Exchange Surfaces and Breathing Flashcards
Exchange Surfaces: Why can small organisms easily exchange substances, compared to larger organisms who need exchange surfaces?
Single cells and small organisms can exchange gases, nutrients and waste across their outer surfaces. They have a large surface area to volume ratio. However, once a multicellular organism becomes larger, its surface area to volume ratio becomes smaller and its cells need more supplies. This means that its outer surface is not large enough to enable gases and nutrients to enter its body fast enough to keep all the cells alive. Nutrients and gases also have to travel a greater distance from the surface to the centre of the organism.
-Larger organisms need a larger area to exchange more substances. Often they combine this with a transport system to move substances around the body.
Exchange Surfaces: Why is diffusion across the outer membrane of large multicellular too slow?
- Some cells are deep within the body; there’s a big distance between them and the outside environment.
- Larger animals have a low surface area to volume ratio; it’s difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface.
Exchange Surfaces: What features does an efficient exchange surface have?
- Large surface area to provide more space for molecules to pass through (often achieved by folding the walls and membranes).
- Thin barrier to reduce diffusion distance.
- Fresh supply of molecule on one side to keep the concentration high.
- Removal of required molecules on the other side to keep the concentration low.
- The latter three are important in maintaining a steep diffusion gradient.
Exchange Surfaces: Where do exchange surfaces occur?
Exchange surfaces do not occur just at the surface of a large organism. They are also found in all the organs where substances are removed from the transport system and where wastes are returned to the transport system.
Exchange Surfaces: What are the different types of exchange surfaces in animals?
- Alveoli
- Villi
- Liver
- Root hair cells
Exchange Surfaces: How is the small intestine adapted to its function as an exchange surface?
Where nutrients are absorbed
-There are villi on the lining, small finger like projections about a millimetre in length. They cover the entire surface of the folded lining. Along with this microvilli lines the villus that is exposed to the lumen. This greatly increases the small intestines surface area, for maximum absorption of nutrients from food into the blood stream, it also allows digestion products to be absorbed quicker. The villi surface is one cell thick and has its own blood stream, allowing substances to be transported directly.
Exchange Surfaces: How is the liver adapted to its function as an exchange surface?
Where the levels of sugars in the blood are adjusted
- The liver is made up of over 60% of hepatic cells. These covert sugars, store and release them as needed. regulating sugar levels. Break down fats and produce cholesterol. Remove ammonia from your body and produce blood proteins, including blood clotting factors. Detoxify drugs and alcohol. Produce bile, which breaks down fats in the food you eat.
- The other important liver cells are the Kupffer cells. They act as a security guard and their main roles is to remove damaged red blood cells and destroy microbes and cell debris.
Exchange Surfaces: How are root hair cells adapted to their function as an exchange surface?
Where water and minerals are absorbed
-The cells have hair like projections on their surface out into the soil. This greatly increases the surface area of the root available to absorb water and minerals from the soil.
Lungs: What are the gas exchange organs in humans?
In mammals, the lungs are gas exchange organs. They help to get oxygen into the blood (for respiration) and to get rid of carbon dioxide (made by respiring cells) from the body.
Lungs: What are the lungs?
The lungs are a large pair of inflatable structures lying in the chest cavity. Air can pass into the lungs through the nose and along the trachea (windpipe), bronchi and bronchioles. Each part of this airway is adapted to its function of allowing the passage of air. Finally the air reaches tiny, air-filled sacs called alveoli. The walls of the alveoli are the surface where the excahnge of gases takes place.
- The lungs are protected by the ribs. Movement of the ribs together with the action of the diaphragm (a layer of muscular tissue beneath the lungs help to produce breathing movement (ventilation).
- Intercostal muscle help to move ribs enabling inhalation and exhalation. The pleural membrane secretes fluid to prevent friction.
Lungs: What are the alveoli?
Lungs contain millions of alveoli - these form the gas exchange surface. Alveoli are arranged in bunches at the end of bronchioles. They are surrounded by a network of capillaries, giving each alveolus its own blood supply.
Lungs: What is the structure of alveoli?
Each alveolus is made from a single layer of thin, flat cells called the alveolar epithelium. The walls of the capillaries are made from capillary endothelium, also a type of epithelium. The walls of the alveoli contain elastic fibres. These help the alveoli to return to their normal shape after inhaling and exhaling air.
Lungs: How is gas exchanged in the alveoli?
- Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium, and into haemoglobin in the blood.
- Carbon dioxide diffuses into the alveoli from the blood, crossing the capillary endothelium, and then the alveolar epithelium. After entering the alveolar space, it is breathed out.
