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Trauma Physiology and Metabolism
Published in Ian Greaves, Keith Porter, Jeff Garner, Trauma Care Manual, 2021
Ian Greaves, Keith Porter, Jeff Garner
In addition to these neurogenic effects the body also compensates in other ways. Selective arteriolar and precapillary sphincter constriction occurs in non-essential organs (for example, skin and gut) helping to maintain vital organ perfusion (especially the brain and the heart). Specialized cells within the juxtaglomerular apparatus of the kidney respond to a reduction in renal blood flow by releasing renin. This leads to the formation of angiotensin II, a vasopressor and stimulator of aldosterone production. Aldosterone, secreted by the adrenal cortex, and antidiuretic hormone (vasopressin), released from the pituitary, increase reabsorption of sodium and water by the kidney, reducing urine output to help maintain the circulating volume.
The patient with acute cardiovascular problems
Published in Peate Ian, Dutton Helen, Acute Nursing Care, 2020
The capillary bed is composed of two types of vessel (see Figure 6.16). The vascular shunt is the main route into the network of capillaries and true capillaries where exchange of substances occurs. Within this network are structures known as precapillary sphincters that control the flow of blood from the vascular shunt through into the capillaries. If the blood is stopped at the precapillary sphincters, it continues through the vascular shunt, bypassing the tissues. If the sphincter is open, blood will flow from the vascular shunt into the capillary bed. For example, a muscle at rest may not need blood flowing through the entire capillary network, because its demands for oxygen and nutrients are reduced, as are the production of waste products. If the muscle becomes active due to exercise, the sphincters will open, allowing flow of blood into the capillary networks.
Microcirculation
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Capillary blood flow depends on the dilation or constriction of the arterioles feeding them. Arteriolar vasoconstriction reduces capillary blood flow, and vasodilatation increases capillary flow. In some tissues, capillaries arise from metarterioles connecting arterioles and venules. Metarterioles, which have structures midway between arterioles and capillaries can serve either as conduits to supply the capillary bed or as channels that bypass the capillary bed to the venules. At the point of origin of a capillary at the metarteriole, a thin band of smooth muscle, the precapillary sphincter, encircles the capillary. The precapillary sphincter is under the control of local tissue metabolites (Figure 29.1). The metarterioles and precapillary sphincters open and close cyclically every minute, a process called vasomotion. The duration of open phases is directly proportional to the tissue oxygen demands. In certain tissues, there are also arteriovenous shunts from arterioles to venules that are under autonomic control and that subserve functions unrelated to tissue nutrition (e.g. arteriovenous shunts in the skin and temperature regulation).
Progression of endolymphatic hydrops and vertigo during treatment in Meniere’s disease
Published in Acta Oto-Laryngologica, 2022
Yue Niu, Wei Chen, Mengyan Lin, Yan Sha
However, there were few studies on the progression of EH in the long-term course of MD. All patients in this study received conventional medical therapy. The mechanism of action of diuretics in MD is to alter the electrolyte balance in the endolymph and to decrease the volume and pressure of the endolymph by increasing its drainage or reducing its production [12]. The pharmacology of Betahistine remains unclear. It may affect the hydrodynamics of the inner ear by improving circulation in the stria vascularis of the cochlea and improve vestibular hair cell function by acting on the precapillary sphincters and reducing excessive endolymph pressure [13]. Intratympanic steroid injection is also considered to be an effective method to control refractory MD. A previous animal study showed that steroids can induce upregulation of inflammatory cytokine genes and ion homeostasis genes in the inner ear [14]. It can also reduce EH by regulating the expression of aquaporin [15]. Among the 42 patients in this study, the degree of EH increased in 18 cases and was relieved in three cases. A study in 2017 which followed patients with MD also showed that patient’s EH developed longitudinally even after treatment [16]. In this study, patients with vestibular hydrops progression were more than those with cochlear hydrops. The reason may be that in the evaluation method of EHs adopted in this study, the grading of vestibular hydrops was more detailed than that of cochlear hydrops.