write an essay on composition of blood

Biology Article

Blood is one of the most important components of life. Almost any animal that possesses a circulatory system has blood. From an evolutionary perspective, blood was speculated to have risen from a type of cell that was responsible for phagocytosis and nutrition. Billions of years later, blood and the circulatory system have drastically helped the evolution of more complex lifeforms.

Types of Blood Cells

We have seen blood consist of cells known as formed elements of blood. These cells have their own functions and roles to play in the body. The blood cells which circulate all around the body are as follows:

Red blood cells (Erythrocytes)

RBCs are biconcave cells without nucleus in humans; also known as erythrocytes. RBCs contain the iron-rich protein called haemoglobin; give blood its red colour. RBCs are the most copious blood cells produced in bone marrows. Their main function is to transport oxygen from and to various tissues and organs.

White blood cells (Leucocytes)

Leucocytes are colourless blood cells. They are colourless because it is devoid of haemoglobin. They are further classified as granulocytes and agranulocytes. WBCs mainly contribute to immunity and defence mechanism.

Red Blood Cells are red due to Hemoglobin , which is a transport molecule and also a pigment. As a result, blood is red.

Types of White Blood Cells

There are five different types of White blood cells and are classified mainly based on the presence and absence of granules.

Granulocytes

Agranulocytes.

There are five types of white blood cells present in the blood

They are leukocytes, with the presence of granules in their cytoplasm. The granulated cells include- eosinophil, basophil, and neutrophil.

Eosinophils

They are the cells of leukocytes, which are present in the immune system.

These cells are responsible for combating infections in parasites of vertebrates and for controlling mechanisms associated with allergy and asthma .

Eosinophil cells are small granulocyte, which are produced in the bone marrow and makes 2 to 3 per cent of whole WBCs. These cells are present in high concentrations in the digestive tract.

They are the least common of the granulocytes, ranging from 0.5 to 1 per cent of WBCs.

They contain large cytoplasmic granules, which play a vital role in mounting a non-specific immune response to pathogens, and allergic reactions by releasing histamine and dilating the blood vessels.

These white blood cells have the ability to be stained when exposed to basic dyes, hence referred to as basophil.

These cells are best known for their role in asthma and their result in inflammation and bronchoconstriction in the airways.

They secrete serotonin, histamine and heparin.

Neutrophils

They are normally found in the bloodstream.

They are predominant cells, which are present in pus.

Around 60 to 65 per cent of WBCs are neutrophils with a diameter of 10 to 12 micrometres.

The nucleus is 2 to 5 lobed and the cytoplasm has very fine granules.

Neutrophil helps in the destruction of bacteria with lysosomes, and it acts as a strong oxidant.

Neutrophils are stained only using neutral dyes. Hence, they are called so.

Neutrophils are also the first cells of the immune system to respond to an invader such as a bacteria or a virus.

The lifespan of these WBCs extends for up to eight hours and is produced every day in the bone marrow.

They are leukocytes, with the absence of granules in their cytoplasm. Agranulocytes are further classified into monocytes and lymphocytes.

These cells usually have a large bilobed nucleus, with a diameter of 12 to 20 micrometres.

The nucleus is generally half-moon shaped or kidney-shaped and it occupies 6 to 8 per cent of WBCs.

They are the garbage trucks of the immune system.

The most important functions of monocytes are to migrate into tissues and clean up dead cells, protect against bloodborne pathogens and move very quickly to the sites of infections in the tissues .

These white blood cells have a single bean-shaped nucleus, hence referred to as Monocytes.

Lymphocytes

They play a vital role in producing antibodies.

Their size ranges from 8 to 10 micrometres.

They are commonly known as natural killer cells.

They play an important role in body defence.

These white blood cells are colourless cells formed in lymphoid tissue, hence referred to as lymphocytes.

There are two main types of lymphocytes – B lymphocytes and T lymphocytes.

These cells are very important in the immune systems and are responsible for humoral and cell-mediated immunity.

Platelets (Thrombocytes)

Thrombocytes are specialized blood cells produced from bone marrow.

Platelets come into play when there is bleeding or haemorrhage.

They help in clotting and coagulation of blood. Platelets help in coagulation during a cut or wound.

Composition of Blood: Plasma, RBCs, WBCs and platelets

Components Of Blood

There are many cellular structures in the composition of blood. When a sample of blood is spun in a centrifuge machine, they separate into the following constituents: Plasma, buffy coat and erythrocytes. Thus blood contains RBC, WBC, platelets and plasma.

The liquid state of blood can be contributed to plasma as it makes up ~55% of blood. It is pale yellow in colour and when separated. Blood plasma consists of salts, nutrients, water and enzymes. Blood plasma also contains important proteins and other components necessary for overall health. Hence, blood plasma transfusions are given to patients with liver failure and life-threatening injuries.

Components of Blood Plasma

Blood plasma has several protein components. Proteins in blood plasma are:

Serum globulin
Serum albumin

The serum contains only globulin and albumin. Fibrinogen is absent in serum because it is converted into fibrin during blood clotting.

Red Blood Cells (RBC)

Red blood cells consist of Haemoglobin, a protein. They are produced by the bone marrow to primarily carry oxygen to the body and carbon dioxide away from it.

White Blood Cells (WBC)

White blood cells are responsible for fighting foreign pathogens (such as bacteria, viruses, and fungi) that enter our body. They circulate throughout our body and originate from the bone marrow.

Tiny disc-shaped cells that help regulate blood flow when any part of the body is damaged, thereby aiding in fast recovery through clotting of blood.

The above-stated elements form the composition of blood in humans. The only vertebrate without haemoglobin is the crocodile icefish. It derives its oxygen requirement directly from the cold, oxygen-rich water where it lives.

Also Read: Difference between Plasma and Serum

Blood Vessels

There are different types of blood vessels in our body each carrying out specialized functions.

Blood vessels are categorized into arteries, veins and capillaries

Types of Blood Vessels

Three types of blood vessels are:

Capillaries

Arteries are strong tubes and muscular in nature. These blood vessels carry oxygen-rich blood from the heart to all the tissues of the body. Aorta is one of the main arteries that arise from the heart and branches further.

Veins are elastic blood vessels which carry deoxygenated blood from all parts of the body to the heart. An exception is the umbilical and pulmonary veins. The Pulmonary vein carries oxygenated blood to the heart from the lungs and the umbilical vein carries oxygenated blood from the placenta to the foetus.

On reaching tissues, arteries branch further into extremely thin tubes called capillaries. Capillaries bring about the exchange of substances between blood and tissues.

Sinusoids are a special type of wider capillaries present in bone marrow, liver, lymph nodes, spleen and some endocrine glands. They may be continuous, discontinuous or fenestrated.

Layers of Blood Vessels

Both arteries and veins consist of three layers.

Tunica Intima : It is one of the innermost and thinnest layers of arteries and veins. It comprises endothelial cells. They are in direct contact with the flow of blood.

Tunica Media : It is the middle layer of an artery or vein. Tunica media is made up of smooth muscle cells.

Tunica Externa: It surrounds tunica media. It is made up of collagen and is also supported by the elastic lamina in arteries.

Functions of Blood

Blood is responsible for the following body functions:

Fluid Connective Tissue

Blood is a fluid connective tissue composed of 55% plasma and 45% formed elements including WBCs, RBCs, and platelets. Since these living cells are suspended in plasma, blood is known as a fluid connective tissue and not just fluid.

