3.1.1 - Exchange surfaces Flashcards
What are the two main reasons that diffusion is enough for single celled organisms ?
- The metabolic activity is low, so the oxygen demand carbon dioxide production of the cell are relatively low
- The SA:V ratio of the organism is large
What happens as organisms get larger ?
- Their metabolic activity is usually much higher
- Their SA:V ratio is smaller. So gases cant be exchanged fast enough or in large enough amounts for the organism to survive
How have large organisms evolved ?
Large multicellular organisms have evolved specialised systems for the exchange of the substances they need and the substances they must remove
What are the common features of effective exchange surfaces ?
- Increased surface area
- Thin layers
- Good blood supply
- Ventilation to maintain diffusion gradient
Why does an increased surface area make an exchange surface efficient ?
It provides the area needed for exchange to overcome the limitations of low SA:V ratio
Why do thin layers make an exchange surface efficient ?
The distances that substances have to diffuse across are short, making it fast and efficient
Why does a good supply make an exchange surface efficient ?
- The greater the difference in concentration the greater the rate of diffusion.
- A good supply means substances are constantly being delivered and removed, maintaining the steep concentration gradient
Why does ventilation make an exchange surface efficient ?
For gases ventilation helps to maintain concentration gradients
Why are specialised exchange surfaces needed by some organisms ?
- They have a low SA:V ratio so exchange surfaces increase that
- Maximise efficiency of diffusion
- Ensure that the demand for glucose and oxygen is met
How is the nasal cavity adapted for the gas exchange system ?
- Good blood supply warms air to body temperature
- Cells secrete mucus to trap dust and bacteria to protect the lung tissue
- Moist surfaces which increase the humidity of the incoming air, reduce evaporation from the exchange surfaces
What is the trachea ?
The trachea is the main airway carrying clean, warm, moist air from the nose down into the chest
How is the trachea adapted for the gas exchange system ?
- Supported by incomplete rings of strong, flexible cartilage to allow for movement and prevent the trachea from collapsing
- Lined with ciliated epithelium and goblet cells
What is the function of the goblet cells ?
To secrete mucus which traps dust and microorganisms that have escaped the nose lining
What is the function of ciliated epithelial cells ?
- The cilia beat and move mucus away from the lungs, protecting them
- Most of it goes into the throat and is then swallowed and digested
What are the bronchi ?
They are similar in structure to the trachea, with the same supporting rings of cartilage, but are smaller
How are the bronchi adapted for the gas exchange system?
They are supported by small rings of cartilage
How are bronchioles adapted for the gas exchange system ?
- They contain no cartilage
- Contain smooth muscle
- Smooth muscle contracts when bronchioles constrict and relaxes when they dilate
What are alveoli ?
- The alveoli are tiny air sacs, which are the main gaseous exchange surfaces of the body
- They are unique to the mammalian structure
How are the alveoli adapted for the gas exchange system ?
- Very thin walls
- Contain elastic fibres which allow alveoli to stretch as air is drawn in and when they return to size help to squeeze air out
- Good capillary blood supply
- Coated in surfactant
What is elastic recoil ?
Elastic recoil is the ability of the alveoli to stretch to allow more air in and to return back to normal size to squeeze the air out
What is breathing ?
The movement of air in and out of the lungs
What is breathing also known as ?
Ventilation
What is the thorax ?
The thorax is basically all of the chest cavity
What is the rib cage ?
The rib cage provides a semi rigid case within which pressure can be lowered with respect to the air outside it
What is the diaphragm ?
The diaphragm is a broad, domed sheet of muscle, which forms the floor of the thorax
What is the pleural membrane ?
The thorax is lined with the pleural membrane, which surround the lungs
What is the pleural cavity ?
- The pleural cavity is the space inbetween the pleural membranes
- It is usually filled with a thin layer of lubricating fluid so that the membranes slide over each other easier
What is inspiration ?
The movement of air into the lungs
Does inspiration require energy ?
Yes
Outline the steps in inspiration
- Diaphragm flattens and contracts
- External intercostal muscles contract making the ribs move up and out
- This increases the volume of the thorax so reduces pressure
- Pressure in the thorax is lower than that of outside
- Air is drawn into the lungs to equalise the pressures inside and outside the chest
What is expiration ?
The movement of air out of the lungs
Does expiration require energy ?
- No, it is a passive process
Outline the steps in normal expiration
- Diaphragm relaxes and curves upwards
- External intercostal muscles relax so ribs move in
- Decreases volume of the thorax
- Pressure in the lungs is less negative than atmospheric air
- Air moves out of the lungs until pressure inside and out is equal
Outline the steps in forced expiration
- Abdominal muscles contract, pushing diaphragm upward quickly making lung pressure less negative
- Internal intercostal muscles contract pulling ribs down hard and fast
What are the three ways that the volume of air can be measured ?
- A peak flow meter
- Vitalograph
- Spirometer
What is a peak flow meter ?
A peak flow meter is a simple device that measure the rate at which air can be expelled from the lungs
What is a vitalograph ?
- More sophisticated versions of the peak flow meter
- Measures the amount of air breathed out and how quickly it is breathed out
What is a spirometer ?
Commonly used to measure different aspects of the lung volume, or to investigate breathing patterns
What is tidal volume ?
- Tidal volume is the volume of air that moves into and out of the lungs with each resting breath
- Typically 15% of the vital capacity of the lungs, can be 50% during exercise
What is vital capacity ?
Vital capacity is the max volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible intake of breath
What is inspiratory reserve volume ?
The maximum volume of air you can breathe in over and above a normal inhalation
What is expiratory reserve volume ?
The extra amount of air you can force out of your lungs above and over the normal tidal volume of air you breathe out
What is residual volume ?
The volume of air that is left in your lungs when you have exhaled as hard as possible. This cannot be measured directly.
What is total lung capacity ?
The sum of the vital capacity and the residual volume
What is the breathing rate ?
The number of breaths taken per minute
What is the ventilation rate ?
The total volume of air inhaled in one minute
How do you calculate ventilation rate ?
Tidal volume x Breathing rate
As organisms get larger, what happens to the size of the diffusion distance ?
The diffusion distance increases
As organisms get larger, what happens to the size of the surface area ?
The surface area increases
