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Home , Diffusion

4/3/2016

Respiration

• Exchange of between air and body cells • Three steps 1. Ventilation Part 2: Respiratory Physiology 2. External 3. Internal respiration

Ventilation Boyle’s Law

• Pulmonary ventilation consists of two phases • The relationship between the and 1. Inspiration: gases flow into the volume of a fixed quantity of 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 P1V1 = P 2V2 – Thoracic – While one increases the other decreases

Ventilation Ventilation

• • Intrapleural pressure is subatmospheric Atmospheric pressure (P atm ) – Inward elastic recoil of – 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

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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 – Pressure in the pleural cavity – Two inward forces promote lung collapse – Fluctuates with breathing • Elastic recoil of lungs decreases lung size – • of alveolar reduces alveolar size Always a negative pressure (

Pulmonary Ventilation Inspiration

• Inspiration and expiration • An active process • Mechanical processes that depend on volume changes in the – Inspiratory muscles contract • Thoracic volume increases – Volume changes → pressure changes • Lungs are stretched and intrapulmonary volume – Pressure changes → → gases flow to increases equalize pressure – Intrapulmonary pressure drops – Air flows into the lungs, down its pressure gradient » Ppul = P atm

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Question Changes in anterior- Changes in lateral posterior and superior- 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 ). 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

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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 – 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

• Dalton’s Law of • 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 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 • P1-P2 = difference in partial pressures • D = diffusion coefficient • T = thickness of membrane

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Gas Exchange External Respiration

• • External respiration Exchange of O 2 and CO 2 across the respiratory – Pulmonary membrane • Internal respiration – Between lung and – Gas exchange between blood 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 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 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

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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 – 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 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 Respiration CO 2 P 40 mm Hg CO 2 Partial • pressure of Capillary gas exchange in body tissues O2 in oxygenated External • Partial pressures and diffusion gradients are respiration blood is Pulmonary Pulmonary greater than arteries veins (P O2 reversed compared to external respiration 100 mm Hg) that of tissues – Blood leaving Blood leaving pO 2 in tissue is always lower than in systemic tissues and lungs and entering lungs: entering tissue P 40 mm Hg capillaries: arterial blood O2 P 45 mm Hg P O 2 100 mm Hg CO 2 O2 flows out P CO 40 mm Hg – 2 of pCO 2 in tissue is higher than in systemic arterial bloodstream blood Heart and into

Systemic Systemic tissues veins arteries Internal respiration Tissues: P less than 40 mm Hg O2 P greater than 45 mm Hg CO 2

Figure 22.19

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Inspired air: Alveoli of lungs: INTERNAL P 160 mm Hg O2 P O 104 mm Hg P 0.3 mm Hg 2 RESPIRATION Gas Transport ( page 12 ) CO 2 P 40 mm Hg CO 2 Partial pressure of • Oxygen (O 2) transport CO 2 in oxygenated • External (CO 2) transport respiration blood is less Pulmonary Pulmonary than that of arteries veins (P O2 100 mm Hg) tissues

Blood leaving Blood leaving tissues and lungs and entering lungs: entering tissue CO flows out P 40 mm Hg capillaries: 2 O2 P 45 mm Hg P O 2 100 mm Hg CO 2 of tissues P CO 40 mm Hg 2 and into bloodstream Heart

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

O2 Transport

óMolecular O 2 is carried in the blood ó in plasma low

ó Few O2 = partial pressure ó Only 1.5% dissolved in plasma

ó paO 2 does not include O 2 bound to hemoglobin

ó Poor measure of total O2

O2 Transport O2 Transport • • Hemoglobin Oxyhemoglobin (HbO 2) – – Bound O 2 does not contribute to partial pressure Hemoglobin-O2 combination • Maintaining partial pressure gradient → diffusion • Reduced hemoglobin (HHb) – 98.5% loosely bound to each Fe of hemoglobin – Hemoglobin that has released O (Hb) in RBCs 2 • (4) O 2 per hemoglobin

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O2 Transport O2 Transport • • Loading and unloading of O 2 is facilitated by Rate of loading and unloading of O 2 is change in shape of Hb regulated by – – As O 2 binds, Hb affinity for O 2 increases pO 2 Modify hemoglobin shape • – 4 heme groups bound to O 2 – Saturated – Blood pH – • pCO 2 1, 2 or 3 heme groups bound to O 2 – – Partially saturated Products of • Measure of oxygen saturation = SO 2

O2 Transport O2 Transport • • Factors that promote oxyhemoglobin Factors that promote oxyhemoglobin formation dissociation – – ↑ pO ↓ pO 2 2 – – ↓ pCO ↑ temperature 2 – ↑ pCO 2 – ↑ products of metabolism

Conditions found in the lungs promote O 2 binding to Hb Conditions found in the tissues promote O 2 unloading

Oxyhemoglobin Dissociation Difference in partial

pressures = some O 2 • unloaded to resting Influence of pO 2 on hemoglobin saturation tissues – Arterial blood • paO 2 = 100 mm Hg Greater difference • Hb is 97-100% saturated in partial pressures = Additional O – 2 SO 2 100% unloaded to – Venous blood (resting tissues) exercising tissues • pO 2 = 40 mm Hg • Hb is 75% saturated – Venous blood still contains oxyhemoglobin!