Provides oxygen to the cells

Blood absorbs oxygen from the lungs and transports it to different cells of the body. The waste carbon dioxide moves from the blood to the lungs and is exhaled.

Transports Hormones and Nutrients

The digested nutrients such as glucose, vitamins, minerals, and proteins are absorbed into the blood through the capillaries in the villi lining the small intestine.

The hormones secreted by the endocrine glands are also transported by the blood to different organs and tissues.

Homeostasis

Blood helps to maintain the internal body temperature by absorbing or releasing heat.

Blood Clotting at Site of Injury

The platelets help in the clotting of blood at the site of injury. Platelets along with the fibrin form clot at the wound site

Transport of waste to the Kidney and Liver

Blood enters the kidney where it is filtered to remove nitrogenous waste out of the blood plasma. The toxins from the blood are also removed by the liver.

Protection of the body against pathogens

The White Blood Cells fight against infections. They multiply rapidly during infections.

To know more about blood, its types, blood vessels, and composition of blood, please register at BYJU’S or download the BYJU’S app for further reference.

More to Explore:

Difference Between Blood and Lymph
Blood Groups

Frequently Asked Questions

1. what is blood, 2. state the types of blood cells found in human blood..

Blood cells are classified into the following types:

Erythrocytes or red blood cells
Leucocytes or white blood cells

3. State the different types of white blood cells found in the blood.

White blood cells can be classified as follows:

lymphocytes
neutrophils
eosinophils

4. What are granulocytes?

Granulocytes are leukocytes with granule-like structures, that contain enzymes capable of digesting microorganisms. Granulocytes are further classified into eosinophils, basophils, and neutrophils.

5. What are agranulocytes?

Agranulocytes are a type of white blood cell that has no distinct granules in their cytoplasm. However, they form an important part of the body’s immune system. They are further classified into monocytes and lymphocytes.

6. Name the various components of blood.

Blood is primarily broken down into the following components:

7. What are the various types of blood vessels present in our body?

Blood vessels are classified as follows:

8. What are sinusoids?

Sinusoids are very small vessels predominantly located inside the bone marrow, liver and spleen. Sinusoids are usually a little larger than capillaries.

9. Name the various layers of blood vessels.

Tunica Intima
Tunica Media
Tunica Adventitia or Externa

10. Name the major functions of blood.

Helps in homeostasis
Transports hormones and nutrients
Help in the clotting process

11. What gives blood its red colour?

12. does plasma contain haemoglobin.

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15.1: Composition of Blood

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You have probably had blood drawn from a superficial vein in your arm, which was then sent to a lab for analysis. Some of the most common blood tests—for instance, those measuring lipid or glucose levels in plasma—determine which substances are present within blood and in what quantities. Other blood tests check for the composition of the blood itself, including the quantities and types of formed elements.

One such test, called a hematocrit , measures the percentage of RBCs, clinically known as erythrocytes, in a blood sample. It is performed by spinning the blood sample in a specialized centrifuge, a process that causes the heavier elements suspended within the blood sample to separate from the lightweight, liquid plasma ( Figure 15.1 ). Because the heaviest elements in blood are the erythrocytes, these settle at the very bottom of the hematocrit tube. Located above the erythrocytes is a pale, thin layer composed of the remaining formed elements of blood. These are the WBCs, clinically known as leukocytes, and the platelets, cell fragments also called thrombocytes. This layer is referred to as the buffy coat because of its color; it normally constitutes less than 1 percent of a blood sample. Above the buffy coat is the blood plasma, normally a pale, straw- colored fluid, which constitutes the remainder of the sample.

The volume of erythrocytes after centrifugation is also commonly referred to as packed cell volume (PCV) . In normal blood, about 45 percent of a sample is erythrocytes. The hematocrit of any one sample can vary significantly, however, about 36–50 percent, according to gender and other factors. Normal hematocrit values for females range from 37 to 47, with a mean value of 41; for males, hematocrit ranges from 42 to 52, with a mean of 47. The percentage of other formed elements, the WBCs and platelets, is extremely small so it is not normally considered with the hematocrit. So the mean plasma percentage is the percent of blood that is not erythrocytes: for females, it is approximately 59 (or 100 minus 41), and for males, it is approximately 53 (or 100 minus 47).

This figure shows three test tubes with a red and yellow liquid in them. The left panel shows normal blood, the center panel shows anemic blood and the right panel shows polycythemic blood.

Figure $\PageIndex{1}$: omposition of Blood The cellular elements of blood include a vast number of erythrocytes and comparatively fewer leukocytes and platelets. Plasma is the fluid in which the formed elements are suspended. A sample of blood spun in a centrifuge reveals that plasma is the lightest component. It floats at the top of the tube separated from the heaviest elements, the erythrocytes, by a buffy coat of leukocytes and platelets. Hematocrit is the percentage of the total sample that is comprised of erythrocytes. Depressed and elevated hematocrit levels are shown for comparison.

Figure $\PageIndex{2}$: Summary of Formed Elements in Blood

18.1 An Overview of Blood

Learning objectives.

By the end of this section, you will be able to:

Identify the primary functions of blood in transportation, defense, and maintenance of homeostasis
Name the fluid component of blood and the three major types of formed elements, and identify their relative proportions in a blood sample
Discuss the unique physical characteristics of blood
Identify the composition of blood plasma, including its most important solutes and plasma proteins

Recall that blood is a connective tissue. Like all connective tissues, it is made up of cellular elements and an extracellular matrix. The cellular elements—referred to as the formed elements —include red blood cells (RBCs) , white blood cells (WBCs) , and cell fragments called platelets . The extracellular matrix, called plasma , makes blood unique among connective tissues because it is fluid. This fluid, which is mostly water, perpetually suspends the formed elements and enables them to circulate throughout the body within the cardiovascular system.

Functions of Blood

The primary function of blood is to deliver oxygen and nutrients to and remove wastes from body cells, but that is only the beginning of the story. The specific functions of blood also include defense, distribution of heat, and maintenance of homeostasis.

Transportation

Nutrients from the foods you eat are absorbed in the digestive tract. Most of these travel in the bloodstream directly to the liver, where they are processed and released back into the bloodstream for delivery to body cells. Oxygen from the air you breathe diffuses into the blood, which moves from the lungs to the heart, which then pumps it out to the rest of the body. Moreover, endocrine glands scattered throughout the body release their products, called hormones, into the bloodstream, which carries them to distant target cells. Blood also picks up cellular wastes and byproducts, and transports them to various organs for removal. For instance, blood moves carbon dioxide to the lungs for exhalation from the body, and various waste products are transported to the kidneys and liver for excretion from the body in the form of urine or bile.

Many types of WBCs protect the body from external threats, such as disease-causing bacteria that have entered the bloodstream in a wound. Other WBCs seek out and destroy internal threats, such as cells with mutated DNA that could multiply to become cancerous, or body cells infected with viruses.

When damage to the vessels results in bleeding, blood platelets and certain proteins dissolved in the plasma, the fluid portion of the blood, interact to block the ruptured areas of the blood vessels involved. This protects the body from further blood loss.

Maintenance of Homeostasis

Recall that body temperature is regulated via a classic negative-feedback loop. If you were exercising on a warm day, your rising core body temperature would trigger several homeostatic mechanisms, including increased transport of blood from your core to your body periphery, which is typically cooler. As blood passes through the vessels of the skin, heat would be dissipated to the environment, and the blood returning to your body core would be cooler. In contrast, on a cold day, blood is diverted away from the skin to maintain a warmer body core. In extreme cases, this may result in frostbite.

