Human Physiology Respiratory System by Talib F. Abbas

Respiratory System 1-Pulmonary ventilation Respiratory system 4 major functions: 1-Pulmonary ventilation 2- Diffusion of oxygen and carbon dioxide between the alveoli and the blood. 3- Transport of oxygen and carbon dioxide in the blood and body fluids to and from the body’s tissue cells. Regulation of ventilation and other facts of respiration.

Respiratory Zones: Mechanics of Respiration Lung ventilation is by two ways: 1-downward and upward movement of the diaphragm. 2-elevation and depression of the ribs . Normal quiet breathing is accomplished by movement of the diaphragm. when the rib cage is elevated, the ribs project almost directly forward, so that the sternum also moves forward, away from the spine. muscles that raise the rib cage are the external intercostals.

Muscles of respiration The most important muscles that raise the rib cage are the external intercostals, but others that help are the (1) sternocleidomastoid muscles, which lift upward on the sternum; (2) anterior serrati, which lift many of the ribs; and (3) scaleni, which lift the first two ribs The muscles that pull the rib cage downward during expiration are mainly the (1) abdominal recti (2) internal intercostals.

Pulmonary Volumes and Capacities, air volume

Measurement of the dead space volume takes a deep breath of oxygen expires through a rapidly recording nitrogen meter. only oxygen appears, and the nitrogen concentration is zero, at the early stage. the gray area represents the air that has no nitrogen. the pink area represents the air that has nitrogen. VD = Volume of Dead space. =

Compliance of the lungs and chest

Compliance of the lungs and chest relaxation pressure curve of the total respiratory system. The pressure is zero at a lung volume that corresponds to the volume of gas in the lungs at the end of quiet expiration (functional residual capacity, or FRC; also known as relaxation volume). It is positive at greater volumes and negative at smaller volumes. The change in lung volume per unit change in airway pressure (ΔV/ΔP) is the compliance (stretchability) of the lungs and chest wall.

Surfactant and the Law of Lablace law of Laplace: equals two times the tension divided by the radius (P = 2T/r). The low surface tension when the alveoli are small is due to the presence in the fluid lining the alveoli of surfactant, a lipid surface-tension-lowering agent. Surfactant is a mixture of dipalmitoylphosphatidylcholine (DPPC). . Surfactant is produced by type II alveolar epithelial cells. Typical lamellar bodies. Formation of the phospholipid film is greatly facilitated by the proteins in surfactant. This material contains four unique proteins: surfactant protein (SP)-A, SP-B, SP-C, and SP-D. SPA is a large glycoprotein and has a collagen-like domain within its structure.

Differences in ventilation and blood flow in lung Pressures in the Pulmonary Artery.(15 mmHg) Pulmonary capillary pressure. ( 7 mmHg) Left Atrial and Pulmonary Venous Pressures.(pulmonary wedge pressure). ( 5 mmHg)

Dead space and an even ventilation It is important to distinguish between the anatomic dead space (respiratory system volume exclusive of alveoli) and the total (physiologic) dead space (volume of gas not equilibrating with blood; ie, wasted ventilation). In healthy individuals, the two dead spaces are identical and can be estimated by body weight. The initial gas exhaled (phase I). mixture of dead space and alveolar gas (phase II). alveolar gas (phase III), closing volume (CV). phase IV, during which the N2 content of the expired gas is increased.

Dead space & Bohr s equation The total dead space can be calculated from the PCO2 of expired air, the PCO2 of arterial blood, and the tidal volume. The tidal volume (VT) times the PCO2 of the expired gas (PECO2) equals the arterial PCO2 (PaCO2) times the difference between the tidal volume and the dead space (VD) plus the PCO2 of inspired air (PICO2) times VD (Bohr’s equation): PECO2 × VT = PaCO2 × (VT – VD) + PICO2 × VD The term PICO2 × VD is so small that it can be ignored and the equation solved for VD. If, for example, PECO2 = 28 mm Hg PaCO2 = 40 mm Hg VT = 500 mL then, Vd = 150 mL

Partial Pressure Unlike liquids, gases expand to fill the volume available to them, and the volume occupied by a given number of gas molecules at a given temperature and pressure is (ideally) the same regardless of the composition of the gas. partial pressure) is equal to the total pressure times the fraction of the total amount of gas it represents. The partial pressure (indicated by the symbol P) of O2in dry air is therefore 0.21×760, or 160 mmHg at sea level. The PN2 and the other inert gases is 0.79×760, or 600 mm Hg; and the PCO2is 0.0004×760, or 0.3 mm Hg.

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