CHAPTER 17 Mechanics of Breathing
Respiration: gas exchange between atmosphere and body cells
System Functions
exchange of gases- inspired air to and from blood, O2 & CO2
Maintain pH
sound production & vocalization
keep air passages clean (coughing & sneezing)
Terms
External Respiration- movement of O2 from lungs to blood. movement of CO2 from blood to lungs
Internal Cellular Resp.- mvmt of O2 from blood to tissue cells. Mvmt of CO2 from tissue to blood.
Pulmonary Ventilation- movement of air in and out of lungs
ANATOMICAL DIVISIONS
Upper Resp. System
Lower Resp. System
outside superior thorax (above chest)
mouth, nasal cavity, pharynx, larynx
inside thorax (within chest cavity)
trachea, primary bronchi, bronchioles, lungs
FUNCTIONAL DIVISIONS
Conducting Zone
Respiratory Zone
nostrils through bronchioles (no gas exchange)
conditions inspired air
warms (37*C)
humidifies
cleans (bacteria viruses dust)
bronchioles through alveoli (gas exchange)
lungs (pink, light, soft, spongy, elastic)
Right: superior, middle, inferior lobe
Left: sm. due to heart position; superior & inferior lobes
Hilus root: where pulmonary vessels, nerves, and bronchi enter and exit the lungs.
Pleurea: each lung is covered w/ pleura. Serous mem. (secretes pleural fluid) which fills pleural cavity. Allows for free movement of lungs as they expand and contract preventing lung collapse.
Alveoli: site of gas exchange in the lung. Thin walled sacs make up most of the lung. Many capillaries here.
TYPE I ALVEOLI "soccer ball"- from walls of alveoli that permit O2 and CO2 diffusion.
TYPE II alveolar cells
Atmospheric Pressure 760 mmHg
GAS LAWS
GASES MOVE DOWN PRESSURE GRADIENT (high to low) ↘
BOYLE'S LAW: if volume in gas containter changes, gas pressure will change in an inverse manner 🔃
DALTON'S LAW: total gas pressure exerted is the sum of individual gas pressures. Partial pressure is pressure exerted by a single gas. ➕
Components of Air
O2 (20%)
CO2 (0.04%)
N (78.6%)
H2O (0.5%)
PN2 + PO2 + PCO2 + H2O (0.5%) = 760 mmHg
PULMONARY PRESSURE
Intrapulmonary pressure (Ppol= 760 mmHg)
Intrapleural pressure (Pip)= 756 mmHg (negative)
pressure in alveoli fluctuates with breathing (rises and falls)
Equalizes with atmospheric pressure
Approx. 4 mmHg below Ppul and Patm
Causes of (-) intrapleaural pressure
Pressure in pleural cavity
surface tension of fluid in alveoli *(tends to collapse alveoli; exerts inward pressure on lungs
Lung enlarging forces- elasticity of chest wall) pull thorax out
lung collapsing (recoil forces)
TRANSPULMONARY PRESSURE
Diff. between Ppul and Pip (760- 756 = 4 mmHg)
KEEPS LUNGS FROM COLLAPSING
INSPIRATION (air flow into lungs)
Lungs stretch and intrapulmonary volume increases
Intrapulmonary pressure decreases (Ppal < Patm = -1 mmHg
Volume of thoracic cavity increases
Air flows down the pressure gradient until pressure equalizes (Ppul= atm)
Inspiratory muscles contract (diaphragm descends and external intercostal muscles raise rib cage)
EXPERATION (air flow out of lungs)
lungs recoil and the interpulmonary volume decreases
intrapulmonary pressure increases (Ppil > Patm = +1 mmHg)
Volume of thoracic cavity decreases
Air flows out of lungs down pressure gradient until pressure equalizes (Ppul = Patm)
Inspiratory muscles relax (diaphragm rises, internal intercoastal muscles recoil the ribcage)
FACTORS INFLUENCING PULMONARY VENTILATION
Airway resistance (length, viscosity (humidity, pollution particles) Radius of air tube
Ventilation (breathing)
Compliance (The ability of the lung to stretch)
mucous
bronchodilation ( increase CO2)
brocnhoconstriciton (parasympathetic input, histamine)
respiratory volumes
measured by spirometer
Tidal Volume (TV) amount of air moving in/out lung with each breath (About 500 ml)
Inspiratory Reserve Volume (IRV) amount of air that can be inspired forcefully
Expiratory Reserve Volume (ERV) air forced out (about 1000-1200 ml)
Residual Volume (RV) Remaining air in lung always (prevents lung collapsing) (about 1200 ml)
RESPIRATORY CAPACITIES
Functional Residual Capacity ( FRC) amnt of air remaining in the lungs after tidal exhalation FRC= RV +ERV
Vital Capacity- Total amount of exchangable air VC= TV + IRV + ERV
Inpiratory Capacity (IC) Total amnt of ait that can be inspired after a tidal experation. IC= TV +IRV
Total Lung Capacity (TLC) Sum of all lung volumes TLC = TV + IRV + ERV + RV
TOTAL PULMONARY VENTILATION (PV)
PV = Ventilation rate x tidal volume (L/min)
4.2 L / min
Volume of aiir moved in/out of lungs per minute
Problems
HYPOVENTILATION quick rate of breathing PO2 levels rise
HYPERVENTILATION breathing does not meet bodies needs (too shallow/ slow) PO2 is too low, inadequete oxygen to lungs
APNEA breathing cessation
GAS EXCHANGE TRANSPORT
Pulmonary ventilation ensures alveoli are supplied with O2 and CO2 is removed.
Occurs between blood and alveolar air across the resp. mem.
FACTORS INFLUENCING DISSUSION EFFICIENCY @ THE RESP. MEM.
Pressure Gradient
Mem. Thickness ⬆⬇
Surface Area ⬆⬆
Solubility ⬆⬆
HENRYS LAW when a mixture of gases is in contact with a liquid, each gas will dissolve in liquid proportion to its partial pressure