Blood also helps to maintain the chemical balance of the body. Proteins and other compounds in blood act as buffers, which thereby help to regulate the pH of body tissues. Blood also helps to regulate the water content of body cells.

Composition of Blood

One such test, called a hematocrit , measures the percentage of RBCs, clinically known as erythrocytes, in a blood sample. It is performed by spinning the blood sample in a specialized centrifuge, a process that causes the heavier elements suspended within the blood sample to separate from the lightweight, liquid plasma ( Figure 18.2 ). Because the heaviest elements in blood are the erythrocytes, these settle at the very bottom of the hematocrit tube. Located above the erythrocytes is a pale, thin layer composed of the remaining formed elements of blood. These are the WBCs, clinically known as leukocytes, and the platelets, cell fragments also called thrombocytes. This layer is referred to as the buffy coat because of its color; it normally constitutes less than 1 percent of a blood sample. Above the buffy coat is the blood plasma, normally a pale, straw-colored fluid, which constitutes the remainder of the sample.

Characteristics of Blood

When you think about blood, the first characteristic that probably comes to mind is its color. Blood that has just taken up oxygen in the lungs is bright red, and blood that has released oxygen in the tissues is a more dusky red. This is because hemoglobin is a pigment that changes color, depending upon the degree of oxygen saturation.

Blood is viscous and somewhat sticky to the touch. It has a viscosity approximately five times greater than water. Viscosity is a measure of a fluid’s thickness or resistance to flow, and is influenced by the presence of the plasma proteins and formed elements within the blood. The viscosity of blood has a dramatic impact on blood pressure and flow. Consider the difference in flow between water and honey. The more viscous honey would demonstrate a greater resistance to flow than the less viscous water. The same principle applies to blood.

The normal temperature of blood is slightly higher than normal body temperature—about 38 °C (or 100.4 °F), compared to 37 °C (or 98.6 °F) for an internal body temperature reading, although daily variations of 0.5 °C are normal. Although the surface of blood vessels is relatively smooth, as blood flows through them, it experiences some friction and resistance, especially as vessels age and lose their elasticity, thereby producing heat. This accounts for its slightly higher temperature.

The pH of blood averages about 7.4; however, it can range from 7.35 to 7.45 in a healthy person. Blood is therefore somewhat more basic (alkaline) on a chemical scale than pure water, which has a pH of 7.0. Blood contains numerous buffers that actually help to regulate pH.

Blood constitutes approximately 8 percent of adult body weight. Adult males typically average about 5 to 6 liters of blood. Females average 4–5 liters.

Blood Plasma

Like other fluids in the body, plasma is composed primarily of water: In fact, it is about 92 percent water. Dissolved or suspended within this water is a mixture of substances, most of which are proteins. There are literally hundreds of substances dissolved or suspended in the plasma, although many of them are found only in very small quantities.

Interactive Link

Visit this site for a list of normal levels established for many of the substances found in a sample of blood. Serum, one of the specimen types included, refers to a sample of plasma after clotting factors have been removed. What types of measurements are given for levels of glucose in the blood?

Plasma Proteins

About 7 percent of the volume of plasma—nearly all that is not water—is made of proteins. These include several plasma proteins (proteins that are unique to the plasma), plus a much smaller number of regulatory proteins, including enzymes and some hormones. The major components of plasma are summarized in Figure 18.3 .

The three major groups of plasma proteins are as follows:

Albumin is the most abundant of the plasma proteins. Manufactured by the liver, albumin molecules serve as binding proteins—transport vehicles for fatty acids and steroid hormones. Recall that lipids are hydrophobic; however, their binding to albumin enables their transport in the watery plasma. Albumin is also the most significant contributor to the osmotic pressure of blood; that is, its presence holds water inside the blood vessels and draws water from the tissues, across blood vessel walls, and into the bloodstream. This in turn helps to maintain both blood volume and blood pressure. Albumin normally accounts for approximately 54 percent of the total plasma protein content, in clinical levels of 3.5–5.0 g/dL blood.
The second most common plasma proteins are the globulins . A heterogeneous group, there are three main subgroups known as alpha, beta, and gamma globulins. The alpha and beta globulins transport iron, lipids, and the fat-soluble vitamins A, D, E, and K to the cells; like albumin, they also contribute to osmotic pressure. The gamma globulins are proteins involved in immunity and are better known as antibodies or immunoglobulins . Although other plasma proteins are produced by the liver, immunoglobulins are produced by specialized leukocytes known as plasma cells. (Seek additional content for more information about immunoglobulins.) Globulins make up approximately 38 percent of the total plasma protein volume, in clinical levels of 1.0–1.5 g/dL blood.
Fibrinogen is the third of the three major groups of plasma proteins. Like albumin and the alpha and beta globulins, fibrinogen is produced by the liver. It is essential for blood clotting, a process described later in this chapter. Fibrinogen accounts for about 7 percent of the total plasma protein volume, in clinical levels of 0.2–0.45 g/dL blood.

Other Plasma Solutes

In addition to proteins, plasma contains a wide variety of other substances. These include various electrolytes, such as sodium, potassium, and calcium ions; dissolved gases, such as oxygen, carbon dioxide, and nitrogen; various organic nutrients, such as vitamins, lipids, glucose, and amino acids; and metabolic wastes. All of these nonprotein solutes combined contribute approximately 1 percent to the total volume of plasma.

Career Connection

Phlebotomy and medical lab technology.

Phlebotomists are professionals trained to draw blood (phleb- = “a blood vessel”; -tomy = “to cut”). When more than a few drops of blood are required, phlebotomists perform a venipuncture, typically of a surface vein in the arm. They perform a capillary stick on a finger, an earlobe, or the heel of an infant when only a small quantity of blood is required. An arterial stick is collected from an artery and used to analyze blood gases. After collection, the blood may be analyzed by medical laboratories or perhaps used for transfusions, donations, or research. While many allied health professionals practice phlebotomy, the American Society of Phlebotomy Technicians issues certificates to individuals passing a national examination, and some large labs and hospitals hire individuals expressly for their skill in phlebotomy.

Medical or clinical laboratories employ a variety of individuals in technical positions:

Medical technologists (MT), also known as clinical laboratory technologists (CLT), typically hold a bachelor’s degree and certification from an accredited training program. They perform a wide variety of tests on various body fluids, including blood. The information they provide is essential to the primary care providers in determining a diagnosis and in monitoring the course of a disease and response to treatment.
Medical laboratory technicians (MLT) typically have an associate’s degree but may perform duties similar to those of an MT.
Medical laboratory assistants (MLA) spend the majority of their time processing samples and carrying out routine assignments within the lab. Clinical training is required, but a degree may not be essential to obtaining a position.

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Essays on blood: why do we actually have it?

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David Irving is employed by the Australian Red Cross Blood Service and has research collaborations with others receiving NHMRC and ARC research grants. Australian governments fund the Australian Red Cross Blood Service for the provision of blood, blood products and services to the Australian community.

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This week we’re running a series in collaboration with the Australian Red Cross Blood Service looking at blood: what it actually does, why we need it, and what happens when something goes wrong with the fluid that gives us life. Read other articles in the series here .

Just as a village can’t grow into a city without some form of transport (road, rail or river) that provides necessary interconnections for it to flourish, living things are limited in the size they can reach unless they have some form of circulatory system to transport nutrients and remove waste.

