Exchange surfaces Flashcards
1
Q
How do you calculate the volume and surface area of a sphere?
A
Surface area of a sphere - 4๐
r2
Volume of a sphere - 4/3๐
r3
2
Q
What are the 4 different types of specialised exchange surfaces?
A
- Increased Surface Area (eg villi in the small intestine, root hair cells in plants)
- Thin Layers (eg alveoli in lungs, villi of small intestine)
- Good blood supply (eg alveoli, gills, villi)
- Ventilation to maintain diffusion gradient (eg alveoli, gills)
3
Q
How is the nasal cavity adapted to its function?
A
- Large surface area with a good blood supply, which warms the air to body temperature
- A hairy lining, which secretes mucus to trap dust and bacteria, protecting delicate lung tissue from irritation and infection
- Moist surfaces, increasing the humidity of incoming air, reducing evaporation from the exchange surfaces
- So after passing through the nasal cavity, air entering the lungs is a similar temperature and humidity to the air already there
4
Q
How is the trachea adapted to its function?
A
- Main airway carrying clean, warm air from nasal cavity to the chest
- Supported by incomplete, flexible, strong cartilage rings
- Incomplete so food can move easily down the oesophagus behind the trachea
- Lined with goblet cells which secrete any mucus on the lining of the trachea that escaped the nose lining
- Ciliated epithelium beats away the mucus with anything else like trapped dirt and microorganisms into the throat, to be digested
- Smoking stops cilia from beating
5
Q
How is the bronchus adapted to its function?
A
- In the chest cavity, the trachea divides to form the left and right bronchus, which lead to the lungs
- Similar structure to trachea, but smaller
6
Q
How are the bronchioles adapted to their function?
A
- In the lungs, the bronchi divide into lots of smaller bronchioles which are less than 1mm diameter, with no cartilage rings
- Bronchiole walls contain smooth muscle. When this contracts, the bronchiole constricts/closes up. - - When it relaxes, the bronchioles dilate/open up
- This can change the volume of air reaching the lungs
- Bronchioles are lined with a thin layer of flattened epithelium, making some gas exchange possible
7
Q
What are alveoli?
A
- Tiny air sacs which are the main gas exchange surfaces of the body
- Unique to mammalian lungs
- Diameter around 200-300 micrometres
- Consist of a layer of thin, flattened epithelial cells, along with some collagen and elastic fibres
- The elastic fibres allow the alveoli to stretch as air is drawn in, and help squeeze air out when they return to their resting size. This is known as elastic recoil of the lungs
8
Q
What are the adaptations of alveoli?
A
- Large surface area
- Thin layers - The alveoli and capillaries surrounding them have walls one cell thick, so the diffusion distances are very short
- Good blood supply - Constant flow of blood maintains a steep concentration gradient
- Good ventilation - Breathing moves air in and out of the alveoli, maintaining steep concentration gradients
9
Q
Explain inspiration
A
- Energy-using process
- Diaphragm contracts and flattens
- External intercostal muscles contracts, moving the ribs upwards and outwards
- This increases the volume of the thorax, so the pressure is reduced, and now lower than in the atmospheric air, so that is drawn in
- This equalises the pressures inside and outside the chest
10
Q
Explain expiration
A
- Passive process
- Muscles of the diaphragm relax so it moves up into its resting dome shape
- External intercostal muscles relax so the ribs move down and inwards under gravity
- Elastic fibres in the alveoli also return to their normal length
- All these changes lead to a decrease in volume of the thorax
- Pressure is therefore greater in the thorax than in the atmospheric air, so air moves out of the lungs until pressure in and out is equal again
- You can exhale forcibly using energy
- Same effects but faster and harder and with contractions
11
Q
What are the 3 different ways of measuring the volume of air drawn in and out of the lungs?
A
- Peak flow metre - Simple device that measures the rate at which air can be expelled from the lungs. Often used by people with asthma
- Vitalographs - More sophisticated version. Patient being tested breathes out as fast as they can through a mouthpiece, and the instrument produces a graph of the volume of air they breathe in and out and how fast it is breathed out. This volume of air is called the forced expiratory volume in one second
- Spirometer - Commonly used to measure different aspects of the lung volume, or to investigate breathing patterns. Many different forms of it but they all use the same principles
12
Q
What are the components of lung volume measured by a spirometer trace?
A
- Tidal volume - Volume of air that moves in and out of the lungs with each resting breath
- Vital capacity - Volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible intake of breath
- Inspiratory reserve - Maximum volume of air you can breathe in over and above a normal inhalation
- Expiratory reserve - Extra volume of air you can breathe out of the lungs over and above the normal tidal volume of air you can breathe out
- Residual volume - Volume of air left in the lungs after a maximum exhalation. This canโt be measured directly
- Total lung capacity - Sum of the vital capacity and the residual volume
13
Q
What is ventilation rate and how is it calculated?
A
The total volume of air inhaled in one minute
Ventilation rate = Tidal Volume x Breathing rate (breaths per minute)
14
Q
Explain how the spiracle contributes towards gas exchange in insects
A
- Spiracles are small openings along the thorax and abdomen
- Air enters and leaves through them, and water is also lost
- They can be opened or closed by sphincters which are closed as much as possible to minimise water loss
- But when oxygen demand is raised or CO2 levels build up, more of the sphincters open up
15
Q
Explain how tracheae contribute towards gas exchange in insects
A
- Leading away from the spiracles are tracheae
- Largest tubes of the insect respiratory system (1mm in diameter)
- They carry air into the body
- Lined by spirals of chitin which keep them open if they are bent or pressed. It is also relatively impermeable to gases so little gas exchange
- They branch to form tracheoles
