Arthur C. Guyton

Bio: Arthur C. Guyton is an academic researcher from University of Mississippi Medical Center. The author has contributed to research in topics: Blood pressure & Angiotensin II. The author has an hindex of 50, co-authored 132 publications receiving 28798 citations.

Textbook of Medical Physiology

Abstract: Textbook of medical physiology , Textbook of medical physiology , کتابخانه دیجیتال جندی شاپور اهواز

Control of glomerular filtration rate by renin-angiotensin system

Abstract: HALL,JOHN E., ARTHUR C. GUYTON,THOMAS E. JACKSON, THOMAS G. COLEMAN, THOMAS E. LOHMEIER, AND NICK C. TRIPPODO. Control of glomerular filtration rate by reninangiotensin system. Am. J. Physiol. 233(5): F366-F372, 1977 or Am. J. Physiol.: Renal Fluid Electrolyte Physiol. 2(5): F366-F372, 1977. -The role of the renin-angiotensin system (RAS) in autoregulating renal blood flow (RBF) and glomerular filtration rate (GFR) during reductions in renal artery pressure (RAP) was examined in the following groups of anesthetized dogs: group I, normal controls, n, 10; group II, normal dogs after intrarenal infusion of angiotensin II antagonist (AIIA), n, 7; group III, sodium-depleted controls, n, 7; group IV, sodium-depleted dogs after intrarenal infusion of AIIA, n, 10. In groups I and III, RBF and GFR did not change significantly between RAP’s of 85-127 mmHg, and decreased only 5-14% below control values at an RAP of approx. 70 mmHg. After AIIA in normal dogs (group II), RBF increased above control values when RAP was lowered; GFR remained relatively constant in group II as RAP was reduced to 85 mmHg, but decreased to 71 t 5% of the control value at 70 mmHg. After AIIA in sodium-depleted dogs (group IV), RBF autoregulation was well maintained, but GFR decreased progressively to 43 t 6% of the control value when RAP was reduced in steps to 70 mmHg. Although filtration fraction (FF) and calculated efferent arteriolar resistance in groups I and III remained relatively constant when RAP was reduced, in groups II and IV (in which the RAS was nonfunctional because of angiotensin II blockade) FF and efferent arteriolar resistance decreased progressively at all RAP’s below control. These observations are consistent with the hypothesis that the RAS plays an important role in controlling GFR through an efferent arteriolar constrictor mechanism, especially during high renin states such as sodium depletion.

Oscillation and Chaos in Physiological Control Systems

Abstract: First-order nonlinear differential-delay equations describing physiological control systems are studied. The equations display a broad diversity of dynamical behavior including limit cycle oscillations, with a variety of wave forms, and apparently aperiodic or "chaotic" solutions. These results are discussed in relation to dynamical respiratory and hematopoietic diseases.

Hydrogels in regenerative medicine

Abstract: Hydrogels, due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics, have been the material of choice for many applications in regenerative medicine. They can serve as scaffolds that provide structural integrity to tissue constructs, control drug and protein delivery to tissues and cultures, and serve as adhesives or barriers between tissue and material surfaces. In this work, the properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed. Recent research involving several different hydrogels polymerized from a variety of synthetic and natural monomers using typical and novel synthetic methods are highlighted. Finally, special attention is given to the microfabrication techniques that are currently resulting in important advances in the field.

Control theory: A useful conceptual framework for personality–social, clinical, and health psychology.

Abstract: Control theory provides a model of self-regulati on that we believe is useful in the analysis of human behavior. As an illustration of the breadth of its applicability, we present the basic construct of control theory—the discrepancy-reducing feedback loop—and discuss certain of its implications for theory in three separate areas of human psychology. In personality-s ocial, clinical, and health psychology, the construct proves to fit well with known phenomena and with the theories most recently developed to account for the phenomena. Moreover, in each case control theory appears to make a distinct and unique contribution to the state of the area. We conclude by noting the integrative potential that is suggested by these illustrations and by noting some issues that should receive attention in future work. Cybernetic or control theory is a general approach to the understanding of self-regulating systems. Its central ideas have been around for a long time (see, for example, Cannon's 1929, 1932, discussion of homeostatic physiological mechanisms), but its birth as a distinct body of thought is usually traced to the publication of Wiener's (1948) book, Cybernetics: Control and communication in the animal and the machine. Since then, control theory (in various forms) has had a major impact on areas of work as diverse as engineering (e.g., Dransfield, 1968; Ogata, 1970), applied mathematics (e.g.,

Hemodynamic Patterns of Age-Related Changes in Blood Pressure: The Framingham Heart Study

