Phagocytosis and the Immune Response
What are the roles of leucocytes in Phagocytosis and secretion of
The roles of cellular components of the blood are vital in the
transport of respiratory gases and in the defence against disease. The
role of white blood cells (also known as leucocytes) are concerned
with the defence of the body against disease.
Leucocytes are nucleated cells present in the blood. They are less
numerous in comparison to red blood cells: there are around 7000 per
nmÂ³ of blood compared with 5000000 red cells. There are three main
types of leucocytes; these are neutrophils and monocytes, which carry
out the process of Phagocytosis, which involves engulfing, and
destroying the bacteria. Lymphocytes are the third and they secrete
antibodies and help form part of the body's immune system. One of the
functions of lysosomes is to digest material taken into the cell body
by the process of Phagocytosis. Once a white cell has left the blood
vessel and migrated to the enemy, the next job is to eat the microbe.
This human macrophage like its cousin the neutrophil is a professional
"phagocyte" or eating cell (phago = "eating", cyte = "cell"). But
eating the organisms is not enough. To insure that the organisms not
grow and divide within the macrophage, the white cell must kill the
organisms by some means such as the oxidative burst. This process is
shown in the diagram below.
Reference: John Adds - 1999 - Respiration and coordination
Lysosome digests the bacteria cell
Oxidative burst occurring to destroy the yeast.
Macrophages, which are similar to the monocytes, are also derived from
the stem cells in the bone marrow. These cells are present in the
liver, spleen and lungs. The lung alveolar macrophages move around the
macrophages in the liver, called Kupffer cells, are fixed. All these
white blood cells confer non-specific or natural immunity and are the
first cells to be active during an infection of the body.
We are all surrounded by bacteria, viruses, fungi and other organisms
that are capable of invading our bodies and causing disease. We are
able to overcome these pathogens (disease-causing organisms) because
we have an immune system. This is a complex system that allows us to
develop immunity - resistance to infections.
The non-specific immune response
Inflammation is triggered by damaged cells. Ruptured cells and some
white cells release alarm chemicals such as histamine and kinins.
These substances dilate blood vessels and increased blood flow leads
to the classic signs of inflammation.
Complement is a collection of several proteins found in the blood
plasma. It is called this because it...