chapter 44

Copyright © 2005 Brooks/Cole — Thomson Learning

Biology, Seventh Edition Solomon • Berg • Martin

Chapter 44

Gas ExchangeGas Exchange


Biology, Seventh Edition CHAPTER 44 Gas Exchange

• Respiration• The exchange of gases between

an organism and its environment• Organismic respiration

–Takes place in animals–O2 taken up and CO2 excreted

• Aerobic cellular respiration–Takes place in mitochondria–O2 is necessary for citric acid cycle



• Simple diffusion • Passive movement of particles

from a region of higher concentration to a region of lower

• Provides gas exchange for small, aquatic organisms such as sponges, hydras, and flatworms



• Comparison of gas exchange in air and water • Air

–Contains a higher concentration of molecular oxygen than water

–Oxygen diffuses more rapidly through air than water

–Less energy needed to move air over gas exchange surface



• Adaptations for gas exchange• Body surface

–Small aquatic animals exchange gases by diffusion, requiring no specialized respiratory structures

–Some invertebrates, including most annelids, and many amphibians exchanges gases across the body surface



Gas exchange across body surface



• Adaptations for gas exchange, cont’d• Trachae

–In insects and some other anthropods, air enters trachae through openings called spiracles

–Trachae branch and extend to all regions of the body



Gas exchange across tracheal tubes



• Adaptations for gas exchange, cont.• Gills

–Moist, thin projections of the body surface found mainly in aquatic animals

–Countercurrent exchange system maximizes O2 into the blood and

CO2 out of the blood



Gas exchange across gills



• Adaptations for gas exchange, cont.• Lungs

–Terrestrial vertebrates have lungs and some means of ventilating them

–Lungs are respiratory structures that develop as ingrowths of body surface or from wall of a body cavity



Gas exchange across lungs



Comparison of vertebrate

lungs



How bird lungs function



• Mammalian respiratory system• Includes the lungs and airways

• Lung occupies pleural cavity and is covered with a pleural membrane

• Breath of air passes in sequence –Nostrils, nasal cavities, pharynx,

larynx, trachea, bronchi, bronchioles, and alveoli



The human respiratory system



Structure of alveoli



• Mechanics of breathing• Diaphragm contracts and chest

cavity expands

• Respiratory centers in the medulla and pons regulate respiration–Stimulated by chemoreceptors

–An increase in hydrogen ions and low oxygen concentration



Mechanics of breathing



• Role of hemoglobin in oxygen transport• Respiratory pigment in vertebrate

blood

• Almost 99% of the O2 in human blood is transported as oxyhemoglobin (HbO2 )



Gas exchange in the lungs and tissues



• Oxygen-carrying capacity• Maximum amount of O2 that can be

transported by hemoglobin

• Oxygen content• Actual amount of O2 bound to

hemoglobin

• Percent oxygen saturation

• Ratio of O2 content to O2 carrying capacity



• Oxygen-hemoglobin dissociation curve• Shows that as O2 concentration

increases, there is progressive increase in hemoglobin that combines with O2

• Bohr effect• Oxyhemoglobin dissociates more

readily as CO2 increases



Oxygen-hemoglobin dissociation curves



Carbon dioxide

transport



• Hyperventilation• Reduces the concentration of CO2 in

the alveolar air and the blood

• Decompression in divers• Rapid decrease in barometric

pressure can cause decompression sickness

• Diving mammals have high concentrations of myoglobin



Deep diver



• Affects of pollution on the respiratory system• Ciliated mucous lining traps inhaled

particles

• Inhaling polluted air results in bronchial constriction–Increased mucous secretion

–Damage to ciliated cells

–Coughing

chapter 44

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