RESPIRATORY SYSTEM

1. RESPIRATORY SYSTEM FOR MEDICAL STUDENTS FEB 2014 در عقيلهالبدري

3. Learning objectives • Pulmonary structure and mechanics. • Gas transport and exchange. • Regulation of respiration.

4. Why We Breathe? We need to breathe because our cells require oxygen for cellular respiration and must remove carbon dioxide from the cell as a by-product of the cellular respiration (metabolism).

5. What is the respiratory system? Your respiratory system is made up of the organs in your body that help you to breathe. Remember, that Respiration = Breathing.

7. Respiration • Respiration means taking up of oxygen (O2), its utilization in the tissues and removal of carbon dioxide (CO2). • In the process, O2 is drawn in as a part of inspired air and then taken up by blood from the lungs. • O2 is then transported by blood to the tissues where it is used up and CO2 is produced. • This CO2 is again taken up by blood and delivered to the lungs wherefrom the CO2 is expelled through the expired air.

8. O2 & CO2 exchange between body tissues & environment Atmospheric air contains approx. 21% O2; 79% N2 and 0.04% CO2.

9. Types of Respiration The general term respiration refers to two integrated processes: external respiration and internal respiration. External respiration • It is the process of bringing air from the external environment and transporting it to the cell while CO2 is carried from the cell to the external environment. • The process of external respiration involves three major events: pulmonary ventilation, pulmonary diffusion and transport of gases. Internal respiration (cellular respiration) • It consists of a series of complex metabolic reactions that utilizes O2 and releases CO2 and energy.

10. Overview of External & Internal Respiration

11. Functional anatomy of the respiratory system • The respiratory system consists of the upper respiratory tract includes the mouth, nose, pharynx and larynx; • The lower respiratory tract starts at the trachea, and includes bronchi and lungs. • The two lungs are enclosed within the thoracic cage which is formed by the ribs, sternum, vertebral column and the dome-shaped diaphragm. • The diaphragm is separating the thorax from the abdomen. • The left lung has two lobes and the right has three. Each lung lobe is made up of several bronchopulmonary segments.

15. Pleura • The lungs are covered by a thin membrane (visceral pleura) and inside surface of the thoracic cage is lined by another thin membrane, parietal pleura. • The tiny space between the two pleura is called pleural cavity which is filled with the ultrafiltrate of plasma called pleural fluid(about 10ml) helps in lubrication of the pleura.

17. Tracheobronchial Tree • The airway tree consists of a series of highly branched hollow tubes that decrease in diameter and become more numerous at each branching (refers by their generation number). • Trachea (zero generation), the main airway in turn branches into two bronchi (first generation), one of which enters each lung. • There is a total of approximately23 generationsof airways.

19. Tracheobronchial Tree (23 generations of airways)

20. As generation number increases (airways become smaller), the amount ofcilia, the number of mucus-secreting cells, the presence of submucosal glands and the amount of cartilage in the airway walls all gradually decrease. • Airways maintain some cartilage to about 10th generation, up to which point they are referred to as bronchi. At about the 11th and succeeding generations, the now cartilage-free airways are called bronchioles. • The cartilage is important for preventing airway collapse. The mucus is important for trapping small foreign particles. The ciliasweep the carpet of mucus and kept moist by secretions. • Bronchial tree:Trachea→ bronchi→ smaller bronchi→ terminal bronchioles.

21. Wall of Tracheobronchial Tree

23. Respiratory air passages • Functionally, the respiratory air passages are divided into two zones: • Conductive zone and • Respiratory zone Conducting zone • The first 16 subdivisions (from trachea to terminal bronchioles) form conducting zone of airway. • The terminal bronchioles redivide to form respiratory bronchioles and then to alveolar ducts and sacs which end as alveoli.

24. The conducting zone of the respiratory system, in summary consists of the following parts: • Mouth→ nose→ pharynx→ larynx→ trachea→ bronchi→ all successive branches of bronchioles including terminal bronchioles. • No gas exchange occurs in these regions. The amount of air present in these regions is called ‘’anatomical dead space’’. • The quantity of air present in these regions is about 150 ml. • The remaining subdivisions form the transitional and respiratory zone where gas exchange occurs.

