The Blood

Constituents of blood and their function

Introduction

• Blood = Cells + Plasma• Average adult human body contains 5 liters of blood• Bone marrow is site of synthesis of various constituents of

blood• Blood is considered as a special connective tissue as it

develops from mesenchyme

Bone Marrow – Site of Synthesis

• Blood contains: – Cellular portion (RBCs, WBCs, & Platelets) are suspended in Plasma

– the fluid portion of blood– The blood volume occupied by blood cells is known as Hematocrit

• Roughly, it should be 45%• Varies with altitude

– Higher the altitude higher would be the hematocrit value

Blood as Transport Medium• Vehicle for the transport of

– Gases like nitrogen, CO2, O2, etc.– Ions like sodium, potassium, chloride, calcium, etc.– Nutrients like glucose, fatty acids, & proteins– Metabolic waste products– Cells– Hormones like insulin, glucagon, estrogen in females,

testosterone in males, etc.– Proteins and lipids

Plasma - Constituents

• 90% water• 8% protein called as Plasma proteins• 1% inorganic salts• 0.5% lipids• 0.1% sugar• The rest being made of lesser components

Plasma - Constituents• Plasma Proteins – 3 Main groups

– Blood coagulation proteins, albumin, and the globulins– Albumin:

• Most abundant plasma protein• Responsible for Colloidal Osmotic Pressure

– Globulins• 3 type of Globulins

– Alpha, Beta, & gamma– Alpha and beta globulins help in transport of hormones and fat-

soluble vitamins– Gamma-globulins are called as immunoglobulins (antibodies)

– Blood coagulation proteins (Fibrinogen)• Help in clotting of blood

Regulating pH and Osmotic pressure

• Plasma proteins, especially albumin, contributes to osmotic pressure

– This pressure regulates the flow of materials in and out of capillaries

• Blood pressure always tries to push things out of a blood vessel. This outward force is counteracted by osmotic pressure of blood vessels

• Similarly, tissue pressure always tries to push things out of interstitial spaces and this pressure is counteracted by osmotic pressure of interstitial spaces

• In essence, sum of all above-mentioned forces will govern the flow of materials in and out of capillaries

• Plasma proteins also regulate pH of blood

– Normal pH of blood is 7.4 and it is highly essential that this pH be maintained for proper function of human body

• Plasma proteins also help in transport of molecules

Blood Cells

• RBCs, WBCs, & Platelets

Erythrocytes (RBC)• Highly flexible cells that transport oxygen in the blood • The erythrocyte is a biconcave disk

– This unique shape increases surface area for exchange of gases• 7 –8 micro meter in diameter

– As the diameter of some of the capillaries is smaller than this, the RBC has to fold on itself to pass through them. This is aided by its unique shape

• Life span – 4 months

Other Unique properties of RBC

• No nucleus

– They do not have nucleus. Hence, cannot produce any new proteins

• No mitochondria

– Mitochondria, powerhouses of cell, use oxygen to produce ATP

– As they do not have mitochondria, RBC cannot use oxygen to produce ATP

– All ATP production occurs by anaerobic method

• Hemoglobin

– RBC are filled with hemoglobin, the oxygen-carrying protein

Erythropoeisis

• Aged RBCs are removed from circulation by liver and spleen

– Most of the iron released from the destruction of aged RBC are reused for synthesis of new RBCs

– Small amounts of iron is lost and this amount has to be replaced from diet

– As iron is a vital component of hemoglobin, deficiency of dietary iron causes deficiency of hemoglobin

• RBCs are replenished by stem cells in bone marrow

• Erythropoeitin (EPO), a hormone released by kidneys, is very important for synthesis of RBC. It stimulates the division of stem cell

– This is released when oxygen levels in blood decline

• With each division of the stem cell and the precursors of RBC, the size of the cell & nucleus will decrease and the amount of hemoglobin will increase

