22 - University of Kentucky

Download Report

Transcript 22 - University of Kentucky

C H A P T E R

The Respiratory System: Part A

Exchanging Materials

• Every organism must exchange materials with its environment.

– This exchange ultimately occurs at the cellular level.

Circulatory Systems Reflect Phylogeny

• Transport systems functionally connect the organs of exchange with the body cells.

Sea level P O2 =760*0.2094 = 159 mmHg P O2 =(760-18)*0.2094 = 155 mmHg

The Respiratory System

• Major function-

respiration

– Supply body with O 2 for

cellular respiration;

dispose of CO 2 , a waste product of

cellular respiration

Processes of Respiration

• • • •

Pulmonary ventilation

(breathing) movement of air into and out of lungs

External respiration

-O 2 and CO 2 exchange between lungs and blood

Transport

-O 2 and CO 2 in blood

Internal respiration

-O 2 and CO 2 exchange between systemic blood vessels and tissues

Respiratory system Circulatory system

Bronchi and Subdivisions

• Air passages undergo 23 orders of branching 

bronchial

(respiratory)

tree

Conducting Zone Structures

• Trachea 

bronchi right and left main

(primary) • Each main bronchus enters hilum of one lung – Right main bronchus wider, shorter, more vertical than left • Each main bronchus branches into

lobar

(secondary)

bronchi

Conducting Zone Structures

• Each lobar bronchus branches into

segmental

(tertiary)

bronchi

– Segmental bronchi divide repeatedly • Branches become smaller and smaller  –

Bronchioles

-less than 1 mm in diameter –

Terminal bronchioles

Figure 22.7 Conducting zone passages.

Superior lobe of right lung Middle lobe of right lung Inferior lobe of right lung

Trachea Superior lobe of left lung Left main (primary) bronchus Lobar (secondary) bronchus Segmental (tertiary) bronchus Inferior lobe of left lung

Conducting Zone Structures

• From bronchi through bronchioles, structural changes occur – Cartilage rings become irregular plates; in bronchioles elastic fibers replace cartilage – Epithelium changes from pseudostratified columnar to cuboidal; cilia and goblet cells become sparse – Relative amount of smooth muscle increases • Allows constriction © 2013 Pearson Education, Inc.

Respiratory Zone

• Begins as terminal bronchioles 

respiratory bronchioles



alveolar ducts



alveolar sacs

– Alveolar sacs contain clusters of

alveoli

Figure 22.8a Respiratory zone structures.

Alveolar duct Respiratory bronchioles Terminal bronchiole Alveoli Alveolar duct Alveolar sac

Figure 22.8b Respiratory zone structures.

Respiratory bronchiole Alveolar duct Alveoli Alveolar sac Alveolar pores

Respiratory Membrane

• Alveolar and capillary walls and their fused basement membranes – ~0.5-µm-thick; gas exchange across membrane by simple diffusion • Alveolar walls – Single layer of squamous epithelium (

type I alveolar cells

) • Scattered cuboidal

type II alveolar cells

secrete

surfactant

Figure 22.9a Alveoli and the respiratory membrane.

Terminal bronchiole Respiratory bronchiole Smooth muscle Elastic fibers Alveolus Capillaries Diagrammatic view of capillary-alveoli relationships

Figure 22.9b Alveoli and the respiratory membrane.

Scanning electron micrograph of pulmonary capillary casts (70 x )

Alveoli

• • • Surrounded by fine elastic fibers and pulmonary capillaries

Alveolar pores

connect adjacent alveoli • Equalize air pressure throughout lung

Alveolar macrophages

Figure 22.9c Alveoli and the respiratory membrane.

Red blood cell Nucleus of type I alveolar cell Alveolar pores Capillary Alveoli (gas-filled air spaces) Red blood cell in capillary

Alveolus

Type II alveolar cell Type I alveolar cell Macrophage Endothelial cell nucleus Respiratory membrane Detailed anatomy of the respiratory membrane

Alveolus

Alveolar epithelium Fused basement membranes of alveolar epithelium and capillary endothelium Capillary endothelium

Capillary

Lungs

• • •

Apex Base

-superior tip; deep to clavicle -inferior surface; rests on diaphragm

Hilum

-on mediastinal surface; site for entry/exit of blood vessels, bronchi, lymphatic vessels, and nerves • Left lung smaller than right –

Cardiac notch

-concavity for heart – Separated into

superior oblique fissure

Figure 22.10a Anatomical relationships of organs in the thoracic cavity.