Exercising Resting Lungs tissues tissues

Figure 22.20

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Oxyhemoglobin Dissociation Oxyhemoglobin Dissociation

– • Utilization coefficient Only 20–25% of bound O 2 is unloaded during • Difference between arterial and venous SO 2 one systemic circulation (at rest) – Example: arterial SO 2 = 100%; venous SO 2 = 75% • – Utilization coefficient 25% If O 2 levels in tissues drop: – – ↑ metabolism = ↓ paO 2 = larger partial pressure More oxygen dissociates from hemoglobin and is difference used by cells • Blood flow and heart rate need not increase!

Oxyhemoglobin Dissociation Factors promoting Oxyhemoglobin dissociation shift curve to the right

Decreased carbon dioxide 10°C (P 20 mm Hg) or H + (pH 7.6) CO 2 • 20°C Other factors influencing hemoglobin 38°C saturation 43°C + Normal arterial • ↑ temperature and ↑ H carbon dioxide

(P CO 240 mm Hg) – Conditions found at cells enhance O unloading Normal body or H + (pH 7.4) 2 temperature Increased carbon dioxide – Shift the O -hemoglobin dissociation curve to the (P 80 mm Hg) 2 CO 2 right or H + (pH 7.2)

(a) P (mm Hg) (b) O2

Figure 22.21

CO 2 Transport CO 2 Transport

• CO 2 is transported in the blood in three forms – 7-10% dissolved in plasma – 20% bound to of hemoglobin CA • - + carbaminohemoglobin or HbCO 2 H2O + CO 2 ↔ H 2CO 3 ↔ HCO 3 + H – – 70% transported as bicarbonate ions (HCO 3 ) in plasma

Key

H2O = water CO 2 = carbon dioxide H2CO 3 = carbonic acid - HCO 3 = bicarbonate ion H+ = hydrogen ion CA =

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Cl - CO 2 Transport In the tissues

Tissue cell Interstitial fluid CO CO (dissolved in plasma) 2 2 Binds to Slow plasma CO CO + H OH CO HCO – + H + 2 2 2 2 3 3 CO 2 HCO – 3 Chloride Fast Cl – – + shift CO 2 CO 2 + H 2OH2CO 3 HCO 3 + H CA Carbonic Cl – (in) via CO 2 anhydrase transport - + HHb H O + CO ↔ H CO ↔ HCO + H CO 2 CO 2 + Hb HbCO 2 (Carbamino- 2 2 2 3 3 hemoglobin)

Red blood cell HbO 2 O2 + Hb

CO 2 O2

O2 O2 (dissolved in plasma) Blood plasma (a) Oxygen release and carbon dioxide pickup at the tissues • Reaction happens in plasma but is 1,000X faster in the RBC because of CA • + H ions = acid = decrease pH = improved O 2 unloading from hemoglobin • - - HCO 3 diffuses out, replaced by Cl to maintain equilibrium = Chloride Shift Figure 22.22a

CO 2 Transport In the lungs

Alveolus Fused basement membranes CO • In pulmonary capillaries reaction is reversed 2 CO 2 (dissolved in plasma) Slow CO – + – – + 2 CO 2 + H 2OH2CO 3 HCO 3 + H HCO moves into the RBCs and binds with H to HCO – 3 3 Chloride – Fast – + Cl CO 2 CO 2 + H 2O H2CO 3 HCO 3 + H shift form H 2CO 3 Carbonic Cl – (out) via anhydrase transport – CO + Hb HbCO (Carbamino- protein H2CO 3 is split by carbonic anhydrase into CO 2 and CO 2 2 2 hemoglobin) + water O2 + HHb HbO 2 + H – CO 2 diffuses into the alveoli

O2

O2 O2 (dissolved in plasma) Blood plasma CA - + (b) Oxygen pickup and carbon dioxide release in the lungs H2O + CO 2 ↔ H 2CO 3 ↔ HCO 3 + H

Figure 22.22b

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