Buccal oscillation and lung ventilation in a semi-aquatic turtle, Platysternon megacephalum

Movements of the hyobranchial apparatus in reptiles and amphibians contribute to many behaviors including feeding, lung ventilation, buccopharyngeal respiration, thermoregulation, olfaction, defense and display. In a semi-aquatic turtle, Platysternon megacephalum, x-ray video and airflow measurements from blowhole pneumotachography show no evidence that above water hyobranchial movements contribute to lung inflation, as in the buccal or gular pump of amphibians and some lizards. Instead, hyobranchial movements produce symmetrical oscillations of air into and out of the buccal cavity. The mean tidal volume of these buccal oscillations is 7.8 times smaller than the mean tidal volume of lung ventilation (combined mean for four individuals). Airflow associated with buccal oscillation occurs in the sequence of inhalation followed by exhalation, distinguishing it from lung ventilation which occurs as exhalation followed by inhalation. No fixed temporal relationship between buccal oscillation and lung ventilation was observed. Periods of ventilation often occur without buccal oscillation and buccal oscillation sometimes occurs without lung ventilation. When the two behaviors occur together, the onset of lung ventilation often interrupts buccal oscillation. The initiation of lung ventilation was found to occur in all phases of the buccal oscillation cycle, suggesting that the neural control mechanisms of the two behaviors are not coupled. The pattern of occurrence of both buccal oscillation and lung ventilation was found to vary over time with no obvious effect of activity levels.     

Buccal oscillation and lung ventilation in a semi-aquatic turtle, Platysternon megacephalum

Movements of the hyobranchial apparatus in reptiles and amphibians contribute to many behaviors including feeding, lung ventilation, buccopharyngeal respiration, thermoregulation, olfaction, defense and display. In a semi-aquatic turtle, Platysternon megacephalum, x-ray video and airflow measurements from blowhole pneumotachography show no evidence that above water hyobranchial movements contribute to lung inflation, as in the buccal or gular pump of amphibians and some lizards. Instead, hyobranchial movements produce symmetrical oscillations of air into and out of the buccal cavity. The mean tidal volume of these buccal oscillations is 7.8 times smaller than the mean tidal volume of lung ventilation (combined mean for four individuals). Airflow associated with buccal oscillation occurs in the sequence of inhalation followed by exhalation, distinguishing it from lung ventilation which occurs as exhalation followed by inhalation. No fixed temporal relationship between buccal oscillation and lung ventilation was observed. Periods of ventilation often occur without buccal oscillation and buccal oscillation sometimes occurs without lung ventilation. When the two behaviors occur together, the onset of lung ventilation often interrupts buccal oscillation. The initiation of lung ventilation was found to occur in all phases of the buccal oscillation cycle, suggesting that the neural control mechanisms of the two behaviors are not coupled. The pattern of occurrence of both buccal oscillation and lung ventilation was found to vary over time with no obvious effect of activity levels.     

Factors influencing the differential sorption of odorant molecules across the olfactory mucosa

By use of a flow dilution olfactometer, tritium-labeled odorants were presented through the external naris to the bullfrog's intact olfactory sac. After stimulation the animal was frozen in liquid nitrogen. The dorsal surface and eminentia of the olfactory sac were then removed and sawed into sections perpendicular to the long axis of the mucosal surface. Each section was dissolved in a tissue solubilizer and counted in a liquid scintillation system. The amount of radioactivity in each section was used to estimate the number of odorant molecules it sorbed. For tritiated butanol there was a significant decrease in radioactivity from the section containing the external naris to that overhanging the internal naris. The steepness of the gradient was unaffected by a rather large range of stimulus flow rates, volumes, and partial pressures. Only when these parameters were pushed to extreme physical limits did this gradient change significantly. When the stimulus was presented through the internal rather than the external naris, the butanol gradient reversed its direction, decreasing from the internal to external. Unlike butanol, tritiated octane presented through the external naris was rather evenly distributed among the mucosal sections. That is, octane showed no distribution gradient across the mucosa. These results complement previous electrophysiological data that suggested a "chromatographic-like" differential sorption of odorant molecules across the mucosa.     

The initiation of diving apnoea in the frog, Rana pipiens.

