Changes

All of the blood from the [[Structure of the Heart - Anatomy & Physiology#Right Ventricle|Right Ventricle]] flows through the capillary network which surrounds the alveoli. Another set of pulmonary capillaries recieve small amounts of arterial blood from the [[Structure of the Heart - Anatomy & Physiology#Left Ventricle|Left Ventricle]], via the Bronchial Arteries. These capillaries provide oxygen and nutrients to the [[Lungs - Anatomy & Physiology|lung] tissue.

All of the blood from the [[Structure of the Heart - Anatomy & Physiology#Right Ventricle|Right Ventricle]] flows through the capillary network which surrounds the alveoli. Another set of pulmonary capillaries recieve small amounts of arterial blood from the [[Structure of the Heart - Anatomy & Physiology#Left Ventricle|Left Ventricle]], via the Bronchial Arteries. These capillaries provide oxygen and nutrients to the [[Lungs - Anatomy & Physiology|lung] tissue.

==Gas Exchange==

==Principles of Gaseous Exchange==

*Gas exchange occurs between the air within the alveoli, and the pulmonary capillaries occurs by ''diffusion''. The oxygen must first dissolve before passing through the [[Respiratory Epithelium - Anatomy & Physiology|respiratory epithelium]].

*Gas exchange between the air within the alveoli and the pulmonary capillaries occurs by ''diffusion''. The oxygen must first dissolve before passing through the [[Respiratory Epithelium - Anatomy & Physiology|respiratory epithelium]].

*Gas moves from a region of high partial pressure to a region of low partial pressure, down a '''Partial Pressure Gradient'''.

*Gas moves from a region of high partial pressure to a region of low partial pressure, down a '''Partial Pressure Gradient'''.

==Oxygen Exchange==

===Oxygen===

*The PO2 is always lower in the alveoli due to the oxygen diffusing across the wall continuously, and the CO2 entering the alveoli which has the effect of 'diluting' the oxygen.

*The PO2 is always lower in the alveoli compared to the external environment due to the oxygen diffusing across the wall continuously, and the CO2 entering the alveoli which has the effect of 'diluting' the oxygen.

*The PO2 in the alveoli is still higher than that in the capillaries, so oxygen diffuses into the blood.

*Once through the alveolar and capillary walls, the Oxygen combines with '''Haemoglobin''' to form '''Oxyhaemoglobin''' and is transported within the bloodstream.

*Once through the alveolar and capillary walls, the Oxygen combines with '''Haemoglobin''' to form '''Oxyhaemoglobin''' and is transported within the bloodstream.

==Carbon Dioxide Exchange==

===Carbon Dioxide===

*Carbon Dioxide enters the red blood cell as a waste product from cells. In the red blood cell it reacts with water to form '''Carbonic Acid''', CA.

*Carbon Dioxide enters the red blood cell as a waste product from cells. In the red blood cell it reacts with water to form '''Carbonic Acid''', CA.

**Approx 5% of the total body CO2 is carried as carboxyhaemoglobin on proteins.

**Approx 5% of the total body CO2 is carried as carboxyhaemoglobin on proteins.

**Approx 90% is carried as bicarbonate ions in the plasma.

**Approx 90% is carried as bicarbonate ions in the plasma.

*

*The PCO2 in the capillaries is higher than that in the alveoli, thus CO2 diffuses into the alveoli, where it is exhaled.

==Species Differences==

==Species Differences==

*

*Terrestrial vertebrates also have the ability to undergo gas exhange within their skin, as well as the lungs. This may account to 2% of the total gas exchange occurring within the body. This is important during it's [[Thermoregulation - Anatomy & Physiology|thermoregulatary]] functions, which involves reduced cutaneous circulation when cold temperatures are experienced.

==Links==

==Links==