Concepts of Human Anatomy & Physiology   5/e   Van De Graaff/Fox
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I. Structure of the Respiratory System

Concept: The respiratory system can be divided anatomically into upper and lower divisions and functionally into a conducting division and a respiratory division. Gas exchange between the air and blood occurs in the respiratory division, so that the blood leaving the lungs has a higher oxygen and a lower carbon dioxide concentration than the blood that enters the lungs.

II. Physical Aspects of Ventilation

Concept: The movement of air into and out of the lungs occurs as a result of pressure differences induced by changes in lung volumes. Ventilation is thus influenced by the physical properties of the lungs, including their compliance, elasticity, and surface tension.

III. Mechanics of Breathing

Concept: Normal, quiet inspiration results from muscle contraction, and normal expiration results from muscle relaxation and elastic recoil. These actions can be forced by contractions of the accessory respiratory muscles. The amount of air inspired and expired can be measured in a number of ways to test pulmonary function.

IV. Gas Exchange in the Lungs

Concept: Gas exchange between the alveolar air and the blood in pulmonary capillaries results in an increased oxygen concentration and a decreased carbon dioxide concentration in the blood leaving the lungs. This blood enters the systemic arteries, where blood gas measurements are taken to assess the effectiveness of lung function.

V. Regulation of Breathing

Concept: The motor neurons that stimulate the respiratory muscles are controlled by two major descending pathways: one that controls voluntary breathing, and another that controls involuntary breathing. The unconscious rhythmic control of breathing is influenced by sensory feedback from receptors sensitive to the PCO2, pH, and PO2 of arterial blood.

VI. Hemoglobin and Oxygen Transport

Concept: Hemoglobin without oxygen, or deoxyhemoglobin, can bond with oxygen to form oxyhemoglobin. This "loading" reaction occurs in the capillaries of the lungs. The dissociation of oxyhemoglobin, or "unloading" reaction, occurs in the tissue capillaries. The bond strength between hemoglobin and oxygen, and thus the extent of the unloading reaction, is adjusted by various factors to ensure an adequate delivery of oxygen to the tissues.

VII. Carbon Dioxide Transport and Acid-Base Balance

Concept: Carbon dioxide is transported in the blood primarily in the form of bicarbonate (HCO3-), which is released when carbonic acid dissociates. Bicarbonate can buffer H+ and thus helps to maintain a normal arterial pH. Hypoventilation raises, and hyperventilation lowers, the carbonic acid concentration of the blood.

VIII. Effects of Exercise and High Altitude on Respiratory Function

Concept: The arterial blood gases and pH do not significantly change during moderate exercise because ventilation increases to keep pace with increased metabolism. This increased ventilation requires neural feedback from the exercising muscles and chemoreceptor stimulation. Adjustments are made at high altitude in both the control of ventilation and the oxygen

IX. Development of the Respiratory System

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