Human gas exchange system

Question 1

Why do humans have specialised surfaces

Answer 1

• to allow efficient gas exchange and to increase the surface area of humans as we have large volumes

Question 2

Describe the function and structure of the lungs

Answer 2

• they are the central part of the respiratory system and are where gas exchange occurs
• they are made of highly branched tubules called bronchioles

Question 3

Describe the function and structure of the trachea

Answer 3

• The trachea is a flexible airway from the mouth to the bronchi which is filled with cilia to dust mucus away from the lungs
• it is supported through rings of cartilage preventing their collapse

Question 4

Describe the function and structure of the bronchi

Answer 4

• two divisions of the trachea, the left and right bronchus
• they also contain cilia to move mucus which traps dust and dirt particles

Question 5

Describe the function and structure of bronchioles

Answer 5

• Narrow tubes which carry air from the bronchi to the alveoli
• the larger bronchioles contain cartilage to prevent their collapse
• they are lined with a epithelial layer and smooth muscle allowing the constrictions and control of air in and out of the alveoli

Question 6

Describe the function and structure of the alveoli

Answer 6

• the main site of gas exchange
• they are tiny sacs with epithelial cells for contractions and stretch of the alveoli
• the alveoli are one cell thick which reduces diffusion distance
• and are surrounded by capillaries to ensure that they have a constant supply of blood
  -having a close constant blood supply ensures that a steep concentration gradient is maintained
• there is a large number of alveoli which provides a large surface area

Question 7

What are the two processes that occur during breathing?

Answer 7

• inspiration (inhalation)
• expiration (exhalation)

Question 8

Name the three muscles involved in ventilation

Answer 8

• the diagram
• the internal intercostal muscles whose contraction leads to expiration
• the external intercostal muscles whose contraction leads to inspiration

Question 9

state the steps of inspiration

Answer 9

• The external intercostal muscles contract whilst the internal intercostal muscles relax
• the ribs are pulled upward and outward, increasing the volume of the thorax
• the diaphragm muscles contract, causing it to flatten which increases the volume of the thorax
• the increased volume of the thorax reduces the pressure in the lungs
• Now atmospheric pressure is greater than pulmonary pressure, forcing air into the lungs

Question 10

State the steps of expiration

Answer 10

– The internal intercostal muscles contract whilst the external intercostal muscles relax
- the ribs are pulled downward and inward, decreasing the volume of the thorax
- the diaphragm muscles relax, causing it to be pushed up which further decreases the volume of the thorax
- the decreased volume of the thorax increases the pressure in the lungs
- Now pulmonary pressure is greater than atmospheric pressure, forcing air out of the lungs

Question 11

What is the role of the alveoli in gas exchange

Answer 11

-they increase the SA of the alveolus
- each alveolus contains a network of capillaries which are lined with epithelial cells
- each alveolus is also lined with epithelial cells

Question 12

How does the alveoli increase the rate of diffusion

Answer 12

• red blood cells are slowed down when passing through the pulmonary cavity, allowing more time for diffusion
• to pass through the pulmonary artery, RBC are flattened which decreases diffusion distance
• the walls of the alveoli and capillaries are very thin,decreasing diffusion distance
• increases SA
• breathing and the circulation of blood from the heart, around the alveoli allow a constant step concentration gradient and a constant supply of oxygen
• blood flow in the capillaries also maintains a steep concentration gradient