Gaseous Exchange & Respiration

Two main reasons why diffusion is not enough to supply the needs of slingle-celled organisms:

         -Metabolic activity of a single celled organism is low, so loxygen   demands and carbon dioxide production are low. 

         -The surface area to volume ratio of the organism is large.

Know this:

-The bigger the organism the smaller the SA:V ratio - gases can't be exchanged fast enough.

-The distance between the cells where the oxygen is needed and the supply of oxygen is too far for effective diffusion to take place. E.G Dolphin   

Amoeba

-The exchange surface is the cell membrane.

Capacity to exchange materials depends on:

-Surface area of the exchange surface.

-The need for oxygen and food.

-The requirements for getting rid of waste

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Nasal Cavity

- A large surface area with good bloody supply, which warms the air to body temperature.

-Hairly lining, wich secretes mucus to trap dust and bacteria, protecting delicate lung tissue.

-Moist surfaces, increase the humidity of the incoming air, this reduces evaporation from the exchange surfaces.

Trachea

-The main airway carrying clean, warm and moist air from the nose to the chest.

-A wide tube supported by cartliage, which stops the trachea from collapsing.

-The cartilage rings are incomplete so that food can move easily down the oesophagus.

-The trachea and it's branches are lined with cilated epithelium with goblet cells.

-Goblet cells secrete mucus onto the lining of the trachea, to trap dust and microorganisms.

-The cilia beat and move the mucus, along with the trapped dirt and microorganisms away from the lungs.

-Cigarette smoke stops the cilia beating.

Bronchus

-The trachea divides to from the left bronchus, leading to the left lung - the right bronchus leads to the right lung.

-Similar in structure to the trachea.

-Same supporting rings of cartilage, but they're smaller.

Bronchioles

-Bronchi divide to form many small bronchioles.

-Small bronchioles(diameter of 1mm or less) have no cartilage rings.

-The walls of the bronchioles contain smooth muscle.

-When the smooth muscle contracts = bronchioles constrict.

-When the smooth muscle relaxes = broncioles dilate (open up).

-This changes the amount of air reaching to the lungs.

-Bronchioles are lined up with a thin layer of flattened epithelium = making some gaseous exchange possible.

Alveoli

-The alveoli are tiny air sacs - the main gas exchange surfaces of the body.

-Each alveolus has a diameter of 200-300µm and they consist of thin, flattened epitelial cells along with collagen and elastic fibres.

-These elastic fibres allow the alveoli to stretch as air is drawn in.

-When the elastic fibres return to their resting size the help squeeze air out.

-This process is known as the elastic recoil of the lungs.

Main adaptations of the alveoli for effective gaseous exchange

-Large surface area: If the lungs were simple ballon-like structure, the surface area would not be big enough for the amount of oxygen needed to diffuse into the body.

-Thin layers: only a single epithelial cell thick, so the diffusion distances between the air and blood are very short.

-Good blood supply: the coinstant blood flow brings carbon dioxide and carries of oxygen mantaining a steep concentration gradient for both carbon dioxide and oxygen.

-Good ventilation: breating helps metain a steep diffusion gradient for oxygen and carbon dioxide between the blood and air in the lungs.

-The inner surface of the alveoli is covered in a thin layer of water, salts and lung surfactant.

-The surfuctant makes it possible for the alveoli to remain inflated. 

Inspiration

-Inspiration: taking air in. 

-The diaphrahm contracts, flattening and lowering,

-The external intercostal muscles contract, moving the ribs upwards and outwards.

-The volume of the thorax increases so the pressure of the thorax is reduced.

-Air is drwan through the nasal passages, trachea, bronchi and bronchioles into the lungs.

Expiration

-Expiration: breathing out.

-The muscles of the diaphragm relax so it moves up.

-The external intercostal muscles relax so the ribs move down and inwards.

-The elastic fibres in the alveoli return to normal length .

-The volume in the thorax is decreased. Pressure inside the thorax is greater.

-Air moves out of the lungs until the pressure is equal again.

Components of Lung Volume

-Tidal volume: the volume of air that moves into and out of the lungs with each resting breath.

-Vital capcity: the volume of air that fcan be breathed in when the strongest possible exhalation is followed by the depest possible intake of breath.

-Inspiratory reserve volume: the maximum volume of air you can breath in over and above a normal exhalation.

-Expiratory reserve volume: the extrea amount of air you can force out of your lungs over and above the normal tidal volume.

-Residual volume: the volume of air that is left in your lungs when you have exhaled as hard as possible. 

-Total lung capacity: the sum of the vital capicity and residual volume.

-Ventilation rate = tidal volume x breathing rate (per minute)