Immune System Overview

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Questions and Answers

What role do surface barriers play in the immune system?

They circulate in blood to destroy cancer cells.

They secrete antibodies directly into the bloodstream.

They initiate the inflammatory response.

They serve as a physical barrier against pathogens. (correct)

Which of the following describes the function of Natural Killer (NK) cells?

They engulf and digest pathogens.

They release histamines during an allergic reaction.

They target and destroy cancer cells and virus-infected cells. (correct)

They produce antibodies to neutralize toxins.

What is the process of diapedesis in the context of inflammation?

The merging of phagocytic vesicles with lysosomes.

The movement of phagocytes through blood vessels to the site of injury. (correct)

The adherence of phagocytes to capillary walls.

The release of histamine by granules in mast cells.

Which statement accurately describes cytokines in the inflammatory response?

They are inflammatory chemicals that attract phagocytes to sites of injury. (A) Signup and view all the answers

What is the primary difference between innate and adaptive defenses in the immune system?

Adaptive defenses involve memory cells that recognize past infections. (A) Signup and view all the answers

What role do antigens play in the adaptive immune response?

They are recognized as 'non-self' and trigger immune responses. (C) Signup and view all the answers

Which of the following is NOT a function of the inflammatory response?

To promote the release of antibodies into the bloodstream. (B) Signup and view all the answers

Which component of the innate immune system serves as a first responder to sites of inflammation?

Neutrophils (C) Signup and view all the answers

What is the primary role of B lymphocytes in the immune system?

To produce antibodies for humoral immunity (B) Signup and view all the answers

What process do lymphocytes undergo to produce thousands of antigen-specific copies of themselves?

Clonal selection (B) Signup and view all the answers

Which class of antibodies is primarily responsible for the secondary immune response?

IgG (B) Signup and view all the answers

What is the main function of antigen-presenting cells (APCs)?

To present antigens to T cells for activation (B) Signup and view all the answers

Which type of T cell is primarily involved in the destruction of infected body cells?

CD8+ T cells (C) Signup and view all the answers

What is the first line of defense provided by the innate immune system?

Immediate and non-specific protection (B) Signup and view all the answers

What type of immunity develops after exposure to an antigen through infection or vaccination?

Active humoral immunity (B) Signup and view all the answers

What are the key components of an antibody structure?

Two heavy chains and two light chains (A) Signup and view all the answers

Which T cells primarily activate other immune cells and release cytokines?

CD4+ T cells (C) Signup and view all the answers

What happens when a new B cell encounters its specific antigen for the first time?

It undergoes endocytosis, then proliferates and differentiates (D) Signup and view all the answers

Study Notes

Immune System

The immune system functions to protect the body against pathogens, which are disease-causing organisms such as bacteria and viruses.

Innate Defenses

The innate defense system is a non-specific line of defense that is always active.
Surface Barriers:
- The skin, the body's largest organ, serves as a physical barrier against pathogens.
- Mucous membranes, found in lining body cavities and openings, provide additional protection.
- Mucous membranes often contain acidic secretions, lysozymes (enzyme that breaks down peptidoglycan), and defensins (antimicrobial peptides), contributing to pathogen inhibition.
Internal Defenses:
- Phagocytosis: Macrophages, derived from white blood cells, and other phagocytes engulf pathogens or cellular debris.
  - The phagocytic vesicle merges with a lysosome, releasing enzymes that break down the engulfed material.
- Natural Killer (NK) Cells: NK cells circulate in blood and lymph and target and destroy cancer cells and virus-infected cells.
  - NK cells recognize abnormalities on the surface of infected cells and induce apoptosis (programmed cell death).
- Inflammatory Response:
  - Triggered by physical trauma, heat, or infection, leading to the release of inflammatory chemicals such as histamine.
  - Macrophages and specific cells in boundary tissues possess receptors that recognize pathogens and release cytokines (another type of inflammatory chemical).
  - Inflammatory chemicals cause vasodilation (dilation of arterioles) and vascular permeability (increased leakage of capillaries), leading to redness, swelling, and pain.
  - These reactions help recruit phagocytes to the site of injury, deliver clotting proteins for repair, and help clear foreign material via lymphatic vessels.
  - Neutrophils (first responders) followed by macrophages arrive at the site of inflammation.
  - Margination refers to phagocytes adhering to capillary walls at the site of injury, recognizing signals on inflamed cells.
  - Diapedesis is the process of phagocytes squeezing out of the capillary.
  - Chemotaxis is the movement of phagocytes following a gradient of molecules toward the source of injury.

