Respiratory Centre Key Concepts

The Path of Air in the Body

• air enters through the nose or mouth, passes into the pharynx and then through the larynx

• it descends into the trachea which branches into the right and left primary bronchi

• the bronchi continue to branch into smaller secondary and tertiary bronchi then into bronchioles

• finally into tiny air sacs called alveoli where gas exchange occurs

O2 transport to a Fingertip

1. external respiration: oxygen diffuses from the alveoli in the lungs into the blood within the pulmonary capillaries

2. transport: oxygen binds to hemoglobin in RBC an is pumped by the heart through the aorta and systemic arteries

3. delivery: the blood reaches the digital arteries of a finger and enters the systemic capillaries

4. internal respiration: oxygen dissociates from hemoglobin and diffuses out of the capillary, through the interstitial fluid, and into the fingertip cell to be used in the mitochondria for cellular respiration

Pulmonary Ventilation

• the mechanical process of breathing

• works based on Boyles law which states that pressure and volume are inversely related

• inspiration and expiration

Inspiration

the diaphragm and external intercostal muscles contract, increasing thoracic cavity volume

this drops intrapulmonary pressure below atmospheric pressure, sucking air into the lungs

Expiration

muscles relax and the elastic recoil of the lungs decreases volume

this increases intrapulmonary pressure above atmospheric pressure forcing air out

Inspiratory Capacity (IC)

• the maximum amount of air that can be inhaled after a normal tidal expiration

• IC = TV + IRV

Functional Residual Capacity (FRC)

• the volume of air remaining in the lungs after a normal tidal expiration

• FRC = ERV + RV

Residual Volume (RV)

• the air that remains in the lungs after the most forceful expiration

• keeps alveoli open

Vital Capacity (VC)

• the maximum amount of air a person can expel from the lungs after maximum inhalation

• VC = TV + IRV + ERV

Total Lung Capacity (TLC)

• total volume of air the lungs can hold

• TLC = VC + RV

External Respiration

• occurs in the lungs

• oxygen moves from alveoli to blood and carbon dioxide moves from blood to alveoli across the respiratory membrane

Internal Respiration

• occurs in tissues

• oxygen moves from blood to cells and carbon dioxide from cells to blood

Partial Pressure Gradients

• both processes driven by diffusion

• gases move from higher to lower pressure areas