Gaseous Exchange
Gaseous Exchange in humans
- Created by: Katrina
- Created on: 15-05-12 16:12
Adaptations
quantity of materials needed are proportional to the volume of the organism
diffusion of substances is proportional to surface are
large organism = small SA:V ratio small organisms = large SA:V ratio
unicellular organism = very large SA:V ratio
the distance materials have to travel is very short so materials are obstained through diffusion
large organisms cannot rely on diffusion alone to provide materials-need special gaseous exchange surfaces and transport systems e.g. gills in fish, lungs in humans
humans = small SA:V and high metabolism so need specialised gaseous exchange surfaces and transport systems
Surface Area to Volume ratio
exchange surfaces: alveoli, blood vessel walls, villi, microvilli - need large SA:V to be effective
adaptations:
flattened body (flatworms)
central region filled with gut (not metabolising cells)
specialised exchange surfaces with large SA:V for diffusion and transport system
Lungs
human gaseous exchange system links circulatory system with atmosphere
adapted to:
provide clean, warm air (moist, hairy nose)
large SA for gaseous exchange
extensive and close blood supply so that diffusion of gases is over a short distance and concentration gradient maintained with constant blood flow
General Principles for Efficient Gas Exchange 1
LARGE SURFACE AREA
actual repiratory surface on alveoli inside lungs
average adult has approx. 600million alveoli=total SA approx. 100m2 (alveoli folded to increase SA)
bronchioles highly branched giving large number pathways for air to move in and out of lungs
CONCENTRATION GRADIENT
without this, nothing would diffuse
blood carries oxgenated blood away from alveoli and deoxygenated to alveoli
ventilation brings oxygen into to alveoli and takes carbon dioxide away
capillaries surrounding alveoli are narrow which slows down blood flow allowing time for gaseous exchange
General Principles for Efficient Gas Exchange 2
THIN PERMEABLE MEMBRANE
walls of alveoli and capillaries are composed of a simple layer of flattened epithelial cells (2 thin cells only 0.1-0.5um) allow rapid diffusion
MOIST EXCHANGE SURFACE
water diffuses rom alveoli cells into alveoli so they are constantly moist
oxygen dissolves into this water before diffuses through these cells into the blood where it's taken up by haemoglobin in the RBC
OTHER FACTORS
where appropriate, good blood supply to carry oxygen away to the tissues and main a steep concentration gradient
Alveoli
site of gaseous exchange
tiny hollow saces of thin, flattened sqamous epithelial cells (short distance to diffuse)
surface is 0.2um thick
elastic fibres to allow expansion when breathing in and recoil when breathing out
water lining alveoli allow diffusion of gases
Surfactant
when a person breathes out, the alveoli deflate and inner surface can touch each other
surface tension of the water on the alveoli could make them stick together and therefore not inflate again
is like a detergent secreted by some cells which reduces surface tension of the water
stops alveoli from collapsing
has antibacterial effect
PREMATURE BABIES
often struggle to breath (respiratory distress syndrome: RDS)
artificial surfactant may be used to treat premature babies before their own lungs secrete surfactant
artificial surfactant decreases amount of time infants spend on the ventilation
Spirometer
inspiratory resever volume-volume of extra air breathed in
tidal volume-volume of air breathed in/out at rest
residual volume-volume or air remaining to prevent lungs from collapsing
expiratory reserve volume-volume of air one can breath in or out in one breath
vital capacity-maximum volume of air one can breath in or out in one breath
total lung capacity-total volume of air in the lungs
limewater used to absorb the carbon dioxide breathed out to prevent you breathing it back in
nose clip to prevent oxygen being lost by your nose so it doesn't affect results
trace gradually falls because the volume of air in the drum will gradually decrease as it is being breathed out as carbon dioxide and absorbed into the limewater
Chronic Bronchitis
tar promotes mucus production (goblet and mucus glands)
cilia destroyed
persistent cough develops to remove mucus
bacteria, viruses and dust block the bronchioles-bronchioles damaged