Adaptive Defenses

The adaptive defense system offers a specific response to each foreign substance encountered.
Antigens:
- Foreign substances recognized as "non-self" are called antigens.
- Examples include proteins, polysaccharides, lipids, and pathogens.
- The antigenic determinant is the specific part of the antigen that is recognized by the immune system.
- Antibodies and lymphocytes bind to specific antigens, similar to enzyme-substrate interactions.
Lymphocytes:
- Lymphocytes originate in the red bone marrow from hematopoietic stem cells.
- They become immunocompetent, gaining the ability to recognize a specific antigen.
- They undergo clonal selection, meaning they proliferate and produce thousands of copies of themselves, all with the same antigen-specific receptors.
B and T Lymphocytes:
- B lymphocytes (B cells) are responsible for humoral immunity.
  - Their surface receptors are membrane-bound antibodies.
- T lymphocytes (T cells) are responsible for cellular immunity.
  - They possess T cell receptors that recognize specific antigens.
Antigen-Presenting Cells (APCs):
- APCs present antigens to T cells, aiding in the T cell activation process.

Humoral Immunity

The humoral immune response relies on antibodies produced by B cells.
Primary Immune Response:
- When a new B cell encounters its antigen, it undergoes endocytosis followed by proliferation and differentiation into plasma cells.
- Plasma cells produce large amounts of antibodies, which circulate in blood and lymph, targeting the antigen.
- This takes several days, making it slow to respond to an initial invasion.
Secondary Immune Response:
- Subsequent exposures to the same antigen result in a rapid and robust antibody production due to memory B cells generated during the primary response.
Active Humoral Immunity:
- Develops after exposure to an antigen through infection or vaccination.
Passive Humoral Immunity:
- Acquired when antibodies are introduced directly into the body through sources like mother's milk or gamma globulin injections.
Antibodies (Immunoglobulins):
- Large, Y-shaped proteins composed of four polypeptide chains linked by disulfide bridges.
- They consist of two heavy chains and two light chains.
- Variable regions (V regions) at the tip of the Y arms are responsible for antigen binding.
- Constant regions (C regions) are similar within each class of antibody.
- Five classes of antibody: IgM, IgA, IgD, IgG, and IgE, differing in structure, function, and location.
- Antibodies tag antigens for destruction.

Cellular Immunity

Cellular immunity is carried out by T cells, which directly target and destroy infected cells.
T Cell Receptors:
- Receptors on T cells recognize specific antigens presented by APCs.
CD4+ T Cells (Helper T cells):
- Activate B cells, T cells, and macrophages.
- Release cytokines that coordinate immune responses.
CD8+ T Cells (Cytotoxic T cells):
- Destroy foreign cells or body cells infected by viruses or bacteria.
Activation and Differentiation of T cells:
- T cell receptors interact with antigens presented by APCs.
- Co-stimulation signals from other molecules on the APC are needed for full T cell activation.
- Activated T cells proliferate and differentiate into various effector T cell types.

Immune System Summary

The innate immune system is the first line of defense, providing immediate and non-specific protection against pathogens.
The adaptive immune system is specific and highly tailored to each encountered antigen.
Humoral immunity relies on antibodies produced by B cells, while cellular immunity involves T cells directly targeting and destroying infected cells.
Understanding the interplay between these systems is key to comprehending the body's defenses against diseases.

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Description

Explore the key functions of the immune system, focusing on its innate defenses. Learn about surface barriers, including the skin and mucous membranes, and internal defenses like phagocytosis and natural killer cells. This quiz will enhance your understanding of how the body protects itself from pathogens.