L-8 Respiratory System

1. Respiration and Control Mechanisms (DVT 1037) L-8 Respiratory System Dr Than Kyaw 16 April 2012

2. Brief Overview of Breathing Inhalation - Contraction of circular M/S of diaphragm pulls its relaxed, doomed position into one that is more flattened and increase the length of thoracic cavity. • Contraction of external intercostalM/S pulls ribs upwards and outwards • Increase thoracic volume • BOTH actions reduce thoracic pressure causing air inflow into the lungs • Exhalation • Diaphragm relaxed; returns to doom-shaped position • External intercostalM/S relaxed; moving ribs downwards and inwards. • Both movements decrease thoracic volume, thereby increasing thoracic pressure. • Lungs recoil and air is driven out through the trachea • Exhalation is primarily passive during quiet breathing, requiring very little effort. However, in loboured breathing, the internalintercostal m/s may also contract to aid the lowering of the rib cage.

3. Contraction of circular M/S of Diaphragm flattened - Contraction of external intercostal M/S pulls ribs upwards and outwards - Diaphragm Relaxed; returns to doom-shaped position - External intercostal M/S relaxed; moving ribs downwars and inwards

4. Respiration rate -- Respiration frequency/min or -- Number of respiratory cycles/min -- One cycle = inspiration+expiration • An indicator of the health status • Need to interpret properly as it is subject to numerous variations • Also species variations

5. Normal resting respiration rate of animals

6. Factors affecting Respiration Rate • Body size • Age • Exercise • Excitement • Environmental temperature • Pregnancy • Degree of digestive fill – - Pregnancy and digestive fill -- restrict the movement of diaphragm during inspiration; therefore adequate ventilation is maintained by increase frequency • State of health

7. Lung sounds -- Good quality stethoscope -- Quiet surrounding -- Sound made by high velocity, turbulent air flow in the trachea and bronchi -- Low velocity flow in the bronchioles made -- no sound -- Adventitious sounds 1. Crackles -- due to edema/exudate within the airways 2. Wheezes -- due to broncho-constriction, bronchial wall thickening, external air way compression -- pneumonia

8. Bronchodilation Bronchodilation and bronchoconstriction • Dilation of bronchial airways • Caused by sympathetic ANS activation • Reduces resistance Bronchoconstriction • Constricts bronchi • Caused by: • parasympathetic ANS activation • histamine release (allergic reactions) Asthma in human (difficult breathing - rale and rushing sound can be heard even without stethoscope; vasodilators)

9. Injury to the Chest Wall • Pneumothorax: • allows air into pleural cavity • Hemothorax - if filled with blood • Atelectasis: • also called a collapsed lung • result of pneumothorax

10. Respiratory pressures Partial pressure • The pressure exerted by a particular gas in a mixture of gases • The sum of partial pressures of the gases within a mixture equals the total pressure. • PaO2 = Partial pressure of oxygen in arterial blood • PvCO2 = Partial pressure of carbondioxide in venous blood • Gas content in arteries approximately the same because none of it has reached capillary system where gas exchanges (loss of O2 and gain of CO2) take places. • Gas content in venous blood – differ depending on the location because of different metabolism associated with the function of body part

11. Atmospheric pressure • 760 mm Hg = one atmosphere under standard temperature and pressure Gas composition of dry air (atmospheric air) andalveoli Humidifcation (presence of water vapour; PH2O) causes dilution of the other gases. Note: the component of vapour pressure (PH2O) which causes difference from atmospheric values.

12. Direction of diffusion For oxygen and carbondioxide

13. Intra - thoracic pressure /Intra pleural pressure • Intra thoracic pressure always remains negative during inspiration as well as during expiration. • At Inspiration - 19 mm Hg • At Expiration - 4 mm Hg • Physiological significance Venous return RegurgitionVomittion, Defecation& Parturition

14. Pulmonary ventilation Ventilation -- the process by which gas in closed places exchanged or renewed Pulmonary ventilation -- exchange of gases (02, and CO2) in the air ways and alveoli with gases from the environment Dead space ventilation -- anatomic dead space: ventilation in the parts of the lungs not involved in gas exchange -- physiologic dead space: anatomic dead space + any alveoli in which normal gas exchange cannot occur

15. RESPIRATORY CENTERS AND REGULATION OF RESPIRATION -- To maintain constant levels of H+, CO2, and O2 Ventilation control A B C Peripheral receptors Chemical - chemoreceptors Neural -stretch receptors -baroreceptors

16. Respiratory centers In the pons and medulla • Pneumotaxic center (in pons) • -- activate termination of • inspiration and facilitate • expiration • Apneustic center (in pons) • -- deep inspiration (sigh) • Dorsal respiratory group (medulla) • -- associated with inspiratory activity • Ventral respiratory group (medulla) • -- assist inspiration begun by DRG; also provide for assisted expiration PRG = Pontine respiratory group DRG = dorsal respiratory group VRG = ventral respiratory group

