Lecture 32. The Respiratory Tract

Question 1

Organisation of the respiratory system?

Answer 1

Air is delivered to the lungs via the trachea from the mouth and nose
There are two lungs, each divided into lobes – 3 lobes in the right lung & 2 lobes in the left lung
Bronchi and bronchioles distribute air throughout the lungs

Question 2

What do the bronchioles subdivide into?

Answer 2

Terminal bronchioles and respiratory bronchioles.

Question 3

What do respiratory bronchioles give rise to?

Answer 3

Alveoli, the sites of gas exchange

Question 4

What is the respiratory system comprised of?

Answer 4

The upper airways
The lower airways
The conducting zone
The respiratory zone

Question 5

What makes up the upper airways?

Answer 5

Also known as the upper respiratory tract
The mouth, nose, pharynx and larynx comprise the upper airways
Infection symptoms include: cough, sneezing, nasal discharge, runny nose, nasal congestion, fever, sore throat
Obstruction of the upper airways causing snoring during sleep

Question 6

What makes up the lower airways?

Answer 6

A.K.A. the lower respiratory tract
The lower airway extends from the top of the trachea to
the alveoli
Infection symptoms include: Bronchitis, oedema shortness of breath, weakness, fever, coughing and fatigue
Affect gas exchange

Question 7

What is the conducting zone?

Answer 7

Conducting zone extends from mouth and nose to terminal bronchioles
Conducts air but does not exchange gas

Question 8

What are the functions of the conducting zone?

Answer 8

Provides a low-resistance pathway for airflow
Does not contribute to gas exchange in the lung
Warms (or cools) and moistens the air
Defends against microbes, toxic chemicals and other foreign matter

Question 9

What are the 4 layers of defence of the airways?

Answer 9

Constriction of bronchioles via smooth muscle
Cilia
Mucus
Macrophages

Question 10

How does the cilia defend the airways?

Answer 10

Hair-like projections from epithelial cells that line the airways
Constantly beat upward toward the pharynx
Are immobilised by many noxious agents

Question 11

How does mucus defend the airways?

Answer 11

Mucus is secreted by glands and epithelial cells lining the airways − 100 mL/day
Particulate matter and bacteria in inspired air sticks to the mucus
Continuously moved by cilia to the pharynx
Swallowed − Every 30 seconds

Question 12

How do macrophages protect the airways?

Answer 12

Phagocytic cells that are present in the airways and
the alveoli
Engulf and destroy inhaled particles and bacteria
Injured by noxious agents, e.g. air pollutants and cigarette smoke

Question 13

What is asthma?

Answer 13

Asthma
Inflammation causes airway smooth muscle to be
hyper-responsive to triggers
Intermittent episodes of smooth muscle contraction
increases airway resistance
Reduced airway diameter increases work of breathing

Question 14

What are common disorders of the conducting zone?

Answer 14

Asthma and Bronchitis

Question 15

What is bronchitis?

Answer 15

Persistent inflammation of the bronchial walls
The airways are inflamed and thickened
Increase in mucus-secreting cells and loss of ciliated cells
Excessive mucus is produced
Obstruction of the airways results, hindering both breathing and oxygenation of the blood

Question 16

What are the functions of the respiratory zone?

Answer 16

Provides oxygen
Eliminates carbon dioxide
Regulates the blood’s pH in coordination with the
kidneys
Influences arterial concentrations of chemical messengers e.g. conversion of angiotensin I to the potent vasoconstrictor angiotensin II
Traps and dissolves blood clots arising from systemic veins

Question 17

What optimises gas exchange in the alveoli?

Answer 17

Thinness of barrier between blood within the alveolar wall capillary and the air within the alveolus
The vast surface area of alveoli in contact with capillaries
The moist surface of the alveolar cells

Question 18

What is Fick’s Law?

Answer 18

Rate of Diffusion ∝ Surface area

Question 19

What is the surface area of the lungs?

Answer 19

50-100m²

Question 20

What is ventilation?

Answer 20

Amount of gas getting to the lungs

Question 21

What is perfusion?

Answer 21

Amount of blood getting to the lungs

Question 22

What causes ventilation-perfusion mismatching?

Answer 22

Altered by hypoxia sensing cells that constrict vessels to
stop blood supplying areas with poor gas exchange

Question 23

What is a disorder of the respiratory zone?

Answer 23

Emphysema

Question 24

What is emphysema?

Answer 24

Lungs undergo self-destruction by proteolytic enzymes secreted by leukocytes
Adjacent alveoli fuse to form fewer but larger alveoli
Reduces surface area available for gas exchange
Destruction of alveolar walls and collapse of lower airways
Increased airway resistance due to inflammation greatly increases the work of breathing