A Deep Dive - Blood Basics

Abstract

Blood serves a vital role in the well-being of human health. With the ability to protect against foreign substances through its immune capabilities, regulate internal body temperature through its predominant water-based composition, and maintain internal balance of pH to prevent acidosis or alkalosis by serving to keep the body at a neutral range, understanding the properties of blood serves to be useful in extreme cases of emergency. In the case of blood transfusion, the characteristics and makeup of blood are important to understand before performing urgent operations. Despite these overall properties, blood types are unique among humans; blood cannot be shared between any two individuals. With differences between antigens and antibodies that prevail among A, B, AB, and O blood types, it is crucial to understand the compatibility among them prior to following through with safe blood transfusions. There is a deeper understanding that must be attained prior to using its properties to benefit the lives of human beings.

Introduction

Contributing 10% to an adult’s total weight, blood is a crucial aspect of our physiology that can be used to gain a deeper understanding as to the function and regulation of the human body. Blood serves to protect the body through its immune components, regulate body temperature despite constantly evolving external environments, and balance internal pH levels to maintain the body’s internal environment, blood proves to be a vital element within life-or-death circumstances, while being independent enough to establish ease among everyday routines. Understanding the characteristics and properties of blood in terms of its function, composition, and production enables the ability to use it as a means of regulating and benefiting human well-being.

The foundation of blood in terms of its function, composition, and production serves a vital role in the application of maintaining and revitalizing human health. Through its ability to regulate human well-being, protect from external threats, and routinely regenerate, blood proves to be significant in the overall balance of human sustenance. With the ability to regulate pH, body temperature, and provide protection, blood serves as a crucial factor in life-or-death situations, while being a self-reliant way of allowing us to thrive in daily activities.

Lesson 1 - Components, Production and Function of Blood

Function of Blood

Blood serves various functions within the body, each of which is vital to maintaining homeostasis, or balance, throughout a constantly fluctuating external environment.

Blood serves as a necessary means of transportation within the body, carrying within it oxygen, carbon dioxide, hormones, and heat and waste products to and from several body tissues.

Blood plays a key role in regulating the body, including maintaining a balance in pH levels through the use of buffers (such as bicarbonate) which help convert strong acids and bases that pose a threat to our health into weaker, more neutral ones. It further acts as an aid in the regulation of body temperature; the water that makes up the majority of blood plasma has both heating and coolant properties, while blood itself has a variable rate of flow through the skin. These two properties allow blood vessels to contract and dilate to control the amount of water that reaches the skin. In times of exercise, for example, when the body produces an excess amount of heat, you may notice that you begin to sweat. This can be credited to the blood vessels near your skin’s surface that dilate to release water and heat from the skin, preventing overheating and serving as an internal means of temperature regulation. In contrast, constriction of these blood vessels will prevent the evaporation of water from skin pores and in turn, retain heat.

Blood finally acts to protect the human body. Blood itself prevents the loss of blood through a complex coagulation cascade and its ability to form clots in the case of injury and exposure of blood to the external environment. Blood operates to prevent disease as it contains components of the immune system such as leukocytes, commonly referred to as white blood cells (WBCs), and several antibodies that can attach to a foreign substance and signal for its destruction.

Components of Blood

Blood is often referred to as a “liquid connective tissue” as it is composed of a liquid extracellular matrix, which we refer to as blood plasma. This component dissolves and suspends within it various cell fragments. The components of blood can be separated and observed with the use of a centrifuge, a device that operates by separating liquids and their components according to their density By obtaining a healthy blood sample and placing it into a centrifuge, its components will separate by weight [Figure 1]. The result reveals that plasma is the least dense, yet most abundant component of blood, making up 55% of its entirety. Plasma is composed mainly of water but is additionally made up of proteins, glucose, hormones, ions, metabolites, and lipids (fats). Proteins such as albumin, fibrinogen, globulins, and other coagulation factors that give blood its protective property can also be found within the plasma of the blood. Slightly more dense than plasma, the second and least abundant component of blood is referred to as the “buffy coat”. The buffy coat is made up of leukocytes (WBCs) and platelets, a vital component in the blood clotting process. During times of an infection, when the white blood cells count is higher, a blood sample may reveal a thicker buffy coat. In general, the buffy coat makes up <1% of the entirety of blood.

