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Biomedical subjects

R A Ackerman

Publications and source records attributed to R A Ackerman.

15 recordsLinked to original sources
PubMed1995

Mathematical models for growth in alligator (Alligator mississippiensis) embryos developing at different incubation temperatures.

A variety of model-based (growth models) and model-free (cubic splines, exponentials) equations were fitted using weighted-nonlinear least squares regression to embryonic growth data from Alligator mississippiensis eggs incubated at 30 and 33 degrees C. Goodness of fit was estimated using a chi 2 on the sum of squared, weighted residuals, and run and sign tests on the residuals. One of the growth models used (Preece & Baines, 1978) was found to be superior to the classical growth models (exponential, monomolecular, logistic, Gompertz, von Bertalanffy) and gave an adequate fit to all longitudinal measures taken from the embryonic body and embryonic mass. However, measurements taken from the head could not be fitted by growth models but were adequately fitted by weighted least squares cubic splines. Data for the stage of development were best fitted by a sum of 2 exponentials with a transition point. Comparison of the maximum growth rates and parameter values, indicated that the growth data at 30 degrees C could be scaled to 33 degrees C to multiplying the time by a scaling factor of 1.2. This is equivalent to a Q10 of about 1.86 or, after solving the Arrhenius equation, an E++ of 46.9 kJmol-1. This may be interpreted as indicating a common rate-limiting step in development at the 2 temperatures.

Alligators and Crocodiles↗
PubMed1991

The energetics of embryonic growth and development. I. Oxygen consumption, biomass growth, and heat production.

A quantitative phenomenological model to describe the relationships between biomass growth rate, oxygen consumption, and heat production in developing embryos has been developed and tested using a wide range of experimental data. The model employs generalized material and energy balances, principles of enzyme kinetics, and an overall metabolic model scheme based on known biochemical principles. The phosphorylation concentration ratio of ATP and ADP occurs naturally and becomes a significant parameter in the analysis. The model is applied to the growth of Escherichia coli, Oryzias latipes, chick spinal cord, and whole chicken eggs. Excellent agreement between the model and the experimental data is obtained. In a succeeding paper (Part II) environmental effects and growth efficiency are discussed.

Animals↗
PubMed1988

Embryonic osmoregulation: consequences of high and low water loss during incubation of the chicken egg.

The rates of water loss of domestic chicken eggs were varied during incubation to measure the osmoregulatory ability of the avian embryo. Egg water loss was increased by drilling holes in the eggshell over the airspace on day 13 (I = 21 days) and then placing these eggs in a low relative humidity (r.h.: 0-10%) incubator until hatch. Egg water loss was decreased by placing other eggs in a high-r.h. (85-90%) incubator on day 0. Eggs with low water loss (approximately 6% of initial fresh mass [IFM]) produced embryos and yolks that were not different in wet or dry mass when compared to control eggs that lost approximately 12% of IFM. However, 1-4 gm of excess albumen were left in low-water-loss eggs on day 21. Hatching success was 71% and 89% for low and control eggs, respectively. Low egg water loss did not appear to disturb embryonic growth. The allantoic fluid volume and millimolar allantoic Na+ and Cl- ions declined faster with high and slower with low rates of water loss. Thus, excess water was lost as a result of increased movement of water out of allantoic fluid, which was due to increased active transport of Na+ ions by the chorioallantoic membrane (CAM). Eggs with high water loss had elevated Cl- levels after day 17 in plasma and amniotic fluid, which indicated a period of osmotic stress after depletion of allantoic fluid between day 18 and hatch. The decrease in wet embryo mass measured in embryos from high-water-loss eggs was due principally to dehydration of skin. Embryonic skin may serve as an emergency water reservoir during osmotic stress. Dehydrated chicks produced from high-water-loss eggs were 6 gm less in wet mass at hatch compared to controls. However, these chicks regained the water deficit 7 days after hatch and grew at a rate not different from control chicks through 6 weeks of age. Total egg water loss of 12% of IFM results in highest hatching success. However, water losses between 6% and 20% of IFM do not appear to affect adversely the growth or water content of the chick. Water losses above 20% of IFM cause early depletion of allantoic fluid, prolong the period of osmotic stress, and result in subsequent dehydration of blood, amniotic fluid, and embryonic skin.(ABSTRACT TRUNCATED AT 400 WORDS)

Allantois↗
PubMed1987

Effects of increased water loss on growth and water content of the chick embryo.

