Gas Exchange
and Smoking
Human Gas exchange System
Trachea
 Inner membrane covered in
cilia,
 C-shaped rings of cartilage
at the front and side which
help protect the trachea and
keep it open.
 Not complete circles due to
oesophagus immediately
behind the trachea - partially
collapses to allow the
expansion of the
oesophagus when
swallowing large pieces of
food.
 Smooth muscle allows it to
regain its shape.
Cartilage – stops the respiratory tract from
collapsing
Cilia and goblet cells
mucus traps solid particles
cilia use periodic beating motion to move the
trapped particles up for clearance.
Mucous glands
• Glands are abundant in the upper respiratory
tract, but there are fewer lower down and they
are absent starting at the bronchioles.
• The same goes for goblet cells, although there
are scattered ones in the first bronchioles.
Smooth muscle and elastic
tissue
• Smooth muscle starts in the trachea,
where it joins the C-shaped rings of
cartilage. It continues down the bronchi
and bronchioles, which it completely
encircles.
• Instead of hard cartilage, the bronchi and
bronchioles are composed of elastic
tissue.
Bronchi
• Irregular rings of
cartilage surround the
bronchi, and as the
bronchi get smaller it
forms small plates and
islands
• Smooth muscle is
present
• As the cartilage
decreases, the amount
of smooth muscle
increases.
Bronchioles
• narrow tubes, less
than 1 millimeter in
diameter.
• No cartilage
• Change diameter to
either increase or
reduce air flow
using smooth
muscle.
• An increase in diameter is
called bronchodilation and
is stimulated by either
epinephrine or
sympathetic nerves to
increase air flow.
• A decrease in diameter is
called bronchoconstriction
and is stimulated by
Histamine,
parasympathetic nerves,
cold air, chemical irritants
and other factors to
decrease air flow.
Alveoli
 Very thin walls of
squamous
epithelium for gas
exchange
 Surrounded by a
network of capillaries
 Approximately 3
million alveoli within
an average adult
lung.
Alveoli have elastic fibres in the walls to allow the
alveoli to expand when breathing in but regain
their shape when breathing out.
Process of gas exchange
Key features of respiratory surface
• Thin – one cell thick alveoli next to one cell
thick capillaries. Therefore diffusion
distance small so it will be quick. (0.3μm
thick)
• Large – many alveoli and capillaries
therefore large area for gas exchange.
• Moist – alveoli covered in a thin layer of
moisture to allow gases to dissolve before
moving.
Smoking
Tar and carcinogens
• 40 known carcinogens in tobacco smoke
• Causes mutations
• Tar stimulates mucus production
Lung Cancer
• Carcinogens cause mutations in the
epithelial cells.
• It then spreads into the lymphatic system
and will then spread around the body.
• Takes 20 – 30 years to develop.
• Symptoms include coughing up blood.
Chronic Bronchitis
• ≡ Damage and blocking of the airways.
• Tar stimulates goblet cells to produce
more mucus.
• It also weakens and destroys cilia which
stops the mucus from being removed.
• This leads to infections in the alveoli and
blockage of the bronchioles.
• Infections like pneumonia develop.
Emphysema
• Inflammation of the lungs causes
phagocytes to leave the blood and
line the airways.
• To reach the lining they release
elastase which destroys elastin in the
alveoli walls so the phagocytes can fit
through.
• No recoil occurs in the alveoli and the
bronchioles collapse trapping air and
causing the alveoli to rupture.
• Air is not refreshed and the surface area
decreases so gas exchange decreases.
• People with emphysema have a rapid
breathing rate, and often need to move
around with a cylinder of oxygen.
Chronic Obstructive Pulmonary
Disease (COPD)
• When chronic bronchitis and emphysema
occur together.
• Causes 30 000 deaths in the UK alone
every year.
• Only noticeable once half the lung is
destroyed so not reversible.
Nicotine
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The main drug
Highly addictive
Travels to brain in a few seconds
Stimulates nervous system to reduce diameter
of arterioles and to release adrenaline
Heart rate and blood pressure increase
Blood supply to the extremities decreases
Increases stickiness of platelets increasing blood
clots
Damages lining of artery walls
Carbon Monoxide
• Joins with haemoglobin to form a stable
compound carboxyhaemoglobin.
• Haemoglobin not fully saturated with
oxygen.
• Strains the heart during exercise
• Carbon monoxide also damages lining of
arteries
Cardiovascular diseases
• Smoking is one of the major risk factors for heart
attack.
• The risk of developing coronary heart disease
(CHD) increases with length and intensity of
exposure to cigarette smoke.
• Among people less than 65 years of age, it is
estimated that 36% of CHD in men and 33% in
women is attributable to cigarette smoking.
• In all cases, risk increases with increased
consumption.
Coronary Heart Disease (CHD)
CHD has two principal forms - angina and heart
attacks.
Both occur because the arteries carrying blood to
the heart muscle become blocked or narrowed,
usually by a deposit of fatty substances, a
process known as atherosclerosis.
Angina is a severe pain in the chest brought on by
exertion and relieved by rest.
A heart attack is due to obstruction of a coronary
artery either as a result of atherosclerosis or a
blood clot: part of the heart muscle is deprived of
oxygen and dies.
Atherosclerosis
• is a condition in which an artery wall thickens as
a result of the accumulation of fatty materials
such as cholesterol.
• Smoking increases blood cholesterol levels.
• Cigarette smokers also have raised fibrinogen
levels and platelet counts which make the blood
more sticky.
• As the blockage progresses, blood flows less
easily through rigid and narrowed arteries and
the blood can form a thrombosis (clot).
• This sudden blockage of an artery may lead to a
fatal heart attack, a stroke or gangrene of the
leg.
Stroke
• When blood supply to part of the brain is blocked
due to atherosclerosis then that part is starved of
oxygen and it dies.
• Smokers are more likely to develop a cerebral
thrombosis (stroke) than non-smokers.
• A form of cerebral haemorrhage (subarachnoid)
is more common in smokers, especially among
women who also take the contraceptive pill.
Epidemiological vs experimental evidence
• Epidemiologists
– collect data
– look for correlations in lifestyle
• Experimental
– Carry out experiments
Epidemiological evidence
linking smoking to disease
• A survey started in 1951 in the UK
• Statistical facts:
– regular smoker 3 times more likely to die
prematurely
– More cigarettes per day the earlier they die
– Pulmonary disease increases with number
smoked
– 98% of emphysema sufferers are smokers
– Death rate from lung cancer 18x greater in
smokers
Experimental evidence linking
smoking and disease
• 1960’s
• Dogs made to inhale smoke directly or
through a filter.
• Dogs without filters developed lung cancer
and pulmonary disease.
• Chemicals trapped in filters were then
analysed
• Discovered tar contains carcinogens
Prevention of CHD
• Reduce risk by making lifestyle changes.
• Eg.
– stopping smoking
– eating more healthily
– doing regular exercise
Cure of CHD
• Coronary artery bypass
surgery
• Expensive ($80 000 +)
• May not last more than 5
years
• Drugs taken after to keep
blood from clotting
• Heart Transplant
• A heart transplant is surgery to remove a
damaged or diseased heart and replace it
with a healthy donor heart
• High risk as body may reject it.
• Finding donor with tissue match
• Expensive ($145 000)