[Figure 1] Centrifugation of a Healthy Blood Sample

At the bottom of the centrifuge is the most dense layer, consisting of the erythrocytes, or Red Blood Cells (RBCs). The erythrocytes are sometimes referred to as the hematocrit, or packed red cell volume and makes up 45\% of whole blood. These Red Blood Cells make up most of the formed elements in the blood, each cell with a diameter of 7.5 microns and a thickness of 2 microns. The Red Blood Cell has a strong, flexible membrane and retains a biconcave disc shape [Figure 2] from ejecting its nucleus during development to make more internal space for oxygen transport. This shape is optimal for the red blood cells as it provides the greatest surface area to volume ratio for such a simple shape, allowing for increased oxygen and carbon dioxide diffusion. Without a nucleus - and thus the absence of DNA - an erythrocyte cannot repair itself upon damage. The cell’s lack of a nucleus also deprives it of mitochondria, preventing the erythrocyte from generating its own energy; the cell must generate ATP for energy anaerobically. Each cell contains a Hemoglobin molecule consisting of two alpha and two beta polypeptide chains, each of which has an iron-containing heme group, which is credited for giving blood its red colour. The iron molecule at the centre of each group is capable of combining with exactly one oxygen molecule. Thus, each Red Blood Cell can carry up to four oxygen molecules, which binds reversibly; oxygen binds at the lungs and is released at body tissues.

[Figure 2] Top and Side View of a Healthy Red Blood Cell (RBC)

Production of Red Blood Cells

The production of Erythrocytes (RBCs) is referred to as Erythropoiesis [Figure 3]. These formed elements start forming in the bone marrow as a pluripotent stem cell; this type of stem cell has the capability of giving rise to a variety of different cell types, including Red Blood Cells. From this stem cell, it becomes what is called a proerythroblast. The term blast indicates that it is a precursor to the desired cell. At this point, the nucleus is ejected from the centre, obtaining its characteristic biconcave disc shape. Once the nucleus is ejected, the cell is referred to as a reticulocyte, which in essence is an immature blood cell. At this stage, the cell exits the bone marrow through a sinusoidal capillary, a vessel with pores large enough to allow for diffusion for larger molecules such as blood cells. Within 1-2 days, the cell matures and is now referred to as an erythrocyte.

[Figure 3] Stages of Erythropoiesis

Lesson 2 - Blood Typing

Understanding the function, composition, and production of the blood paves way for applying knowledge within the medical field. Most commonly, in emergency situations, blood transfusions require assessing the blood type of both the donor and recipient. Blood transfusions cannot occur between any two participants; mixing incompatible blood types will lead to fatality for the recipient whose body mistakes foreign blood components as a threat.

Terminology

Antigens (Agglutinogens)	Existing on the surface of RBCs, they are any substance that can cause an antibody response to be generated
Antibodies (Agglutinins)	Found in blood plasma; a blood protein responsible for responding to and counteracting specific antigens.

[Figure 4] Antibodies and Antigen Interaction on a Red Blood Cell

It is important to note that you do not have antibodies in your plasma that will react with the antigens on your own red blood cells. You will have antibodies in your plasma for antigens that your Red Blood Cells lack. There are four blood types; A, B, AB, and O. [Table 1] shows the antigen and antibody characteristics present within each of these blood types, while [Table 2] explains which blood types are compatible with one another.

Blood Type	A	B	AB	O
RBC	A Antigen	B Antigen	A Antigen B Antigen	None
Plasma	Anti-B Antibody	Anti-A Antibody	None	Anti-A Antibody Anti-B Antibody

[Table 1] Antigen and Antibody characteristics of each blood type

Blood Type	Antigen	Antibody	Compatible Donor Blood Types
O	None	Anti-A Anti-B	O
A	A	Anti-B	A, O
B	B	Anti-A	B, O
AB	AB	None	A, B, AB, O

[Table 2] Compatibility among different blood types

From the following information, it can be seen that blood with a specific antibody cannot be compatible with another blood type with that corresponding antigen. For example, a patient with Type A blood will have only the A-antigen and the Anti-B antibody. If, in a state of emergency, the patient requires a blood transfusion, they cannot receive blood from a donor with Type B blood. This is due to the patient having Anti-B antibodies, which will attack B-antigens that are present on donor Red Blood Cells, as these antigens are foreign to the recipient. In essence, blood transfusion is incompatible if the recipient blood contains the antibody corresponding to the antigen present in the donor’s blood.

From [Figure 6], it can be seen that individuals with Type O blood are referred to as Universal Donors, as there are no antigens present on their Red Blood Cells. Any individual with type A, B. AB, or O blood types will not be able to attack their antigens with their antibodies as there are no antigens to attack. Moreover, individuals with Type AB blood can be referred to as Universal Recipients as this blood type has no antibodies; without antibodies, they cannot attack any antigens that may exist on the Red Blood Cell of any donor.

The makeup and characteristics of blood serve as an important field of knowledge within the medical field in that it is paramount in life-or-death situations; in cases of volumetric shock (extreme blood loss), anemia (lack of adequate blood transfusion), cancer, hemophilia (insufficient blood clotting), and many severe cases, understanding blood and its properties proves to be a vital factor in saving lives.

Conclusion

The foundation of blood in terms of its function, composition, and production serves a vital role in the application of maintaining and revitalizing human health. Through its ability to regulate human well-being, protect from external threats, and routinely regenerate, blood proves to be significant in the overall balance of human sustenance. With the ability to regulate pH, body temperature, and provide protection, blood serves as a crucial factor in life-or-death situations, while being a self-reliant way of allowing us to thrive in daily activities.

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