Domestic chicken eggs that lost 25.1% of their initial mass during incubation produced embryos with smaller wet masses than control eggs that lost 12.5% of their initial mass. However, water-stressed embryos did not differ from control embryos in dry body mass, indicating that water-stressed embryos were dehydrated. Yolk, albumen, heart, and gizzard wet and dry masses were not different between water-stressed and control groups during the last week of incubation. However, wet mass of the liver was significantly greater and that of the right leg significantly less in water-stressed embryos. Tarsometatarsal length, dry mass of the liver and right leg, and daily rates of oxygen consumption were not different between groups. Hatching success was 20.5% for water-stressed eggs and 85% for control eggs. These results show that increased egg water loss during the last week of incubation results in embryos that weigh less because they have a lower water content, not because they grow more slowly. The reduction in water content, with respect to the individual organs and body parts examined, is due primarily to a difference in leg tissue water content. We conclude that embryos do not alter their growth in response to a change in the amount of water available in the egg.

Animals↗
PubMed1987

Modelling heat and mass exchange of buried avian eggs.

The eggs of the Megapodiidae are incubated while buried in a substrate with which they exchange heat and water. The eggs may be buried in sand or in a mound composed in part or totally of organic material. We have analyzed the heat and water exchange of these buried eggs by constructing egg heat and mass balances. The equations are used to examine changes in egg temperature and water exchange during incubation in different environments. The thermal conductivities of the substrates are likely to vary by a factor of 5 to 10, with sand having the greatest thermal conductivity and organic litter the smallest. We predict that eggs incubated in sand will increase in temperature by 1 degree C or less, whereas eggs incubated in organic material will increase in temperature by 4 degrees C or more. Mound temperatures should remain low (less than 35 degrees C) to prevent overheating of eggs and hatchlings. Eggs can be incubated in sand at higher temperatures with less risk of overheating. Egg water loss in mounds is likely to be variable depending on mound humidity and considerably greater than 0 even in very high humidities. We expect that the rate of water loss by the eggs will increase many fold during incubation because of the low thermal conductivity of the mound material and the consequent increase in egg temperature.

Animals↗
PubMed1986

Influence of temperature on the CO2 dissociation curve of the turtle Pseudemys scripta.

Carbon dioxide dissociation curves were constructed for blood of Pseudemys scripta. These were shifted by temperature and CCO2 was inverse to temperature at common PCO2. CO2 capacitance coefficients for oxygenated and deoxygenated blood (beta oxy, beta deoxy) were inverse to temperature at reported in vivo arterial PCO2's as was the Haldane effect. Data for in vivo PCO2 and Hb saturation of pulmonary arterial and venous blood allowed determination of effective beta which closely reflected values of beta oxy and beta deoxy at different temperatures. This indicates an influence of curve shape on beta eff at in vivo PCO2's. A high degree of correlation was found between air convection requirement (liters of gas ventilated per mmol CO2 produced) and beta eff at different temperatures. The inverse relationship between beta eff and temperature strongly influenced perfusive conductance of CO2 (Gperf = Vb X beta) and contributes to the temperature-independent stability of ventilatory to perfusive conductance ratio and the CO2 content of the animal. The influence of variable curve shape and Haldane effects must be considered as determinants of beta eff in the quantitative assessment of CO2 transport in this species.

Animals↗
PubMed1982

Metabolic and acid-base changes during selection of warmer water by cold-acclimated fish.

