Bio18 Ch13 Respiration Spr12

8/2/2019 Bio18 Ch13 Respiration Spr12

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Chapter 13The Respiratory System

Respiration

Respiration has two functions:

obtains O2for use by the bodys cells and

eliminates CO2 produced by body cells

Encompasses 2 separate but related processes

Internal respiration aka Cellular Respiration

Metabolic processes carried out within themitochondria, which use O2 and produce CO2, whilederiving energy (ATP) from nutrient molecules

External respiration

Sequence of events involved in the exchange of O2and CO2 between the external environment and thecells of the body

Nonrespiratory Functions of RespiratorySystem

Route for water loss and heat elimination

Enhances venous return

Helps maintain normal acid-base balance

Enables speech, singing, other vocalizations Defends against inhaled foreign matter

Removes, modifies, activates, or inactivatesvarious materials passing through the pulmonarycirculation

Nasal passages include the receptors for smell

External Respiration

4 steps

1. Ventilation movement of air into and out of thelungs

2. Pulmonary Gas Exchange - O2 and CO2 diffusebetween air in alveoli and blood within the pulmonary

capillaries3. Transport - Blood transports O2 and CO2 between

lungs and tissues

4. Systemic Gas Exchange - O2 and CO2 areexchanged between blood and tissues and bydiffusion across systemic (tissue) capillaries


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External andInternal

Respiration

Respiratory System

Consists of three major types of structures:

Respiratory airways leading to the lungs

Lungs

Structures of the thorax involved in producingmovement of air through the airways into and outof the lungs

Respiratory Airways Tubes that carry air between the atmosphere and

the air sacs

Nasal passages (nose)

Pharynx (common passageway for resp & dig)

Trachea (windpipe)

Larynx (voice box)

Right and left

bronchi

Bronchioles Alveoli (air sacs)

are clustered at

ends of terminal

bronchioles

Respiratory Airways

Trachea and larger bronchi

Fairly rigid, nonmuscular tubes

Rings of cartilage prevent collapse

Bronchioles

No cartilage to hold them open

Walls contain smooth muscle innervated byautonomic nervous system

Sensitive to certain hormones and localchemicals


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Alveoli Thin-walled

inflatable sacs

Function in gasexchange

Pulmonarycapillariesencircle eachalveolus

Walls consist of asingle layer of flat

Type I alveolar cells

Type II alveolar cells secrete pulmonary surfactant

Alveolar macrophages guard lumen

Lungs

Occupy much of thoracic cavity

Heart, associated vessels, esophagus, thymus,

and some nerves also occupy space

Two lungs

Each is divided into several lobes

Tissue consists of highly branched airways, thealveoli, the pulmonary blood vessels, and largequantities of elastic connective tissue

Thoracic Cavity

Outer chest wall (thorax)

Formed by 12 pairs of ribs which join sternum anteriorlyand thoracic vertebrae posteriorly

Diaphragm

Dome-shaped sheet of skeletal muscle

Separates thoracic cavity from the abdominal cavity

Pleural sac

Double-walled, closed sac that separates each lungfrom the thoracic wall

Pleural cavity interior of plural sac

Intrapleural fluid

Lubricant, secreted by surfaces of the pleura

Pleural Sac


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Respiratory Mechanics

Interrelationships among pressures inside andoutside the lungs are important in ventilation

3 different pressure considerations important inventilation

Atmospheric (barometric) pressure

Intra-alveolar (intrapulmonary) pressure

Intrapleural (intrathoracic) pressure

Pressures Important in Ventilation

Respiratory Mechanics

Changes in intra-alveolarpressure produce flow of airinto and out of the lungs

If intra-alveolar pressure is lessthan atmospheric pressure, airenters lungs.

If the opposite occurs, air exitslungs.

Boyles law states that at anyconstant temperature, thepressure exerted by a gas variesinversely with volume of a gas.