Lung Intercostal muscle Rib Parietal pleura Pleural cavity Visceral pleura Trachea Thymus Apex of lung Left superior lobe Right superior lobe Horizontal fissure Right middle lobe Oblique fissure Oblique fissure Left inferior lobe Right inferior lobe Heart (in mediastinum) Diaphragm Base of lung Anterior view.

Cardiac notch The lungs flank mediastinal structures laterally.

Mechanics of Breathing

• Pulmonary ventilation consists of two phases –

Inspiration

-gases flow into lungs –

Expiration

Pressure Relationships in the Thoracic Cavity

•

Atmospheric pressure

(

P atm

) – Pressure exerted by air surrounding body – 760 mm Hg at sea level = 1 atmosphere • Respiratory pressures described relative to P atm – Negative respiratory pressure-less than P atm – Positive respiratory pressure-greater than P atm – Zero respiratory pressure = P atm © 2013 Pearson Education, Inc.

Intrapulmonary Pressure

•

Intrapulmonary

(intra-alveolar)

pressure

(

P pul

Intrapleural Pressure

•

Intrapleural pressure

(

P ip

) – Pressure in pleural cavity – Fluctuates with breathing – Always a negative pressure (

Intrapleural Pressure

• Negative P ip caused by opposing forces – Two inward forces promote

lung collapse

• Elastic recoil of lungs decreases lung size • Surface tension of alveolar fluid reduces alveolar size – One outward force tends to enlarge lungs • Elasticity of chest wall pulls thorax outward © 2013 Pearson Education, Inc.

Pressure Relationships

• If P ip = P pul or P atm  lungs collapse • (P pul – P ip ) =

transpulmonary pressure

Figure 22.12 Intrapulmonary and intrapleural pressure relationships.

Atmospheric pressure ( P atm ) 0 mm Hg (760 mm Hg) Thoracic wall Parietal pleura Visceral pleura Pleural cavity Transpulmonary pressure 4 mm Hg (the difference between 0 mm Hg and −4 mm Hg) – 4 0 Intrapleural pressure ( P ip ) −4 mm Hg (756 mm Hg) Lung Diaphragm

Intrapulmonary pressure ( P pul ) 0 mm Hg (760 mm Hg)

Homeostatic Imbalance

•

Atelectasis

(lung collapse) due to – Plugged bronchioles  collapse of alveoli –

Pneumothorax

Pulmonary Ventilation

• Inspiration and expiration • Mechanical processes that depend on volume changes in thoracic cavity – Volume changes  – Pressure changes  pressure changes gases flow to equalize pressure © 2013 Pearson Education, Inc.

Boyle's Law

• Relationship between pressure and volume of a gas – Gases fill container; if container size reduced  increased pressure • Pressure (

) varies inversely with volume (

): –

P 1 V 1

P 2 V 2

Inspiration

• Active process – Inspiratory muscles (diaphragm and external intercostals) contract – Thoracic volume increases  pressure drops (to  1 mm Hg) intrapulmonary – Lungs stretched and intrapulmonary volume increases – Air flows into lungs, down its pressure gradient, until P pul = P atm © 2013 Pearson Education, Inc.

Forced Inspiration

Figure 22.13 Changes in thoracic volume and sequence of events during inspiration and expiration. (1 of 2) Slide 1 Sequence of events 1 Inspiratory muscles contract (diaphragm descends; rib cage rises).

2 Thoracic cavity volume increases.

3 Lungs are stretched; intrapulmonary volume increases.

4 Intrapulmonary pressure drops (to –1 mm Hg).

5 Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is 0 (equal to atmospheric pressure).

Changes in anterior-posterior and superior-inferior dimensions Changes in lateral dimensions (superior view) Ribs are elevated and sternum flares as external intercostals contract.

Diaphragm moves inferiorly during contraction.

External intercostals contract.

Expiration

• Quiet expiration normally passive process – Inspiratory muscles relax – Thoracic cavity volume decreases – Elastic lungs recoil and intrapulmonary volume decreases  pressure increases (P pul rises to +1 mm Hg)  – Air flows out of lungs down its pressure gradient until P pul = 0 • Note:

forced expiration

Figure 22.13 Changes in thoracic volume and sequence of events during inspiration and expiration. (2 of 2) Slide 1 Sequence of events 1 Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages).

Changes in anterior-posterior and superior-inferior dimensions 2 decreases.

3 Thoracic cavity volume Elastic lungs recoil passively; intrapulmonary Volume decreases.

Ribs and sternum are depressed as external intercostals relax.

Changes in lateral dimensions (superior view) External intercostals relax.

