The Respiratory System

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Human Anatomy & PhysiologySEVENTH EDITION

Elaine N. MariebKatja Hoehn

PowerPoint® Lecture Slides prepared by Vince Austin, Bluegrass Technical and Community College

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22The Respiratory System

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Questions 1. Why do we breath oxygen? What is the ultimate

role of O2 in the body? 2. Why is the majority of our respiratory system

inside our body?


Oxygen’s Journey 98% of the O2 serves to make ATP by going inside

the mitochondrion and becoming the terminal acceptor of electrons in the Electron Transport Chain

2% unfortunately becomes free radicals causing unwanted oxidation

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.2







Cytochrome Oxidase


Why is the majority of our respiratory system inside our bodies?

When living creatures left the waters and came to the terrestrial (land) environment – the respiratory system had to be internalized or “the respiratory epithelium would dry out.”

But still needed lots of surface area for enough diffusion of oxygen to supply the trillions of body cells in accordance with Fick’s Diffusion Equation

In order to not make body larger but still have lots of diffusion surface area – must branch the respiratory system inside the body – 70 meters squared –tennis court size


Respiratory System Consists of the respiratory and conducting zones Respiratory zone:

Site of gas exchange Consists of bronchioles, alveolar ducts, and alveoli


Respiratory System Conducting zone:

Conduits for air to reach the sites of gas exchange Includes all other respiratory structures (e.g., nose,

nasal cavity, pharynx, trachea) Respiratory muscles – diaphragm and other

muscles that promote ventilation

PLAY InterActive Physiology ®: Anatomy Review: Respiratory Structures, page 3


Respiratory System

Figure 22.1


Upper vs. Lower Respiratory System The upper respiratory tract consists of the nasal

cavity (nose), pharynx, and the larynx. The "lower respiratory tract" consists of the lower part of the respiratory system. This consists of the trachea (wind pipe), bronchial tubes, bronchioles, and lungs. The upper and lower respiratory tracts make up our whole respiratory system and work in a synchronizing pattern to make it possible to breathe.



Major Functions of the Respiratory System To supply the body with oxygen and dispose of

carbon dioxide Respiration – four distinct processes must happen

Pulmonary ventilation – moving air into and out of the lungs

External respiration – gas exchange between the lungs and the blood


Major Functions of the Respiratory System Transport – transport of oxygen and carbon dioxide

between the lungs and tissues Internal respiration – gas exchange between

systemic blood vessels and tissues


The Nose Composed of an external part Composed of an internal part – nostrils and other

features


Function of the Nose The only externally visible part of the respiratory

system that functions by: Providing an airway for respiration Moistening and warming the entering air Filtering inspired air and cleaning it of foreign

matter Serving as a resonating chamber for speech Housing the olfactory receptors


Structure of the Nose Nose is divided into two regions:

External nose, including the root, bridge, dorsum nasi, and apex

Internal nasal cavity Philtrum – a shallow vertical groove inferior to the

apex The external nares (nostrils) are bounded laterally

by the alae


Structure of the Nose

Figure 22.2a


Structure of the Nose

Figure 22.2b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 7.2a



Internal Nose -- Nasal Cavity Lies in and posterior to the external nose Is divided by a midline nasal septum Opens posteriorly into the nasal pharynx via

internal nares The ethmoid and sphenoid bones form the roof The floor is formed by the hard and soft palates


Inside the Nose 1. When first come into nose (Nasal Vestibule)–

you have the skin of the nose – covered by a non-keratinized stratified squamous epithelium with plenty sweat and oil glands plus Vibrissae (Nose hairs)

2. Come in further and find two types of mucous membranes

Olfactory mucous membrane – smell area

Respiratory mucous membrane – the other membrane


Respiratory mucous membrane – covered by a ciliated pseudostratified columnar

epithelium with plenty of goblet cells interspersed. The lamina propria had many blood vessels and serous and mucous glands plus lots of lymphatics and white blood cells.




Nasal Mucosae


Nasal Cavity Vestibule – nasal cavity superior to the nares

Vibrissae – hairs that filter coarse particles from inspired air

Olfactory mucosa Lines the superior nasal cavity Contains smell receptors


Nasal Cavity Respiratory mucosa

Lines the balance of the nasal cavity Glands secrete mucus containing lysozyme and defensins to help

destroy bacteria Plasma cells that secrete IgE and IgA Mast Cells and other WBC’s Sneeze reflex areas Swell Bodies Kiesselbach’s Area - Capillary and Venous Plexuses


Kiesselbach’s Area & Swell Bodies Kiesselbach’s Area - a region in the anteroinferior part of the

nasal septum, where four arteries anastomose to form a vascular plexus called Kiesselbach's plexus. usual site for epistaxis as it is exposed to drying effect of inspiratory current. Ninety percent of nose bleeds arise there.