Boyles Law

Respiratory Mechanics: Inspiration

Major inspiratory muscles:

Diaphragm

External intercostal muscles

During Quiet Respiration, 75% of thoracic cavityenlargement is due to diaphragm contraction

Diaphragm contraction decreases intrapleural pressure

The lungs expand, increasing volume

Increased volume lowers the intra-alveolar pressure toa level below atmospheric pressure.

Air enters the lungs.

Accessory inspiratory muscles can further enlarge thethoracic cavity.


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Anatomy of theRespiratory

Muscles

Respiratory Mechanics: Expiration

Onset of expiration begins with relaxation ofinspiratory muscles

Relaxation of diaphragm and muscles of chestwall, plus the elastic recoil of the alveoli,

decrease the size of the chest cavity Intrapleural pressure increases; lungs arecompressed

Intra-alveolar pressure increases When pressure increases to level above atmosphericpressure, air is driven outexpiration occurs

Forced expiration can occur by contraction ofexpiratory muscles Abdominal wall muscles

Internal intercostal muscles

Respiratory Muscle ActivityDuring Inspiration

Respiratory Muscle ActivityDuring Expiration


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Airway Resistance

Primary determinant of resistance to airflow is theradius of the conducting airway

Autonomic nervous system controls contraction ofsmooth muscle in bronchioles (changes radii)

Chronic obstructive pulmonary disease (COPD)

abnormally increases airway resistance

Expiration is more difficult than inspiration

Diseases

Chronic bronchitis

Asthma

Emphysema

Compliance

Lungs have elastic recoil rebound if stretched

Compliance

Refers to how much effort is required to stretch

or distend the lungs

The less compliant the lungs are, the morework is required to produce a given degree ofinflation

Decreased by factors such as pulmonaryfibrosis

Elastic Recoil

Refers to how readily the lungs rebound afterhaving been stretched

Responsible for lungs returning to theirpreinspiratory volume when inspiratory muscles

relax at end of inspiration Depends on 2 factors

Highly elastic connective tissue in the lungs

Alveolar surface tension

Thin liquid film lines each alveolus

Reduces tendency of alveoli to recoil

Helps maintain lung stability

Newborn respiratory distress syndrome

Work of Breathing

Normally requires 3% of total energy expenditurefor quiet breathing

Lungs normally operate at about half full

Work of breathing is increased in the following

situations: When pulmonary compliance is decreased

When airway resistance is increased

When elastic recoil is decreased

When there is a need for increased ventilation


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Variations inLung Volume

Lung Volumes and Capacities

Can be measured by a spirometer

Spirogram is a graph that records inspiration

and expiration


Description Average

Value

Tidal volume (TV) Volume of air entering or leaving lungs during a

single breath

500 ml

Inspiratory reserve

volume (IRV)

Extra volume of air that can be maximally

inspired over and above the typical resting tidal

volume

3000 ml

Inspiratory capacity

(IC)

Maximum volume of air that can be inspired at

the end of a normal quiet expiration (IC =IRV

+ TV)

3500 ml

Expiratory reservevolume (ERV)

Extra volume of air that can be actively expiredby maximal contraction beyond the normal

volume of air after a resting tidal volume

1000 ml

Residual volume

(RV)

Minimum volume of air remaining in the lungs

even after a maximal expiration

1200 ml


Description Average Value

Functional residual

capacity (FRC)

Volume of air in lungs at end of normal

passive expiration (FRC = ERV +

RV)

2200 ml

Vital capacity (VC) Maximum volume of air that can be

moved out during a single breath

following a maximal inspiration (VC =IRV + TV + ERV)

4500 ml

Total lung capacity (TLC) Maximum volume of air that the lungs

can hold (TLC = VC + RV)

5700 ml

Forced expiratory volume

in one second (FEV1)

