An Overview of Human Cells for Light
Microscopists Part II - Human Skin
& Human Lungs
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Page: 1 | 2 | 3 | 4 | For Part 1 The Human Cell - go here!
The Human Lung People tend to think of the lungs in a very simplistic
way, imagining them to be like a pair of balloons inflating and deflating. In fact, the lungs are far more sophisticated.
They are yet another marvel of Nature's sophisticated engineering and, along with the heart, form a critical major
organ of the body. Most Microscopists look at the lung in a series of sections through the lobes or Bronchi with
an optical microscope. Even at relatively low powers, it is fairly easy to determine diseased cells from healthy
The greatest enemy of human lungs is cigarette smoke, not least because it contains carcinogenic substances which
increase the risk of cancers. Many people are also genetically susceptible to other compounds present in the smoke.
These compounds will cause a cessation of lung elasticity over time, resulting in ever decreasing lung capacity
and functionality, and ultimately causing a slow and miserable death. Although the lungs have mechanisms for clearing
dust and particles from their interior, it is not possible for them to unlock and clear carbon particles from the
cells. All damage caused by smoke is therefore irreversible! Any article about the human lungs would be less than
beneficial if it did not also cover some of the critical diseases, especially where they are preventable. So, I
will discuss both healthy and diseased lungs here. If you smoke (like me) you may prefer to negate the awful truth
about the consequences, but since I already suffer from COPD and my mother recently died of Lung Cancer, I can
only say to any reader that the sooner you give up the better. If you are so addicted (and I know what that is
like) consider switching to the new electronic
cigarette and you can continue with
your habit with a massively reduced risk of lung damage (almost zero risk).
Almost the whole of your chest region is allocated as the home of your lungs and heart. You can see in my 3D model
below (if you have 3D red/cyan glasses, wear them now for true 3D), how the lungs and heart are prominently set
above the stomach and intestines.
The Lungs are in two halves with the Right side
(1st person perspective) larger than the left side - which (the latter) is smaller to make room for the heart next
to it. You can see the various major processes and the Lung's close association to the heart in the 3D model below,
where I have made the lungs semi-transparent to reveal the Bronchiole, Alveoli, and other processes inside.
You may wish to consider the model against the x-ray below.
An outline of each of the main processes in the lung and also associated with both the lung and the heart are below.
This is the basic windpipe with one opening arriving within the mouth and the other dividing off into the left
and right lungs forming the Bronchi.
Bronchus / Bronchi
The major two branches coming from the lower Trachea into the lungs (one into each lung). The right bronchus divides
into three Bronchi, which extend separately into the three lobes of the right lung. The left bronchus divides into
two bronchi which penetrate the two lobes of the left lung.
Bronchiole / Bronchi
(see Bronchus above)
The bronchioles (bronchi) divide repeatedly into many alveolar tubes lined with cuboidal epithelium. These terminate
in hollow lobed air sacs called Alveoli. There
are over 700 million alveoli present in human lungs, representing a surface area of approx. 85 square metres. The wall of each alveoli is just 0.0001 mm
thick, and on the outside is a dense network of blood capillaries which have originated from the pulmonary artery
and ultimately will rejoin with the pulmonary vein. Oxygen diffuses across the thin membrane represented by the
alveolar epithelium and capillary endothelium to pass into the blood plasma. It then combines with hemoglobin in
the red blood cells to form Oxyhemoglobin, whilst carbon dioxide diffuses ion the reverse direction into the alveolar
cavity. Note: the alveolar capillaries diameter is smaller than the diameter of the red corpuscles. This means
blood pressure squeezes the cell through the capillary, resulting in a slower progress and allowing more time for
the gas exchange to take place over a wider area of the blood cell.
This is not shown on the 3D model. The pleura consist of two membranes separated for most of their area by a visceral
fluid (a bit like a super fine film) in contact with both surfaces, which allows the two membranes to slide smoothly
over each other. The two layers meet only at the hilum of the lung. (hilum : point at which the lung is connected to the trachea by its bronchus).
Any pain a person
may feel from their lungs, is probably originating from the Pleura as the lung interior does not contain pain receptors!
(Inflammation of the pleura or excessive fluid within the two membranes will cause pain! It is the surface tension
between the inner membrane and the outer membrane which hold the lungs open and prevent them from collapsing like
This is not shown on the 3D model but is part represented by the broken blue line. The action of the diaphragm
is responsible for the movement of the lungs (inhalation and exhalation). The diaphragm is an area of muscle attached
to the chest cavity. When they pull on the cavity, the chest area expands (the ribs flex to allow this) and the
action of the pleural membranes (and the fluid sticking them together) pulls the lungs into expansion. When the
Diaphragm relaxes the chest wall contracts allowing the lungs to return to normal - exhalation / expiration occurs.
An interesting point to remember is that not all lungs are equal, in the fact that the lungs of birds, reptiles,
amphibians, and Invertebrates all differ from mammalian lungs (ours) and each other. More info herewiki.
The Optical Microscope can be used to recognise many diseases in sections of lungs of tissue. Before we move on
to look at this aspect through an optical microscopist's perspective, you can see an interesting 3D (red/cyan)
video of the lungs, and their position in the human frame in the movie below.
The lungs are almost completely transparent so you can see their location
with respect to the heart and other organs more clearly.
Published in May 2010 Micscape Magazine.
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