The body loses about 2 L of water every day through excretion, perspiration (sweat), and breathing (respiration). Obviously, the amount of water lost increases if you are physically active. When your body needs water, it sends messages to the brain, which stimulates a thirst response.

Drinking water usually restores homeostasis. Byron drinks about 8 L of water per day to avoid dehydration from the effects of physical exertion and high altitude.

Characteristics of Life

Living things reproduce and form offspring which are similar to their parents. Living things grow by using nutrients and energy from their environment to increase in size. Living things develop. Living things need food for energy growth and repair. (Food and Energy) Living things use energy to do work. Animals get their energy from the food they eat. Plants get energy from the food they make during the process of photosynthesis. All living things carry out a process called cellular respiration. Living things are made of small units called cells. Living things respond to their environment. Living things are adapted to their environment. An adaptation is any characteristic that increases an organisms chance for survival.

Cellular Respiration
Food contains chemical energy stored or locked inside it. Cellular respiration is the process by which food is broken down and energy is released. Through cellular respiration, carbohydrates are processed to produce energy that the cell can use for all of the life processes list above.

Glucose is the carbohydrate that most organisms use for cellular respiration. The process of cellular respiration occurs inside special structures (organelles) found inside the cell. This tiny organelle is called the mitochondrion. Besides the sugar glucose, humans also need oxygen in the process of cellular respiration. Oxygen is absorbed by the lungs and transported by the circulatory system to all cells of the body.

Also in the process of cellular respiration, the glucose molecule is split apart to release its energy. This type of chemical reaction is called oxidation.

The waste products of cellular respiration are carbon dioxide (CO₂) and water (H₂0). This reaction is summarized below:

All cells, and therefore all organisms, need energy to keep going. The way in which they usually get their energy is by the aerobic (with oxygen) respiration of glucose. To do this they need oxygen. In the human body, the lungs, heart and blood have the job of delivering the oxygen. The lungs absorb the oxygen from the air and pass it into the blood. The oxygen rich blood is pumped by the heart to all cells of the body.

ATP
To function properly, all living cells must be able to perform a large number of chemical reactions. Some of these, chiefly cellular respiration, release energy. Other chemical reactions require energy before they will start. A single chemical substance links these two types of reactions. This substance is a high-energy molecule called ATP.

ATP is found in all living cells and all living cells can make it. ATP is constantly being made and then broken down. Every time ATP is broken down, the energy locked in the molecule is released and used for the work of the cell.

Body Temperature and Metabolism
The process of cellular respiration captures some of the energy released by the oxidation of carbohydrates. This captured energy is converted into a high energy chemical compound called ATP. The process of cellular respiration fails to capture approximately 60 per cent of the energy in glucose.

The rest of the energy is released as heat. Most living things lose this heat to their environment. There are, however, a few animals, notably mammals and birds, that can make use of this heat energy. Such animals are called "warm blooded."

Warm blooded animals are properly called homeothermic or endothermic. The body temperature of these animals, including humans, is fairly high - usually higher than the temperature of the environment. The temperature is kept relatively constant (37 degrees C in humans) even when the temperature of their surroundings fluctuates.

The overall use of chemical energy by a living thing is called its metabolism. The level at which an organism's metabolism is operating is called its metabolic rate. Metabolic rate in humans depends on a variety of factors including activity, temperature of the environment, food intake, and availability of oxygen.

For example:

It is not surprising that warm-blooded animals have body temperatures considerably higher than the average temperature of their environment. The high body temperature produces a high metabolic rate and makes a high level of activity possible.

Being endothermic also permits people to be active on cold days. However, unlike other mammals such as polar bears and whales, humans do not have the adaptations to survive for very long in cold conditions. As you will see, cold related injuries such as frostbite and hypothermia can be dangerous when temperatures drop and the wind blows.

Cold

The core body temperature of a human must stay constant. The heart, lungs, liver and kidneys must be maintained close to a temperature of 37 degrees C. Prolonged exposure to a combination of low temperatures, wind or moisture can result in cold-related injuries such as frostbite and hypothermia. Hypothermia, if not treated quickly and properly, can result in death.
JUMP TO: Cold Injuries

There are several basic methods by which energy is transmitted from one body to another. All of these, to some degree, apply to the human body. The factors by which heat energy is transmitted are: conduction, convection, radiation, and evaporation.

Conduction
Conduction is the flow of heat energy from a warm object to a cold one by direct contact. The rate of conduction is determined by the temperature difference between the two objects. Without insulating clothing, mountain climbers would lose heat by conduction when they sit or lie down on snow, ice or even a cold rock.

Convection
Convection occurs when heat is transferred by a moving fluid, such as air flowing over skin or clothing. In winter, meteorologists describe this process as "wind-chill."
JUMP TO: Wind Chill

As Byron and the other climbers on Mt. Everest reach higher altitudes they will be constantly exposed to wind and colder temperatures. The faster the wind blows, the faster the heat is carried away by convection. The rate of heat loss is also controlled by the amount of skin exposed to the air and wind. The rate of heat loss by convection can, to some extent, be controlled by wearing special wind-proof clothing and protecting the head.

