Wood C E, Tong H
Department of Physiology, University of Florida College of Medicine, Gainesville, Florida 32610-0274, USA.
Am J Physiol. 1999 Dec;277(6):R1541-52. doi: 10.1152/ajpregu.1999.277.6.R1541.
The ability of the fetus to survive, grow, and successfully complete the transition from fetal to neonatal life is critically dependent on the appropriate regulation of fetal blood pressure, blood volume, and fluid dynamics. This is a short review of the physiological mechanisms controlling the fetal cardiovascular system, focusing mainly on the neural and endocrine elements in the schema of cardiovascular function and control. The fetal cardiovascular system is arranged anatomically to provide for perfusion of the umbilical-placental circulation, the organ of gas exchange of the fetus, and to largely bypass the lungs. Fetal blood volume and pressure, maintained at levels that are appropriate for this function, are influenced by neural and endocrine control mechanisms, which are similar to, but quantitatively different from, the adult animal. Baroreceptors and chemoreceptors located in the carotid sinuses and aortic arch sense changes in blood pressure and blood gases and comprise the afferent limb of the major reflexes that maintain normal fetal blood pressure and volume. Fetal hypotension stimulates reflex decreases in fetal heart rate, which are apparently mediated by chemoreceptor input. Arginine vasopressin responses to hypotension are most likely mediated by baroreceptor input. Recent evidence suggests that the reflex responses to hypotension in the fetus are modulated by paracrine or endocrine factors. For example, baroreceptor or chemoreceptor reflex pathways are modulated by the endogenous production of prostanoids and by the preparturient changes in fetal plasma estrogen concentration.
胎儿存活、生长并成功完成从胎儿到新生儿生命过渡的能力，严重依赖于对胎儿血压、血容量和流体动力学的适当调节。本文简要回顾了控制胎儿心血管系统的生理机制，主要关注心血管功能与调控模式中的神经和内分泌因素。胎儿心血管系统在解剖结构上的安排，是为了确保脐 - 胎盘循环（胎儿的气体交换器官）的灌注，并在很大程度上绕过肺部。胎儿的血容量和血压维持在适合该功能的水平，受神经和内分泌控制机制影响，这些机制与成年动物相似，但在数量上有所不同。位于颈动脉窦和主动脉弓的压力感受器和化学感受器感知血压和血气的变化，并构成维持胎儿正常血压和血容量的主要反射的传入支。胎儿低血压会刺激胎儿心率反射性下降，这显然是由化学感受器输入介导的。精氨酸加压素对低血压的反应很可能是由压力感受器输入介导的。最近的证据表明，胎儿对低血压的反射反应受旁分泌或内分泌因素调节。例如，压力感受器或化学感受器反射通路受前列腺素的内源性产生以及胎儿血浆雌激素浓度的产前变化调节。
