Exchange surfaces Flashcards
(50 cards)
1
Q
Why do single-celled organisms not require a specialised exchange surface?
A
- The metabolic acticity of a single-celled organisms is usually low, so the oxygen demands and carbon dioxide production of the cell are relatively low
- The surface area to volume (SA:V) ratio of the organism is large => distance between oxygen demanding cells and oxygen supply is short
2
Q
How does the SA:V ratio differ between large and small organisms?
A
- Large organisms have a small SA:V
- Small organisms have a large SA:V
3
Q
What are the features of an effective exchange surface?
A
- Increased surface area => provides the area needed for exchange and overcomes the limitations of the SA:V ratio of larger organisms
- Thin layers/walls => these meann the distances that substances have to diffuse are short, making the process fast and efficient
- Good blood supply => the steeper the concentration gradient, the faster the diffusion takers place. Having a good blood supply ensures substances are constantly delivered to and removed from the exchange surface. This maintains a steep concentration gradient for diffusion
- Ventilation to maintain diffusion gradient => for gases, a ventilation system also helps maintain concentration gradients and makes the process more efficient
4
Q
What factors affect the need for a specialised exchange surface?
A
- Size
- Level of metabolic activity
- SA:V ratio
5
Q
What are the key features of the nasal cavity?
A
- A large surface area with a good blood supply, which watms the air to body temperature
- A hairy lining, which secrets mucus to trap dust and bacteria, protecting delicate lung tissue from irritation and infection
- Moist surfaces, which increase the humidity of the incoming air, reducing evaporation from the exchange surfaces
After passing through the nasal cavity, the air entering the lungs is a similar temperature and humidity to the air already in the body
6
Q
What is the trachea?
A
It is the main airway carrying clean, warm, moist air from the nose down into the chest
7
Q
What is the structure of the trachea?
A
- The trachea is lined with ciliated epithelium with goblet cells between and below the epithelial cells. Goblet cells secrete mucus onto the lining of the trachea, to trap dust and microorganisms from reaching the alveoli
- Cilia beat and move the mucus, along with any trapped dirt and microorganisms upwards away from the alveoli towards the mouth where it is swallowed and digested. This prevents lung infection
- Smooth muscle in the walls of the trachea allows their diameter to be controlled. During exercise the smooth muscle relaxes, making the tubes wider. This means there’s less reisstance to airflow and air can move in and out of the lungs more easily. Constriction happens to minimise bad air from entering the lungs
- Elastic fibres in the walls of the trachea help the process of breathing out. On breathing in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to help push the air out when exhaling
- Incomplete rings of cartilage in the walls provide support. The cartilage is strong but flexible and stops the airways from collapsing. The rings are incomplete so that food can move easily down the oesophagus behind the trachea
8
Q
What is the structure of the bronchus?
A
- Smaller than the trachea
- The bronchus is lined with ciliated epithelium with goblet cells between and below the epithelial cells. Goblet cells secrete mucus onto the lining of the bronchus, to trap dust and microorganisms from reaching the alveoli
- Cilia beat and move the mucus, along with any trapped dirt and microorganisms upwards away from the alveoli towards the mouth where it is swallowed and digested. This prevents lung infection
- Smooth muscle in the walls of the bronchus allows their diameter to be controlled. During exercise the smooth muscle relaxes, making the tubes wider. This means there’s less reisstance to airflow and air can move in and out of the lungs more easily. Constriction happens to minimise bad air from entering the lungs
- Elastic fibres in the walls of the bronchus help the process of breathing out. On breathing in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to help push the air out when exhaling
- Incomplete rings of cartilage in the walls provide support. The cartilage is strong but flexible and stops the airways from collapsing.
9
Q
What is the structure of bronchioles
A
- Smooth muscle in the walls of the bronchioles allows their diameter to be controlled. During exercise the smooth muscle relaxes, making the tubes wider. This means there’s less reisstance to airflow and air can move in and out of the lungs more easily. Constriction happens to minimise bad air from entering the lungs
- Elastic fibres in the walls of the bronchioles help the process of breathing out. On breathing in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to help push the air out when exhaling
- Bronchioles are lined with a thin flat layer of flattened epithelium, making some gaseous exchange possible
- Only larger bronchioles contain incomplete rings of cartilage
10
Q
What is the structure of the alveoli?
A
- Tiny air sacs
- Have a diameter of 200-300µm
- Consists of a layer of thin, flattened squamous epithelial cells, along with some collagen and elastic fibres (composed of elastin)
- These elastic tissues allow the alveoli to stretch as air is drawn in
- When they return to their resting size, they help squeeze the air out
- This is known as the elastic recoil of the lungs
11
Q
How is are the alveoli adapted for effective gaseous exchange?
