|The Body's Sentinels|
|Czech Title||Tělesná stráž|
|Original (French) Title||Les Sentinelles du corps|
|Birth||The Bone Marrow|
The episode begins with a short montage of a male prehistoric Homo sapiens facing off biologic factors that used to threaten him, and then the scene from present where the similar looking human takes his son to visit to the zoo. Then, the narrator neglects any signs that the dangerous animals that can be found at the zoo and pretty small ones are man's greatest enemies and introduces our microscopic tiny enemies: bacteria, viruses, toxins etc. that can cause terrible infections.
The scene cuts to a brief presentation of all White Blood Cells explained by the Colonel. He states the following facts to the young Leukocytes that are being taught the basics of defending the body:
- There are approximately 4 billion white blood cells in human body.
- Most of white blood cells are created in the bone marrow.
- Average number of newborn leukocytes per day is 15 billion.
The scene changes to the fresh leukocytes having fun and playing in the bloodstream. Then, Lieutenant Jumbo assembles them in a group so they can prepare for their classes in the thymus and are dismissed with promise that their lives will be interesting and that their jobs will be the best of all blood cells.
The Colonel introduces the mechanisms of Viruses (represented by Nabot) and Bacteria (represented by Stroppy) and that it's important to recognize them on first glance and destroy them. He also informs the class to make sure they never attack the bacteria of intestinal flora because of their contributions to digestion. During the class, Paul, a future T Lymphocyte, has problems keeping his colleague awake to pay attention to class.
The Colonel offers Lieutenant Claire to join the class and teach the class for some time by herself. She complies and begins teaching the class on basics of traversing the bloodstream, changing their surroundings and recognizing the components of blood. She also points out that mistakes can happen if the Leukocyte is poorly educated which contributes to anemia. As soon as she mentions this, Paul, annoyed, wakes up his sleepy colleague.
The Colonel requests Captain Peter to join the class as well and he quickly arrives. He takes charge of the class and gives a presentation of Macrophages, Basophils and Neutrophil Granulocytes. He introduces the battle mechanics of B and T Lymphocytes and introduces Antibodies, where Paul is confused to why are they programmed to react to only one type of enemy. He is also confused by the fact that there can be very few police vehicles and that there can be too many enemies, to which Peter gives the answer:
"In the first place, we're never alone. The others arrive as soon as we call. And then, there's mitosis, the divison of the cell."After introducing the Basophils, an Interferon arrives and informs of an ongoing infection and Peter, Claire and Jumbo leave the thymus. The Colonel resumes the class and gives a "What have we learned today" tour, showing the pictures of pathogens and then a picture of E. coli. Colonel sternly calls Paul's colleague who mistakes it for a dangerous bacterium. Disappointed, he requests him to stay and repeat the class.
Paul, now a T Lymphocyte, heads on a mission with Claire. They set off from a lymphatic vessel and reach their destination, where he and his colleague examine a mutated tissue. They find cancerous cells and quickly unleash their cytotoxic substances. Soon after, the group enters the jugular vein, reaches the heart and enters pulmonary circulation where they separate.
Paul enters a bronchiole where the air circulates peacefully. Then, a drop of water splashes on the inner wall, revealing a virus that infests the other cells with his colleagues, threatening to cause pneumonia. Paul, determined and unconvinced by chastising from the virus leader, contacts Claire and tries to fight the viruses off in the meantime. He soon feels the lose of hope seemingly unable, but his two Lymphocyte B colleagues arrive and help him out, and perform mitosis in the end. Paul requests for Macrophages and Claire congratulates him on trying to stop a virus infestation.
- This is the first episode to center on a type of blood cell.
- This is the first episode to openly feature pathogens.
- This episode is given as an educational presentation of leukocytes in the body.
- First episode not to feature Maestro.
- White blood cells, commonly known as leukocytes, are blood cells coming from immune system with a role to defend the body from disease and foreign intruders.
- They are the only blood cells that possess nuclei and are less numerous, but also the most diverse.
- When it comes to the structure of their nuclei, white blood cells are classified as granulocytes (grainy cytoplasm and the nucleus divided into lobes) and agranulocytes (clear cytoplasm and circular nucleus).
- White blood cells are commonly created in the bone marrow just like the most of blood cells. This is not the only case, as they can also come from and develop in thymus, lymph nodes and the spleen.
- There are three basic types of leukocytes:
- Type B lymphocytes are created and they develop in bone marrow. They create antibodies to recognize pathogens and destroy them.
- Type T lymphocytes are also created in bone marrow, but they develop in thymus, contrary to B lymphocytes. They can be cytotoxic, which are the only ones that fight enemies directly, while helper cells and suppressor cells have a role of regulation in immunologic response by releasing cytokines which triggers the behavior of (mainly) effecting cells in lymphatic system.
- Natural killer cells are created in bone marrow and are abbreviated as NK cells. Their role is unique and that is to prevent malignant cells and tumors from developing.
- Granulocytes, which make up the most of white blood cells and are recognized for having nuclei divided into lobes and grainy cytoplasm. There are three main types: neutrophils, eosinophils and basophils.
- Monocytes, which convert to macrophages when changing their surroundings. Then, macrophages have roles of "vacuum cleaners" that, just like neutrophil granulocytes, have the ability to perform phagocytosis ("eating") natural debris and pathogens.