4 Intrapulmonary pressure rises (to +1 mm Hg).

5 Air (gases) flows out of lungs down its pressure gradient until intrapulmonary pressure is 0.

Diaphragm moves superiorly as it relaxes.

Figure 22.14 Changes in intrapulmonary and intrapleural pressures during inspiration and expiration.

Intrapulmonary pressure.

Pressure inside lung decreases as lung volume increases during inspiration; pressure increases during expiration.

Intrapleural pressure.

Pleural cavity pressure becomes more negative as chest wall expands during inspiration. Returns to initial value as chest wall recoils.

Volume of breath. During each breath, the pressure gradients move 0.5 liter of air into and out of the lungs.

+2 Inspiration Expiration Intrapulmonary pressure 0 –2 –4 –6 –8 Trans pulmonary pressure Intrapleural pressure Volume of breath 0.5

0 5 seconds elapsed

Physical Factors Influencing Pulmonary Ventilation

• Three physical factors influence the ease of air passage and the amount of energy required for ventilation.

–

Airway resistance

–

Alveolar surface tension

–

Lung compliance

Airway Resistance

• Friction-major

nonelastic

source of resistance to gas flow; occurs in airways • Relationship between flow (F), pressure (P), and resistance (R) is: –

∆P

Airway Resistance

• Resistance usually insignificant – Large airway diameters in first part of conducting zone – Progressive branching of airways as get smaller, increasing total cross-sectional area – Resistance greatest in medium-sized bronchi • Resistance disappears at terminal bronchioles where diffusion drives gas movement © 2013 Pearson Education, Inc.

Homeostatic Imbalance

• As airway resistance rises, breathing movements become more strenuous • Severe constriction or obstruction of bronchioles – Can prevent life-sustaining ventilation – Can occur during acute asthma attacks; stops ventilation • Epinephrine dilates bronchioles, reduces air resistance © 2013 Pearson Education, Inc.

Alveolar Surface Tension

•

Surface tension

– Attracts liquid molecules to one another at gas-liquid interface – Resists any force that tends to increase surface area of liquid – Water–high surface tension; coats alveolar walls  reduces them to smallest size © 2013 Pearson Education, Inc.

Alveolar Surface Tension

•

Surfactant

– Detergent-like lipid and protein complex produced by type II alveolar cells – Reduces surface tension of alveolar fluid and discourages alveolar collapse – Insufficient quantity in premature infants causes

infant respiratory distress syndrome

Lung Compliance

• Measure of change in lung volume that occurs with given change in transpulmonary pressure • Higher lung compliance  expand lungs easier to • Normally high due to – Distensibility of lung tissue – Surfactant, which decreases alveolar surface tension © 2013 Pearson Education, Inc.

Lung Compliance

Total Respiratory Compliance

• The total compliance of the respiratory system is also influenced by compliance (distensibility) of the thoracic wall, which is decreased by: – Deformities of thorax – Ossification of costal cartilage – Paralysis of intercostal muscles © 2013 Pearson Education, Inc.

Respiratory Volumes

• Used to assess respiratory status –

Tidal volume (TV)

–

Inspiratory reserve volume (IRV)

–

Expiratory reserve volume (ERV)

–

Residual volume (RV)

Figure 22.16b Respiratory volumes and capacities.

Respiratory volumes Measurement Tidal volume (TV) Inspiratory reserve volume (IRV) Expiratory reserve volume (ERV) Residual volume (RV) Adult male average value Adult female average value 500 ml 3100 ml 1200 ml 500 ml 1900 ml 700 ml Description Amount of air inhaled or exhaled with each breath under resting conditions Amount of air that can be forcefully inhaled after a normal tidal volume inspiration Amount of air that can be forcefully exhaled after a normal tidal volume expiration 1200 ml 1100 ml Amount of air remaining in the lungs after a forced expiration Respiratory capacities Total lung capacity (TLC) Vital capacity (VC) Inspiratory capacity (IC) Functional residual capacity (FRC) 6000 ml 4800 ml 3600 ml 2400 ml 4200 ml 3100 ml 2400 ml 1800 ml Maximum amount of air contained in lungs after a maximum inspiratory effort: TLC = TV + IRV + ERV + RV Maximum amount of air that can be expired after a maximum inspiratory effort: VC = TV + IRV + ERV Maximum amount of air that can be inspired after a normal tidal volume expiration: IC = TV + IRV Volume of air remaining in the lungs after a normal tidal volume expiration: FRC = ERV + RV Summary of respiratory volumes and capacities for males and females

Figure 22.16a Respiratory volumes and capacities.