Single celled organisms such as bacteria and fungi, and some multicellular creatures such as sponges, corals and flatworms, simply absorb the nutrients they need and get rid of their waste using a passive process known as diffusion (which is much like soaking in and draining out).

More complex animals have developed some kind of circulatory system. A variety of different systems and pumps (hearts) have developed, but they all have a few things in common. These include something to carry oxygen around their bodies, a fluid of some sort, and some “plumbing” – in humans (and a number of other species) the fluid is called blood and the plumbing is our arteries, veins and capillaries. The oxygen carrier is haemoglobin.

Depending on the organism and where it has adapted to live, its oxygen carrier can come in different forms, often giving its “blood” different colours. Spiders, crustaceans, octopuses and squid use haemocyanin, which is based on copper and gives them blue blood. This carrier works well in low oxygen environments and in the cold.

Segmented worms and some leeches use an iron based carrier called chlorocruorin, which can appear either green or red, depending on its chemical environment. Vertebrates, including humans, use haemoglobin, which makes their blood red.

A truly special case is the Antarctic icefish , which lost its haemoglobin long ago as a result of a presumably random mutation. It has adapted though, and now survives by transporting oxygen that is simply dissolved in its blood. This is possible thanks to the cold conditions it lives in.

What is our blood made of?

Human blood, and that of all creatures with backbones (Antarctic ice fish excepted), is red. The colour comes from a chemical known as haem, which contains iron. It’s the iron that is the crucial ingredient for carrying oxygen. Oxygen is needed for our cells to burn sugars, fats and proteins in a controlled way. This provides us with the energy we need to live.

Outside our bodies, we know that when iron is exposed to oxygen, it rusts. And it doesn’t easily “unrust”. But to work as an oxygen carrier in our bodies, iron needs to “rust” and “unrust” on demand - picking up oxygen where it is in plentiful supply (our lungs), and releasing it where it is required (the cells in our organs).

This on/off oxygen switch is made possible with help from complex larger molecules. The first is haem, a flat ring structure that holds an iron atom at its centre. Haem is held closely by proteins known as globin, and this combination forms haemoglobin, which is itself packaged up in red blood cells to be transported around the body.

Infographic - From animal experiments to saving lives: a history of blood transfusions

The molecular structure of haemoglobin is delicately tuned to allow it to bind oxygen in the lungs and drop it off in areas where there is less oxygen available.

Red cells are specialised parcels, lacking DNA, that are able to squeeze through the tiniest capillaries, down to four millionths of a meter (equivalent to roughly half their diameter). Their donut shape maximises their surface area to make sure they can efficiently deliver oxygen, while keeping them small enough to fit through the smallest blood vessels.

More than just the red stuff

As well as red cells, our blood contains other cells and chemicals that repair and maintain the transport system and send signals around the body.

White blood cells, also known as leukocytes, repel or destroy invaders. Some white blood cells (lymphocytes) manufacture molecules known as antibodies that tag viruses and bacteria for destruction, while others called neutrophils and macrophages (literally “big eaters”) engulf bacteria, fungi and parasites to keep our circulation clean. When neutrophils have done their job you sometimes might see them as the main component of pus.

Platelets are very small fragments of larger cells called megakaryocytes. They react to any breaches to the walls of blood vessels, gathering together and triggering reactions that form a plug (or a clot) for the damaged section. If a person doesn’t have enough platelets, they can suffer from uncontrollable bleeding.

Where does it come from?

All blood cells (red cells, white cells and platelets) develop from haematopoietic (literally meaning “blood-making”) stem cells, located in the bone marrow. It has recently been found that many platelets are made in the lungs , from megakaryocytes that have migrated there from the bone marrow.

As stem cells develop, they progressively specialise into the many different types of blood cells, making developmental choices along the way. The specialisation of cells during development is tightly controlled by a symphony of growth factors. In some types of blood cancers and serious diseases, stem cell or bone marrow transplants can be used to “reboot” the blood making system.

As our knowledge of the control of blood cell development grows, we’re making progress towards being able to reproduce this process in cells grown in the laboratory . This is still some time away from being a broadly available process, but an exciting area to watch as it develops.

Update: the sentence outlining the shape of red blood cells was incorrect and has been reworded.

White blood cells
Blood series
Essays on blood
Australian Red Cross Blood Service
Red blood cells

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Blood Cells and Their Functions Essay

Blood is the fluid that transports oxygen nutrients through the whole body and carries away the waste products of the organism. An average human adult has about five liters of blood, which constitutes 8% of the entire body weight (Shier et al., 2019). Due to its complex nature and transport function, a single drop of blood can contain a countless number of viruses. Therefore, the extraction of blood requires the strictest precautions to avoid infection.

It is essential to analyze its structure to have a better understanding of blood’s functions. Blood consists of white and red blood cells, and platelets, which are cellular fragments. Shier et al. (2019) explain the origin of blood cells: “Blood cells originate in red bone marrow from hematopoietic stem cells, also known as hemocytoblasts” (p. 531). The function of red blood cells lies in carrying oxygen from the lung to the rest of the body. They are shaped into a biconcave disc, with a thinner layer in the middle and a thicker layer around the rims. Such a shape allows them to increase the area of the surface, which, in turn, creates space for the diffusion of gases into and out of the cell (Shier et al., 2019). Moreover, this shape shortens the distance for diffusion, where the cell membrane is set closer to hemoglobin molecules. Therefore, red blood cells assist the transference of oxygen across the organism, which supplements the body with needed nutrients.

Another significant part of blood is white blood cells, or leukocytes, that serve as protectors of the organism. They fight bacteria, viruses, and other damaging bodies that threaten human health. They are responsible for preventing illnesses, and a person’s health directly depends on the quality of their work. There are five main types of white blood cells in circulating blood. They differ in the shape of their nucleus, size, and the nature of the cytoplasm. These are neutrophils, eosinophils, basophils, monocytes, and lymphocytes. The first three belong to the granulocytes group, while the last two to the agranulocytes group. They differ in the composition of their cytoplasmic granules, where granulocytes have a more prominent granular cytoplasm. Shier et al. (2019) describe the functions of each type of white blood cell. Neutrophils are the blood cells that come first at the site of the infection. Their task is to phagocytize bacteria, some viruses, and fungi. Eosinophils manage allergic reactions and protect the rest of the body from the infestation of parasitic worms. Basophils respond to neutrophils by migrating “to damaged tissues where they release histamine, which promotes inflammation and heparin, which inhibits blood clotting, actions that increase blood flow to injured tissues” (Shier et al., 2019, p. 537-39). Therefore, the function of the granulocytes group is to take the first act in fighting the infection.

Agranulocytes are responsible for the composition of the organism’s adaptive immunity to prevent potential reoccurring infections. For example, monocytes are similar to neutrophils because they also phagocytize bacteria and other debris in the tissues, only outside the bloodstream. Lymphocytes divide into two groups: T cells and B cells which are essential for the immune system. While “T cells directly attack microorganisms, tumor cells, and transplanted cells, B cells produce antibodies, which are proteins that attack foreign molecules” (Shier et al., 2019, p. 537-39). Thus, granulocytes and agranulocytes represent the protectors of the body from infections and help to develop a stronger immune system.

Shier, D., Butler, J., & Lewis, R. (2019). Hole’s human anatomy and physiology (15th ed.). McGraw-Hill Education.

