respiratory physiology.pptx and anatomy eee

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1. Pulmonary Function: Introduction Respiration, as the term is generally used, includes two processes: External respiration, the absorption of O 2 and removal of CO 2 from the body as a whole; Internal respiration, the utilization of O 2 and production of CO 2 by cells and the gaseous exchanges between the cells and their fluid medium .

2. ventilation ’ refers to circulation or replacement of air or gas in a space . In respiratory physiology, ventilation is the rate at which air enters or leaves the lungs. Ventilation in respiratory physiology is of two types: 1 . Pulmonary ventilation 2 . Alveolar ventilation. VENTILATION

3. Pulmonary ventilation is defined as the volume of air moving in and out of respiratory tract in a given unit of time during quiet breathing. It is also called minute ventilation or respiratory minute volume (RMV). Pulmonary ventilation is a cyclic process, by which fresh air enters the lungs and an equal volume of air leaves the lungs. PULMONARY VENTILATION

4. Normal value of pulmonary ventilation is 6,000 mL (6 L)/ minute . It is the product of tidal volume (TV) and the rate of respiration (RR). It is calculated by the formula: Pulmonary ventilation = Tidal volume × Respiratory rate = 500 mL × 12/minute = 6,000 mL/minute.

5. Alveolar ventilation is the amount of air utilized for gaseous exchange every minute. Alveolar ventilation is different from pulmonary ventilation . In pulmonary ventilation, 6 L of air moves in and out of respiratory tract every minute. But the whole volume of air is not utilized for exchange of gases . Volume of air subjected for exchange of gases is the alveolar ventilation. Air trapped in the respiratory passage (dead space) does not take part in gaseous exchange . ALVEOLAR VENTILATION

6. The goals of respiration are to provide oxygen to the tissues and to remove carbon dioxide. To achieve these goals, respiration can be divided into four major functions : (1) pulmonary ventilation, which means the inflow and outflow of air between the atmosphere and the lung alveoli ; (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; and (4 ) regulation of ventilation and other facets of respiration

7. Inspiration is an active process. The contraction of the inspiratory muscles increases intrathoracic volume. The intrapleural pressure at the base of the lungs, which is normally about –2.5 mm Hg (relative to atmospheric) at the start of inspiration, decreases to about –6 mm Hg. The lungs are pulled into a more expanded position. The pressure in the airway becomes slightly negative, and air flows into the lungs Mechanism of Respiration

8. At the end of inspiration, the lung recoil begins to pull the chest back to the expiratory position, where the recoil pressures of the lungs and chest wall balance. The pressure in the airway becomes slightly positive, and air flows out of the lungs. Expiration during quiet breathing is passive in the sense that no muscles that decrease intrathoracic volume contract. However, some contraction of the inspiratory muscles occurs in the early part of expiration. This contraction exerts a braking action on the recoil forces and slows expiration.

9. Strong inspiratory efforts reduce intrapleural pressure to values as low as –30 mm Hg, producing correspondingly greater degrees of lung inflation. When ventilation is increased, the extent of lung deflation is also increased by active contraction of expiratory muscles that decrease intrathoracic volume.

10. The amount of air that moves into the lungs with each inspiration (or the amount that moves out with each expiration) is called the tidal volume. The air inspired with a maximal inspiratory effort in excess of the tidal volume is the inspiratory reserve volume. The volume expelled by an active expiratory effort after passive expiration is the expiratory reserve volume, and the air left in the lungs after a maximal expiratory effort is the residual volume. The space in the conducting zone of the airways occupied by gas that does not exchange with blood in the pulmonary vessels is the respiratory dead space. Lung Volumes

11. The forced vital capacity (FVC), the largest amount of air that can be expired after a maximal inspiratory effort, is frequently measured clinically as an index of pulmonary function. It gives useful information about the strength of the respiratory muscles and other aspects of pulmonary function. The fraction of the vital capacity expired during the first second of a forced expiration is referred to as FEV 1 (formerly the timed vital capacity) (Figure 35–8). The FEV 1 to FVC ratio (FEV 1 /FVC) is a useful tool in the diagnosis of airway disease (Clinical Box 35–1). The amount of air inspired per minute (pulmonary ventilation, respiratory minute volume) is normally about 6 L (500 mL / breath x 12 breaths/min). The maximal voluntary ventilation (MVV) is the largest volume of gas that can be moved into and out of the lungs in 1 min by voluntary effort. The normal MVV is 125 to 170 L/min.

