the human gaseous exchange system Flashcards
how does oxygen dissolve into the body surfaces
gaseous exchange systems are moist so oxygen dissolves in the water before dissolving into the body surfaces
what are moist conditions ideal for
evaporation of water
how are mammals able to exchange gases efficiently
they have complex systems that enable them to exchange gases whilst minimising the loss of water from the body
why do mammals need exchange systems
they have a small surface area to volume ratio and a large volume of cells.
why do mammals have a high metabolic rate
they have a high metabolic rate because they are active and maintain their body temperature independant of the environment
what do mammals need lots of and need to get rid of
they need lots of oxyegn for cellular respiration and produce carbon dioxide which needs to be removed
where does exchange of gases take place in mammals
the lungs
what does the gaseous exchange system consist of
the lungs and associated airways that carry air into and out of the lungs
how can air pass into the lungs
through the nose and along the trachea, bronchi and bronchioles.
where does air reach to when it passes into the lungs
it reaches tiny air filled sacs called alveolis
where does exchange of gases takes place
alveoli
what protects the lungs
ribcage
how are the ribs held
by the intercostal muscles
how are breathing movements produced
the action of the intercostal muscles and the diaphragm
what are the lungs
pair of inflatable sacs that carry air into and out of the lungs
what are the bronchi and bronchioles
smaller airways leading into the lungs
what is the trachea
the main airway leading from the back of the mouth to the lungs
what is the alveoli
tiny folds of the lung epithelium to increase the surface area
what is the diaphragm
a layer of muscle beneath the lungs
what are the intercostal muscles
muscles between the ribs. contraction of the external intercostal muscles raises the ribcage
what is ventilation
the refreshing of the air in the lungs so there is a higher oxygen concentration than in the blood and a lower carbon dioxide concentration
what do all organisms require
nutrients and the ability to excrete wastes
what can many simple organisms do
exchange substances directly across their external surfaces
what do larger organisms require to exchange and transport substances efficiently
specialised gas exchange and transport systems
how do fish exchange substances
across gills, while insects have openings called spiracles on their surface
how do mammals exchange substances
in the lungs and in particular the alveoli
what are the lungs enclosed in
a pleural membrane (double membranes)
what is the space between the two membranes in the lungs called
the pleural cavity
what is the pleural cavity filled with
pleural fluid
what does the pleural fluid do
it lubricates the lungs and adheres to the outer walls of the lungs to the thoracic cavity by water cohesion so that the lungs expand with the chest while breathing
what are the features of the nasal cavity
- has a large surface area with a good blood supply
- hairy lining
- moist surfaces which increase the humidity of the incoming air reducing evaporation from the exchange surfaces
what does the large surface area and good blood supply in the nasal cavity do
which warms the air to body temperature
what does the hairy lining in the nasal cavity do
secretes mucus to trap dust and bacteria protecting delicate lung tissue from irritation and infection
what do the moist surface of the nasal cavity do
increase the humidity of the incoming air reducing evaporation from the exchange surface
where does the air travel after passing the nasal cavity
the air enters the lungs
what is the temperature of the air that enters the lungs from the nasal cavity
similar temperature and humidity to the air already in the lungs
what are the adaptations of the lungs to exchange gases
very large surface area in close contact with the bloodstream so oxygen can diffuse in and carbon dioxide can diffuse out
how does air enter the lungs
via the trachea or windpipe
what does the trachea carry
clean, warm, moist air from the nose down into the chest
describe the trachea
wide tube surrounded by a layer of smooth muscle supported by incomplete rings of strong, flexible cartilage which stop the trachea from collapsing
why are the rings incomplete
so food can move easily down the oesaphagus behind the trachea
what are the trachea and its branches lined with
ciliated epithelium and goblet cells between and below the epithelial cells
what do the goblet cells do
secrete mucus onto the lining of the trachea to trap dust and microorganisms that have escaped the nose lining.
what do the cilia in the trachea do
beat and move the mucus away along with any trapped dirt and microorganisms preventing it from reaching the lungs.