6000 5000 Inspiratory reserve volume 3100 ml 4000 3000 Tidal volume 500 ml 2000 Expiratory reserve volume 1200 ml 1000 0 Spirographic record for a male Residual volume 1200 ml Inspiratory capacity 3600 ml Vital capacity 4800 ml Functional residual capacity 2400 ml Total lung capacity 6000 ml

Dead Space

• •

Anatomical dead space

– No contribution to gas exchange – Air remaining in passageways; ~150 ml

Alveolar dead space

–non-functional alveoli due to collapse or obstruction •

Total dead space

Pulmonary Function Tests

•

Spirometer

-instrument for measuring respiratory volumes and capacities • Spirometry can distinguish between –

Obstructive pulmonary disease

—increased airway resistance (e.g., bronchitis) • TLC, FRC, RV may increase –

Restrictive disorders

Pulmonary Function Tests

• To measure

rate

of gas movement –

Forced vital capacity

(FVC) —gas forcibly expelled after taking deep breath –

Forced expiratory volume

Alveolar Ventilation

•

Minute ventilation

—total amount of gas flow into or out of respiratory tract in one minute – Normal at rest = ~ 6 L/min – Normal with exercise = up to 200 L/min – Only rough estimate of respiratory efficiency © 2013 Pearson Education, Inc.

Table 22.2 Effects of Breathing Rate and Depth on Alveolar ventilation of Three Hypothetical Patients

Gas Exchanges Between Blood, Lungs, and Tissues

• •

External respiration

–diffusion of gases in lungs

Internal respiration

Basic Properties of Gases: Dalton's Law of Partial Pressures

• • Total pressure exerted by mixture of gases = sum of pressures exerted by each gas

Partial pressure

Basic Properties of Gases: Henry's Law

• Gas mixtures in contact with liquid – Each gas dissolves in proportion to its partial pressure – At equilibrium, partial pressures in two phases will be equal – Amount of each gas that will dissolve depends on • Solubility–CO 2 O 2 ; little N 2 20 times more soluble in water than dissolves in water • Temperature–as temperature rises, solubility decreases © 2013 Pearson Education, Inc.

Composition of Alveolar Gas

Table 22.4 Comparison of Gas Partial Pressures and Approximate Percentages in the Atmosphere and in the Alveoli

External Respiration

• Exchange of O 2 and CO 2 respiratory membrane across • Influenced by – Thickness and surface area of respiratory membrane – Partial pressure gradients and gas solubilities – Ventilation-perfusion coupling © 2013 Pearson Education, Inc.

Thickness and Surface Area of the Respiratory Membrane

• Respiratory membranes – 0.5 to 1  m thick – Large total surface area (40 times that of skin) for gas exchange • Thicken if lungs become waterlogged and edematous  gas exchange inadequate • Reduced surface area in emphysema (walls of adjacent alveoli break down), tumors, inflammation, mucus © 2013 Pearson Education, Inc.

Partial Pressure Gradients and Gas Solubilities

• Steep partial pressure gradient for O 2 lungs in – Venous blood Po 2 = 40 mm Hg – Alveolar Po 2 = 104 mm Hg • Drives oxygen flow to blood • Equilibrium reached across respiratory membrane in ~0.25 seconds, about 1/3 time a red blood cell in pulmonary capillary  – Adequate oxygenation even if blood flow increases 3X © 2013 Pearson Education, Inc.

Figure 22.18 Oxygenation of blood in the pulmonary capillaries at rest.

150 100 P O2 104 mm Hg 50 40 0 0 Start of capillary

0.25

0.50

Time in the pulmonary capillary (s) 0.75

End of capillary

Partial Pressure Gradients and Gas Solubilities

• Partial pressure gradient for CO 2 less steep in lungs – Venous blood Pco 2 – Alveolar Pco 2 = 45 mm Hg = 40 mm Hg • Though gradient not as steep, CO 2 diffuses in equal amounts with oxygen – CO 2 20 times more soluble in plasma than oxygen © 2013 Pearson Education, Inc.

Figure 22.17 Partial pressure gradients promoting gas movements in the body.