17. Pneumotaxic centre -ve Apneustic centre +ve Respiratory centre -ve +ve LUNGS Neuronal control of respiration

18. 1. Hering-Breuer Reflex A. Ventilation control (neural) Over stretched lungs Stretch receptors (Visceral pleura, Bronchi, alveoli) Impulses through Vagus Respiratory center (Inhibit inspiratory center) inspiration is stopped

19. A. Ventilation control (neural) 2. Receptors in upper air passage Stimulation of Upper air passage Reflex inhibition of breathing (A) Inhibit breathing Powerful expiratory effort (coughing) Stimulation of Laryngeal mucosa (B) Stimulation of nasal mucosa Sneezing Coughing and sneezing are protective respiratory reflexes which protect delicate respiratory passages and alveoli from harmful substances (e.g., irritating gases, dusts, smoke, food particles)

20. A. Ventilation control (neural) 3. Baroreceptors (pressure receptors) • Baroreceptors in • Carotic & aortic sinuses High pressure • Inhibit • respiration • Reduction of inspiration slow down the return of the blood to the heart. This helps to lower blood pressure.

21. B. Ventilation control (chemical) 1. Central Chemoreceptors (medulla) Respond to H+ concentration changes Central Chemoreceptors (medulla) -- CO2 in readily diffuses into the ISF of the brain but not H+ due to BBB -- increases H+ concentration CO2 + H2O = H+ + HCO3- (Henderson – Hasslebach equation) ventilation In H+ in brain

22. cerebral blood flow Cerebrospinal fluid CO2 + H2O H+ + HCO3- CO2 central chemoreceptors in medulla H+ central chemoreceptors respond to blood CO2 and CSF H+ Insensitive to blood H+ or O2 blood-brain barrier

23. B. Ventilation control (chemical) 2. Carotid and aortic chemoreceptors • Carotid bodies and aortic bodies • - Sensitive to pH, PCO2, PO2 in arterial blood • - More sensitive to CO2 changes • Stimulation: increase in depth and rate of respiration

24. C. Ventilation control (Peripheral receptors) Excitatory to respiratory center Receptors in the skin Stimulation Deep inspiation E.g., Rubbing the skin in newborn animals often initiate breathing

25. Involuntary and Voluntarily Control • Normal respiration -- involuntary in nature • but can be altered voluntarily within wide limits. • E.g., hasten, slowed, stopped -- for awhile -- Voluntary system -- located in the cerebral cortex. -- Sends impulses to the respiratory motor neurons via the corticospinal tracts. -- The automatic system is driven by a group of pacemaker cells in the medulla. -- Impulses from these cells activate motor neurons in the cervical and thoracic spinal cord that innervate inspiratory muscles. -- Those in the cervical cord activate the diaphragm via the phrenic nerves. -- Those in the thoracic spinal cord activate the external intercostal muscles. However, the impulses also reach the innervation of the internal intercostal muscles and other expiratory muscles.

26. Medullaryrhythmicity (The Central Controller/Central pattern generator) - Involuntary (or Automatic) Control of Breathing - rhythmic output of the CNS to the muscles of ventilation takes place automatically & subconsciously. - this respiratory rhythmogenesis takes place in the medullaoblongata, beneath the floor of the 4th ventricle

27. Gas exchange and transport • Gas exchange between blood and alveoli -- across alveolar wall • Both O2 and CO2 dissolve in plasma • Quantity very small in compared with the amounts transported in other forms in blood • O2 7%; CO2 1.5% in plasma • O2 98.5% in Hb-bound form in RBCs Lung - CO2 70% in RBCs Tissues - Low pH - High temperature - High CO2 Less affinity for O2 to Hb

28. Percent saturation of Hb at different partial pressure of oxygen at pH 7.

29. Bohr effect Oxygen-hemoglobin dissociation curve showing the effect of pH. As pH decreases Hb has less affinity for oxygen and more oxygen is released into the tissues.

30. Haldane Effect

31. CO2 in RBC=93% Lung CO2 released in tissues are carried to lung in 3 forms: Dissolved form in plasma Bound to Hb As bicarbonate in plasma ( in the lung, reaction is reversed to release CO2)

32. Ventilation/perfusion ratio - VA /Q ratio amount of air reaching the alveoli VA /Q = the amount of blood reaching the alveoli. VA /Q may be between zero and 1. • When VA /Q is zero or 1 = no gas exchange; • (no alveolar ventilation) the ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli. • The situation, in a normal lung, is intermediate between these two extremes and VA /Q = 0.8 • Whenever VA /Q is below normal - a physiological shunt occurs. • Whenever VA /Q is greater than normal - physiological dead space occurs.

