Exchange Surfaces Flashcards
What is the need for specialised exchange surfaces?
- all living things need O2 and nutrients remove waste products
- small organisms exchange over whole body, big organisms two layers not sufficient
- size = several layers of cells longer diffusion pathway too slow for supply to innermost cells
- SA:V = small have large and big have small as SA:V decreases rate of diffusion decreases
- level of activity = metabolic activity uses energy and oxygen good supply for energy
What are the features of a good exchange surface?
- large surface area = folding of walls provides more space for molecules to pass through
- thin barrier = reduce diffusion distance permeable
- good blood supply = fresh supplies keeping conc high or low maintain a steep conc gradient diffusion occur rapidly
Give a brief description of mammalian gas exchange system
Nasal cavity, trachea, bronchi, bronchioles, alveoli
Protected by, ribcage held together by intercostal muscles, diaphragm and intercostal muscles produce ventilation
How do alveoli achieve a large surface area and what is inside them?
Very small and numerous, lined by thin layer of moisture evaporates, must produce surfactant that coats internal surface of alveoli reduce cohesive forces, make alveoli collapse
Describe the features of the thin barrier of the alveoli that reduce the diffusion distance
- alveolus wall one cell thick
- capillary wall one cell thick
- squamous
- capillaries close contact with alveolus
- narrow capillaries RBC squeezed against wall, makes them closer to alveoli and reduces rate of flow
Describe the significance of good blood supply in alveoli
Helps maintain steep concentration gradient so gases continue to diffuse
- blood transports CO2 from tissues to lungs ensures conc of CO2 is higher than in alveoli air so CO2 diffuses into alveoli
- blood transports O2 away from lungs ensures conc O2 kept lower that alveoli so O2 diffuses into blood
Describe what ventilation ensures
Breathing movements that ventilate the lungs replaces used air with fresh air
ensures that the conc of O2 in alveoli air is higher than blood and conc CO2 in alveoli is lower than blood
Describe the process of ventilation
Inspiration
- diaphragm contracts to move down and become flatter
- external intercostal muscles contract to raise the ribs
- volume of chest cavity increased
- pressure in chest cavity below atmospheric pressure
- air moves into lungs
- elastic fibres stretch
Expiration
- diaphragm relaxes pushes up by displaced organs
- external intercostal muscles relax ribs fall intercostal contact to push out forcefully
- volume chest cavity decreased
- pressure in lungs increases above atmospheric pressure
- air moves out of the lungs
- elastic fibres recoil
What requirements must the airways have
- large allow sufficient air flow without obstruction
- supported to prevent collapse when air pressure inside is low inspiration
- flexible to allow movement
What tissues are involved in the airways
- ciliated epithelium keeps lungs healthy
- goblet cells release mucous traps pathogens cilia moves mucus to top of airway swallowed
- loose tissue contains elastic fibres, glands and blood vessels
- trachea and bronchi cartilage prevent collapse inspiration C shaped allows flexibility and space for food
- bronchioles smooth muscle can contract constrict the airway makes lumen narrower restrict the flow of air, control flow to alveoli (harmful substances)
- elastic fibres elongate smooth muscles again, returns to original size recoil dilate airways (deforms when sm contracted)
What is a spirometer?
Measure lung volumes device measures movement of air in and out of the lungs as person breath
- float chamber has a chamber of medical grade oxygen on a tank of water
- inspiration air drawn down so lids moves down
- expiration air returns raises the lid recorded data logger
- CO2 passed through chamber soda lime absorbs allows measure of oxygen consumption
Small and simple hand held devices don’t measure rate of oxygen consumption
What precautions must be taken when using a spirometer?
- healthy and free from asthma
- soda lime fresh and functioning
- no air leaks give invalid results
- mouthpiece sterilised
- must not be over filled (water enter tubes)
Describe the different lung volumes and label a graph
Vital capacity
= max volume of air that is moved by lungs in one breath depends on size, age and gender, level of exercise 2.5-5.0 dm3
Residual volume
= air that remains in the lungs after forces expiration remains in airways and alveoli
Tidal volume
= volume of air moved in and out (exhalation) measured at rest (during regular breathing) 0.5dm3
What is oxygen uptake?
As a person breathes from spirometer oxygen is absorbed by blood replaced by CO2
CO2 absorbed by soda lime so volume of air in chamber decreases measured on trace
- volume of CO2 absorbed by soda lime = volume of oxygen absorbed by blood
- measure gradient of decrease calculate rate of O2 uptake
- increased O2 uptake = increased breathing rate and deeper breaths
Breathing rate = no. peaks in each minute
Explain why the peaks go diagonally down the trace
The air chamber in spirometer rises and falls as person breathes
Oxygen is removed from spirometer and CO2 breathed out is absorbed
So air chamber does not rise as high
