Exchange Systems

F211

• Explain, in terms of surface-area-to-volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not.

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Exchange surfacesExchange surfaces

What do cells need to keep them alive?What do cells need to keep them alive?

Oxygen for aerobic respiration Glucose for energy Proteins Fats to make membranes Minerals- to maintain water potential

and help action

Exchange surfacesExchange surfaces

What waste do cells need to get rid of?What waste do cells need to get rid of? Carbon dioxide Oxygen Other wastes such as ammonia or urea

which contain excess nitrogen

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1cm31cm3 organism

Surface area : volume ratio = 6:1

8cm3 organism surface area:volume ratio = 3:1

27 cm3 organism surface are : volume ratio = 2:1

Larger organisms need a larger area to exchange more substances

What makes an exchange surface efficient?Feature How it helps

Large surface area Larger area for molecules to diffuse

Thin barrier Shorter distance for diffusion

Permeable membrane Allow molecules through

Good supply/removal of molecules required

Maintain diffusion gradient

ExamplesExamples

Small intestine Liver Lungs Root hairs Hyphae of fungi

• Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus.

• Describe the features of the mammalian lung that adapt it to efficient gas exchange.

• Outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function of the rib cage, intercostal muscles and diaphragm.

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Week 7

Label as many parts as you can.

Lungs and breathing

Label as many parts as you can.

Lungs and breathing

Larynx

Trachea

Right lungLeft lung

Left bronchusRight bronchus

BronchiolesIntercostalMuscles

HeartAlveoli

Ribs

Diaphragm

Pleural cavity

Pleural Membrane

Video Clip

Lungs and breathing

Capillary network over the surface of alveoli and details of gaseous exchange

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Week 7

Can you say what is happening at each stage

1.

2.

1.

2.

3.

4.

5.

6.

7.

8.

Feature that make the lungs adapted to exchange

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Week 7

• Large surface area - An average adult has about 600 million alveoli, giving a total surface area of about 70m² (Half size of tennis court)

• Permeable to O2 and CO2

• Thin barrier to reduce diffusion distance1. The walls of the alveoli are composed of a

single layer of flattened epithelial cells, as are the walls of the capillaries, so gases need to diffuse through just two thin cells (less than 1µm thick)

2. Both cells made of squamous cells (meaning flattened or very thin cells)

3. Capillaries very close to alveolus wall4. Narrow capillaries- RBCs squeezed

against cell wall

Feature that make the lungs adapted to exchange

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Week 7

• Water diffuses from the alveoli cells into the alveoli so that they are constantly moist.

• Oxygen dissolves in this water before diffusing through the cells into the blood, where it is taken up by haemoglobin in the red blood cells.

• The water also contains a soapy surfactant which reduces its surface tension and stops the alveoli collapsing.

• The alveoli also contain phagocyte cells to kill any bacteria that have not been trapped by the mucus

The steep concentration gradient across the respiratory surface is

maintained in two ways:

1) by blood flow on one side

2) by air flow on the other side.

This means oxygen can always diffuse down its concentration

gradient from the air to the blood, while at the same time carbon

dioxide can diffuse down its concentration gradient from the

blood to the air.

The flow of air in and out of the alveoli is called ventilation and has

two stages: inspiration (or inhalation) and expiration (or

exhalation). Lungs are not muscular and cannot ventilate

themselves, but instead the whole thorax moves and changes

size, due to the action of two sets of muscles: the intercostal

muscles and the diaphragm.

Describe the stages of Inhalation and exhalation Must give reference to

Diaphragm Intercostal muscles Volume of chest cavity pressure

Exhalation is a passive process, We breathe out when our muscles relax

Breathing is a passive process

Inhalation Exhalation

Diaphragm Contracts, moving downwards increasing the volume of the chest cavity and displacing the organs beneath

The diaphragm relaxes, the organs below move back into place

The intercostal muscles contract moving the ribcage up and out

The intercostal muscles relax, the ribcage moves down and in

The volume of the chest cavity increases decreasing the pressure in the thorax below atmospheric pressure

The volume of the chest cavity decreases causing air pressure in the lungs to increase above atmospheric pressure

Air is sucked into the lungs as a result

Air is forced out of the lungs as a result

• Describe the distribution of cartilage, ciliated epithelium, goblet cells, smooth muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli of the mammalian gaseous exchange system.

• Describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres in the mammalian gaseous exchange system.

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Week 7

(a) Bronchiole and (b) trachea in transverse section

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Week 7

What is the role of each tissue?

Cartilage

Smooth Muscle

Elastic fibres

Goblet cells and glandular tissue

Cilliated epithelium

• Explain the meanings of the terms tidal volume and vital capacity.

• Describe how a spirometer can be used to measure vital capacity, tidal volume, breathing rate and oxygen uptake.

• Analyse and interpret data from a spirometer.

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Week 7

Removes CO2

Total Lung Capacity- The maximum amount of air that the lungs can hold Residual Volume- The volume of air that remains in the lungs after breathing

approx 1.5dm3

Vital Capacity- The maximum usable lung volume (total lung capacity minus the residual volume). The average vital capacity is 4.5-5 dm3 for men and 3.5-4 for women.

Tidal Volume- The volume of air that moves in and out of the lungs in each breath (during normal breathing). In a normal adult this is about 0.5 dm3.

Inspiratory Reserve Volume- The amount of air that the lungs will hold after a normal expiration (i.e. inspiratory reserve + tidal volume).

Expiratory Reserve Volume- The amount of air remaining in the lungs after a normal quiet expiration (i.e. expiratory reserve volume + residual volume).

Exam questions

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