25. Functions of conducting zone • Warming and cooling of inspired air • Moistening or humidification of the inspired air • Filtration and cleaning • Secretion of IgA in the bronchial secretions, an additional protection against respiratory infections • Tonsils and adenoids, immunologically active lymphoid tissue in the pharynx • Distribute air to the gas exchange surface of the lung.

26. Respiratory zone • The respiratory zone includes the respiratory bronchiole which opens into a number of alveolar ducts and each alveolar duct opens into number of alveoli. Alveoli are tiny air sacs, having a diameter of 0.25 mm. There are about 300 million alveoli in the two lungs.

28. Acinus • The acinus is the functional or terminal respiratory unit of the lung and includes all structures from respiratory bronchiole to the alveolus (alveolar ducts, alveolar sacs and alveoli). • An acinus averages 0.75 mm diameter. • Each person has about 20,000 acini.

29. Acinus

30. The alveolar surface • The alveolar lining consists of two distinct types of epithelial cells, type-I and type-II alveolar pneumocytes. • The elongated type I cells cover 90% to 95% of the alveolar surface, and it is the primary site for gas exchange. • The cuboidal type-II cells are secreting surfactant, responsible for preventing the collapse of lungs. • After an injury, type-I cells degenerate, whereas type-II cells proliferate and line the alveolar space (repairing cell). • Third typesof cells, the pulmonary alveolar macrophage, are found which ingest the inhaled bacteria and small particles.

33. Muscular wall of respiratory passageways and its control: • The rings of cartilage in the walls of the trachea and bronchi prevent them from collapse. • The smooth muscle fibers in their walls can alter (change) the size of their lumen and vary airway resistance. • The terminal bronchioles have abundant of smooth muscle and no cartilage but the respiratory bronchioles are occupied by pulmonary epithelium and underlying fibrous tissue plus few smooth muscle fiber.

34. These respiratory smooth muscles are richly innervated by cholinergic parasympathetic nerve fibers. • Their stimulation causes mild to moderate bronchial constriction. • Histamine and slow reactive substance of anaphylaxis are potent broncho-constrictor. During allergic reactions, these are released by mast cells in the lung tissues. • Direct control of the bronchioles by sympathetic nerve fiber is relatively weak but bronchial smooth fibers contain β2 adrenergic receptors. • Therefore, they respond to circulating epinephrine and norepinephrine (from adrenal medulla) and inhaled or injected sympathomimetic drugs (salbutamol, isoproterenol etc,) resulting in bronchodilation.

35. learning objectives • Pulmonary circulation& pressure • Ventilation

36. Circulation through lungs • The lungs receive blood from two sources: • The bronchial circulation and • The pulmonary circulation. Bronchial circulation • It accounts for only a small part of the cardiac output (~2%). The walls of the large airways are supplied by bronchial circulation (oxygenated blood) through bronchial arteries from the aorta.

37. Pulmonary circulation • The output of the right ventricle passes through the pulmonary artery, branched and supplies the individual alveoli of the lung. • The capillaries lie in the walls of the alveoli. This network is so dense that the blood forms almost a continuous sheet in the alveolar wall. • There may be about 1000 pulmonary capillaries per alveolus. • The entire pulmonary vasculature is a distensible low-pressure system (normal pulmonary capillary pressure is 7 mm Hg).

40. Capillary fluid exchange in the lung and pulmonary interstitial fluid dynamics • The differences in fluid dynamicsbetween lung capillary membranes and peripheral tissues: • The pulmonary capillary pressure is low about 7 mm Hg (peripheral tissue pressure 17 mm Hg). • The interstitial fluid pressure in the lung is slightly negative than peripheral tissue. • Pulmonary capillaries are leaky to protein molecules, so oncotic pressure is 14 mmHg (28 mmHg in peripheral tissues). • Alveolar walls are extremely thin and the alveolar epithelium covering the alveolar surfaces is so weak that it can be ruptured by any positive pressure in the interstitial spaces greater than alveolar air pressure (greater than 0 mm Hg).

