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Collin County Community College

BIOL. 2402Anatomy & Physiology

WEEK 9

Respiratory System

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Respiratory Zone

Starts where the terminal bronchioli feed into therespiratory bronchioli

Respiratory bronchioli feed into alveolar ducts that endin clusters of alveolar sacs

There are roughly 300 million alveolar sacs = surfacearea for gas exchange

Respiratory Zone

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[AIR]

[BLOOD]

EXCHANGE

Respiratory Zone

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Each of the clusteredalveoli includes anabundance ofpulmonary capillaries,thereby assuring thatthe ventilated air isbrought into closeproximity to the“pulmonary” blood,allowing efficient andthorough gasexchange between theair and the blood.

Respiratory Zone

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Wall of alveolus is made up from simple squamous epithelialcells (called Type I cells)

Type II cellsproducesurfactant

Dust cells(macrophages)keep alveoli clean

Respiratory Zone

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Respiratory MembraneThe Respiratory Membrane is made up from :

• Squamous epithelial cells of alveoli• endothelial cells of the capillary wall• basement membranes of each layer

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The Respiratory Membrane is the area across which gasexchange occurs

These Alveolar and capillary walls are thin, permitting rapiddiffusion of gases.

Respiratory Membrane

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Type II cells producesurfactant ; this keepsthe alveoli fromcollapsing

X = Resp. membrane thickness

Respiratory Membrane

Fick’s Equation for Diffusion

Rate = A. D. (C2 - C1) / x

A = Total alveolar area

(C2 - C1) = Conc. gradient

D = Diff. constant for a molecule

Depends on MW, Temp,medium

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Rate = A. D. (C2 - C1) / x

So what happens when x increases, Adecreases, C2 decreases, C1 increases ?

Fick’s Equation for Diffusionand Respiration !

10Both lungs rest on the diaphragm.

Lungs

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Left lung has 2 lobesRight lung has 3 lobes

External Lung Anatomy

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Just like the heart, the lungs are enclosed by a set ofmembranes called the pleura.

Lungs

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13The intrapleural space is between the two pleura and is filled with fluid

Diaphragm

Parietal pleura is attached to the thoracic wall and diaphragm.Visceral pleura is attached to the lungs.

Lungs

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It is the movement of airbetween the lungs (alveoli)and the environment =breathing

The first exchange inrespiratory physiologyis ventilation

Ventilation

Lung Physiology

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Inhalation of air occurs through the nasal passage ways orvia the mouth. Breathing through the nose has severaladvantages

• Warms air to body temperature before it reaches thealveoli

• Adds moisture

• Foreign material is filtered out

When air reaches trachea, it is at 37 C and 100% humidity

Lung Physiology

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Smoking paralyzes themovement of the cilia

Additional filtration occurs in trachea and bronchi by ciliatedpseudostratified epithelium

• mucus traps particles• cilia move mucus upwards towards the pharynx

Lung Physiology

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Cystic fibrosis : the most common lethal inherited diseaseamong Caucasions from Northern European descent (1 : 2500)

Lung Physiology

Due to a mutation inchromosome 7. It results ina defective Chloride channeland prevents water to beformed by the glands in theepithelium.

The result is a thickening ofthe mucus that clogs theairways.

a defective Chloride channel prevents water to be formed bythe glands in the epithelium, resulting in a thick mucus thatclogs the airways.

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Boyle’s law states that the pressure of a fixednumber of molecules is related to the volumeof a container in which they are placed.

Lung Physiology

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Flow = Δ P / R

Air flows because of a Pressure Gradient

Lung Physiology

Airflow (F) is a function of thepressure differences betweenthe atmosphere (Patm) and thealveoli (Palv), divided by airflowresistance (R).

Air enters the lungs when :Palv< Patm

Air exits the lungs when : Palv > Patm

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Obviously, we cannot change atmospheric pressure withevery breath.

The body however adjusts alveolar pressure to start theprocess of air intake according to Boyle’s Law

Lung Physiology

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Pressure Systems in the lungs

• Pressure in the lungs (alveoli) = intra pulmonary pressure (Palv)

• Pressure within intrapleural cavity = intra pleural pressure (Pip)

• Pressure outside the lungs = atmospheric pressure (Patm)

(Palv) - (Pip) = transpulmonary pressure

Lung Physiology

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Changes in the pressure of the intrapleural fluid (Pip) affect the pressure inthe alveolus. The difference between atmospheric pressure (Patm) andalveolar pressure (Palv) is the major pressure driving ventilation.

