Physiology: Respiratory System

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1 In the name of God Physiology: Respiratory System Moradian MD, MPH, PhD candidate Tehran University of Medical Sciences 2013

2 Respiratory Anatomy The primary function of the respiratory system is to exchange O2 and CO2 between blood and air

3 Respiratory Anatomy

4 Respiratory Anatomy Alveoli are where gas exchange between air & blood occurs

5 Respiratory airway: Alveoli Alveolar wall is formed by simple squamous epithelium = type I cells (SSE) gas exchange Large surface area from the numerous alveoli better gas exchange Presence of elastic fibers between alveoli

Alveolar structure Type I cells gas exchange Type II cells secrete surfactant (lipoproteins) decrease surface tension allowing for easier alveoli

6 Alveolar structure Type I cells gas exchange Type II cells secrete surfactant (lipoproteins) decrease surface tension allowing for easier alveoli inflation Surfactants start to be secreted by the 7 th month of pregnancy risk of lung disease in premature babies Presence of macrophages in alveoli

7 Respiratory Airways

8 Factors affecting air flow Costs Energy > Diaphragm Contraction! 1) Pressure needed to expand sphere (alveoli) Pulmonary Surfactant decreases ST required to expand alveoli during inspiration Pressure = Surface Tension Alveolar Radius Very Small>>>>>Huge Pressure Needed

9 Medical Relevance of Surfactant Normal Infant Infant Respiratory Distress Syndrome (IRDS) Premature infants (< 32 weeks), leading cause of infant mortality in US

10 Factors affecting Airflow Airway Resistance = 1/ airway diameter Resistance increases as airway diameter decreases Smooth Muscle Smooth Muscle control: ANS, Hormones & Local Chemicals

Smooth Muscle control: ANS, Hormones & Local Chemicals Bronchoconstriction (contraction of smooth muscle) ANS Parasympathetic > acetylcholine > muscarinic receptors (weak) Local

11 Smooth Muscle control: ANS, Hormones & Local Chemicals Bronchoconstriction (contraction of smooth muscle) ANS Parasympathetic > acetylcholine > muscarinic receptors (weak) Local Histamines due to irritation or damage Bronchodilation (relaxation of smooth muscle) Hormonal - Epinephrine (adrenal) > β 2 receptors (Epi-Pen for bee sting!) Local high CO2 during expiration

12 Lungs Compliance Lung compliance: ease with which lungs can be stretched Compliance is a measure of the elasticity of lung tissue and the alveolar surface tension C= V/ P ميسان تغيير حجم ريوىا بو ازاي تغيير در اختالف فشار در دو طرف ريوىا

13 Lung compliance Factors that decrease compliance surface tension of fluid lining alveolar surface elastic tissue in alveolar walls expansion of lungs (stretched lungs are less compliant) Factors that increase compliance pulmonary surfactant secreted by type II alveolar cells reduces surface tension of alveolar fluid mixture of phospholipid and protein low levels in premature infants (respiratory distress syndrome)

Inspiration and expiration Inspiration: chest wall expands due to muscle contraction (diaphragm and/or other muscles) Pressure in alveoli air moves

14 Inspiration and expiration Inspiration: chest wall expands due to muscle contraction (diaphragm and/or other muscles) Pressure in alveoli air moves toward alveoli Expiration: passive process muscle relax chest wall return to resting state alveoli become compressed alveolar pressure move moves out

15 Ventilation

16 Structure of the thoracic cavity فشار در فضاي جنب منفي است )2.5 تا 6-(

17 The pleura prevents friction of the lungs against the rib cage (due to the thin layer of liquid present in the pleural space) maintains lung expansion: due to the negative pressure within the pleural space

18 Lung pressures during ventilation Purple line: alveolar pressure (P alv ) -1 mm Hg during inspiration +1 mm Hg during expiration Green line: pleural pressure (P ip ) -4 mm Hg at functional residual capacity -7 mm Hg after inspiration P tp is transpulmonary (transmural) pressure i.e. P alv P ip (e.g. at 2, -1 (-5) = 4 mm Hg Lower curve (black): labeling accidentally omitted x axis should read 4 sec i.e. time y axis is tidal volume = 500 ml

19 Pleura and negative pressure Pneumothorax: lung collapse due to air entering in the pleural cavity

20 Gas Exchange Occurs between blood and alveolar air Across the respiratory membrane Depends on: partial pressures of the gases diffusion of molecules between gas and liquid

