Components of blood Introduction

The different components that make up blood. Plasma, white blood cells, red blood cells, .  If you prick your finger or scrape your knee, you'll see some droplets of blood form. Just by eye, these droplets may seem to be made of uniform red liquid, similar to food coloring or paint.

 However, if you were to look under a microscope, you would see that your blood is actually a mixture of liquid and cells.

 And if you could zoom in even further, you would see that there are also many macromolecules (such as proteins) and ions (such as sodium) floating in the liquid. All of these components are important to the roles blood plays in the body.

What is blood?

Blood, by definition, is a fluid that moves through the vessels of a .

In humans, blood includes plasma (the liquid portion), blood cells (which come in both red and white varieties and platelets.

1. Plasma is the main component of blood and consists mostly of water, with proteins, ions, nutrients, and wastes mixed in.

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2. Red blood cells (erthrocytes) are responsible for carrying oxygen and carbon dioxide.

3. Platelets (thrombocytes) are responsible for blood clotting.

4. White blood cells (Leukocytes) are part of the immune system and function in immune response.

Cells make up about 45%percent percent of human blood, while plasma makes up the other 55%percent percent.

Plasma

 Plasma, the liquid component of blood, can be isolated by spinning a tube of whole blood at high speeds in a centrifuge.

 The denser cells and platelets move to the bottom of the tube, forming red and white layers, while the plasma remains at the top, forming a yellow layer.

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 The plasma is about 90%, percent water, with the remaining 10%, percent made up of ions, proteins, nutrients, wastes, and dissolved gases.

 The ions, proteins, and other molecules found in plasma are important for maintaining blood pH and osmotic balance, with albumin (the main protein in human plasma) playing a particularly important role.

 Some of the molecules found in the plasma have more specialized functions include;

I) hormones act as long-distance signals,

II) antibodies recognize and neutralize pathogens, and

III) clotting factors promote blood clot formation at the site of wounds.

 Plasma that’s without clotting factors is called serum.

 Lipids, such as cholesterol, are also carried in plasma, but must travel with escort proteins because they don’t dissolve in water.

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Red blood cells(erythrocytes)

 Red blood cells, or erythrocytes, are specialized cells that circulate through the body and deliver oxygen to tissues.

 In humans, red blood cells are small and biconcave and do not contain mitochondria or a nucleus when mature.

 These characteristics allow red blood cells to effectively perform their task of oxygen transport. Small size and biconcave shape increase the surface area- to-volume ratio, improving gas exchange, while lack of a nucleus makes additional space for hemoglobin, a key protein used in oxygen transport. Lack of mitochondria keeps red blood cells from using any of the oxygen they’re carrying, maximizing the amount delivered to tissues of the body.

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 In the lungs, red blood cells take up oxygen, and as they circulate through the rest the body, they release the oxygen to the surrounding tissues.

 Red blood cells also play an important role in transport of carbon dioxide, a waste product, from the tissues back to the lungs.

 Some of the carbon dioxide binds directly to hemoglobin, and red blood cells also carry an enzyme that converts carbon dioxide into bicarbonate. The bicarbonate dissolves in plasma and is transported to the lungs, where it's converted back into carbon dioxide and released.

 Red blood cells have an average life span of 120 days.

 Old or damaged red blood cells are broken down in the liver and spleen, and new ones are produced in the bone marrow.

 Red production is controlled by the hormone erythropoietin, which is released by the kidneys in response to low oxygen levels.

 This negative feedback loop ensures that the number of red blood cells in the body remains relatively constant over time.

Platelets and clotting

 Platelets, also called thrombocytes, are cell fragments involved in blood clotting.

 They are produced when large cells called break into pieces, each one making 2000-3000 platelets as it comes apart.

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 Platelets are roughly disc-shaped and small.

CLOTTING PROCESS

 When the lining of a blood vessel is damaged (for instance, if you cut your finger deeply enough for it to bleed), platelets are attracted to the wound site, where they form a sticky plug.

 After injury, clotting cascade can result from the blood cells or the injured tissues (tissue factor or contact clotting cascade pathways)

 Coagulation (clotting) is the process by which blood changes from a liquid to a gel, forming a clot

 The tissue factor pathway is named for the protein that triggers it—that is, a cell-surface, integral- membrane protein commonly known as tissue factor (TF). TF is also known as thromboplastin (perhaps more correctly, tissue thromboplastin), coagulation factor III, or CD142. TF is abundant in adventitial cells surrounding all blood vessels larger than capillaries, in keratinocytes in the skin, and in a variety of epithelial layers such as organ capsules. This way of triggering blood clotting is also sometimes called the Extrinsic Pathway, because it requires that plasma come into contact with something “extrinsic”—i.e.,TF—to trigger it. The TF pathway is the mechanism of triggering blood clotting that functions in normal hemostasis, and probably also in many types of thrombosis.

