Anatomical barriers

Skin and mucus membrane are the examples of anatomical barriers that provides immunity.

Skin and mucus membrane:

• Skin consists of two distinct layer; a thin outer layer called epidermis and thick inner layer called dermis.
• Epidermis consists of mostly dead cell filled with keratin. Dermis is composed of connective tissue, hair follicle, sebaceous gland and sweat gland.
• Skin provides first line of defense by preventing entry of microorganisms. However skin may be penetrated by injury or insects.
• Below skin, the mucus membrane prevents the entry of microorganism to the body. And also it secrets mucus that entraps microorganisms.

Anatomical barriers provide immunity by following ways.

• At first skin and mucus membrane prevent entry of microorganism into host body by mechanical separation. For example, Skin surrounds the host body from external and mucus membrane surrounds the body tracts.
• They also have mechanism to kill the pathogen before entry to body. For example; lysozyme, acidic pH, sebum, high salt concentration in sweat are antimicrobial agents found in skin and mucus membrane.
• Skin and mucus membrane provides first line of defense against microorganism as they are first component to encounter with microorganism.

Physico-chemical barriers

• Physicochemical barrier includes physiological barrier and chemical barrier.
• Physiological conditions of body such as normal body temperature, normal body pH etc provides immunity.
• Some species are resistant to certain disease simply because of their higher body temperature. For example, mammals are susceptible to anthrax but birds are resistant to anthrax. It is because Bacillus anthracis are killed by higher body temperature of birds (39°C).
• Similarly, body pH also provides immunity. For example acidity of stomach kills most of the ingested bacteria and provides immunity. In infants stomach is less acidic. This is the reason why infants suffer more from gastrointestinal disturbance than adults.
• Chemical barriers include various antimicrobial chemicals found in body fluids. For examples, Lysozyme found in tear and mucus kills many Gram +ve bacteria.
• Interferon found in blood and lymph kills viruses. Other antimicrobial chemicals found in body fluids include complement protein, collectins, etc.

Anatomical and Physico-chemical barriers of immune system

The post Anatomical and Physico-chemical barriers of immune system appeared first on Online Biology Notes.

• Phagocytosis is an important defense mechanism of host to provide immunity. Most of the bacteria that enter into host are killed by phagocytic cells such as Neutrophils, monocytes and macrophages.
• Phagocytosis is an example of endocytosis.
• There are two types of endocytosis; phagocytosis and pinocytosis.

Steps in phagocytosis:

1. At first phagocyte approaches to the site of infection
2. Phagocyte extends pseudopodia around bacterial cell.
3. Pseudopodia gradually increase in size and finally fused so that bacteria is engulfed in the form of phagosome or food vacuole.
4. The phagosome and lysosome come nearer to each other and fuse to form phago-lysosome.
5. Inside phago-lysosome ingested bacteria is killed by hydrolytic and digestive enzyme of lysosome.
6. Required materials released from digested bacteria are absorbed into surrounding cytoplasm and undigested residues are excreted out by exocytosis.

Killing Mechanism of phagocytosis:

Killing of ingested bacteria during phagocytosis occur by two different mechanism

1. Oxygen dependent mechanism
2. Oxygen independent mechanism

1. Oxygen dependent mechanism:

• During phagocytosis, phagocytic cell increases uptake of O2. At the same time rateof pentose phosphate pathway increases to generate more NADPH.
• NADPH reduces molecular O2 to produce various toxic metabolic products such as Hydroxyl free radical, H2O2 and superoxide ions that kill ingested bacteria.
• This process is also known as respiratory burst.
• It is the major mechanism of killing of ingested bacteria during phagocytosis.

2. Oxygen independent mechanism:

• In this mechanism, ingested bacteria are killed by hydrolytic and digestive enzymes of lysozyme.

Phagocytosis or Phagocytic barrier of immune system

The post Phagocytosis or Phagocytic barrier of immune system appeared first on Online Biology Notes.

• Immunity is derived from Latin word “immunis” which means free from burden. In this case burden refers to disease caused by microorganisms or their toxic products.
• Therefore Immunity is defined as the state of resistance or in susceptibility to disease caused by particular microorganisms or their toxic products. For example some individuals having genetic deficiency of glucose-6-phosphate dehydrogenase are resistant to malaria. Such individuals are said to be immune to Plasmodium.

Types of immunity:

Broadly there are two types of immunity.

1. Innate or natural immunity
2. Acquired immunity

Innate or Natural immunity:

• Immunity with which an individual is born is called innate or natural immunity.
• Innate immunity is provided by various components such as Skin, mucus membrane, Phagocytic cells etc
• Innate immunity acts as first line of defense to particular microorganisms.

Mechanism of innate immunity:

1. Anatomical barrier
2. Physicochemical barrier
3. Phagocytic barrier or Phagocytosis
4. Inflammatory barrier or Inflammation

Types of innate immunity:

1. Species immunity
2. Racial immunity
3. Individual immunity

1. Species immunity:

• If one species is resistant to certain infection and the other species is susceptible to the same infection then it is called as species immunity.
• Anatomic, physiological and metabolic differences between species determine species immunity. For example, Birds are resistant to anthrax but Human are susceptible. It is simply because higher body temperature of birds kills Bacillus anthracis.
• Anatomic differences between species also determine species immunity. For example, Human are more susceptible to skin infection whereas Cattles are more resistant to the same skin infection. It is because of tough and hairy skin (hides) of Cattles.

2. Racial immunity:

• If one race is susceptible while other race is resistant to same infection, then it is called Racial immunity.
• For examples; certain African race are more resistant to malaria and yellow fever where are Asian or Americans are susceptible to same infection. Similarly Orientals (East Asia) are relatively resistant to syphilis.
• Racial immunity is determined by difference in Socio-economic status, habitat, culture feeding habits, environments, genetic, etc.

3. Individual immunity:

• If one individual of certain race or cast is resistant while other individuals of same race or cast are susceptible to certain infection, then it is called as individual immunity
• Individual immunity is determined by various factors such as health status, nutritional status, previous illness, personal hygiene, genetic differences etc.
• For examples; Individual with genetic deficiency of glucose-6 phosphate dehydrogenase are resistant to Malaria.

Acquired or Developed immunity:

• Immunity which is developed later in life after microbial infection in host is called as Acquired or developed immunity. For example, If an individual is infected with chicken pox virus, he/she become resistant to same virus in later life.
• Acquired immunity is provided by Antibodies and certain T-lymphocytes.
• Components of acquired immunity such as Antibodies and T- cells are specific to particular microorganism. Therefore acquired immunity is also known as Specific immunity.

Characteristics of Acquired immunity:

• Specificity
• Self/non-self recognition
• Immunological memory
• Diversity

Types of acquired immunity:

1. Active immunity
2. Passive immunity

1. Active immunity:

• If host itself produces antibodies, it is called active immunity.
• It is of two types; artificial active immunity and natural active immunity.
• Artificial active immunity: Immunity provided by vaccination.
• Natural active immunity: immunity provided by natural infection.

2. Passive immunity:

• If host does not produce antibodies itself but antibodies produced in other host provides immunity, than it is known as Passive immunity.
• It is of two types; natural passive immunity and Artificial passive immunity
• Natural passive immunity: IgG antibody produced in mother cross placenta and protects fetus up to 6 month old age.
• Artificial passive immunity: if preformed antibody are injected into host for immunity. Eg. Anti-venom, Rabies vaccine (* it is not a vaccine, it is preformed anti rabies antibody)

Immunity and its types: Innate and Acquired immunity

The post Immunity and its types: Innate and Acquired immunity appeared first on Online Biology Notes.