Swell Bodies - The nasal swell body is a widened region of the septum located superior to the inferior turbinates and anterior to the middle turbinates, and of potential importance to the airflow-regulating nasal valve. Although little is known of this structure in terms of vasoreactivity and tendency to limit airflow by vascular engorgement, some consider the swell body to be physiologically analagous to the inferior turbinate.



Kiesselbach’s Area


Nasal Cavity Inspired air is:

Humidified by the high water content in the nasal cavity

Warmed by rich plexuses of capillaries Ciliated mucosal cells remove contaminated mucus


Nasal Cavity Superior, medial, and inferior conchae:

Protrude medially from the lateral walls Increase mucosal area Enhance air turbulence and help filter air

Sensitive mucosa triggers sneezing when stimulated by irritating particles


Nasal Cavity

Figure 22.3b



Functions of the Nasal Mucosa and Conchae During inhalation the conchae and nasal mucosa:

Filter, heat, and moisten air During exhalation these structures:

Reclaim heat and moisture Minimize heat and moisture loss


Paranasal Sinuses Sinuses in bones that surround the nasal cavity Sinuses lighten the skull and help to warm and

moisten the air



Pharynx Funnel-shaped tube of skeletal muscle that

connects to the: Nasal cavity and mouth superiorly Larynx and esophagus inferiorly

Extends from the base of the skull to the level of the sixth cervical vertebra


Pharynx It is divided into three regions

Nasopharynx Oropharynx Laryngopharynx


Nasopharynx Lies posterior to the nasal cavity, inferior to the

sphenoid, and superior to the level of the soft palate

Strictly an air passageway Lined with pseudostratified columnar epithelium Four entrances in nasopharynx – two internal nares

and two openings from the eustachian (auditory) tubes

Pharyngeal Tonsil – when enlarged is Adenoid



Nasal Cavity

Figure 22.3b


Lymphatics in Nasal and Oral Areas Waldeyer's tonsillar ring is an anatomical term describing the

lymphoid tissue ring located in the pharynx and to the back of the oral cavity.

It was named after the nineteenth century German anatomist Heinrich Wilhelm Gottfried von Waldeyer-Hartz.

The ring consists of (from superior to inferior): Pharyngeal tonsil (also known as 'adenoids' when infected) Tubal tonsils Palatine tonsils (commonly called "the tonsils" in the

vernacular, less commonly termed "faucial tonsils") Lingual tonsils



Olfactory Mucosae How we smell


Nasal Cavity

Figure 22.3b




Nasopharynx Closes during swallowing to prevent food from

entering the nasal cavity The pharyngeal tonsil lies high on the posterior

wall Pharyngotympanic (auditory) tubes open into the

lateral walls


Oropharynx Extends inferiorly from the level of the soft palate

to the epiglottis Opens to the oral cavity via an archway called the

isthmus of the fauces Serves as a common passageway for food and air


Oropharynx The epithelial lining is protective stratified

squamous epithelium Palatine tonsils lie in the lateral walls of the fauces Lingual tonsil covers the base of the tongue



Laryngopharynx Serves as a common passageway for food and air Lies directly posterior to the upright epiglottis Extends to the larynx, where the respiratory and

digestive pathways diverge


Larynx (Voice Box) Attaches to the hyoid bone and opens into the

laryngopharynx superiorly About 2 inches in length extending from the 3rd to

6th cervical vertebrae Continuous with the trachea posteriorly The three functions of the larynx are:

To provide a patent airway To act as a switching mechanism to route air and

food into the proper channels To function in voice production


Framework of the Larynx Cartilages (hyaline) of the larynx

Shield-shaped anterosuperior thyroid cartilage with a midline laryngeal prominence (Adam’s apple)

Signet ring–shaped anteroinferior cricoid cartilage Three pairs of small arytenoid, cuneiform, and

corniculate cartilages Epiglottis – elastic cartilage that covers the

laryngeal inlet during swallowing


Framework of the Larynx

Figure 22.4a, b

Copyright © 2010 Pearson Education, Inc.

Figure 10.8a Muscles of the anterior neck and throat that promote swallowing.

MylohyoidAnteriorbellyPosteriorbelly

Stylohyoid (cut)ThyrohyoidThyroid cartilageof the larynx

Median raphe

Sternothyroid

StylohyoidHyoid boneOmohyoid(superior belly)SternohyoidSternocleido-mastoid Omohyoid(inferior belly)

Digastric

Thyroid gland

(a)

Copyright © 2010 Pearson Education, Inc.

