, of a clot after it has been formed.
5.4 Coagulation (Clotting Of Blood)
When there is an injury to blood vessel, blood comes out and within a few minutes, it loses its fluidity and forms a red-colored, semisolid jelly-like mass, i.e. clot. This process is known as blood coagulation or blood clotting.”
Mechanism of Blood Coagulation/Process of Blood Clotting
The injury to blood vessel leads to formation of a rough surface. The platelets when come in contact with rough surface, they are rupturedand thromboplastin is released. It is also released by damaged tissues. This thromboplastin in the presence ofcalcium converts inactive prothrombin present in the blood into active thrombin.
Importance of Blood Group
The accurate grouping of blood is very important when it comes to having a blood transfusion. If blood is given to a patient that has a blood type that is incompatible with the blood type of the blood that the patient receives, it can cause intravenous clumping in the patient’s blood which can be fatal. The patient’s body can start producing antibodies that attack the antigens on the blood cells in the blood that was given to the patient, causing reaction and rejection.
Human body contains blood, inwhich antigens and antibodies are present.
- Antigens are present in the R.B.C.
- Antibodies are present in plasma.
- Antigens are of two types. They are “A & B”
- Antibodies are of the two types. They are “a & b”
Depending upon the types of antigens & antibodies, the blood can divided into–
A – Blood Group
B – Blood Group
AB – Blood Group
O – Blood Group
Blood Group -A:
If blood contains antigen ‘A’ in RBC and antibody. ‘b’ in the plasma, they are called as blood group “A”.
Blood Group -B:
If blood contains antigen B in RBC and antibody ‘a’ in plasma are called as blood group “B”.
Blood Group -“AB”:
Blood contains “AB” antigen in RBC and doesn’t contains any antibody in plasma. That is called as blood group “AB”. It is universal receiver
Blood Group -‘O’:
RBC doesn’t contains any antigen and plasma contains antibodies “a and b”. That is called as blood group ‘O’. It is universal donor.
It is an agglutinogen (antigen) of “Rhesus monkey”. Apart from antigen ‘A’ and antigen ‘B’ about 80 to 90% of the people contain one or more antigens on the membranes of RBCs called Rh-antigen or Rhesus factor. If Rh factor is present in the person’s blood then blood group is described as Rh +ve and if Rh factor is absent in blood then blood group is described as Rh-ve.
Significance/Importance of Rh Factor
- Rh factor has a great value in blood transfusion because transfusion of Rh +ve blood to Rh-ve person stimulates the immune response which causes haemolysis of transfused blood cells.
- Rh factor is helpful in detecting the blood group of child by considering father’s and mother’s blood group study.