 Oxygen is essential for the existence of animals  All oxygen in the air comes from the process of photosynthesis  Air consists of:  Nitrogen-78.09%  Oxygen-20.95%  Inert gasses-0.93 %  Carbon dioxide-0.03%

 Purpose: to obtain oxygen and remove carbon dioxide from the body  Gases are exchanged across membranes, through water by diffusion(surfaces must be wet)  Gases are then distributed by the circulatory system

 Diffusion of oxygen is slow and only diffuse over 0.5mm.  Special organs had to be developed to have larger organisms  Protists can use simple diffusion because of their size

 Others use water currents to carry oxygen across membranes  Need large surface area  Others developed internal organs to provide contact between the outside and internal circulation

 External gills V. Internal gills  External gills are outside of the body and the many branched gills are resistant to water.  Internal are found in an internal body cavity that allow water to flow from the mouth through the cavity and out another opening(creates a one way current)

 Gills would not work for terrestrial animals. Why? Amphibians –have primitive lung but can also diffuse Oxygen through skin (ectothermic-Oxygen needs low) Reptiles-more active (need more Oxygen), can't obtain oxygen through skin therefore have more advanced lung with greater surface area therefore have more lung with greater surface area

 Mammals have higher activity and higher body temperature so Oxygen needs are greater

 Air is breathed in by the nostrils  Nostrils are lined with hair and mucous › These are used to trap invaders › Air then passes nasal passages into the trachea. › Trachea branches in to two bronchi.(one for each lung) › These bronchi continue branching into smaller and smaller tubes. › The smallest are bronchioles › Bronchioles end in clusters of sacs called alveoli › All gas exchange takes place in the thin walled alveoli › Total surface are of 6080 square meters

 Rib intercostal muscles contract and expand the rib cage  Diaphragm contracts and increases the volume of the thoracic cavity  More volume means less pressure and air rushes in

 Diaphragm and intercostals relax and decreases the volume of the thoracic cavity  This action increases the pressure in the cavity  This causes air to rush out of the lungs

 Tidal Volume  Amount of air in and out in a single breath.  Usually around 500ml.(can increase to 3000 with exercise)  Inspiratory reserve volume(IRV) excess air when breathing in maximumly  Expiratory reserve volume(ERV) amount of air when breathing out maximumly.

 Vital capacity (VC)total lung volume when breathing in and out maximumly.  VC=IRV +TV +ERV  Not all air is breathed out during maximum expiration this residual volume(RV)  Total lung capacity: › Y= VC + RV

 Respiratory rate = number of breaths per unit time.  Such as Breaths/minute.  respiratory rate and tidal volume =lung ventilization  TV X respiratory rate per minute  Normal is 5L per minute but can be up to 1300L per minute during exercise

 Controlled in brain by the breathing control center(BRC)  Automatic process › BRC sends impulses to the intercostal muscles of the rib cage and the diaphragm and we inhale › When the signal stops we exhale. › When breathing stops Carbon Dioxide levels rise and trigger cells in the aorta and carotid arteries to signal the BRC to breathe. › In hyperventilation so much CO2 is removed that the cells signal BRC to stop breathing

 Allergens-cause release of histamines to constrict airways  Bronchitis-inflammation of the bronchi- excess mucous and retards ciliary action  Emphysema-walls of alveoli become less flexible and can be damages. This reduces surface area for gas exchange.  Caused by chronic bronchitis, infection, genetics, and environmental conditions(smoking)

 Paralyzes cilia  Stimulates mucous production  Coughing helps, but still leads to bronchitis and other lung illnesses  Smoke contains substances that convert to carcinogens in the body  80% of lung cancer is caused by smoking