Gas Exchange

Question 1

What are the adaptation of the human gas exchange surfaces?

Answer 1

The human gas exchange surfaces link the circulatory system with the atmoshphere and is adapted to:
* Clean and warm the air that enters during breathing.
* Maximise the surface area for diffusion of oxygen and carbon dioxide between blood and atmosphere.
* Minimise the distance for this diffusion.
* Mantain adequent gradients for diffusion.

Question 2

Why do multicellular organisms usually have a specialised gas exchange surface?

Answer 2

Most organism need a supply of oxygen for respiration. In a single celled organism, the oxygen simply diffuses from the fluid outside of the cell, through the cell surface membrane and into the cytoplasm. In a multicellular organism such as a human, most of cells are a considerable distance away from the external enviroment from which oxygen is obtained.

Multicellular organisms, therefore, usually have a specialised gas exchange surface where oxygen from the external enviroment can diffuse into the body and carbon dioxide can diffuse out.

Question 3

What is the gas exhange surface in humans and where is it located?

Answer 3

In humans, the gas exchange surface is the alveoli (singular:alveolus) in the lungs.

Question 4

Describe the distrubution of alveoli in the lungs and their structure.

Answer 4

Although each induvidual alveolus is tiny, the alveoli collectively have a huge surface area, probably totalling about 70-75m^2 in an adult human. This means that a large number of oxygen and carbon dioxide molecules can diffuse through the surface at any one moment giving a high rate of gas exchange.

Question 5

Why is the large surface area of alveoli required?

Answer 5

The large surface area of alveoli is required as oxygen is not very soluble in water.

Question 6

Where are the lungs present?

Answer 6

The lungs are in the thoracic (chest) cavity surrounded by the pleural membranes, which enclose an aritight space. This space contains a small quantity of fluid to allow friction free movement as the lungs are ventilated by the movement of the diaphragm and the ribs.

Question 7

Define alveolus

Answer 7

A small air sac in the lungs composed of a single layer of squamous epithelium and some elastic fibres. Each alveolus is surrounded by capillaries that transport blood from the pulmonary artery to the pulmonary vein.

Question 8

Define a gas exchange surface.

Answer 8

Any part of the organism that allows the movement of gases between the surroundings and the body. Gas exchange occurs across the body surface of some organisms to have a large surface area: volume ratios. Organisms with small ratio’s have specialised gas exchange surfaces, such as the lungs of mammals and the gills of fish.

Question 9

Define ventilation

Answer 9

Breathing is the movement of air into and out of lungs. Ventilation is the scientific word for breathing.

Question 10

Define respiration.

Answer 10

Respiration is a chemical reaction to release energy in the form of ATP.

Question 11

What are the lungs ventilated with?

Answer 11

The lungs are ventilated with air that passes through a branching system of airways.

Question 12

Describe the location of the airways present in the lung?

Answer 12

Leading from the throat to the lungs is the trachea. At the base of the trachea are two bronchi (singular:bronchus) which subdivide and branch extensively forming a bronchiole “tree” in each lung. Each bronchus divides many times to form smaller and smaller bronchioles. Terminal broncholes divide to form even narrower respiratory bronchioles that supply the alveolur ducts with air.

Question 13

Define trachea.

Answer 13

Trachea (windpipe): The tube-like structure that extends from the larynx to the bronchi. It allows movement of air into and out of the lungs.

Question 14

Define bronchus

Answer 14

A major branch of the trachea that extends into the lungs.

Question 15

Define bronchiole.

Answer 15

A microscopic branch of a bronchus that leads to the alveoli.

Question 16

Define cartillage.

Answer 16

A type of skeletal tissue that is strong and flexible and supports the larynx, trachea and bronchi in the gas exchange system. Cartilage is also found at joints between bones and in the external ear.

Question 17

What is the function of cartilage in the trachea and bronch?

Answer 17

Cartilage in the trachea and bronchi keep these airways open and air resistance low. It prevents them from collapsing or bursting as the air pressure changes during breathing. In trachea, there is a regular arrangement of C-shaped rings of cartilage. In bronchi there are irregular blocks of cartilage.

Question 18

Define goblet cell

Answer 18

A cell shaped like a drinking goblet that secretes mucus. Goblet cells are found in epithelia lining parts of the gas exchange system and other systems for example reproductive and digestive system.

Question 19

Define ciliated epithelium.

Answer 19

An epithelium that consist of mainly ciliated cells, may also contain goblet cells.

Question 20

Define mucin.

Answer 20

Any glycoprotein that forms part of the mucus secreted by goblet cells and mucous cells.

Question 21

Where is mucus produced in the trachea and bronchi?

Answer 21

In the trachea and bronchi, the mucus produced is by goblet cells of the ciliated epithelium.

Question 22

What is mucus?

