Assignment: A2

Introduction

In this assignment I am going to describe and discuss the human body’s immune system, its structure, function and operation by analyzing each section below.

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 infections, because we have an immune system. This is a complex system involving many different cells and tissues that allow us to develop immunity resistance to infections.

Common pathogens include bacteria, fungi, viruses and protoctists. This last group includes microscopic parasites such as Plasmodium, which causes malaria, and larger parasitic animals such as tapeworms. A pathogenic organism is able to:

  • Break through the physical barriers of the body and enter tissue or cells
  • Resist the efforts of the immune system to destroy it, long enough to multiply inside the host body
  • Transfer from one host and infect others
  • Damage the host’s tissue either directly or indirectly by means of toxins that it releases.

Immunity is a system of the body defense which offers protection against disease caused by infection. The immune system can detect the difference between your own (self) cells and non-self cells by recognizing unique protein markers which exist at cell surfaces (any cells perceived as foreign by a body’s immune system is called an antigen). The immune response is a set of reactions mostly brought about by lymphocytes to counteract infection. The main mechanisms for doing this are producing antibodies-engulfing non-self particles and neutralizing toxins. The responsibility of the immune system is huge; it must encompass a vast variety in order to react appropriately with the thousands of different and potential disease causing antigens that invade the body.

The Body’s Barriers To Infection

One of the most obvious ways to avoid infection is to stop potential pathogens getting into the body in the first place. The four main strategies that the body uses are summarized below:

  • Mechanical defense. Nasal hairs filter the air that is drawn into the upper airways. Cilia which line the airways sweep bacteria and other particals away from the lungs.
  • Physical defense. The skin made from stratified squamous epithelium, forms a tough impermeable barrier that normally keeps out bacteria and viruses. The mucous membranes that line the entry points to the body such as the nose, eyes, mouth, airways, genital openings and anus produce fluids and/or sticky mucus. These fluids trap microorganisms and stop them attacking the cells underneath.
  • Chemical defense. Fluids such as sweat, saliva and tears contain chemicals that create harsh environments for microorganisms sweat contains lactic acid and the enzyme lysozyme, both of which slow down bacterial growth. Stomach acid kills many microorganisms that manage to get that far. When we are injured blood clots at the injury site, sealing the breach to prevent entry of bacteria.
  • Biological defense. Normally a vast number of non-pathogenic bacteria live on the skin and mucous membranes. These do not harm the body but they compete with pathogenic bacteria, preventing them from gaining a foothold from which to launch a full-scale infection.    

Components

The immune system has six major components, three of which are different kinds of cells and the other three are soluble proteins. All six components can be found circulating in the blood in some form.

Cells  

The three kinds of immune system cells are granulocytes, monocyte/macrophages, and lymphocytes.

Granulocytes

Granulocytes are the most numerous nucleus containing cells in the blood and are composed of three cell types identified as neutrophils, eosinophils and basophils, based on their staining characteristics with certain dyes. These cells are important in the removal of bacteria and parasites (antigens) from the body. They seem to act as a first line of defense, as they rush toward an infected area and engulf offending antigens. They kill antigens by ingesting then destroying them using powerful enzymes usually present in the granulocytes. 

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Monocytes/Macrophages

Monocytes are only a small percentage of the many kinds of blood cells when found localized outside the blood circulation, in tissues they undergo physical and morphological changes and are called macrophages. Macrophages are important in the regulation of immune responses. They are often referred to as scavengers or antigen-presenting cells (APC) because they pick up and ingest foreign materials and present these antigens to other cells of the immune system such as T cells and B cells.

Lymphocytes

There are two kinds of lymphocytes: B lymphocytes and the T lymphocytes. Lymphocytes start out in the bone marrow and ...

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