We planet Earth

The acceleration of gravity is here 9,81 m/s2.
It is difficult to overcome the earth's gravity to get up in the morning out of bed, to storm the Everest climb to space. It was hard and lobe-finned fish out of water on a high shore, on steep. It's not in muscular force: a newborn baby would be enough strength to stand on his feet, but his blood system has not had time to adapt to gravity - because in the mother's womb he was, as in zero gravity.
Mechanisms of vascular regulation, opposing force of gravity exist but require training after birth (except for "stelarastelara animals, such as ungulates). Children raised by apes,and such cases are described many,these "Mowgli" at the age of seven excellent cross, but only on all fours. They are almost unable to teach speech. Bipedalism, as it contains a social component. Although brown bear superb walks on its hind legs, but it vascular system has a huge margin of safety - blood pressure in 3-4 times above, than at us. Blood pressure giraffe, when he lies about 340 mm Hg. However, giraffe or a healthy horse even sleep standing up, preventing the brain from excessive blood pressure.
A person change poses not accompanied by a significant change in blood pressure. It is provided segmental redistribution of vascular tone: the tone at the top when standing up increases less than the bottom, as well as the blood flows into the vessels that are closer to the earth, the systolic pressure is not changed. Only in the first seconds of orthostasis (vertical position) pressure below normal: until the vascular tone was not rebuilt in a new way, until blood flow to the feet have not decreased. Reverse flow down through the veins of the legs prevent valves and tone muscles of the legs, which are thicker capacitive Vienna. Growing and venous tone, but to blood him away. The situation is gradually getting worse, because the return of venous blood to heart "from below" almost impossible: the outlet pressure of the capillaries in the norm does not exceed 10-15 mm Hg, and blood under such pressure may not reach the Atria, despite the suction action of the chest, pressure in the cavity which is always lower atmospheric, especially when you inhale, and despite "sucked" blood right ventricle, and diastole can bite sufficiently elastic to develop negative pressure. Gradually in the veins of the legs and the lower half of the body accumulates in excess of venous blood, are excluded from the total circulation: she could not reach the heart. This blood can accumulate 1 l and more. According to the figurative expression of one of the Russian clinicians nineteenth century, comes the "intravascular bleeding". It is complicated by the fact that in the lower extremities capillary pressure gradually reaches the arterial, venous pressure is also close to this level, filtering of blood plasma in the intercellular space accelerated, and the reverse filtering impossible. Intercellular space of all muscles of an adult male can accommodate about 1 l of extra fluid that threatens edema.
Despite the gravity of the situation, it is enough to make 2-3 steps - and leg muscles squeeze their capacitive veins, the blood rushes of them in venous line and right atrium, cardiac output is now secured, and we don't even know what were the dangers. In fact one does not tend to stay long in the pose still standing. He walks around the column, waiting for appointments; he walks along the counter, behind which operates; lathe he does not stand still; he peremenitsya from foot to foot, instinctively avoiding danger.
Let us consider what is happening at this time in the body.
Reactions to the vertical position is more convenient to study in special conditions, for example on the turntable is rotating about the horizontal axis.
The accumulation of blood in the vessels of the lower half of the body is not as fast as emergency measures, taken in advance by the body: under normal conditions of danger signal pulses of receptors in the bottom areas, the joints of the feet and the vestibular apparatus. If an acrobat, a yogi or testirovanie animal takes the position, upside down, vascular tone is redistributed in the opposite direction - in any case, vascular tone opposes the earth's gravitation.

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