– So that by the end of the division, we have non-nucleated RBC filled will Hemoglobin

• Maturation of RBCs (formation of RBC from stem cells) requires vitamin B12 and Folic acid

Type of Bone marrow

• Red Bone marrow– Red in color due to abundant dividing cells, especially those

belonging to RBC• Yellow Bone marrow

– Yellow in color due to excess of fat– With age, number of dividing stem cells will decrease and the

amount of fat will increase

Hemoglobin• Made of 2 groups

– Iron-containing heme group linked to Protein globin group

– Globin group

• Consists of 4 subunits

– 2 alpha & 2 beta polypeptide chains

– Heme group

• Contains iron in ferrous form

• Oxygen transport

– In lungs, oxygen diffuses into the plasma, and then into the RBCs

– In RBCs, oxygen binds with the iron to form oxyhemoglobin

– 98% of oxygen is carried as oxyhemoglobin. Remaining 2% is carried by blood as dissolved form in plasma

Pathologies associated with RBC and Hb• Anemia

– Anemia is a blood condition occurring due to decreased hemoglobin concentration

– It could be due to decreased production of Hb or decreased number of RBC or presence of abnormal Hb

– Results in microcytic hypochromic RBC

• Common reason for decreased production is deficiency of iron

– Decreased number of RBC could be due excessive bleeding (hemorrhage) or due to decreased production of RBC (problem in bone marrow like tumor) or increased destruction of RBC (infections like malaria or abnormally-shaped RBC like sickle-shaped RBC)

– Macrocytic or megaloblastic anemia

• Folic acid and Vit B12 deficiency (dietary)

• Pernicious anemia (Vit B12 due to defective absorption because of lack of intrinsic factor)

– Anemic patients appear pale

• Pale conjunctiva and tongue

anemic normal

Hypochromic microcystic blood film. This is seen in iron-deficiency anemia

ocular signs may be present - Pale conjunctiva

•Sickle cell anemia – RBC are deformed into elongated crescents (sickles) which leads to premature RBC destruction

Normally after 100 –120 days, RBC are phagocytosed, by

macrophages in the spleen but sickle celled

RBC get destroyed even before that time

White Blood Cells• LEUKOCYTES are nucleated cells that are part of body’s protective

mechanism• They are subdivided into 5 types• Granular leukocytes (Contain large granules in cytoplasm)

– Eosinophils– Basophils– Neutrophils (polymorph nuclear leukocytes)

• Agranulocytes (Contain very fine granules in cytoplasm)– Lymphocytes– Monocytes

•Neutrophils (polymorphs)•Constitutes 50% - 70% of the total leukocyte count.•Most of them are mature•The nucleus is segmental, with two to five lobes interconnected by fine strands and chromatin that is condensed and dark staining

• Neutrophils circulate with blood for 6 – 10 hours. They then enter the tissues as motile cells and continue their phagocytic activities for another 2 or 3 days

• They are the “first responders” for any infection or inflammation

• They engulf bacteria and destroy them by using lysosomalgranules, hydrogen peroxide produced by peroxisomes.

• LYMPHOCYTES• Comprise 20 – 40% of peripheral blood leukocytes• They are also found outside blood in specialized organs called

lymphoid organs like spleen, thymus, lymph nodes

• Types of Lymphocytes– T lymphocytes

• They attack foreign cells directly– B lymphocytes

• On getting exposed to foreign cells, they transform into plasma cells, which in turn produces antibodies

• Antibodies coats these foreign cells and neutralizes them

Eosinophils• Deep red granules in acid stain

• Bi-lobed nucleus

• Play a role in moderate allergic reactions and defend against parasitic worm infestations

• Constitute 1-3% of leukocytes

Basophils• Deep blue granules in basic stain

• Release histamine (inflammation) and heparin (blood flow)

• Involved in allergic reactions like cutaneous hypersensitivity syndrome.