Extrinsic Laryngeal MusclesInfrahyoid Group (Pull larynx and hyoid bone down)• Sternohyoid• Sternothyroid• Thyrohyoid• Omohyoid

Suprahyoid Group• Stylohyoid• Myohyoid• Digastric• Geniohyoid• Stylopharyngeas


Internal Larynx


Movements of Vocal Cords

Figure 22.5


Vocal Ligaments Attach the arytenoid cartilages to the thyroid

cartilage Composed of elastic fibers that form mucosal folds

called true vocal cords The medial opening between them is the glottis They vibrate to produce sound as air rushes up

from the lungs


Vocal Ligaments False vocal cords

Mucosal folds superior to the true vocal cords Have no part in sound production


Vocal Production Speech – intermittent release of expired air while

opening and closing the glottis Pitch – determined by the length and tension of the

vocal cords Loudness – depends upon the force at which the air

rushes across the vocal cords The pharynx resonates, amplifies, and enhances

sound quality Sound is “shaped” into language by action of the

pharynx, tongue, soft palate, and lips


Movements of Vocal Cords

Figure 22.5


Intrinsic Laryngeal Muscles Cricothyroid muscles lengthen and stretch the vocal folds. Posterior cricoarytenoid muscles abduct and externally rotate

the arytenoid cartilages, resulting in abducted vocal cords. Lateral cricoarytenoid muscles adduct and internally rotate the

arytenoid cartilages, which can result in adducted vocal folds. Transverse arytenoid muscle adducts the arytenoid cartilages,

resulting in adducted vocal cords. Oblique arytenoid muscles narrow the laryngeal inlet by

constricting the distance between the arytenoid cartilages and epiglottis.

Vocalis muscles adjust tension in vocal folds. Thyroarytenoid muscles - sphincter of vestibule, narrowing the

laryngeal inlet.


Wave Description


Sphincter Functions of the Larynx The larynx is closed during coughing, sneezing, and

Valsalva’s maneuver Valsalva’s maneuver

Air is temporarily held in the lower respiratory tract by closing the glottis

Causes intra-abdominal pressure to rise when abdominal muscles contract

Helps to empty the rectum Acts as a splint to stabilize the trunk when lifting

heavy loads


Trachea Flexible and mobile tube extending from the

larynx into the mediastinum – about 4 inches long and ¾ inch wide

Composed of three layers Mucosa – made up of goblet cells and ciliated

epithelium Submucosa – connective tissue deep to the mucosa Adventitia – outermost layer made of C-shaped

rings of hyaline cartilage


Trachea

Figure 22.6a


Conducting Zone: Bronchi Carina of the last tracheal cartilage marks the end

of the trachea and the beginning of the bronchi Air reaching the bronchi is:

Warm and cleansed of impurities Saturated with water vapor

Bronchi subdivide into secondary bronchi, each supplying a lobe of the lungs

Air passages undergo 23 orders of branching

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Conducting Zone: Bronchial Tree Tissue walls of bronchi mimic that of the trachea As conducting tubes become smaller, structural

changes occur Cartilage support structures change Epithelium types change Amount of smooth muscle increases


Conducting Zone: Bronchial Tree Bronchioles

Consist of cuboidal epithelium Have a complete layer of circular smooth muscle Lack cartilage support and mucus-producing cells


Conducting Zones

Figure 22.7


Respiratory Zone Defined by the presence of alveoli; begins as

terminal bronchioles feed into respiratory bronchioles

Respiratory bronchioles lead to alveolar ducts, then to terminal clusters of alveolar sacs composed of alveoli

Approximately 300 million alveoli: Account for most of the lungs’ volume Provide tremendous surface area for gas exchange


Respiratory Zone

Figure 22.8a


Respiratory Zone

Figure 22.8b


Respiratory Membrane This air-blood barrier is composed of:

Alveolar and capillary walls Their fused basal laminas

Alveolar walls: Are a single layer of type I epithelial cells Permit gas exchange by simple diffusion Secrete angiotensin converting enzyme (ACE)

Type II cells secrete surfactant


Alveoli Surrounded by fine elastic fibers Contain open pores that:

Connect adjacent alveoli Allow air pressure throughout the lung to be

equalized House macrophages that keep alveolar surfaces

sterile


Respiratory Membrane

Figure 22.9b


Respiratory Membrane

Figure 22.9c ,d


Surfactant is secreted by the type II pneumonocytes Composition Lipids Over 90% of the surfactant is lipids; around half (50%) of

which is dipalmitoylphosphatidylcholine (DPPC). Phosphatidylcholine molecules form ~85% of the lipid in surfactant. Phosphatidylglycerol (PG) forms about 11% of the lipids in surfactant, it has unsaturated fatty acid chains that fluidize the lipid monolayer at the interface. Neutral lipids and cholesterol are also present. The components for these lipids diffuse from the blood into type II alveolar cells where they are assembled and packaged for secretion into secretory organelles called lamellar bodies.


