Leukocytes

Special Characteristics

Leukocytes, or white blood cellsThe basic structural and functional units of life., leave the bloodstream to respond to infection or tissue damage through a process called diapedesis. This process involves three main steps: adhesionThe tendency of water molecules to stick to other substances., diapedesis itself, and chemotaxis. First, during adhesion, leukocytes slow down and adhere to the blood vessel wall near the site of infection. This occurs due to cellular signals such as cytokines. They lead endothelial cells lining the blood vessels to express adhesion moleculesGroups of atoms bonded together. like selectins and integrins. Leukocytes bind to these molecules, rolling along the vessel wall and eventually sticking firmly, a process known as margination.

Next, the leukocytes undergo diapedesis, where they squeeze between endothelial cells to exit the bloodstream. The cells loosen their tight junctions, allowing leukocytes to migrate through without damaging the vessel wall. Once outside the vessel, the leukocytes follow a chemical gradient—a process called chemotaxis—toward the site of infection or injury. This gradient is created by signaling molecules such as chemokines or other pathogen-associated signals. By detecting these gradients through surface receptorsProteins located on the surface or inside cells that bind specific molecules (e.g., neurotransmitter, leukocytes move directionally toward the highest concentration of signals. This allows them to arrive at the site of infection where they can combat pathogens. They also contribute to tissue repair.

Leukocytes

The first line here shows your lymphocytes—these are B and T cells. They have very big nucleiClusters of neurons in the CNS responsible for processing information., almost engulfing the whole cell. The first cell here is a B cell, and B cells have antibodies on them. The official name for an antibody is an immunoglobulin, and we’re going to call them Igs. B cells have Igs on them. These other cells here are T cells, and these T cells have their own receptors called TLRs. You don’t have to worry about that name. Just know they have their own receptors that are different from antibodies.

Cell Lineage

Hematopoietic stem cells are responsible for giving rise to all the formed elementsThe cellular components of blood, including red blood cells, white blood cells, and platelets. in your blood and osteoclasts (just FYI).  Hematopoietic stem cells can divide into myeloid stem cells. You can see that these stem cells lead to a majority of the formed elements in blood.  They can also divide into lymphoid stem cells. These lymphoid stem cells give rise to all the different types of lymphocytes such as B, T, and NK cells.  So, these are all lymphocytes over here.  The myeloid stem cell differentiates into a megakaryocyte. The megakaryocyte fragments into platelets and red blood cells. It also produces the remaining four leukocytes: basophile, eosinophils, monocytes, and neutrophils.

Monocytes

Monocytes float in your blood and then enter into tissues like the liverA large organ that produces bile, detoxifies blood, and stores nutrients., lungs, and skinThe body’s largest organ, providing protection and regulation., where they permanently live. Once they enter tissues, they end up with receptors that help them eat certain cells or any foreign invader. Interestingly, B cells have the same receptors. Monocytes can enter tissues and become macrophages where they eat items in the cell through endocytosisThe process of a cell engulfing material by wrapping its membrane around it. usually carrier mediated. Monocytes can also turn into dendritic cellsImmune cells in the epidermis that help fight infections. which are pinocytes. These cells drink the interstitial fluids and are common in skin and lymph nodes.

Microphages

In your blood are two types of cells referred to as microphages. Neutrophils and eosinophils are granular leukocytes with pink stained granules in the cytoplasmThe gel-like substance within a cell that contains organelles and cytosol.. The granules in eosinophils are much larger than those in neutrophils. This gives neutrophils a pinkish color to their cytoplasm. Neutrophils have multi lobed nuclei they’re also the most common leukocyte found in blood. So when in doubt the answer is probably neutrophil.. As you age, neutrophils gain more compartments as they record pathogens they encounter in DNA. For example, if you get chickenpox, your body records that as DNA, storing it in the nuclei of neutrophils. Eosinophils, another granular leukocyte, stain red and are parasitic fighters. If you’re infected with a digestive parasite, eosinophils come to the rescue

Basophils

Basophils are the only granular leukocyte that has purple granules in the cytoplasm. Similar to eosinophils the granules in basophils are enormous. In factA statement based on direct observation that is repeatedly confirmed. they’re so large that they tend to block out the view of the nucleusThe control center of the cell that contains DNA and directs cellular activities. in the cell. The purple granules contain heparin and histamine two molecules that respond to allergic reactions. Heparin and histamine, among other things, act as vasodilators. They dilate blood vessels, allowing neutrophils to enter into damaged tissues via chemotaxis and diapedesis.

Lymphocytes

Lymphocytes all derive from a lymphoid cell not a myeloid cell. Lymphoid cells have a whole bunch of different machinery than any other cells in your body. These cells are specifically made to kill other cells or pump out a whole bunch of antibodies. Lymphocytes can break into natural killer cells, T cells, or B cells. Within those 3 categories, there are other classifications. The cells can be divided based on the protein receptors embedded in their cell membranes. Lymphocytes are usually much smaller than all of the other leukocytes and their nucleus takes up almost the entirety of the cell period