Unit 16: The Circulatory and Respiratory Systems
How your heart, blood vessels, and lungs work together to get oxygen from the air into every one of your cells.
7 topics · 22 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Why the Body Needs a Circulatory System
- How it worksHow does a closed circulatory system move blood through a continuous loop of vessels?
- Common mistakeWhy isn't blood delivered to tissues through open spaces the way it is in some invertebrates?
- Going furtherWhat happens to oxygen delivery to distant tissues if the circulatory system's pressure drops too low?
Your turn1 of 2
Oxygen molecules move fast at the microscopic level, yet they still can't simply diffuse on their own from your lungs all the way to your toes. Why can't oxygen just diffuse directly from your lungs to your toes without a delivery system?The Structure of the Heart and How It Pumps
- How it worksWalk me through how blood flows through the heart's atria and ventricles in one full heartbeat.
- How it worksHow do heart valves keep blood flowing in one direction and prevent it from flowing backward?
- Worked exampleFind a person's resting heart rate given 70 heartbeats measured over exactly one minute.
- Common mistakeWhy doesn't blood mix between the heart's left and right sides in a healthy heart?
Your turn1 of 2
A nurse counts 117 heartbeats while measuring a patient's pulse over exactly 44 seconds. What is the patient's heart rate in beats per minute?Arteries, Veins, and Capillaries
- How it worksHow do capillary walls become just one cell thick to allow oxygen and nutrients to diffuse out?
- Going furtherWhat happens to blood pressure and speed as blood moves from a large artery into countless tiny capillaries?
- Common mistakeWhy don't veins carry only deoxygenated blood and arteries only oxygenated blood in every single case?
Your turn1 of 2
An artery wall is thick and muscular while a vein wall is comparatively thin, and only veins contain one-way valves along their length. Why do arteries have thick, muscular walls while veins have thin walls and one-way valves?Blood Composition and Function
- How it worksHow do red blood cells, white blood cells, platelets, and plasma each contribute a different function to blood?
- Common mistakeWhy isn't blood just a red liquid with nothing else dissolved or suspended in it?
- Going furtherWhat happens to a blood sample when it's spun in a centrifuge and separates into distinct layers?
Your turn1 of 2
A single drop of blood under a microscope reveals disc-shaped red blood cells, several distinct kinds of white blood cells, tiny platelet fragments, and a pale yellow fluid surrounding them all. Why does a single drop of blood contain several completely different types of cells doing different jobs?How Breathing Moves Air In and Out of the Lungs
- How it worksHow does the diaphragm contracting and flattening create the pressure change that pulls air into your lungs?
- Worked exampleFind whether air flows into or out of the lungs when the diaphragm relaxes and the chest cavity shrinks.
- Common mistakeWhy doesn't the lung tissue itself do the work of pulling air in?
Your turn1 of 2
A person breathes 17 times per minute while at rest, moving about 560 milliliters of air with each individual breath. About how many milliliters of air do they move through their lungs per minute?Gas Exchange in the Alveoli
- How it worksHow does oxygen diffuse from an alveolus into a surrounding capillary while carbon dioxide diffuses the opposite way?
- Common mistakeWhy doesn't gas exchange in the alveoli require any active pumping or energy from the cells involved?
- Ties togetherHow does the alveoli's huge surface area connect back to the surface-area principle covered in the cell unit?
Your turn1 of 2
A person's lungs branch into hundreds of millions of tiny air sacs called alveoli, rather than staying as two large, simple balloon-like chambers. Why do your lungs branch into hundreds of millions of tiny air sacs instead of staying as two big balloons?How Circulation and Respiration Work Together
- How it worksWalk me through the full path an oxygen molecule takes from the alveoli to the heart to a working muscle cell.
- Going furtherWhat happens to breathing rate and heart rate together during intense physical exercise?
- Ties togetherHow do the circulatory and respiratory systems together support the demands of cellular respiration during exercise?
Your turn1 of 2
An oxygen molecule you just inhaled can reach a working leg muscle cell within a matter of seconds, despite the substantial physical distance it has to travel through the body. Why does an oxygen molecule you just inhaled reach your leg muscles within seconds?