PGY 300 Respiratory Physiology Review
Interactions of Major Organ System of Human Body ○ Respiration involves ventilation (breathing), gas exchange (between air and capillaries in lung or systemic capillaries and tissues of body), and oxygen utilization (cellular respiration) ○ Respiration as ...
● Interactions of Major Organ System of Human Body
○ Respiration involves ventilation (breathing), gas exchange (between air and capillaries in lung or
systemic capillaries and tissues of body), and oxygen utilization (cellular respiration)
○ Respiration as two separate processes: gas exchange and cellular metabolism
■ Pulmonary respiration: primarily obtain oxygen for use via cells of body and to eliminate
carbon dioxide produced by cells
● Pulmonary gas exchange: ventilation (between atmosphere and alveoli)
○ Diffusion: transport over short distances
○ Convection (bulk flow): transport over long distances
○ Both diffusion and convection driven by pressure differences
■ Cellular respiration: set of metabolic reactions within cell or organism converting nutrient
biochemical energy into adenosine triphosphate (ATP)
○ Four integrated processes for respiration
■ Ventilation (breathing): inspiration and expiration
■ Exchange of O2 and CO2 between lungs and blood
■ Transport of O2 and CO2 in blood
■ Exchange of gases between blood and cells
■ Diseases affecting respiration can occur at any of these processes
● Anaerobic and Aerobic Respirations
○ Anaerobic respiration: glycolytic metabolism or glycolysis
■ No oxygen used; no carbon dioxide produced; but only small amount of ATP produced
○ Aerobic respiration
■ Glycolysis in cytoplasm; citric acid cycle in mitochondria
■ Net gain: 30~38 ATP
■ Energy consumption of skeletal muscle cells increases up to 100-fold when going from rest
to high-intensity exercise
○ Cytoplasm and mitochondria
■ ATP-phosphocreatine system (cytoplasm)
■ Anaerobic ATP generation: glycolysis → oxygen-independent ATP generation (cytoplasm)
■ Aerobic ATP generation: oxidative phosphorylation → oxygen-dependent ATP generation
(mitochondria)
○ Humans surrounded by air with plenty of oxygen (21%)
■ Necessary to have pulmonary and circulatory systems
○ Earth worm: gas diffusion takes place through thin skin
■ O2 diffuses in and CO2 diffuses out
■ Blood vessels absorb the O2 and carry it to body
○ Diffusion
■ Fick’s second law of diffusion: 𝜕C/𝜕t = D (𝜕2C/𝜕x2)
■ Diffusion time (t) ≈ x2/(2D)
● 𝑡 = elapsed time since diffusion began
, ● 𝑥 = mean distance traveled by diffusing solute in one direction along one axis after
elapsed time (t)
● D = diffusion coefficient of a solute in free solution
○ Units of area/time (e.g. cm2/s)
● Major Functions of Respiratory System
○ Exchange of gases between atmosphere and blood
○ Warm air to body temperature (37°C)
○ Adding water vapor until inspired air reaches 100% humidity.
○ Filtering out foreign material such as particulates (dust, pollen, smoke), viruses, or bacteria
○ Vocalization
● Organization of Respiratory System
○ Lungs and thoracic cavity
■ Respiratory system divided into upper and lower regions
● Upper: nasal cavity, pharynx, tongue, vocal cords, larynx, and esophagus
● Lower: trachea, left and right lungs, diaphragm, and left and right bronchi
● Left lung divided into two lobes (superior and inferior with cardiac notch), right
lung divided into three lobes (superior, middle, and inferior)
○ Lobes of lung increase flexibility
○ 60% of total lung volume found in right lung
○ Each lung enclosed in two pleural membranes; esophagus and aorta pass
through thorax between pleural sacs
■ Pleural sacs enclose lungs (double membranes including parietal and
visceral): fluid filled (25~30 ml); provide a slippery surface; holds
lungs tight against thoracic wall due to cohesiveness of water
■ Muscles of thorax, neck, and abdomen create force to move air during breathing
● Inspiration: sternocleido-mastoids, scalenes, external intercostals, and diaphragm
● Expiration: internal intercostals and abdominal muscles
● Between ribs: internal and external intercostals
○ Respiratory tract = conducting zone + respiratory zone
■ Bronchi and alveoli
● Branching of airways creates about 80 million bronchioles
● Each alveoli cluster surrounded by elastic fibers and network of capillaries
● Deoxygenated blood enters via pulmonary artery
● 80-90% of alveolar surface covered by capillaries
● Alveoli as site of gas exchange: blood supplies to air sac; alveoli and capillary
network allowing gas exchange with red blood cells
○ Type I alveolar cell for gas exchange
○ Endothelial cell of capillary
○ Type II alveolar cell synthesizes surfactant
○ Limited interstitial fluid
○ Alveolar macrophage ingests foreign material
● Conducting zone: non-collapsible airway; cartilaginous rings; hyaline
cartilage; no gas exchange
○ Including larynx, trachea (branches into two primary bronchi), cartilage
ring, left and right primary bronchus (divides 22 more times terminating in
cluster of alveoli), and secondary bronchus
● Respiratory zone: collapsible airway; gas exchange
○ Including bronchiole (terminal and respiratory) and alveoli
○ Chronic obstructive pulmonary disease (COPD)
■ Common chronic disease with increasing prevalence (5% of global population)
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