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Discuss the composition and functions of mammalian blood - KCSE Biology Essays

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Mammalian blood consists of two main components: Blood plasma; and the blood cells; (Red blood cells/Erythrocytes, White blood cells/Leucocytes and Platelets/Thrombocytes);

Blood plasma transport nutrients (glucose, amino acids, vitamins, fatty acids and glycerol, dissolved oxygen) to tissues; transports hormones, enzymes/metabolic regulators to target organs and tissues; Transport excretory substances/wastes from the cells; to excretory organs for elimination from the body; Distribute heat energy; helping in thermoregulation; Transports/contains water, plasma proteins and dissolved mineral salts; important in osmoregulation; Suspends blood cells;

Red blood cells transport oxygen; and dissolved carbon (IV) oxide; helps in regulation of pH;

White blood cells help in protection/immunity; by engulfing or producing antibodies to kill/destroy invading micro-organisms/pathogens;

Platelets help in blood clotting; preventing excessive blood loss; entry of pathogens; and promotes healing of wounds;

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Composition of the Blood and Reflection of the Health State of Human Body

Federal Research and Clinical Center for Reanimatology and Rehabilitation; MRC Immunculus - Biomarker Group, Moscow, Russia.

Corresponding Author E-mail: [email protected]

DOI : https://dx.doi.org/10.13005/bpj/1551

Blood (blood plasma) is a special all-pervading substance, functionally co-tuning all organs, tissues and cells of the body. To some extent blood is similar to the Ether of the ancients. In addition to performing house-keeping functions, blood is a medium for the transfer of huge amounts of information, which is continuously exchanged between all the compartments and structures of the macro-organism and its microbiome. This information is transmitted mostly in the form of chemical signals (peptides, micro-RNA, extracellular DNA, the products of the microbiome, antibodies, etc.), the totality of which controls lots of biological processes. Blood is not only a controlling, but also a reflecting environment: dynamic changes in the composition of this environment carry information about the smallest changes in the state of individual populations of cells, tissues, organs and the body as a whole. The prospects of practical using of information about the state of the organism, transmitted by blood and reflected in individual’s serum immunoreactivity profiles are analyzed.

Autoantibodies; Blood Plasma; Disease Markers; Micro-RNA; Peptides; Preventive Medicine

Blood has long been perceived as a kind of sacred substance that can, in particular, rejuvenate the body and stimulate tissue regeneration. Ovid in “Metamorphosis” talked about return to youth Jason’s father after replacing an old blood by a new one. Hippocrates believed that the consumption of new blood can change the mental and physical properties of a person. Pliny and Celsius reported that the sick and elderly Romans drank the blood of dying gladiators, because it was believed that it has a healing and rejuvenating effect. Many such examples are given in the article Butkevich. 1 These views have recently been confirmed in experiments, indicating a real anti-aging effect of the blood of young rats on the brain of old animals. 2

Blood (blood plasma) can be considered as a special substance that binds together, i.e. functionally matches all the organs, tissues and cells of the body. Blood is an all-pervading, peculiar environment, to some extent similar to the Ether of the ancients (all-filling entity, providing the transmission and distribution of interactions between all objects of the Universe). On the one hand, the blood performs house-keeping functions – brings oxygen and nutrients to the tissues and takes out the products of catabolism, and on the other hand is a medium for the transfer of huge amounts of information, which are continuously exchanged between the numerous structures of the macro-organism and its microbiome. This information is transmitted, for the most part, in the form of chemical signals.

Multiple chemical signals of blood plasma – hormones, growth factors, cytokines, chemokines, extracellular nucleic acids, antibodies, etc., creates a highly ordered information environment that controls lot of simultaneously occurring biological processes of the human body. It is important that the blood is not only the controlling, but also the reflecting medium – dynamic changes in its composition reflect the smallest changes in the state of individual cells, tissues, organs and the body as a whole. The “mirror of chemical signals” reflects any beginning pathological events that accompany existing diseases or can lead to future diseases. Besides this “mirror” allows to objectively and impartially assess the dynamics of an individual’s aging. It is only important to learn how to use this magic mirror.

Of course, it would be very tempting to have at your disposal and all the necessary technical equipment and have a powerful mathematical apparatus that allows you to identify and analyze the correlation between changes in the content of thousands of molecular components of blood in different functional states of the body. This would allow to engage in a systematic “bridging” between the whole set of dynamic changes occurring at the molecular, cellular, tissue and other levels and the functioning of integral living systems in norm and pathology. However, even if we had everything necessary for the analysis of everything at once, it is not necessary to amuse yourself with deterministic illusions a la Laplace (« The Brain that this moment would know all forces acting in nature, and relative location of its component parts … for him, there would be nothing unclear in the future and in the past…». 3 ) Let’s not forget that living systems, like any super complex systems, are characterized by a high degree of uncertainty (indeterminacy, stochasticity).

Blood Peptides

The peptides (oligopeptides, i.e. containing less than 50 amino acid residues) are hormone-like molecules involved in the regulation of many physiological functions. Peptides are functioning as intercellular and intersystem communicators in many cases. In particular, changes within the ratios between several dozens of pro -inflammatory and anti-inflammatory cytokines in blood set resultant vectors of development of systemic and local immuno-inflammatory and regenerative processes. Oligopeptides participate in the modulation of neurophysiological mechanisms of the most motivations, regulate circadian sleep-awake rhythms, as well as the mechanisms of learning and memory. 4,5

Micro-RNA and Extracellular DNA in the Blood

A separate “Kingdom” is presented by circulating in the blood many thousands of short (usually 18-25 nucleotides) interfering micro-RNA molecules, potentially able to quickly control gene expression and, accordingly, participate in the regulation of a wide range of physiological processes. 6 It is assumed, although even less studied, the regulatory properties of extracellular blood DNA. 7

Exogenous Regulatory Molecules in the Blood

Since the beginning of the XXI century, biologically active molecules of non-organism origin involved in the regulation of body functions have attracted considerable attention. For example, recently it was found that molecules synthesized by the symbiotic microflora directly participate in the regulation of the physiological functions of the host-organism. For instance, short-chain fatty acids of microbial origin, act as specific ligands that bind some forms of olfactory chemoreceptors of vascular walls and participate in the regulation of vascular tone. 8 Products of partial hydrolysis of food, entering the general blood flow from the intestinal villi, can affect the emotional status of children and adults: for example, peptide ligands of opiate receptors derived from our food or exorphines. 9

The role of biologically active microbiota products, as well as derivatives of our daily food entering the blood, is getting down to be disclosed. The structure and functions of numerous small RNAs and extracellular DNAs and regulatory peptides (oligopeptides) of blood plasma also have been investigated insufficiently. The high lability of most of them, as well as the complexity or high cost of dynamic measurements of their content greatly hinders their study. In this respect, the obvious advantage belongs to the other, probably the most numerous and most diverse macromolecules of blood, namely antibodies. In addition, it should be noted that antibodies are characterized by an extremely wide range of antigenic (epitopic) specificity, i.e. molecular-functional variants. It is very important that antibodies are characterized by high stability in vivo and in vitro, that permits operating with antibodies not only to trained researchers, but to laboratory doctors with using simple and cheap equipment of typical clinical laboratories.

Immune Reflection

New opportunities for research of an organism in norm and pathology, were opened as a result of transformation of views on a role of a biological role of the immune system. The beginning of this transformation was laid by Elia Mechnikoff, who believed that the fight against harmful microbes is no more than one of the particular manifestations of much more wider homeostatic functions of the immune system. 10 In the last 20 years, it has come to realize that the immune system is a reflective system, which accurately reflecting any changes occurring in the body. As a result, today the biological role of the immune system is considered not so much from the “classical” microbiological positions, but based on the following provisions 11-14 :

The immune system provides a constant screening of the molecular structure of the body.

