Ch 12 Respiration

Pulmonary Ventilation

• During inspiration, factors decrease the intrapleural cavity pressure, allowing air to flow into the lungs.
• Diaphragm contraction and rib movement increase the thoracic volume, decreasing intrapleural pressure, and air flows into the lungs.
• During expiration, the diaphragm relaxes, ribs are pulled down, increasing intrapleural pressure, and air moves out of the lungs.

Lung Capacities

• Tidal volume (TV): amount of air moving in and out of the lungs during normal breathing (average value: 500 ml).
• Inspiratory reserve volume (IRV): amount of air that can be inhaled after normal inspiration (average value: 3,000 ml).
• Expiratory reserve volume (ERV): amount of air that can be exhaled after normal expiration (average value: 1,100 ml).
• Inspiratory capacity (IC): total amount of air that can be inhaled (average value: 4,000 ml).
• Vital capacity (VC): total amount of air that can be exhaled (average value: 5,000 ml).
• Residual volume (RV): amount of air always left in the lungs after expiration.

Inspiration and Expiration

• Inspiration is an active process where nerve impulses cause diaphragm and external intercostals muscle contraction, increasing thoracic volume, and decreasing intraalveolar pressure.
• Expiration is a passive process where elastic tissues of the lungs and diaphragm recoil to their original position, decreasing thoracic volume, and increasing intraalveolar pressure.

Control of Breathing

• Four major factors affect normal breathing: stretching of the lungs and thoracic walls, O2 level in the blood, CO2 level in the blood, and H+ level in the blood.
• Chemicals, emotional state, and other factors also affect breathing.

The Respiratory Tract

• The bronchial tree is a tree-like branching tube system extending from the trachea into the lungs.
• The respiratory tract changes histologically along its length, with ciliated pseudostratified columnar epithelium in the trachea, cuboidal epithelium in the bronchioles, and simple squamous epithelium in the alveoli.

Functions of The Respiratory System

• To allow gases from the environment to enter the bronchial tree through inspiration.
• To allow gas exchange to occur at the respiratory membrane, so that oxygen diffuses into the blood while carbon dioxide diffuses into the bronchial tree.
• To permit gases in the lungs to be eliminated through expiration by decreasing the thoracic volume.

General Anatomy of The Respiratory System

• Consists of a tube that divides into small branching tubes in the lungs: External nares → nasal cavity → nasopharynx → laryngopharynx → larynx → trachea → primary bronchi → lungs.

Lungs

• Cone-shaped organs located in the thoracic cavity, lined with visceral pleura, with the parietal pleura lining the thoracic cavity.
• The pleural cavity is filled with a clear fluid called plural fluid, which minimizes friction between the tissues and provides surface tension.

Oxygen Transport in the Blood

• Each hemoglobin (Hb) molecule can bind up to four oxygen (O2) molecules.
• At approximately 40 mmHg of O2, roughly 75% of Hb is saturated.
• At approximately 80 mmHg of O2, close to 98% of Hb is saturated, and the curve becomes flattened beyond this point where only about 98-99% of Hb can be saturated.

Factors Affecting O2-Hb Dissociation Curve

• Four main factors that can shift the O2-Hb dissociation curve:
  • Decrease in O2 pressure shifts the curve to the right.
  • Increase in CO2 pressure shifts the curve to the right.
  • Decrease in pH of blood (more acidic) shifts the curve to the right.
  • Increase in body temperature shifts the curve to the right.

Bohr and Haldane Effects

• When the dissociation curve shifts to the right, it is called the Bohr effect, where less Hb saturation occurs and more O2 is released from oxyhemoglobin.
• When the dissociation curve shifts to the left, it is called the Haldane effect, where more Hb saturation occurs and less O2 is released.

Carbon Dioxide Transport

• 7% of CO2 is dissolved in the blood plasma.
• 23% of CO2 binds with hemoglobin in erythrocytes, forming carbaminohemoglobin.
• 70% of CO2 reacts with water and forms carbonic acid in erythrocytes, which is broken down by the enzyme carbonic anhydrase to form hydrogen ion and bicarbonate ion.

Alveolar Gas Exchange

• Gas exchanges between the air and the blood occur within the alveoli.
• The alveoli are tiny sacs clustered at the distal ends of alveolar ducts.
• The respiratory membrane consists of the alveolar and capillary walls.
• Gas exchange takes place through these walls.
• O2 diffuses from the alveolar air into the blood, while CO2 diffuses from the blood into the alveolar air.

Pulmonary vs. Systemic Capillaries

• In pulmonary capillaries:
  • O2 enters the capillaries from the alveoli.
  • CO2 enters the alveoli from the capillaries.
• In systemic capillaries:
  • O2 enters the tissues from the capillaries.
  • CO2 enters the capillaries from the tissues.

Gas Exchange at the Alveoli and Cells

• 98% of O2 is transported by binding to hemoglobin in erythrocytes.
• 2% of O2 is dissolved in the blood plasma.
• The resulting oxyhemoglobin is relatively unstable and releases its O2 in regions where PO2 is low.

Carbon Monoxide Transport

• Carbon monoxide (CO) forms as a result of incomplete combustion of fuels.
• CO combines with hemoglobin more readily than O2 and forms a stable compound.
• CO is toxic because the hemoglobin with which it combines is no longer available for O2 transport.

Clinical Terms

• Anoxia: absence or deficiency of O2 within tissues.
• Asphyxia: deficiency of O2 and excess of CO2 in the blood and tissues.
• Atelectasis: collapse of a lung or some portion of it.
• Bronchitis: inflammation of the bronchial lining.
• Cheyne-stokes respiration: irregular breathing pattern.
• Dyspnea: difficulty in breathing.
• Hyperoxia: excess oxygenation of the blood.
• Hyperpnea: increase in the depth and rate of breathing.
• Hypoxia: diminished availability of O2 in the tissues.
• Pneumothorax: entrance of air into the space between the pleural membrane, followed by collapse of the lung.
• Tachypnea: rapid, shallow breathing.
• Asthma: dyspnea, wheezing, and other symptoms produced by obstruction of air flow through the bronchioles.
• Lung cancer: leading cause of cancer death in the U.S., with smoking being the leading cause.