RESPIRATORY PHYSIOLOGY

The Thorax and its contents

◦ Ventilation:  Action of breathing with muscles and lungs ◦ Gas exchange:  Between air and capillaries in the lungs.  Between systemic capillaries and tissues of the body Respiration

 Gas Exchange ◦ O 2, CO 2  Acid-base balance ◦ CO 2 +H 2 O←→ H 2 CO 3 ←→ H + + HCO3 -  Phonation  Pulmonary defense  Pulmonary metabolism and handling of bioactive materials

Inspiration:  lung volume increases -> ◦ decrease in intrapulmonary pressure, to just below atmospheric pressure -> ◦ air goes in!  Expiration: vice versa

 Compliance: ◦ This the ability of the lungs to stretch during inspiration ◦ lungs can stretch when under tension.  Elasticity: ◦ It is the ability of the lungs to recoil to their original collapsed shape during expiration ◦ Elastin in the lungs helps recoil

 Inspiration – Active process  Diaphragm contracts -> increased thoracic volume vertically.  Intercostals contract, expanding rib cage - > increased thoracic volume laterally.  More volume -> lowered pressure -> air in.  Negative pressure breathing

 Expiration – Passive ◦ Due to recoil of elastic lungs. ◦ Less volume -> pressure within alveoli is just above atmospheric pressure -> air leaves lungs. ◦ Note: Residual volume of air is always left behind, so alveoli do not collapse.

 Conducting zone:  Includes all the structures that air passes through before reaching the respiratory zone.  Mouth, nose, pharynx, glottis, larynx, trachea, bronchi.

 Conducting zone  Warms and humidifies until inspired air becomes: ◦ 37 degrees ◦ Saturated with water vapor  Filters and cleans: ◦ Mucus secreted to trap particles ◦ Mucus/particles moved by cilia to be expectorated.

 Respiratory zone  Region of gas exchange between air and blood - Respiratory bronchioles - Alveolar ducts, Alveolar Sacs and - Alveoli

Air duct Air Sac

 Alveoli ◦ Air sacs ◦ Honeycomb-like clusters ◦ ~ 300 million.  Large surface area (60–80 m 2 ). ◦ Each alveolus: only 1 thin cell layer. ◦ Total air barrier is 2 cells across (2  m) (alveolar cell and capillary endothelial cell).

◦ Alveolar cells ◦ Alveolar type I: structural cells. ◦ Alveolar type II: secrete surfactant.

Respiratory Zone

 Mechanical process that moves air in and out of the lungs.  Diffusion of…  O 2 : air to blood.  C0 2 : blood to air.  Rapid: ◦ large surface area ◦ small diffusion distance. 19 Insert 16.1

Alveolar capillary interface

Cellular Respiration

◦ Oxygen: large “reservoir” attached to hemoglobin. ◦ So chemoreceptors are more sensitive to changes in P C0 2 (as sensed through changes in pH). ◦ Ventilation is adjusted to maintain arterial PC0 2 of 40 mm Hg. ◦ Chemoreceptors are located throughout the body (in brain and arteries).

 Affinity between hemoglobin and 0 2 :  pH falls -> less affinity -> more unloading (and vice versa if pH increases)  temp rises -> less affinity -> more unloading  exercise, fever

 C0 2 transported in the blood: ◦ - most as bicarbonate ion (HC0 3 - ) ◦ - dissolved C0 2 ◦ - C0 2 attached to hemoglobin (Carbaminohemoglobin)

Carbonic anhydrase in RBC promotes useful changes in blood PC0 2 H C0 2 -> H 2 C0 3 -> HC0 3 - high P C0 2 CA H C0 2 <- H 2 C0 3 <- HC0 3 - low P C0 2 CA

 Normal blood pH: 7.40 ( )  Alkalosis: pH up  Acidosis: pH down

 H C0 2  Hypoventilation: ◦ P C0 2 rises, pH falls (acidosis).  Hyperventilation: ◦ P C0 2 falls, pH rises (alkalosis). H 2 C0 3 H + + HC0 3 -

 Ventilation is normally adjusted to keep pace with metabolic rate, so homeostasis of blood pH is maintained.

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