RESPIRATORY PHYSIOLOGY. The Thorax and its contents

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◦ O2, CO2

Acid-base balance◦ CO2 +H2O←→ H2CO3 ←→ 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 m2).◦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… O2: air to blood. C02: blood to air. Rapid:

◦ large surface area ◦ small diffusion

distance.

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Insert 16.1

Alveolar capillary interface

Alveolar capillary interface

Cellular Respiration

◦Oxygen: large “reservoir” attached to hemoglobin.

◦So chemoreceptors are more sensitive to changes in PC02

(as sensed through changes in pH).

◦Ventilation is adjusted to maintain arterial PC02 of 40 mm Hg.

◦Chemoreceptors are located throughout the body (in brain and arteries).

Affinity between hemoglobin and 02: pH falls -> less affinity -> more unloading (and vice versa if pH increases)

temp rises -> less affinity -> more unloading

exercise, fever

C02 transported in the blood: ◦- most as bicarbonate ion (HC03

-)◦- dissolved C02

◦- C02 attached to hemoglobin (Carbaminohemoglobin)

• Carbonic anhydrase in RBC promotesuseful changes in blood PC02

H20 + C02 -> H2C03 -> HC03-

high PC02

CA

H20 + C02 <- H2C03 <- HC03

- low PC02

CA

Normal blood pH: 7.40 (7.35- 7.45)

Alkalosis: pH up Acidosis: pH down

H20 + C02

Hypoventilation: ◦ PC02 rises, pH falls (acidosis).

Hyperventilation: ◦ PC02 falls, pH rises (alkalosis).

H2C03 H+ + HC03-

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

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