Changes

The air in the alveoli is renewed regularly, thanks to the [[Ventilation - Anatomy & Physiology|ventilation]] process. Gas Exchange in the [[Lungs - Anatomy & Physiology|lungs]]takes place between the blood in the capillary network surrounding the alveoli, and the air in the alveoli itself.  

The air in the alveoli is renewed regularly, thanks to the [[Ventilation - Anatomy & Physiology|ventilation]] process. Gas Exchange in the [[Lungs - Anatomy & Physiology|lungs]]takes place between the blood in the capillary network surrounding the alveoli, and the air in the alveoli itself.  

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.

==Principles of Gaseous Exchange==

==Principles of Gaseous Exchange==

*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 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'''.

*The distance between the air within the alveoli, and the blood is approx 0.7micrometers. This distance is decreased when the animal exhales, as the lung distends. This tiny distance allows extremely fast and efficient diffusion.

*The distance between the air within the alveoli, and the blood is approx 0.7micrometers. This distance is decreased during [[Ventilation - Anatomy & Physiology#Inhalation|inhalation]], as the [[Lungs - Anatomy & Physiology|lung]] distends. This tiny distance allows extremely fast and efficient diffusion.

===Oxygen===

===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 is always lower in the alveoli compared to the external environment due to the oxygen diffusing across the alveolar 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.

*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.

**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.

*The PCO2 in the capillaries is higher than that in the alveoli, thus CO2 diffuses into the alveoli, where it is [[Ventilation - Anatomy & Physiology#Exhalation|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.

*Terrestrial vertebrates also have the ability to undergo gas exhange within their [[Skin - Anatomy & Physiology|skin]], as well as the [[Lungs - Anatomy & Physiology|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==