Abstract: Background We attempted to characterize age-related changes in blood pressure in both normotensive and untreated hypertensive subjects in a population-based cohort from the original Framingham Heart Study and to infer underlying hemodynamic mechanisms. Methods and Results A total of 2036 participants were divided into four groups according to their systolic blood pressure (SBP) at biennial examination 10, 11, or 12. After excluding subjects receiving antihypertensive drug therapy, up to 30 years of data on normotensive and untreated hypertensive subjects from biennial examinations 2 through 16 were used. Regressions of blood pressure versus age within individual subjects produced slope and curvature estimates that were compared with the use of ANOVA among the four SBP groups. There was a linear rise in SBP from age 30 through 84 years and concurrent increases in diastolic blood pressure (DBP) and mean arterial pressure (MAP); after age 50 to 60 years, DBP declined, pulse pressure (PP) rose steeply, and MA...

A Functional Analysis of Circadian Pacemakers in Nocturnal Rodents. I. The Stability and Lability of Spontaneous Frequency

Abstract: 1. In the first part of the paper, the model of non-parametric entrainment of circadian pacemakers is tested for the case of nocturnal rodents. The model makes use of the available data on freerunning period (τ) in constant darkness and on phase response curves (PRC) for short light pulses. It is tested in experiments using 1 or 2 light pulses per cycle. 2. Mesocricetus auratus and Peromyscus leucopus entrain to Zeitgebers involving 1 pulse (15' or 60') per cycle. The phase angle differences between rhythm and light cycle depends on the periods (τ and T) as predicted by the model. Entrainment of P. leucopus is unstable due to the after effects on τ created by the light pulse. 3. The limiting values of Zeitgeber period to which the animals entrain are much closer to 24 h than in Drosophila pseudoobscura, as the model predicts. However, frequent failures to entrain to T = 23 and T = 25 h are only explained if we take considerable interindividual variation in both τ and PRC into account. 4. With 2 pulses per cycle, the model predicts that entrainment will be more stable when activity is in the longer interval between the pulses than when it is in the shorter interval. This is true in the experimental data, where the phase relationships match predictions for skeleton photoperiods up to ca. 14 h. Increasing asymmetry forces animals into a "phase jump", so that activity shifts from the shorter to the longer interval. These ψ-jumps are accurately predicted in the hamster, but they occur at much longer photoperiods than predicted in P. leucopus. 5. Thus, the unqualified model, using a rigidly fixed species τ and PRC, is surely inadequate to explain entrainment. The extent to which variations in τ and PRC-shape, both "spontaneous" and induced by the entrainment process, can be known or inferred restricts the validity of the predictions. Yet we conclude, from a good deal of agreement between experiment and prediction (i), from the close correspondence between complete and skeleton photoperiods (ii), and on behavioural grounds (iii), that non-parametric entrainment by short light signals has a major share in the entrainment of nocturnal rodent rhythms in nature. 6. With these restrictions in mind, we analyse in the second part of the paper how the empirical regularities concerning τ and PRC contribute to the stabilization of the phase angle difference (ψ) between the pacemaker and the external world. Use is made of computer simulations of artificial pacemakers with variable τ and PRC. 7. ψ is most sensitive to instabilities in τ when ¯τ is close to 24 h. Thus the very circadian nature of these pacemakers helps to conserve ψ. Selection pressure for homeostasis of τ has been large in a species (M. auratus) where ¯τ = 24 h. The effect of ψ-instability is further reduced by entrainment with 2 pulses (dawn and dusk), made possible by the PRC's having both an advance and a delay section. 8. To analyze the contributions to ψ-conservation with seasonally changing photoperiod, we have assumed that it is of functional significance to conserve the phase of activity with respect to dusk (nocturnal animals) or to dawn (diurnal animals). We distinguish three contributions of nocturnal pacemaker behaviour to this type of ψ-conservation: increased amplitude of the PRC (i), asymmetry in the PRC, such that the slope of the delay-part is steeper than the slope of the advance-part (ii), and a short freerunning period in DD (iii). 9. A further contribution must derive from parametric effects of light, which are not traceable by the model, but certainly effective in preventing in complete photoperiods the ψ-jump which is seen in skeleton photoperiods. The existence of parametric effects is further demonstrated by the change of τ with light intensity in LL, described by Aschoffs Rule, which presumably reflects differences in PRC-shape between nocturnal and diurnal animals. 10. The paper concludes with an attempt to distinguish the features of circadian clocks that are analytically necessary for entrainment to occur (i), or have functional meaning, either in the measurement of the lapse of time (ii) or in the identification of local time (iii).