Neutrophil
Overview
Neutrophils are the most abundant type of white blood cells in most mammals. They form an essential part of the innate immune system. Their primary function is to neutralize pathogens through phagocytosis, a process of engulfing and then digesting cellular debris and foreign particles.
Structure
Neutrophils are spherical cells, approximately 12-15 micrometers in diameter. They possess a characteristic multi-lobed nucleus, typically composed of three to five lobes connected by thin strands. This unique structure has led to neutrophils being colloquially referred to as "polymorphonuclear leukocytes". The cytoplasm of neutrophils is rich in granules, which contain a variety of enzymes and proteins crucial for the cell's function.
Function
Neutrophils play a key role in the body's defense against bacterial infections. They are among the first responders to arrive at the site of an infection, where they perform their primary function - phagocytosis. This process involves the engulfment of pathogens, which are then trapped in a phagosome, or a vacuole within the neutrophil. The phagosome then fuses with a lysosome, another smaller organelle within the neutrophil that contains digestive enzymes. These enzymes break down the pathogen, effectively neutralizing it.
In addition to phagocytosis, neutrophils can combat pathogens through a process known as neutrophil extracellular trap (NET) formation. During NETosis, a neutrophil undergoes a unique form of cell death, releasing its DNA and granular contents into the extracellular space. These components form a sticky network that can trap and neutralize pathogens.
Life Cycle
The life cycle of a neutrophil begins in the bone marrow, where it is produced from a stem cell in a process known as hematopoiesis. Once mature, neutrophils are released into the bloodstream, where they circulate for about 6-7 hours. They then migrate into tissues, where they can survive for 1-2 days before undergoing programmed cell death, or apoptosis.
Clinical Significance
Changes in the number of neutrophils in the blood can be indicative of various health conditions. A higher than normal count, or neutrophilia, can be a sign of an ongoing bacterial infection, inflammation, or stress. On the other hand, a lower than normal count, or neutropenia, can make an individual more susceptible to infections. Neutropenia can occur due to various reasons, including certain medications, chemotherapy, radiation therapy, or bone marrow disorders.