The immune system is involved in molecular-cellular homeostasis, primarily through participation in auto-clearance and auto-repair processes.

The immune system is involved in the functional adjustment (co-tuning) of many different cells, tissues and organs for the orderly and harmonious functioning of a whole organism.

Many “alien” entities are present in a healthy body permanently or for a long time (normal microflora, fetus), not causing a pathological immune response, 15 but bringing obvious benefits to the host organism. 16

The immune system fights against harmful microorganisms, but ignores the non-threatening “foreign”, and actively preserves and promotes the integration of useful “foreign” in the structure of the host organism. 12,15

Natural autoantibodies and auto-reactive lymphocytes are the main tools of immune reflection and immune clearance of the body.

Serological studies on antibodies to pathogenic microbes, for example to HIV-1 antigens or Chlamidia trachomatis , etc., have long been routine – elevated titers of specific antibodies against microbial antigens indicate the presence of appropriate viruses or bacteria in the body. Parenteral administration of self-antigens, such as human chorionic gonadotropin (HCG) in pharmacological dosages, also lead to an increase of antibodies to HCG. 17 Similarly, the increase in the production of self-antigens causes an increase in the synthesis of antibodies to them. For example, an increase in the expression of insulin receptors, for many months and years precedes the development of type-2 diabetes, is accompanied by an increase in anti-receptor antibodies 18 ; increased synthesis of apoptosis regulatory protein p53 leads to the rise of antibodies to p53. 19 These and similar examples illustrate the phenomenon of immune reflection, i.e. the ability of the immune system to respond to changes in the content of any antigens in the body by quantitative changes in the production of appropriate antibodies. The corresponding antibodies are involved in the implementation of the basic (archetypal) function of the immune system – its participation in the body’s clearance from the excess of any molecules that potentially can disturb homeostasis. 13 Antibodies mark particles or molecules intended for disposal by macrophages and stimulate phagocytic activity in dozens and hundreds of times. The content of autoantibodies of different specificity can vary significantly, but serum levels of autoantibodies of the same antigen specificity are similar in all healthy adults. 20 In the pathology, accompanied by the death of certain specialized cells, the synthesis of autoantibodies to their antigens prominently grows.

Autoantibodies as Markers of Disease

Today it has become common place to talk about the rise of serum levels of certain autoantibodies, as markers of conditions and diseases, not attributable to a cohort of autoimmune, for example, in stroke, cancer, myocardial infarction, complicated pregnancy, etc. 12,15,21,22 The development of any chronic disease is associated either with the activation of certain cell types of cell death, or with abnormalities in the expression, secretion or utilization of their antigens. The persistent increase in the extracellular content of any autoantigen is accompanied by an increase in the production of autoantibodies to this antigen. 23 Thus, the transient increase in autoimmune reactions caused by tissue damage or disorders represent a universal physiological response of the immune system, aimed at increasing clearance of damaged tissue and activation of regeneration.

The possibility to use the phenomenon of immune reflection of pathological changes in practical medicine was realized with the help of ELI-Test technology based on the analysis of serum immunoreactivity profiles, i.e. on selective changes in serum content of autoantibodies of certain specificity. 13 It is important that the increased production of certain antibodies can be detected after a few days from the beginning of the pathological process, long before the clinical manifestation of the disease. Therefore, the analysis of changes in the markers of future disease (“mirror of antibodies”) provides an opportunity to “work” with the disease ahead of the curve, i.e. months and years before its clinical manifestation. Such approaches allow us to move from words to action, in relation to the needs of preventive medicine.

Conflict of Interest

There is no conflict of interest.

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Poletaev A. B. Antibodies to insulin receptors as biomarkers-precursors of type 2 diabetes mellitus. Terra Medica. 2013;1(71):22–26.
Lubin R., Schlichtholz B., Bengoufa D. Analysis of p53 antibodies in patients with various cancers define B-Cell epitopes of human p53: Distribution on primary structure and exposure on protein surface . Cancer Res. 1993;53:5872–5876.
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18.1 Functions of Blood

Learning objectives.

By the end of this section, you will be able to:

Identify the primary functions of blood, its fluid and cellular components, and its characteristics

Identify the primary functions of blood in transportation, defense, and maintenance of homeostasis
Identify the primary proteins and other solutes present in blood plasma
Name the fluid component of blood and the three major types of formed elements, and identify their relative proportions in a blood sample

Recall that blood is a connective tissue. Like all connective tissues, it is made up of cellular elements and an extracellular matrix. The cellular elements—referred to as the formed elements —include red blood cells (RBCs) , white blood cells (WBCs) , and cell fragments called platelets . The extracellular matrix, called plasma , makes blood unique among connective tissues because it is fluid. This fluid, which is mostly water, suspends the formed elements and enables them to circulate throughout the body within the cardiovascular system.

Functions of Blood

The primary function of blood is to deliver oxygen and nutrients to, and remove wastes from, the body cells; but that is only the beginning of the story. The specific functions of blood also include defense, and maintenance of homeostasis, such as distributing heat where it is needed.

Transportation

Nutrients from the foods you eat are absorbed in the digestive tract. Most of these travel in the bloodstream directly to the liver, where they are processed and released back into the bloodstream for delivery to body cells. Oxygen from the air you breathe diffuses into the blood, which moves from the lungs to the heart, which then pumps it to the rest of the body. Moreover, endocrine glands scattered throughout the body release hormones into the bloodstream, which carries them to distant target cells. Blood also picks up cellular wastes and byproducts, and transports them to various organs for removal. For instance, blood moves carbon dioxide to the lungs for exhalation from the body, and various waste products are transported to the kidneys and liver for excretion from the body in the form of urine or bile.

When damage to the vessels results in bleeding, blood platelets and certain proteins dissolved in the plasma, interact to create clots which block the ruptured areas of the blood vessels involved. This protects the body from further blood loss.

Maintenance of Homeostasis

Recall that body temperature is regulated via a negative-feedback loop. If you were exercising on a warm day, your rising core body temperature would trigger several homeostatic mechanisms, including increased transport of blood from your core to your body periphery, which is typically cooler. As blood passes through the vessels of the skin, heat would be dissipated to the environment, and the blood returning to your body core would be cooler. In contrast, on a cold day, blood is diverted away from the skin to maintain a warmer body core. In extreme cases, this may result in frostbite.

Blood also helps to maintain the chemical balance of the body. Proteins and other compounds in blood act as buffers, which help to regulate the pH of body tissues. Blood also helps to regulate the water content of body cells because it has large proteins that exert osmotic pressure, which resist excessive fluid loss from the blood.

Composition of Blood

If you have had a blood test, it was likely drawn from a superficial vein in your arm, which was then sent to a lab for analysis. Some of the most common blood tests—for instance, those measuring lipid or glucose levels in plasma—determine which substances are present within blood and in what quantities. Other blood tests check for the composition of the blood itself, including the quantities and types of formed elements.