1. Diving apnoea in Rana pipiens was initiated by submerging the external nares. As the water level was raised above the frog, both buccal and lung pressure increased by an amount corresponding to the water head. During submergence the external nares remained closed, although the apnoeic period was punctuated by ventilation movements which moved gas between the lungs and buccal cavity. 2. Bilateral section of the ophthalmic nerves did not alter the normal pattern of ventilation in air, although it often resulted in the intake of water into the buccal cavity on submergence. Introduction of water into the buccal cavity, either naturally as in denervates or by injection through a catheter in intact frogs, triggered sustained electromyographical activity in some respiratory muscles. 3. Electroneurograms recorded from the cut peripheral end of an ophthalmic nerve showed that receptors in the external narial region were stimulated by movement of a water meniscus across them. Activity could also be recorded in the ophthalmic nerve in response to water flow past the submerged nares. Punctate stimulation of the narial region confirmed that these receptors were mechanosensitive. 4. Bilateral electrical stimulation of the central ends of cut ophthalmic nerves in lightly anaesthetized frogs caused apnoea with a latency of less than 200 ms. The external nares remained closed throughout the period of stimulation although buccal pressure events, resembling underwater ventilation movements, occurred when stimulation was prolonged.     

An assessment of dead space in pulmonary ventilation of the toad Bufo schneideri

The respiratory cycles of Rana and Bufo has been disputed in relation to flow patterns and to the respiratory dead-space of the buccal volume. A small tidal volume combined with a much larger buccal space motivated the "jet steam" model that predicts a coherent expired flow within the dorsal part of the buccal space. Some other studies indicate an extensive mixing of lung gas within the buccal volume. In Bufo schneideri, we measured arterial, end-tidal and intrapulmonary PCO(2) to evaluate dead-space by the Bohr equation. Dead-space was also estimated as: V(D)=(total ventilation-effective ventilation)/f(R), where total ventilation and f(R) were measured by pneumotachography, while effective ventilation was derived from the alveolar ventilation equation. These approaches were consistent with a dead space of 30-40% of tidal volume, which indicates a specific pathway for the expired lung gas.     

Social control of air ventilation in colonies of honey bees,Apis mellifera

Fanning behaviour inside the nest of honey bees is an effective mechanism of ventilation. The following results are reported: (1) With only a single small entrance, the fanning is controlled so as to induce tidal ventilation of the nest as in a typical breathing pattern. (2) Periodic active fanning moves an air current out followed by a passive influx of air. (3) Fanning bees show negative phototaxis. (4) The colonial respiratory activity decreases at night following a pronounced day-night cycle.     

Effect of menstrual cycle phase on the ventilatory response to rising body temperature during exercise

To examine the effect of menstrual cycle on the ventilatory sensitivity to rising body temperature, ten healthy women exercised for ~60 min on a cycle ergometer at 50% of peak oxygen uptake during the follicular and luteal phases of their cycle. Esophageal temperature, mean skin temperature, mean body temperature, minute ventilation, and tidal volume were all significantly higher at baseline and during exercise in the luteal phase than the follicular phase. On the other hand, end-tidal partial pressure of carbon dioxide was significantly lower during exercise in the luteal phase than the follicular phase. Plotting ventilatory parameters against esophageal temperature revealed there to be no significant menstrual cycle-related differences in the slopes or intercepts of the regression lines, although minute ventilation and tidal volume did significantly differ during exercise with mild hyperthermia. To evaluate the cutaneous vasodilatory response, relative laser-Doppler flowmetry values were plotted against mean body temperature, which revealed that the mean body temperature threshold for cutaneous vasodilation was significantly higher in the luteal phase than the follicular phase, but there were no significant differences in the sensitivity or peak values. These results suggest that the menstrual cycle phase influences the cutaneous vasodilatory response during exercise and the ventilatory response at rest and during exercise with mild hyperthermia, but it does not influence ventilatory responses during exercise with moderate hyperthermia.     

