Human Immune System, Body Organization, and Homeostasis
The Body’s Defenses: Immune System
Understanding the Immune System
The immune system is a complex network of cells and structures within our body that provides immunity, meaning resilience and the ability to fight against pathogens. The system’s reaction to an agent is called the immune response. There are two main types:
- Innate Immunity: The immunity we are born with.
- Adaptive Immunity: Immunity that develops and refines throughout our lives.
Innate Immunity
External Barriers
These are physical barriers, like the skin, or chemical barriers, such as hydrochloric acid in the stomach.
Internal Barriers
These act if pathogens cross the external barriers. There are three main components:
- Inflammation
- Phagocytosis
- Complement System
Internal Defenses Against Infection
Inflammation
This involves swelling caused by a massive release of fluids and substances from damaged tissue. This process forms a clot that isolates microbes, preventing their spread.
Phagocytosis
This is the capture and digestion of foreign microbes by specialized cells called macrophages and neutrophils.
Complement System
This is a set of proteins that attack microbes and attract macrophages and neutrophils to the infection site.
Adaptive Immunity
Humoral Response
Certain cells produce substances called antibodies.
Cellular Response
Other lymphocytes become sensitized cells that recognize cells infected by the pathogen.
Allergies: Immune System Malfunction
An allergy occurs when the immune system mistakenly identifies a harmless substance (like plant pollen) as a pathogen and mounts an inappropriate response.
Infection Control Mechanisms
The chemist Louis Pasteur and other scientists showed that infectious diseases were caused by microorganisms.
Antibiotics
Alexander Fleming discovered antibiotics almost by accident. These are substances that selectively target bacteria and can be ingested or injected. He observed that a fungus produced substances capable of destroying bacteria and managed to isolate one, naming it penicillin. Penicillin was the first antibiotic discovered.
Vaccines
Vaccines are a preventive mechanism that achieves artificial immunization. A vaccine typically contains the pathogenic agent (or parts of it) in a weakened or inactive form.
Common Drug Types and Uses
- Anti-infective drugs: Includes antibiotics and vaccines.
- Pain-relieving drugs (Analgesics): Alleviate headaches, muscle aches, etc. Anesthetics keep patients unconscious during surgery.
- Drugs affecting life processes: Includes vitamin complexes, birth control, and others.
Body Organization: Cells to Systems
Cells group together to form tissues. Tissues, in turn, organize into more complex structures called organs. Organs are coordinated into groups called apparatuses (or organ systems) and systems.
Organs
Organs have distinct shapes, are formed by various tissues, and perform specific functions.
Apparatuses and Systems
These are groups of organs working collaboratively to perform a common activity or function.
Major Human Body Systems
Nutrition Function Systems
- Digestive System
- Respiratory System
- Excretory System
- Circulatory System
Reproductive System
- Male Reproductive System
- Female Reproductive System
Relationship Function Systems (Coordination & Movement)
- Nervous System: Receives information from sensory organs, processes it, and develops responses.
- Endocrine System: Responds by producing and releasing hormones into the blood.
- Locomotor System: Comprises muscles and the skeleton, enabling movement.
The Internal Environment and Homeostasis
The internal environment refers to the fluid that bathes all body cells, interacting indirectly with the external environment via the blood.
Homeostasis
The coordinated activities of the body’s organs, systems, and apparatuses maintain a stable internal environment. This process, called homeostasis, involves constantly renewing and maintaining the characteristics of the internal fluid. Maintaining this balance is crucial, as significant disturbances to the internal environment would be fatal to cells.
Acquiring Adaptive Immunity
Primary Immune Response
When a pathogen first enters the body, the primary immune response is initiated. This response takes several days to develop fully and involves the activation and proliferation of sensitized cells (T lymphocytes) and antibody-producing plasma cells (derived from B lymphocytes).