When the ambient temperature is high, blood flow to the skin increases to help dissipate heat and cool internal organs.
On particularly hot days or during intense physical activity, up to 15-25% of the blood expelled from the heart passes through the skin with each beat.
We can think of the circulatory system as a set of vessels regulated by many taps, which depending on the conditions can be more open (vasocrystallation) or less (vasoconstriction). Therefore, when it is hot we will have an opening of the taps in the skin, with a consequent increase in the flow of blood to the skin .
Vasodilation leads to a reduction in peripheral resistance, thus reducing arterial pressure. When the drop in blood pressure becomes important it can cause problems of fatigue and dizziness until the fainting, since the brain does not bear a reduction in the flow of blood.
To avoid sudden drops in pressure, when it is very hot skin vasodilation tends to be associated with a vasoconstriction in other body areas, which can withstand a temporary reduction in blood flow. Among these districts, one of the most important is visceral. Put simply, the increase in blood flow to the skin is compensated by a reduction in blood flow at a visceral level, in order to avoid sudden drops in blood pressure and keep it at an acceptable level.
If a particularly heavy meal is consumed, the digestive system seizes large amounts of blood needed to support the digestive processes. As a result, the flow of blood to the skin and the heat dispersion are penalized, as is the arterial pressure, which can be reduced to the point of causing dizziness and malaise.
If, on the other hand, the meals eaten are light and easy to digest, the quantities of blood required by the digestive system are low, in favor of cardio-circulatory balance and thermoregulation.
This explains the reason why doctors advise eating light, easy-to-digest meals in the summer.