A
- Large surface area => there are 300-500 million alveoli per adult lung. The alveolaqr surface area for gaseous exchange in the two lungs combined is around 50-75m2
- Thin layers => both the alveoli and the capillaries that surround them have walls that are only a single epithelial cell thick, so the diffusion distance between the air in the alveolus and the blood in the capillaries is very short
- Good blood supply => the millions of alveoli in each lung are supplied by a network of around 280 million capillaries. The constant flow of blood through these capillaries brings carbon dioxide and carries off oxygen, maintaining a steep concentration gradient for both carbon dioxide and oxygen between the air in the alveoli and the blood in the capillaries
- Good ventilation => breathing moves air in and out of the alveoli helping maintain steep diffusion gradients for oxygen and carbon dioxide between the blood and the air in the lungs
- Surfactants => inner wall of alveoli is covered in a thin layer of a solution of water, salts and lung surfactant. The surfactant make it possible for the alveoli to remain inflated. Oxygen dissolves in the water before diffusing into the blood, but water can also evaporate into the air in the alveoli
12
Q
What is the function of the rib cage?
A
Provides a semi-rigid case within which pressure can be lowered with respect to the air outside it
13
Q
What is the diaphragm?
A
A broad, domed sheet of muscle, which forms the floor of the thorax
14
Q
Where are the external and internal intercostal muscles found?
A
Between the ribs
15
Q
What is the pleural membrane?
A
- Surrounds and cushions the lungs
- The space between the lungs and pleural membrane is called the pleural cavity which is usually filled with a thin layer of lubricating fluid so the membranes slide easily over each other as you breathe
16
Q
What occurs during inspiration/inhalation?
A
- This is an active, energy-using process
- The diaphragm muscles contract; the diaphragm flattens and lowers
- The external intercostal muscles contract
- The ribs and sternum move upwards and outwards
- The volume of the thorax (and the lungs) increases
- The pressure in the thorax (and the lungs) decreases
- Pressure in the thorax is lower than the atmospheric air pressure, so air is drawn through nasal passages, trachea, bronchi and bronchioles into the lungs
- This equalises the pressures inside and outside the chest
17
Q
What happens to the internal intercostal muscles during inspiration and expiration?
A
Internal intercostal muscles are relaxed unless air is forced out e.g. during coughing
18
Q
What occurs during expiration/exhalation?
A
- This is a passive process
- The diaphragm muscles relax; the diaphragm becomes more dome shaped
- The external intercostal muscles relax
- The ribs and sternum move downards and inwards under gravity
- The elastic fibres in the alveoli of the lungs return to their normal length
- The volume of the thorax (and the lungs) decreases
- The pressure in the thorax (and the lungs) increases
- Pressure in the thorax is higher than the atmospheric air pressure, so air moves out of the lungs until the pressure inside and outside the chest is equal
19
Q
What are the different ways in which air (that is drawn in and out of the lungs) can be measured?
A
- A peak flow meter => it is a simple device that measures that rate at which air can be expelled from the lungs
- Vitalographs => they are more sophisticated versions of the peak flow meter. The patient being tested breathes out as quickly as they can through a mouthpiece, and the instrument produces a graph of the amount of air they breathe out and how quickly it is breathed out
- Spirometer => it is commonly used to measure different aspects of the lung volume, or to investigate breathing patterns. There are many different forms of the spirometer
20
Q
Draw and label a graph with volume of gas in lungs against time.
A
Answer on revision card
21
Q
What is tidal volume?
A
The volume of air that moves into and out of the lungs with each resting breath
22
Q
What is vital capacity?
A
The maximum volume of air the can be breathed in and out
23
Q
What is inspiratory reserve volume?
A
It is the maximum volume of air you can breathe in over and above a normal inhalation
24
Q
What is expiratory reserve volume?
A
It is the extra amount of air you can force out of your lungs over and above the normal tidal volume of air you breathe out
25
What is residual volume?
- The volume of air that is left in your lungs when you have exhaled as hard as possible
- It is the air that can't be expelled from the lungs because the rings of cartialge maintains the airways to open at all times
26
How do you calculate total lung volume?
vital capacity + residual volume
27
What is breathing rate?
How many breaths are taken, usually in a minute
28
What is the rate of oxygen consumption or oxygen uptake?
- The rate at which an organism consumes oxygen
- The volume of oxygen used in a minute
Units:
- dm^3 min^-1
- or cm^3 min^-1
29
What is ventillation rate?
The total volume of air inhaled in one minute
30
How do you calculate ventillation rate?
tidal volume x breathing rate (per minute)
31
Why do insects require a different way of exchanging gases?
- They have a tough exoskeleton (made from chitin and a waxy cuticle) through which little or no gaseous exchange can take place
- They do not usually have blood pigments that can carry oxygen
32
How does gas exchange take place in insects?
- Air enters and leaves the system through spiracles (water can also be lost)
- The opening and closing of spiracles are controlled by sphincters
- Leading away from the spiracles is the main trachea which into and along the body of the insect
- The trachea is lined with spirals of chitin to keep them open and prevent them from being bent or pressed
- The trachea branch to form narrower tubes until they divide to into tracheoles which run along individuals cells
- This is where most of the gaseous exchange takes place between the air and respiring cells
33
How are spiracles adapted to their function?
