Question

MCAT Tutorial: The Respiratory System

Answer 1

\({\bf{Pathway~of~Air:}}\)
enters nose --> passes through nasal cavity --> pharynx --> larynx --> trachea --> bronchi --> bronchioles --> alveoli

\({\bf{Structure:}}\)
- mucociliary tract: located in nose and upper respiratory tract, filters out particles from the air
- alveoli: do not have cilia or mucus; have macrophages and leukocytes to de-contaminate air
- bronchus: name given to the major passageways of the lungs
- bronchioles: end of airways, made of smooth muscles, stimulated to contract by the PNS
- diaphragm: dome-shaped muscle between thorax and abdomen, major muscle involved in breathing
- pharynx: cavity that links to esophagus
- larynx: muscular organ that contains vocal chords and links to the lungs (informally, the voice box)

Answer 2

\({\bf{Ventilation:}}\)
- phenic nerve connects to diaphragm and controls breathing
- basic breathing mechanism: diaphragm contracts upon inhalation --> creates low pressure zone inside lungs --> draws air in
> pulmonary air pressure < atmospheric pressure, air enters alveoli
> inhalation is active, exhalation is passive
> exhalation: thoracic cavity decreases in V, increases P, air exits lungs
- intercostal muscles/scalenes: can aid in breathing if diaphragm is impaired
- medulla oblongata: provides impulse for inspiration

p = 2T/r

p = inflation pressure, T = surface tension, r = radius of alveoli

- transpulmonary pressure: pressure that maintains inflated state
> intrapulmonary pressure (alveoli, positive) minus intrapleural pressure (pleural cavity, negative)

- tidal volume (TV): amount of air that is moved in/out of lungs with a breath
- inspiratory reserve volume (IRV): maximum amount of air that can be inhaled
- expiratory reserve volume (ERV): maximum amount of air that can be exhaled
- residual volume (RV): amount of air left in lungs after exhalation
- vital capacity (VC): total amount of air that can be exchanged
- anatomical dead space: air that cannot be exchanged, takes up passages outside the alveoli. TV - anatomical deadspace = actual amount of air exchanged in alveoli during inhalation

- *** Total Lung Capacity *** = VC + RV
aveolar ventilation rate (AVR) = frequency * (TV - dead space)

Answer 3

\({\bf{Gas~Exchange:}}\) occurs in the alveoli

pathway: alveolar air spaces --> surfactant --> epithelium of alveoli -> basal laminae of the alvaeoli/capillary --> capillary endothelium --> blood plasma --> erythrocytes

Factors affecting gas exchange: pH, partial pressure of oxygen, partial pressure of CO2, pH, concentration of DPG, temperature

Oxygen: bound to hemoglobin (oxyhemoglobin), shows cooperativity (binding/unbinding increases the rate of binding/unbinding for other oxygen molecules)
one gram hemoglobin --> combines with 1.39 mL oxygen

The following graph plots the partial pressure of oxygen against the percentage of oxyhemlglobin saturation, or in other words, the affinity that oxygen has for hemoglobin as a function of pressure

Answer 4

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT