Collin County Community College. Respiratory Zone

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1 Collin County Community College BIOL Anatomy & Physiology WEEK 9 Respiratory System 1 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 1

2 Respiratory Zone [AIR] EXCHANGE [BLOOD] 3 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. 4 2

3 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 5 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 6 3

4 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. 7 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 8 4

5 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? 9 Lungs Both lungs rest on the diaphragm. 10 5

6 External Lung Anatomy Right lung has 3 lobes Left lung has 2 lobes 11 Lungs Just like the heart, the lungs are enclosed by a set of membranes called the pleura. 12 6

7 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 with 13fluid Ventilation The first exchange in respiratory physiology is ventilation It is the movement of air between the lungs (alveoli) and the environment = breathing 14 7

8 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 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 16 8

9 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. 17 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. 18 9

10 Air flows because of a Pressure Gradient Flow = Δ P / R Airflow (F) is a function of the pressure differences between the atmosphere (P atm ) and the alveoli (P alv ), divided by airflow resistance (R). Air enters the lungs when :P alv < P atm Air exits the lungs when : P alv > P atm 19 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 20 10

11 Pressure Systems in the lungs Pressure in the lungs (alveoli) = intra pulmonary pressure (P alv ) Pressure within intrapleural cavity = intra pleural pressure (P ip ) Pressure outside the lungs = atmospheric pressure (P atm ) (P alv ) - (P ip ) = transpulmonary pressure 21 In Physics : (P atm ) = 760 mm Hg In Respiratory Physiology (P atm ) = 0 mm Hg Changes in the pressure of the intrapleural fluid (P ip ) affect the pressure in the alveolus. The difference between atmospheric pressure (P atm ) and alveolar pressure (P alv ) is the major pressure driving ventilation. Air flows into the lungs when P alv < P atm 22 11

12 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 P ip Since the parietal pleura is attached to the thoracic wall, it keep the lungs open. 23 (P atm ) = 0 mm Hg (P alv ) = 0 mm Hg (P ip ) = - 4 mm Hg Lung recoil = - 4 mm Hg (P alv - P ip ) = + 4 mm Hg (Net) = 0 mm Hg When airflow is stopped,the atmospheric pressure (P atm ) and alveolar pressure (P alv ) are equal. Alveolar collapse is prevented because the negative pressure of the intrapleural fluid (P ip ) is exactly offset by the elasticity of the lungs

13 25 (P ip ) = 0 mm Hg Atelactasis = collapsed lung Lung recoil = - 4 mm Hg (P alv - P ip ) = 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 (P ip ) cannot offset the elastic recoil of the lungs. 13

14 Ventilation Process Inhalation or Inspiration Exhalation or Expiration 27 Inhalation or Inspiration Initiated by contraction of the diaphragm Since lungs have now a greater volume, P alv will decrease! Air flows into the lungs since now P alv < P atm 28 14

15 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. 29 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. P atm = 760 mm Hg P alv = 760 mm Hg P ip = 756 mm Hg P atm = 760 mm Hg P alv = 759 mm Hg P ip = 754 mm Hg 30 15

16 Inspiration is the result of the expansion of the thoracic cage in response to skeletal muscle contraction. The expansion reduces alveolar pressure (P alv ) below atmospheric pressure (P atm ), so air moves into the lungs. At the end of Inspiration, equilibrium between inside and outside is reached and (P alv ) = (P atm ) Air movement into the lungs stops. 31 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 P alv < P atm Additional forced exhalation takes place by involving rib muscles and abdominal muscles

17 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 (P alv ) above atmospheric pressure (P atm ), so air moves out of the lungs. At the end of Expiration, equilibrium between inside and outside is reached and once again, (P alv ) = (P atm ) Air movement out of the lungs stops. 33 Tidal Volume : Amount of air moved in per breath Equal to the amount of air moved out 34 17

18 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. 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 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

19 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 37 19