Red Blood Cell Study Guide: Exploring Structure and Function
A River of Life
Red blood cells also known as erythrocytes are the river of life. Although their life span is short, (about 120 days) they are numerous, making up 99 percent of all blood cells outnumbering white blood cells 1,000 to 1. This is good news for us because without this little red wonder our body cells would shut down and quickly drown in their own poisonous waste. It is the one cell that operates without a nucleus (the nucleus pops out shortly before leaving the bone marrow and entering the bloodstream) or mitochondria. Ironically, it provides all the oxygen but takes none for itself and so must rely on anaerobic respiration. Without a nucleus and mitochondria to take up space, this leaves lots of room for transporting what all cells need, oxygen.
Shape Fits The Function
Under a microscope, a red blood cell looks like a jelly donut with its center pushed in. The biconcave shape allows for increased surface area and flexibility as it squeezes through the tiniest of capillaries for delivery of oxygen from the lungs to body tissues. The oxygen is exchanged for carbon dioxide, the chief waste product of cellular respiration, which gets shuttled back to the lungs to be exhaled.
Red blood cells use the protein hemoglobin to transport oxygen. Hemoglobin occupies about a third of the cell body-roughly 280 million molecules of the stuff are packed into a single cell! Each of the four identical subunits that make up hemoglobin contain a heme portion, a globin chain, and an iron atom that binds to oxygen. Increases in temperature and blood acidity (low pH) as well as the presence of certain chemicals cause hemoglobin to release more oxygen to body cells. For example, when you exercise, your metabolism increases. This causes body temperature to go up. Blood acidity also rises due to all that carbon dioxide being dumped out by body cells, increasing the need for oxygen. Hemoglobin is more attracted to carbon monoxide than oxygen which is why CO is so dangerous to breathe in. Carbon monoxide squeezes out oxygen for space and you suffocate to death.
Sickle Cell Anemia
It’s a big problem when red blood cells can’t carry enough oxygen to meet the needs of body cells. A genetic disease known as sickle cell anemia changes the hemoglobin, transforming the red blood cell’s round biconcave shape into a longer, thinner sickle like shape. This not only cuts down on the surface area available for O2 but makes it difficult for red blood cells to squeeze through the capillaries without getting stuck. When this happens it causes severe pain and can be life threatening.
1. Trace the path of a RBC delivering O2 from the lungs, to the heart and body tissues.
2. Compare RBC to other cells (neurons, for example) contrasting their similarities and differences (RBC have no nuclei or mitochondria, live a short time due to inability to replace worn out parts; neurons don’t divide but have a nucleus, mitochondria, etc.) Compare normal RBC to sickle celled shaped ones using slides or pictures. List reasons why the RBC shape is advantageous? How does the sickle cell shape limit surface area and transport of oxygen? Construct a normal and abnormal RBC using modeling clay, pipecleaners, beads, etc. Include hemoglobin, oxygen, iron atom in model.
3. For fun, try Dracula’s Dinner experiment to show how alteration of RBC shape impairs movement through capillaries.
Test Your Knowledge
1.Red blood cells don’t have mitochondria or a ____________.
2. The red blood cell’s _______________shape provides increased surface area for oxygen transport.
3. Red blood cells use the protein __________________ to transport oxygen.
4. _________________ is a genetic disease that causes the red blood cell to change its shape and impair oxygen transport.
5. Factors that affect hemoglobin’s release of oxygen to body cells are ______________, _____________, and ____________.
1. nucleus 2. biconcave 3. hemoglobin 4. sickle cell anemia 5. temperature, blood acidity, other chemicals.