The Respiratory System

1. The Respiratory System Anatomy Ch. 13

2. The Conducting Zone • Nose • Only external visible part of the respiratory system • Air enters the nose by passing through the nostrils • The interior of the nose consists of the nasal cavity which is divided by the nasal septum • The respiratory mucosa lines the nasal cavity and warms the entering air • This mucosa also moistens the air and traps foreign particles

3. The mucosa also contains ciliated cells which sweep contaminated mucus toward the throat • The lateral walls of the nasal cavity contain 3 projections called conchae which increase surface area • The nasal cavity is separated from the oral cavity by the hard and soft palate

5. The nasal cavity is surrounded by a ring of paranasal sinuses • The sinuses are located in the frontal, sphenoid, ethmoid, and maxillary bones • The sinuses lighten the skull, act as resonance chambers for speech, and produce mucus.

7. Pharynx • The throat • Serves as a common passageway for food and air • Path of air: • Nasopharynx • Oropharynx • laryngopharynx • The eustachian tube drains the middle ear and open into the pharynx • The tonsils are also found in the pharynx

9. Larynx • The voice box • Routes air and food into proper channels and plays a role in speech • Composed of 8 pieces of cartilage and a flap of cartilage called the epiglottis • The largest cartilage is the thyroid cartilage which is commonly called the adam’s apple • The epiglottis protects the superior opening of the larynx

10. The epiglottis forms a lid over the larynx when we swallow • When we breathe the epiglottis does not cover the opening • A pair of folds found in the larynx forms the true vocal cords • The vocal cords vibrate when we expel air and allow us to speak. • The vocal cords and the slit like passageway between them forms the glottis

12. Trachea • The windpipe • Composed of C-shaped rings of cartilage • The open parts of the rings allow the esophagus to expand • The solid portion of the rings support the trachea wall and keep it open • The trachea is lined with ciliated mucosa • The cilia move opposite the direction of air to propel mucus and other foreign particles to the throat

14. Main (Primary) Bronchi • The right and left primary bronchi are formed by the division of the trachea • Each bronchi enters the medial sides of the lungs • The bronchi enter at the hilum of the lungs • By the time air reaches the bronchi it is warm, clean, and well humidified • Smaller divisions of the bronchi are routes to the alveoli (air sacs)

15. Lungs • Each lung is divided into lobes • Left lung – 2 • Right lung - 3 • The lungs are mostly air spaces • The walls of the lungs are composed of elastic tissue which allows the lungs to recoil when we exhale

16. The surface of each lung is surrounded by the visceral pleura • The walls of the thoracic cavity are lined by parietal pleura • The area between the visceral and parietal pleura is filled with serous pleural fluid which allows the lungs to glide easily during breathing

17. After entering the lungs the primary bronchi divide into smaller branches (secondary, tertiary,…) • The smallest of the conducting passageways are the bronchioles • This branching is sometimes called the respiratory tree

19. The Respiratory Zone • The respiratory zone includes • Respiratory bronchioles • Alveolar ducts • Alveolar sacs • Alveoli • The alveoli is the only site of gas exchange • The alveoli makes up the bulk of the lungs

20. The Respiratory Membrane • The walls of the alveoli are composed of a single layer of squamous epithelium • Alveolar pores connect neighboring alveoli and provide alternative routes for air • The alveoli are covered with pulmonary capillaries • The alveolar and capillary walls make up the respiratory membrane

21. Gas exchange occurs by simple diffusion • Oxygen moves from the alveoli into the blood • CO2 moves from the blood into the alveoli • The final line of defense for the respiratory system is in the alveoli. Macrophages found in this region pick up bacteria and other debris • Cuboidal cells are also found in the alveoli which produce a molecule called surfactant which is important in lung function

23. Respiratory Physiology • The 4 events of respiration • Pulmonary ventilation • Air moving into and out of the lungs (breathing) • External respiration • Gas exchange between the pulmonary capillaries and alveoli • Respiratory gas transport • Movement of O2 and CO2 by the blood stream • Internal respiration • Gas exchange at the systemic capillaries

24. Mechanics of Breathing • Breathing depends on volume changes occurring in the thoracic cavity • Volume changes lead to pressure changes which lead to the flow of gases to equalize the pressure • Boyles Law • As volume increases the pressure decreases because gas molecules are farther apart • As volume decreases the pressure increases because gas molecules will be closer together

25. Inspiration • When the inspiratory muscles, the diaphragm and external intercostals, contract the size of the thoracic cavity increases • Because the lungs adhere tightly to the thoracic wall they are stretched to the larger size of the thorax • As the volume in the lungs increases there is a decrease in gas pressure in the lungs

26. The resulting decrease in gas pressure produces a vacuum which sucks air into the lungs • The pressure in the lungs is less than the atmospheric pressure outside of the body • Air continues to move into the lungs until both pressures are equal

27. Expiration • Expiration is a passive process that depends more on the natural elasticity of the lungs than on muscle contraction • As the inspiratory muscles relax and resume their resting size the lungs recoil • Volume in the lungs decreases and pressure rises to a point higher than atmospheric pressure • This causes the gases to flow out to equalize pressure inside and outside the lungs

28. Expiration is normally an effortless process but if conditions cause the air passageways to work ineffectively expiration becomes an active process. • During forced expiration the internal intercostals and abdominal muscles contract to help force air from the lungs

29. Normally the pressure of the pleural space, which is the space between the visceral and parietal pleura, is negative • This negative pressure prevents the collapse of the lungs • Lung collapse occurs when the interpleural pressure becomes equal to atmospheric pressure