Surfactant Reduces surface tension on alveolar surface Complex mixture of phospholipids, triglycerides,

fatty acids, and proteins Ps = 2T/r

Ps is pressure in a sphere As radius gets smaller the pressure in the sphere

gets greater – thus its air would empty into larger alveoli


Proteins Proteins make up the remaining 10% of surfactant. Half of this

10% is plasma proteins but the rest is formed by the apoproteins SP-A (SFTPA1), B (SFTPB), C (SFTPC) and D (SFTPD). (SP standing for "surfactant protein".)

SP-A and SP-D confer innate immunity as they have carbohydrate recognition domains that allow them to coat bacteria and viruses promoting phagocytosis by macrophages. SP-A is also thought to be involved in a negative feedback mechanism to control the production of surfactant.


SP-B and SP-C are hydrophobic membrane proteins that increase the rate that surfactant spreads over the surface. SP-B and SP-C are required for proper biophysical function of the lung. Humans and animals born with a congenital absence of SP-B suffer from intractable respiratory failure whereas those born lacking SP-C tend to develop progressive interstitial pneumonitis.


Numerous agents such as Beta adrenergic agonists, activators of protein Kinase C, leukotrienes and purinergic agonists stimulate secretion of surfactant.

Respiratory Distress of the Newborn is due to lack of surfactant particularly the PG.


Gross Anatomy of the Lungs Lungs occupy all of the thoracic cavity except the

mediastinum Root – site of vascular and bronchial attachments Costal surface – anterior, lateral, and posterior

surfaces in contact with the ribs Apex – narrow superior tip Base – inferior surface that rests on the diaphragm Hilus – indentation that contains pulmonary and

systemic blood vessels


Organs in the Thoracic Cavity

Figure 22.10a


Transverse Thoracic Section

Figure 22.10c


Lungs Cardiac notch (impression) – cavity that

accommodates the heart Left lung – separated into upper and lower lobes

by the oblique fissure Right lung – separated into three lobes by the

oblique and horizontal fissures There are 10 bronchopulmonary segments in each

lung



Serous Membranes (Peritoneum, Pericardium, Pleura) a serous membrane (or serosa) is a smooth membrane consisting of

a thin layer of cells which secrete serous fluid – lining several body cavities, known as serous cavities, where they secrete a lubricating fluid which reduces friction.

Each serous membrane is composed of a secretory epithelial layer and a connective tissue layer underneath.

The epithelial layer, known as mesothelium, consists of a single layer of avascular flat nucleated cells (simple squamous) which produce the lubricating serous fluid. This fluid has a consistency similar to watery mucus. These cells are bound tightly to the underlying connective tissue.

The connective tissue layer provides the blood vessels and nerves for the overlying secretory cells, and also serves as the binding layer which allows the whole serous membrane to adhere to organs and other structures.


Pleurae Thin, double-layered serosa Parietal pleura

Covers the thoracic wall and superior face of the diaphragm

Continues around heart and between lungs


Pleurae Visceral pleura covers the external lung surface and the parietal

pleura is stuck to the inside of the chest wall. The space between the two is the pleural space (cavity). It contains pleural fluid.


Blood Supply to Lungs Lungs are perfused by two circulations: pulmonary

and bronchial Pulmonary arteries – supply systemic venous

blood to be oxygenated Branch profusely, along with bronchi Ultimately feed into the pulmonary capillary

network surrounding the alveoli Pulmonary veins – carry oxygenated blood from

respiratory zones to the heart


Main Pulmonary artery (trunk)

Pulmonary veins


Blood Supply to Lungs Bronchial arteries – provide systemic blood to the

lung tissue itself (akin to the coronary circulation for the heart – which supplies blood to the heart itself

Arise from aorta and enter the lungs at the hilus Supply all lung tissue except the alveoli

Bronchial veins anastomose with pulmonary veins Pulmonary veins carry most venous blood back to

the heart


Bronchial arteries come off theAorta

Bronchial veins dump into pulmonary veins


Important Mathematical Concepts in Respiratory 1. Resistance R = 8ηL/πR4

2. Compliance C = ∆V/∆P 3. Flow Flow = ∆P/ R 4. Diffusion D = A x Dc /t (Co – Ci) 5. Surface Tension of Water ? 6. Ideal Gas Equation ? 7. Boyle’s Law ? 8. Charles Law ? 9. Dalton’s Law of Partial Pressures? 10 . Henry’s Law ?


