1. Chapter 6: Respiratory System1 1

2. Structure and Function of the Respiratory System
Structures
Nose/nostrils
Nasal cavity
Pharynx
Larynx
Trachea
Bronchi
Bronchioles
Alveoli 2 2

3. Structure and Function of the Respiratory System (cont’d)
Anatomical structures of respiratory system. 3 3

4. Structure and Function of the Respiratory System (cont’d)
Functions
Conducts air into & out of lungs
Exchanges gases between air & blood
Humidifies air: prevents damage to membranes due to drying out
Warms air: helps maintain body temperature
Filters air
Mucus traps airborne particles
Cilia move mucus toward oral cavity to be expelled 4 4

5. Structure and Function of the Respiratory System (cont’d)
Alveoli
Saclike structures surrounded by capillaries in lungs
Attached to respiratory bronchioles
Site of exchange of oxygen & carbon dioxide
300 million in lungs
Provide tremendous surface area where diffusion can take place
Respiratory membrane: 2 cell membranes that aid diffusion
Membrane of alveolar cells
Membrane of cells of capillary wall 5 5

6. Structure and Function of the Respiratory System (cont’d)
Respiratory membrane.

7. Mechanics of Ventilation
Pleural Sac
Double-layered membrane that encases each lung
Visceral (pulmonary) pleura: outer surface of lungs
Parietal pleura: inner surface of thoracic cavity & diaphragm
Pleural fluid: lubricating fluid between 2 membranes
Intrapleural pressure: pressure in pleural cavity between 2 membranes; less than atmospheric pressure 7 7

8. Mechanics of Ventilation (cont’d)
Pressure Changes During Ventilation
Increase in volume of intrathoracic cavity:
Increases lung volume
Decreases intrapulmonic pressure
Causes air to rush into lungs (inspiration)
Decrease in volume of intrathoracic cavity:
Decreases lung volume
Increases intrapulmonic pressure
Causes air to rush out of lungs (expiration) 8 8

9. Mechanics of Ventilation (cont’d)
Inspiration
Inspiratory muscles increase intrathoracic cavity volume
Diaphragm: most important inspiratory muscle
Flattens as it contracts
Puts in motion pressure changes that cause inspiration
Contraction moves abdominal contents forward & downward
Muscles that elevate ribs: external intercostals, scalenes, sternocleidomastoid, pectoralis minor 9 9

10. Mechanics of Ventilation (cont’d)
Expiration
No muscular effort needed at rest
Passive recoil of diaphragm & other muscles decreases intrathoracic cavity volume
During exercise or voluntary forced expiration, accessory muscles of expiration contract, pulling ribs downward:
Internal intercostals
Rectus abdominis
Internal oblique muscles of abdominal wall 10 10

11. Mechanics of Ventilation (cont’d)
Inspiration and expiration. 11 11

12. Mechanics of Ventilation (cont’d)
Muscles involved in inspiration & expiration. 12 12

13. Mechanics of Ventilation (cont’d)
Airflow Resistance
Airflow = P1 − P2/Resistance
Where P1 − P2 is pressure difference between 2 areas & Resistance is resistance to airflow between 2 areas
Thus, airflow can be increased by:
Amplifying pressure difference between 2 areas
Decreasing resistance to airflow
Diameter of airway is biggest factor affecting airflow at rest
In exercise, bronchodilation decreases resistance to airflow 13 13

14. Mechanics of Ventilation (cont’d)
Pulmonary Ventilation
Amount of air moved in & out of lungs in given time period
Tidal volume: amount of air moved per breath
Volume of air moved per minute can be calculated as:
VE = VT × f
Where VE = volume of air expired per minute; VT = tidal volume; f = breathing frequency per minute
Greater in trained athletes
Pulmonary ventilation = anatomical dead space + alveolar ventilation 14 14

15. Mechanics of Ventilation (cont’d)
Lung Capacities and Volumes
Determined using spirometry equipment
Reserve of tidal volume at rest allows increase in tidal volume during maximal exercise
Residual volume: air left in lungs after max. exhalation
Frequency and Depth of Breathing
Increase in depth of breathing occurs first after onset of exercise
If increase in depth not sufficient, rate of breathing will increase 15 15

16. Mechanics of Ventilation (cont’d)
Lung volumes and capacities. 16 16

17. Diffusion at the Lungs Factors Promoting Diffusion
Large surface area of alveoli
Thinness of respiratory membrane (2 cells thick)
Pressure differences of oxygen & carbon dioxide between air in alveoli & blood
Partial pressure: portion of pressure due to a particular gas in a mixture of gases
Dalton’s law: total pressure of gas mixture = sum of partial pressures of each gas
Henry’s law: amount of gas dissolved in any fluid depends on temperature, partial pressure of gas, & solubility of gas 17 17

18. Diffusion at the Lungs (cont’d)
Oxygen Diffusion
Partial pressure of oxygen (PO2) must be > in alveoli than in blood & > in blood than in tissue
PO2 at sea level = mm Hg
PO2 in alveoli = 105 mm Hg
PO2 in arterial blood entering lungs = 40 mm Hg
PO2 in blood leaving lungs = 100 mm Hg
PO2 in tissues = 40 mm Hg
Thus, differences between PO2 in alveoli & blood (65 mm Hg) and between blood & tissue (60 mm Hg) provide driving force for diffusion of oxygen 18 18