Load compensation in obese patients during quiet tidal breathing

Seventeen eucapnic massively obese patients and eight normal subjects had their respiratory cycle parameters studied while breathing room air at rest. Despite large variations in the degree of obesity, our patients demonstrated normal mean inspiratory and expiratory flow rates, duty cycles, and minute ventilation. The maintenance of normal mean inspiratory flow rates was found to be dependent on an augmentation of neuromuscular drive (P0.1); furthermore, a strong positive correlation between percentage ideal body weight (i.e., the degree of obesity) and P0.1 was present. The obese were found to partition their tidal volume preferentially to their rib cage compartment, choosing to leave the abdominal compartment relatively immobile. Analysis of the diaphragmatic electromyogram revealed a persistence of activity into early expiration, the length of which also depended on the degree of obesity. These findings suggest that the diaphragm's volume-generating function in the obese is reduced, and furthermore the persistence of its activity in expiration serves to attenuate the rate of expiratory flow. No significant difference in any respiratory cycle parameter was found between simple obesity patients and formerly hypercapnic obese patients.     

On the mechanism of respiration in the bullfrog,Rana catesbeiana: A reassessment

The mechanism of respiration in the bullfrog has been analyzed by means of pressure recordings from the buccal cavity, the lungs and the abdominal cavity, by cinematography and cinefluorography, and by electromyography of buccal, laryngeal and abdominal muscles. Gas flow was investigated by putting frogs in atmospheres of changing argon and nitrogen content and monitoring the concentration of the nostril efflux. Three kinds of cyclical phenomena were found. (1) Oscillatory cycles consist of rhythmical raising and lowering of the floor of the mouth, with open nares. They have a definite respiratory function in introducing fresh air into the buccal cavity. (2) Ventilatory cycles involve opening and closing of the glottis and nares and renewal of a portion of the pulmonary gas. More muscles are involved and the pattern of muscular activity is more complex than in the oscillatory cycles. (3) Inflation cycles consist of a series of ventilation cycles, interrupted by an apneic pause. The intensity of the ventilatory cycles increases before this pause and decreases immediately thereafter. This results in a stepwise increase in pulmonary pressure, to a plateau (coincident with the pause) followed by a sudden or stepwise decrease. The respiratory mechanism depends on the activity of a buccal force pump, which determines pulmonary pressure whose level is always slightly less than the peak pressure values of the ventilation cycles. The elevated pulmonary pressure is responsible for the expulsion of pulmonary gas during the second phase of the next ventilation cycle. This pressure is maintained by the elastic fibers (and the smooth masculature) of the lungs.     

Sound Production in the Salientia: Mechanism and Evolution of the Emitter

Frog sounds involve expulsion of air through the larynx. Inmating, release, rain, and territorial calls, the air vibratesvocal cords and/or arytenoid cartilages. Sound is amplifiedand radiated by the distended buccal cavity and vocal sacs.Distress calls are emitted with open mouth, with minimum laryngealmodulation. The trunk is filled by inflation cycles, but airis driven out by synchronized contractions of the body wallmusculature. The pressure levels are more than five times thoseduring ventilation. In the release call of Bufo valliceps the dilatators and constrictorsof the larynx fire simultaneously keeping the larynx closed.As the pulmonary pressure reaches a peak they cease firing.The arytenoids then separate and vibrate, as do the vocal cords.The dilatators terminate the sound pulse by pulling vibratorsout of the air stream, hence the very sharp termination. Prolongedrelease call sequences include interpulse Teinflations thatreturn air from buccal cavity to lung. Frogs apparently evolved from amphibians too small to use aspirationbreathing. Vocalization represented a critical factor in theirsocial organization and its importance locked these animalsinto reliance upon pulse-pumping rather than the more efficientaspiration breathing.     

Respiratory and abdominal muscle responses to expiratory threshold loading in cystic fibrosis.

We hypothesized that the hyperinflation and pulmonary dysfunction of cystic fibrosis (CF) would distort feedback and therefore alter the abdominal muscle response to graded expiratory threshold loads (ETLs). We compared the respiratory and abdominal muscle responses with graded ETLs of seven CF patients with severe lung dysfunction with those of matched healthy control subjects in the supine and 60 degrees head-up positions. Breathing frequency, tidal volume, and ventilatory timing were determined from inspiratory flow recordings. Abdominal electromyograms (EMGs) were detected with surface electrodes placed unilaterally over the external and internal oblique and the rectus abdominis muscles. Thresholds, times of onset, and durations of phasic abdominal activity were determined from raw EMGs; peak amplitudes were determined from integrated EMGs. Graded ETLs were imposed by submerging a tube from the expiratory port of the breathing valve into a column of water at depths of 0-25 cmH2O. We found that breathing frequency, tidal volume, and expired minute ventilation were higher in CF patients than in control subjects during low ETLs; a change in body position did not alter these ventilatory responses in the CF patients but did in the control subjects. All CF patients, but none of the control subjects, had tonic abdominal activity while supine. CF patients recruited abdominal muscles at lower loads, earlier in the respiratory cycle, and to a higher recruitment level in both positions than the control subjects, but burst duration of phasic activity was not different between groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

