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Biomedical subjects

G K Snyder

Publications and source records attributed to G K Snyder.

At least 37 records · Page 2Linked to original sources
PubMed1987

Muscle capillarity in chicks following hypoxia.

1. Muscle capillarity was examined in chicks exposed to normobaric hypoxia with and without increased workload. 2. Capillarity was higher in the lateral head of the gastrocnemius, but not in the other muscles examined. Increased workload did not contribute to the effects of hypoxia. 3. Thus, hypoxia served as a stimulus for the development of new capillaries in muscle containing twitch fibers, but not in muscle containing tonic fibers.

Analysis of Variance↗
PubMed1987

Estimating diffusion distances in muscle.

Models of fibers and capillaries in cross sections of muscle were used to quantify the relationships between diffusion distances and tissue capillarity. The fibers were constructed as square and hexagonal arrays, and the placement of capillaries around the perimeters of the fibers ordered them in similar arrays. Diffusion distances were measured as the percent cumulative frequency of fiber area within a given distance of a capillary when capillary-to-fiber ratio was increased from 0.5 to 4.0. Equations fitted to the data make it possible to estimate diffusion distances in muscle and to correlate changes in diffusion distances with fiber growth, capillary growth, and the geometrical arrangement of capillaries in the muscle bed.

Animals↗
PubMed1985

Effects of hypoxia on muscle capillarity in rats.

Capillary density, fiber cross-sectional area, capillary/fiber ratio and fiber composition were determined in gastrocnemius and diaphragm muscles of laboratory rats following five weeks at 350 Torr ambient pressure. Growth rates of hypoxic rats were lower than normoxic controls, but the periods of sacrifice were adjusted to achieve similar body masses for the two groups. Hypoxic rats had significantly higher hematocrits and heart masses, characteristic of acclimation to hypoxia. However, capillary/fiber ratios in gastrocnemius and diaphragm were similar for hypoxic and normoxic rats suggesting that hypoxia did not stimulate capillarity in either muscle. In diaphragm, but not gastrocnemius, diffusion distances were significantly shorter in hypoxic rats than in controls. We conclude that the differences in diffusion distances represent an important secondary effect of hypoxia on the diaphragm associated with changes in demands on ventilation in response to low oxygen pressures.

Animals↗
PubMed1984

Effects of maturation on tissue capillarity in chickens.

Tissue capillarity, diffusion distances and myoglobin concentrations in the anterior latissimus dorsi (ALD), consisting entirely of slow tonic fibers, the posterior latissimus dorsi (PLD), consisting entirely of twitch fibers, and the gastrocnemius (GST), consisting of both twitch and tonic fibers, were determined for the domestic chicken throughout maturation. Increases in muscle mass for the three muscles are due to fiber hypertrophy and are quantified as changes in the average cross-sectional area (FCSA) of the fibers. Capillary densities were highest in the newly hatched chicks: ALD = 3967 +/- 888 caps/mm2, PLD = 8360 +/- 1078 caps/mm2, and GST = 8360 +/- 8360 +/- 1283 caps/mm2; and decreased in proportion to the increase in FCSA, to adult values of ALD = 450 +/- 50, PLD = 120 +/- 20 and GST = 267 +/- 33 caps/mm2. In contrast to mammals, the ratio of the numbers of capillaries to the numbers of muscle fibers appears to be fixed at or shortly after hatch; there is not an increase in the numbers of capillaries to offset fiber hypertrophy. Consistent with the observations on capillary densities, the diffusion distances are shortest in the newly hatched chicks where the maximal diffusion distance is 17.9 +/- 1.06 micron in the ALD, 12.5 +/- 1.08 micron in the PLD and 17.4 +/- 0.93 micron in the GST. The maximal diffusion distance increased in proportion to FCSA; to 42.4 +/- 5.75 micron in the ALD, 88.8 +/- 1.33 micron in the PLD and 64.4 micron +/- 8.59 micron in the GST. In the adult the diffusion distances varied with the fiber type of the muscle. Myoglobin concentrations were similar in the ALD and PLD and were lowest at hatch but increased to plateau values of 4.3 +/- 0.51 mg/g for the slow-tonic ALD and 2.2 +/- 0.33 mg/g for the fast-twitch PLD. In contrast, myoglobin concentrations in the GST were highest in the newly hatched chicks and decreased to a low-level plateau of 1.8 +/- 0.83 mg/g in the adult. The very high myoglobin concentrations in the GST of the newly hatched chicks may represent an adaptation to conditions of extreme hypoxia in the hind limb of the developing embryo.

