exchange surfaces and breathing Flashcards
What are the three main factors that affect the need for an exchange system
Size of the organism
Surface are to volume ratio
Level of activity
Explain the effect of size on the need for an exchange system
In very small organisms, such as single celled organisms, all the cytoplasm is very close to the environment in which they live. Diffusion will supply enough oxygen and nutrients to keep the cells alive and active. However, multicellular organisms may have several layers of cells. Here, any oxygen or nutrients diffusing in from the outside have a longer diffusion pathway. Diffusion is too slow to enable a sufficient supply to the innermost cells.
Explain the effect of SA/V ratio on the need for an exchange system
Small organisms have a small surface area, but they also have a small volume. Their surface area is relatively large compared to their volume. So we say they have a large surface area to volume ratio. This means their surface area is large enough to supply all their cells with sufficient amounts of oxygen.
Larger organisms have a larger surface area, but they also have a larger volume. As size increases, the volume rises more quickly than surface area. Therefore, their surface area to volume ratio is relatively small .
However some organisms can adopt a larger surface area by adopting a different shape. An animal such as a flat worm has a very thin and flat body. Which gives it a larger surface area to volume ratio.
Explain the effect of the level of activity on the need for an exchange system
Some organisms are more active than others, metabolic activity uses energy from from food and requires oxygen to release this energy in aerobic respiration. The cells of an active organism need good supplies of nutrients and oxygen to supply the energy for movement.
What are the features of a good exchange system
A large surface area to provide more space for molecules to pass through
A thin barrier to shorten the diffusion pathway
A good blood supply. Keeping a steep concentration gradient.
Describe the system of gaseous exchange in the lungs
The gaseous exchange system in mammals consists of the lungs and associated airways that carry air into and out of the lungs. The lungs are a pair of inflatable sacs lying in the chest cavity. Air can pass into the lungs via the nose and along the trachea, bronchi and bronchioles. Finally, it reaches tiny air filled sacs called alveoli. These are the surfaces where exchange of gas takes place. The lungs are protected by the ribcage. Which are held together by the intercostal muscles. The action of these muscles and the diaphragm helps to products breathing movements (ventilation)
How does carbon dioxide and oxygen get exchanged within the lungs
Gases pass by diffusion through the thin walls of the alveoli. Oxygen passes from the air in the alveoli to the blood in the capillaries. Carbon dioxide passes from the blood to the air in the alveoli. The lungs must maintain a steep concentration gradient in each direction in order to ensure that diffusion can continue.
What makes the lungs a good gaseous exchange system
It has a large surface area to provide space for molecules to pass through- the individual alveoli are very small around 100-300 micro meters in diameter. However, they are so numerous that the total surface area of the lungs is much larger than that of our skin. It is around 70m squared.
The alveoli are also lined with a thin layer of moisture, which evaporates and is lost when we breathe out. The lungs must produce a surfactant that coats the internal surface of the alveoli to reduce the cohesive forces between water molecules, as these forces tend to make the alveoli collapse.
The barrier to exchange is permeable to oxygen and carbon dioxide, as the molecules are small and non polar.
Diffusion distance is short as alveoli walls are only one cell thick as well as capillary cell walls. And both walls consist of squamous epithelial cells which are very thin. The capillaries are also very close to the alveoli and finally they are so narrow that red blood cells are squeezed against the capillary wall- making flow slow travelling and making them closer to the air in the alveoli. The diffusion distance overall is around 1 micrometer thin .
Finally, there is a good blood supply which keeps a steep concentration gradient.
Describe the processes involved in inspiration (inhailing)
-the diaphragm contracts to move down and become flatter- displacing digestive organs downwards
-the external intercostal muscles contract to raise the ribs
-the volume of the chest cavity increases
-the volume of the chest cavity drops below atmospheric pressure
-air moves into the lungs
Describe the processes involved in expiration (exhaling)
The diaphragm relaxes and it is pushed up by the displaced organs underneath
-the external intercostal muscles relax and the ribs fall; the intercostal muscles can contact to help to push out air more forcefully- this happens during exercise and coughing
-volume of chest cavity decreases
-pressure in the lungs increases above atmospheric pressure
-air moves out of the lungs
Describe the structure of the alveoli in lung tissue
Alveoli are compromised of squamous epithelium and are surrounded by blood capillaries, so that diffusion distances are shorter. The alveoli walls contain elastic fibres that stretch during inspiration but then recoil to help push out air during expiration. The alveolus walls are thin meaning it may not be possible to distinguish separate cells under a light microscope.
Describe the structure of the airways to the lungs
The airways are lined with ciliated epithelium, which contributes to keeping the lungs healthy. Goblet cells in the epithelium release mucus, which traps pathogens. The cilia then move the mucus up to the top of the airway where it is swallowed. The glandular tissue in the loose tissue also produces mucus.
Describe the structure of the trachea and bronchi
The trachea and bronchus walls have similar structures. However the bronchi are narrower than the trachea. These airways are supported by rings of cartilage which prevent collapsing during inspiration. The rings of cartilage in the trachea are c shaped rather than a complete ring which allow flexibility and space for food to pass down the oesophagus.
Describe the structure of the bronchioles
The bronchioles are much narrower than the bronchi. The larger bronchioles may have some cartilage, but smaller ones have no cartilage. The wall is comprised of mostly smooth muscle and elastic fibres. The smallest bronchioles end in clusters of alveoli.
Describe the functions of smooth muscle and elastic tissue
The smooth muscle can contract. The action of the smooth muscle will constrict the airway. This makes the lumen of the aireway narrower. Constriction of the lumen can restrict the flow of air to and from the alveoli. Controlling the flow of air to the alveoli may be important if there is harmful substances in the air. The contraction of the smooth muscle is involuntary and irreversible.
