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Gas exchange
>all gas exchange occurs via diffusion
> two processes; internal and external respiration
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Internal respiration
- >The exchange of
- O2 & CO2 between the systemic
- capillaries and the body’s cells.
- >oxygenated blood leaves the heart through Left
- ventricle, into aorta and travels to tissue.
- >as it reaches the capillaries, O2 diffuses out of
- capillaries across to tissues.
>CO2 diffuses out of tissues and into capillaries
>Blood returns to heart via vena cava, into Right atrium
>blood is now poor in O2 and rich in CO2
-
External respiration
- >the exchange of
- O2 & CO2 between the capillaries
- & Alveoli
- >Blood leaves the heart via Right ventricle, into
- pulmonary arteries.
- >O2 diffuses from alveoli, across the respiratory
- membrane & into the capillaries.
- >CO2 diffuses from capillaries across respiratory membrane
- to the alveoli and into lungs to be expelled
- > blood returns to
- the heart via Left atrium/ pulmonary veins
> blood is rich in O2 and poor in CO2
>ready to be pumped into systemic circuit
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Partial pressure gradient
Is the Movement of a specific gas (O2/CO2)
- >dependent upon concentration of gas and its solubility
- in plasma or blood.
>Each gas acts independently of each other
- >Movement is either between lungs and blood or blood and
- tissues.
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Oxygen transportation in blood
-
- >partial pressure of O2 is higher in the alveoli where
- concentration is higher
- >O2 moves down its concentration gradient form the
- alveoli into capillaries where its concentration is lower
- >attaches to haemoglobin molecules called oxyhaemoglobin
- (HBO2)
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CO2 transportation in
blood
>Leaves the tissue and enters the blood as CO2
>Is transferred in blood as bicarbonate (HCO3)
- >moves down pressure gradient from blood to alveoli to be
- expelled by the lungs.
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Control of
respiration in nervous system
>NS controls breathing in the medulla and the pons
- >Medulla sets rhythm & Pons stimulate the inhibit
- breathing in/out
- >Surrounding the respiratory centre is a complex
- collection of neurons
- >Neuron are stimulated and activate phrenic and intercostal
- nerves responsible for stimulating the diaphragm & intercostal muscles to
- contract and begin breathing.
- >Impulses go back & forth to medulla to maintain
- respiratory rate and pons to maintain depth of breathing.
- >Relaxation of intercostals & diaphragm occurs as
- process shut down
- >to allow air to move out of the lungs in response to
- elasticity of lungs as they recoil to normal size
Other factors controlling breathing
- >Coughing, laughing, exercising, increased body
- temperature increase respiratory rate
>Hypothermia- reduce/suppress respiratory rate
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Hypoxia
Impaired oxygen transportation
- >Causes include anaemia, COPD, impaired/block circulatory
- systems.
>Easily recognised by impaired respiration & cyanosis
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Carbon monoxide (CO)
- >odourless and colourless gas that completes with O2 for
- same binding sites on haemoglobin molecule.
>CO poisoning is a type of hypoxia
>signs of CO poisoning often misdiagnosed
- > person becomes confused, headachy, skin becomes red and
- passively looses consciousness
> treatment involves 100% O2 to rid the body of CO2
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Chronic obstructive
pulmonary disease (COPD)
- >Leading cause of death and sickness as number of
- diagnosed increased
>Likely to affect middle to older adult
- >Irreversible disorder that is progressive but
- preventable disease
> smoking is the most common cause
- >common symptoms include fever, fatigue with increasing
- dypsonea
- Increasing cough, wheezing, and increase production of
- sputum
- >characterised by airflow obstruction caused by either
- emphysema or chronic bronchitis or both
- >Emphysema is characterised by breakdown of elastin &
- collagen
- >chronic bronchitis is characterised by excessive
- production of mucous along with recurrent cough.
- > high risk of dehydration, high energy requirements
- & exhaustion
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Development aspects
>Foetus – gas exchange occurs via placenta
- >Birth- respiratory passages fill with air and alveoli
- inflate; takes 2 weeks
- >process dependent upon presence of surfactant – present
- between week 28-30weeks gestation
>Surfactant prevent alveolar from collapsing
- >does this by decreasing surface tension within the
- lining of the alveolar
>gas exchange will not occur if alveoli collapse
- >Lungs continued to mature until young adulthood- smoking
- affect development
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Respiratory rate during lifespan
- >higher at birth and gradually decrease until normal
- adulthood
>rate may increase in older adult
- >As one age, thorax becomes rigid, lungs loose their
- elasticity and protective mechanisms become less effective making more
- susceptible to developing respiratory infections.
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