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Ventilation: the Mechanics of Breathing. The way mammals ventilate their lungs. Organs of the Respiratory system. Lungs close up…. Bronchial Tree Consisting of the Passageways that Connect the Trachea and Alveoli . Breathing.
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Ventilation: the Mechanics of Breathing The way mammals ventilate their lungs
Lungs close up… • Bronchial Tree Consisting of the Passageways that Connect the Trachea and Alveoli
Breathing • The movement of air into and out of the lungs (ventilation) results from a pressure difference between the thoracic cavity and the atmosphere. • This pressure difference is created by changing the volume of the thoracic cavity as shown in the animation below.
Involuntary Respiration. The basic rhythm of breathing occurs without conscious effort. The inspiratory center located in the medulla sets the basic rhythm by automatically initiating inspiration with a two second burst of nerve impulses to the diaphragm and the external intercostal muscles. Contraction of the diaphragm and the external intercostal muscles draws air into the lungs. Involuntary Respiration
The Expiratory Center. The expiratory center is located in the medulla. This center functions during forced expiration stimulating the internal intercostal and abdominal muscles to contract.
During inhalation, the diaphragm contracts and flattens and the external intercostal muscles draw the ribs upward and outward. This increase in thoracic volume results in a decrease in intrapulmonary pressure. Air enters the lungs to stabilize the pressure difference between the external atmosphere and the internal compartments of the lungs. Normal inhalation is an active process, requiring muscular work. Inhalation
During quiet breathing, intercostals maintain the rigidity of the chest wall. Otherwise, reduced intra-thoracic pressure would cause the chest wall to collapse inwards. External Intercostals are attached to the inferior border of the rib above, passing antero-inferiorly to the rib below. They elevate the ribs. Internal Intercostals are attached to the inferior border of the rib above, passing postero-inferiorly to the rib below. They depress the ribs.
Expiration • Exhalation is normally a passive process. • The diaphragm and external intercostal muscles relax decreasing the volume of the thoracic cavity. • This causes the pressure within the lungs to exceed the atmospheric pressure. • Air is expelled from the lungs.
Forced Exhalation • During a forced exhalation, the internal intercostal muscles contract, depressing the rib cage. • The abdominal muscles contract, pushing the organs in the abdominal cavity against the diaphragm. • The thoracic volume decreases to a level lower than achieved in normal exhalation. • These muscles are used to counteract the effects of obstructive pulmonary disorders.
ERV • These muscles are used during a forced exhalation to determine the expiratory reserve volume (ERV). • ERV is - the maximum volume of gas that can be forcefully exhaled after a normal exhalation.
The volume of the lungs is divided into four functional compartments, lung volumes. Combinations of two or more lung volumes are called a lung capacity. BTPS- Body Temperature, ambient Pressure and Saturated with water vapor. Standard conditions for calculating lung volumes. Other Terms of Breathing
Terms • tidal volume ( TV ) - the volume of gas inspired or expired during each normal (unforced) ventilation cycle. • inspiratory reserve volume ( IRV ) -the maximum amount of gas that can be forcefully inhaled after a normal inhalation. • expiratory reserve volume ( ERV ) - the maximum volume of gas that can be forcefully exhaled after a normal exhalation.
Terms • residual volume ( RV ) - the amount of gas left in the lungs after a maximum (forced) exhalation. Necessary otherwise the lungs would collapse. • total lung capacity ( TLC ) - the amount of gas in the lungs after a maximum (forced) inhalation. TLC = IRV + TV + ERV + RV • vital capacity ( VC )-the maximum volume of gas that can be exhaled by voluntary effort after a maximum inhalation. VC = IRV + TV + ERV
Terms • inspiratory capacity ( IC ) - the maximum amount of gas that can be inhaled after a normal (unforced) exhalation. IC = IRV + TV • functional residual capacity ( FRC ) - the amount of gas left in the lungs after a normal (unforced) exhalation. FRC = ERV + RV
Terms • minute volume ( MV ) - or minute respiratory volume - the volume of air breathed per minute - MV = tidal volume x respiratory rate (normally 5-8 liters per minute). • Alveolar ventilation/minute ( VA )- is the portion of the minute volume of ventilation which reaches those areas of the lung concerned with gas exchange. VA = (Tidal volume minus Dead Space) x Rate. Averages about 3.5 to 5.0 liters per minute. Alveolar ventilation/minute is the best criterion for effectiveness of breathing.
Question?? • As Stanley sits in the drivers seat at rest, which muscles are contributing the majority of his breathing? 1. Internal intercostals2. External intercostals3. Accesory muscles4. Diaphragm5. Psoas major
4. Diaphragm • In a healthy adult, the diaphragm is the dominant muscle of respiration at rest • The diaphragm is a musculotendinous sheet separating the thorax from the abdomen. It is attached to the thoracic cage under the lower ribs.
Remember Gills • They occur in a variety of animal groups including arthropods (including some terrestrial crustaceans), annelids, fish, and amphibians. • Gills typically are convoluted outgrowths containing blood vessels covered by a thin epithelial layer. • Typically gills are organized into a series of plates and may be internal (as in crabs and fish) or external to the body (as in some amphibians).
Counter-current Flow happens in Gills • The fish gills are used to extract oxygen from the water and in return excrete carbon dioxide and toxic metabolic wastes, like ammonia and acid. • The gills are located behind the head and consist of arches and rows of filaments, which transport densely packed flat lamellae in rows. • Oxygen is extracted from the water by moving it in the opposite direction to the blood via the lamellae.
Counter-current Flow • Fish employ a method known as the countercurrent system to extract oxygen from the water • This system moves water flowing across the gills, in an opposite direction to the blood flow creating the maximum efficiency of gas exchange.
Counter-current Flow • When he blood and water flows in the same direction, the co-current system, it will initially diffuses large amounts of oxygen but the efficiency reduces when the fluids start to reach equilibrium. • The concentration of oxygen gained from this system would not meet the physiological needs of the fish; therefore the countercurrent system is used.
This method removes almost all of the oxygen (80-90%) from the water that passes over the gills and then transfers it to the blood, compared to the co-current that is approximately 50% The surface size of the gills is very important as the larger they are with respect to the size of the fish, the more oxygen will be diffused. Counter-current Flow
Lungs in Birds • Lungs are ingrowths of the body wall and connect to the outside by as series of tubes and small openings. • Lung breathing probably evolved about 400 million years ago. • Lungs are not entirely the sole property of vertebrates, some terrestrial snails have a gas exchange structures similar to those in frogs.
