Chapter 23

Chapter 23

The Respiratory System

Upper respiratory tract

Lower respiratory tract

Respiratory System Anatomy

• Structurally, the respiratory system is divided into

upper and lower divisions or tracts.

– The upper respiratory tract

consists of the nose, pharynx

and associated structures.

– The lower respiratory tract

consists of the larynx,

trachea, bronchi and

lungs.


Functionally, the respiratory system is divided into

the conducting zone and the respiratory zone.

– The conducting zone is involved with bringing air to the

site of external respiration and consists of the nose,

pharynx, larynx, trachea, bronchi, bronchioles and

terminal bronchioles.

– The respiratory zone is the main site of gas exchange

and consists of the respiratory bronchioles, alveolar

ducts, alveolar sacs, and alveoli.

Air passing through the respiratory

tract traverses the: – Nasal cavity

– Pharynx

– Larynx

– Trachea

– Primary (1o) bronchi

– Secondary (2o) bronchi

– Tertiary (3o) bronchi

– Bronchioles

– Alveoli (150 million/lung)


The external nose is visible on the face.

The internal nose is a large cavity beyond the nasal

vestibule.

– The internal nasal

cavity is

divided by a

nasal septum into

right and

left nares.


Three nasal conchae (or turbinates) protrude from each lateral wall into the breathing passages.– Tucked under each nasal concha is an opening, or

meatus, for a duct that drains secretions of the sinuses and tears into the nose.

– Receptors in the olfactory epithelium pierce the bone of the cribriform plate.


Respiratory System AnatomyThe pharynx is a hollow tube that starts posterior to the internal nares and descends to the opening of the larynx in the neck.– It is formed by a complex arrangement of skeletal

muscles that assist in deglutition.– It functions as: • a passageway for air and food• a resonating chamber• a housing for the tonsils

Respiratory System AnatomyThe pharynx has 3 anatomical regions: – The nasopharynx; oropharynx; and laryngopharynx

In this graphic, slitting the muscles of the posterior pharynx shows the

back of the tongue in the laryngopharynx.

The nasopharynx is separated from the oropharynx by the hard and soft palate.

The nasopharynx lies behind the internal nares.– It contains the pharyngeal tonsils (adenoids) and

theopenings of the Eustachian tubes (auditory tubes) which come off of it and travels to the middle ear cavity.



The oropharynx lies behind the mouth and participates in both respiratory and digestive functions.– The main palatine tonsils (those usually taken in a

tonsillectomy) and small lingual tonsil are housed here.

The laryngopharynx lies inferiorly and opens into the larynx (voice box) and the esophagus.– It participates in both respiratory and digestive

functions.


Respiratory System Anatomy• The larynx, composed of 9 pieces of cartilage,

forms a short passageway connecting the laryngopharynx with the trachea (the “windpipe”).– The thyroid cartilage (the large

“Adam’s apple”) and the one below it (the cricoid cartilage) are landmarks for making an emergency airway (called a cricothyrotomy).

Anterior view of the larynx

• The epiglottis is a flap of elastic cartilage covered with a mucus membrane, attached to the root of the tongue.– The epiglottis guards the entrance of the glottis, the

opening between the vocal folds.• For breathing, it is held

anteriorly, then pulled back-ward to close off the glottic opening during swallowing.


Respiratory System AnatomyThe rima glottidis (glottic opening) is formed by a pair of mucous membrane vocal folds (the true vocal cords).– The vocal folds are situated high in the larynx just

below where the larynx and the esophagus split off from the pharynx.

Cilia in the upper respiratory tract move mucous and trapped particles down toward the pharynx.Cilia in the lower respiratory tract move them up toward the larynx.


Upper respiratory tract

Lower respiratory tract


As air passes from the laryngopharynx into the larynx, it

leaves the upper respiratory tract and enters the lower

respiratory tract.

