3.1.1 Exchange Surfaces Flashcards
Why is there the need for an exchange system for large organisms?
- when diffusion alone isnt sufficient, too slow to enable sufficient supply of nutrients to all tissues: e.g. due to long diffusion distance or small SA:V rato
- Level of activity: organisms with higher metabolic activity need a good supply of oxygen to supply energy for movement and warmth in mammals.
What are the features of a good exchange system?
increased surface area e.g. alveoli and folding membranes
thin membranes to reduce diffusion distance – alveoli, narrow capillaries
good blood supply to maintain gradient so diffusion can occur rapidly -> gills, fast flow of blood in alveoli
ventilation to maintain gradient once again.
Gaseous exchange in lungs -> what happens, and why is it an efficient system?
- oxygen diffuses into blood through alveoli, and CO2 to air througj alveoli.
- LARGE SA due to numerous alveoli.
- Alveoli lined by layer of moisture that evaporates as we breathe out
- Lungs produce a surfactant that coats internal surface of alveoli - reduces cohesive forces to avoid collapse.
- Permeable barrier: readily allow diffusion
- Thin barrier: alveolus and capillary walls are very thin = short diffusion pathway
- Good blood supply: Blood transports CO2 from tissue to lungs and transports O2 away from lungs to maintain gradients.
What is the mechanism of inhalation?
- Active
1) Diaphragm contracts, flattens
2) Internal ICM relax
3) External ICM contract to raise ribs up and out
4) Volume of thorax increased
5) Pressure in thorax drops below atmospheric
6) Air moves into lungs down gradient
What is the mechanism of exhalation?
- Passive ( apart from when its forced)
1) Diaphragm relaxes
2) Internal ICM contract during forced exhalation
3) External ICM relax and ribs fall
4) Volume of thorax is decreased
5) Pressure in thorax increases above atmospheric
6) Air moves out of lungs
Tissues in the exchange system: ALVEOLI. Describe the features.
- Squamous epithelium + surrounded by capillaries
- Elastic fibres that stretch in inspiration and RECOIL during expiration
Tissues in the exchange system: AIRWAYS (trachea, bronchi AND bronchioles). Describe the features.
- Lined by ciliated epithelium
- Goblet cells and glandular tissue produce mucus to trap pathogens
-Cilia move to waft mucus to throat - Smooth muscle contracts to constrict airways
Tissues in the exchange system: TRACHEA AND BRONCHI. Describe the features.
- Supported by rings of cartiliage to prevent collapse. C-shaped to allow flexibility
Tissues in the exchange system: BRONCHIOLES. Describe the features.
- Larger: cart, smaller: no cart
- Wall comprised mostly of smooth muscle that contract to constrict airway and elastic fibres
What does smooth muscle do to the airways during allergic reactions? What is the role of elastic fibres?
- Contract -> constrict airway and restricts airflow
- Once contracted it cannot reverse effect on its own, elongated by elastic fibres
- Contraction = deforms elastic fibres. Relaxation = elastic fibres recoil to dilate airway again
How do you measure lung volumes? Precautions?
- spirometer
- chamber of air floats on tank of water
- inspiration: lid down. expiration: lid up
- movements recorded as datalogger to produce trace
- fresh soda lime, healthy subject, sterilised mouthpiece
What is total lung volume?
vital capacity and residual volume
What is vital capacity?
this is the maximum volume of air that can be breathed in or out in one breath
What is tidal volume?
Volume of air breathed in or out at rest in one breath. usually 0.5dm3
What is residual volume?
the volume of air remaining in the lungs after maximum forceful expiration.
