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 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

Decompression in divers 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