Characteristics of Blood

Physical Characteristics

If we were in class, I would ask the students, “What blood diseases do you know of?” They would respond with many terms, some of which I might not have heard before. Some might mention lymphoma, leukemia, thalassemia, sickle cell anemiaA condition characterized by a deficiency of red blood cells or hemoglobin, leading to reduced oxyge, pernicious anemiaA type of anemia caused by a deficiency of intrinsic factor, leading to poor vitamin B12 absorption., or iron deficiency anemia. We will cover all of these diseases, but we will focus specifically on anemia. All these conditions relate to red blood cellsThe basic structural and functional units of life. and, ultimately, your ability to carry oxygen.

Next, I would ask the class, “What are some of the characteristics of blood that you know?” Someone might yell out, “It’s thicker than waterThe universal solvent essential for life.,” which is true—this is called viscosityThe thickness or resistance to flow in a fluid, such as blood.. Viscosity means resistanceThe opposition to airflow in the respiratory tract, influenced by airway diameter. to flow. Blood flows more slowly than water and is similar to maple syrup. Others might say it tastes like metal. This taste comes from hemoglobinThe oxygen-carrying protein in red blood cells that gives blood its red color., a molecule in blood that contains iron. Some might note that blood is red. They may mention that it can appear dark red. It can also appear ruby red, depending on whether it has oxygen bound to it or not.

In textbooks, systemic circuitThe part of the circulatory system that carries oxygenated blood from the heart to the body and retu diagrams often show arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr as red. This indicates oxygenated blood. Veins are shown as blue to represent deoxygenated blood. Capillaries are displayed as purple, where the exchange of gases occurs. Blood in your veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge is not blue; the color coding is simply a teaching tool. In the pulmonary circuitThe circulation of blood between the heart and the lungs, where blood is oxygenated., the colors are reversed. Arteries transport deoxygenated blood to the lungs to pick up oxygen, while veins carry oxygenated blood back to the heart. Remember, the colors indicate oxygen levels and not the actual color of the blood.

Blood is a CT

Recall that any connective tissue is basically just a bunch of cells suspended in a gooey substance much like gelatin. Similar to this disgusting fruit mold, the fruit pieces are like the specialized cells. The gelatin acts as the matrix of this connective tissue. Remember that a matrix is composed of a ground substance which is usually water and proteinsLarge molecules made of amino acids with various functions in the body.. Blood and lymph are fluid connective tissues. Although these 3 terms still apply, they are used in very special circumstances. Instead of calling things cells in blood we call them formed elementsThe cellular components of blood, including red blood cells, white blood cells, and platelets.. This is because some people don’t consider red blood cells to be fully functional cells because they lack a nucleusThe control center of the cell that contains DNA and directs cellular activities.. Other people don’t consider platelets to be cells since they are technically fragments of cell. So we say that blood has formed elements not specialized cells. As far as the ground substance that’s just water. But contained in this water are a bunch of nutrients a bunch of ionsCharged atoms or molecules. and specifically lots of plasmaThe liquid component of blood. proteins. This abundance of plasma proteins is an exception to the usual three proteins found in connective tissue. These include collagenA structural protein in the dermis that provides strength and elasticity., elastin, and reticular fibers.

Blood is a fluid connective tissue. It consists of specialized cells such as red blood cells, white blood cells, and platelets. It also contains plasma proteins and water as its “ground substance.” On a histological slide of blood, you can see red blood cells. They look like Cheerios. You also see white blood cells, which are larger with visible nucleiClusters of neurons in the CNS responsible for processing information., and tiny platelets.

Components of Whole Blood

Whole blood is a very specific term and I need you to start using it.  What you see in the test tube on the left here can be referred to as blood. However, the technical term is whole blood. This is similar to calling these cells over here white blood cells. Their technical term is leukocytes. Also, down here we have red blood cells. Their technical term is erythrocytes(RBCs): Red blood cells responsible for oxygen transport.. When you say whole blood to me, I think of all of these components. These include red blood cells, white blood cells, platelets, and plasma. This makes a difference because not all of these components are given to patients when they need blood transfusions.

What’s in the bag depends on what the patient needs. If we were to centrifuge this test tube of whole blood very fast, we would see three different layers. We could also rotate it rapidly. These layers separate by density. The lightest component is this yellowish substance called plasma. The white band in the center is the Buffy coat. It contains our leukocytes and platelets. I guess I should mention that the official word for platelets is thrombocytes. We also have this big proportion of red blood cells which are officially called erythrocytes. When you use the term whole blood in this class, I know that you mean all of these components. However, when you talk about the oxygen carrying capacity of blood, you should refer to the erythrocytes and leukocytes. When you refer to your blood’s ability to fight infection, you are specifically referring to these leukocytes.

What’s in the bag?

The blood bag on the right is obviously full of plasma containing that yellowish color. However the two blood bags on the left looked deceptively similar. One contains whole blood. This indicates that there are leukocytes and plasma contained. The other one contains only red blood cells. A bag containing only red blood cells is usually referred to by its packed cell volume. But using this term we are saying that there are only erythrocytes in an isotonicA solution with the same solute concentration as the inside of a cell, maintaining equilibrium. solutionA homogeneous mixture of two or more substances.. This slide makes it very clear why you cannot use the word blood during this class period. You need to refer to whole blood or specifically to some of its components.