B3- Human gas exchange

describe the gross structure of the human gas exchange system and how we breathe in and out (6)

Gross structure
trachea → bronchi → bronchioles → alveoli

How we breath in:

1. external intercoastal muscles contract and rib cage moves up and out

2. diaphragm contracts and flattens

3. increasing volume and decreasing pressure in thoracic cavity

4. air forced into lungs down pressure gradient

How we breathe out:

1. external intercostal muscles relax and rib cage moves down and in

2. diaphragm relaxes and becomes dome shaped

3. decreasing volume and increasing pressure in thoracic cavity

4. air moves out of lungs down pressure gradient

describe and explain the mechanism that causes forced expiration (4)

1. contraction of internal intercostal muscles

2. relaxation of diaphragm muscles

3. causes a decrease in volume of the thoracic cavity, so pressure increases

4. air moves out down pressure gradient

active process

describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs (details of breathing are not required)

(4)

1. air moves through trachea→ bronchi → bronchioles → alveoli

2. down pressure gradient

3. oxygen diffuses across alveolar epithelium

4. across capillary endothelium

5. down diffusion gradient

where is the main site of gas exchange in a human

alveoli

what is the function of pleural fluid

• acts as a lubricant - so surface of lungs don’t stick to inside of chest wall when we breathe

• acts as a shock absorber

what is the function of the mucus in the nasal cavity and the trachea

• traps dust and microorganisms that are breathed in

what is the function of cilia cells which line trachea

• beat back and forwards

• waft away mucus and trapped particles out towards the mouth

• prevent bacteria and dirt reaching lungs

• preventing infection

describe and explain how alveoli are adapted for effect gas exchange

1. many alveoli and alveoli walls are folded to provide a larger SA

2. alveolar epithelium made from squamous cells is one cell thick and capillary endothelium is one cell thick → providing a short diffusion distance between alveoli and blood

3. walls of alveoli contain elastin protein→ helps alveoli recoil to their normal shape after inhaling and exhaling air

4. ventilation and circulation → maintains a steep concentration gradient → so fast diffusion

5. surrounded by a network of blood capillaries → maintaining a steep concentration gradient → so fast diffusion

6. moist inner wall of alveolus helping diffusion as gases diffuse better in solution

explain why oxygen uptake is a measure of metabolic rate in organisms

1. oxygen is used in respiration which is a metabolic process

give 2 ways in which an organism might be adapted to allow efficient gas exchange when it doesn’t have a gas exchange system

1. long and thin → large SA

2. thin/small → so short diffusion distance

describe and explain how the lungs are adapted for effect gas exchange (5)

1. many alveoli / alveoli walls are folded to provide a large SA

2. many capillaries provide a large SA

3. so fast diffusion

4. alveolar epithelium and capillary endothelium are one cell thick

5. alveolar epithelium made from squamous cells

6. so short diffusion distance

7. so fast diffusion

8. ventilation / circulation

9. maintains a diffusion gradient

10. so fast diffusion

describe the pathway taken by an oxygen molecule from an alveolus to the blood

1. moves across alveolar epithelium

2. across capillary endothelium

explain how an asthma attack causes a drop in mean FEV

1. muscle wall of bronchi/ bronchioles contract

2. walls of bronchi/ bronchioles secrete more mucus

3. diameter of airways reduced

4. therefore flow of air reduced

difference between effects of fibrosis and emphysema vs asthma on breathing

fibrosis and emphysema

• reduce FVC/ total volume breathed out

• by reducing SA of lungs

asthma

• reduce size of airways / affect bronchi and bronchioles by making muscle in walls contract and them to secrete more mucus

• therefore reducing FEV / volume of air able to be forced out in a second

when given a graph comparing FEV/ FVC you should

• common on obvious conclusion

• comment on rate of decrease / increase in comparison

e.g. see question 9b in PPQs booklet

suggest 2 changes in lungs of people that causes FEV to decrease

1. airways narrowed / blocked

2. excess mucus in airway

3. inflammation of airways

4. elasticity is lost / scar tissue builds up

explain the importance of ventilation

1. brings in air containing higher conc. of oxygen and removes air with lover conc. of oxygen

2. maintaining concentration gradient

suggest why expiration is normally passive at rest

1. internal intercostal muscles do not normally need to contract

2. expiration aided by elastic recoil in alveoli

suggest how different lung diseases reduce the rate of gas exchange (FVC)

1. thickened alveolar tissue (e.g. fibrosis) → increases diffusion distance

2. alveolar wall breakdown → reduces surface area

3. reducing lung elasticity → lungs expand / recoil less → reduces concentration gradients of O₂ and CO₂

suggest how different lung diseases affect ventilation

1. reduce lung elasticity (eg. fibrosis- build up of scar tissue)→ lungs recoil less

• reducing volume of air in each breath (tidal volume)

• reducing FVC

2. narrow airways (eg. asthma)

• reducing maximum volume of air breathed out in 1 second (FEV)

3. reduced rate of gas exchange → increased ventilation rate to compensate for reduced oxygen in blood

suggest why people with lung disease experience fatigue

cells receive less oxygen → rate of aerobic respiration reduced → less ATP made

suggest how you can analyse and interpret data relating to the effects of pollution, smoking and other risk factors on the incidence of lung disease

• describe overall trend → eg positive/neg correlation between risk factor and incidence of disease

• manipulate data → eg. calculate percentage change

• interpret standard deviations → overlap suggests difference in means are likely to be due to chance

• use stats test → identify whether difference / correlation is significant or due to chance

name the 3 different stats tests and what they are used for

1. Spearman’s rank→ examining correlation between 2 sets of data

2. students t-test → comparing means of 2 sets of data

3. Chi-squared test → for categorical data

suggest how you can evaluate the way in which experimental data led to statutory restrictions on the sources of risk factors

1. analyse and interpret data as described on previous flashcard and identify what does and doesn’t support statement

2. evaluate method of collecting data

• sample size → large enough to be representative of population?

• participant diversity eg age sec ethnicity health status → representative of whole population?

• control groups → used to enable comparison?

• control variables eg. health, previous medications → valid?

• duration of study → long enough to show long term effects?

3. evaluate context → has a broad generalisation been made from a specific set of data?

4. other risk factors that could have affected results?

define correlation

change in one variable reflected by a change in another - identified on a scatter diagram

define causation

change in one variable causes a change in another variable

what is the common relationship between correlation and causation

correlation does not means causation

→ may be other factors involved