Respiratory System - Anatomy and Physiology

Function of respiratory system

Supplies O2 to the blood while removing CO2

Parts of nose

External nares (nostrils)

Nasal cavities

Conchae

Nasal septum

Functions of parts of nose

• Cleans: mucus and cilia

• Warms: superficial veins

• Humidifies incoming air: mucus

• Separates nasal and oral cavities: hard and soft palate

Pharynx

common passage for air and food

Larynx

voicebox

Trachea

air tubes

Bronchi + bronchioles

• Bronchi: main airways

• Bronchioles: smallest airways leading to alveoli

Alveoli

• Simple squamous epithelium

• Macrophages engulf debris

• Some cuboidal cells secrete surfactant (fatty molecule that lowers surface tension of the water film lining each alveolus so that they don’t collapse between breaths)

• Produced at 28-30 weeks if born before them, they have IRDS

Lungs

• Left lung has 2 lobes

• Right lung has 3 lobes

Pleural membranes

• Pulmonary (visceral) pleura: membrane that covers the lungs

• Parietal pleura: membrane that lines the thoracic cavity

• Pleural fluid in between: cling together, help keep lungs inflated

4 events of respiration

1. Pulmonary ventilation

2. External respiration

3. Internal respiration

4. Gas transport

Pulmonary ventilation

• Breathing: air moving in and out of lung

• Boyle’s law: pressure of gas inversely proportional to volume of container

• Inhale: diaphragm contracts and moves downward, external intercostals contract and move ribcage up and out → increasing volume, decreasing pressure, air flows in

• Exhale: expiration is largely passive but it is possible to engage internal intercostals and abdominal muscles to forcibly decrease the volume of the thoracic cavity → increases air pressure, thus forcing air out

External respiration

• Gas exchange between pulmonary blood and alveoli

• Gases will move down their partial pressure gradient via diffusion across membranes (alveoli, capillaries, systemic tissues)

• Dalton’s law: Sum of partial pressures = total pressure

• Driven by partial pressure gradients

Internal respiration

• Gas exchange between systemic capillaries and body cells/tissues

• Gradient promotes diffusion of oxygen into tissues and carbon dioxide into the capillaries

Gas transport

• Oxygen and carbon dioxide

Gas transport (oxygen)

• 98.5% of O₂ in blood travels attached to hemoglobin as a molecule called oxyhemoglobin (HbO₂)

• O₂ attached to hemoglobin

• 250 million Hb molecules in each red blood cell

• Each Hb binds 4 O₂ molecules

• Hb’s affinity for O₂ increases as more oxygen binds to it

• O₂ binds reversibly: Hb + O₂ → HbO₂

• 1.5% of oxygen in blood is dissolved directly into blood plasma

Gas transport (Carbon dioxide)

• 7% of carbon dioxide in blood is dissolved directly in the blood plasma

• 23% of carbon dioxide binds to Hb (at a different site than O₂) forming a molecule called carbaminohemoglobin (Hb + CO₂ → HbCO₂)

• 70% of CO₂ in blood travels as part of bicarbonate ion (HCO₃^-)

• HCO₃^- and H⁺ are formed inside the RBC but diffuse out and travel in the plasma where they play a key role in maintaining blood pH

Tidal volume

• Amount of gas inspired or expired with each breath

• 500mL

Inspiratory reserve volume

• Maximum amount of additional air that can be inhaled at the end of a normal inspiration

• 3100mL

Expiratory reserve volume

• Maximum amount of additional air that can be expired at end of normal expiration

• 1200mL

Residual volume

• Volume of air left in lungs at end of maximum expiration, can’t be measured w/ spirometer

• 1200mL

Dead space volume

• Volume of air in airways (trachea, bronchi, etc.) not involved in gas exchange

Forced expired volume

• Volume that can be forcibly exhaled in 1 sec while measuring FVC

Total lung capacity

• Volume of air in lungs at the end of max inhalation

• 6000mL

• TLC = RV + IRV + V_T + ERV

Forced vital capacity

• Maximum amount of air that can be forcibly expelled after a max inspiration

• 4800mL

• FVC = IRV + V_T + ERV = TLC - RV

Restrictive lung disease

• Diseases that make it difficult to get air into lungs

• Ex. fibrosis, muscular diseases, chest wall deformities such as severe scoliosis

• FEV1/FVC ratio is normal or slightly higher than normal (80% is normal)

Obstructive lung disease

• Those that make it difficult to move air OUT OF lungs

• Ex. emphysema, asthma, chronic bronchitis

  • Decreases VC, increases TLC, RV, FRC

  • FEV1/FVC ratio is less than 80%

Control of respiration

• Rate and depth of breathing is controlled by a negative feedback mechanism

  1) Receptors

  2) Afferent neurons (sensory neurons)

  3) Control center

  4) Efferent neurons (motor neurons)

  5) Effector(s)

1) Receptors

• Central chemoreceptors: in medulla oblongata

  • Monitor pCO₂ and pH

• Peripheral chemoreceptors: in aorta and carotid arteries

  • Monitor pCO₂ and pH and O₂

• Stretch receptors (less important): in bronchioles and alveoli → too much stretch initiates exhale

Medulla Oblongata

• Inspiratory center

• Sets the rhythm of breathing by initiating each inspiration by sending action potentials down the phrenic nerve to the diaphragm every 3 seconds

Pons

• Smooths out transition between inspiration and expiration

• Less important than medulla oblongata

2) Effectors

• Breathing muscles

  • Diaphragm: innervated by phrenic nerve

  • Intercostal muscles: innervated by intercostal nerves

What controls respiration?

• Blood pH

• Chemical reaction: CO₂ + H₂O → H₂CO₃ → HCO₃^- + H⁺

• Decrease in blood pH (becoming more acidic) causes an increase in rate and depth of breathing

• Increase in blood pH (becoming more alkaline) causes a decrease in rate and depth of breathing

Blood pH

• Set point: pH of 7.4

• pH below 7.35 = respiratory acidosis (can be acute or chronic)

  • Causes: heroin, sedatives (acute), pneumonia, COPD (chronic), asthma, myasthenia gravis, guillain barre, or polio

• pH above 7.45 = respiratory alkalosis

  • Causes: hyperventilation, anxiety (panic attack), fever

Plays a minor role in control of respiration

• Oxygen levels in blood only control rate and depth of breathing in rare circumstances

  • High altitudes (mountain climbing)

  • When blood O₂ falls very low such as during a disease state (long term emphysema)

Hyperventilation

• Fast respiratory rate

• Reaction goes to LEFT

• CO₂ + H₂O ← H₂CO₃ ← HCO₃^- + H⁺

• Alkalosis (pH above 7.4) because CO₂ levels are low (exhaling lots of CO₂ with the quick breaths)

• Triggers decrease in rate of breathing or a cessation of breathing (inspiratory center of the medulla stops sending action potential down the phrenic nerve to tell the diaphragm to contract until enough CO₂ builds up to bring pH back to normal)

• Feel light-headed, may faint

  • Alkalosis of blood causes vasoconstriction = not enough O₂ to brain → you faint

• Solution: breath in paper bag → CO₂ diffuses in opposite direction (out of alveoli and into blood)

Hypoventilation

• Very slow breathing

• Reaction goes to RIGHT

• CO₂ + H₂O → H₂CO₃ → HCO₃^- + H⁺

• Causes blood pH to become more acidic because CO₂ is building up in the blood and H⁺ levels increase

• Confusion, tachycardia, drowsiness

• Quick fix = yawning

• Big problem = overdose → rescue breathing and/or administer O₂