AU Biology Dept Spring 2008

Anatomy & Physiology II Lecture Outline

Text Saladin, K.S. 2007. Anatomy & Physiology: The Unity of Form and Function. 4th ed. McGraw-Hill, NY.

Chapter 22 The Respiratory System

Memory Verse:

John 20:21, 22 "Jesus therefore said to them again, "Peace be with you; as the Father has sent Me, I also send you." And when He had said this, He breathed on them, and said to them "Receive the Holy Spirit" NASB

A. Topics

1) Anatomy of the Respiratory System

2) Mechanics of Ventilation

3) Neural Control of Ventilation

4) Gas Exchange and Transport

B. Lecture Outline

Introduction

The term respiration has 3 meanings:

a. Ventilation of the lungs (breathing).

b. Exchange of gases between:

i. air and blood (pulmonary capillaries).

ii. blood and interstitial fluid (systemic capillaries).

c. Use of O2 in cellular respiration.

1) Anatomy of the Respiratory System

The principal organs of the respiratory system are the nose, pharynx, larynx, trachea, bronchi, and lungs (fig 22.1).

Divisions of the respiratory system:

a. Conducting division - passages serve only for airflow, nostrils to bronchioles.

b. Respiratory division - alveoli and distal gas-exchange regions.

c. Upper respiratory tract - organs in head and neck, nose through larynx.

d. Lower respiratory tract - organs of the thorax, trachea through lungs.

i. Nose (fig 22.2)

The nasal cavity extends from the anterior nares (nostrils) to the posterior nares (choanae).

Functions - warms, cleanses, and humidifies inhaled air; detects odors; resonating chamber that modifies the voice.

Structure - superior, middle and inferior nasal conchae and meatuses.

olfactory mucosa lines roof of nasal fossa.

Respiratory mucosa lines rest of nasal cavity with ciliated pseudostratified epithelium.

ii. Pharynx (fig 22.3)

Muscular tube extending approx 13 cm from posterior nares to the larynx. Composed of 3 regions:

a. Nasopharynx

b. Oropharynx

c. Laryngopharynx

iii.Larynx (fig 22.4)

A cartilaginous chamber approx 4 cm long.

Functions - prevent food/drink from entering trachea; production of sound by vocal cords.

Structure - superior opening is the glottis; epiglottis directs food/drink to esophagus.

iv. Trachea (fig 22.7)

Rigid tube 12 cm long and 2.5 cm in diameter, anterior to esophagus.

Supported by 16 to 20 C-shaped cartilaginous rings.

v. Bronchi (figs 22.7 and 22.9)

Primary, secondary, and tertiary bronchii.

vi. Lungs (figs 22.9 and 22.11)

The lungs receive the primary bronchi through the hilum.

The lungs consist of a spongy parenchyma containing the bronchial tree:

a. Bronchii, terminal and respiratory bronchioles – smooth muscle layer allows for bronchoconstriction and bronchodilation.

b. Alveolar ducts and alveolar sacs.

c. Alveoli – composed of simple squamous epithelial cells with pulmonary surfactant forming a respiratory membrane of approx 70 m2.

vii.Pleurae and Pleural Fluid

The pleurae is composed of visceral and parietal membranes holding pleural fluid within the cavity.

Functions:

a. Reduction of friction.

b. Creation of pressure gradient - lower pressure assists in inflation of lungs.

c. Compartmentalization - prevents spread of infection.

2) Mechanics of Ventilation

Gas laws (table 22.1).

a. Pressure and the Flow of Air

The flow of air into and out of the lungs is caused by a difference between atmospheric and intrapulmonary pressure created by changes in volume of thoracic cavity.

1. Muscles of Inspiration (fig 22.13):

i. Quiet inspiration - diaphragm, scalenes, external intercostals.

ii. Deep inspiration - pectoralis minor, sternocleidomastoid, erector spinae.

2. Expiration:

i. Quiet expiration – elastic recoil of lungs and thoracic cage.

ii. Forced expiration – internal intercostals, abdominal muscles.

b. Alveolar Ventilation

Dead air - fills conducting division of airway, cannot exchange gases (150 ml).

Anatomic dead space - conducting division of airway.

Physiologic dead space - sum of anatomic dead space and any pathological alveolar dead space.

Alveolar ventilation rate:

Air that actually ventilates alveoli x respiratory rate (eg. 350 ml x 12 breaths/min = 4.2 L/min).

