Biology Notes of BLOOD RBC, WBC, PLATELETS for SSC and UPSC EXAMS

Blood is a fluid connective tissue. It quantity is 6.8 litres in man and 500 ml less in the woman. It constitutes 6­8% of body weight and ahs a pH of 7.4. 

Three types of Blood Cells: – 

1)Red Blood Cells(RBC) 
2)White Blood cells (WBC)
 3)Platelets 

Red Blood Corpuscles (RBC): – 

• They are also called erythrocytes, disc shaped, no nucleus.
• It contains a pigment which is called Haemoglobin, which gives blood its red color and transports oxygen and carbon dioxide 
• Red blood cells are manufactured in Bone marrow 
• The Life of Red Blood Cells is 120 days. Number of RBCs is 4.5 – 5 million/ cubic mm of blood 

White Blood Corpuscles (WBC): –

•  Also called leukocytes, they are rounded with a nucleus and far less numerous than RBCs(8,000 per cubic mm of blood) 
• Manufactured in Red Bone marrow 
• Act as the soldiers of Body’s defence system 

Platelets: – 

• Also called thrombocytes and are about 2,50,000 per cubic mm of blood 
• Manufactured in red Bone marrow 
• It helps the blood to clot 

Blood Groupings:-

• Father of Blood Grouping : Karl Landsteiner 
• He discovered A, B and O blood groups 
• Decastello and Sturle discovered AB blood groups 

RH Factor :-

• It is a blood antigen found in RBC 
• A person can be Rh+ or Rh­ depending upon the presence of Rh factor in RBC 
• Rh+ can receive blood from both Rh+ and Rh­- but Rh­- can receive blood only from Rh-­ only 
• Blood transfusion techniques was developed by James Blundell

THE CARDIOVASCULAR SYSTEM: THE BLOOD

I. Introduction

A. The internal environment is regulated by the fluids which bathe the cells:

1. Interstitial fluid (IF) is found outside cells and in between the cells

2. Lymph inside lymph vessels

3. Blood within blood vessels

B. Hematology is the science which studies blood and blood disorders

II. Functions of Blood

A. Blood is critical in the transportation of oxygen, carbon dioxide, nutrients, heat, wastes, and hormones

B. It assists in the regulation of pH, body temperature, and water content (osmotic status) of cells

C. It has a vital role in prevention of blood loss through the various processes known as hemostasis

D. It provides defense mechanisms against pathogens via white blood cells

III. Physical Characteristics of Blood

A. Greater viscosity than water (Water’s viscosity = 1; Blood’s viscosity = 3.0 -4.5)

B. Temperature of blood: 38°C (100.4^oF)

C. pH of 7.35 to 7.45 (Below 7.35 = Acidosis; Above 7.45 = Alkalosis)

D. Blood constitutes approximately 8% of body weight

E. Blood volume ranges between 4 to 6 liters (for females: 4-5 L; for males: 5-6 L)

IV. Blood components

A. 55% plasma and 45% formed elements (Hematocrit “crit” for males: 40%-54% (47%); Females: 38%-46% (42%)

B. Blood plasma composition

1. 91.5% water

2. 8.5% solutes

a. Proteins (albumins; globulins (alpha, beta, gamma); fibrinogen)

b. Nutrients

c. Enzymes

d. Hormones

e. Respiratory gases (oxygen, carbon dioxide)

f. Electrolytes (sodium, chloride, potassium)

g. Waste products (urea, uric acid, creatinine, H+, etc)

C. Formed Elements

1. Erythrocytes (Red Blood Cells or RBC’s)

2. Leukocytes (White Blood Cells or WBC’s)

3. Thrombocytes (platelets) ,

D. Hematocrit represents the percentage of red blood cells in blood (called Packed Cell Volume (PCV) in animals

1. A lower than normal hematocrit is representative of a condition known as anemia

2. An abnormally high hematocrit is representative of polycythemia

V. Formation of Blood Cells

A. Blood cells are formed from pluripotent hyematopoietic stem cells found in the red bone marrow (myeloid)

1. Myeloid stem cells give rise to RBC’s, platelets, and all WBC’s except lymphocytes

2. Lymphoid stem cells give rise to lymphocytes

B. Hemopoiesis (hematopoiesis) is stimulated by several hematopoietic growth factors. These hematopoietic

growth factors stimulate differentiation and proliferation of blood cells

1. Erythropoietin increases the number of RBC precursors

2. Thrombopoietin increases the number of platelet precursors

3. Cytokines (colony stimulating factors and interleukins) increase the number of WBC precursors

VI. Red blood cells

A. Erythrocytes (Red Blood Cells) contain the oxygen-carrying protein hemoglobin

B. There are approximately 5.4 million red blood cells/microliter of blood (1 drop of blood = 50uL)

C. Erythrocytes are biconcave discs without nuclei

D. RBC physiology

1. Hemoglobin functions to transport oxygen (oxyhemoglobin) and carbon dioxide (carbaminohemoglobin)

2. Hemoglobin functions to regulate blood pressure

a. Unsaturated hemoglobin picks up CO2 and nitric oxide (NO), a gas which it releases to

the lungs to be exhaled

b. Saturated hemoglobin carries fresh oxygen and supernitric oxide (SNO) from the lungs

and releases them in body tissues.

c. NO tends to cause vasoconstriction; SNO causes vasodilation

d. By ferrying NO and SNP throughout the body, hemoglobinhelps regulate blood pressure

by adjusting the amount of NO or SNO to which blood vessels are exposed.