In hamsters dopamine D2 receptors affect ventilation during and following intermittent hypoxia

We tested the hypothesis that in golden Syrian hamsters (Mesocricetus auratus) carotid body dopaminergic D2 receptors modulate ventilation in air, during exposure to intermittent hypoxia (IH) and reoxygenation. Ventilation was evaluated using the barometric method and CO2 production was determined using the flow through method. Hamsters (n=8) received either subcutaneous injections of vehicle, haloperidol (0.5 mg/kg) or domperidone (0.5 mg/kg). Ventilatory and metabolic variables were determined 30 min following injections, after each of 5 bouts of 5 min of 10% oxygen interspersed by normoxia (IH), and 15, 30, 45 and 60 min following IH when hamsters were exposed to air. Haloperidol, but not domperidone decreased body temperature in hamsters. Neither treatment affected CO2 production. Vehicle-treated hamsters exhibited ventilatory long-term facilitation (VLTF) following IH. Haloperidol or domperidone decreased ventilation in air, during IH and eliminated VLTF due to changes in tidal volume and not frequency of breathing. Thus, in hamsters D2 receptors are involved in control of body temperature and ventilation during and following IH.     

Breathing during exercise in subjects with mild-to-moderate airflow obstruction: effects of physical training.

In this study we explored the effects of physical training on the response of the respiratory system to exercise. Eight subjects with irreversible mild-to-moderate airflow obstruction [forced expiratory volume in 1 s of 85 +/- 14 (SD) % of predicted and ratio of forced expiratory volume in 1 s to forced vital capacity of 68 +/- 5%] and six normal subjects with similar anthropometric characteristics underwent a 2-mo physical training period on a cycle ergometer three times a week for 31 min at an intensity of approximately 80% of maximum heart rate. At this work intensity, tidal expiratory flow exceeded maximal flow at control functional residual capacity [FRC; expiratory flow limitation (EFL)] in the obstructed but not in the normal subjects. An incremental maximum exercise test was performed on a cycle ergometer before and after training. Training improved exercise capacity in all subjects, as documented by a significant increase in maximum work rate in both groups (P < 0.001). In the obstructed subjects at the same level of ventilation at high workloads, FRC was greater after than before training, and this was associated with an increase in breathing frequency and a tendency to decrease tidal volume. In contrast, in the normal subjects at the same level of ventilation at high workloads, FRC was lower after than before training, so that tidal volume increased and breathing frequency decreased. These findings suggest that adaptation to breathing under EFL conditions does not occur during exercise in humans, in that obstructed subjects tend to increase FRC during exercise after experiencing EFL during a 2-mo strenuous physical training period.     

Effect of head-down tilt on respiratory responses and human inspiratory muscle activity

The effect of a head-down tilt on the responses of the external respiration system and the functional capacity of the diaphragm and parasternal muscles were investigated in 11 healthy subjects. A 30-min head-down tilt posture (−30° relative to the horizontal) significantly increased the inspiratory time, decreased the respiration rate and the inspiratory and expiratory flow rates; and increased the airway resistance compared to these values in the vertical posture. There were no significant changes in tidal volume or minute ventilation. The electromyograms (EMGs) of the diaphragm and parasternal muscles showed that the constant values of tidal volume and minute ventilation during head-down tilt could be provided by an increase in the electric activity of the thoracic inspiratory muscles. It was established that the contribution of the thoracic inspiratory muscles increased, while the diaphragms’ contribution decreased, during patient, spontaneous breathing. The maximal inspiratory effort (Muller’s maneuver) during a head-down tilt evoked the opposite EMG-activity pattern: the contribution of inspiratory thoracic muscles was decreased and the diaphragm EMG activity was increased compared to the vertical posture. These results suggest that coordinated modulations in inspiratory muscle activity make it possible to preserve the functional reserve of human inspiratory muscles during a short-term head-down tilt.     

Effects of oral contraceptives on peak exercise capacity.