Inspired air: P O2 P CO2 160 mm Hg 0.3 mm Hg Alveoli of lungs: P O2 P CO2 104 mm Hg 40 mm Hg External respiration Pulmonary arteries Blood leaving tissues and entering lungs: P O2 P CO2 40 mm Hg 45 mm Hg Systemic veins Internal respiration

Alveoli

Pulmonary veins (P O2 100 mm Hg) Blood leaving lungs and entering tissue capillaries: P O2 P CO2 100 mm Hg 40 mm Hg

Heart

Systemic arteries Tissues: P O2 P CO2 less than 40 mm Hg greater than 45 mm Hg

Ventilation-Perfusion Coupling

• •

Perfusion

-blood flow reaching alveoli

Ventilation

-amount of gas reaching alveoli • Ventilation and perfusion matched (coupled) for efficient gas exchange – Never balanced for all alveoli due to • Regional variations due to effect of gravity on blood and air flow • Some alveolar ducts plugged with mucus © 2013 Pearson Education, Inc.

Ventilation-Perfusion Coupling

• Perfusion – Changes in Po 2 in alveoli cause changes in diameters of arterioles • Where alveolar O 2 • Where alveolar O 2 is high, arterioles dilate is low, arterioles constrict • Directs most blood where alveolar oxygen high © 2013 Pearson Education, Inc.

Ventilation-Perfusion Coupling

• Changes in Pco 2 in alveoli cause changes in diameters of bronchioles – Where alveolar CO 2 – Where alveolar CO 2 constrict is high, bronchioles dilate is low, bronchioles – Allows elimination of CO 2 more rapidly © 2013 Pearson Education, Inc.

Figure 22.19 Ventilation-perfusion coupling.

Ventilation less than perfusion Mismatch of ventilation and perfusion ventilation and/or perfusion of alveoli causes local P and P 2 O 2 O 2 autoregulates arteriolar diameter Pulmonary arterioles serving these alveoli constricts Match of ventilation and perfusion ventilation, perfusion Ventilation greater than perfusion Mismatch of ventilation and perfusion ventilation and/or perfusion of alveoli causes local P and P 2 O 2 O 2 autoregulates arteriolar diameter Pulmonary arterioles serving these alveoli dilate Match of ventilation and perfusion ventilation, perfusion

Transport of Respiratory Gases by Blood

O

Transport

O

and Hemoglobin

• •

Oxyhemoglobin

(HbO 2 )-hemoglobin-O 2 combination

Reduced hemoglobin

(

deoxyhemoglobin

O

and Hemoglobin

• • • Loading and unloading of O 2 change in shape of Hb facilitated by – As O 2 – As O 2 binds, Hb affinity for O 2 increases is released, Hb affinity for O 2 decreases

Fully saturated

groups carry O 2 (100%) if all four heme

Partially saturated

Figure 22.20 The amount of oxygen carried by hemoglobin depends on the P O2 locally. (1 of 3) (the amount of oxygen) available

This axis tells you how much O 2 is bound to Hb. At 100%, each Hb molecule has 4 bound oxygen molecules.

Hemoglobin 100

•

Oxygen 80 60 In the lungs, where PO 2 is high (100 mm Hg), Hb is almost fully saturated (98%) with O 2 .

If more O 2 is present, more O 2 is bound.

However, because of Hb’s properties (O 2 binding strength changes with saturation), this is an S-shaped curve, not a straight line.

40 20 0 0

•

20 This axis tells you the relative Amount (partial pressure) of O 2 disslolved in the fluid Surrounding the Hb.

40 60 P O 2 (mm Hg) 80 100 In the tissues of other organs, Where P O 2 is low (40 mm Hg), Hb is less saturated (75%) with O 2 .

Influence of Po

on Hemoglobin Saturation

• In arterial blood – Po 2 = 100 mm Hg – Contains 20 ml oxygen per 100 ml blood (20 vol %) – Hb is 98% saturated • Further increases in Po 2 (e.g., breathing deeply) produce minimal increases in O 2 binding © 2013 Pearson Education, Inc.

Influence of Po

on Hemoglobin Saturation

• In venous blood – Po 2 = 40 mm Hg – Contains 15 vol % oxygen – Hb is 75% saturated –

Venous reserve

Figure 22.20 The amount of oxygen carried by hemoglobin depends on the P O2 locally. (2 of 3) (the amount of oxygen) available In the lungs 100 80 60 40 20 0 0 20 40 P O2 60 (mm Hg) 80 At high P O 2 , large changes in P O 2 small changes in Hb saturation.

cause only Notice that the curve is relatively flat here. Hb’s properties 100 produce a safety margin that ensures that Hb is almost fully saturated even with a substantial P O 2 decrease. As a result, Hb remains saturated even at high altitude or with lung disease.

At sea level, there is lots of O 2 .

