Innate Defenses Diagram – Barriers and Internal Defenses

All 10 defenses on the diagram

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The barriers 4

Skin The body's outer cover. Most microbes cannot get through it.
Mucous membranes Wet linings of the airways and gut. Their mucus traps microbes.
Barriers They keep microbes out. They are the first line of defense.
Innate immunity The defenses a body is born with. They act against every microbe alike.

Inside the body 6

Phagocytes Cells that swallow microbes and digest them.
Fever A raised body temperature, set off by signals of the immune system.
Inflammation Fluid and white cells leave the blood and gather at one spot.
Natural killer cells Cells that kill body cells infected by a virus.
Interferons Signal proteins from infected cells. They help nearby cells resist viruses.
Complement Blood proteins that mark bacteria and break them open.

How this list was compiled: Every name and every line of words on the chart checked on 2026-10-03 in at least two of these. (1) Wikipedia, text only: Innate immune system, Complement system, Interferon and Fever, https://en.wikipedia.org/wiki/Innate_immune_system : epithelial surfaces are a physical barrier and the first line of defense; phagocytes engulf pathogens; natural killer cells destroy virus-infected host cells; inflammation; complement proteins target and kill pathogens; interferons are signaling proteins released by virus-infected cells. (2) MedlinePlus, United States National Library of Medicine, Immune response, https://medlineplus.gov/ency/article/000821.htm : innate (nonspecific) immunity is the defense system you are born with; barriers (skin, mucus) are the first line of defense; complement, interferon and interleukin-1, which causes fever; inflammation and phagocytes. (3) National Institute of Allergy and Infectious Diseases, Overview of the Immune System, and Immune Cells, https://www.niaid.nih.gov/research/immune-system-overview : skin as the first line of defense, mucosal surfaces, phagocytosis by neutrophils and macrophages, natural killer cells, interferons, complement. (4) SEER Training Modules, National Cancer Institute, Membranes, https://training.seer.cancer.gov/anatomy/cells_tissues_membranes/membranes.html : mucous membranes line cavities that open to the outside and secrete mucus. Licence: own work

The drawing: Drawn for this site on 2026-10-03. Own original chart; nothing traced or copied. Licence: own work

How it works

Each box of this innate defenses diagram draws one defense and says in plain words what it does. Only its name is blank. The first chart holds the barriers; the second holds the defenses inside the body.

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The barriers

Innate immunity is the set of defenses a body has from birth. Its barriers keep microbes out: the skin covers the body, and the mucous membranes line the airways and the gut, where mucus traps microbes.

Inside the body

Microbes that get past the barriers meet cells and proteins. Phagocytes swallow microbes, and natural killer cells kill infected body cells. Inflammation brings fluid and white cells to one spot, and fever raises body temperature. Interferons help cells resist viruses, and complement proteins break bacteria open.

Innate defenses are nonspecific: they act the same way against every kind of microbe.
The quiz accepts NK cells, and surface barriers for barriers.

Questions and answers

What are the innate defenses of the body?

The defenses a body is born with: barriers such as the skin and mucous membranes, and, inside the body, phagocytes, natural killer cells, inflammation, fever, interferons and complement proteins.

What is the first line of defense?

The barriers. The skin and the mucous membranes, with their mucus, keep most microbes from getting into the body at all.

What is the difference between innate and adaptive immunity?

Innate immunity is present from birth and acts the same way against every microbe. Adaptive, or acquired, immunity develops after the body meets a particular microbe and is specific to it.

What do natural killer cells do?

They recognize body cells that have been infected by a virus and kill them.

How do I drag the labels onto the diagram to identify the types of innate defenses?

Sort them into two sets. Skin and mucous membranes are barriers at the surface. Phagocytes, natural killer cells, inflammation, fever, interferons and complement act inside the body. Here you tap, not drag: this chart is the site's own drawing, not a figure from any course.