4/3/2016 Respiration • Exchange of gases between air and body Respiratory System cells • Three steps 1. Ventilation Part 2: Respiratory Physiology 2. External respiration 3. Internal respiration Ventilation Boyle’s Law • Pulmonary ventilation consists of two phases • The relationship between the pressure and 1. Inspiration: gases flow into the lungs volume of a fixed quantity of gas in a closed 2. Expiration: gases exit the lungs container • Relies on pressure gradients • Pressure ( P) varies inversely with volume ( V): – Atmosphere and alveoli • Negative pressure breathing P1V1 = P 2V2 – Thoracic pressures – Atmospheric pressure While one increases the other decreases Ventilation Ventilation • • Intrapleural pressure is subatmospheric Atmospheric pressure (P atm ) – Inward elastic recoil of lung tissue – Pressure exerted by the air surrounding the body Resting lung volume – – Outward elastic recoil of chest wall 760 mm Hg at sea level • Thoracic pressures are described relative to P atm – Negative respiratory pressure is less than P atm – Positive respiratory pressure is greater than P atm 1 4/3/2016 Atmospheric pressure Parietal pleura Ventilation Thoracic wall Visceral pleura Pleural cavity • Transpulmonary Intrapulmonary (intra-alveolar) pressure (Ppul ) pressure – 760 mm Hg Pressure in the alveoli –756 mm Hg – Fluctuates with breathing = 4 mm Hg – Always eventually equalizes with Patm 756 Intrapleural pressure 760 756 mm Hg (–4 mm Hg) Intrapulmonary Lung pressure 760 mm Hg Diaphragm (0 mm Hg) Figure 22.12 Ventilation Ventilation • • Intrapleural pressure (P ip ): Negative P ip is caused by opposing forces – Pressure in the pleural cavity – Two inward forces promote lung collapse – Fluctuates with breathing • Elastic recoil of lungs decreases lung size – • Surface tension of alveolar fluid reduces alveolar size Always a negative pressure (<P atm and <P pul ) – One outward force tends to enlarge the lungs • Elasticity of the chest wall pulls the thorax outward Pulmonary Ventilation Inspiration • Inspiration and expiration • An active process • Mechanical processes that depend on volume changes in the – Inspiratory muscles contract thoracic cavity • Thoracic volume increases – Volume changes → pressure changes • Lungs are stretched and intrapulmonary volume – Pressure changes → pressure gradient → gases flow to increases equalize pressure – Intrapulmonary pressure drops – Air flows into the lungs, down its pressure gradient » Ppul = P atm 2 4/3/2016 Question Changes in anterior- Changes in lateral posterior and superior- dimensions Sequence of events inferior dimensions (superior view) 1 Inspiratory muscles • What part of the lung tissue expands during contract (diaphragm Ribs are elevated descends; rib cage rises). and sternum flares inspiration? as external 2 Thoracic cavity volume intercostals increases. contract. 3 Lungs are stretched; External intrapulmonary volume intercostals increases. contract. 4 Intrapulmonary pressure drops (to –1 mm Hg). 5 Air (gases) flows into lungs down its pressure Diaphragm gradient until intrapulmonary moves inferiorly pressure is equal to during contraction. atmospheric pressure Figure 22.13 (1 of 2) Expiration Changes in anterior- Changes in Sequence posterior and superior- lateral dimensions of events inferior dimensions (superior view) • Quiet expiration is normally a passive process 1 Inspiratory muscles relax (diaphragm rises; rib Ribs and sternum – Inspiratory muscles relax cage descends due to are depressed recoil of costal cartilages). as external • Thoracic cavity volume decreases intercostals 2 Thoracic cavity volume relax. • Elastic lungs recoil and intrapulmonary volume decreases. decreases 3 Elastic lungs recoil External – P rises passively; intrapulmonary intercostals pul volume decreases. • Air flows out of the lungs down its pressure gradient relax. 4 Intrapulmonary pres- until P pul = 0 sure rises (to +1 mm Hg). Diaphragm 5 Air (gases) flows out of moves lungs down its pressure superiorly gradient until intra- as it relaxes. pulmonary pressure is 0. Figure 22.13 (2 of 2) Air Flow Intrapulmonary Inspiration Expiration pressure. Pressure inside lung decreases as Intrapulmonary lung volume increases pressure during inspiration; • Physical factors influencing efficiency of air flow pressure increases during expiration. Trans- – Inspiratory muscles overcome three factors that hinder pulmonary Intrapleural pressure. pressure air passage and pulmonary ventilation Pleural cavity pressure becomes more negative 1. Airway resistance as chest wall expands Intrapleural 2. Alveolar surface tension during inspiration. pressure Returns to initial value as chest wall recoils. 3. Lung compliance Volume of breath. Volume of breath During each breath, the pressure gradients move NOTE: Study guide, Respiratory pg 10 0.5 liter of air into and out of the lungs. 