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LAB: Blood Exploration

Introduction

A liquid called plasma makes up about half (55%) of the content of blood. Plasma contains proteins

that help blood to clot, transport substances through the blood, and perform other functions. Blood

plasma also contains glucose and other dissolved nutrients. The other half (45%) of blood volume is

composed of blood cells: Red blood cells, which carry oxygen to the tissues and remove carbon

dioxide as waste, white blood cells, which fight infections, and platelets, smaller cells that help blood

to clot. In this lab investigation, we will focus mainly on the structure and function of the RBCs,

examining the various morphologies of blood cells, determining the ABO blood type of individuals,

and exploring the ability of blood to buffer the circulatory system against drastic changes in pH.

PART A – Histology of Blood Smears

Red blood cells (erythrocytes) have a unique structure and properties that allow them to fulfill crucial

functions within the body. They are biconcave discs, having a depressed center on both sides. These

depressed centers allow the cells to have more cell membrane surface which can be exposed to

diffusing oxygen while transiting the lungs. This structure, along with a small size (about 7.8

micrometers) also allows them to be more flexible when negotiating tight passages.

Sometimes structural changes occur in RBCs that indicate a possible pathological

condition. For instance, one may observe enlarged RBCs with folate or vitamin

B12 deficiency (macrocytic anemia). Small RBCs may be observed with iron

deficiency or chronic blood loss (microcytic anemia). Sickle cell anemia is a

condition where a genetic flaw leads to defective hemoglobin that changes shape

under certain conditions. This shape change induces the cell to lose its original

biconcave disc confirmation and take on a more “sickled” appearance.

PART B – Introduction to Blood Typing

Red blood cells also play a role in an individual’s immune system. The basic premise

of your immune system relies on antigens and antibodies. Antigens are glycolipids that

antige

your body uses to generate antibodies, which are proteins that attack foreign invaders

that may enter your body, and prevent them from doing harm. Each antigen

produces a specific antibody that will attack a very specific foreign invader.

The surface of erythrocytes contains genetically determined glycolipids called

agglutinogens. Antigens are categorized into blood groups, two of which are the ABO and Rh groups.

There are at least 20 different blood groups in red blood cells; the major group is the ABO system.

Type A has only the A-antigen. Type B has only the B-antigen. Type AB has both A- and B-antigens,

and Type O has neither. Blood type denotes the class of antigens (glycolipids) found on the surface of

the red blood cells. Each person inherits two genes that control the production of ABO antigens. A and

B are codominant (I

and I

, respectively), and O (i) is recessive. A secondary group is the Rh factor.

85% of the population is known to have the Rh factor, and is said to be Rh+. The 15% that do not are

said to be Rh-.

A-antigens make antibodies (in the plasma) against B-antigens, etc. (This is believed to result from the

presence in the plasma of preformed antibodies, made in response to some common bacteria in the

digestive tract.) O produces both anti-A and anti-B antibodies. AB produces neither. The immune

system does not attack its own red blood cell antigens. One person’s antigens may be recognized as

foreign if transferred into another person’s body. This will trigger an immune response in which

particular lymphocytes secrete proteins called antibodies (agglutinins), which bind to antigens.

Lab: Blood Exploration

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