We examined the effects of menstrual cycle phase and oral contraceptive (OC) use on peak oxygen consumption (VO(2 peak)). Six moderately active, eumenorrheic women (25.5 +/- 1.5 yr) were studied before and after 4 mo of OC. Subjects were tested during the follicular and luteal phases before OC and the inactive and high-dose phases after OC. Before OC, there were no significant differences between the follicular and luteal phases in any of the variables studied. There were also no differences between the inactive and high-dose phases. Dietary composition, exercise patterns, and peak heart rate, minute ventilation, and respiratory exchange ratio did not change with OC use. However, OC use significantly (P 相似文献   

Lung ventilation in salamanders and the evolution of vertebrate air-breathing mechanisms

Functional analysis of lung ventilation in salamanders combined with historical analysis of respiratory pumps provides new perspectives on the evolution of breathing mechanisms in vertebrates. Lung ventilation in the aquatic salamander Necturus maculosus was examined by means of cineradiography, measurement of buccal and pleuroperitoneal cavity pressures, and electromyography of hypaxial musculature. In deoxygenated water Necturus periodically rises to the surface, opens its mouth, expands its buccal cavity to draw in fresh air, exhales air from the lungs, closes its mouth, and then compresses its buccal cavity and pumps air into the lungs. Thus Necturus produces only two buccal movements per breath: one expansion and one compression. Necturus shares the use of this two-stroke buccal pump with lungfishes, frogs and other salamanders. The ubiquitous use of this system by basal sarcopterygians is evidence that a two-stroke buccal pump is the primitive lung ventilation mechanism for sarcopterygian vertebrates. In contrast, basal actinopterygian fishes use a four-stroke buccal pump. In these fishes the buccal cavity expands to fill with expired air, compresses to expel the pulmonary air, expands to fill with fresh air, and then compresses for a second time to pump air into the lungs. Whether the sarcopterygian two-stroke buccal pump and the actinopterygian four-stroke buccal pump arose independently, whether both are derived from a single, primitive osteichthyian breathing mechanism, or whether one might be the primitive pattern and the other derived, cannot be determined. Although Necturus and lungfishes both use a two-stroke buccal pump, they differ in their expiration mechanics. Unlike a lungfish (Protopterus), Necturus exhales by contracting a portion of its hypaxial trunk musculature (the m. Iransversus abdominis) to increase pleuroperitoneal pressure. The occurrence of this same expiratory mechanism in amniotes is evidence that the use of hypaxial musculature for expiration, but not for inspiration, is a primitive tetrapod feature. From this observation we hypothesize that aspiration breathing may have evolved in two stages: initially, from pure buccal pumping to the use of trunk musculature for exhalation but not for inspiration (as in Necturus); and secondarily, to the use of trunk musculature for both exhalation and inhalation by costal aspiration (as in amniotes).     

Depressed ventilatory reflexes after capsaicin challenge in streptozotocin-treated rats

Diabetic sensory neuropathy is an affliction that decreases sensory perception in a number of organ systems. Although little is known of its pulmonary effects certain diabetic patients have reduced airway reactivity to cold air and elevated cough threshold to irritant inhalation, reflexes reported to be mediated by pulmonary C-fibers. Therefore we studied the effects the selective C-fiber activator capsaicin (0.01% aerosol, 30 s) on variables of ventilation using a whole-body plethysmograph in age-matched rats treated with streptozotocin (STZ) or its vehicle at 6 and 12 weeks after treatment. Body weight increased and plasma glucose and glycosylated hemoglobin were stable in vehicle-treated rats. In STZ-treated rats body weight decreased and plasma glucose and glycosylated hemoglobin increased. Capsaicin challenge decreased tidal volume, respiratory rate and therefore minute ventilation in non-treated and vehicle-treated rats. However capsaicin challenge increased tidal volume thereby altering minute ventilation in STZ-treated rats. Specific airway resistance increased in both groups after capsaicin challenge. Changes in ventilation in response to capsaicin challenge in STZ-treated rats may involve C-fiber sensory neuropathy.     

The effects of tidal currents on the rhythm of feeding and digestion in Pecten maximus L.

