Problem 24 - Biology E/M

Question

All of the following are true about blood EXCEPT (A) white blood cells are formed in the bone marrow (B) platelets are not cells but are cell fragments (C) arteries contain valves to help in the pumping of blood (D) the liquid portion of the blood is called plasma (E) red blood cells live about 120 days

Step-by-Step Solution

Answer

C is the false statement; arteries do not contain valves.

Step 1: Identify the task

We need to determine which of the given statements about blood is NOT true.

Step 2: Analyze Statement A

Statement A claims that white blood cells are formed in the bone marrow. This is a true statement as the bone marrow is the primary site for the formation of white blood cells.

Step 3: Analyze Statement B

Statement B claims that platelets are not cells but are cell fragments. This is true since platelets, or thrombocytes, are indeed fragments of larger cells called megakaryocytes.

Step 4: Analyze Statement C

Statement C claims that arteries contain valves to help in the pumping of blood. Typically, veins contain valves to prevent backflow of blood, not arteries. Therefore, this statement is false.

Step 5: Analyze Statement D

Statement D claims that the liquid portion of the blood is called plasma. This statement is true, as plasma makes up over half of the blood's volume.

Step 6: Analyze Statement E

Statement E claims that red blood cells live about 120 days. This is a true statement since red blood cells typically have a lifespan of around 120 days.

Step 7: Identify the exception

Based on our analysis, Statement C is the only statement that is false, making it the exception.

Key Concepts

White Blood Cells

White Blood Cells (WBCs), also known as leukocytes, are an essential part of the body's immune system. They help protect the body against infections and foreign invaders. The process of white blood cell formation is called hematopoiesis, and it primarily occurs in the bone marrow.
The bone marrow produces different types of white blood cells, including:

• Lymphocytes: which include B cells, T cells, and natural killer cells
• Neutrophils: important for phagocytosing bacteria
• Monocytes: which develop into macrophages and dendritic cells
• Eosinophils: involved in allergic reactions and parasitic infections
• Basophils: which release histamine during allergic responses

White blood cells constantly circulate in the bloodstream and transport themselves to sites of injury or infection. They can live from a few days to several months, depending on the type.

Bone Marrow

Bone Marrow is a spongy tissue found in the hollow spaces of bones. It is crucial for producing blood cells, including white blood cells, red blood cells, and platelets. There are two types of bone marrow: red and yellow.

• Red Bone Marrow: Responsible for producing blood cells. It is found in flat bones like the ribs, pelvis, and sternum.
• Yellow Bone Marrow: Contains fat cells and is found in long bones. It can convert to red marrow if the body needs more blood cells.

In addition to producing cells, bone marrow is also involved in storing iron and other minerals. The health of bone marrow is vital for a functioning immune system and maintaining overall health.

Platelets

Platelets, also known as thrombocytes, are not actually cells but rather fragments of a larger cell type known as megakaryocytes. They play a crucial role in blood clotting, which prevents excessive bleeding when injuries occur.

• Origin: Formed in the bone marrow from megakaryocytes.
• Function: Platelets adhere to blood vessel walls at the site of an injury, where they clump together to form plugs.
• Lifespan: Generally last about 7-10 days in circulation.

Platelets release chemicals that signal other platelets to the site, thus facilitating clot formation and starting the healing process. This function is critical for stopping bleeding and repairing blood vessels.

Plasma

Plasma is the liquid component of blood, making up more than half of its volume. It is a pale yellow fluid that serves many purposes in maintaining homeostasis in the body.

• Components: Plasma is primarily composed of water, but it also contains proteins, glucose, electrolytes, hormones, carbon dioxide, and blood cells.
• Functions: It transports nutrients, hormones, and proteins to the parts of the body that need it. It also helps in the removal of waste products.
• Coagulation: Plasma contains clotting factors that help in blood coagulation. When separated from blood cells, these factors are active, turning blood from a liquid into a gel during the clotting process.

Plasma also plays a role in maintaining pH balance and blood pressure, acting as a buffer in chemical reactions that occur within the body.

Red Blood Cell Lifespan

The lifespan of a red blood cell (RBC) is approximately 120 days, after which it is removed from the bloodstream by the spleen and liver. Red blood cells are crucial for transporting oxygen from the lungs to other tissues in the body and aiding in carbon dioxide removal.

• Formation: Red blood cells are produced in the bone marrow in a process called erythropoiesis.
• Structure: They have a biconcave shape, which increases their surface area for oxygen exchange.
• Hemoglobin: This is the protein inside red blood cells that carries oxygen.

The body continuously produces new red blood cells to replace the old ones, ensuring a stable supply for efficient oxygen transportation. Understanding the lifespan of RBCs helps in diagnosing and managing various health conditions associated with anemia and other blood disorders.