Answer 22

Mucus is a slimy solution of mucin, which is composed of glycoproteins with many carbohydrate chains that make them sticky and able to trap inhaled particles. Mucus is also made by mucous glands beneath the epithelium.

Question 23

What organelles does a goblet cell contain?

Answer 23

The upper part of each goblet cell is swollen with mucin droplets which have been secreted by the cell.
The goblet cell also contains:
Golgi body/apparatus
RER
Mitochondria
Nucleus

Question 24

Where did a goblet cell get its name from?

Answer 24

The lower part of the cell is thin so that the cell resembles a drinking vessel known as a goblet.

Question 25

What happens if a chemical pollutant dissolves in the mucus?

Answer 25

Some chemical pollutants such as sulfur dioxide and nitrogen dioxide, can dissolve in mucus to form an acidic solution that irritates the linings of the airways.

Question 26

Where are ciliated epithelium cells found and what is their function?

Answer 26

Between the goblet cells are ciliated epithelial cells. The continual beating of their cilia carries the layer of mucus upwards towards the larynx at a speed of about 1cm min-1.

Question 27

What happens to the mucus when it reaches the top of trachea?

Answer 27

When mucus reaches the top of the trachea it is usually swallowed so that pathogens are destroyed by acid in the stomach.

Question 28

Where is the smooth muscle in bronchioles located and what is its function?

Answer 28

Bronchioles are surrounded by smooth muscle, which can contract or relax to adjust the diameter of these tiny airways.
When the smooth muscle contacts the airway constricts and when the smooth muscle relaxes the airway widens (during excercise).

Question 29

What happens to the smooth muscle in bronchioles during exercise?

Answer 29

During exercise, the muscles relax to allow a greater flow of air to the alveoli. The absence of cartilage in bronchioles makes these adjustments possible.

Question 30

What is the role of macrophages in cleaning the air?

Answer 30

Phagocytic white blood cells known as macrophages patrol the surfaces of the airways scavenging small particles such as bacteria and fine dust particles. During an infection, the macrophages are joined by other phagocytic cells which leave the capillaries to help remove pathogens.

Question 31

Where are the elastic fibers in alveoli and what is their function?

Answer 31

Alveolar walls contain elastic fibers which stretch during inspiration and recoil during expiration to help push put the air. This elasticity allows alveoli to expand according to the volume of air breathed in.

Question 32

What happens when the alveoli are fully expanded?

Answer 32

When the alveoli are fully expanded during exercise, the surface area available for diffusion increases, and the air is expelled efficiently when the elastic fibers recoil during exhalation.

Question 33

Where are collagen fibers present in alveoli and what is their function?

Answer 33

The alveolar walls also contain collagen fibers to provide support and help prevent alveoli from bursting.

Question 34

Where is squamous epithelial cells present in the alveoli?

Answer 34

The alveoli have extremely thin walls, each consisting of a single layer of squamous epithelium cells. These cells are like fried eggs. The nucleus is like the yolk surrounded by a thin layer of cytoplasm which is only 25nm thick. No part of the cell is more than 0.5 μm thick.

Question 35

Why can oxygen and carbon dioxide molecules diffuse quickly between air and blood?

Answer 35

Pressed closely against the alveoli walls are blood capillaries, lined by endothelial cells that are also very thin, Oxygen and carbon dioxide molecules can diffuse quickly between the air and the blood because the distance is very small.

Question 36

How is a steep concentration gradient maintained for gas exchange to occur rapidly?

Answer 36

For gas exchange to occur a steep concentration gradient must be maintained. This is done by breathing and by the movement of the blood. Breathing brings supplies of fresh air into the lungs, with a relatively high oxygen concentration and a relatively low carbon dioxide concentration. Blood is brough to the lungs with a lower concentration of oxygen and a higher concentration of carbon dioxide than the air in the alveoli. Both gases then diffuse down their concentration gradients in opposite directions. The blood is constantly flowing through and out of the lungs so as the oxygenated blood leaves more oxygenated blood enters to maintain a steep concentration gradient with each new breath.

Question 37

Define elastic fibres.

Answer 37

Bundles of the fibrous protein elastin which can stretch and recoil like elastic bands. They can stretch up to twice their length before breaking.

Question 38

What is the function of cilla?

Answer 38

Cillia moves mucus to the back of the throat/away from the lungs. The mucus is swallowed and the pathogens are destroyed by acid in the stomach.

Question 39

Describe the structure of bronchioles.

Answer 39

Bronchioles do NOT contain any cartilage, are close to the alveoli and may have folded epithelium when its smooth muscle (if present) contracts.
They have very few ciliated cells and mostly squamous cells.
They have ciliated epithelium.
Terminal bronchiole (closer to the bronchus) have some smooth muscle.
Respiratory bronchioles (further from the bronchus) do not have smooth muscle and have less cilia and sometimes have none.