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  • 1
    ISSN: 1432-0878
    Keywords: Carotid body ; Duck ; Cervical vagotomy ; Innervation ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Carotid bodies of ducks show no detectable changes in ultrastructure up to periods of four weeks following the removal of 2–3 cm of the cervical vagus (decentralization). This indicates that the majority, and possibly all the nerves terminating on the glomus cells are afferent (sensory) in nature. These nerve endings are in reciprocal synaptic contact with the glomus cells and therefore have efferent and afferent functions. Theories concerning the carotid body receptor mechanism are discussed with particular reference to those theories which ascribe functions to the reciprocal synapses.
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  • 2
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. TheP IO2 at which crabs emerged from shallow seawater during progressive hypoxia (Table 1), as well as theP c levels for $$\dot V_{O_2 }$$ (Fig. 2) and $$\dot V_g $$ (Fig. 4) of submerged crabs, increased with acclimation temperature and following exposure to 50% seawater at low temperatures (Fig. 6). This pattern of variation resembles the changes in relative oxygen demand with temperature and salinity. 2. TheP c levels for heart rate increased with acclimation temperature but were unaffected by dilution (Fig. 6). 3. Percentage extraction of oxygen from the respired water (Table 2) as well as the levels of motor activity (Fig. 5) were not affected by exposure to hypoxia. 4. Lactic acid concentration in the blood of submerged crabs increased markedly during hypoxia and there was an enhanced $$\dot V_{O_2 }$$ on recovery in normoxia (Fig. 2), which apparently served to completely repay an accumulated oxygen debt. 5. It was concluded that when exposed to environmental hypoxiaCarcinus can adopt the alternative strategies of either accumulating an oxygen debt when in deep water or emerging into air from shallow water to aerate the branchial chambers.
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  • 3
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The effectiveness of oxygen transfer across the gills of dogfish was measured during normoxia and hypoxia, both before and after transection of the cardiac vagus nerves. Direct measurement of ventilation volume ( $$\dot Vw$$ ) agreed with values calculated by the Fick technique. 2. Hypoxia caused a significant reduction in blood oxygen tension and content and in rate of oxygen consumption ( $$\dot M_{O_2 }$$ ). There was a marked bradycardia accompanied by a compensatory increase in cardiac stroke volume (Table 1). The ventilation/perfusion ratio ( $$\dot Vw/\dot Vb$$ ) increased due to an increase in respiratory stroke volume. % Extraction (% Ext) and effectiveness of transfer (Ew) of oxygen from water were maintained during hypoxia, possibly due to an increase in the transfer factor ( $$T_{O_2 }$$ ). 3. Cardiac vagotomised fish showed an increase in normoxic heart rate accompanied by a decrease in cardiac stroke volume. There was no bradycardia during hypoxia. The absence of the bradycardia had no observable effect on the efficacy of oxygen transfer during hypoxia (Table 3). 4. Following cardiac vagotomy, the oxygen tension in the venous blood ( $$P\bar v_{O_2 }$$ ) was reduced both during normoxia and hypoxia, and $$\dot Vw$$ did not increase during hypoxia (Table 3). These differences were, however, apparent in sham-operated fish (Table 2). 5. The measured variables and derived values for effectiveness of oxygen transfer are compared with those described for other fish.
