6.4 Gas exchange Flashcards
what is the role of ventilation and how does it occur
ventilation maintains conc gradients of oxygen and carbon dioxide between air in teh alveoli and blood flowing the capillaries
you need oxygen for cell respiration
this gas exchange occur in the alveoli in teh lungs
gas exchange happens by diffusion between the air in the alveoli and blood flowing in the capillaries - conc higher o2 in the alveoli lower conc gradient of CO2 in alveoli
to maintain this conc gradient stale air must be removed and fresh air must be pumped in - ventilation
describe the structure of an alveoli
teh alveoli cavity is about 100 micrometers wide
capillary wall is about 5-10 micrometers in diameter
the inside of the alveoli will also have phagocytes attacked to teh pathogenic invaders
how to measure ventilation
volume of air drawn in and expelled is the tidal volume, the breaths per minute is ventilation rate
- count number of breaths
- use a data logging device attached to an inflatable chest belt placed around the thorax which measures teh differential pressure
- use the water displacement method to measure tidal volume
- use a spirometer wiht data logging to measure flow rate into and out of lungs
what is a type 1 pneumocyte
these are thin alveolar cells that area adapted to carry out gas exchange
lungs have a singel layer of cells called the epithelium most of which are type 1 pneumocytes , flattened cells with thickness of about 0.15 micrometers of cytoplasm
the walls of adjacent capillaries also have a single layer of very thin cells so teh air in alveolus and capillary is only 0.5 micrometers apart - small diffusion distance
these are thin alveolar cells that area adapted to carry out gas exchange
the layers from the alveolus to the erythrocyte (RBC) in the capillary are as follows
air in alveolus
epithelium of alveolus wall
nucleus of epithelium cell
basement membrane
endothelium of capillary
blood plasma
erythrocyte
type 2 pneumocyte what is it
it secrets a solution containing surfactant that creates a moist surface inside the alveoli to prevent teh sides of teh alveolus adhereing to each other by reducing surface tension
these are rounded cells that occupy 5% of alveolar surface area
teh surfactant allows oxygen in teh alveolus to dissolve and porvides an area from which co2 can evaporate
teh fluid has pulmonary surfactant (similar strucutre to phosphoipids) which form a monolayer on teh surface of the moisture lining the alveoli wiht the hydrophilic heads facing the water and the hydrophobic tails facing the air.
this reduces surface tension and prevents the water from causing the sides of teh alveoli from adhereing to eachother when air is exhaled so that the lungs do not collapse
if babies are born prematurely they can have insufficient pulmonary surfactant and suffer from respiratory distress syndrome - treat give the baby oxygen and one of more doses of surfactant from animal lungs
how is the airway divided up
air enters through the mouth or nose and then passes to teh trachea which has rigns of cartillage to keep it open even when it has low airpressure or when surrounging tissue has high pressure
this then divides into two bronchi tehn bronchioles whihc have smooth fibres in their walls so the width of these airways can vary
then alveoli
how does pressure change during ventilation?
inspiration
- air is drawn into the lungs as the pressure is lower than atmospheric pressure
- volume increases
- diaphrgam lowers and contracts
- external intercostal muscles contract so ribcage moves upwards and outwards
- abdomen wall relax allowing pressure from the diaphgram to push out
- internal intercostal muscles relax
exhalation
- lower volume
- diphragm relaxes so it goes up
- external intercostal muscles relax
- internal intercostal muscles contract
- ribcage moves down and inwards
- this increases pressure
- muscles in teh abdoment contract pushing the abdominal organs and diaphgram upwards
muscles can be in two states -contracted (shorten)or relaxed (longer)
lengthening happens passively - usually pulled into the elongated state by the contraction of another muscle - no compression force is exerted
antagonistic muscles elongate or contract eachotehr
examples
- diaphragm and abdomen
- external and internal intercostal muscles
causs and consequences of lung cancer
- smoking causes 87% of cases - tobacco has mutagenic chemicals - increases as number per day and number of years increase
- passive smoking causes 3% of deaths , number declines where public smoking is banned
- air pollution causes 5% of deaths - e.g. diesel exhaust fumes, nitrogen oxide, smoke from burning woods, coal or other orgnaic matter
- radon gas - radioactive gas that leaks out of rocks that can accumulate in badly ventilated buildings
- asbestos, silica etc. if inhaled in particles - usually on construction sides, quarries, mines or factories
consequences
- difficulties breathing
- presisten coughing
- coughing up blood
- chest apain
- weight loss
- loss of appetite
- general fatigue
only 15% of patients survive as often teh tumour is metastasized when found , usually treated with chemotherapy or radiotherapy
even if cured pain will continue often
causes and consequenecs of emphysema
alveoli are replaced with a smaller number of larger air sascs with thicker walls
- less SA for gas exchange
- more diffusion distance
- less gas exchange
- lungs are less elastic
not fully understood why but some theories
- phagocytes insides alveoli usually produce elastase (a protein digesting enzyme) to kill bacteria
- an enzyme inhibitor called A1AT (alpha 1-antitrypsrin) usually prevents elastase from digesting lung tissue
- in smokers more phagocytes so more elastase
- genetics affect the quantity and effectiveness of A1AT
- in 30% of smokers teh protein in the alveolus’ is digested destroying and weakening alveoli walls
emphysema is chronic and irreversible
low o2 in blood
high co2 in blood
lack of energy in patient
laboured and rapid ventilation
