Collin County Community College BIOL. 2402 Anatomy & Physiology WEEK 9
Respiratory System
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Respiratory Zone Respiratory Zone Starts where the terminal bronchioli feed into the respiratory bronchioli Respiratory bronchioli feed into alveolar ducts that end in clusters of alveolar sacs There are roughly 300 million alveolar sacs = surface area for gas exchange 2
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Respiratory Zone
[AIR] EXCHANGE
[BLOOD]
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Respiratory Zone Each of the clustered alveoli includes an abundance of pulmonary capillaries, thereby assuring that the ventilated air is brought into close proximity to the “pulmonary” blood, allowing efficient and thorough gas exchange between the air and the blood.
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Respiratory Zone Wall of alveolus is made up from simple squamous epithelial cells (called Type I cells) Type II cells produce surfactant Dust cells (macrophages) keep alveoli clean
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Respiratory Membrane The 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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Respiratory Membrane The Respiratory Membrane is the area across which gas exchange occurs These Alveolar and capillary walls are thin, permitting rapid diffusion of gases.
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Respiratory Membrane Fick’s Equation for Diffusion Rate = A. D. (C2 - C1) / x (C2 - C1) = Conc. gradient X = Resp. membrane thickness A = Total alveolar area Type II cells produce surfactant ; this keeps the alveoli from collapsing D = Diff. constant for a molecule Depends on MW, Temp, medium
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Fick’s Equation for Diffusion and Respiration ! Rate = A. D. (C2 - C1) / x
So what happens when x increases, A decreases, C2 decreases, C1 increases ?
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Lungs
Both lungs rest on the diaphragm.
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External Lung Anatomy Left lung has 2 lobes
Right lung has 3 lobes
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Lungs Just like the heart, the lungs are enclosed by a set of membranes called the pleura.
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Lungs
Diaphragm
Parietal pleura is attached to the thoracic wall and diaphragm. Visceral pleura is attached to the lungs. The intrapleural space is between the two pleura and is filled with13fluid
Lung Physiology Ventilation The first exchange in respiratory physiology is ventilation It is the movement of air between the lungs (alveoli) and the environment = breathing
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Lung Physiology Inhalation of air occurs through the nasal passage ways or via the mouth. Breathing through the nose has several advantages • Warms air to body temperature before it reaches the alveoli • Adds moisture • Foreign material is filtered out When air reaches trachea, it is at 37 C and 100% humidity 15
Lung Physiology Additional filtration occurs in trachea and bronchi by ciliated pseudostratified epithelium • mucus traps particles • cilia move mucus upwards towards the pharynx
Smoking paralyzes the movement of the cilia
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Lung Physiology Cystic fibrosis : the most common lethal inherited disease among Caucasions from Northern European descent (1 : 2500) a defective Chloride channel prevents water to be formed by the glands in the epithelium, resulting in a thick mucus that clogs the airways. Due to a mutation in chromosome 7. It results in a defective Chloride channel and prevents water to be formed by the glands in the epithelium. The result is a thickening of the mucus that clogs the airways.
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Lung Physiology
Boyle’s law states that the pressure of a fixed number of molecules is related to the volume of a container in which they are placed.
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Lung Physiology Air flows because of a Pressure Gradient Flow = Δ P / R Airflow (F) is a function of the pressure differences between the atmosphere (Patm) and the alveoli (Palv), divided by airflow resistance (R).
Air enters the lungs when :Palv< Patm Air exits the lungs when : Palv > Patm
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Lung Physiology
Obviously, we cannot change atmospheric pressure with every breath. The body however adjusts alveolar pressure to start the process of air intake according to Boyle’s Law
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Lung Physiology 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
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Lung Physiology In Physics : (Patm) = 760 mm Hg In Respiratory Physiology (Patm) = 0 mm Hg
Changes in the pressure of the intrapleural fluid (Pip) affect the pressure in the alveolus. The difference between atmospheric pressure (Patm) and alveolar pressure (Palv) is the major pressure driving ventilation.