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  • 4
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The first afferent branchial blood vessel of dogfish was cannulated and the animals were allowed 24 h to recover from the operation. Control animals were then left for 3 days in normoxic sea water, while experimental fish were exposed to hypoxic sea water ( $$P_{O_2 }$$ 55 mmHg) for 3 days. It was not possible to keep the fish for this period of time at an environmental $$P_{O_2 }$$ below 50 mmHg. 2. In the control animals, there was a significant (24%) reduction in haematocrit during the 3 day period of normoxia. There was a significant increase in the concentration of bicarbonate ions [HCO 3 − ] which, together with a slight increase in $$pH\bar v$$ , indicates a metabolic alkalosis following a decrease in the concentration of plasma lactate and the lactate/pyruvate ratio. There were no significant changes in any of the other measured variables. 3. In the experimental fish, there was no significant change in Hct during the 3 day period of hypoxia. There was, therefore, a potentialincrease in Hct during this period (cf. change in control fish). Heart rate declined initially, but then recovered to a value which was close to the normoxic rate. There was an increase in $$pH\bar v$$ , while [HCO 3 − ] and $$P\bar v_{CO_2 }$$ decreased. Plasma lactate and the lactate/pyruvate ratio increased and it was deduced that there was a combination of a respiratory alkalosis with a metabolic acidosis. The only catecholamine to increase significantly was noradrenaline. 4. The failure of dogfish to survive prolonged exposure to more severe hypoxia ( $$P_{O_2 }$$ 〈50 mmHg) is probably related to their inability to increase oxygen transport by large increases in ventilation volume or by reducing theP 50 of their hemoglobin. Anaerobiosis and severe acidosis then occur.
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  • 5
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The rates of oxygen consumption ( $$\dot V_{{\text{O}}_2 } $$ ) of individual crabs varied with their live mass. Mean $$\dot V_{{\text{O}}_2 } $$ increased with acclimation temperature in 100% seawater (Q10 2.36) but not in 50% seawater. 2. Exposure to 50% seawater caused a significant increase in $$\dot V_{{\text{O}}_2 } $$ to twice the rate in 100% seawater at 10°C. There was no significant increase in $$\dot V_{{\text{O}}_2 } $$ on dilution at 18°C (Fig. 5). 3. Heart rate, ventilation volume ( $$\dot V$$ ) and a-VO 2 content difference were unaffected by dilution. The rise in $$\dot V_{{\text{O}}_2 } $$ , following dilution at 10°C may, as far as the cardiovascular system is concerned, arise from an increase in cardiac stroke volume. 4. Crabs were isosmotic with 100% seawater at 10°C, 14°C and 18°C. In 50% seawater all crabs showed a significant reduction in blood osmolarity, though they maintained the ΔF.p. and Na+ concentration significantly above that of the medium. Crabs acclimated to 10°C maintained a significantly higher blood ΔF.p. and Na+ concentration in 50% seawater than crabs at 18°C (Fig. 6). 5. Crabs acclimated to 10°C were significantly more active after exposure to 50% seawater. There was no significant change in activity, following dilution, in crabs at 18°C (Fig. 7). 6. The variations in $$\dot V_{{\text{O}}_2 } $$ with temperature and salinity seem to relate to the measured changes in patterns of osmoregulation and activity. At 10°CCarcinus osmoregulates more effectively than at 18°C and is hyperactive in low salinities, which may represent an avoidance reaction. At 18°C, the summer temperature, the crab tolerates internal dilution and is relatively quiescent.
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  • 6
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Oxygen consumption $$(\dot V_{O_2 } )$$ and heart rate of crabs acclimated to 15°C and exposed to water or air for 3 h were not significantly different (Fig. 1). 2. When in air crabs ventilate their branchial chambers in both the forward and reversed direction (Fig. 3). 3. Exposure to air caused a marked reduction in oxygen tension of the postbranchial haemolymph $$(Pa_{O_2 } )$$ and a fall in pHa associated with an increase in $$Pa_{CO_2 }$$ . Oxygen content $$(Ca_{O_2 } )$$ and the $$a - v_{O_2 }$$ content difference were maintained relatively high due to the oxygen binding characteristics of the haemocyanin (Table 1 and Fig. 4). 4. The concentration of lactic acid in the haemolymph was not affected by exposure to air (Table 1). 5. Exposure to air for 3 h was associated with a small reduction in total mass caused by evaporative water loss with a concomitant increase in haemolymph sodium concentration (Table 1). 6. The gill lamellae are relatively well spaced out and derive physical support from their covering of chitin. They may, therefore, be suited structurally for respiratory gas exchange in both water and air (Fig. 5).
