Example answers for Lung questions

Alveoli and capillary walls are thin - short distance for diffusion

Alveoli and pulmonary capillaries have a large SA - speeds up diffusion

Flattened red blood cells against capillary wall reduce diffusion path

Red blood cells slowed through capillaries so more time for diffusion

Blood flow maintains steep concentration gradient 

Breathing ventilates lungs and heart action circulates blood, maintains steep concentration gradient

Large surface area - to speed up rate of diffusion 

Thin - keep a short diffusion path

Partially permeable membrane - allow easy diffusion of selected molecules/particles

Movement of Internal Medium - eg. blood, to maintain diffusion gradient

Movement of External Medium - eg. air, to maintain diffusion gradient

The diaphragm contracts, moves down and flattens

This increases chest cavity space and volume of the thorax

The pressure then decreases and as the atmospheric pressure is greater than the pulmonary pressure, air is drawn into the lungs

In inspiration, the external intercostal muscles contract and the internal intercostal muscles relax.

The ribcage moves up and out, increasing the volume of the thorax.

The diaphragm then contracts and flattens, also increasing the volume of the thorax.

As the thorax volume has been increased, the pressure decreases.

This means that pulmonary pressure is not as great as the atmospheric pressure, so air is drawn into the lungs.

This can be carried out by the equation for Pulmonary Ventilation.

PV = BR x TV

The breathing rate is how many breaths there have been in one minute

The tidal volume is the volume taken in by each breath when a person is at rest

This gives the air accumulated in ventilation for one minute = Pulmonary Ventilation

Air moves down in a pressure gradient so there is a lower pressure, allowing air to be taken into the lungs due to two differences in external and internal pressures.

Fick's law is when the rate of diffusion is proportional to the (surface area x difference in concentration)/thickness of diffusion surface.

Therefore, the larger the surface area, steeper the concentration gradient, and thinner the surface, the faster the rate of diffusion.

Breathing maintains steep concentration gradients, therefore the rate of diffusion should stay efficient. 

The gas exchange surface is the alveolar membrane.

Air passes through the alveoli, then the bronchioles, the bronchi, and the trachea. It then goes by the larynx and the pharynx, before out of the nose (or mouth). 

The trachea is the long airway running down the centre of the ventilation system. It is known as the wind pipe.

It is supported by rings of cartilage.

Inside it is lined by muscle and ciliated epithelium, with goblet cells.

Goblet cells produce mucus. 

There are two parts to the intercostal muscles. External muscles contract upon inspiration. They relax on expiration. Internal intercostal muscles relax on inspiration and contract on expiration.

External elevate the ribs and increase volume of thorax

Internal used in depression of the ribs and reduce volume of thorax