 The contact pathway of triggering blood clotting has also been termed the “intrinsic” pathway, since it can be triggered without adding a source of TF to the blood or plasma. This pathway is actually triggered when plasma comes into contact or in presence of (patho)physiological materials and invasion

pathogens. This pathway does not contribute to normal hemostasis. Contact activation system seems to be more involved in , and innate immunity.

 The platelets release signals, which not only attract other platelets and make them become sticky, but also activate a signaling cascade that ultimately

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converts fibrinogen, a water-soluble protein present in , into fibrin (a non-water soluble protein).

 The fibrin forms threads that reinforce the plug, making a clot that prevents further loss of blood.

White blood cells (Leukocytes)

 White blood cells, also called leukocytes, are much less common than red blood cells and make up less than 1%, percent of the cells in blood.

 Their role is also very different from that of red blood cells: they are primarily involved in immune responses, recognizing and neutralizing invaders such as bacteria and viruses.

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 White blood cells are larger than red blood cells, and unlike red blood cells, they have a normal nucleus and mitochondria.

 White blood cells come in five major types, and these are divided into two different groups, named for their appearance under a microscope.

 One group, the , includes , , and , all of which have granules in their cytoplasm when stained and viewed on a microscope.

 The other group, the agranulocytes, includes and , which do not have granules in the cytoplasm.

 Agranulocyte Any (see leucocyte) with a nongranular cytoplasm and a large spherical nucleus; lymphocytes and monocytes are examples.

 Agranulocytes are produced either in the or in the bone marrow and account for 30% of all leucocytes.

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Any white blood cell (see leucocyte) that contains granular material (secretory vessels) and lysosomes in its cytoplasm.

 Neutrophils, basophils, and eosinophils are examples of granulocytes

Immune cells

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See more analysis of the functions

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Types of lymphocytes

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 There are two categories of lymphocytes known as B lymphocytes and T

lymphocytes.

 These are commonly referred to as B cells and T cells.  Both types originate from stem cells in the bone marrow.

 From there, some cells travel to the thymus, where they become T cells.

 Others remain in the bone marrow, where they become B cells.

B cells

 The job of B cells is to make antibodies, which are proteins produced by the immune system to fight foreign substances known as antigens.

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 Each is set to make one specific antibody. Each antibody matches an antigen in the same way that a key matches a lock, and when this happens, the antigen is marked for destruction.

T cells

 The job of T cells is to help the body kill cancer cells and control the immune response to foreign substances.

 They do this by destroying cells in the body that have been taken over by viruses or become cancerous.

Natural Killer (NK)cells

 A third type of , known as a natural killer or NK cell, comes from the same place as B and T cells.

 NK cells respond quickly to several foreign substances and are specialized in killing cancer cells and virus-infected cells.

Stem cells and blood cell production

 Red blood cells, white blood cells, and platelet-producing cells are all descended from a common precursor: a .

 A hallmark of stem cells is that they divide asymmetrically. That is, one daughter cell remains a stem cell of the same type, while the other daughter cell acquires a new identity.

 For hematopoietic stem cells, which are found in the bone marrow, one daughter cell remains a hematopoietic stem cell, while the other goes on to become a different type of stem cell: either a myeloid stem cell or a lymphoid stem cell.

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Image modified from "Hematopoietic system of bone marrow," by OpenStax College, Anatomy & Physiology

 The myeloid stem cells and lymphoid stem cells also divide asymmetrically, with their non-stem cell daughters generating the mature cell types of the blood.

 Myeloid stem cells give rise to red blood cells, platelets, and some types of white blood cells, while lymphoid stem cells give rise to the types of white blood cells classified as lymphocytes.

 Hematopoietic, myeloid, and lymphoid stem cells divide throughout a person's lifetime, generating new blood cells to replace old and worn-out ones.

ANTIBODIES AND ANTIGENS

Antigens are molecules capable of stimulating an immune response. Each antigen has distinct surface features, or epitopes, resulting in specific responses.

Antibodies are Y-shaped proteins produced by B cells of the immune system in response to exposure to specific antigens; sometimes referred to as (immunoglobulins)

Specific Antibodies combine chemically with substances (or with specific antigen) which the body recognizes as alien, such as bacteria, viruses, and foreign substances in the blood.

