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.
Lungs: What is 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 made mostly of smooth muscle and elastic fibres. The smallest bronchioles have clusters of alveoli (air sacs) at their ends.
Lungs: What are the different types of lung tissue?
- Cartilage
- Smooth muscle
- Elastic fibres
- Goblet cells and glandular tissue
- Ciliated epithelium
Lungs: What is cartilage?
The cartilage pays a structural role. It supports the trachea and bronchi, holding them open. This prevents collapse when the air pressure inside is low during inhalation. The cartilage does not form a complete ring so that there is some flexibility. This allows you to move your neck without constricting the airways. It also allows for the oesophagus (the tube that carries food down to the stomach) to expand during swallowing.
Lungs: What is smooth muscle?
The smooth muscle can contract. When the smooth muscle contracts, it will constrict the airways, making the lumen of the airway narrower. The effect of the smooth muscle is most obvious in the bronchioles. Constricting 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 are harmful substances in the air. The contraction of the smooth muscle and control of air flow is not a voluntary act. Some people have an allergic reaction to certain substances in the air and their bronchioles constrict making it difficult to breath. This is one of the causes of asthma.
Lungs: What are elastic fibres?
When the smooth muscles contracts, it reduces the diameter of the lumen of the airway. The smooth muscle cannot reverse this effect. When the airway constricts it deforms the elastic fibres in the tissue. As the smooth muscle relaxes, the elastic fibres recoil to their original size and shape. This helps to dilate (or widen) the airway.
Lungs: What are goblet cells and glandular tissue?
The goblet cells and glandular tissue under the epithelium secrete mucus. The role of the mucus is to trap tiny particles from the air. These particles may include pollen and bacteria. Trapping the bacteria so that they can be removed will reduce the risk of infection.
Lungs: What is ciliated epithelium?
The epithelium consists of ciliated cells. These cells have numerous tiny, hair like structures projecting from their membrane. These are the cilia. Cilia move in a synchronised pattern to waft the mucus up the airway to the back of the throat. Once there, the mucus is swallowed and the acidity in the stomach will kill any bacteria.
Lungs: What happens in inspiration?
(Inhalation)
- Diaphragm contracts to become flatter and pushes digestive organs down.
- External intercostal muscles contract to raise ribs.
- Volume of chest cavity increases.
- Pressure in chest cavity drops below atmospheric pressure.
- Air moves into lungs.
Lungs: What is expiration?
(Exhalation)
- Diaphragm relaxes and is pushed up by displaced organs underneath.
- External intercostal muscles relax and ribs fall.
- Volume of chest cavity decreases.
- Pressure in lungs increases and rises above atmospheric pressure.
- Air move out of lungs.
Lung Capacity: What happens when you breathe?
Air moves in and out of your lungs about 12 times per minutes as your diaphragm and intercostal muscles contract and relax. Each breath refreshes some of the air in your lungs and carries away some of the carbon dioxide generated by your body. If you exercise, or if you are frightened, you breathe more deeply and more quickly. This gets more oxygen rich air into your lungs and remove more carbon dioxide rich air out of your lungs.
Lung Capacity: What is tidal volume?
The volume of air moved in and out of the lungs with each breath when you are at rest.
-This provides the body with enough oxygen for its resting needs while removing enough carbon dioxide to maintain a safe level.
Lung Capacity: What is the average tidal volume?
0.5dm^3
Lung Capacity: What is vital capacity?
The largest volume of air that can be moved into and out of the lungs in any one breath.
-This varies between gender, size and age. Regular exercise increases vital capacity.
Lung Capacity: What is the average vital capacity?
5dm^3
Lung Capacity: What is residual volume?
The volume of air that always remains in the lungs, even after the biggest possible exhalation.
Lung Capacity: What is the average residual volume?
1.5dm^3
Lung Capacity: What is dead space?
The air in the bronchioles, bronchi and trachea. There is no gas exchanged between the air and the blood.
Lung Capacity: What is inspiratory reserve volume?
How much more air can be breathed in (inspired) over and above the normal tidal volume when you take a big breath. You call on this reserve when exercising.
Lung Capacity: What is expiratory reserve volume?
How much more air can be breathed out (expired) over and above the amount that is breathed in a tidal volume breath.
Lung Capacity: What is a spirometer?
A spirometer consists of a chamber filled with oxygen that floats on a tank of water. A person breathes in from a disposable mouthpiece attached to a tube connected to the chamber of (medical-grade) oxygen. Breathing in take oxygen from the chamber, which them sinks down (this is why on a spirometer trace and a wiggly line is produced, the line going shows inhalation). Breathing out pushes air into the chamber, which then floats up.
-The movements of the chamber are recorded using a data logger so that a spirometer trace can be produced. The longer the line, the deeper the breath.
Lung Capacity: How is carbon dioxide removed from the spirometer?
If someone breathes in and out of a spirometer for a period of time, the level of carbon dioxide will increase dangerously.
-To avoid this, soda lime is used to absorb the carbon dioxide that is exhaled. This means that the total volume of gas in the spirometer will go down.
Lung Capacity: Why are spirometer traces slanted downwards?
The total volume of gas in the chamber decreases over time. This is because the air that’s breathed out is a mixture of oxygen and carbon dioxide. The carbon dioxide is absorbed by the soda lime - so there’s only oxygen in the chamber which the subject inhales from. As this oxygen gets used up by respiration, the total volume decreases.
Lung Capacity: How is the oxygen uptake in a minute measured from a spirometer?
Oxygen uptake is the decrease in the volume of gas in the spirometer chamber. It can be read from the graph by taking in the average slope of the trace (how much it decreases.
