human exchange surface Flashcards
Describe and explain how the structure of the mammalian breathing system enables efficient uptake of oxygen into the blood.
- alveoli provide a large surface area;
- walls of alveoli thin to provide a short diffusion pathway;
- walls of capillary thin / close to alveoli provides
a short diffusion pathway; - walls (of capillaries / alveoli) have flattened cells;
- cell membrane permeable to gases;
- many blood capillaries provide a large surface area;
- intercostal / chest muscles / diaphragm muscles / to ventilate lungs /
maintain a diffusion / concentration gradient; - wide trachea / branching of bronchi / bronchioles for efficient
flow of air; - cartilage rings keep airways open;
(reject moist and thin membranes)
Describe the gross structure of the human gas exchange system and how we breathe in and out.
Named structures – trachea, bronchi, bronchioles, alveoli;
Reject mp1 if structures from other physiological systems are named but award mp2 if the correct structures are in the correct order.
- Above structures named in correct order
OR
Above structures labelled in correct positions on a diagram;
Reject mp1 if structures from other physiological systems are named but award mp2 if the correct structures are in the correct order.
- Breathing in – diaphragm contracts and external intercostal muscles contract;
- (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
For thoracic cavity accept ‘lungs’ or ‘thorax’.
Reference to ‘thoracic cavity’ only required once.
- Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
Accept diaphragm relaxes and (external) intercostal muscles relax and lung tissue elastic (so recoils).
- (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);
Breathing out as hard as you can is called forced expiration.
(a) Describe and explain the mechanism that causes forced expiration.
Contraction of internal intercostal muscles;
- Relaxation of diaphragm muscles / of external intercostal muscles;
- Causes decrease in volume of chest / thoracic cavity;
- Air pushed down pressure gradient.
The people in group B were recovering from an asthma attack.
Explain how an asthma attack caused the drop in the mean FEV shown in the figure above.
Muscle walls of bronchi / bronchioles contract;
- Walls of bronchi / bronchioles secrete more mucus;
- Diameter of airways reduced;
- (Therefore) flow of air reduced.
Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing are not required.
Trachea and bronchi and bronchioles;
- Down pressure gradient;
- Down diffusion gradient;
- Across alveolar epithelium.
Capillary wall neutral
- Across capillary endothelium / epithelium.
Scientists determined the mean FEV1 value of 25-year-olds in the population.
Suggest two precautions that should have been taken to ensure that this mean FEV1 value was reliable.
Large sample size;
Accept: 20 + as equal to large sample size.
- Individuals chosen at random;
- Are healthy;
- Equal number of males and females;
Accept: same sex/gender.
- Repeat readings;
Explain the importance of determining a mean FEV1 value of 25-year-olds in this investigation.
Forced expiration volume (FEV1) is the volume of air a person can breathe out in 1 second
For) comparison;
Accept: provides a benchmark/standard.
- To see effect of age/emphysema/smoking
OR
Takes into account outliers/anomalous results;
The mean FEV1 value of non-smokers decreases after the age of 30.
Use your knowledge of ventilation to suggest why.
Forced expiration volume (FEV1) is the volume of air a person can breathe out in 1 second.
Internal intercostal muscle(s) less effective
OR
Less elasticity (of lung tissue);
One of the severe disabilities that results from emphysema is that walking upstairs becomes difficult.
Explain how a low FEV1 value could cause this disability.
Forced expiration volume (FEV1) is the volume of air a person can breathe out in 1 second.
Less carbon dioxide removed;
Accept: carbon dioxide increases/high (in body/blood).
1 and 2. Accept: ‘low amount’ as equivalent to ‘less’.
- Less oxygen (uptake/in blood);
Accept: less oxygen inhaled.
2 and 3. Accept: less oxygen for respiration = 2 marks.
- Less (aerobic) respiration/ATP
OR
(More) anaerobic respiration;
Accept: (more) lactic acid.
Explain the role of the diaphragm in breathing out
. Diaphragm moves up /becomes dome shaped;
- Reduces volume of thorax / increase pressure in thorax;
Accept ‘space’ for volume, chest/lungs for thorax
- Pressure in thorax higher than outside (air);
Accept chest/lungs
Smoking causes changes in the lungs and airways of smokers.
Suggest two changes in the lungs of people who continue to smoke that could explain the change in their FEV1.
Airways are narrowed/blocked;
- Excess mucus (in airway);
- Inflammation (of airways);
- Elasticity is lost/scar tissue builds up;
The photograph shows a fire-breather creating a ball of fire. Fire-breathers do this by blowing a fine mist of paraffin oil onto a flame. Some of this mist can be inhaled and may eventually lead to fibrosis.
People who have been fire-breathers for many years often find they cannot breathe out properly. Explain why.
________________________
Loss of elasticity / elastic tissue / increase in scar tissue;
- Accept elastin
- Less recoil;
When a person starts to breathe out, the percentage of oxygen in the air first exhaled is the same as the percentage of oxygen in the atmospheric air. Explain why.
Air is from nose / trachea / bronchi / not been in alveoli / dead space;
Gas exchange / diffusion only in alveoli / not in these structures;