Volume of air that can be expired

during the first second of expiration ina VC determination


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Respiratory Dysfunction

2 general categories of dysfunction that yieldabnormal results during spirometry

Obstructive lung disease

Restrictive lung disease

Additional conditions affecting respiratory function

Diseases affecting diffusion of O2 and CO2 acrosspulmonary membranes

Reduced ventilation due to mechanical failure

Failure of adequate pulmonary blood flow

Ventilation/perfusion abnormalities involving a poormatching of air and blood so that efficient gasexchange does not occur

Abnormal Spirograms Associated with Obstructive and

Restrictive Lung Diseases

Pulmonary Ventilation

Volume of air breathed in and out in one minute

Pulmonary ventilation = tidal volume x respiratory rate

(ml/min) (ml/breath) (breaths/min)

Alveolar Ventilation

More important than pulmonary ventilation

Volume of air exchanged between theatmosphere and the alveoli per minute

Less than pulmonary ventilation due to

anatomic dead space Volume of air in conducting airways that isuseless for exchange

Averages about 150 ml in adults

Alveolar ventilation =

(tidal volume dead space) x respiratory rate


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Effect of Different Breathing Patterns onAlveolar Ventilation

Alveolar Ventilation Alveolar dead space

Quite small and of little importance in healthy people

Can increase to lethal levels in several types ofpulmonary disease

Local controls act on smooth muscle of airways andarterioles to match airflow to blood flow

Accumulation of CO2 in alveoli decreases airwayresistance leading to increased airflow

Increase in alveolar O2 concentration brings aboutpulmonary vasodilation which increases blood flow tomatch larger airflow

Gas Exchange

At both pulmonary capillary and tissue capillary levels,gas exchange involves simple diffusion of O2 and CO2down partial pressure gradients

Partial pressure exerted by each

gas in a mixture equals total

pressure times the fractionalcomposition of this gas in mixture

O2 is 21% of atmosphere, so

21% of the atmospheric

pressure is due to O2

Oxygen and CarbonDioxide Exchange AcrossPulmonary and Systemic

Capillaries Caused byPartial Pressure Gradients


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Gas Exchange

Factors that affect the rate of gas transfer acrossalveolar membrane:

As surface area increases, diffusion rate increases

Differences in thickness of barrier separating airand blood

Rate of gas exchange is directly proportional to thediffusion coefficient for the gas

Partial pressure gradients of O2 and CO2

Diffusion Constant

Gas Exchange

Exchange across systemic capillaries also occursdown partial pressure gradients

O2 equilibrates to 100 (partial pressure) in alveoli; O2in body tissues is ~40 (cells are using O2)

The PCO2 in systemic capillaries is low (e.g., 40)compared to tissue cells (e.g., 46), (cells are makingCO2 by metabolism)

O2 diffuses from the systemic capillaries into the tissuecells (higher concentration to lower = diffusion)

CO2 diffuses from tissues to capillaries Overall: Blood equilibrates with tissue cells, so blood

leaving systemic capillaries is low in O2 and high in CO2.

The blood returns to the heart and then the lungs. At the pulmonary capillaries, the blood acquires O2 and

releases some CO2.

Gas Transport Most oxygen in the blood is transported bound to

hemoglobin.

Hb + O2 HbO2(reduced hemoglobin or (oxyhemoglobin)

deoxyhemoglobin)

Gas Transport Hemoglobin and O2 combine to form oxyhemoglobin

This is a reversible process, favored to form oxyhemoglobinin the lungs.

Hemoglobin tends to combine with O2 as it diffuses from the

alveoli into the pulmonary capillaries.

A small percentage of O2 is dissolved in plasma.

The dissociation of oxyhemoglobin into hemoglobinand free O2 occurs at the tissue cells.

The reaction is favored in this direction as O2 leaves thesystemic capillaries and enters tissue cells.


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Gas Transport

Partial pressure of O2 (PO2) is the main factor determiningpercent hemoglobin saturation

The percent saturation is high where the PO2 is high (lungs).

The percent saturation is low where the PO2 is low (tissues).

