Shock, in physiology, it is a state of acute circulatory insufficiency of the blood. It is the result of the inability of the heart to pump an adequate volume of blood at sufficient pressure for normal blood passage through the major organs of the body.

Shock may be caused by heart failure, injury, burns, hemorrhage, or major surgery. Sudden infection or poisoning and abnormal extracellular fluid volume resulting from excessive loss of water and electrolytes (ionic conductors) from the gastrointestinal tract, kidneys, or skin may also cause a state of shock.

Symptoms of a shock :
* Paleness, especially around the lips and the inside of the eyelids
* By pushing the fingernails, it takes more than 2 seconds, until the rose colour comes back
* Rapid heartbeat and rapid feeble pulse
* Lowered blood pressure
* Apathy
* Coldness of the skin
* Strong thirst sensation

During the early stage consciousness is retained, but alertness is diminished. Sudden peripheral circulatory failure, however, affects the brain and causes fainting. In less severe shock, compensatory constriction of the blood vessels helps restore circulation, but if shock persists, compensatory mechanisms may fail and local anemia could damage vital organs, such as the brain, heart, liver, and lungs.

First aid for shock includes having the victim lie down, keeping him or her warm but not overheated, stopping any bleeding, and, if the person is not breathing, performing artificial respiration. A physician or paramedic may administer oxygen and sedative drugs and take measures to lower the body temperature if it is very high. Medical personnel may give intravenous glucose and salt solutions, and transfusions of plasma or whole blood may be required when shock is due to blood loss. In medical centers, treatment is monitored by direct measurements of arterial blood pressure and arterial blood gases. Sometimes blood pressure is increased by vasopressors (drugs that constrict blood vessels).

How to react in a shock situation :
* Search carefully, if there are any traces of bleeding on the clothes of an injured person or around that person
* if possible lay down the victim (very carefully because of any eventual trauma) to facilitate  blood circulation
* calm down the victim ( even when unconscious) to slow down the heart rate
* cover the victim to maintain the body temperature

* An injured person should certainly neither drink nor eat ( resist, since the desire to drink might be very strong) since in case of collapsing, the estomac could turn around and empty into the lungs, which can hamper the respiration. It would be helpful to slightly humidify the lips of the victim.