E. RBC Life Cycle

1. Red Blood Cells only live about 120 days because of the wear and tear on their plasma

membranes as they squeeze through blood capillaries

2. In the RBC life cycle, after phagocytosis of warn-out RBC's by macrophages, hemoglobin is

recycled; the globin portion is split from the heme with the amino acids being reused for protein

synthesis. The iron in the heme portion is reclaimed with the rest of the heme molecule; the rest

becomes a component of bile in the digestive process.

F. Erythropoiesis (production of RBC's)

1. Erythropoiesis is the production of red blood cells in the red bone marrow of some bones

2. Proerythroblasts give rise to cells which begin to synthesize hemoglobin

3. At the end of development, the nucleus is ejected (causing it to become biconcave) and becomes reticulocyte

4. Reticulocytes pass from the bone marrow to the circulatory system; now are called erythrocytes

5. Hypoxia (low cellular oxygen) is detected by cells within the kidney which stimulates the

production of erythropoietin

6. Erythropoietin travels to the red bone marrow where it speeds the development of pro-erythrocytes

into reticulocytes

Vll. White blood cells

A. Leukocytes ( WBC’s) are nucleated cells, do not contain hemoglobin, but do contain cytoplasmic granules.

1. Granular leukocytes include eosinophils, basophils, and neutrophils based on the staning of

the enclosed granules.

2, Agranular leukocytes have small, resistant-to-staining-cytoplasmic granules and included lymphocytes

and monocytes (which differentiate into fixed and wandering macrophages)

B. Leukocytes have surface proteins, as do erythrocytes. Thse are called major histocompatibility antigens

(MHC), are unique for each person (except for identical siblings), and can be used to identify a tissue.

C. WBC physiology

1. White blood cells usually live for only a few hours or a few days

2. Normal blood contains 5,000 to 10,000 leukocytes/uL

3. Leukocytosis refers to an increase in the number of WBC's (-philia for increased eos, basos, neuts)

4. Leukopenia refers to an abnormally low number ofWBC's (-penia for decrease in any WBC)

5. The general function of leukocytes is to combat inflammation and infection

a. WBC's leave the blood stream by emigration.

b. Some WBC’s particularly neutrophils and macrophages, are active in phagocytosis

c. Chemotaxis is the chemical attraction of WBC’s to a disease or injury site

d. Different WBC’s combat inflammation and infection in different ways:

(1) Neutrophils and wandering or fixed macrophages (which develop from monocytes

do so through phagocytosis

(2) Eosinophils combat the effects of histamine in allergic reactions, phagocytize, antigen-

antibody complexes, and combat parasitic worms

(3) Basophils develop into mast cells that liberate heparin, histamine, and serotonin in

allergic reactions that inteniify the inflammatory response

(4) B-lymphocytes, in response to the presence of foreign substances called antigens,

differentiate into plasma cells that produce antibodies (humoral-mediated immunity) and

T-lymphocytes destroy foreign invaders directly (cell-mediated immunity)

NK lymphocytes kill a wide variety of infectious microbes and certain self-tumor cells.

(5) Monocytes emigrate from blood to tissues where they enlarge and differentiate into either fixed

or wandering macrophages; depending on where they reside are called Langerhan’s cells (skin),

Kupffer’s cells (liver sinusoids), alveolar cells (lung); osteoclasts (bone c.t.), etc.

e. A differential white blood cell count is a diagnostic test in which specific white blood cells are

enumerated. Because each type of WBC plays a different role, determining the percentage of each

type in the blood assists in diagnosing the condition

6. Bone marrow transplants may be used to treat several types of anemia, leukemia, and other blood disorders

VIII. Platelets

A. Thrombopoietin stimulates myeloid stem cells to produce platelets

1. Myeloid stem cells develop into megakaryocyte-colony-forming cells that develop into megakaryoblasts

2. Megakaryoblasts transform into megakaryocytes, which ultimately fragment

3. Each fragment, enclosed by a piece of cell membrane, is a platelet (thrombocyte)

B. Normal blood contains 250,000 to 400,000 platelets/uL.

C. Platelets have a life span of only 5 to 9 days. Aged and dead platelets are removed by fixed macrophages in the spleen and liver

D. Platelets help stop blood loss from damaged vessels by forming a platelet plug. Their granules also

contain chemicals that promote blood clotting.

IX. Hemostasis

A. Hemostasis refers to the stoppage of bleeding. When blood vessels are damaged or ruptured,

the hemostatic response must be quick, localized to the region of damage, and carefully controlled.