where does most of the mucus go
into the throat where it is swallowed and digested
what do epithelial cells contain
many mitochondria to provide energy for the beating cilia
what do the trachea divide into in the chest cavity
they divide to form the left bronchus leading to the left lung and the right bronchus leading to the right lung
describe the bronchi
supported by cartilage which is deposited in partial rings and irregular blocks. the rings of cartilage are smaller
what does each bronchus divide into
smaller tubes -bronchioles
what do the bronchioles divide into
primary bronchioles divide into terminal bronchioles then respiratory bronchioles where gas exchange takes place
which bronchioles does gas exchange take place
respiratory bronchioles
describe the bronchioles
they are about 1 mm or less in diameter. they have not got cartilage and are held open by smooth muscle. when this muscle contracts the bronchioles contract, this is dependant on air flow
what are the bronchioles lined with
epithelial tissues making gas exchange possible
what are on the ends of the respiratory bronchioles
tiny air sacs or alveoli
what do the alveoli do
gives the lungs a huge surface area making gas exchange surface area
describe an alveolus
- each is about 200-300µm diameter
- made of a thin layer of flattened epithelial cells as well as some collagen and elastin fibres
what do the elastin fibres do
they cause recoil which helps air move out of the alveoli
what is elastic recoil
alveoli can squeeze as air is drawn in. when they return to their resting size, they help squeeze the air out
where do alveoli exist in
alveolar ducts
what is the exchange surface of alveoli
each sac is 0.05mm across increasing to 0.1mm when inflated. there are over 250 million altogether giving an exchange surface of about 80m²
what is each alveolus covered in
a fine network of blood capillaries
how do the alveoli and capillary walls allow efficient gas exchange
they are made of squamous epithelium (flattened cells)
what does squamous epithelium consist of
one layer of cells
how do narrow capillaries allow efficient gas exchange
the capillaries are so narrow that blood cells must squeeze through. this slows blood flow and minimises the distance that gases have to diffuse
what happens to the oxygen and carbon dioxide
oxygen diffuses continuously into red blood cells and carbon dioxide diffuses out of the blood plasma. some air is replaced with each breath maintaining the concentration gradients
what are the features of efficient gas exchange
large surface area
moist
thin layers
good blood supply
good ventilation
how do alveoli provide large surface area
there are 300-500 million alveoli per adult lung. the alveolar surface area for gaseous exchange in the two lungs is about 50-75m²
how do the alveoli provide moisture
alveoli have a thin layer of moisture which evaporates and is lost as we breathe out. the lungs must produce a surfactant that coats the internal surface of the alevoli to reduce the cohesive forces between the water molecules as these forces tend to make the alveoli collapse
how do the alveolis thin layers minimise the diffusion distance
alveoli and capillaries surrounding them have walls that are one cell thick so the diffusion distances between the air in the alveolus and the blood in the capillaries are very short. the total diffusion barrier is less than 1µm thick
how do the alveoli use their good blood supply
helps maintain their steep concentration gradient so the gases continue to diffuse. the blood system transports from the tissues to the lungs ensuring the concentration of the carbon dioxide in the blood is higher than in the alveoli so that carbon dioxide diffuses into the alveoli. the blood transports the oxygen away from the lungs ensuring the concentration of oxygen in the blood is kept lower than in the alveoli so oxygen diffuses in the blood
how are the alveoli ventilated
breathing moves air in and out of the alveoli helping maintain the steep diffusion gradients for oxygen and carbon dioxide between the blood and the air in the lungs
what is the inner surface of the alveoli covered in
a thin layer of a solution of salts, water and lung surfactant
what is lung surfactant
makes it possible for the alveoli to remain inflated
where does oxygen dissolve before it diffuses into the blood
dissolves in the air before diffusing into the blood
which adaptations help reduce water loss
oxygen dissolves in the air before diffusing into the blood but water can evaporate into the air in the alveoli
what is the role of smooth tissue
constricts the airway making the lumen narrower.
what can constriction of the lumen cause
restriction of the flow of air to and from the alveoli
when can controlling the flow of the air to the alveoli be important
if there are harmful substances in the air
when can contraction of the smooth muscle occur
as a result of an allergic reaction as it is not voluntary
what happens once the smooth muscle is contracted
it cannot reverse the effect on its own. the smooth muscle is elongated again by the elastic fibres. when the muscle contracts, it deforms the elastic fibres
what happens as the muscles relax
the elastic fibres recoil to their original size and shape. this acts to dilate the airway
