Respiratory system (Topic 6.4)

Question 1

What is Physiological respiration?

Answer 1

Physiological respiration involves the transport of oxygen to cells within the tissues, where energy production occurs

Question 2

How is ventilation defined

Answer 2

The exchange of air between the atmosphere and the lungs – achieved by the physical act of breathing

Question 3

What is gas exchange?

Answer 3

The exchange of oxygen and carbon dioxide between air in the alveoli and blood flowing in the adjacent capillaries via passive diffusion.

Question 4

What is the purpose of ventilation?

Answer 4

The purpose of ventilation is to maintain concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries. This is because gas exchange is a passive process.

Question 5

Why do the gases undergo passive diffusion?

Answer 5

Because there is a concentration gradient: the air in the alveolus has a higher concentration of oxygen and a lower concentration of carbon dioxide than the blood in the capillary.

Question 6

How lungs function as a ventilation system

Answer 6

The lungs function as a ventilation system by continually cycling fresh air into the alveoli from the atmosphere
This means O2 levels stay high in alveoli (and diffuse into the blood) and CO2 levels stay low (and diffuse from the blood)
The lungs are also structured to have a very large surface area, so as to increase the overall rate of gas exchange

Question 7

How is breathing defined?

Answer 7

Breathing is the active movement of respiratory muscles that enables the passage of air into and out of the lungs

Question 8

What is the mechanism of breathing

Answer 8

The mechanism of breathing occurs according to the principle of Boyle’s Law (pressure is inversely proportional to volume)

• When the volume of the thoracic cavity increases, pressure in the thorax decreases
• When the volume of the thoracic cavity decreases, pressure in the thorax increases

Question 9

What is inspiration?

Answer 9

Inspiration is when Muscles contractions causes an increase in the volume of the chest (thorax) which causes pressure in the lungs to become lessthan the atmospheric pressure, so air will moveintothe lungs from the atmosphere

Question 10

What is expiration?

Answer 10

Muscles contractions causes a decrease in the volume of the chest (thorax) which causes pressure to become greaterthan the atmospheric pressure, so air will moveoutof the lungs to the atmosphere

Question 11

Why are different muscles required for inspiration and expiration?

Answer 11

Because muscles only do work when they contract (generate a pulling force which is tension), and thus causes a movement in one direction, different groups of muscles are required to expand and contract chest volume

Question 12

What does it mean by antagonistic pair of muscles? (Define and explain)

Answer 12

A pair of muscles which perform opposite movements at different times. One muscle will contract to cause a movement in one direction, and for this muscle to cause a movement in the opposite direction, another second muscle will contract to bring this muscle in the elongated state, doing work in the opposite direction.

Question 13

If the alveoli were not ventilated, what would happen?

Answer 13

If the alveoli were not ventilated, equilibrium would be reached and no gas would be exchanged

Question 14

Describe the ventilation system

Answer 14

Air enters the respiratory system through the nose or mouth and passes through the pharynx to the trachea
The air travels down the trachea until it divides into two bronchi (singular: bronchus) which connect to the lungs
The right lung is composed of three lobes, while the left lung is only comprised of two (smaller due to position of heart)
Inside each lung, the bronchi divide into many smaller airways called bronchioles, greatly increasing surface area
Each bronchiole terminates with a cluster of air sacs called alveoli, where gas exchange with the bloodstream occurs

Question 15

Describe the structure of alveoli which makes it specialised for gas exchange

Answer 15

Alveoli function as the site of gas exchange, and hence have specialised structural features to help fulfil this role:

They have a very thin epithelial layer (one cell thick) to minimise diffusion distances for respiratory gases
They are surrounded by a rich capillary network to increase the capacity for gas exchange with the blood
They are roughly spherical in shape, in order to maximise the available surface area for gas exchange
Their internal surface is covered with a layer of fluid, as dissolved gases are better able to diffuse into the bloodstream

Question 16

Define pneumocytes

Answer 16

Pneumocytes (or alveolar cells) are the cells that line the alveoli and comprise of the majority of the inner surface of the lungs

Question 17

Outline type 1 pneumocytes

Answer 17

Type I pneumocytes

Type I pneumocytes are involved in the process of gas exchange between the alveoli and the capillaries
They are squamous (flattened) in shape and extremely thin (~ 0.15µm) – minimising diffusion distance for respiratory gases
Type I pneumocytes are connected by occluding junctions, which prevents the leakage of tissue fluid into the alveolar air space
Type I pneumocytes are amitotic and unable to replicate, however type II cells can differentiate into type I cells if required

Question 18

Outline type 2 pneumocytes

Answer 18

Type II pneumocytes are responsible for the secretion of pulmonary surfactant, which reduces surface tension in the alveoli
They are cuboidal in shape and possess many granules (for storing surfactant components)
Type II pneumocytes only comprise a fraction of the alveolar surface (~5%) but are relatively numerous (~60% of total cells)

Question 19

Why are type 2 pneumocytes important?