19. Diffusion at the Lungs (cont’d)
Capillary gas exchange at lungs & tissue. 19 19

20. Diffusion at the Lungs (cont’d)
Carbon Dioxide Diffusion
Partial pressure of carbon dioxide (PCO2) must be > in blood than in alveoli & > in tissue than in blood
PCO2 in atmospheric air = 0.2 mm Hg
PCO2 in alveoli = 40 mm Hg
PCO2 in arterial blood entering lungs = 46 mm Hg
PCO2 in blood leaving lungs = 40 mm Hg
PCO2 in tissues = 46 mm Hg
Thus, differences between PCO2 in alveoli & blood (6 mm Hg) and between blood & tissue (6 mm Hg) provide driving force for diffusion of carbon dioxide 20 20

21. Diffusion at the Lungs (cont’d)
Lung Blood Flow
Determines velocity at which blood passes through pulmonary capillaries
Increased blood flow during exercise results in increased gas diffusion
Blood pressure in pulmonary circulation is low compared with systemic
Equilibration of oxygen between alveoli air & lung capillary blood takes 0.25 seconds
As blood flow increases with exercise, less time is available for this equilibration
However, increased capillary blood volume slows blood flow 21 21

22. Blood Gas Transport Oxygen Transport
Only 9 to 15 mL of oxygen can be dissolved in plasma, which is insufficient to meet needs of body
RBCs containing hemoglobin transport 98% of oxygen
Oxyhemoglobin: oxygen bound to hemoglobin
Deoxyhemoglobin: hemoglobin not bound to oxygen
Concentration of hemoglobin determines amount of oxygen that can be transported 22 22

23. Blood Gas Transport (cont’d)
Oxyhemoglobin disassociation curve. 23 23

24. Blood Gas Transport (cont’d)
Oxyhemoglobin Disassociation Curve
Temperature effect
Increase in temp.
Shifts curve to right
Decreases affinity of hemoglobin for oxygen
Decrease in temp.
Shifts curve to left
Increases affinity of hemoglobin for oxygen 24 24

25. Blood Gas Transport (cont’d)
Effect of temperature & acidity on hemoglobin disassociation curve. 25 25

26. Blood Gas Transport (cont’d)
Oxyhemoglobin Disassociation Curve (cont’d)
pH effect (Bohr effect)
Increase in acidity
Shifts curve to right
Decreases affinity of hemoglobin for oxygen
Decrease in acidity
Shifts curve to left
Increases affinity of hemoglobin for oxygen 26 26

27. Blood Gas Transport (cont’d)
Oxyhemoglobin Disassociation Curve (cont’d)
2,3-Diphosphoglycerate (2,3 DPG) effect
Increase in 2,3 DPG
Shifts curve to right
Decreases affinity of hemoglobin for oxygen
Decrease in 2,3 DPG
Shifts curve to left
Increases affinity of hemoglobin for oxygen 27 27

28. Blood Gas Transport (cont’d)
Carbon Dioxide Transport
3 methods
7% to 10% is dissolved in plasma
20% is bound to hemoglobin
70% is transported as bicarbonate 28 28

29. Blood Gas Transport (cont’d)
Ability of hemoglobin to bind oxygen & carbon dioxide. 29 29

30. Gas Exchange at the Muscle
Occurs due to partial pressure differences between oxygen & carbon dioxide between tissue & blood
Myoglobin
Oxygen transport molecule similar to hemoglobin
Found in skeletal & cardiac muscle
Reversibly binds with oxygen
Assists in passive diffusion of oxygen from cell membrane to mitochondria
Functions as oxygen reserve at start of exercise 30 30

31. Control of Ventilation
Respiratory Control Center
Portion of medulla oblongata & pons
Serves as pacemaker, generating a rhythmical breathing pattern
Rate & depth of breathing can be modified by:
Higher brain centers
Chemoreceptors in medulla
Other peripheral inputs
Pulmonary ventilation is generally involuntary, but can changed voluntarily 31 31

32. Control of Ventilation (cont’d)
The respiratory control center in the medulla. 32 32

33. Control of Ventilation (cont’d)
Central Chemoreceptors
Located in medulla, separate from respiratory control center
Respond to changes within CSF, esp. in H+ concentration or pH
Peripheral Chemoreceptors
Located in carotid arteries & aortic arch
Respond to changes in blood PCO2 & H+ concentration
Other Neural Input
Stretch receptors in lungs & respiratory muscles
Proprioceptors & chemoreceptors in skeletal muscle & joints 33 33

34. Effects of Exercise on Pulmonary Ventilation
Three phases of changes in pulmonary ventilation. 34 34

35. Ventilation Is Associated With Metabolism
Ventilatory Equivalents
Amount of air ventilated needed to obtain 1 L of oxygen or expire 1 L of carbon dioxide
Ventilatory equivalent of oxygen: ratio of pulmonary ventilation (VE) to oxygen (VO2): VE/VO2
Ventilatory equivalent of carbon dioxide: ratio of pulmonary ventilation (VE) to carbon dioxide (VCO2): VE/VCO2
Ventilatory Threshold (VT)
Technique using ventilatory equivalents to estimate lactate threshold 35 35

36. Ventilation is Associated With Metabolism (cont’d)
VT and RCP.

37. Ventilation Is Associated With Metabolism (cont’d)
Respiratory Compensation Point (RCP)
The work intensity at which both VE/VO2 & VE/VCO2 increase
Characterized by a decrease in end-trial partial pressure of O2
Indicates end of control of VE by PCO2
VT & RCP can be used to create 3 training zones of exercise intensity, based on heart rate:
Light-intensity: <VT
Moderate-intensity: between VT & RCP
High-intensity: >RCP 37 37