One such test examines hematocrit, which measures the percentage of RBCs (erythrocytes) in a blood sample. It is performed by spinning the blood sample in a specialized centrifuge, a process that causes the heavier elements suspended within the blood sample to separate from the lightweight, liquid plasma ( Figure 18.1.1 ). Because the densest elements in blood are the erythrocytes, these settle at the bottom of the hematocrit tube. Located above the erythrocytes is a pale, thin layer composed of the remaining formed elements of blood. These are the WBCs (leukocytes) and the platelets (thrombocytes). This layer is referred to as the buffy coat, and it normally constitutes less than 1 percent of a blood sample. Above the buffy coat is the blood plasma, normally a pale, straw-colored fluid, which constitutes the remainder of the sample.

The volume of erythrocytes after centrifugation is also commonly referred to as packed cell volume . Typically, blood contains about 45 percent erythrocytes, however, samples can vary significantly from about 36–50 percent. Normal hematocrit values for females range from 37 to 47%, with a mean value of 41%; for males, hematocrit ranges from 42 to 52%, with a mean of 47%. The percentage of other formed elements, the WBCs and platelets, is extremely small so it is not normally considered with the hematocrit. Therefore, the mean plasma percentage is the percent of blood that is not erythrocytes: for females, approximately 59% (or 100 minus 41), and for males, approximately 53% (or 100 minus 47).

Characteristics of Blood

When you think about blood, the first characteristic that probably comes to mind is its color. Blood that has just taken up oxygen in the lungs is bright red, and blood that has released oxygen in the tissues is a darker red. This is because hemoglobin is a pigment that changes color, depending upon the degree of oxygen saturation.

Blood is viscous, with a viscosity approximately five times greater than water. Viscosity is a measure of a fluid’s thickness or resistance to flow, and is influenced by the presence of the plasma proteins and formed elements within the blood. The viscosity of blood has a dramatic impact on blood pressure and flow. Consider the difference in flow between water and honey. The more viscous honey would demonstrate a greater resistance to flow than the less viscous water. The same principle applies to blood. Blood viscosity is inversely proportional to hydration; the more hydrated you are, the less viscous your blood becomes. In severely dehydrated individuals, blood can become excessively viscous sometimes resulting in infarction or other cardiovascular events.

The normal temperature of blood is slightly higher than normal body temperature—about 38 °C (or 100.4 °F), compared to 37 °C (or 98.6 °F) for an internal body temperature reading. Although the surface of a blood vessel is relatively smooth, blood experiences friction and resistance to its flow. This produces heat, accounting for the slightly higher temperature of blood.

Blood constitutes approximately 8 percent of adult body weight. Adult males typically average about 5-6 liters of blood, and females average 4–5 liters.

Blood Plasma

Plasma is 92% water. Dissolved or suspended within this water is a mixture of substances, most of which are proteins. There are hundreds of substances dissolved in the plasma, although many of them are found only in very small quantities.

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Plasma Proteins

Approximately 7 percent of the plasma is made of proteins. These include several plasma proteins (proteins that are unique to the plasma), plus a much smaller number of regulatory proteins, including enzymes and hormones. The major components of plasma are summarized in Figure 18.1.2 .

The three major groups of plasma proteins are as follows:

Albumin is the most abundant of the plasma proteins. Manufactured by the liver, albumin molecules serve as binding proteins—transport vehicles for fatty acids and steroid hormones. Recall that lipids are hydrophobic; however, binding to albumin enables their transport in the watery plasma. Albumin is also the most significant contributor to the osmotic pressure of blood; that is, its presence holds water inside the blood vessels and draws water from the tissues, across blood vessel walls, and into the bloodstream. This in turn helps to maintain both blood volume and blood pressure. Albumin normally accounts for approximately 54 percent of the total plasma protein content, or 3.5–5.0 g/dL of blood.
The second most common plasma proteins are the globulins . A heterogeneous group, there are three main subgroups known as alpha, beta, and gamma globulins. The alpha and beta globulins transport iron, lipids, and the fat-soluble vitamins A, D, E, and K to the cells; like albumin, they also contribute to osmotic pressure. The gamma globulins are proteins involved in immunity and are better known as an antibodies or immunoglobulins . Unlike alpha and beta globulins, which are produced in the liver, immunoglobulins are produced by specialized leukocytes known as plasma cells. Globulins make up approximately 38 percent of the total plasma protein volume, or 1.0–1.5 g/dL of blood.
The least abundant plasma protein is fibrinogen . Like albumin and the alpha and beta globulins, fibrinogen is produced by the liver. It is essential for blood clotting, a process described later in this chapter. Fibrinogen accounts for about 7 percent of the total plasma protein volume, or 0.2–0.45 g/dL of blood.

Other Plasma Solutes

In addition to proteins, plasma contains a wide variety of other substances. These include various electrolytes, such as sodium, potassium, and calcium ions; dissolved gases, such as oxygen, carbon dioxide, and nitrogen; various organic nutrients, such as vitamins, lipids, glucose, and amino acids; and metabolic wastes. All of these non-protein solutes combined contribute approximately 1 percent to the total volume of plasma.

This table lists the components of blood, the percentage of each component, their site of production, and their major functions.

Career Connection – Phlebotomy and Medical Lab Technology:

Medical or clinical laboratories employ a variety of individuals in technical positions:

Medical technologists (MT), also known as clinical laboratory technologists (CLT), typically hold a bachelor’s degree and certification from an accredited training program. They perform a wide variety of tests on various body fluids, including blood. The information they provide is essential to the primary care providers in determining a diagnosis and in monitoring the course of a disease and response to treatment.
Medical laboratory technicians (MLT) typically have an associate’s degree but may perform duties similar to those of an MT.
Medical laboratory assistants (MLA) spend the majority of their time processing samples and carrying out routine assignments within the lab. Clinical training is required, but a degree may not be essential to obtaining a position.

Chapter Review

Blood is a fluid connective tissue critical to the transportation of nutrients, gases, and wastes throughout the body; to defend the body against infection and other threats; and to the homeostatic regulation of pH, temperature, and other internal conditions. Blood is composed of formed elements—erythrocytes, leukocytes, and cell fragments called platelets—and a fluid extracellular matrix called plasma. More than 90 percent of plasma is water. The remainder is mostly plasma proteins—mainly albumin, globulins, and fibrinogen—and other dissolved solutes such as glucose, lipids, electrolytes, and dissolved gases. Because of the formed elements and the plasma proteins and other solutes, blood is more viscous than water. It is also slightly alkaline, and its temperature is slightly higher than normal body temperature.

Interactive Link Questions

There are values given for percent saturation, tension, and blood gas, and there are listings for different types of hemoglobin.

Review Questions

Critical thinking questions.

1. A patient’s hematocrit is 42 percent. Approximately what percentage of the patient’s blood is plasma?

2. Why would it be incorrect to refer to the formed elements as cells?

3. True or false: The buffy coat is the portion of a blood sample that is made up of its proteins.

Answers for Critical Thinking Questions

The patient’s blood is approximately 58 percent plasma (since the buffy coat is less than 1 percent).
The formed elements include erythrocytes and leukocytes, which are cells (although mature erythrocytes do not have a nucleus); however, the formed elements also include platelets, which are not true cells but cell fragments.
False. The buffy coat is the portion of blood that is made up of its leukocytes and platelets.

This work, Anatomy & Physiology, is adapted from Anatomy & Physiology by OpenStax , licensed under CC BY . This edition, with revised content and artwork, is licensed under CC BY-SA except where otherwise noted.

Images, from Anatomy & Physiology by OpenStax , are licensed under CC BY except where otherwise noted.

Access the original for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .

Anatomy & Physiology Copyright © 2019 by Lindsay M. Biga, Staci Bronson, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Kristen Oja, Devon Quick, Jon Runyeon, OSU OERU, and OpenStax is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License , except where otherwise noted.