smooth muscle and epithelial membranes develop scar tissues which narrow airways
lungs susceptible to pneumonia
Emphysema
many infections e.g. industrial dust, smoking, lead to migration of phagocytes from blood to respiratory tract
they release enzyme elastase (protease) to clear a pathway for phagocytes to clear irritant in alveoli
elastase destroys elastin in alveoli-unable to expand a recoil and alveoli sometimes bursts and large spaces appear
very little air exchanged with each breath so breathing rate increases due to lack of oxygen
blood pressure increases due to resistance of blood vessels in the lungs to blood
right side of hreat increases
irreversible-oxygen mask required
emphysema and chronic bronchitis known as chronic pulmonary obstructive disease (CPOD)
Lung Cancer
tar in tobacco contains carcinogens
carcinogens react with DNA of lung epithelial cells causing mutation of cells
a malignant tumour is formed
cells break off, enter lymph system and carried to other organs (metastasis) to form secondary tumours
cannot be detected until tumours are 1cm2 causing person to cough blood and the tumour surgically removed
secondary tumours treated with radiation of chemotherapy
cigarette smoking linked to mouth, oesophagus, larynx, bladder, pancreas, kidney and cervical cancers
lung cancer diagnosed by bronchioscope (endoscope views epithelial lining), chest x-ray or CT scan
Epidemiological Data - Smoking and Lung diseases
50% smokers die of smoking-related disorders
98% people with emphysema are smokers and 20% smokers have emphysema
90% deaths from COPD are smokers-COPD rare in non-smokers
pneumonia and influenza 2x as high in smokers and lung cancer 18x more likely in smokers than non-smokers
25% smokers die of lung cancer
risks increase if: inhale, start young, high tar, high number, smoke a long time
risks decrease if: stop smoking
takes 10 years to return to non-smoker risk
as smoking in developed world decreases, smoking related diseases are decreasing
increasing in developing world
Epidemiological Data - conclusions and evidence
CONCLUSIONS
it is an associative link
experiments on animals show a direct causal link between smoking and lung cancer
EXPERIMENTAL EVIDENCE
carcinogens and co-carcinogens identified in tar
animals exposed to cigarettes developed tumours similar to those in humans-carcinogens from tar painted onto skin of mice; cancerous growths developed
Asthma
normal airway = some mucus, wide and open, not inflamed
asthmatic airway = membranes inflamed (histamine released), smooth muscle contracts and narrows lumen
asthmatic airway during attack = excess mucus produced blocks airways and creates wheezing sound
CAUSES
allergy-esp. dust mites (protein found in faeces), pollen, pet hair
atmospheric pollution and smoking
exercise induced asthma
inheritance
often develops after viral infection of lungs
TREATMENTS
steroids (e.g. beclmethasone):
- most common as they mimic action of hormones
- taken through inhaler
- slow to take effect but long lasting
- taken regularly to control asthma
- reduce inflammation
- used to stop an already happening attack
beta-agonists (e.g. salbutamol):
- via inhaler
- immediate relief
- relax smooth muscle
- keep airways open (bronchodilators)
Smoking and Disease
Carbon Monoxide
- combines readily with haemoglobin (more so than oxygen)
- causes reduction of oxygen in blood so physical activity harder to partake in
- hardening of arteries esp. coronary arteries supplying heart muscle
Nicotine
- makes tobacco addictive-stimulates release of adrenaline
- causes raised blood pressure and increased heart rate
- can lead to atherosclerosis-build up of fatty acids in arteries so increases blood pressure
- coronary heart disease and strokes
Tar
- goblet cells in lungs to over-produce mucus
- ciliated cells destroyed which waft mucus and dirt
- build up of mucus in bronchioles and bacteria and viruses multiply in mucus
- results in chronic bronchitis
Ventilation of the Lungs
inspiration->expiration
intercostal muscles contracts -> relaxes
ribs up an out -> down and in
diaphragm contracts and flattens -> relaxes
volume of thorax increases -> decreases
pressure in thorax decreases -> increases
outside air (atmospheric) pressure greater thus air moves in -> less thus air moves out
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