Animals↗
PubMed1984

Effects of hypoxia on tissue capillarity in geese.

Tissue capillarity in the gastrocnemius and myoglobin concentrations in the gastrocnemius and heart were determined for hatchling Canada geese, Branta canadensis, following incubation of the embryos under either normoxic (Po2 = 120 torr) or hypoxic (Po2 = 94 torr) conditions. Similar observations were made on a limited number of hatchling bar-headed geese, Anser indicus, a species native to high altitude. Capillary densities were higher and diffusion distances shorter in the hypoxic Canada geese and the bar-headed geese than in the normoxic Canada geese. The concentrations of myoglobin in the heart and gastrocnemius increased with mass, but not as a function of hypoxia. We conclude that bird embryos respond to hypoxia by increasing capillarity. The increased capillarity is found in species native to high altitude when incubated under conditions of normoxia and can be induced in species native to sea level by exposure to hypoxia during development.

Adaptation, Physiological↗
PubMed1983

Respiratory adaptations in diving mammals.

This report examines the evidence for the presence of oxygen stores in the lungs, blood and systemic musculature of diving mammals, the modifications in the respiratory functions of blood that may be important in utilizing the lung and blood oxygen stores, and the potential importance of the oxygen stores and the respiratory functions of blood in supporting short-duration, aerobic dives. Increasing oxygen stores by increasing lung volume does not occur in diving mammals. The long-duration diving whales have small lung volumes which results in lung collapse during dives and the seals dive following partial expiration which produces the same effect. The short-duration diving dolphins, porpoises and rodents have lung volumes comparable to terrestrial mammals, dive following inspiration and appear to use the lungs as an oxygen store. Adaptations in the oxygen affinity of the blood parallel the modifications in lung volume. Where the lungs do not represent a potential oxygen store the oxygen affinity is low, maximizing the unloading of oxygen while maintaining a high tissue oxygen tension. Where the lungs do represent an oxygen store, the affinity is high, maximizing the uptake of oxygen from the alveolar space. Increases in the concentration of respiratory pigment in the blood and in muscle are important adaptations in diving mammals. The blood oxygen stores in diving mammals vary from near normal to over three times normal for terrestrial mammals while the muscle oxygen stores vary from near normal to nearly ten times normal. The degree to which the blood and muscle oxygen stores are increased can be equated to the duration of the dive and demands for oxygen; longer duration divers and those with higher metabolic demands have greater oxygen stores than divers that remain submersed for shorter periods or have lower rates of oxygen utilization.

Animals↗
PubMed1982

Water loss and survival in embryos of the domestic chicken.

In this report we show that the amount of water lost during incubation is an important determinant of hatchability in embryos of the domestic chicken. However, when the loss of water is restricted to the first half versus the second half of the total incubation period, it is the loss of water during the first half that affects hatching success. We propose that regulating the permeability of the egg shell may be important in preventing excessive drying of the inner shell membrane during early development along with limiting the total amount of water lost from the embryo during incubation.

Animals↗
PubMed1982

Respiratory properties of blood from embryos of highland vs. lowland geese.

Respiratory properties of whole blood during development were studied in embryos of the bar-headed and Canada geese. In both species, affinity of the blood for O2 [expressed as O2 half-saturation pressure (P50)] increased with development, to a low and stable value. The low and stable P50 at pH 7.4 for the bar-headed goose, 20.1 +/- 0.3 Torr, is significantly lower than that for the Canada goose, 26.9 +/- 0.8 Torr. The data suggest a higher Bohr effect for the bar-headed goose. Hill's coefficients, buffering capacity, red cell 2,3-diphosphoglycerate, and blood hemoglobin concentrations are similar in both species. We suggest that the affinity of the whole blood for O2 is an important genetically based adaptation to ensure a high O2 content in the blood in the face of reductions in ambient PO2 associated with nesting at high altitudes. The higher Bohr effect may ensure high tissue PO2 in the presence of the high-affinity hemoglobin.