At tissue cells, O2 tends to dissociate from hemoglobin, theopposite of saturation.

This relationship is shown in the oxygen-hemoglobin

dissociation curve.

The plateau of the curve is where the PO2 is high (lungs).

The steep part of the curve exists at the systemic capillaries,where hemoglobin unloads O2 to the tissue cells.

Oxygen-Hemoglobin Dissociation Curve

Gas Transport

Hemoglobin promotes the net transfer of oxygen atboth the alveolar and tissue levels.

Net diffusion of oxygen from alveoli to blood. continuous until hemoglobin is as saturated as possible

(97.5% at 100 mm of Hg). At tissue cells hemoglobin rapidly delivers O

2into blood

plasma and on to tissue cells.

Bohr Effect: shift of the curve to right (more dissociation) isrelated to: high CO2 or acidity (low pH)

Hemoglobin has more affinity for carbon monoxide comparedto O2.

Gas Transport: CO2Most CO2 (about 60%) is transported as Bicarbonate Ion.

CO2 combines with H2O to form carbonic acid (H2CO3).

Carbonic anhydrase facilitates this in the erythrocyte.

Carbonic acid dissociates into H+ and bicarbonate ion (HCO3-).

2-step, reversible process is favored at the tissue cells

The reverse of this process (bicarbonate ions forming freemolecules of CO

2) occurs in the lungs.

30% of the CO2 is bound to hemoglobin in the blood. This is anothermeans of transport.

About 10% of transported CO2 is dissolved in the plasma.

By the chloride shift, the plasma membrane of erythrocytes passivelyfacilitates the diffusion of bicarbonate ions (out of the red cell) andchloride ions.

By the Haldane effect the removal of O2 from hemoglobin at the tissuecells increases the ability of hemoglobin to bind with CO2.


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Abnormalities in Arterial PO2

Hypoxia: Insufficient O2 at the cell level

Categories

Hypoxic hypoxia

Anemic hypoxia Circulatory hypoxia

Histotoxic hypoxia

Hyperoxia: Above-normal arterial PO2

Can only occur when breathing supplemental O2

Scuba divers, hyperbaric chambers, neonates,space exploration

Can be dangerous

Abnormalities in Arterial PCO2

Hypercapnia: excess CO2 in arterial blood

Caused by hypoventilation

Hypocapnia: Below-normal arterial PCO2 levels

Brought about by hyperventilation which can betriggered by

Anxiety states

Fever

Aspirin poisoning

Control of Respiration

Respiratory centers in brain stem establish a rhythmicbreathing pattern

Medullary respiratory center Dorsal respiratory group (DRG)

Mostly inspiratory neurons

Ventral respiratory group (VRG)

Inspiratory neurons

Expiratory neurons

Pre-Btzinger complex Widely believed to generate respiratory rhythm

Pneumotaxic center Sends impulses to DRG that help switch off inspiratoryneurons

Dominates over apneustic center

Control of Respiration

Apneustic center

Prevents inspiratory neurons from being switched off

Provides extra boost to inspiratory drive

Hering-Breuer reflex

Triggered to prevent overinflation of the lungs

Chemical factors that play role in determining

magnitude of ventilation

PO2

PCO2

H+


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Control ofRespiration

Influence of Chemical Factors on Respiration

Peripheral Chemoreceptors

Carotid bodiesare located in thecarotid sinus

Aortic bodies arelocated in theaortic arch

Factors That May Increase VentilationDuring Exercise

Reflexes originating from body movement

Increase in body temperature

Epinephrine release

Impulses from the cerebral cortex


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Influences on VentilationUnrelated to Gas Exchange

Protective reflexes such as sneezing, coughing

Inhalation of noxious agents

can trigger immediate cessation of breathing Pain originating anywhere in body reflexively

stimulates respiratory center

Involuntary modification of breathing occursduring expression of various emotional states

Respiratory center is reflexively inhibited duringswallowing

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Bio18 Ch13 Respiration Spr12