Final answer:
A decrease in fetal blood pressure leads to decreased baroreceptor firing rates, prompting an increase in sympathetic stimulation and a decrease in parasympathetic stimulation, both of which act to raise blood pressure and maintain vascular homeostasis.
Step-by-step explanation:
A decrease in fetal blood pressure results in a decreased firing rate of baroreceptors, which are blood-pressure receptors. These receptors, located in the arch of the aorta and the carotid arteries, detect decreases in blood pressure. When this occurs, the cardiac centers respond to restore blood pressure to normal by increasing sympathetic stimulation (which generally increases heart rate and force of contraction) and decreasing parasympathetic stimulation (which generally decreases heart rate). This response aims to maintain vascular homeostasis.In addition to these changes in the nervous system, a decrease in blood pressure may also cause increased release of epinephrine and norepinephrine by the adrenal glands, increased levels of thyroid hormones T3 and T4 in the blood, and may result from various factors such as a decrease in blood volume due to water loss. These physiological responses work together to help increase the blood pressure and ensure adequate blood flow to the fetal circulation.