Radiation
Radiation is the method by which heat is transferred by infrared (heat) radiation. All warm objects produce infrared radiation (this is why night-vision goggles work). When the temperatures are lower than 37 degrees C, the human body will radiate heat to the cooler environment. On the other hand, humans receive infrared radiation from fires, the sun or reflection off snow or ice. Once again, insulated clothing can help reduce the amount of heat Byron and the other climbers will lose as a result of radiation.

Evaporation
It takes a great deal of energy to evaporate water - change it from a liquid to a gas. It takes energy to evaporate water and this heat loss accounts for about 20 per cent of the body's normal heat loss. The rate of energy loss by evaporative cooling depends on the wind, humidity of the air, and the temperature. About 2/3 of the energy lost by evaporation is through the skin. The other third is lost from the lungs when air is exhaled.

Energy loss through the lungs by evaporation during breathing increases as the breathing rate increases. As well, colder and dryer air will also increase the amount of heat lost through evaporation.

Wind Chill
Wind chill is the term used to describe the chilling effects of wind on exposed sections of skin. As the table below shows, what may be just "cool air temperatures" with no wind can result in freezing skin temperatures with only 20 km/h wind. The effects of wind can lead to frostbite and can be a factor in the development of hypothermia.

Regulating Human Body Temperature

Humans are endothermic (warm blooded) and strive to maintain a constant body temperature regardless of the temperature of the environment. The optimum temperature for chemical reactions to take place in the body is 37 degrees C. Above that temperature many body enzymes become denatured and chemical reactions can not take place. Below this temperature chemical reactions slow down with various complications which can lead to death.

Keeping the body temperature relatively constant is a classic example of homeostasis - maintaining a steady state. Body temperature is controlled by balancing heat production against heat loss. Humans have, to some extent, ways to adjust the amount of heat lost to the environment.

Most heat produced in the body is generated in deep organs such as the liver, brain, and heart, as well as in skeletal muscles. The heat energy is transferred from the core of the body to skin. The skin, acting much like the radiator in a car, controls the heat loss to the environment. Human body temperature is regulated in a special area of the brain called the hypothalamus.

Endocrine glands of the brain From "Ultimate Visual Dictionary of Science," Stoddart 1998.

The hypothalamus contains a number of both heat sensitive and cold sensitive neurons. These receptors respond to the temperature of arterial blood flowing through this region of the brain. If the arterial blood is below normal temperatures, the hypothalamus initiates a series of responses that result in the increased production of heat. The three main ways the human body can increase the amount of heat produced are: increasing metabolic rate, exercise, and shivering.

Metabolism
Heat is a by-product of metabolism. Mechanisms that tend to increase cellular metabolism consequently increase the amount of heat produced. If, however, the human body is exposed to cold for a long period of time, the increased metabolic rate alone will not be sufficient to produce enough heat to keep the person alive.
JUMP TO: Body Temperature and Metabolism

Exercise
Exercise is simply movement of the human body. Movement is caused by the contractions of skeletal muscles - muscles attached to bones. Skeletal muscles are attached to bones by tough, fibrous cords called tendons. Typically, each muscle connects two bones by stretching across a joint between them. When the muscle contracts, one bone remains fixed in position, while the other moves. Muscles only do work when they contract (shorten). Our muscles make up approximately 50% of our total body weight.

When our skeletal muscles do work they can produce tremendous amounts of heat. Moderate levels of exercise can produce heat for sustained periods of time. Physical conditioning, strength, stamina, food energy and water are necessary to sustain the muscle activity for extended periods of time.
JUMP TO: Food and Energy

Shivering
Shivering generates heat through an increase in chemical reactions required for muscle activity. It is a random, inefficient quivering of muscles that is the human body's first line of defense against cold. Shivering can increase surface heat production by 500 per cent. Shivering occurs when temperature receptors in our skin sense cold. These sensory neurons transmit impulses to the brain, which stimulates a shivering response.

Shivering, however, is limited to a few hours. Shivering requires energy and how long a person can shiver depends on the amount of glucose stored in muscle tissue and by the amount of oxygen and water available. In order to shiver, the body pumps blood to muscles close to the surface of the body. Warm blood flowing near the surface of the body actually increases the amount of heat lost by radiation, conduction, and convection.

Blood Vessels in the Skin

Cross-section of human skin From "Ultimate Visual Dictionary of Science," Stoddart 1998.

When the body temperature increases, blood vessels in the skin dilate - get bigger. This brings more warm blood to the skin. The surface area of the skin is very large and a great deal of heat can be removed from the body through the skin.

When body temperatures drop too low, the reverse occurs. The blood vessels in the skin get smaller (constrict) and the warm blood is channeled deeper into the body where the heat can be conserved.