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  • 7
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Heart rate and pulmonary artery blood flow of resting green turtles,Chelonia mydas, at 29°C increased with lung ventilation (heart rate from 24±5 to 51±8 beats min). When swimming at 0.6 m s−1 in water at 30°C, oxygen uptake was 2.83 times and respiratory frequency was 2.75 times the resting values. Heart rate was 1.33 times that during ventilation at rest but 2.83 times that at the end of a breath hold at rest. Partial pressures of oxygen and carbon dioxide, lactic acid concentration and pH of arterial blood, when swimming at 0.5 m s−1, were similar to those soon after ventilation at rest. Pulmonary blood flow did not decline to low levels between breaths, when the animals were swimming, as it did when they were at rest. In active turtles it appears that pulmonary perfusion remains elevated, supplying oxygen to the locomotory muscles at a sufficiently high rate to support the complete aerobic production of energy, and that respiratory frequency is kept as low as possible, as surfacing for air increases the metabolic cost of swimming.
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  • 8
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The role of the natural increases in the circulating levels of adrenaline and noradrenaline in response to hypoxia has been investigated using pharmacological blockade of alpha-and beta-adrenergic receptors. Fish were equipped with indwelling arterial cannulae and rubber funnels over the gills to allow detailed analysis of branchial oxygen transfer. Although blood oxygen levels, oxygen consumption and branchial oxygen transfer were reduced following adrenergic receptor blockade, similar changes in these variables also occurred with time in control animals. In conclusion, we can find no substantial evidence that the increase in circulating levels of catecholamines plays any crucial role in the cardiovascular or respiratory responses of these animals to hypoxia.
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  • 9
    ISSN: 1432-136X
    Keywords: Thyroxine ; Citrate synthase ; Locomotor muscles ; Birds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Following extended periods of relative inactivity, or prior to migration, birds are able to increase the aerobic capacity of their locomotory muscles. Thyroid hormones may influence this process. A preliminary study was undertaken to assess the ability of elevated levels of thyroxine to increase the aerobic capacity of the locomotory and cardiac muscles of adult tufted ducks. Administration of thyroxine in the food for 8 weeks had little effect on body mass or on the masses of the pectoralis, semitendinosus and iliofibularis muscles, although there were increases in resting oxygen consumption and in the mass of the cardiac ventricles. The maximum activity of the aerobic enzyme, citrate synthase, was significantly greater in the left ventricle, liver, and iliofibularis muscles (P〈0.005) of treated birds. However, while there was clearly no difference in activity in the semimembranosus leg muscle, that of the pectoralis was not quite significant (P=0.078). It is concluded that addition of supra-physiological levels of exogenous thyroxine may induce a differential increase in the maximum activity of citrate synthase in the locomotor muscles of the tufted duck, which is correlated with the fibre type composition of these muscles. These results are consistent with those found in studies on rats, with slow oxidative fibres being the most sensitive, and fast glycolytic fibres the least sensitive, to thyroxine treatment.
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  • 10
    ISSN: 1432-136X
    Keywords: Key words Thyroxine ; Triiodothyronine ; Citrate synthase ; Muscle development ; Birds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The role of thyroid hormones in the development of the locomotor and cardiac muscles of the barnacle goose (Branta leucopsis) was investigated. From 2 weeks of age, goslings were treated with thyroxine, triiodothyronine, or methimazole (a thyroid inhibitor). Birds were killed at 6 weeks (n = 5) or 9 weeks (n = 4) and various locomotor and cardiac muscle masses recorded and tissue samples taken for analysis of citrate synthase activity. The effects of thyroxine and triiodothyronine were not significantly different from each other, except in the case of the iliofibularis at 9 weeks. The mass-specific citrate synthase activity of the iliofibularis, semimembranosus muscles and liver were significantly increased by thyroid hormone treatment. Cardiac muscle showed a significant hypertrophy at 9 weeks of age following treatment with thyroxine. Hypothyroidism induced by treatment with methimazole exhibited the greatest effect on the pectoralis muscle, reducing citrate synthase activity by 33%. Mass-specific citrate synthase activity of the pectoralis and pectoralis mass (% body wt.) were found to be highly correlated (r 2 = 0.74) at 6 weeks of age. It is suggested that thyroid hormones may be involved in controlling the tissue-specific timing of the maturation of locomotor and cardiac muscles.
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