Immunity

The human body has the ability to defend itself against a wide range of organisms and toxins that can harm tissues and organs, a capability known as immunity. This immunity consists of two main components: the less specific innate immunity and the more specific adaptive immunity.

1.0Types of Immunity

  1. Innate Immunity  -  Innate immunity serves as the body's first line of defense against infections. Most components of innate immunity are present prior to any infection and consist of a range of disease-resistance mechanisms that are not tailored to specific pathogens. Instead, they include cellular and molecular elements that identify common molecules found in frequently encountered pathogens. Innate immunity encompasses four main types of defensive barriers:
  • Anatomic
  • Physiologic
  • Phagocytic
  • Inflammatory

Summary of nonspecific host defenses

Type

Mechanism

Skin

Mechanical barriers prevent the entry of microbes. An acidic environment (pH 3-5) inhibits microbial growth.

Mucous membranes

Protective role by trapping foreign microorganisms, while normal flora compete with pathogens for attachment sites and nutrients. Additionally, cilia help propel microorganisms out of the body, forming an essential part of physiological barriers.

Physiological barriers

 

Temperature

Normal body temperature helps inhibit the growth of certain pathogens, while fever responses further enhance this effect. 

Low pH

The low pH of stomach contents effectively kills most ingested microorganisms. 

Chemical mediators

Lysozyme breaks down bacterial cell walls.

Interferon  triggers an antiviral state in uninfected cells.

Complement proteins can lyse microorganisms or enhance phagocytosis.

Toll-like receptors detect microbial molecules, prompting cells to secrete immunostimulatory cytokines.

Collections disrupt the cell walls of pathogens.

Phagocytic/endocytic barriers

Specialized cells, including blood monocytes, neutrophils, and tissue macrophages, internalize (endocytose) and degrade foreign macromolecules through phagocytosis, allowing them to engulf, kill, and digest entire microorganisms.

Inflammatory barriers

Tissue damage and infections trigger the leakage of vascular fluid containing serum proteins with antibacterial properties, along with the influx of phagocytic cells to the affected area.

  1. Adaptive Immunity  - Adaptive immunity does not come into play until there is an antigenic challenge to the organism. It is capable of recognizing and selectively eliminating specific foreign microorganisms and molecules (i.e., foreign antigens). Unlike innate immune responses, adaptive immune responses are not the same in all species but are reactions to specific antigenic challenges. 

Adaptive immunity displays four characteristic attributes:

  • Antigenic specificity
  • Diversity
  • Immunologic memory 
  • Self/nonself recognition
  • The Adaptive Immune System Requires Cooperation between Lymphocytes and Antigen-Presenting Cells. 
  • Lymphocytes are one of many types of white blood cells produced in the bone marrow by the process of hematopoiesis .
  • Lymphocytes leave the bone marrow, circulate in the blood and lymphatic systems, and reside in various lymphoid organs.
  • Because they produce and display antigen binding cell-surface receptors, lymphocytes mediate the defining immunologic attributes of specificity, diversity, memory, and self/nonself recognition.
  • The two major populations of lymphocytes—B lymphocytes (B cells) and T lymphocytes (T cells).

Acquired immunity consists of two key components: 

  • T lymphocytes, which mediate cellular immunity
  • humoral immunity, which is mediated by circulating immunoglobulin antibodies found in the plasma's γ-globulin fraction. These immunoglobulins, produced by differentiated B lymphocytes known as plasma cells, activate the complement system and help neutralize and eliminate antigens.

Formation of acquired immunity

Image showing the classification of immunity

2.0Signs of Weak Immune System

  • Feeling  Tiredness
  • Frequent fever and chills
  • Frequent Diarrhea
  • Feeling Stress
  • Poor Wound healing 
  • Frequent Infections
  • Sudden High Fevers
  • Muscle and Joint Aches
  • Frequently on Medication for one Illness or the other
  • Severe hair loss
  • Skin infections

Frequently Asked Questions

Immunity is the body's ability to resist or fight off infections and diseases.

There are two main types: innate immunity (the body's first line of defense, including physical barriers like skin) and adaptive immunity (specific responses developed after exposure to pathogens).

Yes, chronic stress can weaken the immune response, making you more susceptible to illness.

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