What is tissue fluid
The environment around the cells of multicellular organisms.
What are the two main ways by which exchange happens in cells
- passively by diffusion or osmosis
- Actively by active transport
What key characteristics do efficient exchange surfaces have
- A large surface area to volume ratio to increase the rate of exchange.
- Very thin which ensures that the diffusion distance is short so materials cross the exchange surface rapidly.
- Selectively permeable to allow selected materials to cross
- Movement of the environmental medium (eg.air) to maintain a concentration gradient.
- A transport system to ensure the movement of the internal medium (eg blood) in order to maintain a concentration gradient.
What is Fiks law
Rate of diffusion is proportional to-surface area x concentration ion difference/ distance
Why is the volume of gas exchange in humans high
- They are large organisms with a large volume of living cells.
- They maintain a high body temperature which is related to them having high metabolic and respiratory rates.
Why is the human gas exchange system located inside the body
- Air is not dense enough to support the lungs as they are very delicate structures.
- the body as a whole would lose a lot of water and dry out if the lungs were located outside of the body.
List the five main parts of the human gas exchange system
1) The lungs
2) The trachea
3) The bronchi
4) The bronchioles
5) The alveoli
Describe the structure and function of the lungs
The lungs are a pair of lobed structures made up of a series of highly branched tubules, called bronchioles, which end in tiny air sacs called alveoli.
Describe the structure and function of the trachea
The trachea is a flexible airway that is supported by rings of cartilage. The cartilage prevents the trachea from collapsing as the air pressure inside falls when breathing in. The tracheal walls are made up of muscle, lined with ciliated epithelium and goblet cells.
Describe the structure and function of the bronchi
- The bronchi are two divisions of the trachea, each leading to one lung.
- They are similar in structure to the trachea and, like the trachea, they also produce mucus to trap dirt particles and have cilia that move dirt-laden mucus towards the throat.
- The larger bronchi are supported by cartilage, and the amount of cartilage is reduced as the bronchi get smaller.
Describe the structure and function of the bronchioles
The bronchioles are a series of branching subdivisions of the bronchi. Their walls are made up of muscle lined with epithelial cells.This muscle allows them to constrict so that they can control the flow of air in and out of the alveoli.
Describe the structure and function of the alveoli
- The alveoli are minute air sacs found at the end of the bronchioles.
- Between the alveoli there are some collagen and elastic fibres.
- The alveoli are lined with epithelium.
- The elastic fibres allow the alveoli to stretch as they fill with air when breathing in.
- They then spring back during breathing out in order to expel the carbon dioxide rich air. The alveolar membrane is the gas-exchange surface.
What is inspiration (inhalation)
When the air pressure of the atmosphere is greater than the air pressure in the lungs, so air enters the lungs.
What is expiration (exhalation)
When the air pressure in the lungs is greater than that of the atmosphere, are leaves the lungs. This is expiration.
Which sets of muscles control the pressure changes within the lungs.
1) The diaphragm which is a sheet of muscle that separates the thorax from the abdomen.
2) The intercostal muscles which lie between the ribs. There are two sets of intercostal muscles:
- The internal intercostal muscles, whose contraction leads to expiration.
- The external intercostal muscles, whose contraction leads to inspiration.
Describe what happens during inspiration
- The external intercostal muscles contract, whilst the internal intercostal muscles relax.
- The ribs are pulled upwards and outwards, increasing the volume of the thorax.
- The diaphragm muscles contract, causing it to flatten, which also increases the volume of the thorax.
- The increased volume of the thorax causes a reduction of pressure in the lungs.
- Atmospheric pressure is now greater than pulmonary pressure, and so air is forced into the lungs.
Describe what happens during expiration
- The internal intercostal muscles contract, whilst the external intercostal muscles relax.
- The ribs move downwards and inwards, decreasing the volume of the thorax.
- The diaphragm muscles relax and so it is pushed up by the contents of the abdomen that were compressed during inspiration. The volume of the thorax is therefore further decreased.
- The decreased volume of the thorax increases the pressure in the lungs.
- The pulmonary pressure is now greater than that of the atmosphere, and so air is forced out of the lungs.
What type of process is inspiration
Active
What type of process is expiration
Largely passive (does require a very small amount of energy)
Explain why the diffusion of gases between the alveoli and the blood will be rapid
- red blood cells are slowed as they pass through pulmonary capillaries which allows more time for diffusion.
- the distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls.
- the walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion takes place is very short.
- the alveoli and pulmonary capillaries have a very large total surface area.
- breathing movements constantly ventilate the lungs, and the action of the heart constantly circulates blood around the alveoli. Together, these ensure that a steep concentration gradient of the gases to be exchanged is maintained.
- blood flow through the pulmonary capillaries maintains the concentration gradient.
What are the two factors that determine wether an organism has a specialised transport medium
1) the surface area to volume ratio
2) How active the organism is
Describe the key features of transport systems
- A suitable medium in which to carry materials, for example blood. This is normally a liquid based on water because water readily dissolves substances that can be moved around easily, but can be a gas such as air breathed in and out of the lungs.
- A form of mass transport in which the transport medium is moved around in bulk over large distances- more rapid than diffusion.
- A closed system of tubular vessels that contains the transport medium and forms a branching network to distribute it to all parts of the organism.
- A mechanism for moving the transport medium within vessels. This requires a pressure difference between one part of the system and another.
- A mechanism to maintain the mass flow movement in one direction, for example, valves.
- A means of controlling the flow of the transport medium to suit the changing needs of different parts of the organism.
- A mechanism for the mass flow of water or gases, for example, intercostal muscles and diaphragm during breathing in mammals.
How to animals achieve the pressure difference required to move the transport medium through the vessels.
Animals use muscular contraction either of the body muscles or of a specialised pumping organisms such as the heart.
How do plants achieve the pressure difference needed to move the transport medium through the vessels
Plants rely on natural, passive processes such as the evaporation of water.