33. Control of Respiration in brief Involuntary (Voluntary )

34. Ventilation in brief In H+ or CO2 ventilation In O2 Maintain Normal level In H+ or CO2 ventilation In O2

35. Non-respiratory functions

36. Non-respiratory functions 1. Respiratory Clearance - Upper respiratory tract clearance - Alveolar respiratory clearance 2. Acid-base balance (acidosis and alkalosis) 3. Panting

37. Non-respiratory functions 1. Respiratory Clearance -- Removal of particles -- inhaled and deposited in the lungs -- Surface area of lung -- 125 times larger than body surface area -- Exposure for many environmental substances -- agricultural chemicals, feedlot dusts, industrial dusts (asbestos, coal) The 02, CO2

38. Upper Respiratory Clearance -- removal of particles deposited cranial to the alveolar ducts -- by moving mucous blanket -- mucus -- secreted by goblet cells and of epithelium lining the airways -- mucous blanket contains deposited particles and is moved towards the pharynx (15mm/min) by cillia of the epithelium.

39. A B A Respiratory epithelium (horse). The cilia project from the surface of the epithelial cell as fine strands; active mucus-secreting cells (B) lie between the ciliated cells (A). Scanning electron micrograph. ×1500. B B

40. Neuroendocrine cell Goblet cell Basal cell ciliated cell

41. Respiratory Clearance(continued) (2) Alveolar Respiratory Clearance Particles deposited in the alveoli, usually smaller than 1 in diameter, are removed by - (a) Phagocytosis by macrophages or continued as free particles (b) Directed to moving mucous blanket with alveolar fluid-film (c) Particles in the interstitial space of alveoli -- transported to lymph nodes -- dissolved and transferred in solution either to lymph/blood (d) Unphagocytized and /or insoluble particles -- Sequestered (isolated) within the lung C/T -- e.g., asbestosi, silicosis, and anthracosis (coal dust)

42. Non-respiratory functions • 2. Acidosis and Alkalosis • Respiratory Acidosis Short-term rise in arterial PCO2 (i.e, above 40 mm Hg) due to decreased ventilation results in respiratory acidosis. Respiratory Alkalosis Short-term increase in ventilation that lowers PCO2 below what is needed for proper CO2 exchange (i.e, below 35 mm Hg) results in respiratory alkalosis. Metabolic Acidosis Metabolic acidosis (or nonrespiratory acidosis) Due to strong acids e.g. Ingestion of a large amount of acid (eg, aspirin overdose); acids in the blood - quickly increased, lowering the available Hb–, Prot–, and HCO3– buffers. Metabolic Alkalosis Occurs when removal of large amounts of acid (e.g, following vomiting)

43. Acidosis and Alkalosis (contd) • Compensation for Acidosis and Alkalosis • Because of compensation systems - Uncompensated acidosis and alkalosis -- seldom seen • 2 compensatory systems • Respiratory • Renal • Metabolic - compensation by respiratory system • acidosis - increase ventilation- • - decrease of PCO2(eg, from 40 mm Hg to 20 mm Hg) - subsequent increase in pH toward normal • Metabolic - compensation by decreased ventilation • alkalosis - PCO2 is increased, • - Subsequent decrease in pH occurs by respiratory compensation - quick response,

44. Acidosis and Alkalosis (contd) • Compensation • Renal • For complete compensation from respiratory or metabolic acidosis/alkalosis, • Acidosis - by actively secreting fixed acids while retaining filtered HCO3– • Alkalosis- by decreasing H+ secretion and by decreasing the retention of filtered HCO3–

45. Non-respiratory functions 3. Panting -- Prevalent in many animal species -- Best seen in dog -- alveolar and dead space ventilation increased by panting which provide for body cooling by evaporation of water from mucous membranes of tissues involved. 3 patterns of panting (1) inhalation and exhalation through the nose (2) inhalation through the nose and exhalation through the nose and mouth (3) inhalation through the nose and mouth and exhalation through the nose and mouth

46. Avian Respiration

47. Avian respiration Respiratory apparatus Differences from mammalian respiratory appratus -- syrinx - located at the bifurcation of the trachea -- tracheal rings -- complete -- lungs do not expand or contract -- fixed in position attaching to the ribs -- ventilation -- through bellow-like extensions from lungs -- k/s air sacs -- air sacs -- expand and extract -- connected with primary, secondary and tertiary bronchi (tertiary bronchi = also k/s parabronchi)

48. Respiratory apparatus Differences from mammalian respiratory apparatus and relatively complex -- air sacs – occupy space in the thoracic and abdominal cavities -- many extend into bones (pneumatic bones; the most prominent one humerus) 2 cranial 2 cranial thoracic 1clavicular Cranial group 2 caudal thoracic 2 abdominal Caudal group

50. Lung of bird