Final answer:
The first stage of cold water immersion is the cold shock response, characterized by involuntary gasping and hyperventilation. Subsequent stages such as shivering and hypothermia can follow if exposure continues. The body has several responses to cold designed to maintain core temperature and protect vital functions.
Step-by-step explanation:
The first stage of cold water immersion is the cold shock response. This response is an involuntary reaction to the sudden drop in skin temperature upon contact with cold water. The body's immediate reaction includes gasping, hyperventilation, and an increased heart rate, which can increase the risk of drowning if the individual cannot calm down or if they inhale water. This is the body's attempt to increase oxygen intake to compensate for the perceived need due to the shock. After the initial cold shock response, other stages like shivering and hypothermia can occur if the person remains in the cold water.
When the body is exposed to cold, several mechanisms are activated to protect core temperature and maintain homeostasis. Shivering is one of those mechanisms, which is a reflex action controlled by the hypothalamus. It creates heat through random muscle movement. As core temperature drops and energy reserves are depleted, serious conditions like hypothermia can set in, leading to confused mental states and eventually loss of consciousness. The body also reduces blood circulation to the extremities to keep the core warm, which can lead to frostbite in severe cold.