Ch 17 LO: Mech of Breathing

What are the four major functions of the respiratory system.

1. Exchange of gases between the atmosphere and blood

• Obtain O2 and eliminate CO2

2. Homeostatic regulation of blood pH

• Retain or excrete CO2

3. Protection from inhaled pathogens and irritating substances

• Epithelium traps and destroys substances

4. Vocalization

• Air movement across vocal cords provides communication

what is the anatomy of the respiratory system and explain the function of each structure?

Conducting System – passages that lead from external

environment to surface of lungs

• Upper respiratory tract – Nose, sinuses, pharynx, larynx

• Lower respiratory tract – Trachea, bronchi, bronchioles

• No gas exchange occurs in the above structures

• Exchange Surfaces– tissues associated pulmonary capillaries

that are specialized for gas exchange between atmosphere and

blood

• Respiratory bronchioles – the terminal segments of airways

that branch into alveoli

• Alveoli – small sacs lined with simple squamous epithelium

• Bones and muscles of the thorax and abdominal cavity

• Inspiratory muscles - sternocleidomastoid, scalenes, external

intercostals, and diaphragm

• Expiratory muscles - internal intercostals and abdominal

muscles

What are the functions of the conducting system?

Warms air

• Humidifies air by adding saline and water vapor to

the airway lumen

• Reduces friction between air and epithelium

• Keeps epithelial cells hydrated

• Traps and clears foreign particles

• Goblet cells – secrete mucins/mucous

what is the epithelial mechanism for saline secretion

What 2 cell types make up alveoli

Type 1 alveolar cells (95% of alveolar cells) – thin, large

cells and promote diffusion

• Simple squamous epithelial cells

Type 2 alveolar cells (5% of alveolar cells) – secrete

pulmonary surfactant and increase ‘compliance’ of alveoli

• Compliance – an alveoli’s ability to stretch and expand

what is the mathematical the relationship between atmospheric pressure, water vapor pressure, and the partial pressures of individual gases?

Dalton’s law

What is the relationship between volume and pressure?

P1​V1 ​= P2​V2​

• Pressure and volume are inversely related

• In lungs:

  • ↑ Volume → ↓ Pressure → air flows in

  • ↓ Volume → ↑ Pressure → air flows out

What are the lung volumes?

Tidal Volume (VT) – volume ventilated during quiet

breathing

• Expiratory Reserve Volume (ERV) – max volume

possible to expire after a normal tidal expiration

• Inspiratory Reserve Volume (IRV) – max volume

possible to inspire after a normal tidal inspiration

• Residual Volume (RV) – The volume of air that remains in

lungs after maximal expiration

What are the lung capacities?

sum of 2 or more lung volumes

Total Lung Capacity = IRV + VT + ERV + RV

Vital Capacity = IRV + VT + ERV

Inspiratory Capacity = VT + IRV

Functional Residual Capacity = ERV + RV

How do pressures and lung volumes change during normal breathing, and how that affects air flow in the respiratory system?

Inspiration

• Thoracic volume ↑

• Alveolar pressure ↓ (below atmospheric)

• Air flows into lungs

Expiration

• Thoracic volume ↓

• Alveolar pressure ↑

• Air flows out

What is the relationship between the atmospheric and intrapleural pressures during a pneumothorax?

• Normally:

  • Intrapleural pressure is negative

  • Keeps lungs inflated

• In pneumothorax:

  • Air enters pleural space

  • Pressure = atmospheric

  • Lung collapses

how does pressure change during breathing cycle

• Alveolar pressure

  • Slightly negative during inspiration

  • Slightly positive during expiration

• Intrapleural pressure

  • Always negative

  • Becomes more negative during inspiration

what is the difference between compliance an elastance in respiratory physiology?

Compliance (stretchability)

• High compliance → easy to expand

• Example: Emphysema

  • Lungs stretch easily but don’t recoil

Elastance (recoil ability)

• Opposite of compliance

• High elastance → strong recoil

what is the he role of surface tension and surfactants in respiratory physiology?

• Alveoli contain fluid → creates surface tension

• This tends to collapse alveoli

Surfactant

• Produced by Type II cells

• Reduces surface tension

• Prevents collapse and improves compliance

law of laplace: P=2T/r

What factors affect airway resistance?

Depends mainly on:

• Airway diameter

Control mechanisms:

• Parasympathetic (ACh) → bronchoconstriction

• Epinephrine (β₂ receptors) → bronchodilation

• Local factors:

  • High CO₂ → dilation

  • Histamine → constriction

What is the difference between total pulmonary ventilation and alveolar ventilation.

Total pulmonary ventilation = Ventilation rate x VT

• “Normal” rates for each:

• Ventilation rate: 12-20 breaths per minute

• Tidal volume: 500 mL

• 12 br/min x 500 mL/br = 6000 mL/min or 6 L/min

Total alveolar ventilation = Ventilation rate x (VT – Vdead space)

• Not all 6L actually reaches the alveoli

• Anatomical dead space: 150 mL

why does gas composition in the alveoli remain relatively constant during normal breathing and how does it change with hyper- and hypoventilation?

Even though we breathe intermittently:

• Large residual volume prevents big swings

• Continuous gas exchange with blood stabilizes levels

Changes:

• Hyperventilation

  • ↓ CO₂

  • ↑ pH (alkalosis)

• Hypoventilation

  • ↑ CO₂

  • ↓ pH (acidosis)

what is the local control mechanisms by which ventilation and alveolar blood flow are matched?

Ventilation-Perfusion Matching

• The body tries to match air flow to blood flow in the alveoli

Local control:

• Low O₂ in alveoli
  → vasoconstriction of nearby vessels
  → redirects blood to better-ventilated areas

• Opposite of systemic circulation!

local control of arterioles and bronchioles

What happens when CFTR is blocked?

Cystic Fibrosis Pathology:

• no Cl transport → no Na+ attracted to by electrochemical gradient → no water/saline secretion → thick undiluted mucous unable to be cleared by mucociliary escalator