B. Hemostasis involves vascular spasm, platelet plug formation, and blood coagulation (clotting)

1. Vascular spasm--the smooth muscle of a vessel wall will contract to constrict vessel’s lumen

2. Platelet plug formation--the clumping of platelets around the damage to slow bleeding

3. A clot is a gel consisting of a network of insoluble protein fibers (fibrin) in which formed

elements of blood are trapped

a. The chemicals involved in clotting are known as coagulation (clotting) factors; most are in blood plasma;

some are released by platelets, and one is released from damaged tissue cells

b. Blood clotting involves a cascade of reactions that may be divided into three stages:

(1) De novo formation of prothrombinase (prothrombin activator)

(2) Conversion of prothrombin (circulating clotting protein) into thrombin

(3) Conversion of soluble fibrinogen into insoluble fibrin threads.

C. Normal coagulation is a positive feedback mechanism; requires Vitamin K; also involves clot retraction

(tightening of the clot) and fibrinolysis (dissolution of the clot)

1. The fibrinolytic system dissolves small, inappropriate clots and clots at a site of damage once

the damage is repaired

2. Plasmin (fibrinolysin) can dissolve a clot by digesting fibrin threads and inactivating

substances such as fibrinogen, protrhombin, and factors V, VIII, and XII.

D. Homeostatic Control of Hemostasis

1. Clots are generally localized due to fibrin absorbing thrombin into the clot, clotting factors

diffusing through blood, and the production of prostacyclin, a powerful inhibitor of platelet adhesion

and release

2. Substances that inhibit coagulation, called anticoagulants (such as heparin) are also present in blood.

E. Despite the anticoagulating and fibrinolytic mechanisms, blood clots sometimes form within the

cardiovascular system

1. Clotting in an unbroken blood vessel is called thrombosis; the clot is called a thrombus.

2. A thrombus (clot), bubble of air, fat from broken bones, or piece of debris transported by

the bloodstream that moves from the site of origin is called an embolus.

X. Blood Groups and Blood Types

A. The surfaces of red blood cells contain genetically determined blood group antigens, called

agglutinogens or isoantigens.

1. Blood is categorized into different blood groups based on the presence or absence of various isoantigens.

2. Within a blood group there may be two or more different blood types.

3. Major blood groups are the ABO and Rh groups. Other blood groups include the Lewis, Kell, Kidd, and Duffy systems.

B. ABO Group

1. In the ABO system, agglutinogens (antigens) A and B determine blood type.

2. Plasma contains agglutinins (antibodies), designated as a and b, that react with

agglutinogens that are foreign to the individual

C. Rh Blood Types

1. In the Rh system, individuals whose erythrocytes have Rh agglutinogens are classified as Rh+.

those who lack the antigen are Rh-.

2. A disorder due to Rh incompatibility between mother and fetus is called hemolytic disease

of the newborn (HDN); it is treatable, but also preventable.

D. Knowledge of blood types is essential to safe transfusion of blood and may also be used in

proving or disproving paternity; linking suspects to crimes, or as part of anthropology studies to

establish a relationship among races.

1. The Rh and ABO blood groups may be detected by a simple medical test, blood typing, in

which a sample of blood is mixed with serum containing agglutinins to each of the major

agglutinognes (A, B, and Rh)

2. Typing is the determination of blood types, whereas cross-matching is the mixing of donor and

recipient blood for compatibility.

XI. Disorders: Homeostatic Imbalances

A. Anemia--condition in which the oxygen-carrying capacity of the blood is reduced; it is a sign, not a

diagnosis and is usually characterized by a decreased erythrocyte count or hemoglobin

deficiency.

B. Sickle-cell disease--inherited disorder due to an abnormal kind of hemoglobin. RBC's

exhibit a characteristic sickle shape, rupture easily, and show a reduced oxygen carrying capacity

which results in hemolytic anemia.

C. Hemophilia--inherited deficiency of clotting in which bleeding may occur spontaneously or

after only minor trauma.

D. Disseminated intravascular clotting - disorder of hemostasis characterized by simultaneous

and unregulated blood clotting and hemorrhage.

E. Acute leukemia - malignant disease of blood-forming tissues characterized by uncontrolled

production and accumulation of immature leukocytes. In chronic leukemia, there is an accumulation

of mature leukocytes in the bloodstream because they do not die at the end of their normal life span.

F. Aplastic anemia - Anemia is a deficiency of hemoglobin in the blood. It can result from a decrease

in the number of erythrocytes, a decrease in the amount of hemoglobin in each erythrocyte, or both.

The decreased hemoglobin reduces the ability of blood to transport oxyten. Anemic patients suffer

from a lack of energy and feel excessively tired and listless. They can appear pale and quickly be-

come short of breath with only slight exertion. One general cause of anemia is insufficient produc-

tion of erythrocytes. It is usually acquired as a result of damage to the myeloid tissue by chemicals,

(e.g., benzene), other toxins, medications (e.g., certain antibiotics and sedatives), or gamma

radiation; all of which inhibit enzymes needed for hemopoiesis The three hallmarks of aplastic

anemia are erythropenia (e.g. low crit), markedly decreased hemoglobin, and leukopenia (with

ALL WBC values markedly "off").