The orientation of individuals in two populations of Pecten maximus L., from the west coast of Ireland, shows that they have a marked preference to face directly into a tidal flow. In both localities examined there was a reversal of tides and the members of the populations were divided equally for flood and ebb tides. Twenty-four hour in situ studies of the animals were made and at all stages of the tide individuals facing either due east or west were observed. A cyclical feeding pattern imposed by the reversal of tidal flow is proposed.The pH of various parts of the digestive tract was investigated and showed a wide range of values. The most acid region was that of the stomach. The variations in pH of all of the regions of the gut examined throughout a 24-h period closely followed the pattern of the tidal cycle.Histological analysis of the stomach and digestive diverticula of representative samples of scallops taken at regular intervals over the 24-h periods clearly indicated a diphasic pattern of digestion within the tubules of the digestive diverticula. A close correlation between the phases of intracellular digestion, the pH variations in different regions of the gut, and the tidal cycle indicate distinct feeding cycles in Pecten. Those scallops facing into the ebb current show the same diphasic patterns as those individuals facing the flood current, but are 6 h out of phase. The cycle is considered as a duplication of a diphasic feeding pattern. The tubules themselves undergo a digestive process similar to that in Lasaea rubra (Montagu). The digestive cells phagocytose food material, begin intracellular digestion, and increase in size until they obscure the lumina. The dispersal of waste material and residual bodies is accomplished dramatically by a dehiscence of the tubule cells together with a loss of both digestive and crypt cells. New tubules are regenerated from the apices of those tubules breaking down. In any section of the diverticula tubules in two different conditions are found. The cycle of digestion takes 24 h and in order to facilitate feeding at each 12-h tidal cycle the tubules are equally divided into two phases with one 12 h behind the other.     

Measurement of Respiratory Volume for Virus Retention Studies in Mice

A pressure plethysmograph for measuring respiratory volume in mice during exposure to virus aerosols is described. The respiratory frequency and tidal volume were measured, and from these data the minute ventilation was calculated. The mean respiratory frequency of adult, male mice was 255 per min; the mean tidal volume of 0.18 ml was inversely related to respiratory frequency. The standardized mean minute ventilation rate was 1.46 ml per g of body weight. The respiratory frequency and tidal volume of CD-1 and HA/ICR strains of mice of the same age were similar. The respiratory retention rate for a 2.7-mum aerosol of vesicular stomatitis virus was 41%, and 58% of the virus retained was found in the trachea and lung.     

On the mechanism of air ventilaton in anabantoids (Pisces: Teleostei)

Summary Air ventilation in most Anabantoid species is diphasic, consisting of exhalation and inhalation. Exhalation is the release of air from the accessory breathing organs (suprabranchial chambers) through the mouth either into the water near the surface (e.g.,Ctenopoma) or directly into the atmosphere (e.g.,Osphronemus goramy). Inhalation, i.e., taking in fresh air through the mouth at the surface, immediately follows exhalation. X-ray films show (Figs. 5 and 6) that evacuation of the suprabranchial chambers during exhalation is total or nearly total. This, together with the fact that these chambers can contract at most to a very small extent, led to the conclusion that gas is replaced by water entering the chambers during exhalation and that this water is replaced by fresh air during inhalation. Further analysis of films, including conventional films showing the behavior of the opercular apparatus during air ventilation (Fig. 7), leads to a theory of a double-pumping mechanism responsible for air ventilation. This mechanism consists of the buccal apparatus and the opercular apparatus. It is suggested that both of these structures are able to act as both suction and pressure pumps, and thus air ventilation may be explained as the result of alternating activity of these two pumps.In the monophasic air ventilation characteristic of (adult)Anabas testudineus, there is no exhalation phase comparable to that of other Anabantoids. Therefore, no water enters the suprabranchial chambers, which remain filled with gas during the whole ventilation process (Fig. 10). Ventilation is limited to one phase comparable to inhalation in other Anabantoids.The structure of the accessory breathing organs (Fig. 1) and its progressive complication with growth (Fig. 4) were studied inOsphronemus goramy. The arrangement of the labyrinthine plates is in accordance with the requirements of transport of water and gas through the suprabranchial chambers. One plate (the inner plate, Fig. 1) separates these chambers into atrium, ventro-caudal, and dorso-caudal compartments, each with its own opening (valve). This organization seems essential for the transport of gas and water through the suprabranchial chambers and ensures that during exhalation, water flows into the chambers from above, so that while water is filling these chambers displaced gas can be sucked through the deep-lying pharyngeal openings into the expanding buccal cavity.Supported by the Deutsche Forschungsgemeinschaft