Air passing through the respiratory tract

Nasal cavityPharynxLarynxTracheaPrimary bronchiSecondary bronchiTertiary bronchiBronchioles Alveoli (150 million/lung)

Respiratory System AnatomyThe trachea is a semi-rigid pipe made of semi-circular cartilaginous rings, and located anterior to the esophagus.It is about 12 cm long and extends from the inferior portion of the larynx into the mediastinum where it divides into right and left primary (1o, “mainstem”) bronchi.It is composed of 4 layers: a mucous secreting epithelium called the mucosa, and three layers of CT (submucosa, hyaline cartilage, and adventitia).

• The tracheal cartilage rings are incomplete posteriorly, facing the esophagus.– Esophageal masses can press into this soft part of

the trachea and make it difficult to breath, or even totally obstruct the airway.



The right and left primary (1o or “mainstem”) bronchi

emerge from the inferior trachea to go to the lungs,

situated in the right and left pleural cavities.

The carina is an internal

ridge located at the junction

of the two mainstem

bronchi – a very sensitive

area for triggering the

cough reflex.


The 1o bronchi divide to form 2o and 3o bronchi which

respectively supply the lobes and segments of each

lung.

– 3o bronchi divide into

bronchioles which in

turn branch through

about 22 more divisions

(generations). • The smallest are the

terminal bronchioles.

Respiratory System AnatomyThe bronchi and bronchioles go through structural changes as they branch and become smaller.– The mucous membrane changes and then

disappears.– The cartilaginous rings become more sparse, and

eventually disappear altogether.– As cartilage decreases, smooth muscle (under the

control of the Autonomic Nervous System) increases.• Sympathetic stimulation causes airway dilation, while

parasympathetic stimulation causes airway constriction.

Respiratory System AnatomyAll the branches from the trachea to the terminal bronchioles are conducting airways – they do not participate in gas exchange.


The cup-shaped outpouchings which participate in

gas exchange are called alveoli.

– The first alveoli don’t appear until

the respiratory

bronchioles

where they are

rudimentary and

mostly

nonfunctioning.

Respiratory System AnatomyRespiratory bronchioles give way to alveolar ducts, and the epithelium (simple cuboidal) changes to simple squamous, which comprises the alveolar ducts, alveolar sacs, and alveoli.

Taken together, these structures form the functional unit of the lung, which is the pulmonary lobule.– Wrapped in elastic

C.T., each pulmonary lobule contains a lymphatic vessel, an arteriole, a venule and a terminal bronchiole.

The pulmonary lobule


Respiratory System AnatomyAs part of the pulmonary lobule, alveoli are delicate structures

composed chiefly of type I alveolar cells, which allow for

exchange of gases with

the pulmonary capillaries.

– Alveoli make up a large

surface area (750 ft2).

Type II cells secrete a

substance called surfactant

that prevents collapse of the

alveoli during exhalation.


Alveoli macrophages (also called “dust cells”) scavenge

the alveolar surface to engulf and remove microscopic

debris that has made it past the “mucociliary blanket” that

traps most foreign particles higher in

the respiratory tract.

The alveoli (in close proximity

to the capillaries) form the

alveolar-capillary membrane

(“AC membrane”).

Blood Supply to the Lungs• The lungs receive blood via two sets of arteries– Pulmonary arteries carry deoxygenated blood from

the right heart to the lungs for oxygenation– Bronchial arteries branch from the aorta and deliver

oxygenated blood to the lungs primarily perfusing the muscular walls of the bronchi and bronchioles

Ventilation-Perfusion Coupling

• Ventilation-perfusion coupling is the coupling of perfusion (blood flow) to each area of he lungs to match the extent of ventilation (airflow) to alveoli in that area

• In the lungs, vasoconstriction in response to hypoxia diverts pulmonary blood from poorly ventilated areas of the lungs to well-ventilated regions

• In all other body tissues, hypoxia causes dilation of blood vessels to increase blood flow

As organs, the lungs are divided into lobes by fissures.– The right lung is divided by the oblique fissure and

the horizontal fissure into 3 lobes .– The left lung is divided into

2 lobes by the oblique fissure.

