Common Requirements of living things - ANIMALS – Chapter 5 Pt C: Exchanging Gases

Exchanging gases with the environment

• All organisms must exchange gases with their environment, usually oxygen and /or carbon dioxide.

• Some unicellular and small multicellular organisms and plants can easily and directly exchange gases with their environment.

• Larger animals have a many more cells and a higher metabolic rate . They require highly developed gas exchange systems.

Respiratory Surfaces

Characteristics of Efficient Respiratory Surfaces• Passive diffusion of gases from high concentration to lower

concentration• Large surface area, • Thin • Moist• Vascularised

Respiratory Surfaces for Gaseous exchange

• Water ventilation- Gills– Supported by water and skeletal rod.– In axolotles water passes over the

external gill surface due to water currents and physical movement.

– In fish water flows through the mouth of the fish and then is pushed over the Internal gills when the mouth is closed.

– Fish gills have counter current flow. Water goes one way and the blood the other way.

– Fish extract 80-90% of oxygen from water, mammals only extract 25% from air, (however air has a lot more oxygen than water).

When the fish’s mouth is open, the operculum closes and water is drawn into the fish’s mouth. Conversely, when the fish closes its mouth, the operculum opens and fresh water is then allowed to flow across the gills.

Ventilation of Fish Gills

• Breathing air requires less energy than breathing water.

• There is much more oxygen in air than in water. (21% )

• Disadvantages of breathing air are water loss, because water evaporates continuously.

• Enclosing the respiratory surface in the body protect them from physical damage and reduces water loss.

Ventilation of Lungs

Grasshopper Respiratory system

• Tracheal system: involves the diffusion of oxygen directly from the atmosphere into the air-filled tubes.

• diffusion through air is more efficient than the diffusion through water (300,000 times more) or tissues (1,000,000 times more).

Ventilation of Human Lungs

Ventilation- RespirationHuman ventilation narrated animation

Tidal Volume:• The volume of air moved in and out of your lungs in each breath.• When we breath in and out we never fully empty our lungs there is always

some stale air left over in the lungs, in our next breath we take this stale air back in.

• This stale air and a fluid called surfactant which covers the alveolar surface, protect the alveoli from collapsing in on themselves.

Lung Volumes

Pulmonary Circulation

Gas Exchange in Mammals

Gas exchange in mammals• Air is drawn in through the pharynx • Air then passes into the trachea,

paired bronchi and branching bronchioles.

• Both the trachea and the bronchi have ciliated cells on their surface and they secrete mucus, which protects the lungs against dust and bacteria.

• Finally air enters the air sacs called alveoli, it is here that gaseous exchange occurs

• The alveoli is made up of only 1 layer of cells which is covered in blood capillaries.

http://www.nlm.nih.gov/medlineplus/ency/anatomyvideos/000059.htm

Gas exchange in lungs and tissues animated overview

Transporting Gases• Oxygen diffuses into the capillaries

surrounding the alveoli & carbon dioxide diffuses from the capillaries into the alveoli.

• The blood transports gases around the body.• Gases are transported either attached to the

red pigment haemoglobin or dissolved in blood plasma

• Each iron containing molecule of haemoglobin can attach to 4 oxygen molecules.

gaseous exchange

Carbon Dioxide out• When cellular respiration occurs, carbon

dioxide is produced as a waste product this must be released if not to cause changes in pH of the blood and tissue fluids.

Carbon dioxide is transported in 3 ways:1. Dissolved carbon dioxide

Carbon dioxide is much more soluble in blood than oxygen and dissolves in the plasma. Approx 5 %

2. Bound to haemoglobin & plasma proteinCarbon dioxide combines reversibly with haemoglobin to form carbaminohaemoglobin. Carbon dioxide binds to amino groups on the polypeptide chains of haemoglobin and plasma proteins. Approx 10 %

3. Bicarbonate ionsApprox 85% of carbon dioxide is transported as bicarbonate ions (HCO3-) and hydrogen ions (H+).

Composition of Inspired v Expired Air

Composition of atmospheric air and expired air in a typical subject.Note that only a fraction of the oxygen inhaled is taken up by the lungs.Component Atmospheric Air (%) Expired Air (%)

N2 (plus inert gases) 78.62 74.9O2 20.85 15.3

CO2 0.03 3.6H2O 0.5 6.2

100.0% 100.0%