OCR AS Biology F211 - Lungs

Just a summary of everything i could find in the textbook about Lungs and gaseous exchange within them :)

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  • Created by: Roshni
  • Created on: 06-01-13 17:48

Lungs - Introduction

DEFINITION - Inflatable structure lying in the chest cavity. They are protected by the rib cage , which move with the diaphragm to allow ventilation.

How does air get in?

> through the NOSE

> along the TRACHEA (wind pipe)

> then the BRONCHI (narrower than the trachea)

> then through BRONCHIOLES (much narrower, usually no cartilage)

> to the ALVEOLI (tiny, air-filled sacs) to allow gaseous exchange.

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Lungs - Adaptations


> More space for molecules to pass through
> Each alveolus is small, but there are SO MANY, so there is a large surface area in comparison to our bodies


> PLASMA MEMBRANES surround the THIN CYTOPLASM to form a barrier
> These readily allow diffusion of the two gases

THIN BARRIER - (total = 2 squamous cells thick, > 1 micrometre)

> Alveolus walls AND capillary walls are 1 cell thick
> Made of SQUAMOUS CELLS --> flattened/very thin cells
> Capillaries are very close to the alveolus walls
> Narrow capillaries SQUEEZE the erythrocytes ( AKA Red Blood Cells or RBCs)
   --> this pushes them closer to the air in the alveoli and essentially slows them down

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Lungs - Diffusion Gradient

HOW?                                                                                         (conc. = concentration)

Blood Transport System -

> Bring carbon dioxide from tissues to lungs (conc. in blood > conc. in air, diffuses out to air)
> Carries oxygen away from the lungs ( conc in blood < conc. in air, diffuses into lungs)
> Heart pumps blood to lungs (pulmonary artery)
> Blood moves to capillaries on alveoli, and RBCs are squeezed to help give up oxygen

Ventilation (Breathing Movements) -

> Replaces used air with fresh air
> Bring more oxygen in and keeps conc. up (see above)
> Removes the air containing carbon dioxide to keep conc. down (see above)

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Lungs - Inhaling and Exhaling

Inhaling AKA inspiration:

> Diaphragm contracts - pushes digestive organs down
> Intercostal muscles contracts - raises ribs
> Volume increase for chest cavity
> Pressure in chest cavity < atmospheric pressure
> Air moves INTO the lungs

Exhaling AKA expiration:

> Diaphragm relaxes - pushed up by organs returning to positions
> Intercostal muscles relax - ribs fall back down
> Volume decrease for chest cavity
> Pressure in chest cavity > atmospheric pressure
> Air moves OUT OF the lungs (and INTO the air)

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Lungs - Airways


> Wall mainly consists of CARTILAGE
> Trachea has C-shaped rings; less regular in Bronchi
> Inner layer is Ciliated Epithelium with Goblet Cells


> Much narrower than bronchi
> Less/NO cartilage
> Walls are mainly smooth muscle and Elastic fibres
> Smallest bronchioles have clusters of alveoli at the ends


> Air-filled sacs, with capillaries on the surface
> Short diffusion path to increase diffusion rate, and large surface area

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Lungs - Tissues (1)

CARTILAGE - Structural role

> Supports trachea and bronchi (incomplete ring, allows flexibility)
> Holds them open, prevents them collapsing when air pressure is low (INHALATION)

SMOOTH MUSCLE - Contracts (one -way motion)

> Constricts airway; Narrows the LUMEN to restrict airflow
> KEY when harmful substances enter through the air
> INVOLUNTARY motion, e.g. allergic reactions, asthma etc.

ELASTIC FIBRES - Recoil (other-way motion)

> Constriction by smooth muscle deforms these
> When the smooth muscles relax, these RECOIL to original size and shape
> This helps to DILATE (widen) the airway again

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Lungs - Tissues (2)


> Under the epithelium
> Secrete MUCUS
> This traps tiny particles from the air e.g. pollen or bacteria
--> they can now be removed to reduce the risk of infection


> Cells that are covered in CILIA
> Cilia are lots of tiny,hair-like structures sticking out of the membrane
> They waft the mucus up to the back of the airway
> Mucus can then be swallowed and bacteria with be killed by the acidity in the stomach

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Lungs - Lung Volume Elements

TIDAL VOLUME - Volume of air going in and out of the lungs during breathing. Around 0.5dm cubed, provides enough oxygen and keeps carbon dioxide levels safe.

INSPIRATORY RESERVE VOLUME - how much MORE air can be breathed IN, over the tidal volume (when you take a big breath), used when EXERCISING.

EXPIRATORY RESERVE VOLUME - how much MORE air can be breathed OUT, over the amount breathed in a tidal volume breath.

RESIDUAL VOLUME - Volume of air ALWAYS REMAINING in the lungs, even after the biggest possible breath out (around 1.5 dm cubed)

VITAL CAPACITY - Largest volume of air that can be moved in and out of lungs in one breath. Regular exercise increases vital capacity (e.g. singers/wind instrument players)

TOTAL LUNG CAPACITY - Vital capacity + Residual Volume

DEAD SPACE - air in Bronchioles, Bronchi and Trachea. No gaseous exchange with blood.

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Lungs - Elements on a Trace


LUNG VOLUME (dm cubed)
TIME (s)

(Ignore FRC)

VT = Tidal Volume

The rest are the same as the previous slide

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Lungs - Spirometer


> A spirometer is a chamber filled with (medical-grade) oxygen floating on a tank of water, with a long tube and a disposable mouthpiece at the end, which the person breathes from.

> When someone breathes in, the lid falls and when they breathe out, it rises again as they breathe out carbon dioxide.

> This is recorded on a datalogger, producing a trace. The inspiratory volume of the LUNGS will show when the SPIROMETER volume decreases, as the lungs are breathing in the air, taking it out of the tank (see trace in textbook), so it is seemingly backwards

(always check the axis on a graph, so you can see whether it is spirometer volume or lung volume)

> The person may be asked to breathe normally at rest, or take deep breaths etc, to show different patterns of breathing.

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Lungs - Spirometer (Soda Lime)


Soda Lime is mainly Calcium Hydroxide, and it is usually used in a granular form in a spirometer.


It absorbs the carbon dioxide that is exhaled before it gets back into the chamber.


Volume of Oxygen breathed in = Volume of Carbon Dioxide breathed out

As the Carbon dioxide is being removed, the total volume of gas in the spirometer goes DOWN.

Bdcause it's equal to the amount of Oxygen breathed in, we can measure the volume of oxygen used up by the person breathing under different conditions.

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Amazing :D 

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