41. Interrelations between interstitial fluid pressure and other pressures in the lung • Forces tending to cause movement of fluid outward from the capillaries and into the pulmonary interstitium:mmHg Capillary pressure 7 Interstitial fluid colloid osmotic pressure (oncotic pressure) 14 Negative interstitial fluid pressure (ISF) 8 Total outward force 29 • Forces tending to cause absorption of fluid to the capillaries: Plasma Colloid osmotic pressure 28 Total inward force 28 • Therefore, the mean filtration pressure is (29-28) = +1 mm Hg.

42. Negative pulmonary interstitial pressure and the mechanism for keeping alveoli dry

43. This filtration pressure causes a slight continual flow of fluid from the pulmonary capillaries into the interstitial space. • Small amount evaporates in the alveoli. • Rest of the fluid is pumped back to the circulation through the pulmonary lymphatic system.

44. Negative interstitial fluid pressure and the mechanism for keeping alveoli dry • There are small pores between alveolar epithelial cells (pores of Kohn) through which water, electrolytes and even protein molecules can pass. • However, alveoli do not fill with fluid (kept dry) because the negative ISF helps the absorption of fluid. • Whenever, fluid appears in the alveoli, it will be simply sucked mechanically into the lung interstitium through the small pores. The excess fluid in lung ISF is carried away through pulmonary lymphatics. • Thus, under normal condition, the alveoli are kept in a ‘dry state’ except for a small amount of fluid that seeps from the alveoli to keep them moist.

45. Pulmonary edema • An organ which is very much sensitive to proper fluid balance is the lung. • Slight increases in the hydrostatic pressure of the pulmonary capillaries can lead to pulmonary edema. • This condition decreases the pulmonary compliance (making lung expansion more difficult). • It may severely compromises gas exchange across the pulmonary capillary bed. • Acute pulmonary edema is a life-threatening condition.

46. Causes of pulmonary edema (a) Left heart failure • Pulmonary edema is often associated with left heart failure. • Contractile properties of the left ventricle are inadequate to eject all of the blood that enters from the lungs. • This causes a sharp rise in left end- diastolic volume and pressure and a resultant increase in pulmonary venous and capillary pressures causing pulmonary edema.

47. (b) Damage to the pulmonary blood capillary membranes • Damage to the pulmonary blood capillary membranes caused by infection such as pneumonia. • Breathing noxious substances (chlorine gas, sulfur dioxide gas) cause rapid leakage of plasma proteins and fluid out of the capillaries into both the lung interstitial spaces and the alveoli. (c) Rapid infusion of intravenous fluids or blood transfusion • Hypervolemia due to rapid infusion of intravenous fluids or blood transfusion may cause pulmonary edema.

48. Functions of the Respiratory System Primary Function • Exchange of oxygen and carbon dioxide Secondary Functions • Voice production • Regulation of plasma pH (acid-base balance) • Temperature regulation • Sense of smell • Infection prevention (lysozyme, IgA, PAM) • Metabolic function (synthesis ofsurfactant, conversion of angiotensin I to II, formation of bradykinin, histamine, serotonin, heparin, prostaglandins).

49. Events of Respiration • The goals of respiration are to provide O2 to the tissues and to remove CO2. • To achieve these goals, respiration can be divided into four major functional events: • Pulmonary ventilation: the inflow and outflow of air between the atmosphere and the lung alveoli. • Diffusion of O2 and CO2 between the alveoli and the blood. • Transport of O2 and CO2 in the blood to and from the cells. • Regulation of respiration.

50. Pulmonary ventilation • Movement of air from the conducting zone to the terminal bronchioles occurs as a result of the pressure differences between the two ends of the airways. • Airflow through the bronchioles is directly proportional to the pressure difference and inversely proportional to the frictional resistance to flow (airway resistance). The pressure differences in the pulmonary system are induced by: • Lung volumes • Compliance and elasticity • Surface tension