30. Respiratory Volumes and Capacities • Tidal volume: amount of air that moves into and out of the lungs during normal quiet breathing • Inspiratory reserve volume: amount of air that can be taken in forcibly over the tidal volume • Expiratory reserve volume: The amount of air that can be forcibly exhaled after a tidal expiration

31. Residual volume: amount of air that still remains in the lungs after the most strenuous expiration, important because it helps to keep the alveoli inflated • Vital capacity: total amount of exchangeable air • TV + IRV + ERV = vital capacity • Dead space volume: amount of air that enters the respiratory tract and never reaches the alveoli

32. Non-respiratory Air Movements • Coughs: clear the lower respiratory passageways • Sneezes: clear the upper respiratory passageways • Crying and laughing: emotionally induced responses • Hiccups: spasms of the diaphragm, occurs when inspired air hits the vocal cords of a closed glottis • Yawn: ventilation of all alveoli

33. Respiratory Sounds • Bronchial sounds: produced by air rushing through the large passageways • Vesicular breathing sounds: occur as air fills the alveoli

34. External Respiration, Gas Transport, and Internal Respiration • All gas exchanges are made according to the laws of diffusion • High to low concentration

35. External Respiration • Change of color of blood is due to O2 pickup by hemoglobin in the blood in the lungs • CO2 is unloaded from the blood • There is always more O2 in the alveoli than in the blood • O2 moves from the air of the alveoli through the respiratory membrane into the O2 poor blood of the pulmonary capillaries

36. In contrast, as tissue cells absorb O2 from the blood in systemic circulation, they release CO2 into the blood • Because the concentrations of CO2 is much higher in pulmonary capillaries than in the alveoli, it will move from the blood into the alveoli where it is removed during expiration

37. Gas Transport • Most O2 is transported in blood by attaching to hemoglobin • Some O2 is carried dissolved in plasma • Most CO2 is transported in plasma as bicarbonate (HCO3-) • The conversion of CO2 to HCO3- happens in RBCs but the HCO3- is transported in plasma • A smaller amount of CO2 is transported by RBCs

38. Before CO2 can diffuse out of blood into the alveoli the HCO3- must enter RBCs and be turned back into CO2 • In order for HCO3- to turn into CO2 it goes through a quick chain of events: • HCO3- + H+→ H2CO3→ CO2 + H2O

39. Internal Respiration • Internal respiration happens in the tissues of the body • The process is the exact opposite of what happens in the lungs • CO2 + H2O → H2CO3→ HCO3- + H+ • Most of this process occurs in RBCs where a special enzyme called carbonic anhydrase speeds up the reaction

40. The HCO3- then diffuses into the plasma where it is transported • At the same time O2 diffuses out of the blood and enters the tissues

41. Control of Respiration • The activity of the respiratory muscles is regulated by impulses from the brain through the phrenic and intercostal nerves • Neural centers in the brain are located in the medulla and pons • Medulla: basic rhythm of breathing • Pons: smooths out the basic rhythm • Eupnea: normal respiratory rate

42. Bronchioles and alveoli have stretch receptors that respond to extreme over inflation • When over inflation occurs the vagus nerve sends messages to the medulla • During exercise we breathe more vigorously and deeply (hyperpnea)

43. Non-neural Factors • Physical factors • Talking, coughing, exercising, temperature • Volition (conscious control) • Voluntary control of breathing is limited and the respiratory centers will simply ignore messages from the cortex when the oxygen supply in the blood is low or when blood pH is falling

44. Emotional factors • Emotional breathing responses result from reflexes acting through centers in the hypothalamus • Chemical factors • Levels of CO2 and O2 in blood • Increased levels of CO2 and decreased blood pH are the most important stimuli leading to an increase in the rate and depth of breathing. • Changes in CO2 levels act on the medulla centers in the brain

45. Changes in O2 levels are detected by chemoreceptors in the aorta and in the carotid artery • These send impulses to the medulla when blood O2 levels are dropping • The most important stimulus for breathing is to rid the body of CO2 • Decreases in O2 levels become important stimuli only when the levels are dangerously low

46. As CO2 or other sources of acids begin to accumulate in blood and blood pH starts to drop you begin to breathe more deeply and more rapidly. This breathing pattern is called hyperventilation. • Hyperventilation removes more CO2 which in turn decreases acid levels

47. Conditions Affecting the Respiratory System • Cleft palate • Genetic defect where bones of the palate do not fuse • Rhinitis • Inflammation of the nasal mucosa • Sinusitis • Sinus inflammation

48. Tonsillitis • Inflammation and swelling of the tonsils due to infection • In mouth breathing, air is not properly moistened, warmed, or filtered • Laryngitis • Inflammation of the larynx or voice box due to overuse, irritation, or infection • Bronchitis • Inflammation of the bronchial tubes due to virus or infection. • 2 types: acute and chronic (COPD) • Large amounts of mucus produced

49. Pleurisy • Inflammation of the pleura from virus or bacteria • Surfaces become dry and rough when there is not enough fluid producing friction and stabbing pain with each breath. • When too much fluid is produced, excess pressure is placed on the lungs.

50. Atelectasis • Lung collapse • Occurs when air enters the pleural space through either a wound or rupture. • Pneumothorax occurs when the air disrupts the fluid bond between the pleura. • Hypoxia • Inadequate oxygen delivery to body tissue • Cyanosis • Bluish color change of the skin due to lack of oxygen to tissue.