At a P O 2 in the lungs of 100 mm Hg, Hb is 98% saturated. 98% At high altitude, there is less O 2 .

At a P O 2 in the lungs of only 80 mm Hg, Hb is still 95% saturated. 95%

Other Factors Influencing Hemoglobin Saturation

• Increases in temperature, H + , Pco 2 , and BPG – Modify structure of hemoglobin; decrease its affinity for O 2 – Occur in systemic capillaries – Enhance O 2 unloading from blood – Shift O 2 -hemoglobin dissociation curve to right • Decreases in these factors shift curve to left – Decreases oxygen unloading from blood © 2013 Pearson Education, Inc.

Figure 22.21 Effect of temperature, P CO2 , and blood pH on the oxygen-hemoglobin dissociation curve.

100 10ºC 80 20ºC 38ºC 43ºC 60 40 Normal body temperature 20 (a) 0 100 Decreased carbon dioxide (P CO2 20 mm Hg) or H + (pH 7.6) 80 60 40 20 0 Normal arterial carbon dioxide (P CO2 40 mm Hg) or H + (pH 7.4) Increased carbon dioxide (P CO2 or H + 80 mm Hg) (pH 7.2) 20 40 P O 2 60 80 (mm Hg) 100

(b)

Factors that Increase Release of O

Hemoglobin by

• As cells metabolize glucose and use O 2 – Pco 2 and H + increase in capillary blood  – Declining blood pH and increasing Pco 2 •

Bohr effect

- Hb-O 2 bond weakens unloading where needed most   oxygen – Heat production increases  directly and indirectly decreases Hb affinity for O 2  increased oxygen unloading to active tissues © 2013 Pearson Education, Inc.

Homeostatic Imbalance

•

Hypoxia

– Inadequate O 2 – delivery to tissues

Anemic hypoxia



cyanosis

–too few RBCs; abnormal or too little Hb – –

Ischemic hypoxia

metabolic poisons –impaired/blocked circulation

Histotoxic hypoxia

–cells unable to use O 2 , as in – –

Hypoxemic hypoxia

–abnormal ventilation; pulmonary disease

Carbon monoxide poisoning

CO

Transport

• CO 2 transported in blood in three forms – 7 to 10% dissolved in plasma – 20% bound to

globin

of hemoglobin (

carbaminohemoglobin

) – 70% transported as

bicarbonate ions

Transport and Exchange of CO

• CO 2 combines with water to form carbonic acid (H 2 CO 3 ), which quickly dissociates • Occurs primarily in RBCs, where

carbonic anhydrase

Transport and Exchange of CO

• In systemic capillaries – HCO 3 – plasma quickly diffuses from RBCs into •

Chloride shift

Figure 22.22a Transport and exchange of CO 2 and O 2 .

Tissue cell Interstitial fluid

(dissolved in plasma)

Slow Fast

Carbonic anhydrase (Carbamino hemoglobin)

Red blood cell

Oxygen release and carbon dioxide pickup at the tissues (dissolved in plasma)

Blood plasma

Binds to plasma proteins Chloride shift (in) via transport protein

Transport and Exchange of CO

• In pulmonary capillaries – HCO 3 – moves into RBCs (while Cl binds with H + to form H 2 CO 3 move out); – H 2 CO 3 split by carbonic anhydrase into CO 2 and water – CO 2 diffuses into alveoli © 2013 Pearson Education, Inc.

Figure 22.22b Transport and exchange of CO 2 and O 2 .

Alveolus Fused basement membranes

(dissolved in plasma)

Slow Fast

Carbonic anhydrase (Carbamino hemoglobin)

Red blood cell

(dissolved in plasma) Oxygen pickup and carbon dioxide release in the lungs

Chloride shift (out) via transport protein

Blood plasma

Control of Respiration

• Involves higher brain centers, chemoreceptors, and other reflexes • Neural controls – Neurons in reticular formation of medulla and pons – Clustered neurons in medulla important •

Ventral respiratory group

•

Dorsal respiratory group

Medullary Respiratory Centers

• Ventral respiratory group (VRG) – Rhythm-generating and integrative center – Sets

eupnea

(12 –15 breaths/minute) • Normal respiratory rate and rhythm – Its inspiratory neurons excite inspiratory muscles via

phrenic

(diaphragm) and

intercostal nerves

Medullary Respiratory Centers

Figure 22.23 Locations of respiratory centers and their postulated connections.

Pons Pontine respiratory centers interact with medullary respiratory centers to smooth the respiratory pattern.

Medulla Ventral respiratory group (VRG) contains rhythm generators whose output drives respiration.

