Circulatory System: Functions of Blood-2

White Blood Cells:

Leukocytes, often known as white blood cells or WBCs (leuko = white; cytes = cell), have a variety of functions in the body's defense against pathogens. When compared to RBCs, they are considerably different in terms of size, number, and purpose. Their count ranges from 4000 to 11000 cells per microlitre of blood, or roughly 1% of the total volume of blood. The typical organelles and nuclei are present in WBCs. The WBCs typically lack color, unlike the RBCs which have a distinct hue.

Protecting the body from harm caused by viruses, bacteria, parasites, and other poisons is the main purpose of WBCs.

Depending on whether they do or do not have obvious chemically loaded cytoplasmic granules, WBCs are divided into two main groups. As follows:

1. Granulocytes:

Granules can be seen in the cytoplasm of granulocytes, therefore the name. Neutrophils, eosinophils, and basophils are granulocytes. These three varieties of granulocytes stain to reveal colored granules under the microscope.

• Neutrophils:
  • Because their granules absorb both basic (blue) and acidic (red) dyes, giving the cytoplasm an overall lilac hue, the neutrophils are named neutrophils (neutral = loving). They have lysozyme, peroxidase, and other antibiotics in their very small cytoplasmic granules. They make up at least half of all WBCs. Typically, the nucleus is separated into three lobes that are joined by incredibly thin chromatin filaments. Because of the variety of nuclear shapes found in neutrophils, they are also known as polymorphonuclear leukocytes (PMNs).
  •  Functions of Neutrophils:
  • Neutrophils serve as the body's major defense against foreign substances that enter the body. When there is an injury or infection, neutrophils move from the blood vessels into the tissues. Through a process known as diapedesis, they pass along the endothelium, adhere to it, and then squeeze between endothelial cells to exit the blood artery. By responding to chemicals emitted by harmed cells and microorganisms, they must also find areas of tissue injury and infection. Chemotaxis is the name given to this chemical phenomenon. Neutrophils do not leave the tissues after they have entered the bloodstream. The main tool of neutrophils in the tissues is phagocytosis. Phagocytosis includes ingesting bacteria or particles, moving them along (by generating flowing cytoplasmic extensions), and then digesting the items inside the cell.
  • Additionally, the neutrophilic granules are expelled extracellularly, which directly triggers the inflammatory response. Additionally, they indirectly stimulate the complement system.
• Eosinophils:
  • Due to their noticeable, typically bi-lobed nucleus and big granules, eosinophils are easily identified. Eosinophils are eosinophilic (eosin - loving) and acidic dyes cause them to color red-orange.
  • Between 1% to 4% of all lice infestations and allergy diseases are caused by them. In cases of parasite infestation and allergic reactions, the blood eosinophil count rises. 
  •  Functions of Eosinophils:
  • Eosinophils are experts at removing parasites that are too big for phagocytosis. Chemicals released by eosinophil granules are harmful to parasite larvae. Additionally, they suppress mast cell degranulation and break down histamine.
• Basophils:
  • The proportion of basophils in the WBC population is only 0.5%. The pale nucleus of basophils is typically covered by the coarse granules. They tint blue and purple with basic dyes because they are basophilic (= basic-loving). 
  •  Functions of Basophils:
  • The role of basophils Basophils' role is not well known. They might contribute to the manifestation of IgE-mediated allergies. Histamine, a vasodilator, is present in the basophil granules and promotes blood flow to tissues. Additionally, it contains the anticoagulant heparin, which increases the mobility of other WBCs by preventing clotting.

 2. Agranulocytes:

The agranulocytes, which lack cytoplasmic granules that may be seen, comprise lymphocytes and monocytes.

