l33-l35: respiratory system

external respiration

the exchange of oxygen and CO₂ between blood, lung tissue, and the external environment

• involves diffusion of gases between blood and air across the alveolar and capillary walls

internal respiration

the exchange of oxygen and CO₂ between blood and other body tissues

• involves diffusion of gases between blood and ISF across capillary walls

pulmonary ventilation

physically moves air into and out of the lungs

airways

allow air to reach gas exchange surfaces in the lungs

upper respiratory system

• nose

• nasal cavity

• paranasal sinuses

• pharynx

lower respiratory system

• larynx

• trachea

• bronchus

• bronchioles

• respiratory bronchioles

• alveoli

lower conducting portions

larynx → trachea → bronchi (3 types) → bronchioles (3 types)

• diameter consistently decreases

lower respiratory portions

respiratory bronchioles and alveolar sacs

alveolus

capillary-wrapped gas exchange structure

respiratory mucosa

mucous membrane that covers most of the respiratory tract

mucus

helps to condition (moisten) air, as well as filters air by trapping particles and pathogens

cilia

make beating movements which constantly sweep secreted mucus toward the pharynx

mobile macrophages

take over the protective functions performed by mucus in the terminal bronchioles

type I alveolar cells

line the inner surface of the alveoli

type II alveolar cells

secrete surfactant, a detergent which reduces the surface tension at the air-water interface

pleura

double-layered membrane that adheres each lung to the wall of the thoracic cage

• lungs are stuck to the thoracic wall by the surface tension of fluid within the pleural cavity

pressure gradients

created by changes in the size of the pleural cavity which drive airflow into and out of the lungs

inhalation

movements of inspiratory muscles expand the lungs, creating a negative pressure gradient

exhalation

when the muscles relax, the pressure gradient and air flow reverse

resting tidal volume

the ~500 mL of air moved into and then out of the lungs by a single quiet breath

quiet breathing

only primary inspiratory muscles are active and exhalation is passive

active breathing

accessory inspiratory and expiratory muscles are recruited to amplify movements

phrenic motor neurons

send their axons in the phrenic nerve and innervate the myofibers of the diaphragm

respiratory centers in the medulla

generate the rate and pattern of breathing movements

spirometry

measures the volume and speed of air moving into or out of the respiratory system

• involves periods of quiet breathing and a forceful inhalation and exhalation

inspiratory capacity

the maximum volume of air that can be breathed into the lungs

• IRV = IC - V_T

vital capacity

the amount of air that can be breathed out in a maximal exhalation

• VC = ERV + V_T + IRV

residual volume

air left in lungs even after maximal exhalation

• TLC = RV + VC

functional residual capacity

air left in lungs at the end of a normal breathing cycle

• TLC = FRC + IC

sigh

reflexive breathing pattern which creates a slow, deep breath that helps reinflate pulmonary lobules

protective reflexes

involve forceful exhalation of air against a partial constriction in the glottis

sneezing

purely involuntary reflex triggered by the presence of irritants or particles in the nasal cavity or nasopharynx

coughing

reflexively triggered by the presence of irritants or particles in the lower respiratory tract

respiratory minute volume (V_E)

measures the amount of air that is moved into the respiratory system per minute

• V_E mL/min = f breath/min × V_T mL/breath

anatomical dead space

portion of inhaled and exhaled air that always remains in the conducting regions of the respiratory tract

• V_D = V_T × 0.3 = 150 mL

alveolar ventilation

measure of the amount of air that actually reaches the alveoli per minute

• V_A = f × (V_T - V_D)

compliance

measurement of how much work it takes to expland/inflate the lungs at a given pressure

restrictive lung diseases

diseases of reduced compliance

• more work to achieve the same volume of air inspired

• detected by reduced FVC (or TLC)

resistance

measurement of how much force is needed to make air flow through conducting pathways

obstructive lung diseases

diseases of increased resistance

• more work to get air to and from the lungs in a set time

• detected by slightly increased residual capacities

emphysema

result of prolonged inflammation and/or exposure to toxic particulates in air, which triggers destruction of lung tissue, especially elastic fibers in alveoli walls

• alveoli walls deteriorate, leading to merging of adjacent alveoli, and losing alveolar surface area

• associated with increased compliance for inflation, but it reduces the elastic recoil of the lung

• more work to achieve the same volume of air exhaled

• reduction in gas exchange surfaces leads to an increase in respiration rate

partial pressure

pressure exerted by a single gas within a mixture of gases

Dalton’s Law

in any gas or gas mixture, each individual molecule contributes the same amount to the overall pressure, no matter its chemical composition

Henry’s Law

for a given temperature, the concentration of a gas in a solution is directly proportional to the partial pressure of that gas in the adjoining air

Fick’s Law

diffusion of a particular gas at a given temperature is enhanced by a large surface area and a steep partial pressure gradient

respiratory reflexes

can increase the rate of gas exchange at the alveoli by refreshing the pressure gradients or increasing functional alveolar surface area

hemoglobin saturation curves

measure the percentage of hem units which are bound to oxygen at different PO₂

tissues are aerobically active (↓PO₂)

hemoglobin automatically offloads more oxygen

tissues become acidic (↓pH)

hemoglobin saturation curves shift, favoring oxygen offload

tissues increase in temperature

hemoglobin saturation curves shift, favoring oxygen offload