Reflection assignment hematology

Take a moment to consider this question: “What is blood made of?” Anatomy not only refers to types of cells, tissues, and structures we can see, but also the ones we do not typically see on the surface. This includes blood. While we may think of blood as a liquid, it is actually a connective tissue. Blood is the body’s only fluid connective tissue. Like other connective tissue, it contains cells and extracellular components. Just one pint of blood contains over 2 trillion red blood cells, and the average human body contains 5 Liters, making up approximately 7% of an adult’s weight. Blood is not solely comprised of red blood cells, though. Blood also contains leukocytes and thrombocytes. The blood cells, also referred to as formed elements, only comprise 45% of the human body’s blood. All of these blood cells originate from hematopoietic stem cells within the red bone marrow.

Components of blood’s formed elements

Erythrocytes

The red blood cells, erythrocytes, have no nucleus. This lack of a nucleus creates space for the red blood cell’s key molecular composition: hemoglobin. 95% of the cell is made up of these hemoglobin molecules, which carry oxygen to tissues and remove waste. They do not survive indefinitely, as their life span is only 100-120 days.

Hematocrit

Hematocrit, a component of a complete blood count (CBC), measures what percent (by volume) of the whole blood is composed of red blood cells. A normal hematocrit for females is 37-47%. A normal hematocrit for males is 42-52%. A low hematocrit may indicate anemia, ulcers, or rapid blood loss. An elevated hematocrit may indicate polycythemia. Polycythemia has a range of causes from low oxygen availability at altitude to bone marrow cancer.

Antigens

The red blood cells carry identification proteins called antigens on their surface; these antigens are like nametags that identify the blood type. Type A blood carries A-antigens. Type B blood carries B-antigens. Type AB blood carries both antigens. Type O blood carries neither antigen. Those with type AB blood are termed universal recipients, as they can receive any blood type. Those with type O blood are called universal donors, as they can donate to any recipient, regardless of blood type.

Rh Factor

Red blood cells may also carry another antigen called Rh factor. When this is present, a + follows the blood type. For example, AB+ means the red blood cells carry A-antigens, B-antigens, and Rh-antigens. When Rh antigens are absent, a – follows the blood type. For example, O- blood has no antigens at all.

Antibodies

After birth, the blood plasma develops antibodies that help protect the body’s own red blood cells. Matching blood types is critical for transfusions to avoid potentially lethal clotting reactions created by plasma antibodies that will attack foreign cells.

Blood-type compatibility (Betts et al., 2013)

Blood type antigens and antibodies (Betts et al., 2013)

Leukocytes and Thrombocytes

While the erythrocytes make up 90% of the cells, the other 10% of the blood cells are leukocytes and thrombocytes. Leukocytes, also known as white blood cells (WBC), protect the body as part of the immune system. Thrombocytes, also known as platelets, serve the body’s hemostasis in vessel blood clotting.

Leukocytes are classified by their structure as granulocytes or agranulocytes. The granulocyte category includes three cell types:

· Neutrophils comprise 50-70% of the overall WBC count. They respond with elevation in the presence of almost any bacterial infection or inflammation.

· Eosinophils comprise 2-4% of the overall WBC count. They respond to parasitic infections.

· Basophils comprise up to 1% of the WBC count. They release histamine to respond to allergens or inflammation.

Agranulocytes come in two varieties:

· Lymphocytes comprise 25-45% of the WBC count. They reside in lymphatic tissue and come in T cell and B cell forms.

· Monocytes comprise 3-8% of the WBC count. Some of these cells become macrophages which are responsible for cleaning up debris within the human body through a process called phagocytosis.

Types of leukocytes (Betts et al., 2013)

Plasma

While 45% of the blood is made of cells, or formed elements, the other 55% is fluid referred to as plasma. The plasma is made of 92% water. 7% is made of proteins such as hormones and enzymes, which include albumin, globulins, and fibrinogen. The remaining 1% is comprised of electrolytes, gasses, vitamins, minerals, lipids, glucose, amino acids, and metabolic wastes.

Components of plasma

Now that we have examined what blood is made of, we will move onto physiology, referring to blood’s functions. 

Resource(s)

Betts, G. J., Desaix, P., Johnson, E., Johnson, J. E., Korol, O., Kruse, D., Poe, B., Wise, J. A., Womble, M., Young, K. A., & O. (2013). Anatomy and Physiology (1st ed.). OpenStax. https://openstax.org/details/books/anatomy-and-physiology