6.4 Gas Exchange Flashcards
How does the air enter the lungs?
- air enters the ventilation system through the nose or mouth then passes down the trachea, which has rings of cartilage in its walls to keep it open during low pressures inside during inhalation or when pressure in the surrounding tissues is high
- divides to form 2 bronchi, that also have cartilage strengthened walls - one bronchus going to each lung
- inside the lungs the bronhi divide repeatedly forming a tree-like structure of narrower airways called bronchioles, which have smooth muscle fibres in their walls to allow these airways to vary their width and the end in groups of alveoli, where gas exchange occurs
What is gas exchange?
- involves absorbing one gas from the environment and releasing a different one
- eg in leaves Co2 is absorbed for photosynthesis and O2 is released
- eg in humans, O2 is absorbed for cellular repiration and CO2 is released
How does gas exchange occur in humans and terrestrial organisms?
- in terrestrial organisms occur via exchanging gases with the air
- in humans it occurs in small air sacs inside the lungs call alveoli and it happens by the diffusion between air in the alveoli and blood flowing in the adjacent capillaries
What is the correlation between ventilation and concentration gradients?
- through gas exchange, it results from diffusion along a concentration gradient where air in the alveolis has a higher O2 and lower CO2 than the blood in the capillary
- ventilation is used to maintaon these concentration gradiesnts by pumping fresh air into the alveoli and removing ‘stale’ air
What is emphysema?
- lung disease present in heavy smokers, damage to the lung parenchyma (which is the lung tissue that carries out gas exchange)
- causes low oxygen saturation in the blood and higher than normal CO2 concentrations
- ventilation is also labored and tends ti be more rapid than usual
What are the symptoms present with a patient with emhysema?
- smaller number of air sacs and thicker walls
- SA for gas exchange is reduced, distance of diffusion of gas is increased resulting in ineffective gas exchange
- results in the lungs become more elastic and ventilation is difficult
- alveolus walls are weakened and destroyed annd the digestion of proteins of proteases are not prevented
What are the molecular mechanisms of emphysema?
- phagocytes inside the alveoli normally prevent lung infections by engulfing bacteria and produce elastase, a proetin-digesting enzyme, to kill them inside the vesicles formed by endocytosis
- an enzyme inhibitor called alpha 1-antitrypsin (A1AT) prevents elastase and other proteases from digesting lung tissue. In smokers, pagophycytes increase as they produce more elastase
- genetic factors affect effectiveness and quantity of A1AT produced in lungs
Causes and consequences of lung cancer:
- smoking = tobacco smoke contains mutagenic chemicals
- passive smoking = non-smokers inhale tobacco smoke produced by smokers
- air pollution = diesel exhaust fumes, nitrogen oxides, smoke from burning coal etc.
- asbestos, silica and other solids = dust or other particles are inhaled, happens at construction sites, mines or factories)
What is the basic physics involved in ventilation?
a) if particles of gas spread out to occupy a larger volume, the pressure of the gas becomes lower and conversely if a gas is compressed to occupy a smaller volume, the pressure rises
b) if gas is free to move, it will always flow from regions of higher pressure to regions of lower pressure
What happens to the thorax volume when muscle contractions occur during ventilation?
- increase = the pressure inside the thorax drops below atmospheric pressure and air flows from the higher pressure to the lower pressure inside the lungs (inspiration) until the lung pressure has risen to atmospheric pressure
- decrease = the pressure inside the thorax rises above atmospheric pressure and air floes from the higher pressure in the lungs out toward the lower pressure outside (expiration) until the pressure equals
- inspiration and expiration involve opposite movements to change the volume of the thorax, so different muscles are required, thus, working antagonistic pairs
Muscles can either be contracting or relaxing. Explain both these phases.
Contracting = where they become shorter and do work by exerting a pulling force (tension) that causes a particular movement
Relaxing = where they length passively by being pulled into an elongated state by the contraction of naother muscle -they do noot work at the same time
Muscle can only cause movement in one direction, so if movement in opposite directions what must happen?
- when one contracts, the other relaxes and elongates, so movement in one direction occurs
- when the second contracts and the first relaxes and elongates, movement is opposite direction is caused
- this movemnt of muscle together is called an antagonistic pair
Ventilation involves two pairs of antagonistic muscles to change the thorax volume:
1) the external intercostals contract to move ribcage outward, while externals relax
2) internal intercostals muscles contract to make ribcage smaller, while externals relax
3) the diaphragm contracts to expend lungs, while abdominal muscles relax
4) abdominal muscles contract ONLY for forced breathing out
Describe 3 ways to measure ventilation rate.
What is tidal volume?
- refers to the amount of air that moves in and out of the lungs during normal, relaxed breathing