This leads to antibody - antigen complex

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ABO BLOOD GROUPING

 The major human blood group system. The ABO type of a person depends on the

presence or absence of two genes, A and B on the red cells.

 These genes determine the configuration of the surface. A person

who has two A genes or an A and an O gene has red blood cells of type A.

 A person who has two B genes or one B and one O gene has red cells of type B. If

the person has one A and one B gene, the red cells are type AB.

 If the person has neither the A nor the B gene, the red cells are type O. It is

essential to match the ABO status of both donor and recipient in blood

transfusions and organ transplants.

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Rh blood group system

 Rh blood group system, system for classifying blood groups according to the presence or absence of the Rh antigen, often called the Rh factor, on the cell membranes of the red blood cells (erythrocytes).

 The designation Rh is derived from the use of the blood of rhesus monkeys in the basic test for determining the presence of the Rh antigen in human blood.

 The Rh blood group system was discovered in 1940 by Karl Landsteiner and A.S. Weiner.

 Since that time a number of distinct Rh antigens have been identified, but the first and most common one, called RhD, causes the most severe immune reaction and is the primary determinant of the Rh trait.

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RHESUS INCOMPATIBILITY

1. During blood transfusion

 The Rh antigen poses a danger for the Rh-negative person, who lacks the antigen, if Rh-positive blood is given in transfusion.

 Adverse effects may not occur the first time Rh-incompatible blood is given, but the immune system responds to the foreign Rh antigen by producing anti- Rh antibodies.

 If Rh-positive blood is given again after the antibodies form, they will attack the foreign red blood cells, causing them to clump together, or agglutinate.

 The resulting hemolysis, or destruction of the red blood cells, causes serious illness and sometimes death.

2. RHESUS INCOMPATIBILITY DURING PREGNANCY

 A similar hazard exists during pregnancy for the Rh-positive offspring of Rh- incompatible parents, when the mother is Rh-negative and the father is Rh- positive.

 The first child of such parents is usually in no danger unless the mother has acquired anti-Rh antibodies by virtue of incompatible blood transfusion.

 During labour or other invasive procedures during pregnancy, however, a small amount of the fetus’s blood may enter the mother’s bloodstream.

 The mother will then produce anti-Rh antibodies, which will attack any Rh- incompatible fetus in subsequent pregnancies.

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 This process produces erythroblastosis fetalis, or hemolytic disease of the newborn, which can be fatal to the fetus or to the infant shortly after birth.

 Treatment of erythroblastosis fetalis usually entails one or more exchange transfusions.

 The disease can be avoided by vaccinating the mother with Rh immunoglobulin after delivery of her firstborn if there is Rh-incompatibility.

 The Rh vaccine destroys any fetal blood cells before the mother’s immune system can develop antibodies.

WHEN IS ANTID INDICATED?

For Rh negative mothers whose babies’ father is RH + or might be Rh positive, a Rh immune globulin injections are recommended after situations in which the maternal blood could come into contact with the conceived baby's blood:

Such indications include;

1) Miscarriage

2) Abortion (see clarification below)

3) Ectopic pregnancy — when a fertilized eggs implants somewhere outside the uterus, usually in a fallopian tube

4) Removal of a molar pregnancy — a noncancerous (benign) tumor that develops in the uterus

5) Amniocentesis — a prenatal test in which a sample of the fluid that surrounds and protects a baby in the uterus (amniotic fluid) is removed for testing or treatment

6) Chorionic villus sampling — a prenatal test in which a sample of the wispy projections that make up most of the placenta (chorionic villi) is removed for testing

7) Cordocentesis — a diagnostic prenatal test in which a sample of the baby's blood is removed from the umbilical cord for testing

8) Bleeding during pregnancy

9) Abdominal trauma during pregnancy

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10) The external manual rotation of a baby in a breech position — such as buttocks first — before labor

11) Delivery (or after 1st delivery)

Clarification arena

1. A miscarriage is a natural or spontaneous termination of a pregnancy (an

embryo or fetus dies before the 20th week of gestation), meaning the body expels the

pregnancy on it’s own without the aid/intervention of medicine or a

surgical procedure.

2. An abortion occurs when a procedure or an intervention is done with the

purpose of ending a pregnancy, either surgically, using drugs or both

3. Abortion is the ending of a pregnancy by removal or expulsion of an embryo or fetus before it can survive outside the uterus.

4. An abortion that occurs without intervention is known as a miscarriage or spontaneous abortion.

5. Stillbirth is typically defined as fetal death at or after 20 to 28 weeks of pregnancy (depending on the source). It results in a baby born without signs of life.

6. Live birth, where the baby is born alive, even if it dies shortly after

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