12. Spirometer Measurements

13. Airway epithelial cells can secrete a variety of molecules that aid in lung defense. Secretory immunoglobulins ( IgA ), collectins (including Surfactant A and D), defensins and other peptides and proteases, reactive oxygen species, and reactive nitrogen species are all generated by airway epithelial cells. These secretions can act directly as antimicrobials to help keep the airway free of infection. Airway epithelial cells also secrete a variety of chemokines and cytokines that recruit the traditional immune cells and others to site of infections. Other Functions of the Respiratory System Lung Defense Mechanisms

14. The hairs in the nostrils strain out many particles larger than 10 µm in diameter. Most of the remaining particles of this size settle on mucous membranes in the nose and pharynx; because of their momentum, they do not follow the airstream as it curves downward into the lungs, and they impact on or near the tonsils and adenoids, large collections of immunologically active lymphoid tissue in the back of the pharynx. Particles 2 to 10 µm in diameter generally fall on the walls of the bronchi as the air flow slows in the smaller passages. There they can initiate reflex bronchial constriction and coughing. Alternatively, they can be moved away from the lungs by the " mucociliary escalator."

15. The epithelium of the respiratory passages from the anterior third of the nose to the beginning of the respiratory bronchioles is ciliated. The cilia are bathed in a periciliary fluid where they typically beat at rates of 10–15 Hz. On top of the periciliary layer and the beating cilia rests a mucus layer, a complex mixture of proteins and polysaccharides secreted from specialized cells, glands, or both in the conducting airway. This combination allows for the trapping of foreign particles (in the mucus) and their transport out of the airway (powered by ciliary beat). The ciliary mechanism is capable of moving particles away from the lungs at a rate of at least 16 mm/min. When ciliary motility is defective, as can occur from smoking, other environmental conditions, or genetic deficiency, mucus transport is virtually absent. This can lead to chronic sinusitis, recurrent lung infections, and bronchiectasis

16. The pulmonary alveolar macrophages (PAMs). PAMs are actively phagocytic and ingest Particles less than 2 m . They also help process inhaled antigens for immunologic attack, and they secrete substances that attract granulocytes to the lungs as well as substances that stimulate granulocyte and monocyte formation in the bone marrow

17. They manufacture surfactant for local use. They also contain a fibrinolytic system that lyses clots in the pulmonary vessels. They release a variety of substances that enter the systemic arterial blood (Table 35–5), and they remove other substances from the systemic venous blood that reach them via the pulmonary artery. Prostaglandins are removed from the circulation, but they are also synthesized in the lungs and released into the blood when lung tissue is stretched. Metabolic Functions of the Lungs

18. Thus, respiratory unit includes: 1 . Respiratory bronchioles 2 . Alveolar ducts 3 . Alveolar sacs 4 . Antrum 5 . Alveoli. Each alveolus is like a pouch with the diameter of about 0.2 to 0.5 mm . It is lined by epithelial cells. RESPIRATORY UNIT

19. Alveolar epithelium consists of alveolar cells or pneumo cytes , which are of two types namely type I alveolar cells and type II alveolar cells. Type I alveolar cells Type I alveolar cells are the squamous epithelial cells forming about 95% of the total number of cells. These cells form the site of gaseous exchange between the alveolus and blood. Alveolar Cells or Pneumocytes

20. Type II alveolar cells Type II alveolar cells are cuboidal in nature and form about 5% of alveolar cells. These cells are also called granular pneumocytes . Type II alveolar cells secrete alveolar fluid and surfactant.

21. 1 . Surfactant reduces the surface tension in the alveoli of lungs and prevents collapsing tendency of lungs. 2 . Surfactant is responsible for stabilization of the alveoli, which is necessary to withstand the collaps ing tendency . 3. It plays an important role in the inflation of lungs after birth. 4 . its role in defense within the lungs against infection and inflammation. Functions of surfactant

22. PULMONARY BLOOD VESSELS Pulmonary blood vessels include pulmonary artery, which carries deoxygenated blood to alveoli of lungs and bronchial artery, which supply oxygenated blood to other structures of lungs (see below). Pulmonary Circulation

23. Pulmonary artery supplies deoxygenated blood pumped from right ventricle to alveoli of lungs (pulmonary circulation). After leaving the right ventricle, this artery divides into right and left branches. Each branch enters the corresponding lung along with primary bronchus. After entering the lung, branch of the pulmonary artery divides into small vessels and finally forms the capillary plexus that is in intimate relationship to alveoli. Capillary plexus is solely concerned with alveolar gas exchange. PULMONARY ARTERY

24. Bronchial artery arises from descending thoracic aorta . It supplies arterial blood to bronchi, connective tissue and other structures of lung stroma, visceral pleura and pulmonary lymph nodes . Venous blood from these structures is drained by two bronchial veins from each side. BRONCHIAL ARTERY

25. Physiological shunt is defined as a diversion through which the venous blood is mixed with arterial blood. Physiological shunt has two components: 1 . Flow of deoxygenated blood from bronchial circula tion into pulmonary veins without being oxygenated makes up part of normal physiological shunt 2 . Flow of deoxygenated blood from thebesian veins into cardiac chambers directly (Chapter 108). PHYSIOLOGICAL SHUNT