21 The Gas Laws Diffusion occurs in response to concentration gradients Rate of diffusion depends on physical principles, or gas laws e.g., Boyle s law

22 Composition of Air Nitrogen (N 2 ) about 78.6% Oxygen (O 2 ) about 20.9% Water vapor (H 2 O) about 0.5% Carbon dioxide (CO 2 ) about 0.04%

23 Gas Pressure Atmospheric pressure (760 mm Hg): produced by air molecules bumping into each other Each gas contributes to the total pressure: in proportion to its number of molecules (Dalton s law)

24 Partial Pressure The pressure contributed by each gas in the atmosphere All partial pressures together add up to 760 mm Hg

25 Partial Pressures of Respiratory Gases

26 O2 & CO2 Partial Pressure in the Alveoli Effect of alveolar ventilation on the alveolar PO2 at two rates of oxygen absorption from the alveoli 250 ml/min and 1000 ml/min. Point A is the normal operating point. Effect of alveolar ventilation on the alveolar PCO2 at two rates of carbon dioxide excretion from the blood 800 ml/min and 200 ml/min. Point A is the normal operating point

27 Henry s Law When gas under pressure comes in contact with liquid: gas dissolves in liquid until equilibrium is reached At a given temperature: amount of a gas in solution is proportional to partial pressure of that gas Figure 23 18

28 Gas Content & Solubility in body fluids The actual amount of a gas in solution (at given partial pressure and temperature) depends on the solubility of that gas in that particular liquid CO 2 is very soluble O 2 is less soluble N 2 has very low solubility

29 Mixing Oxygenated blood mixes with unoxygenated blood from conducting passageways Lowers the PO 2 of blood entering systemic circuit (about 95 mm Hg) Anatomical Shunt (Dead Sapce)

30 Gas Pickup and Delivery Blood plasma can t transport enough O 2 or CO 2 to meet physiological needs Red Blood Cells (RBCs) Transport O 2 to, and CO 2 from, peripheral tissues Remove O 2 and CO 2 from plasma, allowing gases to diffuse into blood

31 Oxygen Transport O 2 binds to iron ions in hemoglobin (Hb) molecules in a reversible reaction Each RBC has about 280 million Hb molecules (each binds 4 oxygen molecules saturated)

32 Oxygen Transport in Blood 98% of diffused oxygen enter RBC binds to Hemoglobin (Hb) 2% of oxygen remains in plasma At tissue, Hb + O2 dissociate O2 dissolves through plasma into ISF Hemoglobin in RBC allows blood to carry 5000% more oxygen!

Oxygen-hemoglobin dissociation curve The blood contains about 15 grams of hb in each 100 mlit.of blood, and each gram of hemoglobin can bind with a maximum of 1.34 mlit.

33 Oxygen-hemoglobin dissociation curve The blood contains about 15 grams of hb in each 100 mlit.of blood, and each gram of hemoglobin can bind with a maximum of 1.34 mlit. of oxygen Therefore, 15 times 1.34 equals 20.1, which means that, on average, the 15 grams of hemoglobin in 100 milliliters of blood can combine with a total of almost exactly 20 milliliters of oxygen if the hemoglobin is 100 per cent saturated

34 Factors That Shift the Oxygen- Hemoglobin Dissociation Curve Shift of the oxygenhemoglobin dissociation curve to the right caused by an increase in hydrogen ion concentration ( ph, 2,3biphosphoglycerate)

35 Hemoglobin in RBCs: KEY CONCEPT carries most blood oxygen releases it in response to low O 2 partial pressure in surrounding plasma If P O2 increases, hemoglobin binds oxygen If P O2 decreases, hemoglobin releases oxygen At a given P O2 : hemoglobin will release additional oxygen if ph decreases or temperature increases

36 Carbon Dioxide Transport in Blood Dissolved CO 2 ~ 7% Hemoglobin transport ~ 23% Bicarbonate Ion ~ 70%

37 Carbon dioxide dissociation curve Portions of the carbon dioxide dissociation curve when the PO2 is 100 mm Hg or 40 mm Hg.