• Lymphocytes:
  • Based on a cell's diameter, lymphocytes (lympha = water) are categorized as tiny or large. A lymphocyte's spherical nucleus almost completely fills the cell, leaving just a little border of transparent, light blue cytoplasm. Although there are many lymphocytes in the body, the blood vessels only contain a small part of all of them. Under a light microscope, lymphocytes can be divided into a number of subclasses with various immunological roles. The bone marrow and other lymphoid tissues create lymphocytes. T lymphocytes and B lymphocytes are the two primary subtypes of lymphocytes. B lymphocytes mature in the bone marrow while T cells do so in the thymus gland.
  • Functions of the Lymphocytes:
  • Indirectly contributing to acquired specific immunity are lymphocytes. The initial antigen recognition is largely mediated by T cells. The effector cells in cell-mediated immunity are these cells. The effector cells in humoral immunity are B lymphocytes. The immune system's capabilities have been covered in great detail.
• Monocytes:
  • The largest of the generated pieces, monocytes (monos = sing), often have a diameter that is twice that of an erythrocyte. The monocyte nucleus is typically kidney-shaped, and it has a lot of blue-gray cytoplasm. From the circulation, the monocytes move into the tissues, where they grow and develop into highly mobile macrophages. The mononuclear phagocytic system (MPS), once known as the reticuloendothelial system, is now thought of as the circulating counterpart of that system (RES). These macrophages, whose population is on the rise, actively phagocytose chronic inflammation or infection.
  • Functions of Monocytes:
  • Macrophages destroy the particles and phagocyte microorganisms. The senescent RBCs are likewise destroyed.

Platelets:

The term "platelet" comes from the Greek word "thrombos," which means "clot," and "kytos," which means "cell." Platelets are tiny (2–4 micron), irregularly shaped blood cells. They are pieces of cells, not cells in and of themselves. Blood coagulation requires platelets (clotting). They have lysosomes, the toplasmic reticulum, a Golgi complex, and Golgi granules, which are home to a number of elements crucial to platelet function. There are between 130,000 and 400,000 mm3 of platelets. The platelet has a life expectancy of 9 to 12 days. The spleen obliterates them. The spleen functions as both a repository and a cemetery for platelets.

Functions of Platelets:

• Hemostasis is mostly connected to platelet functions.
• They release substances known as procoagulants or clotting factors that help blood clot.
• They release vasoconstrictors, which ruptured arteries experience as vascular spasms.
• For a momentary clotting effect, they create platelet plugs.
• Blood clots that have outlived their usefulness are broken up by them.
• They release substances that entice neutrophils and monocytes to inflammatory areas.
• Growth factors that mimic mitosis in the vascular wall are secreted by them. These protect the blood vessel linings that have been injured.

Haemostasis:

When blood arteries rupture, a sequence of reactions known as hemostasis cause the blood flow to cease.

This reaction is prompt, focused, and precisely managed. It involves numerous blood coagulations found in plasma as well as additional compounds that platelets and wounded tissues release. Haemostatic mechanisms include:

• Vascular Spasm (Vasoconstriction):
  • Vascular spasm, or the prompt constriction of the ruptured vessel, is the most effective immediate defense against blood loss. Several elements contribute to the spas response being triggered when the blood vessels are injured. Pain receptors are stimulated by an injury, which causes them to contract. This impact only lasts for a short while, but by the time it fades, other systems have taken over. Vasoconstriction lasts longer when the blood vessel's smooth muscle is injured. Serotonin is released when platelets come into contact with injured blood arteries. The vessels are constricted by a chemical vasoconstrictor. The vascular spasm is thus maintained for a long enough period of time for the other haemostatic mechanisms to kick in.
•  Platelet Plug Formation:
  • In healthy blood arteries, platelets ordinarily do not cling to the endothelium (inner lining). Collagen fibers from the vessel's wall are exposed to the blood when a vessel is damaged, though. Platelets become sticky when they come into touch with collagen and attach to the vessel and to other platelets. Serotonin, adenosine diphosphate (ADP), and thromboxane are just a few of the chemicals that platelets emit as they aggregate and draw more platelets to the damaged location. The resulting mass of platelets is known as a platelet clog. It can rapidly cause a modest blood vessel burst and lessen or halt minimal bleeding.