This constriction of blood vessels in the skin is one of the reasons why frostbite usually occurs first in fingers and toes.
JUMP TO: Cold Injuries

Behavioral Responses
Humans, unlike mammals such as polar bears or whales, are not well adapted to living in cold regions of the world. Humans do not have a great deal of hair or fur, nor do we have a layer of insulating blubber to protect us from cold temperatures.

However, unlike these other mammals, humans can respond to changes in our internal body temperature by:

If these physiological and behavioral mechanisms fail, humans can be in serious trouble. Frostbite and hypothermia can result.

Cold Injuries

Core Body Temperature (degrees C)
43 C	Upper limits of fever
37 C	Normal body temperature
36 C	Increased metabolism - shivering Confusion Disorientation
33 C	Amnesia Irregular heart beat Shivering stops
30 C	Persistent muscle rigidity
28 C	Unconsciousness Lower limits of survival - heart stops working properly
24 C	Death

Prolonged exposure to low temperatures, wind or moisture - whether you are climbing to the top of the world or walking home from school - can result in cold-related injuries such as frostbite and hypothermia.
JUMP TO: Cold

Frostbite
Frostbite is the most common injury resulting from exposure to cold temperatures. It is the freezing of the skin and underlying body tissues. It occurs when part of the body is affected by exposure to temperatures well below freezing. Any part of the body can get frostbite but it normally affects hands, feet, nose, and ears first.

The body responds to cold temperatures by generating heat through increasing metabolism, exercise, and shivering. The circulatory system responds by trying to keep as much warm blood as possible in the core of the body. One way to keep the body core warmer is to reduce the blood supply to areas such as fingers and toes. As the flow of blood to these areas decreases, these tissues begin to drop to the freezing point.
JUMP TO: Regulating body temperature

When human tissue is exposed to near freezing temperatures, the tissue temperature decreases. As the tissue temperature drops, it goes through four phases of frostbite.

1. In the first phase, the blood vessels constrict, causing inadequate flow of blood and oxygen to the tissues.

2. In the second phase, the tissue temperature drops below - 2 degrees C and ice crystals form in the tissues. Unless the body part is warmed, frostbite will progress to the next level.

3. In the third phase, fluid leaks from the blood vessels into the damaged tissue.

4. In the fourth phase, the blood vessels clot, resulting in the irreversible loss of blood flow to the damaged tissue.

The severity of frostbite can be classified as follows:

1. Superficial: Frostbitten skin initially tingles, then becomes very painful and absolutely numb. The exposed area appears blanched with slight swelling. It then proceeds to become hard, pale, waxy and cold. It is usually characterized by grey or yellowish patches on the affected areas. The skin remains soft and pliable, but becomes red and flaky after thawing.
Treatment: Treat superficial frostbite by taking the victim inside immediately and warming the affected areas with warm, not hot, water. Do NOT rub the frozen skin with snow or anything else. Rubbing the ice crystals in the tissues can cause more damage than the original frostbite.

2. Deep Frostbite: Usually affects the feet or hands and is characterized by waxy, pale, cold skin, which may turn blue or purple upon thawing. Deeper frostbite causes deep blisters filled with purplish fluid. In all types of frostbite, the damaged tissue may swell and darken in colour after warming.
Treatment: A person suffering from deep frostbite must be treated by a doctor as soon as possible. Protect the injured area by wrapping with towels or blankets to prevent additional damage during transport to a medical facility. If the area is deeply frozen, there is a risk of gangrene. If frostbite is treated quickly, it may have no long term damage.

Hypothermia
Hypothermia is a much more serious problem than frostbite. Hypothermia occurs when the body's core temperature drops below 37 degrees C. Surprisingly, hypothermia can even occur at mild temperatures if exposure is prolonged. During prolonged exposure to cold, more body heat may be lost than can easily be replaced by shivering, exercise, and the constriction of blood vessels. As the body temperature drops, hypothermia sets in. Death is likely if the core body temperature drops below approximately 26 degrees C.

Signs and Symptoms of Hypothermia
Mental condition:

Muscular responses:

Body systems:

Treatment of Hypothermia
A person with hypothermia must receive prompt attention from a doctor. If a doctor is not immediately available, remove all cold, wet clothing and replace it with warm, dry clothing to prevent further heat loss. If a person is not breathing or has no pulse, begin cardiopulmonary resuscitation (CPR) immediately. Do not stop CPR until medical personnel arrive.

Protecting the Climbers from the Cold

Clothing
Most of the clothing worn by Byron and other members of the team are made of synthetic fibres. The climbers will wear a series of layers to trap air, insulate, and protect against the loss of heat by conduction, convection, and radiation.

On Mt. Everest, Byron will wear different clothing at different altitudes and temperatures. Clothing is designed to do one of two jobs (1) protect from the elements and (2) insulate.
JUMP TO: Cold | Clothes and Equipment

Protection from the elements is accomplished by wearing a shell of water and windproof outer wear. For examples, to protect Byron from the wind he wears a parka that is made from a material that is both windproof but breathable. Breathable clothing allows the moisture from perspiration to evaporate. Without this type of clothing, the climbers would get wet from their own perspiration and would lose a great deal of heat in the process.