2,3-Diphosphoglycerate↗
PubMed1981

Oxygen permeability of the shell and membranes of chicken eggs during development.

Oxygen permeability (KO2) was measured through the shell and shell membranes of chicken eggs throughout incubation. Shell KO2 was constant at 1.90 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Outer shell membrane KO2 was constant at 1.78 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Inner membrane KO2 increased from 0.11 x 10(-6) cm3 O2 STP . sec-1 . cm-2. Torr-1 to 1.56 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Calculations of KO2 from oxygen uptake rates and air cell PO2's were in close agreement with direct measurement of KO2. Resistance to oxygen flux was partitioned at each level. The outer membrane added 6% to the resistance of the shell. The inner membrane initially accounted for 88% of the shell/membrane complex resistance, but fell to 12% of the resistance by the end of incubation. The hypothesis is discussed that the increased permeability of the inner membrane is related to the evaporation of water from the membrane surface. The possibility is rejected that the shell membranes may be potential sites for respiratory adaptation to incubation at altitude.

Adaptation, Physiological↗
PubMed1977

Blood corpuscles and blood hemoglobins: a possible example of coevolution.

A model which equates oxygen transport to hemoglobin concentration and molecular weight is used to demonstrate that high concentrations of hemoglobin will augment oxygen transport only if the molecular weight of the hemoglobin is low. The evolution of corpuscles is a necessary counterpart to having high concentrations of the low molecular weight hemoglobins. corpuscles prevent loss of the small molecules by way of excretory filters and prevent the development of exceedingly high plasma osmotic pressures.

Biological Evolution↗
PubMed1977

Hematology, viscosity, and respiratory functions of whole blood of the lesser mouse deer, Tragulus javanicus.

Blood samples from the lesser mouse deer were examined for hematology, viscosity, oxygen dissociation curve, and magnitude of the Bohr effect. Red corpuscle dimensions, determined under oil immersion with an ocular micrometer, averaged 2.2 micron while the cell counts averaged 53 million/micronl blood, and the packed cell volume averaged 31.2%. Blood hemoglobin concentration averaged 11.2 g/100 ml and the calculated mean cell hemoglobin concentration was 38 g/100 ml. The relative viscosity of the mouse deer plasma was 1.97 and increased in a nonlinear manner with hematocrit to 100 at 80% packed cell volume. Oxygen-hemoglobin equilibrium curves, determined with a mixing technique at 37 degrees C and 10, 36 and 71 Torr PCO2, have the same configuration observed in blood from mammals in general. The P50 of the mouse deer blood at pH = 7.40 is 34 Torr and the Bohr effect (deltalog P50/deltapH) is -0.483. The mouse deer have blood hematocrits which are well below the hematocrits observed in mammals with larger erythrocytes, but similar to the blood hematocrits observed in other mammals with small erythrocytes. We suggest that the low hematocrit is an adaptation which circumvents the hemodynamic problems associated with a high blood viscosity and that, in the mouse deer, the expected concomitantly low total blood hemoglobin concentration is compensated by a higher than average mean cell hemoglobin concentration.

Animals↗
PubMed1977

Hemodynamics of the lesser mouse deer, Tragulus javanicus.

Mouse deer possess the smallest known erythrocytes. In contrast to the usual biconcave shape, mouse deer corpuscles are spherical which results in an appreciable increase in vitro blood viscosity. In the absence of compensation, increased viscosity should produce hemodynamic consequences. However, we find that cardiac output, arterial pressure, and total peripheral resistance are all within normal limits, while packed cell volume is considerably lower than normal. We suggest that reduced packed cell volume represents a compensation for the spherical shape of the corpuscles, serving to maintain blood viscosity and dependent hemodynamic parameters within normal limits. These results contrast markedly with the pattern observed in man where conditions which result in a high in vitro blood viscosity also have significant hemodynamic consequences. Mean values for three mouse deer were: body mass, 1.18 kg; packed cell volume, 29.8%; heart rate, 182 beats/min; cardiac output, 145 ml-(kg-min)-1., mean arterial pressure, 99 Torr; total peripheral resistance, 4.90 X 10(5) dyn-s-cm-5.

Animals↗