CONTENTS:

3.1 Lung Anatomy and Function
3.1.1 The Normal Lung
3.1.2 The Smoker’s Lung

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If you’re in a bad situation, don’t worry it’ll change. If you’re in a good situation, don’t worry it’ll change.

Section 3 describes the normal lung anatomy, benign lung conditions including infections, vascular abnormalities and inflammatory disease as well as benign lung tumors. These benign conditions may appear in lung screening imaging as solitary pulmonary nodules (SPN), as multiple nodules or as lung masses.

Finally an account will be given of the benign causes of solitary pulmonary nodules (SPN) Indeed, solitary pulmonary nodules are a regular and important finding in screening and lung CT imaging.

My wife accused me of over-complicating things. I almost suffered a mechanical obstruction of the flow of air from the environment into the lungs!

3.1 Lung Anatomy and Function

 
So, in order to understand the way that lung abnormalities are classified and described in diagnostic reports, particularly in pathology reports, some understanding of the components of the lung tissue is helpful.

3.1.1 Normal Lung Anatomy

 
Firstly, inhaled air is transmitted down the trachea to the main bronchi and then to the bronchioles.   In addition, cartilage surrounds the Bronchi and helps to  retain the shape and keep them open. The bronchi contain mucinous glands within their wall that contain ‘goblet cells.’

Indeed, larger bronchioles are lined by ciliated columnar epithelium or cuboidal epithelium (smaller bronchioles leading to alveoli).  The epithelium contains ciliated columnar cells in larger bronchioles, or non-ciliated in smaller bronchioles.

Bronchioles have a diameter of 1 mm or less and do not have goblet cells, but there are Clara cells that are secretory.  Clara cells secrete one of the components of surfactant. A rim of smooth muscle surrounds the bronchioles but they do not have cartilage.

Terminal bronchioles are the smallest of the conducting airways.  The terminal bronchioles lead to the respiratory bronchioles.  Again, the respiratory bronchioles lead to the alveoli where oxygen exchange to the blood occurs via the alveolar capillaries.
 

Figure 3.1 Diagram of the Normal
Respiratory System

A dog walker was found dead in the local park. Police found the dog, but as yet they have no lead.

What are the Alveoli

 
Thin tissue sections of lung examined using a microscope give an appearance of a fine lace-like structure.  However, most of the normal lung consists of air spaces lined by thin-walled alveoli.

A single layer of epithelial cells make  up the alveoli.  Endothelial cells line alveolar capillaries. Between the alveoli, there is a thin layer of connective tissue.

There are two main types of alveolar epithelial cells:

• Type I pneumocytes: large flattened cells – (95% of the total alveolar area) which present a very thin diffusion barrier for air exchange.
• Secondly, we have Type II pneumocytes (5% of the total alveolar area and 60% of the total number of cells). Type II pneumocytes secrete ‘surfactant’ that decreases the surface tension between the thin alveolar walls and stops alveoli collapsing on breathing out.

Figure 3.2 Normal glandular bronchial epithelium.

The glandular cells of the normal bronchi and bronchioles
have surface cilia and contain mucin within their cytoplasm.
This high power photomicrograph is stained for mucin
(purple / pink). PAS (x 60)

Wow! Doesn’t that look like a lovely pink caterpillar?

Do pink caterpillars actually exist?

Alveolar macrophages are important cells of the immune system that ingest bacteria and foreign particles, and they arise from circulating cells (monocytes) in the blood.

The respiratory portion of the lung consists of respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli.
 

Figure 3.3 Diagram showing the main
constituents of the lung alveolus.

The alveolar-capillary barrier varies from 0.2 to 2.5 µm in thickness.
A very thin basement membrane  separates the capillary endothelial cells (in red) and the alveolar epithelial cells.  The basement membrane allows
oxygen and carbon dioxide to diffuse. Alveolar capillaries branch
from the pulmonary arterioles.

3.1.2 The Smoker’s Lung Anatomy

 
Cigarette smoking causes a number of changes in the lung tissue, with the most obvious being the accumulation of fine particles of black carbon.  Indeed,  although carbon settles within the lung tissue, most of it concentrates  in the lymph nodes in the lungs.

Smoking also destroys the cilia that line the bronchi and bronchioles that bring air into the lung. In normal lungs, cilia provide an important defense. The cilia move mucus that contains trapped foreign particles and can be coughed up. In smokers, these particles and carcinogens cannot be removed from the lung, increasing the risk of lung cancer and infection.

Chronic smoking also causes a change to the ciliated glandular epithelium of the bronchi. As a response to injury, the normal glandular epithelium is replaced by squamous epithelium in a process known as ‘squamous metaplasia.’ Squamous metaplasia explains why squamous carcinoma of the bronchus is so common in smokers.

Smoking increases the risk of emphysema, a loss of the elasticity of the lung, causing destruction of alveolar walls and loss of the ability for oxygen to diffuse to the blood.

There are so many reasons up there to stop smoking.

Yes, and there are some good links in patient information to help you get started.

Figure 3.4 Comparison of the Normal Lung (N)
and the Smoker’s Lung (S).

Photomicrographs show that the normal lung (N) alveolar spaces are clear.
A small bronchus (B) has cartilage (C) in its wall. An arteriole (A) is
included. The smoker’s lung (S) contains deposits of black carbon pigment.

I was so horrified when I read about the effects of smoking that I gave up…. reading

References:

Brudin LH, Rhodes CG, Valind SO, Wollmer P, Hughes JM. (1987) Regional lung density and blood volume in nonsmoking and smoking subjects measured by PET. J Appl Physiol (1985). 1987 Oct;63(4):1324-34. (Retrieved 10^th Aoril 2015): http://www.ncbi.nlm.nih.gov/pubmed/3500940

Auerbach O, Stout AP, Cuyler Hammond E, Garfinkel L. (1961) Changes in Bronchial Epithelium in Relation to Cigarette Smoking and in Relation to Lung Cancer. N Engl J Med 1961; 265:253-267August 10. (Retrieved 10^th Aoril 2015):
 

More references for this section are on this page.

Patient Information:

National Cancer Institute Harms of Smoking and Health Benefits of Quitting. (Retrieved 10^th April 2015): http://www.cancer.gov/cancertopics/causes-prevention/risk/tobacco/cessation-fact-sheet

Medicine Net.com Smoker’s Lung: Pathology Photo Essay (Retrieved 10^th April 2015): http://www.medicinenet.com/smokers_lung_pathology_photo_essay/article.htm
 

More patient information for this section is on this page.

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