The body's defences Flashcards
Immune system
The immune system is the body’s defense mechanism comprising various cells, tissues, and organs that work together to protect the body against pathogens, such as bacteria, viruses, and other harmful invaders. It includes innate and adaptive immunity, with key components like white blood cells, antibodies, and lymphatic organs.
Pathogens
Pathogens are microorganisms or agents that cause disease in their host. They include bacteria, viruses, fungi, and parasites. Pathogens can invade the body, multiply, and interfere with normal bodily functions, leading to illnesses and infections.
Innate immunity
Innate immunity is the body’s first line of defense against pathogens, providing a rapid but non-specific response. It includes physical barriers like skin and mucous membranes, as well as immune cells such as macrophages, neutrophils, and natural killer cells. Other components include proteins like cytokines and the complement system, which help identify and eliminate invaders.
External and internal innate defence.
Adaptive immunity
Adaptive immunity is a specific and slower-acting defense mechanism that develops in response to exposure to pathogens. It involves the activation of lymphocytes (B cells and T cells) which recognize specific antigens. B cells produce antibodies that neutralize pathogens, while T cells destroy infected cells. Adaptive immunity has a memory component, providing long-lasting protection by remembering previous encounters with pathogens.
The lymphatic system
The lymphatic system is a network of tissues, vessels, and organs that help maintain fluid balance, protect against infections, and remove waste products from the body. It includes lymph nodes, lymphatic vessels, the spleen, thymus, and tonsils. Lymph, a clear fluid, circulates through this system, carrying immune cells (like lymphocytes) to fight pathogens and remove toxins and waste.
External innate defences
External innate defenses are the body’s first barrier against pathogens, preventing their entry and spread. These include:
-Skin: Acts as a physical barrier.
-Mucous membranes: Trap and expel pathogens.
- Secretions: Such as saliva, tears, and mucus, contain antimicrobial enzymes.
- Cilia: Hair-like structures in the respiratory tract that move mucus and trapped particles out.
- Acidic environments: Like stomach acid, which destroys ingested pathogens.
Internal innate defenses
Internal innate defenses are mechanisms inside the body that respond to pathogens after they bypass external barriers. These include:
- Phagocytic cells: Such as macrophages and neutrophils, which engulf and destroy pathogens.
- Natural killer (NK) cells: Attack and kill virus-infected cells and tumors.
- Inflammatory response: Increases blood flow and recruits immune cells to the infection site.
- Fever: Elevates body temperature to inhibit pathogen growth.
- Antimicrobial proteins: Such as interferons and the complement system, which attack pathogens directly or impede their reproduction.
Inflammation
Inflammation is the body’s immediate response to injury or infection, characterized by redness, heat, swelling, and pain. It aims to eliminate the cause of cell injury, clear out damaged cells, and initiate tissue repair. Key steps include:
Vasodilation: Increased blood flow to the affected area.
Increased permeability: Allows immune cells and proteins to move into tissues.
Phagocyte recruitment: White blood cells like macrophages and neutrophils engulf and destroy pathogens.
Release of signaling molecules: Such as cytokines, which coordinate the inflammatory response.
Circulatory function
The lymphatic system is a complementary component of the circulatory system responsible for:
Fluid Balance: Absorbing excess fluid from tissues and returning it to the bloodstream to maintain fluid balance.
Immunity: Transporting lymphocytes and other immune cells throughout the body to help defend against infections.
Fat Absorption: Absorbing fats and fat-soluble vitamins from the digestive system and transporting them to the bloodstream.
Waste Removal: Removing cellular waste, pathogens, and toxins from tissues and organs.
It works in parallel with the blood circulatory system, utilizing lymphatic vessels, lymph nodes, and lymphoid organs to perform its functions.
Immune function
The lymphatic system is the main battleground. Because the lymphatic vessels penetrate
nearly every tissue, lymph can pick up pathogens from infection sites just about anywhere in the body.
As this fluid circulates, phagocytic cells inside the lymphatic tissues and organs engulf the invaders.
Lymph nodes are key sites where particular white blood cells called lymphocytes multiply during times of infection. The size of lymph nodes expand when there is an infection.
B cells
B cells, or B lymphocytes, are a type of white blood cell crucial to the adaptive immune system. Their primary functions include:
Antibody Production: B cells differentiate into plasma cells that produce antibodies, which neutralize pathogens.
Antigen Presentation: B cells present antigens to T cells, initiating a more specific immune response.
Immune Memory: Some B cells become memory B cells, which remember past infections and respond more rapidly upon re-exposure to the same pathogen.
B cells are produced in the bone marrow and play a key role in humoral immunity by targeting extracellular pathogens and toxins.
T cells
T cells, or T lymphocytes, are a type of white blood cell essential to the adaptive immune system. Their primary functions include:
Cytotoxic T Cells (CD8+): Directly kill infected or cancerous cells.
Helper T Cells (CD4+): Coordinate the immune response by activating other immune cells, such as B cells and macrophages, and by releasing cytokines.
Regulatory T Cells: Maintain immune system balance by suppressing overactive immune responses and preventing autoimmune reactions.
Memory T Cells: Provide long-term immunity by remembering past infections and responding more quickly upon re-exposure to the same pathogen.
T cells are produced in the bone marrow and mature in the thymus, playing a crucial role in cellular immunity by targeting infected or abnormal cells.
How do T cells and B cells recognize invaders?
B- and T cells are receptor proteins that bind to an antigen. Any given antigen receptor detects and binds to only a single type of antigen.
Antigen receptors on B cells specialize in recognizing intact antigens that are on the surface of pathogens or circulating freely in the bodily fluid.
The unique shape of the antigen and the complementary antigen receptor on the B cell connect and activate the B cell.
Antigen receptors on the T cells only recognize fragments of antigens, and the fragments must be displayed, or presented on the surface of body cells by special proteins before the T cells are activated. The pathogens are fragments because they got broken down by enzymes when they entered the body. T cell antigen that is complementary binds to the self protein that displays the specific antigen fragment.
Cloning the responders
Once a pathogen enters the body it multiplies. At frist, an antigen activates only a tiny number of lymphocytes with specific antigen receptors. These selected lymphocytes then multiply through cell division.
1) Antigens bind to B cell with complementary receptors.
2) Binding causes the B cell to divide, forming a clone of identical cells with the same antiigen receptors.
3) Some cells develop into short-lived cells that secrete antibodies specific for the antigen. (effector cells B).
4) Some cells develop into long-lived memory cells. If later exposed to the same antigen, they produce larger clones of memory and effector cells. (memory cells B).
How do B cells and T cells respond to invaders?
B cells and T cells respond to invaders through specific actions:
B Cells:
Antibody Production: After recognizing an antigen, B cells differentiate into plasma cells, which secrete antibodies. These antibodies bind to pathogens, neutralizing them or marking them for destruction by other immune cells.
Memory B Cells: Some activated B cells become memory B cells, providing long-term immunity by responding quickly upon re-exposure to the same pathogen.
T Cells:
Helper T Cells (CD4+): Upon activation by antigen-presenting cells (APCs), they release cytokines that stimulate other immune cells, including B cells, cytotoxic T cells, and macrophages, enhancing the overall immune response.
Cytotoxic T Cells (CD8+): Recognize and directly kill infected or cancerous cells by inducing apoptosis
(programmed cell death).
Regulatory T Cells: Suppress immune responses to maintain tolerance to self-antigens and prevent autoimmune diseases.
Memory T Cells: Provide long-lasting immunity by quickly responding to previously encountered antigens.
These responses ensure a coordinated and effective defense against a wide variety of pathogens.