- Open and closed by valves to facilitate ventilation
- They are lined with fine hairs to stop dust particles, entry of pathogense and reduce moisture loss
34
Why doesn't gas exchange occur at the trachea in insects?
The trachea is lined with chitin which is impermeable to carbon dioxide and oxygen
35
What is the diameter of the trachea in insects?
1mm
36
How is the tracheole adapted to its function in insects?
Has no chitin so it is very permeable to gases
37
How is oxygen delivered from the tracheoles to respiring cells at rest (in insects)?
Oxygen dissolves in moisture on the walls of the tracheoles and diffuses into the surrounding cells
38
How is oxygen delivered from the tracheoles to respiring cells when active (in insects)?
- Towards the ends of tracheoles there is tracheal fluid, which limits the penetration of air for diffusion
- A lack of oxygen leads to anaerobic respiration taking place in respiring cells
- Lactic acid accumulates in respiring cell as anaerobic respiration proceeds
- The lactic acid lowers the water potential of the respiring cell
- The water potential of the cell becomes lower than that of the tracheal fluid
- Fluid drains from the tracheole into respiring cell
- The fluid takes dissolved oxygen with it
- The tracheole becomes air-filled, increasing the SA for diffusion of oxygen from air
39
How are insects adapted to to increase the level of gaseous exchange?
- Mechanical ventilation of the tracheal system
- Selective opening and closing of spiracles
- Collapsible enlarged tracheae or air sacs, which act as reservoirs
40
Explain how insects mechanically ventilate the tracheal system.
- Air is actively pumped into the system by muscular pumping movements of the thorax and/or the abdomen
- These movements change the volume of the body and this changes the presure in the tracheae and tracheoles
- Air is drawn into the tracheae and tracheoles, or forced out, as pressure changes
41
Explain how air sacs in insects act as reservoirs.
- The air sacs are used to increase the amount of air moved through the gas exchange system
- They are usually inflated and deflated by the ventilating movements of the thorax and abdomen
42
Explain how insects selectively open and close spiracles in expiration and inspiration.
Inspiration:
- Body cavity increases in volume
- Spiracels in thorax (front half of insect) open
- Spiracles in abdomen closed
- Air enters system via thoracic spiracles
Expiration:
- Body cavity decreases in volume
- Spiracels in abdomen (front back of insect) open
- Spiracles in thorax closed
- Air leaves system via abdominal spiracles
43
Why do fish require a specialised respiratry system?
- Oxygen content of water is only 0.1% (compared to 20% in air)
- Oxygen diffusion rate in water is slow
- Water has a high viscosity compared to air
44
What features of the gills make them efficient for gas exchange?
- Large number of filaments with large number of lamellae so there is an increased surface area (high SA:V ratio)
- Thin wall of lamellae => one layer of squamous epithelium (one layer of squamous epithelium in capillaries allowing for short diffusion pathway)
- Rich blood supply (lots of capillaries means large surface area) to maintain steep concentration gradient
- Countercurrent flow of water (over gills) and blood (in gill filaments)
- The tips of adjacent gill filaments overlap. This increases the resistance to the flow of water over the gill surfaces and slows down movement of the water. As a result there is more time for gaseous exchange to take place
45
How does a countercurrent exchange system work in fish?
- Blood flows in the opposite direcrion (in the lamellae) to the flow of water
- This ensure that steeper concentration gradients are maintained opposed to a parallel system
- As a concentration gradient is maintained all along the capillary, diffusion of gases occurs all along the capillary
- 80% of oxygen is extracted from the water (opposed to 50% if it were a parallel system)
46
How does ventillation work in bony fish while swimming?
Mouth and operculum remain open as therre is a continous flow of water over the gills
47
What occurs during inspiration in fish when stationary?
**_Mouth is open:_**
- Floor of buccal cavity is lowered
- Volume of buccal cavity increases and pressure decreases
- Water is drawn into the buccal cavity due to pressure gradient
- Opercular valve is closed and the opercular cavity containing the gills expands (operculum moves outwards while closed increasing volume)
- This lowers the pressure in the opercular cavity containing the gills
- The floor of the buccal cavity starts to move up, increasing the pressure there so water moves from the buccal cavity over the gills
48
What occurs during expiration in fish when stationary?
**_Mouth is closed:_**
- Floor of buccal cavity is raised mainting a flow of water over the gills
- The sides of the opercular cavity move inwards
- Volume of buccal cavity decreases and pressure increases
- This forces water over the gills (and gill lamellae) and out of the operculum due to pressure gradient
- Maximum gas exchange occurs between water blood flowing through the gills because of the countercurrent mechanism
49
When stationary how is water moved into fish?
Water is pumped over gills
50
Draw the graph for counter current flow in bony fish.
Answer on revision card