Pons Medulla Dorsal respiratory group (DRG) integrates peripheral sensory input and modifies the rhythms generated by the VRG.

To inspiratory muscles External intercostal muscles Diaphragm

Generation of the Respiratory Rhythm

• Not well understood • One hypothesis – Pacemaker neurons with intrinsic rhythmicity • Most widely accepted hypothesis – Reciprocal inhibition of two sets of interconnected pacemaker neurons in medulla that generate rhythm © 2013 Pearson Education, Inc.

Figure 22.25 Changes in P CO2 and blood pH regulate ventilation by a negative feedback mechanism.

Arterial P CO 2

P CO 2 decreases pH in brain extracellular fluid (ECF) Central chemoreceptors in brain stem respond to H + in brain ECF (mediate 70% of the CO 2 response) Peripheral chemoreceptors in carotid and aortic bodies (mediate 30% of the CO

Afferent impulses

response) 2 Medullary respiratory centers

Efferent impulses

Respiratory muscle Ventilation (more CO 2 exhaled) Arterial P CO 2 and pH return to normal Initial stimulus Physiological response Result

Figure 22.26 Location and innervation of the peripheral chemoreceptors in the carotid and aortic bodies.

Brain Sensory nerve fiber in cranial nerve IX (pharyngeal branch of glossopharyngeal) External carotid artery Internal carotid artery Carotid body Common carotid artery Cranial nerve X (vagus nerve) Sensory nerve fiber in cranial nerve X Aortic bodies in aortic arch Aorta Heart

Inflation Reflex

•

Hering-Breuer Reflex (inflation reflex)

– Stretch receptors in pleurae and airways stimulated by lung inflation • Inhibitory signals to medullary respiratory centers end inhalation and allow expiration • Acts as protective response more than normal regulatory mechanism © 2013 Pearson Education, Inc.

Figure 22.24 Neural and chemical influences on brain stem respiratory centers.

Higher brain centers (cerebral cortex —voluntary control over breathing) Other receptors (e.g., pain) and emotional stimuli acting through the hypothalamus Respiratory centers (medulla and pons) Peripheral chemoreceptors + + Central chemoreceptors Receptors in muscles and joints + – – Stretch receptors in lungs Irritant receptors

Respiratory Adjustments: Exercise

• Adjustments geared to both intensity and duration of exercise •

Hyperpnea

Respiratory Adjustments: Exercise

• Three neural factors cause increase in ventilation as exercise begins – Psychological stimuli—anticipation of exercise – Simultaneous cortical motor activation of skeletal muscles and respiratory centers – Excitatory impulses to respiratory centers from proprioceptors in moving muscles, tendons, joints © 2013 Pearson Education, Inc.

Respiratory Adjustments: High Altitude

• Quick travel to altitudes above 2400 meters (8000 feet) may  symptoms of acute mountain sickness (AMS) – Atmospheric pressure and Po 2 levels lower – Headaches, shortness of breath, nausea, and dizziness – In severe cases, lethal cerebral and pulmonary edema © 2013 Pearson Education, Inc.

Acclimatization to High Altitude

•

Acclimatization

—respiratory and hematopoietic adjustments to long-term move to high altitude – Chemoreceptors become more responsive to Pco 2 when Po 2 declines – Substantial decline in Po 2 directly stimulates peripheral chemoreceptors – Result—minute ventilation increases and stabilizes in few days to 2 –3 L/min higher than at sea level © 2013 Pearson Education, Inc.

Homeostatic Imbalances

•

Chronic obstructive pulmonary disease

(

COPD

) – Exemplified by chronic bronchitis and emphysema – Irreversible decrease in ability to force air out of lungs – Other common features • • History of smoking in 80% of patients

Dyspnea

- labored breathing ("air hunger") • Coughing and frequent pulmonary infections • Most develop respiratory failure (

hypoventilation

Homeostatic Imbalance

• Emphysema – Permanent enlargement of alveoli; destruction of alveolar walls; decreased lung elasticity  • Accessory muscles necessary for breathing –  exhaustion from energy usage • Hyperinflation  flattened diaphragm ventilation efficiency  reduced • Damaged pulmonary capillaries  enlarged right ventricle © 2013 Pearson Education, Inc.

Homeostatic Imbalance

• Chronic bronchitis – Inhaled irritants   chronic excessive mucus – Inflamed and fibrosed lower respiratory passageways  – Obstructed airways  – Impaired lung ventilation and gas exchange  – Frequent pulmonary infections © 2013 Pearson Education, Inc.