Largemouth bass (Micropterus salmoides) acclimated to 3 degrees C were placed in a thermal gradient. The bass selected the final thermal preferendum of 28 degrees C in about 18 h. The movement into warmer water was initially rapid but became progressively slower. 2) Other bass were acclimated to 8 degrees C, cannulated in the dorsal aorta, and placed in a temperature-controlled chamber. Oxygen uptake, blood pH, and total CO2 were measured as the chamber temperature was increased to 28 degrees C following a time course similar to that followed by bass in the gradient. 3) Oxygen uptake was always elevated above the resting level, and this elevation increased as higher temperatures were encountered. 4) Just prior to placement in the chamber the pH of the arterial blood was 7.98 +/- 0.05 (mean +/- SE). As the temperature was increased neither the pH nor the total CO2 content of the blood exhibited major changes. At temperatures between 26 and 28 degrees C, the pH (8.01 +/- 0.03) was about 0.3 pH units above predicted normal values. 5) During the return to the final thermal preferendum fish experience overall metabolic rates and extracellular acid-base levels that deviate progressively farther from normal resting levels. Neither factor appears likely to be the major determinant of the behavioral response.

Acclimatization↗
PubMed1981

In vivo O2 and water vapor permeability of the hen's eggshell during early development.

The area of the chorioallantois was measured from the time it makes contact with the eggshell membranes on day 6 until it has completely enveloped the egg content on day 12. The oxygen uptake and air cell O2 tension were also determined during this period. These observations allow one to calculate that the O2 flux is confined to those areas of the shell which cover the chorioallantois and that the O2 permeability of the shell (including the outer membrane), KO2, is constant. The water vapor permeability of the shell, KH2O, was also measured. Since the ratio of KH2O/KO2 is essentially equal to the ratio of their diffusion coefficients, DH2O/DO2, it suggests a common diffusion path for O2 and water molecules.

Allantois↗
PubMed1980

The effects of temperature on acid-base balance and ventilation of the marine iguana.

Marine iguanas, Amblyrhynchus cristatus, held for 12-18 h at 16, 24 and 35 degrees C exhibited an arterial pH change of -0.001 delta pH/delta degree C. The arterial pH changed by -0.004 delta pH/delta degree C between 16 and 24 degrees C and by -0.015 delta pH/delta degree C between 24 and 35 degrees C. When the animals were allowed to cool to 16 degrees C and remarm to 35 degrees C after 12-18 h at 35 degrees C, the pH change was -0.015 delta pH/delta degree C. Arterial pH measured during warming to 35 degrees C after 12-18 h at 16 degrees C was relatively constant at around pH approximately equal to 7.60 returning slowly toward the 35 degrees C equilibrijm pH approximately equal to 7.44. An increase in VE/MCO2 (L . mmol-1) is seen with decline in equilibrium body temperature from 0.79 at 35 degrees C to 1.66 at 16 degrees C. The ventilatory response is associated with a fall in PaCO2 (24 Torr, 35 degrees C; Torr, 16 degrees C). Arterial CO2 content and [HCO3-] remain relatively constant. The observed arterial pH-body temperature relationshi is similar to other reptiles; however, thermal history appears to influence the relationship. Marine iguanas probably experience only brief periods of time at body temperature as low as 18 degrees C.

Acid-Base Equilibrium↗
PubMed1977

The respiratory gas exchange of sea turtle nests (Chelonia, Caretta).

Sea turtles lay about 100 leathery-shelled eggs in a 25 cm diameter chamber carefully excavated about 50 cm deep in a nesting beach, where the eggs exchange gases (at approximately 28 degrees C) during their 60-day incubation period. The sand surrounding the spherical nest chamber restricts the diffusion of gases into and out of the nest so that as embryonic development progresses, PO2 decreases and PCO2 increases in the gas inside the nest. PO2 falls to 80-100 torr and PCO2 rises to 40-60 torr inside 100-egg man-made Chelonia and Caretta nests. The change in gas tensions in the nest during development is very similar to that seen in the air cell of the chicken egg. Gas tensions inside the turtle nest and in the sand surrounding the nest can be described by a radial steady-state diffusion model. The rate of diffusion of gases in the sand is 30-50% of the rate found in the nest and 6-12% of the rate found in an equal volume of air. The sand surrounding the turtle nest appears to determine the gas exchange of the eggs in the nest and is functionally analogous to the shell surrounding the chicken embryo. The female sea turtle may construct her nest so as the maximize its gas exchange and minimize gas partial pressure gradients inside the nest.

Animals↗