Welcome to Lesson 18 of the Human Biology Masterclass and the final lesson of Section 4: Transport and Defense.
In Lesson 17, we introduced white blood cells as components of blood. Now we look at what these cells actually do when pathogens enter the body.
The immune system is a highly coordinated defence network that can distinguish foreign threats, eliminate pathogens, and develop long-lasting immunological memory.
In this lesson, you'll learn:
• The physical and chemical barriers that prevent pathogens from entering the body
• How skin, tears, mucus, cilia, stomach acid, and the gut microbiome contribute to defence
• What the mucociliary escalator does in the respiratory tract
• How the innate immune system responds rapidly to infection
• Pattern recognition receptors and pathogen-associated molecular patterns
• The roles of inflammation, phagocytosis, fever, and the complement system
• How natural killer cells help identify and eliminate abnormal cells
• How the adaptive immune system differs from innate immunity
• The roles of B cells, helper T cells, and cytotoxic T cells
• How plasma cells produce antibodies
• The major functions of antibodies, including neutralisation, opsonisation, and complement activation
• The different antibody classes: IgM, IgG, IgA, IgE, and IgD
• How immunological memory develops after infection or vaccination
• The difference between primary and secondary immune responses
• How vaccines safely stimulate adaptive immune memory
• The major vaccine platforms, including live attenuated, inactivated, subunit, mRNA, and viral-vector vaccines
• How population-level immunity can reduce transmission and provide indirect protection to vulnerable individuals
The immune system combines physical barriers, rapid innate defence, and highly specific adaptive immunity into an integrated system of protection.
Section 4 – Transport and Defense
Lesson 16: The Heart & Circulatory System
Lesson 17: Blood – Cells, Plasma & Clotting
Lesson 18: The Immune System – Defenses, Antibodies & Vaccines
Section 4 is now complete.
What's Next?
In Section 5, we move to the respiratory system.
We'll explore how the lungs bring oxygen into the body and remove carbon dioxide, how breathing is mechanically controlled, and how gases move across the alveolar surface.
This creates a direct connection with the cardiovascular system and blood: the lungs load oxygen onto the blood, and the circulatory system transports that oxygen to tissues throughout the body.
Continue the complete Human Biology Masterclass through the playlist on Human Science Academy.
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