3. Human Respiratory System

Question 1

Why do trachea and bronchi have C-shaped rings of cartilage but the bronchioles do not?

Answer 1

Cartilage keeps the airways open
By being C shaped, with the open side next to the oesophagus, means that the trachea maintains its shape without endangering or being endangered by the oesophagus.Also the C shape allows the trachea to expand during inspiration

As the branching bronchi get smaller and smaller, the proportion of cartilage in their walls decreases, while the amount of smooth muscle increases. This arrangement makes it possible to change the diameters of the small bronchi and bronchioles

Question 2

Inspiration

Answer 2

The diaphragm contracts and flattens downwards
The external intercostal muscles contract, pulling the ribs up and out
this increases the volume of the thorax
this increases the lung and alveoli volume
this decreases the pressure of air in the alveoli below atmospheric (Boyle’s law)
air flows in to equalise the pressure

Question 3

Expiration

Answer 3

Normal expiration
The diaphragm relaxes and curves upwards
The external intercostal muscles relax, allowing the ribs to fall
this decreases the volume of the thorax
this decreases the lung and alveoli volume
this increases the pressure of air in the alveoli above atmospheric (Boyle’s law)
air flows out to equalise the pressure

Question 4

Forced expiration

Answer 4

The abdominal muscles contract, pushing the diaphragm upwards
The internal intercostal muscles contract, pulling the ribs downward
This gives a larger and faster expiration, used in exercise

Question 5

The Mechanism of Breathing

Answer 5

These movements are transmitted to the lungs via the pleural sac surrounding each lung.
The outer membrane is attached to the thorax and the inner membrane is attached to the lungs.
Between the membranes is the pleural fluid, which is incompressible, so if the thorax moves, the lungs move too.
The alveoli are elastic and collapse if not held stretched by the thorax (as happens in stab wounds).

Question 6

Ciliated columnar epithelial tissue

Answer 6

Colum-shaped ciliated cells with hair-like structures called cilia covering an exposed cell surface
Line the trachea in the respiratory system in order to protect the lungs from infection
Cilia sweep pathogens away from the lungs

Question 7

Goblet cells in columnar epithelial tissues

Answer 7

Colum shaped cells in the respiratory tract as well

Goblet cells are specialised for secreting mucus - a mixture of glycoproteins and proteoglycans synthesised in the ER and Golgi

Secrete mucus to protect the lungs Prevents unwanted particles reaching the lungs from the air we breathe
Prevents bacteria reaching the alveoli

Question 8

Pleural membranes

Answer 8

are serous membranes

• one side lines body cavity wall and the other lines lungs
• secrete serous fluid that reduces friction and enables the membranes to slide over each other
• prevent lungs adhering to body cavity wall

Question 9

Surfactant in alveoli

Answer 9

surface of alveoli has to be moist so oxygen can dissolve in the water before it can diffuse through into blood in capillaries
Prevents sticking of membranes together in ‘bunches’