THE EXCHANGE OF GASES BETWEEN AN ORGANISM AND ITS ENVIRONMENT

Respiration

2 types:

Organismic Oxygen taken up from environment and delivered to

individual cells Simple diffusion Respiratory systems

Aerobic cellular respiration Cells use O2 as final electron acceptor to produce

energy CO2 created as waste

Gas Exchange

Requires MOIST MEMBRANES

Air Higher concentration of O2

Less viscous than water O2 diffuses quickly

Water Less threat of dessication More energy needed

Respiratory Surfaces

Body Surface High SA : Volume Low metabolic rate

Tracheal Tubes Air enters through

spiracles Branching tubules Fluid-filled tracheoles

= gas exchange

Gills Folded or split into

filaments Capillaries deliver

blood to filaments Countercurrent exchan

ge

Lungs Terrestrial Ingrowth of body

cavity

Mammalian Respiratory System

Nostrils/Nasal Cavity Filter Moisture Warmth

Pharynx/Larynx Cartilage give support Epiglottis closes off larynx during swallowing to

prevent choking

Trachea

Divides into 2 bronchi – lead to each lung Further divides into bronchioles Ends at alveoli

Surfactants

Ventilation: The Mechanics of Breathing

Inhalation/Inspiration Thoracic cavity is closed Diaphragm contracts & moves downward Ribs may also move upward Air pressure in lungs falls Air from outside moves to area of lower pressure

Ventilation, cont.

Exhalation/Expiration Diaphragm relaxes Pressure in cavity increases Air sacs deflate

http://www.smm.org/heart/lungs/breathing.htmhttp://sprojects.mmi.mcgill.ca/resp/

inspiration.htm

Total air in and out during normal/resting breath = tidal volume

Maximum amount exhaled after maximum filling = vital capacity

Gas Exchange at Alveoli

Made possible by thin epithelium Alveoli Capillaries

Dalton’s Law of Partial Pressure PO2 = 160 mm Hg PCO2 = 0.3 mm Hg

Flick’s law of diffusion

http://www.wisc-online.com/objects/index_tj.asp?objID=AP2404

Gas exchange at tissues

PO2 in arteries ~ 100 mm Hg

PO2 in tissues = 0 – 40 mm Hg

PO2 in veins ~ 40 mm Hg

Respiratory Pigments

Combine reversibly with O2

Examples: Hemocyanin Hemoglobin Myoglobin

Increases amount of O2 blood can carry from 0.25 mL/100mL to 20 ml/100 mL

% O2 saturation Affected by pH, temperature, CO2 concentration

CO2 Transport

Transported in blood in 3 forms: Dissolved in plasma (10%)

Hb in RBCs (30%) Causes release of O2

HCO3-

Combination of CO2 & H2O forms carbonic acid In cells, catalyzed by carbonic anhydrase Dissociates into H+ & HCO3

-

Hb buffers H+ HCO3

- diffuses out of cell into plasma At lung, reaction reverses

Regulation of Breathing

Medulla regulates basic rhythm

Pons – controls inhalation/exhalation transition

Chemoreceptors in medulla/aorta/carotid arteries detect changes in CO2 concentration Increased CO2 lowers blood pH

Respiratory rate increases to get rid of excess CO2