Gas Exchange

Chapter 22

The Air Up There• Air is a fixed ratio of partial

pressures (Px)

• Air thins with increasing altitude– Gas in same ratio, but less of– 3000 m 1/3 less O2

• Sherpas, athletic training, and blood doping

• Mountain sickness

Revisiting Respiration

Gas Exchange

• Organismal level• O2 in CO2 out via

diffusion

• Cellular level• Use O2 to produce

CO2 and ATP

Cellular Respiration

Breathing

Application

Exchange

Respiratory Surfaces

• Thin– Diffusion distance– Speed

• Moist– Gases dissolved in

solution

• Large– SA to volume ratio– Energy demands

Respiratory Mediums

Water• Pro

– Direct contact of respiratory surface to medium

• Con– Less O2

• warm and salty even less

– O2 diffusion slower

– More energy to ventilate• Larger structures• Water supports weight

Air• Pro

– High concentration of O2

– Less dense– O2 diffusion faster

• Con– Desiccation of respiratory

surface• Small openings externally• Indirect contact of

respiratory surface to medium

Gill Systems• Aquatic organisms

• Convoluted extensions of body surface (pink)

• Ventilation varies between organisms– Move respiratory medium

across respiratory surfaces

• Inefficient on land– Desiccation– Tissue Mass

• Mollusks, annelids, arthropods, echinoderms, fish, and amphibians

Countercurrent Exchange• Exchange between 2 oppositely flowing

currents• Maximizes O2 diffusion out of H2O– Concentration gradient maintained entire length– Compare to concurrent

‘Skin Breathers’

• Earthworms and some amphibians

• Skin is respiratory surface– Circulatory system to

distribute (hemoglobin assists)

– Lower invertebrates without

• Moist environments

Tracheal System

• Insects• Internal branched tube system– Connect all cells to environment– Prevents desiccation

• Direct exchange– Open circulatory system

• Hemolymph = nutrients only

• Body movements assist

Lungs

• Branched internal sacs– Moist epithelium

• Pigmented, closed circulatory system– Nutrient and gas transport

• Most terrestrial vertebrates – Elaboration with movement to land– Variations between classes

Lung Adaptation• Amphibians– O2 via positive pressure into small

sacs– Skin also for exchange

• Birds– 1 way flow increases efficiency– 2 cycles to complete

• Mammals– Negative pressure– Incomplete removal– Myoglobin content varies

Mammalian Respiratory System

• Upper respiratory system– Nasal cavity

• Warms air• Smells

– Pharynx– Larynx

• Vocal cords tensed to create sound• Lower respiratory system

– Trachea• Cartilage rings

– Bronchi (2)– Bronchioles– Alveoli

• Diffusion with capillaries through interstial fluid

Respiratory CycleInhale

• Rib muscles (up) and diaphragm (down) contract

• Chest cavity increases• Lowers air pressure in alveoli

Exhale• Rib muscles (down) and

diaphragm (up) relax• Chest cavity decreases• Increases air pressure in alveoli

Respiratory Disruptions• Smoking

– Inhibit cilia movement causes ‘smoker’s cough’• Thicken bronchioles and reduce elasticity• Alveoli rupture

– Stopping allows cilia and alveoli damage to reverse• Premature birth (37 weeks or less)

– Surfactant production incomplete• Keeps alveoli from collapsing

– Each breath requires large effort• Emphysema

– Bronchi swell, tearing alveoli– Reduced SA for gas exchange

• Pneumonia– Fluid in alveoli

• Bronchitis inflames of bronchioles

• Blood circulates to all cells– Hemoglobin binds/carries

• Protein bound to a metal• Carry 4 O

2 molecules, some CO

2 too

• PO2 and PCO2

vary within the circulatory system– Blue and red vessels – Lungs: high O2, low CO2

– Body tissues: low O2, high CO2

• Pressure gradient facilitates gas exchange in tissue capillaries (purple)

Respiratory Gas Transport

Control of Human Breathing• Most is involuntary

– Control centers in brain• Medulla: inhalation signaling • Pons: smoothes out rhythm and depth

• Driven by [CO2] in blood– Reactions

• CO2 + H2O H2CO3 (carbonic acid)• H2CO3 H+ + HCO3

– CO2 levels increase• pH in blood/CSF lowered• Respiratory centers signaled

• Carotid arteries and aorta monitor O2 also – Severe deficit, i.e high altitude– Increase rate and depth

Human Fetus

• Amniotic sac in uterus– Lungs are fluid filled

• Placental role– Blood exchange with mother– Fetal hemoglobin

• Birth stops gas exchange– pH drop, why?– First breath