6b. Friction is inversely proportional to airway diameter 5 seconds elapsed Figure 22.14 3 4/3/2016 Air Flow Lung Compliance • Broncoconstriction • Measure of lung’s ability to stretch and expand – Smooth muscle contracts • Diminished by – – Reduced air flow Nonelastic scar tissue (fibrosis) – Reduced production of surfactant – Decreased flexibility of the thoracic cage • Emphysema/COPD is associated with increased compliance – Due to diminished elastic recoil – patient has no trouble filling lungs with air, but great effort is required for exhalation Gas Laws Gas Laws • Dalton’s Law of Partial Pressure • Dalton’s Law of Partial Pressure – Describes how a gas behaves when it is part of a mixture – Example: • • Partial pressure = pressure exerted by a single gas in Air contains 20.9% O 2 the mixture = proportional to the percentage of gas in • Atmospheric Pressure = 760 mmHg a mixture • Total pressure exerted by a mixture of gases is the sum 0.209 P o 2 x 760 mmHg = 160 mmHg of the pressures exerted by each gas = partial pressure of oxygen in the atmosphere Gas Laws Gas Laws • Fick’s Law of Diffusion • Diseases related to gas diffusion – Gives the rate of diffusion for a given gas across a – Pulmonary edema membrane – – COPD CO 2 has a high diffusion coefficient and diffuses 20 times more rapidly across a membrane than O 2 Vg = (A) (P 1-P2) (D) (T) • A = membrane surface area • P1-P2 = difference in partial pressures • D = diffusion coefficient • T = thickness of membrane 4 4/3/2016 Gas Exchange External Respiration • • External respiration Exchange of O 2 and CO 2 across the respiratory – Pulmonary gas exchange membrane • Internal respiration – Between lung and blood – Gas exchange between blood capillaries and tissues Thought Question External Respiration • Can you think of some factors that might • Respiratory membrane influence the exchange of gases between the – Site of gas exchange between lung and blood lungs and the blood? Hint: remember Fick’s • Not actually a membrane, but a collection of Law? associated structures – Membrane of lung epithelium – Pulmonary capillary membrane – Surfactant – Connective tissue Red blood External Respiration cell Nucleus of type I (squamous • epithelial) cell Partial pressure gradient for O 2 in the lungs is Alveolar pores steep Capillary O Capillary – 2 Venous blood pO2 = 40 mm Hg Type I cell CO 2 of alveolar wall Alveolus – Macrophage Alveolar pO2 = 104 mm Hg Alveolus Endothelial cell nucleus Alveolar epithelium Fused basement Oxygen readily diffuses from alveoli to lung membranes of the Respiratory alveolar epithelium capillaries Red blood cell membrane and the capillary Alveoli (gas-filled in capillary Type II (surfactant- endothelium air spaces) secreting) cell Capillary endothelium (c) Detailed anatomy of the respiratory membrane Figure 22.9c 5 4/3/2016 EXTERNAL Inspired air: Alveoli of lungs: P 160 mm Hg O2 P O 104 mm Hg RESPIRATION P 0.3 mm Hg 2 External Respiration CO 2 P 40 mm Hg CO 2 Partial • pressure of Partial pressure gradient for CO 2 in the lungs O2 in inspired air is greater – External Venous blood pCO 2 = 45 mm Hg than that of respiration blood Pulmonary Pulmonary – arteries veins (P Alveolar pCO = 40 mm Hg O2 2 entering the 100 mm Hg) lungs • Blood leaving Blood leaving But… tissues and lungs and entering lungs: entering tissue P 40 mm Hg capillaries: – O2 CO is 20 times more soluble in plasma than P 45 mm Hg P O 100 mm Hg 2 2 O2 flows out CO 2 P CO 40 mm Hg oxygen of alveoli and 2 into – bloodstream Heart CO 2 diffuses in equal amounts with oxygen! Systemic Systemic veins arteries Internal respiration Tissues: P less than 40 mm Hg O2 P greater than 45 mm Hg CO 2 Figure 22.19 EXTERNAL Inspired air: Alveoli of lungs: P 160 mm Hg O2 P O 104 mm Hg RESPIRATION P 0.3 mm Hg 2 Factors Affecting External Respiration CO 2 P 40 mm Hg CO 2 Partial pressure of Anatomical adaptations CO 2 in inspired air is • Moist surfaces less than that External respiration • of blood Pulmonary Pulmonary Thickness and surface area arteries veins (P entering the O2 100 mm Hg) • Narrow capillaries = RBC’s single file lungs Blood leaving Blood leaving tissues and lungs and entering lungs: entering tissue P 40 mm Hg capillaries: O2 Physiological and physical factors P 45 mm Hg P O 2 100 mm Hg CO 2 flows out CO 2 P CO 40 mm Hg of 2 • Pulmonary disease bloodstream and into Heart • Affect of drugs on minute volume alveoli, Systemic Systemic • Partial pressure changes with altitude where it is veins arteries exhaled Internal respiration Tissues: P less than 40 mm Hg O2 P greater than 45 mm Hg CO 2 Figure 22.19 Inspired air: Alveoli of lungs: INTERNAL P 160 mm Hg O2 P O 104 mm Hg P 0.3 mm Hg 2 RESPIRATION Internal