Lungs: How are the lungs adapted for exchange?
- Large surface area
- A barrier permeable to oxygen and carbon dioxide
- Thin barrier to reduce diffusion distance
- Maintaining the diffusion gradient
Lungs: How does having a large surface area mean the lungs are adapted for exchange?
The large surface area provides more space for molecules to pass through. The individual alveoli are very small - about 100-300μm across. But they are so numerous that the total surface area of the lungs is much larger than that of our skin. It has been calculated that the total surface area of the lung exchange surface is about 70m^2.
Lungs: How does having a barrier permeable to oxygen and carbon dioxide mean the lungs are adapted for exchange?
The plasma membranes that surround the thin cytoplasm of the cells form the barrier to exchange. These readily allow the diffusion of oxygen and carbon dioxide.
Lungs: How does having a thin barrier to reduce diffusion distance mean the lungs are adapted for exchange?
There are a number of adaptation to reduce the distance the gases have to diffuse:
- The alveolus wall is one cell thick
- The capillary wall is one cell thick
- Both walls consist of squamous cell; this means flattened or very thin cell
- The capillaries are in close contact with the alveolus walls
- The capillaries are so narrow that the red blood cells are squeezed against the capillary wall, making them closer to the air in the alveoli and reducing the rate at which they flow past in the blood.
- The total barrier to diffusion is only two flattened cells thick and is less than 1μm thick.
Lungs: Why must the lungs produce a surfactant?
A thin layer of moisture lines the alveoli. This moisture passes through the cell membranes from the cytoplasm of the alveolus cells. As we breathe out, it evaporates and is lost. The lungs must produce a substance called a surfactant to reduce the cohesive forces between the water molecules. Without the surfactant, the alveolus would collapse due to the cohesive forces between the water molecules lining the air sac.
Lungs: How does maintaining the diffusion gradient mean the lungs are adapted for exchange?
For diffusion to be rapid, a steep diffusion gradient is needed. This means having a high concentration of molecules on the supply side on the exchange surface and a low concentration on the demand side. To maintain a steep diffusion gradient, a fresh supply of molecules on one side is needed to keep the concentration there high, and a way of removing molecules from the other side is needed to keep the concentration there low.
-This is achieved by the action of the blood transport system and the ventilation (breathing) movements. This constant supply of gas to one side of the exchange surface and its removal from the other side ensures that diffusion, and therefore exchange, can continue.
Lungs: How does the blood transport system help to maintain a steep diffusion gradient for exchange?
-The blood brings carbon dioxide from the tissues to the lungs. This ensures that concentration of carbon dioxide in the blood is higher than that in the air of the alveoli. It also carries oxygen away from the lungs. This ensures that the concentration of oxygen in the blood is kept lower than the concentration in the air inside the alveoli. The heart pumps the blood along the pulmonary artery to the lungs. In the lungs, the artery divides up to form finer and finer vessels. These eventually carry blood into tiny capillaries that are only just wide enough for a red blood cell to squeeze through. These capillaries lie over the surface of the alveoli.
Lungs: How does ventilation help to maintain a steep diffusion gradient for exchange?
-The breathing movements of the lungs ventilate the lungs. They replace the used air with fresh air. This brings more oxygen into the lungs and ensures that the concentration of oxygen in the air of the alveolus remains higher than the concentration in the blood. Ventilation also removes air containing carbon dioxide from the alveoli. This ensures that the concentration of carbon dioxide in the alveoli remains lower than that in the blood.
Lungs: What are the airways that allow passage of air into and out of the lungs?
- Trachea
- Bronchi
- Bronchioles
Lungs: What requirements must the airways meet to be effective?
- The larger airways must be large enough to allow sufficient air to flow without obstruction.
- They must also divide into smaller airways to deliver air to all the alveoli.
- The airways must be strong enough to prevent them from collapsing when the air pressure inside is low (this low pressure occurs during inhalation).
- They must be flexible, to allow movement.
- They must also be able to stretch and recoil.
Lungs: What is the structure of the trachea and bronchi?
The trachea and bronchi have a similar structure. They differ only in size - the bronchi are narrower than the trachea. They have relatively thick walls that have several layers of tissue.
- Must of the wall consists of cartilage.
- The cartilage is in the form of ‘c’ shaped rings in the trachea, but is less regular in the bronchi.
- On the inside surface of the cartilage is a layer of glandular tissue, connective tissue, elastic fibres, smooth muscle and blood vessels. This is often called the ‘loose tissue’.
- The inner lining is an epithelium layer that has two types of cell. Most of the cells have cilia. This is called ciliated epithelium. Among the ciliated cells, are goblet cells.