Answer 19

While this moist lining assists with gas exchange, it also creates a tendency for the alveoli to collapse inwards and resist inflation

This is because of the formation of hydrogen intermolecular bonds between liquid molecules which will cause the alveolus to collapse inwards. This is surface tension which minimises surface area and makes gas exchange impossible.

Type II pneumocytes secrete a liquid known as pulmonary surfactant which reduces the surface tension in alveoli (prevents or breaks hydrogen bonds between liquid molecules)

As an alveoli expands with gas intake, the surfactant becomes more spread out across the moist alveolar lining
This slows the rate of expansion, ensuring all alveoli inflate at roughly the same rate

Question 20

Explain how inspiration occurs

Answer 20

The muscles responsible for inspiration are the diaphragm and external intercostals (plus some accessory muscles)

Diaphragm muscles contract, causing the diaphragm to flatten and increase the volume of the thoracic cavity
External intercostals contract, pulling ribs upwards and outwards (expanding chest)
abdominal muscles and internal intercostal muscles are relaxed
These movements increases volume of the thorax cavity and hence decreases pressure inside
Air flows into the lungs from outside

Question 21

Explain how expiration occurs

Answer 21

The muscles responsible for expiration are the abdominal muscles and internal intercostals (plus some accessory muscles)

Diaphragm muscles relax, causing the diaphragm to curve upwards and reduce the volume of the thoracic cavity
Internal intercostal muscles contract, pulling ribs inwards and downwards (reducing breadth of chest)
Abdominal muscles contract and push the diaphragm upwards during forced exhalation
external intercostal muscles remain relaxed
Thorax cavity volume decreases and inside pressure increases
Air flows out of the lungs into the atmosphere

Question 22

What is lung cancer, its impact and types

Answer 22

Lung cancer describes the uncontrolled proliferation of lung cells, leading to the abnormal growth of lung tissue (tumour)

The abnormal growth can impact on normal tissue function, leading to a variety of symptoms according to size and location
The tumours can remain in place (benign) or spread to other regions of the body (malignant)

Question 23

Lung cancers are the most common cause of cancer-related death worldwide for two main reasons:

Answer 23

The lungs are vital to normal body function and thus the abrogation of their normal function is particularly detrimental to health
The lungs possess a very rich blood supply, increasing the likelihood of the cancer spreading (metastasis) to other body regions

Question 24

The common symptoms of lung cancers include

Answer 24

The common symptoms of lung cancers include coughing up blood, wheezing, respiratory distress and weight loss

If the cancer mass compresses adjacent organs it can cause chest pain, difficulty swallowing and heart complications

Question 25

State causes of lung cancer

Answer 25

There are many causes for lung cancer, including smoking, passive smoking, asbestos and silica, radon gas inhalation, air pollution, certain infections and genetic predispositions

Question 26

What is emphysema and the result of this condition

Answer 26

Emphysema is a lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls

The loss of elasticity results in the abnormal enlargement of the alveoli, leading to a lower total surface area for gas exchange
The degradation of the alveolar walls can cause holes to develop and alveoli to merge into huge air spaces (pulmonary bullae)

Question 27

What is the cause of emphysema and the consequence of its development

Answer 27

The major cause of emphysema is smoking, as the chemical irritants in cigarette smoke damage the alveolar walls

The damage to lung tissue leads to the recruitment of phagocytes to the region, which produce an enzyme called elastase
This elastase, released as part of an inflammatory response, breaks down the elastic fibres in the alveolar wall

Question 28

What is another minor cause of emphysema and a related possible solution to this condition

Answer 28

Possible solution- Elastase activity can be blocked by an enzyme inhibitor (α-1-antitrypsin), but not when elastase concentrations are increased (lower chances of this solution working)

A small proportion of emphysema cases are due to a hereditary deficiency in this enzyme inhibitor due to a gene mutation

Question 29

Common symptoms of emphysema include

Answer 29

Common symptoms of emphysema include shortness of breath, phlegm production, expansion of the ribcage, cyanosis and an increased susceptibility to chest infections