26. 1. Pulmonary artery has a thin wall. Its thickness is only about one third of thickness of the systemic aortic wall. Wall of other pulmonary blood vessels is also thin. 2 . Pulmonary blood vessels are highly elastic and more distensible 3 . Smooth muscle coat is not well developed in the pulmonary blood vessels 4. True arterioles have less smooth muscle fibers CHARACTERISTIC FEATURES OF PULMONARY BLOOD VESSELS

27. 5. Pulmonary capillaries are larger than systemic capillaries. Pulmonary capillaries are also dense and have multiple anastomosis, so, each alveolus occupies a capillary basket . 6 . Vascular resistance in pulmonary circulation is very less; it is only one tenth of systemic circulation 7 . Pulmonary vascular system is a low pressure system. Pulmonary arterial pressure and pulmo nary capillary pressure are very low (see below). 8 . Pulmonary artery carries deoxygenated blood from heart to lungs and pulmonary veins carry oxygenated blood from lungs to heart 9 . Physiological shunt is present.

28. Lungs receive the whole amount of blood that is pumped out from right ventricle. Output of blood per minute is same in both right and left ventricle. It is about 5 liter . PULMONARY BLOOD FLOW

29. Pulmonary blood vessels are more distensible than systemic blood vessels. So the blood pressure is less in pulmonary blood vessels. Thus, the entire pulmonary vascular system is a low pressure bed. Pulmonary Arterial Pressure Systolic pressure : 25 mm Hg Diastolic pressure : : 10 mm Hg Mean arterial pressure : 15 mm Hg. Pulmonary capillary pressure is about 7 mm Hg. This pressure is sufficient for exchange of gases between alveoli and blood. measured by applying Fick principle PULMONARY BLOOD PRESSURE

30. Pulmonary blood flow is regulated by the following factors: 1 . Cardiac output 2 . Vascular resistance 3 . Nervous factors 4 . Chemical factors 5 . Gravity and hydrostatic pressure. REGULATION OF PULMONARY BLOOD FLOW

31. 1. CARDIAC OUTPUT Pulmonary blood flow is directly proportional to cardiac output. Cardiac output is in turn regulated by four factors: i . Venous return ii. Force of contraction iii. Rate of contraction iv . Peripheral resistance.

32. Pulmonary blood flow is inversely proportional to the pulmonary vascular resistance . During inspiration, pulmonary blood vessels are distended because of de creased intrathoracic pressure. This causes decrease in vascular resistance resulting in increased pulmonary blood flow. During expiration, the pulmonary vascular resistance increases resulting in decreased blood flow. . VASCULAR RESISTANCE

33. Stimulation of sympathetic nerves under experimental conditions increases the pulmonary vascular resis tance by vasoconstriction the stimulation of para sympathetic, i.e. vagus nerve decreases the vascular resistance by vasodilatation. 3. NERVOUS FACTORS

34. 4 . CHEMICAL FACTORS Excess of carbon dioxide or lack of oxygen causes vasoconstriction. 5 . GRAVITY AND HYDROSTATIC PRESSURE Normally in standing position, blood pressure in lower extremity of the body is very high and in upper parts above the level of heart, the pressure is low . This is because of the effect of gravitational force.

35. Ventilationperfusion ratio is the ratio of alveolar ventilation and the amount of blood that perfuse the alveoli . It is expressed as VA /Q. VA is alveolar ventilation and Q is the blood flow (perfusion ). Normal Value Normal value of ventilationperfusion ratio is about 0.84. VENTILATION-PERFUSION RATIO

36. Calculation Alveolar ventilation is calculated by the formula :

37. Ventilation-perfusion ratio signifies the gaseous ex change. It is affected if there is any change in alveolar ventilation or in blood flow. Ventilation without perfusion = dead space Perfusion without ventilation = shunt SIGNIFICANCE OF VENTILATION- PERFUSION RATIO

38. Ventilation perfusion ratio is not perfect because of existence of two factors on either side of alveolar membrane. These factors are: Physiological dead space, which includes wasted air 2 . Physiological shunt, which includes wasted blood WASTED AIR AND WASTED BLOOD

39. Physiological Variation 1 . Ratio increases, if ventilation increases without any change in blood flow 2 . Ratio decreases, if blood flow increases without any change in ventilation 3 . In sitting position, there is reduction in blood flow in the upper part of the lungs (zone 1) than in the lower part (zone 3). Therefore, in zone 1 of lungs ventilation perfusion ratio increases three times. At the same time, in zone 3 of the lungs, because of increased blood flow ventilation-perfusion ratio decreases (Chapter 119). VARIATIONS IN VENTILATION- PERFUSION RATIO

40. In chronic obstructive pulmonary diseases (COPD), ventilation is affected because of obstruction and des truction of alveolar membrane. So , ventilationper fusion ratio reduces greatly. Pathological Variation