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Blood Circulation in The Human Body

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Short / Long answer type questions. Write an essay on the composition of blood.

$$\textbf{solution:}$$ $$\bullet$$ blood is a type of connective tissue that is fluid in nature. $$\bullet$$ blood is divided into two components. $$\bullet$$ there are two parts in blood. namely, plasma and formed elements (red and white blood cells and platelets. $$\textbf{red blood cells}$$ the most prevalent cells in blood are red blood cells, also known as erythrocytes. $$\bullet$$ they have a biconcave form and are devoid of a nucleus. $$\bullet$$ rbcs contain the pigment haemoglobin, which binds to oxygen and transports it. $$\textbf{white blood cells}$$ leucocytes are another name for white blood cells. $$\bullet$$ they're amoeboid, which means they can squeeze their way through blood arteries. $$\bullet$$ diapedesis is the medical term for this condition. $$\bullet$$ granulocytes and agranulocytes are two types of leucocytes. $$\bullet$$ neutrophils, basophils, and eosinophils are granulocytes. $$\bullet$$ monocytes (phagocytic in nature) and lymphocytes are agranulocytes (responsible for immune responses). $$\textbf{platelets}$$ platelets are also known as thrombocytes. $$\bullet$$ they are the tiniest produced elements and are not real cells, but rather cell fragments. $$\bullet$$ they are devoid of nuclei and perform a crucial function in clotting..

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Essay On Blood Pressure Notes

Updated essay on blood pressure notes.

Physiology and Pharmacology

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How is blood pressure physiologically regulated? How can this be modulated by drugs?

Blood pressure

The mean arterial pressure is calculated by cardiac output x peripheral resistance. Changes in either of these factors lead to changes in blood pressure. In an average person the blood pressure measured by a sphygomomanometer is 120/80, however these measurements often vary during the day and increases with age due to atherosclerosis. During excercise and intense emotion the release of systemic hormones causes an increase in blood pressure whereas during sleep there is a drop in blood pressure. However deviations in blood pressure from its set point leads to autoregulatory mechanisms which restore it to its normal level. It is important for the body to maintain a high constant blood pressure within a narrow range as it ensures optimum organ perfusion and efficient glomerular filtration. It also overcomes high tissue pressure in eye. If the pressure is too low the patient is in shock whereas the pressure is too high the patient is hypertensive and if pressure is at either of these two extremes local blood flow can no longer be regulated by myogenic and metabolic autoregulation. Short term regulation of blood pressure, which takes seconds to minutes occurs through neural pathways and targets the heart, vessels and the adrenal medulla. In comparison long term regulation targets mostly the kidneys which control the extracellular fluid. In patients whose biological mechanisms that regulate blood pressure have failed require drugs are required to maintain a constant blood pressure.

One way blood pressure is regulated is through neural reflexes. During rest the C1 neurons of the medulla vasomotor centre exerts a tonic activity on the sympathetic vasoconstrictor nerves which results in basal vasoconstriction. The activity of C1 neurons was shown when clonidine was injected which bound to imidazole receptors and resulted in an inhibition of the C1 neurons and this led to a decrease in blood pressure. When there is an acute change in blood pressure there is a change in the activity of baroreceptors which results in a neural reflex that brings mean arterial pressure back to normal. Baroreceptors are stretch receptors that detect expansion in vascular walls. The activity of baroreceptor reflexes was shown by an expirement carried out by Heyman. When adrenaline was injected into dogs there was a subsequent rise in blood pressure but due to the neural reflex this was followed by a decrease in heart rate. To show that is was neuronal activity rather than hormones in the blood stream that resulted in bradycardia Heyman cross perfused 2 dogs where one dog had nerves connected but its blood supply to its head coming from the 2 nd dog. When the 1 st dog was injected with adrenaline there was a decrease in heart rate showing that it was neuronal activity.

Baroreceptor control of arterial pressure

High pressure baroreceptors are found at the carotid sinus and the aortic arch. The carotid sinus is very elastic and is located on the internal carotid artery just above the position where the carotid artery bifurcates into the internal and external artery. The second high pressure baroreceptor is found in the aortic arch which is also elastic but has a high compliance that allows it to distend during left ventricular ejection. Both of the aortic arch and carotid sinus baroreceptors are made up of a mixture of A and C fibres. A fibres have a large diameter, are fast conducting, myelinated and have a low threshold. These fibres are active at normal blood pressure. Whereas C fibres which are more abundant, are myelinated, slow conducting, have a small diameter and high thresholds. Having a mixture of the two types of muscle fibres allows recruitment of different fibres according to the blood pressure. The terminals of these fibres express nonselective cation channels which are from the TRP family.

When there is an increase in transmural pressure difference the blood vessel is enlarged and this deforms TRPC1 channels which results in a depolarising inward current and forms the receptor potential. To show that these channels are stretch sensitive rather than pressure sensitive, the vessels was prevented from being stretched which resulted in the failure to open the TRPC1 channels even when there is an increase in transmural pressure.

The receptor potential is a graded response where the amplitude of the depolarisation is proportional to the amount the blood vessel is stretched. The depolarisation produced results in a biphasic response as there is an initial large increase in depolarisation, known as the dynamic component, followed by steady depolarisation. If the carotid sinus or the aortic arch is distended rapidly it results in a high frequency of action potentials which is then followed by a lower frequency of action potentials. In the carotid sinus the impulses travel through the sinus nerve which joins the glossopharngeal nerve. Likewise the aortic arch baroreceptor transmits its impulses through the depressor branch of the vagus nerve. In both cases the afferent nerves transmit impulses to the medullary cardiovascular centre and synapse with neurons in the nucleus tractus solitarii by releasing glutamate which binds to AMPA receptors. This results in the stimulation of inhibitory interneurons which originate in the nucleus tractus solitarii and synapse with C1 neurons in the vasomotor area. The inhibition of the C1 neurones results in a decrease in the amount of neurotransmitter released that results in vasoconstriction. This results in a decrease in basal activity of the sympathetic vasoconstriction which causes vasodilation and causes a reduction in a total peripheral resistance. The afferent nerve fibres in the nucleus tractus solitarii also innervate excitatory interneurons which synapse with the cardioinhibitory area which includes the nucleus ambiguous and dorsal motor nucleus of the vagus. Innervation...

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Oxbridge Notes
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Types of Blood Cells

Red blood cells (Erythrocytes)

White blood cells (Leucocytes)

Types of White Blood Cells

Granulocytes

Eosinophils

Neutrophils

Lymphocytes

Platelets (Thrombocytes)

Components Of Blood

Red Blood Cells (RBC)

White Blood Cells (WBC)

Blood Vessels

Recommended Video:

Types of Blood Vessels

Layers of Blood Vessels

Functions of Blood

Fluid Connective Tissue

Transports Hormones and Nutrients

Homeostasis

Blood Clotting at Site of Injury

Transport of waste to the Kidney and Liver

Protection of the body against pathogens

Frequently Asked Questions

3. State the different types of white blood cells found in the blood.

4. What are granulocytes?

5. What are agranulocytes?

6. Name the various components of blood.

7. What are the various types of blood vessels present in our body?

8. What are sinusoids?

9. Name the various layers of blood vessels.

10. Name the major functions of blood.

11. What gives blood its red colour?

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Blood Cells and Their Functions Essay

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Blood Circulation in The Human Body

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