Directly relevant to body’s ability to exchange gases.

c. Measurements of Ventilation (fig 22.17)

Spirometer - device a subject breathes into that measures ventilation.

1. Respiratory volumes:

Tidal volume: air inhaled or exhaled in one quiet breath (500 ml).

Inspiratory reserve volume: air in excess of tidal inspiration inhaled with maximum effort (3000 ml).

Expiratory reserve volume: air in excess of tidal expiration exhaled with maximum effort (1200 ml).

Residual volume: air remaining in lungs after maximum expiration, keeps alveoli inflated (1300 ml).

2. Respiratory Capacities: (fig 22.17)

Vital capacity: amount of air that an be exhaled with maximum effort after maximum inspiration (4700 ml).

Inspiratory capacity: maximum amount of air that can be inhaled after a normal tidal expiration (3500 ml).

Functional residual capacity: amount of air in lungs after a normal tidal expiration (2500 ml).

Total lung capacity: maximum amount of air lungs can contain (6000 ml).

3) Neural Control of Ventilation

Breathing depends on repetitive stimuli from respiratory control centers in medulla oblongata and pons which travel via the spinal cord and phrenic/intercostals nerves to the muscles of inspiration and expiration.

Regulate unconscious (quiet) breathing.

Voluntary control provided by the motor cortex of frontal lobe of cerebrum.

The respiratory control centers receive nervous input (afferent neurons) from:

a. limbic system and hypothalamus - respiratory effects of pain and emotion.

b. chemoreceptors - brainstem and arteries monitor blood pH, CO2 and O2 levels.

c. airways and lungs – response to inhaled irritants, results in bronchoconstriction or coughing.

4) Gas Exchange and Transport

a. Gas Exchange (fig 22.19)

i. Composition of Atmospheric Air

Atmospheric air is a mixture of gases, each contributes its partial pressure (at sea level 1 atm. of pressure = 760 mmHg).

Partial pressures determine rate of diffusion of gas and gas exchange between blood and alveolus.

ii. Composition of Alveolar Air

Alveolar air is humidified, exchanges gases with blood, mixes with residual air.

PN2 = 569, PO2 = 104, PH2O = 47, PCO2 = 40 mmHg.

Summary of Alveolar PO2 and PCO2

PO2 = 104 in alveolar air versus 40 in pulmonary capillaries.

PCO2 = 46 in pulmonary capillaries versus 40 in alveolar air.

The concentration gradients for these gases provides the driving force for diffusion.

Other factors affecting diffusion of gases: solubility, surface area (70 m2) and thickness (0.5 um) of respiratory membane, ventilation-perfusion coupling.

b. Gas Transport

i. Oxygen Transport in the Blood

Concentration in arterial blood = 20 ml/dl (98.5% bound to hemoglobin, 1.5% dissolved).

Binding to hemoglobin:

each heme group of 4 globin chains may bind O2 .

oxyhemoglobin (HbO2 ), deoxyhemoglobin (HHb).

The Oxyhemoglobin Dissociation Curve (fig 22.23).

ii. Carbon Dioxide Transport in the Blood

As carbonic acid - 90% (CO2 + H2O Æ H2CO3 Æ HCO3- + H+).

As carbaminohemoglobin (HbCO2) - 5% binds to amino groups of Hb (and plasma proteins).

As dissolved gas - 5%.

iii. Systemic Gas Exchange

1. CO2 loading

carbonic anhydrase in RBC catalyzes CO2 + H2O Æ H2CO3 Æ HCO3- + H+.

chloride shift: exchanges HCO3- for Cl-, H+ binds to hemoglobin.

2. O2 unloading

H+ binding to HbO2 Ø its affinity for O2.

Hb arrives 97% saturated, leaves 75% saturated.

iv. In the pulmonary capillaries reactions are reverse of systemic gas exchange.

v. Factors affecting O2 unloading (fig 22.26)

1. ambient PO2: active tissue has Ø PO2 , O2 is released.

2. temperature: active tissue has increased temp, O2 is released.

3. Bohr effect: active tissue has ≠ CO2, which raises H+ and lowers pH, O2 is released.

4. bisphosphoglycerate (BPG): RBC’s produce this as a metabolic intermediate, BPG binds to Hb and causes HbO2 to release O2.

≠ body temp (fever), TH, GH, testosterone, and epinephrine all raise BPG and cause O2 unloading.

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