Download Provide anatomy and physiology advice to clients

Provide anatomy and
physiology advice to clients
Gaseous exchange and breathing
Lung macro structure
• In our last session we looked at the
respiratory system histology. In this
session we are going to look closely at
how oxygen from our lungs enters our
blood. But before we come to that lets
revise briefly the macro structure of our
lungs. Note in this slide that the left lung
has a notch it. This allows the heart to
snuggle in because the heart’s apex is not
in the medial plane.
The lobes are separated into
segments
• From the diagram you can see that in each lobe
there are quite distinct branches of the bronchial
tree that align to segments. There are 10
segments in the lung and each is served by their
own artery and vein. Each segment is
separated by connective tissue and this makes it
easier to dissect out diseased components.
Look at the bronchial tree in this slide. Here
each segment has been painted in different
colours so that you can see them easily.
Mechanics of breathing
• When we breathe in, the muscles in our diaphragm
contract and move inferiorly (i.e. move downwards). At
the same time, the external intercostal muscles lift the rib
cage and pull the sternum forward. These two actions
expand the volume of the thoracic space by about 500ml
and the lung tissue can expand by that amount. So air
can rush in to fill the volume. During exercise when
deep breathing is required, several other muscles that
include the scalenes and the sternocleidomastoid
muscles raise the rib cage even further to permit more
air to enter. When we breathe out the reverse occurs.
Blood vessels
• Deoxygenated blood travels from the left
ventricle of the heart through the
pulmonary artery to the lungs, where it is
delivered to a fine network of capillaries.
These capillaries surround each alveoli.
Remember, that alveoli are composed of
squamous epithelial cells held together by
threads of smooth muscle. You can
visualise this in this slide. We have about
8 million alveoli in our lungs.
Lung structure revision
• The alveoli walls are very, thin single layers of squamous
epithelial cells. These are called Type 1 cells. In
amongst these cells are cuboidal cells which are called
Type 2 cells. These produce a surfactant which covers
the surface of Type 1 cells and this reduces surface
tension. This is very important because water molecules
tend to stick to each other and gas molecules, like
oxygen, would have difficulty moving across the
membrane if it was not for the surfactant. Type 3 cells or
macrophages can also been seen wandering around
looking for bacteria and viruses to devour.
Gas Exchange
• Oxygen readily diffuses from the lung across the
respiratory membrane (composed largely of
squamous epithelial cells) into the capillary
network. It diffuses across because the
pressure of oxygen is less in the capillaries than
in the lung. The oxygen readily combines with
haemoglobin in the red blood cells. Each red
blood cell can carry about 250 oxygen
molecules. Carbon dioxide from metabolism
diffuses out of the plasma into the lungs, where
it is expelled when a person breathes out.
Control of respiration
• Fortunately, we don’t have to sit and think about our
breathing. It just happens most of the time. That is easy
to say but the control mechanisms are quite complex
and is still the matter of extensive research.
• A portion of the brain is known as the inspiratory centre.
The neurons there fire regular bursts of impulses that
travel along the phrenic and intercostal nerves to excite
the diaphragm and the external intercostal muscles.
These contract and air rushes into the lungs. When
lactic acid builds up from anaerobic exercise or where
hypoxia occurs for any reason then the neurons
generate a gasping or puffing response.
Respiratory rhythm
• We all breath on a regular rhythm but the regulation for
that rhythm is obscure. It has been proposed that
pacemaker neurons control our breathing rate whilst
others have proposed that stretch receptors in the lungs
feedback to the brain. None of these explain why we
breathe slowly when asleep or why our breathing speeds
up when we think about something exciting like studying
anatomy and physiology. We do know that our breathing
rate is related to our emotional state and that the limbic
part of the brain has a role to play in this, so perhaps that
part of the brain is involved in deep regulation of
breathing rhythm.
Some clinical conditions
• The trachea and bronchus have smooth muscle
bands around the tubes and these can contract
if histamine is present in the blood. Histamine is
present as a response to inflammation such as a
cold virus or an allergy; hay fever or asthma.
The effect is to tighten up the air ways and this
constricts the amount of oxygen that can enter
and carbon dioxide that can leave. When
people take an antihistamine, they are opening
up the airway by reducing the effects of
histamine. When asthmatics inhale their reliever
puffer are also doing the same thing.
Activity
• Prepare a presentation aimed at high
school students to describe how oxygen
from the air makes its way into the lungs.