Figure 22.27 The pathogenesis of COPD.

• Tobacco smoke • Air pollution α-1 antitrypsin deficiency

Continual bronchial irritation and inflammation Breakdown of elastin in connective tissue of lungs Chronic bronchitis • Excess mucus production • Chronic productive cough Emphysema • Destruction of alveolar walls • Loss of lung elasticity • Airway obstruction or air trapping • Dyspnea • Frequent infections • Hypoventilation • Hypoxemia • Respiratory acidosis

Homeostatic Imbalances

• Asthma–reversible COPD – Characterized by coughing, dyspnea, wheezing, and chest tightness – Active inflammation of airways precedes bronchospasms – Airway inflammation is immune response caused by release of interleukins, production of IgE, and recruitment of inflammatory cells – Airways thickened with inflammatory exudate magnify effect of bronchospasms © 2013 Pearson Education, Inc.

Homeostatic Imbalances

•

Tuberculosis (TB)

– Infectious disease caused by bacterium

Mycobacterium tuberculosis

Homeostatic Imbalance

• Cystic fibrosis – Most common lethal genetic disease in North America – Abnormal, viscous mucus clogs passageways  bacterial infections • Affects lungs, pancreatic ducts, reproductive ducts – Cause–abnormal gene for Cl channel membrane © 2013 Pearson Education, Inc.

Homeostatic Imbalances

•

Lung cancer

– Leading cause of cancer deaths in North America – 90% of all cases result of smoking – Three most common types •

Adenocarcinoma

(~40% of cases) originates in peripheral lung areas - bronchial glands, alveolar cells •

Squamous cell carcinoma

(20 –40% of cases) in bronchial epithelium •

Small cell carcinoma

Figure 22.28 Embryonic development of the respiratory system.

Future mouth Eye Frontonasal elevation Olfactory placode Stomodeum (future mouth) 4 weeks: anterior superficial view of the embryo’s head Laryngotracheal bud Trachea Bronchial buds 5 weeks: left lateral view of the developing lower respiratory passageway mucosae Pharynx Foregut Olfactory placode Esophagus Liver

Developmental Aspects

Homeostatic Imbalance

• Treatments for cystic fibrosis – Mucus-dissolving drugs; manipulation to loosen mucus; antibiotics – Research into • Introducing normal genes • Prodding different protein  Cl channel • Freeing patient's abnormal protein from ER to  Cl channels • Inhaling hypertonic saline to thin mucus © 2013 Pearson Education, Inc.

Haldane Effect

• Amount of CO 2 transported affected by Po 2 – Reduced hemoglobin (less oxygen saturation) forms carbaminohemoglobin and buffers H + more easily  – Lower Po 2 more CO 2 and hemoglobin saturation with O 2 ; carried in blood • Encourages CO 2 lungs exchange in tissues and © 2013 Pearson Education, Inc.

Haldane Effect

• At tissues, as more CO 2 enters blood – More oxygen dissociates from hemoglobin (

Bohr effect

Influence of CO

on Blood pH

•

Carbonic acid –bicarbonate buffer system

–resists changes in blood pH – If H + concentration in blood rises, excess H + removed by combining with HCO 3 –  H 2 CO 3 is – If H + concentration begins to drop, H 2 CO 3 dissociates, releasing H + – HCO 3 – is

alkaline reserve

Chemical Factors

• Influence of arterial pH – Can modify respiratory rate and rhythm even if CO 2 and O 2 levels normal – Mediated by peripheral chemoreceptors – Decreased pH may reflect • CO 2 retention; accumulation of lactic acid; excess ketone bodies – Respiratory system controls attempt to raise pH by increasing respiratory rate and depth © 2013 Pearson Education, Inc.

Summary of Chemical Factors

• Rising CO 2 levels most powerful respiratory stimulant • Normally blood Po 2 affects breathing only indirectly by influencing peripheral chemoreceptor sensitivity to changes in Pco 2 © 2013 Pearson Education, Inc.

Summary of Chemical Factors

• When arterial Po 2 falls below 60 mm Hg, it becomes major stimulus for respiration (via peripheral chemoreceptors) • Changes in arterial pH resulting from CO 2 retention or metabolic factors act indirectly through peripheral chemoreceptors © 2013 Pearson Education, Inc.

Acclimatization to High Altitude

• Always lower-than-normal Hb saturation levels – Less O 2 available • Decline in blood O 2 stimulates kidneys to accelerate production of EPO • RBC numbers increase slowly to provide long-term compensation © 2013 Pearson Education, Inc.