Depth 1 · 70 s

Walls, then memory

Name: Walls, then memory
Uploaded: 2026-11-07T00:09:31.634670Z
Duration: 70 s
Description: You scrape your knee and germs get in, yet a week later it has healed. The four layers of your immune system, from skin to antibodies to a memory that makes the next fight easier, and what a fever really is.

You scrape your knee and germs get in, yet a week later it has healed. The four layers of your immune system, from skin to antibodies to a memory that makes the next fight easier, and what a fever really is.

About this video

You scrape your knee in the park. By evening the skin around it is pink, warm and a little puffy, and a week later it has healed. Your immune system, everything in your body that fights germs, dealt with it, in layers.

First come the walls. Skin is a tough barrier that most germs can't get through when it is unbroken. Mucus, the sticky liquid in your nose, throat and lungs, traps germs and dust. Stomach acid kills many germs you swallow.

When germs do get in, a fast, general defence starts straight away. Nearby blood vessels let more fluid out, so the area turns red, warm and swollen: inflammation. It brings white blood cells, the body's germ fighters, and some of them swallow germs whole. This defence treats every germ the same way.

Later, a slower, targeted defence joins in. Some white blood cells make antibodies, small Y-shaped pieces that stick to one particular germ and only that one, marking it so it is easier to destroy. Others kill your own cells that a virus has got into.

After the fight, some of these targeted cells stay, often for many years. This is immune memory: if the same germ comes back, the defence is faster and stronger, often so fast that you don't get ill at all. That is why most people get measles or chickenpox only once.

A fever, usually 38 °C or more, is a sign your body is fighting an infection. Your body makes it, not the germ. If it is very high, lasts several days or worries you, ask a doctor, nurse or pharmacist. This video goes with the lesson Your Body's Defences in Health Level 1 on Knaph.

This video shows depth 1 of Immune system.

Learn Immune system

Transcript

0:00You scrape your knee. By evening it is pink and puffy. A week later, healed. Who dealt with the germs?
0:07Your immune system defends in layers. First, the walls. Skin, mucus that traps germs, and stomach acid that kills many you swallow.
0:18When germs get in, a fast defence starts. The spot turns red, warm and swollen, and white blood cells arrive and swallow germs whole.
0:30Later comes a targeted defence. Antibodies, small Y-shaped pieces, stick to one particular germ and only that one, so it is easier to destroy.
0:42Some of those cells stay for years. If the same germ comes back, the defence is faster and stronger. Often you don't get ill at all.
0:54And a fever, about 38 degrees or more, is made by your body as part of the fight, not by the germ.
1:03Walls, a fast defence, a targeted one, and a memory.