Each lobe receives it own 2o bronchus that branches into 3o segmental bronchi (whichcontinue to further divide).


The apex of the lung is superior, and extends slightly above

the clavicles. The base of the

lungs rests on the diaphragm.

The cardiac notch –

in the left lung (the

indentation for the

heart) makes the left

lung 10 % smaller

than the right lung.


• The lungs are separated from each other by the heart and other structures in the mediastinum.

• Each lung is enclosed by a double-layered pleural membrane.– The parietal pleura line the

walls of the thoracic cavity.– The visceral pleura adhere

tightly to the surface of the lungs themselves.



On each side of the thorax, a pleural cavity is formed.

– The integrity of this space (really potential space) between

the parietal and visceral pleural layers is crucial to the

mechanism of breathing.

• Pleural fluid reduces friction and produces a surface tension so

the layers can slide across one another.

The pleura, adherent to the chest wall and to the

lung, produces a mechanical coupling for the two

layers to move together.

Understanding Gases

To understand how this mechanical coupling between the lungs, the pleural cavities and the chest wall results in breathing, we first need to discuss some physics of gases called the

gas laws.

Understanding GasesThe respiratory system depends on the medium of the earth’s atmosphere to extract the oxygen necessary for life.The atmosphere is composed of these gases:– Nitrogen (N2) 78%

– Oxygen (O2) 21%

– Carbon Dioxide (CO2) 0.04%– Water Vapor variable, but on average

around 1%

Understanding GasesThe gases of the atmosphere have a mass and a weight (5 x 1018 kg, most within 11 km of the surface).– Consequently, the atmosphere exerts a

significant force on every object on the planet (recall that pressure is measured as force applied per unit area, P = F/A.)

– We are “accustomed” to the tremendous force pressing down on every square inch of our body.

Understanding GasesA barometer is an instrument that measures atmospheric pressure.– Baro = pressure or

weight– Meter = measure

Air pressure varies greatly depending on the altitude and the temperature.

Understanding GasesThere are many different units used to measure atmospheric pressure. At sea level, the air pressure is:– 14.7 lb/in2 = 1 atmosphere– 760 mmHg = 1 atmosphere– 76 cmHg = 1 atmosphere– 29.9 inHg = 1 atmosphere

At high altitudes, the atmospheric pressure is less; descending to sea level, atmospheric pressure is greater.

Understanding GasesGases obey laws of physics called the gas laws.– These laws apply equally to the gases of the

atmosphere, the gases in our lungs, the gases dissolved in the blood, and the gases diffusing into and out of the cells of our body.

– To understand the mechanics of ventilation and respiration, we need to have a basic understanding of 3 of the 5 common gas laws.

Understanding Gases

• Boyle’s law applies to containers with flexible

walls – like our thoracic cage.

– It says that volume and pressure are inversely

related.• If there is a decrease in volume – there will be an

increase in pressure.

• V 1/P∝

Understanding GasesDalton’s law applies to a mixture of gases.– It says that the pressure of each gas is directly

proportional to the percentage of that gas in the total mixture: PTotal = P1 + P2 + P3 …

– Since O2 = 21% of atmosphere, the partial pressure exerted by the contribution of just O2 (written pO2 or PAO2) = 0.21 x 760 mmHg = 159.6 mmHg at sea level.

Gas Exchange

Gas Exchange

You must be connected to the internet to run this animation

http://www.wiley.com/college/tortora/0470084715/animations/anim_gas_exch/screen0.swf

Understanding GasesHenry’s law deals with gases and solutions.– It says that increasing the partial pressure of a gas

“over” (in contact with) a solution will result in more of the gas dissolving into the solution.

– The patient in this picture is getting more O2 in contact with his

blood - consequently, more oxygen goes

into his blood.Medicimage/Phototake

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Chapter 23

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