Air flows into the lungs when Palv < Patm

Lung Physiology

In Physics :(Patm) = 760 mm Hg

In Respiratory Physiology(Patm) = 0 mm Hg

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• Parietal pleura is attached to the thoracic wall

• The small distance between the two pleural membranes, together withthe adhesive character of fluids, results in a negative transpulmonaryforce (outward force)

the two pleural membranes to stick toeach other like two glass plates

• The lungs have an elastic character and want to recoil inward , thesame way an balloon with no air collapses on itself.

Forces working on the lungs

At rest ( between breathing), this inward force equals the Pip

Since the parietal pleura is attached to the thoracic wall, it keep thelungs open.

Lung Physiology

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When airflow is stopped,the atmospheric pressure (Patm) and alveolarpressure (Palv) are equal.

Alveolar collapse is prevented because the negative pressure of theintrapleural fluid (Pip) is exactly offset by the elasticity of the lungs.

Lung Physiology

(Patm) = 0 mm Hg

(Palv) = 0 mm Hg

(Pip) = - 4 mm Hg

Lung recoil = - 4 mm Hg

(Palv - Pip) = + 4 mm Hg

(Net) = 0 mm Hg

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Lung Physiology

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Lung Physiology

When the outer pleura is punctured, it equilibrates with atmosphericpressure.

Alveolar collapse occurs because the absence of negative pressure ofthe intrapleural fluid (Pip) cannot offset the elastic recoil of the lungs.

Lung recoil = - 4 mm Hg

(Palv - Pip) = 0 mm Hg

(Pip) = 0 mm Hg

(Net) = - 4 mm Hg

Atelactasis = collapsed lung

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Ventilation Process

Inhalation or Inspiration

Exhalation or Expiration

Lung Physiology

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Lung Physiology

Inhalation or Inspiration

Initiated by contraction of the diaphragm

Since lungs have now a greatervolume, Palv will decrease !

Air flows into the lungs since nowPalv < Patm

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Additional help is provided by the

• external intercostal muscles.• internal intercostal muscles.

They provide uplifting motion of theribcage and broaden the lateral andlength-wise dimensions, expandingthe volume of the lung area.

Lung Physiology

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Both actions stretches the lungs open and intrapulmonarypressure drops.

The stretching of the thoracic cage also causes a drop inintrapleural pressure.

The final result is that transpulmonary pressure goesfrom - 4 mm Hg to about -6 mm Hg, with intrapulmonarypressure being about 1 mm Hg lower than atmosphericpressure.

Patm = 760 mm Hg Palv = 760 mm Hg Pip = 756 mm Hg

Patm = 760 mm Hg Palv = 759 mm Hg Pip = 754 mm Hg

Lung Physiology

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Inspiration is the result ofthe expansion of the thoraciccage in response to skeletalmuscle contraction.

The expansion reduces alveolar pressure (Palv) belowatmospheric pressure (Patm),so air moves into the lungs.

At the end of Inspiration,equilibrium between inside andoutside is reached and(Palv) = (Patm)

Air movement into the lungsstops.

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Exhalation or expiration

Is purely a passive action due to the relaxation of the diaphragm

Air flows out of the lungsbecause volume decreases andthus Palv < Patm

Additional forced exhalationtakes place by involving ribmuscles and abdominalmuscles.

Lung Physiology

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Expiration is the result ofreducing the volume of thethoracic cage; in a restingperson, this occurs in response to skeletalmuscle relaxation.

The volume reduction increases alveolar pressure (Palv) aboveatmospheric pressure (Patm),so air moves out of the lungs.

At the end of Expiration,equilibrium between inside andoutside is reached and onceagain, (Palv) = (Patm)

Air movement out of the lungsstops.

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Lung Physiology

Tidal Volume :• Amount of air moved in per breath• Equal to the amount of air moved out

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Cycles of inspiration and expiration result from cycles of pressurechanges. Note that the intrapleural pressure is always sub-atmospheric !

If it were equal to or greater than atmospheric pressure (as in apneumothorax), then the alveoli would collapse, terminating gas exchange.

Lung Physiology

inspiration

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Lung Physiology

In Trained individuals, pressure differentials in thealveoli can reach as much as - 30 mm Hg, andintrapleural pressure can drop as much as - 18 mmHg.

This allows for maximum capacity inhalation.

In a similar way, exhalation can createmaximum alveolar pressures of + 100mm Hg ( with glottis closed).

That’s why it is always a good idea toexhale when lifting weights in order toprevent to prevent alveolar damage.

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• Quiet breathing (eupnea)– Inhalation uses diaphragm and/or external intercostals muscles– Exhalation is purely passive relaxation of these muscles

• Deep breathing or diaphragmatic breathing• Costal breathing or shallow breathing

• Forced breathing (hyperpnea)– Involves active inspiratory and active expiratory movements– Uses the accessory muscles such as internal intercostals, abdominal

muscles

Lung Physiology

Mechanism of Breathing