• Form less than 1% of leukocytes in blood

• Similar to eosinophils in size and shape of nuclei

Monocytes• Largest of all blood cells

• Spherical, kidney-shaped, oval, or lobed nuclei

• Leave bloodstream to become macrophages

• Form 3-9% of leukocytes in blood

• Phagocytize bacteria, dead cells, and other debris

Conditions associated with WBC

• Normal count of WBC is between 5000 to 10,000 cells per cubic millimeter of blood

• Leukoctyosis

– Excess WBC count

– Typically happens during infections

• Leukopenia

– Low WBC count

– Abnormal and mostly due to Irradiation of the body by x-rays or gamma rays, or exposure to drugs and chemicals

– Patients become more susceptible to infection

– Without treatment, death often ensues in less than a week after acute total leukopenia begins

Leukemia• Cancer of WBC

• Uncontrolled production of white blood cells can be caused by cancerous mutation of a myelogenous or lymphogenous cell

• Types:

– lymphocytic leukemias and myelogenous leukemias

• Basing on disease progress: Leukemia can be acute or chronic

• More frequently, the leukemia cells are bizarre and undifferentiated and not identical to any of the normal white blood cells.

• Usually, the more undifferentiated the cell, the more acute is the leukemia, often leading to death within a few months if untreated.

• With some of the more differentiated cells, the process can be chronic, sometimes developing slowly over 10 to 20 years.

• Leukemic cells, especially the very undifferentiated cells, are usually nonfunctional for providing the normal protection against infection.

Leukemia - Features & Effects• The first effect of leukemia is spread of leukemic cells into abnormal areas of the

body. Leukemic cells from the bone marrow may reproduce so greatly that they invade the surrounding bone, causing pain and, eventually, a tendency for bones to fracture easily. Almost all leukemias eventually spread to the spleen, lymph nodes, liver, and other vascular regions, regardless of whether the origin of the leukemia is in the bone marrow or the lymph nodes.

• Common effects in leukemia are the development of infection, severe anemia (lack of RBCs), and a bleeding tendency caused by thrombocytopenia (lack of platelets). These effects result mainly from displacement of the normal bone marrow and lymphoid cells by the nonfunctional leukemic cells.

• Finally, an important effect of leukemia on the body is excessive use of metabolic substrates by the growing cancerous cells. The leukemic tissues reproduce new cells so rapidly that tremendous demands are made on the body reserves for food stuffs, specific amino acids, and vitamins. After metabolic starvation has continued long enough, this alone is sufficient to cause death.

• Platelets: (Thromobcytes)• Are small plate like structures • 2 micro meter to 3 micrometer

• Are produced by ‘megakaryoctyes’ of red bone marrow.• They are cytoplasmic fragments, covered by cell membrane,

lacks nucleus.• They tend to aggregate – ‘platelet clumps’

Platelet granules• Alpha granules

– Contains• Fibrinogen• Fibronectin• Factor v and VIII• Platelet factor 4• PDGF• Transforming growth factor

• Platelets can discharge their granular contents by Exocytosis• The maximum circulation time for platelets is about 10 days, after which

they are phagocytosed by macrophages in the spleen

Thrombocytopenia• Low quantity of platelets

• Bleeding occurs if < 50.000/L ; if count is < 10.000/ L then it is lethal

• Bleeding mostly occur in small capillaries and venules

• Mostly idiopathic (unknown cause)

• Idiopathic thrombocytopenic purpura, possibly auto-immune reactions after transfusions

• Distinguish between vascular purpura

• Treatment:

– Administration of fresh whole blood with high amounts of platelets

– Splenectomy

BLOOD CLOTTING

Hemostasis

Clotting process:1. Severed vessel2. Platelets agglutinate3. Fibrin appears4. Fibrin clot forms5. Clot retraction occurs after ± 30 min. :

– Fibrin stabilizing factor– platelet factors (thrombosthenin, actin and

myosin molecules)

