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PubMed1978

[Further study of the descending sympathoactivating pathways of the dorsolateral funiculus of the spinal cord].

The localization and conduction velocities of descending pathways which activate the different groups of sympathetic preganglionic nerons were studied in the cat cervical spinal cord. Certain evidences have been obtained that the fibres located near the dorsal surface of the dorsolateral funiculi with conduction velocities about 24--29 m/sec. can activate the ventral horn preganglionic neurons monosynaptically. In contrast to previous ideas, the sympathetic preganglionic neurons of the lateral horns seem to be activated not by different but by a single group of descending fibers with the conduction velocity 4--8.9 m/sec and localization in more ventral portions of the dorsolateral funiculus. The transmission from these fibers to the sympathetic preganglionic neurons of the lateral horns occurs in two ways: oligosynaptically (probably, disynaptically) and polysynaptically through a more complicated interneuronal chain. The sympathetic preganglionic neurons with unmyelinated axons, localized in the intermediate zone, for the first time were shown to be activated polysynaptically, probably via the same ways as the lateral horn neurons.

Animals↗
PubMed1983

Role of splanchnic resistance vessels in overall cardiovascular homeostasis.

The reactions of splanchnic resistance vessels elicited reflexly from cardiovascular baroreceptors, volume receptors, and chemoreceptors are briefly reviewed. Unloading the baroreceptors and/or the volume receptors evokes a chiefly neurogenic constriction of resistance vessels in the splanchnic region. There is no significant change in the post- to precapillary resistance ratio to evoke any change in mean capillary hydrostatic pressure. In contrast, the post- to precapillary resistance ratio of the skeletal muscle vascular bed falls, thus lowering mean capillary pressure and causing an autotransfusion of the cardiovascular system. Stimulating the chemoreceptors induces vascular effects in the splanchnic organs and the skeletal muscle similar to that of unloading the baroreceptors. In hemorrhagic hypotension an integrated response from the different receptors is observed. No change occurs in the post- to precapillary resistance ratio in the splanchnic area even during prolonged hemorrhagic hypotension.

Animals↗
PubMed1983

Role of splanchnic venous system in overall cardiovascular homeostasis.

A blood reservoir is an organ or region containing a significant portion of the blood volume that can be mobilized by the sympathetic nervous system to subserve overall cardiovascular homeostasis. To be effective, the reservoir must be as insensitive as possible to the passive effects of changes in flows or external pressures. Evidence is presented that the splanchnic venous bed fulfills these criteria. Hepatic venous resistance maintains portal pressure and intrinsic hepatic arterial mechanisms maintain total hepatic flow. These mechanisms minimize passive effects of portal flow changes on splanchnic blood volume, whereas enclosure of the liver in the peritoneal cavity minimizes effects of external pressures. Up to 27% of total blood volume can be mobilized from the splanchnic venous bed by sympathetic stimulation. Maintenance of cardiac preload depends on the ability of the central nervous system to control venous compliance and hence to redistribute blood volume between peripheral organs and the cardiopulmonary compartment. Three examples of the role of the splanchnic blood reservoir in overall homeostasis are discussed: hemorrhage, splanchnic nerve stimulation, and responses to epinephrine. Reflex and central control of the splanchnic blood reservoir are discussed but available information is fragmentary.

Animals↗