The Body's Organ Tour
Major Organs, Their Jobs, and What Goes Wrong
Learning Objectives
Explain how the body is organized in levels from cells to tissues to organs to organ systems to the whole organism.
Identify the major organs of the human body and describe the one main function of each.
Describe how the major organ systems interact with one another to keep the body alive.
Explain how a common disease or malfunction disrupts an organ's function, using the structure and function relationship.
Hook: your body never clocks out
~2 minutesRight now, without you thinking about it, your heart is beating, your lungs are filling, and your stomach is squeezing your breakfast. You are running a whole biology lab made of organs, and you never even clock in. In the next 45 minutes you will tour the body's major organs, learn the one main job each one does, and find out what goes wrong when an organ stops doing that job.
How the body is built
~4 minutesYour body is built in levels, smallest to largest. A single cell is the basic unit of life. Many similar cells together form a tissue. Different tissues team up to make an organ, like the heart. Organs that share a big job form an organ system. All of your systems together make one organism: you.
An organ is a structure made of two or more kinds of tissue that work together to perform one main job. The heart, brain, lungs, and even your skin all qualify.
Check your understanding
~2 minutesPut the levels of organization in order from smallest to largest.
Which statement best describes an organ?
Brain (nervous system)
~4 minutesThe brain is the control center of the nervous system. It takes in information from your senses, makes decisions, and sends out signals through the spinal cord and nerves, all in a fraction of a second. It runs everything from solving math problems to keeping your heart beating.
A stroke happens when blood flow to part of the brain is blocked, so those brain cells stop getting oxygen and can be damaged within minutes. Because different brain areas control different jobs, a stroke can affect speech, movement, or memory depending on where it occurs.
Check your understanding
~1 minutesThe brain is the control center of the nervous system.
Heart (circulatory system)
~4 minutesThe heart is the pump of the circulatory system. This fist-sized muscle beats about 100,000 times a day, pushing blood through a loop of vessels so that oxygen and nutrients reach every cell and waste gets carried away.
In coronary artery disease, the vessels that feed the heart muscle get clogged with fatty buildup. If a vessel becomes fully blocked, part of the heart muscle is starved of oxygen, which is a heart attack. It is a leading cause of death worldwide, and habits like exercise and diet affect the risk.
Check your understanding
~1 minutesWhat is the heart's main job?
Lungs (respiratory system)
~4 minutesYour two lungs run the respiratory system. Air travels down your windpipe into millions of tiny air sacs. There, gas exchange happens: oxygen passes into the blood and carbon dioxide passes out to be breathed away.
In asthma, the small airways become swollen and tight, sometimes triggered by exercise, allergies, or smoke. The narrowed tubes make it hard to move air, causing wheezing and shortness of breath. Inhalers work by relaxing those airways back open.
Check your understanding
~1 minutesIn the lungs, ______ moves into the blood and carbon dioxide moves out. This swap is called gas ______.
Digestive organs
~5 minutesThe digestive system turns lunch into fuel. The stomach is a muscular bag that mashes food and adds acid. The small intestine absorbs nutrients into the blood. The large intestine absorbs water and packs the leftover waste. Two helper organs pitch in: the liver makes a fluid called bile and filters the blood, and the pancreas makes digestive juices plus insulin, the messenger that lets cells use sugar.
When digestive organs break down
Stomach: a peptic ulcer is a raw sore in the lining, most often caused by a bacterium called H. pylori (a germ, or pathogen).
Small intestine: in celiac disease, the immune system reacts to gluten and flattens the tiny absorbing folds, so nutrients slip past unabsorbed.
Large intestine: appendicitis is when the appendix gets inflamed and infected, which is a medical emergency.
Liver: hepatitis is inflammation of the liver, often from a virus, that hurts its ability to filter blood.
Pancreas: in type 1 diabetes the pancreas cannot make insulin; in the more common type 2, the body stops responding to it well. Either way, blood sugar climbs too high.
Notice the pattern: some breakdowns come from a pathogen (a germ), and some come from the body's own parts wearing out or misfiring. You will study germs and disease in much more depth in 8th grade.
Check your understanding
~1 minutesWhich of these organs are part of the digestive system? (Select all that apply.)
Select all that apply.
Kidneys and bladder (urinary system)
~3 minutesThe urinary system is the cleanup crew. Your two bean-shaped kidneys filter your entire blood supply many times a day, pulling out waste and extra water. That liquid waste, urine, travels to the bladder, a stretchy bag that stores it until you reach a bathroom.
Kidney stones are hard mineral crystals that form in the kidney and can be very painful to pass. A urinary tract infection (UTI) happens when bacteria get into the bladder, causing burning and the constant urge to go. Drinking enough water helps prevent both.
Check your understanding
~1 minutesThe ______ filter waste and extra water out of the blood, and the ______ stores the urine until it leaves the body.
Skin (integumentary system)
~3 minutesSurprise: your largest organ is your skin, the star of the integumentary system. Spread out, an adult's skin would cover about two square meters. It blocks germs, holds in water, senses touch, and helps control your temperature by sweating and flushing.
Too much ultraviolet (UV) light from the sun or tanning beds can damage the DNA inside skin cells, sometimes causing skin cancer. The good news: it is one of the most preventable cancers. Sunscreen, shade, and protective clothing lower the risk a lot.
Check your understanding
~1 minutesThe skin is the largest organ of the human body.
How it all works together
~2 minutesHere is the big idea: no organ works alone. Your lungs grab oxygen, your digestive system grabs nutrients, your heart delivers both to every cell, and your kidneys haul the trash away. Together they keep your body in homeostasis, a steady balance. That is also why a problem in one organ can ripple out to the rest, the heart of structure and function thinking.
Each organ has a structure built for its job. When the structure is damaged, the function fails, and because the systems are connected, the whole body feels it.
Wrap-up assessment
~6 minutesMatch each organ to its main job.
Asthma makes it hard to breathe. Which organ does it directly affect?
Pick one organ from today's tour. Name its main job, name a disease or problem that can affect it, and explain how that problem keeps the organ from doing its job. Then explain how it could affect the rest of the body.
Expected length: 40-120 words