Water exerts a surface tension Surface tension is the expression of

intermolecular attraction at the surface of a liquid, in contact with air or another gas, a solid, or another immiscible liquid, tending to pull the liquid inward from its surface.

Water sticks to water and the top of its surface is very, very tight – all of this due to its trillions and trillions of hydrogen bonds – holding the water molecules tightly together.


The surface tension of water will cause the alveolus to collapse when

the alveolus gets smaller duringexhalation – if it were not forsurfactant (discussed later).


Ps = 2T/rT = Ps x r/2

Ps – pressure in a sphereT – Tensionr - radius

As radius gets smaller pressureincreases.


Ideal Gas Equation & Boyle’s LawPV = nRT

P – pressure V- Volume n- number of moles R- gas rate constant (8.314472 J·K−1) T – Temperature

in Kelvin Boyles Law: There is an inverse relationship between

Pressure and Volume. Volume is how much space a set amount (number of

atoms or molecules) of gas or liquid occupies. If the volume (space occupied) got larger– but the amount (number of atoms/molecules) stayed the same – the pressure exerted by the gas or liquid would go down.


Charles Law and Dalton’s Law Charles Law: There is a direct relationship

between Volume and Temperature. When a gas is heated it will expand PV = nRT

Dalton’s Law of Partial Pressures: Each type gas in a mixture of gases will exert a pressure independent of the other types of gases in the mixture. The amount of the pressure exerted by each type of gas is in accordance with its percent present in the mixture times the total pressure exerted by all of the gases.


Dalton’s Law Atmospheric Pressure at Sea Level –

760 mmHg/square inch (14.7 lbs./square inch)

Composition of Atmosphere N2 – 78.0826% O2 – 29.94% CO2 - .034%


Dalton’s Law of Partial Pressures 760 mm Hg x .21 = O2 = 159 mm Hg

760 mm Hg x .0004 = CO2 = .30 mm Hg

760 mm Hg x .79 = N2 = 600.4 mm Hg Percent of other gases = ________________ Total 760 mm Hg


Henry’s Law The amount of gas that will dissolve in a liquid

depends on the partial pressure of the gas above the liquid (push down force) and the solubility coefficient of the gas for the liquid (pull down force).

Solubility Coefficients of Gases in H2O

(Determination of how much a certain gas likes a certain liquid)

Oxygen --- 0.024 Carbon Dioxide - 0.57 (likes to dissolve in water the best)

Nitrogen – 0.012 Carbon Monoxide – 0.018


Henry’s Law

Push down force – pressure above the liquid

How much does that particular liquid want to pull into itself that Particular gas. (Determined by Solubility Coefficient)


Breathing (Inhalation and Exhalation) This process depends on Boyle’s Law – the inverse

relationship between Pressure and Volume A mechanical process that depends on volume

changes in the thoracic cavity Volume changes lead to pressure changes, which lead

to the flow of gases to equalize pressure Breathing, or pulmonary ventilation, consists of two

phases Inspiration (Inhalation) – air flows into the lungs Expiration – (Exhalation )gases exit the lungs


Factors involved in inhalation and exhalation 1. Terms 2. Muscles involved 3. Volumes of air inhaled and exhaled 4. Compliance


Terms Normal breath rate is 12 – 20 breaths per minute Fast breath rate – Tachypnea Slow breath rate – Bradypnea Cessation of Breathing - Apnea Average volume during restful inhalation and

exhalation – 500cc (ml.) Deep Breathing – Hyperpnea Shallow Breathing – Hypopnea Quiet Breathing – Eupnea Stressful Breathing - Dyspnea


Muscles for Breathing It is unusual in the body that although breathing is

an involuntary action – it operates using skeletal muscles – thus using the somatic nervous system rather than the autonomic nervous system

Main muscle for breathing is the Diaphragm Muscles for inhalation – external intercostals,

scalenes, pectoralis minor, sternocleidomastoid, trapezius

Muscles of exhalation – internal intercostals, internal and external obliques, rectus abdominus, transversalis


Diaphragm

Each hemi-diaphragm is controlled by the Phrenic nerve on itsRespective side. Originates from spinal nerves C3, C4 and C5


An average of 10 cm at the top of the dome

When the diaphragm contracts it lowers – thus increasing chest size for inhalation – when it relaxes it domes again – thus decreasing chest sizein exhalation

