The Respiratory System

1. The Respiratory System Chapter 15 Pgs 457-485

2. Overview Functions of the Respiratory System Organization of the Respiratory System The respiratory tract The nose The pharynx The larynx The trachea The bronchi The bronchioles The alveolar ducts and alveoli The respiratory membrane The lungs The pleural cavity Respiratory Physiology Pulmonary ventilation Gas exchange Gas transport The Control of Respiration Local control Respiratory centers of the brain Reflex control of respiration Control by higher centers

3. Functions of the Respiratory System Provides large area for gas exchange between air and circulating blood Moves air to and from the gas-exchange surfaces of lungs Protects: Respiratory surfaces from dehydration and temp changes Provides nonspecific defenses against invading pathogens Produces sounds permitting speech, singing, and nonverbal communication Provides olfactory sensations to the CNS for sense of smell

4. Organization of Respiratory System Nose Nasal cavities Paranasal sinuses Pharynx Larynx Trachea Bronchi and lungs Bronchioles Alveoli

14. Respiratory Membrane Consists of 3 components Squamous epithelium lining alveolus Endothelial cells lining capillary Fused basement membrane between alveolus and endothelial cells Very rapid diffusion due to Short distance Solubility of oxygen and carbon dioxide Both are lipid soluble

19. Respiratory Physiology 3 steps Pulmonary ventilation Breathing; involves physical movement of air into and out of lungs Gas exchange Gas diffusion across respiratory membrane and capillary and other cells Gas transport Transport of oxygen and carbon dioxide between alveolar capillaries and capillary beds in other tissues

20. Pulmonary Ventilation Respiratory cycle Single breath Consists of: Inspiration exhalation

21. Pulmonary Ventilation: Pressure and Airflow to the Lungs Pressure gradient between atmosphere and lungs Occur when volume of lung changes Volume dependent on volume of pleural cavities Movement of thoracic wall or diaphragm directly affects volume in lungs Diaphragm forms floor of thoracic cavity Relaxed: dome shaped; projects up into thoracic cavity and compresses lungs (decreases volume; increases pressure) Contracted: flattens; increases volume of thoracic cavity (expansion of lungs) Thoracic wall (rib cage) Elevation of rib cage: increases volume of thoracic cavity External intercostals, sternocleidomastoid Lowering rib cage: decreases volume Internal intercostal muscles, abdominal muscles

24. Modes of Breathing Quiet Breathing Inhalation requires muscles Contraction of diaphragm (75%), external intercostals (25%) Exhalation passive Lungs recoil due to elasticity Forced Breathing Inhalation Accessory muscles include sternocleidomastoid and scalenes (muscles of the neck) Exhalation Internal intercostals, abdominal muscles

25. Lung Volumes and Capacities Tidal Volume Amount of air moved into or out of lungs during a single respiratory cycle 500 mL Expiratory Reserve Volume (ERV) Amount of air that can be voluntarily expelled at end of tidal cycle 1000 mL Inspiratory Reserve Volume (IRV) Amount of air taken in over and above tidal volume Males: 3300 mL; Females: 1900 mL

26. Lung Volumes and Capacities Vital Capacity Maximum amount of air that can be moved into and out of the respiratory system in a single respiratory cycle Sum of IRV + ERV + Tidal Volume Residual Volume Air that is not exhaled even after expiratory reserve volume 1200 mL in alveoli, resp passageways Exists because lungs held against thoracic wall Prevents elastic fibers from further contracting Minimal Volume Occurs when chest cavity opened (pneumothorax) Minimal volume air left in lungs due to surfactant preventing alveoli from collapsing

29. Gas Exchange Alveoli supplied with oxygen; carbon dioxide removed from bloodstream Occurs on respiratory membrane Depends on: Partial pressures of gases involved Diffusion of molecules from gas into a liquid

30. Mixed Gases and Paritial Pressures Atmospheric pressure at sea level = 760 mm Hg Atmosphere made up of different gases One gas alone makes up partial pressure Sum of all partial pressures = atm pressure Partial pressure determines rate of diffusion

31. Partial Pressures within the Circulatory System External respiration Diffusion of gases between the alveoli and capillaries across respiratory membrane Internal respiration Diffusion of gases between cells and capillaries

33. Gas Transport RBCs remove dissolved O2 and CO2 from plasma (limited solubility) Binds (O2) Manufactures soluble compounds (CO2) Reactions temporary and easily reversible Plasma gas concentrations high, excess removed by RBC Plasma concentrations low, RBCs release reserve

