Blood Vessels and Respiratory Structures

Delivering the oxygen

When you exercise, your muscles need more oxygen and produce more carbon dioxide. Your body has to deliver one and remove the other, fast. This module follows that job through the blood vessels that carry the blood and the respiratory structures that take air down to the lungs, where gas exchange happens. (The heart itself is covered in its own module.)

Vessel and lung words

Four terms run through the whole topic.

Match each airway to its job

Name that vessel

Which statement best describes an artery?

• It carries blood away from the heart at high pressure
• It carries blood towards the heart at low pressure
• Its walls are only one cell thick
• It is the place where gas exchange happens

Why alveoli are brilliant

Alveoli are built to move gases into and out of the blood as fast as possible. Four features do the work: - A large surface area (millions of tiny sacs) for lots of exchange\n- Walls only one cell thick, so gases have a short distance to travel\n- A moist lining, so gases dissolve and diffuse\n- A rich blood supply, which keeps a steep concentration gradient\n\nTogether they make gas exchange by diffusion quick and efficient.

What helps gas exchange?

Select the TWO features of alveoli that help gas exchange.

• A large surface area
• Walls that are only one cell thick
• Thick, muscular walls
• No blood supply nearby

Artery vs vein

The two main vessels are built for opposite jobs - carrying blood out under pressure, and bringing it gently back.

Match each vessel to its description

Breathing in

What does the diaphragm do when you breathe IN?

• It contracts and flattens
• It relaxes and domes upwards
• It stays completely still
• It stops the ribs from moving

Follow the air

Put the structures that air passes through on its way into the lungs into the correct order.

• Mouth and nose
• Trachea
• Bronchi
• Bronchioles
• Alveoli

The delivery in words

An _____ carries blood away from the heart at high pressure, while a _____ carries it back with the help of valves. The tiny _____ have walls one cell thick for exchange. In the lungs, oxygen moves into the blood at the _____ by _____.

Identify the structure

Three descriptions. Pick the structure each one is describing.

• A blood vessel with thick, muscular walls carrying blood away from the heart at high pressure. Which is it?
• A blood vessel with walls just one cell thick, where oxygen passes into the tissues. Which is it?
• Tiny air sacs in the lungs with a huge surface area, where gas exchange happens. What are they?

Your turn: explain the alveoli

Explain how the alveoli in the lungs are adapted for efficient gas exchange. Give at least three features and say why each one helps.

• Name at least three features of the alveoli
• For each feature, explain how it helps gas exchange
• Refer to surface area, wall thickness, moisture or blood supply
• Link the features to keeping a steep concentration gradient for diffusion

Tie structure to function

Always tie structure to function. Arteries have thick walls because they carry blood at high pressure; veins have valves because their blood is at low pressure; capillaries are one cell thick so gases can diffuse quickly. For the lungs, remember the alveoli features all serve one goal - fast diffusion - and do not fall for the classic trap: when you breathe in, the diaphragm contracts and flattens, it does not relax.