Hiccups- singultus


Muscle origin is back of upper rib – insertionfront of rib below – pulls chest outward for inhalation

Origin front of upper rib – insertion is back of rib below – pulls chest Inward for exhalation


Scalenes raise ribs 1 and 2


Inhalation musclesPectoralis minor raises ribs 3, 4 and 5


Trapezius – keeps upper back straight


Muscles of Exhalation


Lung Volumes


Respiratory Volumes Tidal volume (TV) – air that moves into and out of

the lungs with each breath (approximately 500 ml) Inspiratory reserve volume (IRV) – air that can be

inspired forcibly beyond the tidal volume (2100–3200 ml)

Expiratory reserve volume (ERV) – air that can be evacuated from the lungs after a tidal expiration (1000–1200 ml)

Residual volume (RV) – air left in the lungs after strenuous expiration (1200 ml)


Respiratory Capacities Inspiratory capacity (IC) – total amount of air that

can be inspired after a tidal expiration (IRV + TV) Functional residual capacity (FRC) – amount of air

remaining in the lungs after a tidal expiration (RV + ERV)

Vital capacity (VC) – the total amount of exchangeable air (TV + IRV + ERV)

Total lung capacity (TLC) – sum of all lung volumes (approximately 6000 ml in males)


Dead Space Anatomical dead space – volume of the conducting

respiratory passages (150 ml) Alveolar dead space – alveoli that cease to act in

gas exchange due to collapse or obstruction Total dead space – sum of alveolar and anatomical

dead spaces


Respiratory Compliance C = ∆V/∆P There are two compliances involved in breathing.

One is chest wall compliance and other is lung compliance.

Chest wall compliance is due to the ease of movement of the rib cage and the tension of the various skeletal muscles associated with the rib cage. When the lungs are removed from the chest the chest cage springs outward.


Lung Compliance C = ∆V/∆P The ease with which lungs can be expanded Specifically, the measure of the change in lung

volume that occurs with a given change in transpulmonary pressure

Determined by two main factors Distensibility of the lung tissue and surrounding

thoracic cage Surface tension of the alveoli


Lung Compliance Two forces act to pull the lungs inward - away from the

thoracic wall, promoting lung collapse. These are also the two forces that determine lung compliance

Elasticity (due to elastic fibers) of lungs causes them to assume the smallest possible size

Surface tension of alveolar fluid draws alveoli to their smallest possible size. This is the main force under normal conditions determining lung compliance.

Opposing force – elasticity of the chest wall pulls the thorax outward to enlarge the lungs


Lung Compliance Curves (Hysteresis) The compliance of the lungis different depending on ifan individual is breathing in (inspiration) versus breathing out -expiration.

When breathing in - it ismore difficult to expand thelungs due mainly to needing to break the surface tension of water.

When breathing out – the surface tension of water helpspull the lungs inward.


Pressure Relationships in the Thoracic Cavity Respiratory pressure is always described relative to

atmospheric pressure Atmospheric pressure (Patm)

Pressure exerted by the air surrounding the body Negative respiratory pressure is less than Patm

Positive respiratory pressure is greater than Patm


Pressure Relationships in the Thoracic Cavity Intrapulmonary pressure (Ppul) – pressure within

tubes (bronchi, bronchioles and the alveoli Intrapleural pressure (Pip) – pressure within the

pleural cavity


Pressure Relationships Intrapulmonary pressure and intrapleural pressure

fluctuate with the phases of breathing Intrapulmonary pressure always eventually

equalizes itself with atmospheric pressure Intrapleural pressure is always less than

intrapulmonary pressure and atmospheric pressure


Pressure Relationships

Figure 22.12


Lung Collapse (Atelectasis) Caused by equalization of the intrapleural pressure

with the intrapulmonary pressure Transpulmonary pressure keeps the airways open

Transpulmonary pressure – difference between the intrapulmonary and intrapleural pressures (Ppul – Pip)


Inspiration The diaphragm and external intercostal muscles

(inspiratory muscles) contract and the rib cage rises The lungs are stretched and intrapulmonary

volume increases Intrapulmonary pressure drops below atmospheric

pressure (1 mm Hg) Air flows into the lungs, down its pressure

gradient, until intrapleural pressure = atmospheric pressure


Inspiration

Figure 22.13.1


Expiration Inspiratory muscles relax and the rib cage descends

due to gravity Thoracic cavity volume decreases Elastic lungs recoil passively and intrapulmonary

volume decreases Intrapulmonary pressure rises above atmospheric

pressure (+1 mm Hg) Gases flow out of the lungs down the pressure

gradient until intrapulmonary pressure is 0


Expiration

Figure 22.13.2


Pulmonary Pressures

Figure 22.14

15 breaths per minute with4 seconds per breath


I to E ratio If a person has a breath rate of 12 breaths per

minute – then each breath (both inspiration and expiration) is 5 seconds. If the breath rate is faster the time of each breath is less.

