Immune System and Infectious Diseases

• The immune system protects the body from infections and diseases caused by germs such as bacteria and viruses
• It comprises cells, tissues, and organs that work together to fight off these germs, distinguishing between the body's own cells and foreign invaders
• The immune system uses general defenses, like skin barriers, and specific responses involving T cells and B cells
• T and B cells destroy germs and "remember" them for a faster response upon re-exposure, aiding in maintaining health and fighting off illnesses.

Infectious Diseases

• Pathogens are microorganisms that can cause sickness and are of many types
• Bacteria are single-celled organisms that multiply rapidly, leading to diseases like strep throat and food poisoning
• Viruses, which are smaller, require a living cell to grow and can cause illnesses like the flu or COVID-19
• Fungi, including molds and yeasts, can cause infections such as athlete's foot
• Parasites live on or inside another organism, causing diseases like malaria
• An infectious disease occurs when pathogens invade the body, causing sickness and discomfort

Types of Pathogens

• Cellular (Living): Parasites, Protozoa, Fungi, Prokaryotes
• Acellular (Non-Living): Virus, Prion

Identifying Self vs. Non-Self

• Antigens, found on cell surfaces, help the immune system recognize what belongs to the body
• The body's own cells have antigens labeled as "self"
• Foreign pathogens have "non-self" antigens, triggering an immune response
• The immune system activates cells to neutralize foreign pathogens
• Telling the difference between "self" and "non-self" antigens is key for staying healthy and warding off infections.

Non-Specific (Innate) Immunity

• Innate immunity is the body's first defense line against infections
• It offers swift response to harmful invaders like bacteria, viruses, and fungi without targeting specific pathogens
• The skin is a barrier in innate immunity that prevents microorganisms from entering the body
• Skin produces antimicrobial oils and sweat to kill germs on contact
• Tears contain enzymes that eliminate bacteria and wash away dirt to protect the eyes
• Saliva contains enzymes that break down bacterial cell walls to prevent infections
• Stomach acid destroys microorganisms in the digestive system
• Phagocytes (macrophages) are white blood cells that engulf and digest harmful microorganisms
• Inflammation increases blood flow to injured areas, delivering immune cells, like macrophages, and promoting healing
• A fever may occur to create an uninhabitable environment for pathogens, also improving immune cell effectiveness

Specific (Adaptive) Immunity

• Adaptive immunity responds to specific pathogens and develops over time
• It involves lymphocytes: T cells and B cells
• When a pathogen enters the body, T and B cells identify its antigens and prepare a response
• Macrophages engulf and digest pathogens, then display pathogen antigens
• Macrophages present antigens to helper T cells that become activated and multiply
• Activated helper T cells release cytokines and stimulate B cells that produce antibodies
• They can also stimulate killer T cells (cytotoxic T cells) that destroy infected or abnormal cells
• B cells release antibodies to mark pathogens for destruction, and killer T cells seek out and destroys infected cells
• After the infection is cleared, some B cells become memory cells, which provide quicker responses if reinfected from the same pathogen

Modern Medicine

• Antibiotics, antivirals, antifungals, antiparasitics, and vaccines are essential for preventing and treating infections
• Antibiotics treat bacterial infections by killing bacteria or stopping their growth but do not work against viruses
• Antivirals treat viral infections by stopping the multiplication of the virus, managing symptoms, and reducing severity
• Antifungals treat fungal infections by killing or stopping the growth of fungal cells
• Antiparasitics target parasitic infections by eliminating parasites from the body and treating related diseases
• Vaccines are preventative; they help the immune system recognize and defend against specific pathogens (bacterial and viral) by introducing a harmless form of the pathogen
• Together, these treatments and preventive measures maintain health and control infectious diseases

Innate Immunity

• Innate immunity responses occur from minutes to hours

Adaptive Immunity

• Adaptive immunity can take days or weeks

The immune system defends the body against infections, using cells, tissues, and organs to differentiate between body cells and foreign invaders. Pathogens such as bacteria, viruses, fungi and parasites cause diseases. Understanding these mechanisms is crucial for health.