UNIT 5 - WATER

What is water?

Water is a transparent, tasteless, odorless, and nearly colorless chemical substance.
It is vital for all known forms of life, even though it provides no calories or organic nutrients.
Water is the most essential constituent of our body. It has fundamental importance in both structure and functioning of all tissues. It accounts for 55-75% of our total body weight.
Lean individuals have more water than the obese, and infants and children have a greater proportion of water than adults.

DIETARY SOURCES OF WATER

1. VISIBLE SOURCES   - The water taken through drinks, plain water, fruit 
                                           juices, hot and cold beverages.

2 .INVISIBLE SOURCES- Water present in food stuffs like vegetables,
                                            whole   fruits, solid food contain varying
                                            percentage of water. 
 3. Apart from this body also contains metabolic water.  It is synthesized in the 
   body as a result of oxidation of macronutrients
The intake of fluid varies among people on the basis of age, gender, climate, physical activity etc.
Adequate amount of water need to be consumed to allow body to perform its daily functions.
8-10 glasses of water should be consumed daily i.e. 2-2.5 litres.

Daily losses of water from body

1. Insensible water loss- water loss which we are not consciously aware of, which occurs continuously in living beings.
loss by evaporation from skin
loss through respiratory tract
2. Through sweat- it depends on physical activity and temperature.

 3. Through urine- it is the most important mechanism by which the body maintains a balance between fluid intake and output.

       4. Loss in faeces- only small amounts of water is normally lost in  faeces, as re-absorption takes place.

FUNCTIONS OF WATER

• The most important function is of quenching thirst.
• It is a structural component of all cells. Water is present in bound form in bones and unbound form in most tissues, thus there is a constant interchange taking place between the body compartments of water.
• It acts as a medium for all chemical reactions to take place.
• It is an essential component of all body fluids such as blood, lymph, cerebrospinal fluid (CSF), bile, digestive juices and urine.
• It acts as a lubricant and helps food to be swallowed and digested food to pass through the GIT (gastro intestinal tract).
• Water regulates body temperature by taking up and distributing heat being produced in cells when metabolic reactions take place.
• It helps in excreting waste products of the metabolic reactions.
• It is important to maintain turgidity of cells.

WATER BALANCE

Water intake/ input  =  Water output
Water available through dietary sources and from food metabolism and the loss of water through bodily processes maintains water balance.

When water balance is disturbed then following conditions arises
Dehydration
In situation where water output increases than water input i.e. there is excessive loss of water from body due to conditions like diarrhea, vomit, fever, diabetes, it can lead to dehydration.
A dehydrated person feels thirsty, has dry mouth, sunken and dry eyes, restless, irritable and can also lead to unconsciousness.
The condition is managed by giving ORT(oral rehydration therapy).
In ORT  oral rehydration solution (ORS) is dissolved in 1 liter of water. It is given till the person body gets normally dehydrated.
Odema
When water input increases than output in such a condition retention of water in body takes place and thus salts are also retained in the interstitial fluid giving rise to swelling of the skin.
This condition of retention of water and salt in interstitial fluids is ODEMA
Its characteristic feature is, when pressure is applied to swollen skin a depression is formed.

MAINTAINING WATER BALANCE

In the body, several mechanisms work together to maintain water balance. These include

Thirst

Thirst is one of the most important mechanisms to maintain water balance. When the body needs water, nerve centers deep within the brain are stimulated, resulting in the sensation of thirst. The sensation becomes stronger as the body’s need for water increases, motivating a person to drink the needed fluids. When the body has excess water, thirst is suppressed.

Interaction of the pituitary gland and kidneys

An interaction between the pituitary gland and the kidneys provides another mechanism. When the body is low in water, the pituitary gland (located at the base of the brain) secretes vasopressin  into the bloodstream. Vasopressin stimulates the kidneys to conserve water and excrete less urine. When the body has excess water, the pituitary gland secretes little vasopressin, enabling the kidneys to excrete excess water in the urine.

Osmosis

In osmosis, water flows passively from one area or compartment of the body to another. This passive flow allows the larger volumes of fluid in the cells and the area around the cells to act as reservoirs to protect the more critical but smaller volume of fluid in the blood vessels from dehydration.