The I (Inspiration) time is generally 2 seconds and the E (Expiration) time is generally 3 seconds – thus and I/E ratio of 2:3 (1:1.5 – 1:2)

The expiration time in actuality is generally no longer than the inspiration time – but it includes the brief moment in time a person is not breathing in or out


Nonrespiratory Air Movements Most result from reflex action Examples include: coughing, sneezing, crying,

laughing, hiccupping, and yawning


Alveolar Ventilation

Alveolar ventilation rate (AVR) which is really exchange zone ventilation rate. This measures the flow of fresh gases into and out of the exchange regions of the lungs. The exchange zones include the respiratory bronchiole, alveolar duct, alveolar sac and alveolus

Slow, deep breathing increases AVR and rapid, shallow breathing decreases AVR

AVR = frequency X (TV – dead space)

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


Ventilation-Perfusion Coupling Ventilation – the amount of gas reaching the

alveoli Perfusion – the blood flow reaching the alveoli Ventilation and perfusion must be tightly regulated

for efficient gas exchange


Ventilation-Perfusion Coupling Changes in PCO2 in the alveoli cause changes in the

diameters of the bronchioles Passageways servicing areas where alveolar carbon

dioxide is high dilate Those serving areas where alveolar carbon dioxide

is low constrict


V/Q ratio and Dead Space Total ventilation (Vt)is the amount of air coming

into the lungs in a minute (ml./min.) on average 500 cc x 12 breaths per minute = 6 Liters

Exchange zone ventilation (VE) is how much air is going into the exchange zone in a minute. This is the amount of air entering the lungs during inspiration – minus the dead space.

Q is perfusion – thus Q is the blood perfusion rate to the lungs in a minute – which is really the cardiac output - approximately 5 Liters per minute


Surface Area and Thickness of the Respiratory Membrane (Exchange areas) Respiratory membranes (all membranes where

exchange takes place): only 0.5 to 1 m Alveolus is the thinnest allowing for efficient gas

exchange Have a total surface area (in males) of about 60 m2

(40 times that of one’s skin) Thicken if lungs become waterlogged and

edematous, whereby gas exchange is inadequate and oxygen deprivation results

Decrease in surface area with emphysema, when walls of adjacent alveoli break through


Respiratory Dead Space The airways in which there is ventilation (air coming in and out) but

the air pipe wall is too thick (all airways prior to the respiratory bronchioles) to allow diffusion of gases (O2, CO2) into and out of the bloodstream. There are two dead spaces – the anatomic and the alveolar - both added together equal the physiologic dead space.

Anatomic Dead Space - the airway pipes prior to the respiratory bronchioles have walls that are too thick to perform exchange of gases between them and the blood. Thus these pipes are conduits (like the arteries and veins in the circulatory system) transferring to the exchange regions (respiratory bronchioles, alveolar ducts, alveolar sacs and alveolus). This is similar to the capillaries which are the exchange vessels in the blood circulation. These airways are termed the anatomic (natural) dead space – in the physiologic demo human – an average of 150 cc.


Physiologic Dead Space = Anatomic Dead Space + Alveolar Dead Space (Alveolar Dead Space is bad airways that should have allowed diffusion into and out of the bloodstream – but for some reason cannot. If an individual has none of these bad airways – the physiologic dead space will equal to the anatomic dead space.

Ideally the exchange zone ventilation rate (air entering) should equal the perfusion rate (blood flow rate) in order to get the best oxygenation of the blood.



Q is perfusion – thus Q is the blood perfusion rate to the lungs in a minute – which is really the cardiac output - approximately 5 Liters per minute

Though the blood supply to lungs as a whole is equal to the cardiac output. Different regions (zones) of the lung get varying blood supplies. Most consider there to be 3 zones. The upper zone which is above the heart gets the least blood – but the best ventilation (high V/Q). The middle zone which is at the level of the heart gets an equal V/Q ratio. The lower zone below the heart gets excellent perfusion but less ventilation – low V/Q.

If the blood can get to an area of the diffusable portion (exchange region) but the ventilation cannot get there – it is termed a shunt.