• Breaks down fibrin• Interferes with fibrin polymerization • Fibrin is split in to Fibrin degradation product (FDP)• FDP or Fibrin split products have weak

anticoagulant effect

Plasmin

Hemophilia• Bleeding disorder, almost exclusively in males (female carrier)

• 85 % : hemophilia A or classic hemophilia (absence of factor VIII)

• 15% : hemophilia B or recessive trait form: absence factor IX

• Factor VIII has 2 parts, large part/ small part

– When small part deficient = Classic hemophilia

– When large part deficient = von Willebrand’s disease

• Bleeding occurs after trauma, in severe cases after minor trauma.

• Treatment: administration of purified F. VIII

Hemarthrosis of the knee in a hemophilia

patient

Blood groups• Discovered after introduction of transfusions

• Different people have different antigenic and immune responses

• These responses are genetic inherited

• Antigens are present on surface of the red blood cells

• Most important:

– O-A-B blood type

– Rhesus blood type

A-B-O blood type• Blood type depends on type of agglutinogen on the surface of the

red blood cell• Agglutinogen A / Agglutinogen B• Agglutinins (gamma-globulins of IgM type or IgG type) are

antibodies against agglutinogens which are not present in the plasma)

A-B-O blood type

A-B-O blood type• People not carrying a certain type of agglutinogen, produce agglutinin during

their life by exposure to these agglutinogens in food, bacteria etc.

• When mismatching of blood groups occur during transfusion, transfusion reactions occur due to agglutination

• Agglutination = clumping of red blood cells because of attachment through agglutinin (antibodies), which can hemolyse during passage in small blood vessels or due to release of proteolytic enzymes by the complement system

Rhesus-blood type• Goes along with the ABO-blood system (i.e. blood type A+, B-)

• Differs from ABO system:

– In ABO-system, agglutinin develops spontaneously

– In Rh-system, person must be exposed to Rh- factor first to develop immunity against it.

• Immune-response:

– Occurs when Rh- person gets exposed to Rh+ blood

– After 1st exposure: anti-Rh-agglutinins develop slowly (maximum concentrations after 2-4 months) delayed reaction

– With multiple exposures, reactions can become more severe

Rhesus-blood type• 6 types of Rhesus-factor:

– type C & type c

– type D & type d

– type E & type e

• People have one of the three pairs of antigens

• If person has type D antigen, he is called Rhesus positive (Rh+)

• If he does not have type D, he is called Rhesus negative (Rh-)

• 85% of the population is Rh+

Blood Transfusion• Blood type: ABO / Rhesus (i.e. blood type O+ or type AB-)

– Universal donor is type O-– Universal receptor is type AB+

Erytrhoblastosis fetalis• Hemolytic disease in the newborn

• Mother is Rh- / father Rh+, baby inherits Rhesus type of father (Rh+), mother develops antigens against r.b.c. of the unborn baby, pass through the placenta and agglutinates with the r.b.c. of the baby)

• 1st child doesn’t develop the disease, but severe reactions can occur in 2nd, 3rd child, reactions getting more severe.

Erytrhoblastosis fetalis

• Clinical symptoms:

• Jaundice/ anemia in newborn baby

• Agglutinins stay in blood for 1-2 months after borth

• liver and spleen enlarged

• production of erythroctyes is increased, many blast form (immature cells) will be seen in peripheral blood (erythroblastosis)

• kernicterus in severe cases (precipitation of bilirubin in neuronal cells of the brain, cause destruction with permanent mental impairment or damage of motor areas)

• Treatment :

– (repetitive) transfusion of the baby with Rh- blood till mother’s agglutinins are disappeared

Prevention of eryhtroblastosisfoetalis

• Fortunately, it is usually possible to prevent sensitization from occurring the first time by administering a single dose of anti-Rhantibodies in the form of Rh immune globulin during the postpartum period.

• Such passive immunization does not harm the mother and prevents active antibody formation by the mother