Explain why a person can catch a cold several times in a year but only catches measles once in his or her lifetime
A person can catch a cold several times in a year because there are many different strains of the cold virus and the body's immune system is not able to build up long-lasting immunity to all of them. This means that even if a person has had a cold before, they can still catch a different strain of the virus.
On the other hand, a person only catches measles once in their lifetime because the measles virus stimulates the immune system to produce long-lasting immunity. Once a person has had measles, their body develops antibodies that can recognize and fight off the virus if they are exposed to it again. Therefore, the person becomes immune to future measles infections.
Distinguish between blood, plasma, serum, tissue fluid and lymph
Blood is a fluid connective tissue that circulates throughout the body, delivering oxygen and nutrients to the tissues and carrying away waste products from the cells.
Plasma is the liquid component of blood that contains water, electrolytes, hormones, clotting factors, and proteins such as albumin, globulin, and fibrinogen.
Serum is the clear, yellowish fluid that remains after blood has clotted and the clot has been removed. It contains the same components as plasma, except that it lacks the clotting factors.
Tissue fluid, also known as interstitial fluid, is the fluid that surrounds the cells in the body's tissues. It is formed from plasma that has leaked out of the capillaries and contains water, electrolytes, nutrients, and waste products.
Lymph is a fluid that is similar in composition to tissue fluid but is found in the lymphatic vessels and lymph nodes. It is formed from tissue fluid that has been absorbed into the lymphatic vessels and contains immune cells and lymphocytes that help to fight infections and diseases.
A person can catch a cold several times in a year because the common cold is caused by various types of viruses, such as rhinovirus or coronavirus. These viruses continuously mutate, which means that even if you have been infected with one strain of the virus and developed immunity to it, you can still catch a cold from a different strain that your immune system hasn't encountered before.
On the other hand, a person typically only catches measles once in their lifetime due to the nature of the virus. Measles is caused by the measles virus, which is highly contagious and spreads through respiratory droplets. However, once a person contracts and recovers from measles, their immune system develops antibodies that provide lifelong immunity against future infections by the same virus.
To get more specific about how the immune system works in this case, when a person is infected with a virus, their immune system produces specialized proteins called antibodies to combat the infection. These antibodies recognize specific antigens on the surface of the virus and neutralize them, preventing the virus from causing further harm. Additionally, the immune system retains a "memory" of previous infections, allowing it to respond more effectively if the same virus is encountered again in the future.
With the common cold, there are many different strains of viruses that cause similar symptoms, but they have enough genetic variability that the immune response to one strain may not fully protect against another. This is why it is possible to catch a cold multiple times in a year.
In the case of measles, the virus has certain unique characteristics that make it less prone to genetic variability. Therefore, once a person's immune system successfully fights off the measles virus, it develops long-lasting immunity, and subsequent encounters with the same virus are effectively prevented.
It is important to note that there are exceptions to these general patterns. Immunity can vary among individuals, and in some cases, the immune system may not develop a strong and lasting response to certain viruses. Additionally, new strains of viruses can emerge, posing challenges to existing immunity. Therefore, vaccines become crucial in providing additional protection against multiple strains of viruses and preventing recurring infections.