Air flows into the lungs when Palv < Patm
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Lung Physiology Forces working on the lungs • Parietal pleura is attached to the thoracic wall • The small distance between the two pleural membranes, together with the adhesive character of fluids, results in a negative transpulmonary force (outward force) the two pleural membranes to stick to each other like two glass plates • The lungs have an elastic character and want to recoil inward , the same way an balloon with no air collapses on itself. At rest ( between breathing), this inward force equals the Pip Since the parietal pleura is attached to the thoracic wall, it keep the lungs open.
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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
When airflow is stopped,the atmospheric pressure (Patm) and alveolar pressure (Palv) are equal. Alveolar collapse is prevented because the negative pressure of the intrapleural fluid (Pip) is exactly offset by the elasticity of the lungs.
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Lung Physiology
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Lung Physiology (Pip) = 0 mm Hg
Atelactasis = collapsed lung
Lung recoil = - 4 mm Hg (Palv - Pip) = 0 mm Hg (Net) = - 4 mm Hg
When the outer pleura is punctured, it equilibrates with atmospheric pressure. Alveolar collapse occurs because the absence of negative pressure of 26 the intrapleural fluid (Pip) cannot offset the elastic recoil of the lungs.
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Lung Physiology Ventilation Process Inhalation or Inspiration Exhalation or Expiration
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Lung Physiology Inhalation or Inspiration Initiated by contraction of the diaphragm Since lungs have now a greater volume, Palv will decrease ! Air flows into the lungs since now Palv < Patm
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Lung Physiology Additional help is provided by the • external intercostal muscles. • internal intercostal muscles.
They provide uplifting motion of the ribcage and broaden the lateral and length-wise dimensions, expanding the volume of the lung area.
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Lung Physiology Both actions stretches the lungs open and intrapulmonary pressure drops. The stretching of the thoracic cage also causes a drop in intrapleural pressure. The final result is that transpulmonary pressure goes from - 4 mm Hg to about -6 mm Hg, with intrapulmonary pressure being about 1 mm Hg lower than atmospheric pressure. Patm = 760 mm Hg
Palv = 760 mm Hg
Pip = 756 mm Hg
Patm = 760 mm Hg
Palv = 759 mm Hg
Pip = 754 mm Hg 30
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Inspiration is the result of the expansion of the thoracic cage in response to skeletal muscle contraction. The expansion reduces alveolar pressure (Palv) below atmospheric pressure (Patm), so air moves into the lungs. At the end of Inspiration, equilibrium between inside and outside is reached and (Palv) = (Patm) Air movement into the lungs stops. 31
Lung Physiology Exhalation or expiration Is purely a passive action due to the relaxation of the diaphragm Air flows out of the lungs because volume decreases and thus Palv < Patm Additional forced exhalation takes place by involving rib muscles and abdominal muscles. 32
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Expiration is the result of reducing the volume of the thoracic cage; in a resting person, this occurs in response to skeletal muscle relaxation. The volume reduction increases alveolar pressure (Palv) above atmospheric pressure (Patm), so air moves out of the lungs. At the end of Expiration, equilibrium between inside and outside is reached and once again, (Palv) = (Patm) Air movement out of the lungs stops. 33
Lung Physiology
Tidal Volume : • Amount of air moved in per breath • Equal to the amount of air moved out 34
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Lung Physiology
inspiration
Cycles of inspiration and expiration result from cycles of pressure changes. Note that the intrapleural pressure is always sub-atmospheric ! If it were equal to or greater than atmospheric pressure (as in a 35 pneumothorax), then the alveoli would collapse, terminating gas exchange.
Lung Physiology In Trained individuals, pressure differentials in the alveoli can reach as much as - 30 mm Hg, and intrapleural pressure can drop as much as - 18 mm Hg. This allows for maximum capacity inhalation. In a similar way, exhalation can create maximum alveolar pressures of + 100 mm Hg ( with glottis closed). That’s why it is always a good idea to exhale when lifting weights in order to prevent to prevent alveolar damage. 36
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Lung Physiology Mechanism of Breathing • 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
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