38 Respiratory Rates and Volumes Respiratory system adapts to changing oxygen demands by varying: the number of breaths per minute (respiratory rate) the volume of air moved per breath (tidal volume)

39 Respiratory Minute Volume حجم دقيقهاي Amount of air moved per minute Is calculated by: respiratory rate tidal volume

40 Anatomical dead space Volume of air remaining in conducting passages is anatomic dead space (~ 150 ml)

41 Alveolar Ventilation Amount of air reaching alveoli each minute Calculated as: (tidal volume - anatomic dead space) RR Alveoli contain less O 2, more CO 2 than atmospheric air: because air mixes with exhaled air respiratory rate tidal volume dead space alveolar ventilation rate 14 /min 500 ml 150 ml 4.9 L/min 24 /min 300 ml 150 ml 3.6 L/min

42 Respiratory Volumes and Capacities Figure 23 17

43 Total lung volume is divided into a series of volumes and capacities useful in diagnosis Lung Volume Pulmonary Function Tests : Measure rates and volumes of air movements

44 Four Pulmonary Volumes حجم جاري volume: 1. Resting tidal in a normal respiratory cycle:500 cc حجم ذخيره بازدمي (ERV): 2. Expiratory reserve volume after a normal exhalation: 1100 cc حجم باقيمانده volume: 3. Residual after maximal exhalation: 1200 cc minimal volume (in a collapsed lung) حجم ذخيره دمي (IRV): 4. Inspiratory reserve volume after a normal inspiration: 3000 cc

45 Respiratory Capacities ظرفيت دمي capacity: 1. Inspiratory tidal volume + inspiratory reserve volume ظرفيت باقيمانده عملي (FRC): 2. Functional residual capacity expiratory reserve volume + residual volume ظرفيت حياتي capacity: 3. Vital expiratory reserve volume + tidal volume + inspiratory reserve volume ظرفيت كل ريوي capacity: 4. Total lung vital capacity + residual volume

46 Lung volumes

47 Respiratory Rhythmicity Centers of the Medulla Oblongata Set the pace of respiration گروه نورنهای تنفسی groups: Can be divided into 2 Dorsal respiratory group (DRG) Inspiratory center Functions in quiet and forced breathing Ventral respiratory group (VRG) Inspiratory and expiratory center Functions only in forced breathing

48 Quiet Breathing Brief activity in the DRG: stimulates inspiratory muscles DRG neurons become inactive: allowing passive exhalation Figure 23 25a

49 Forced Breathing Increased activity in DRG: stimulates VRG which activates accessory inspiratory muscles After inhalation: expiratory center neurons stimulate active exhalation Figure 23 25b

50 The Apneustic and Pneumotaxic Centers of the Pons Apneustic Centers RR+ Deep ventilation Inhibit the Apneustic centers Promote passive or active exhalation PneumotaxicCenter Decrease DRG active time hence RR Provides continuous stimulation to its DRG center

52 Control of Ventilation Chemoreceptor pathways ALWAYS override Voluntary pathways You can t hold you breath until you die!

53 The Cerebral Cortex and Respiratory Centers Strong emotions: can stimulate respiratory centers in hypothalamus Anticipation of strenuous exercise: can increase respiratory rate and cardiac output (اراده برای حرکت) stimulation by sympathetic (حس های مفصلی) Properioceptive

54 Sensory Modifiers of Respiratory Stretch receptors: Center Activities respond to changes in lung volume (deep inspiration: Hering-Breuer Inflation Reflex) Irritating physical or chemical stimuli: in nasal cavity, larynx, or bronchial tree Other sensations including: Pain, changes in body temperature, High Blood Pressure (بويايی بينايی شنوايی) Smell, visual, auditory

55 Chemoreceptor Reflexes Cranial nerve IX (from carotid bodies ) and nerve X (from aortic bodies): stimulated by changes in blood ph or P O2 Receptors that monitor cerebrospinal fluid Are on ventrolateral surface of medulla oblongata Respond to P CO2 and ph of CSF

56 Chemoreceptor Responses to PCO2 Figure 23 27

57 محرك هاي تنفس Blood PCO2 (Chemoreceptors & CNS:Acute) Blood PH ( Chemoreceptors & CNS :Chronic) Blood PO2 (Chemoreceptors Carotid>Aortic)

58 Ventilation-Perfusion (V/Q) Normal V/Q=1 (5 Lit/min) Apex=3, Base of Lung=0.6 Obstruction of Air (Physiologic Shunt): V/Q 0 Obstruction of Circulation (Physiologic Dead Space) : V/Q

59 Respiratory Performance and Age Figure 23 28

Respiratory System Physiology. Dr. Vedat Evren

Respiratory System Physiology. Dr. Vedat Evren Respiratory System Physiology Dr. Vedat Evren Respiration Processes involved in oxygen transport from the atmosphere to the body tissues and the release and transportation of carbon dioxide produced in