34. Oxygen Transport 98.5% oxygen bound to iron heme in hemoglobin (Hb) Reversible reaction Hb + O2 ? HbO2 Amount O2 bound or released by Hb depends on: Partial pressure of oxygen Temperature pH PO2 in surroundings The lower the O2 content in tissues, the more O2 is released by Hb in nearby capillaries Temperature Hb releases more O2 when temp rises pH Active tissues lower pH of ISF When pH declines, Hb release bound O2 more readily

35. Carbon Dioxide Transport Generated by aerobic metabolism Enters bloodstream and either: Dissolves in plasma Binds to Hb of RBC Converted to molecule of carbonic acid (H2CO3) All three completely reversible

37. Carbon Dioxide Transport Plasma Transport 7% absorbed in peripheral capillaries is transported as a dissolved gas Hemoglobin Binding Some are bound to globin in Hb Forms carbaminohemoglobin Does not interfere with binding of O2 Carbon dioxide partial pressure low in pulmonary capillaries Released from Hb

38. Carbon Dioxide Transport: Carbonic Acid Formation Most converted to carbonic acid Enzyme is carbonic anhydrase Carbonic acid is then broken down to a hydrogen ion and a bicarbonate ion CO2 + H2O ? H2CO3 ? H+ + HCO3- Happens quickly and continuously Once dropped off in alveoli, reactions occur in other direction

41. Control of Respiration Normal conditions: cellular rates of absorption and generation are equal to capillary rates of delivery and removal If unbalanced, homeostasis must be maintained by cardiovascular and respiratory systems Mechanisms involve: Changes in blood flow and oxygen delivery under local control Changes in depth and rate of respiration under control of brain�s respiratory centers

42. Local Control of Respiration Rate of delivery and efficiency of oxygen pick up regulated locally Activity in peripheral tissues ISF ? PO2 and ? PcO2 more O2 delivered; more CO2 carried away (also results in vasodilation) Local adjustments in lungs Precapillary sphincters direct blood to alveoli when PO2 is high (constrict when low) Bronchodilation in response to high PCO2 Directs airflow to lobules

43. Respiratory Centers of the Brain Found in 3 pairs of basal nuclei in medulla and pons Medulla contains respiratory rhythmicity centers Set pace for respiration Pons adjusts rate and depth in response to sensory stimuli, emotions, speech Control both voluntary and involuntary Involuntary center in brain controls: Respiratory muscles Respiratory rate 12-18 breaths/min (normal adult) Respiratory depth

44. Respiratory Rhythmicity Centers Dorsal respiratory group (DRG) Contains inspiratory center Functions in every respiratory cycle Ventral respiratory group (VRG) Contains expiratory center Used only during forced breathing Can be affected by any factor that alters metabolic or chem act of neural tissue Increase: Elevated body temp, stimulants (meth, caffeine) Decrease: low body temp, depressants (opiates, alcohol)

47. Reflex Control of Respiration Normal breathing automatic Activities of respiratory centers modified by sensory information from mechanoreceptors Stretch receptors Pressure (baro)receptors Chemoreceptors Info from the receptors alter pattern of respiration

48. Mechanoreceptors Respond to changes in volume of lungs or to changes in arterial blood pressure Hering-Breuer reflexes Only involved in forced breathing Inflation reflex (stretch receptors and vagus nerve) Prevents lungs from over expanding during forced breathing Vol of lungs increase, inspiratory center gradually inhibited, expiratory stimulated Deflation reflex Inhibits expiratory center; stimulates inspiratory center

49. Baroreceptors Carotid and aortic baroreceptors Affects respiratory centers, cardiac centers, vasomotor centers ? bp ?resp rate Adjustment results from stimulation or inhibition of inspiratory and expiratory centers in glossopharyngeal and vagus nerves

50. Chemoreceptor Reflexes Respond to chemical changes in blood, CSF Centers: Carotid bodies and aortic bodies Sensitive to pH, PCO2, PO2 in arterial blood Medulla Sensitive to pH and PCO2 in CSF Stimulation Stimulation: increase in depth and rate of respiration

51. Chemoreceptor Reflexes Much more sensitive to changes in PCO2 than PO2 Due to small increase in PCO2 stimulates receptors (regulates under normal conditions) PO2 generally does not decline enough to stimulate receptor Cannot hold your breath

52. Control by Higher Centers Influence respiration through effects on resp centers of pons and directly through resp muscles Contractions of resp muscles can be voluntarily suppressed or exaggerated (talking, singing) Resp rate can change following activation of limbic system and hypothalamus (rage, eating, sexual arousal) involuntary