Ventilation-Perfusion Coupling

Figure 22.19

Reduced alveolar ventilation;excessive perfusion

Reduced alveolar ventilation;reduced perfusion

Pulmonary arteriolesserving these alveoliconstrict

Enhanced alveolar ventilation;inadequate perfusion

Enhanced alveolar ventilation;enhanced perfusion

Pulmonary arteriolesserving these alveolidilate

PO2

PCO2

in alveoli

PO2

PCO2

in alveoli


Friction is the major nonelastic source of resistance to airflow

The relationship between flow (F), pressure (P), and resistance (R) is:

Physical Factors Influencing Ventilation: Airway Resistance

PRF =

R = 8ηL/πR4


Resistance to airflow in the respiratory system is composed of three individual resistances; airway resistance, pulmonary (lung) resistance, and chest wall resistance.

Airway resistance is the resistance of the entire airway system from the tip of the nose (for nasal breathing) or mouth (for mouth breathing) to the alveoli.

Pulmonary resistance (lung resistance) is the resistance of the lungs and airways combined.

Chest wall resistance is the resistance of the chest wall and abdominal structures.

Airway resistance is subsumed into upper airway resistance ( nose to glottis) and lower airway resistance (glottis to alveoli)


25% - 40% of the total resistance to airflow is located in the upper airways, namely the nose, nasal turbinates, oropharynx, nasopharynx and larynx

Airflow resistance of the lower airways can be divided between the large airways (> 2mm in diameter) – first 8 generations of branchings, the medium sized airways (segmental bronchi, ≥ 2 mm) and the small airways (bronchioles < 2 mm)

It would be thought that the greatest resistance in the airways should be in the smaller airways since their diameters are small. However the smallest airways contribute very little to overall resistance even their individual resistances are high. The greatest resistance is in the medium sized airways.

The reason for this is (1) the cross sectional area of the smaller airways is large – thus the velocity of flow is low and (2) the smaller airways are in parallel arrangement – thus their total resistances is low.


Resistance in Repiratory Passageways

Figure 22.15

Greatest resistancein the medium sized airways


Respiratory Zone

Figure 22.8a


Formulas of Importance Resistance –a force of impedance (holding back) R =

8ηL/πR4 , η is viscosity of the gas or liquid, L is the length of the vessel, and R is the resistance raised to the 4th power

Summation (∑) of Resistances – adding up the resistors in flow arrangement a series arrange

Resistors in series – one resistor in front of another ∑ = R1 + R2 + R3 + ……

Resistors in parallel – a pipe leads into a branching set of pipes ∑ = 1/R1 + 1/R2 + 1/R3 +..

Note: resistors in parallel give less total resistance than those in series (think of the capillary arrangement)


Formulas of importance Flow = ∆P/ R, ∆P is the change in pressure from one area to

another (P1 – P2) – in the direction of flow, R is the resistance (Note: pressure drops off as a fluid or gas passes further down the pipe – thus the pressure in proximal area 1 (P1) is higher than the pressure is distal area 2. The more pressure drop off the more the flow. Also, the less the resistance the better the flow.

Rate of Flow = amount of gas or liquid/time (example ml/min) Velocity of flow = amount of gas or liquid/time/cross sectional area

(another way of looking at it is Vf = rate of flow/cross sectional area)

example of velocity of flow ml. /min per cm2

Note: Area of a circle (like the inside of a vessel ) = equals pi (π) times the radius squared (π⋅r2), example ml. /min per cm2

Flow formula derived Ohm’s Law


Resistance in Repiratory Passageways

Figure 22.15

Greatest resistancein the medium sized airways


Airway Resistance As airway resistance rises, breathing movements

become more strenuous Severely constricted or obstructed bronchioles:

Can prevent life-sustaining ventilation Can occur during acute asthma attacks which stops

ventilation Epinephrine release via the sympathetic nervous

system dilates bronchioles and reduces air resistance


Alveolar Surface Tension Surface tension – the attraction of liquid molecules

to one another at a liquid-gas interface The liquid coating the alveolar surface is always

acting to reduce the alveoli to the smallest possible size

Surfactant, a detergent-like complex, reduces surface tension and helps keep the alveoli from collapsing


Lung Compliance The ease with which lungs can be expanded Specifically, the measure of the change in lung

volume that occurs with a given change in transpulmonary pressure

Determined by two main factors Distensibility of the lung tissue and surrounding

thoracic cage Surface tension of the alveoli


Factors That Diminish Lung Compliance Scar tissue or fibrosis that reduces the natural

resilience of the lungs Blockage of the smaller respiratory passages with

mucus or fluid Reduced production of surfactant Decreased flexibility of the thoracic cage or its

decreased ability to expand


Factors That Diminish Lung Compliance Examples include:

Deformities of thorax Ossification of the costal cartilage Paralysis of intercostal muscles

Documents

The Respiratory System