Cold and flu symptoms explained

What is Cold?

A viral infection involving the upper respiratory tract is called cold. It is also called rhinopharyngitis, nasopharyngitis and acute coryza. There are over 200 viruses which cause cold. Most of these viruses are rhinoviruses. The symptoms of cold are cough, sore throat, blockage and runny nose, sneezing and fever. Cold is one of the commonest illnesses humans face each year. Everyone gets at lest one attack of cold each year. The symptoms of cold may last seven to ten days.  Even though it is very common, the attacks of cold are self limiting and therefore, does very little harm compared to flu.

What is Flu?

Flu, also known as influenza is an illness caused by influenza viruses. Influenza viruses are a family of RNA viruses called orthomyxoviridae. The symptoms of flu include chills, fever, sore throats, myalgia (muscle pains), severe headache, fatigue, and generalized feeling of ill health.  The word ‘influenza’ may remind you of the recent outbreaks of bird flue and swine flu, which became pandemics.

Cold and Flu Symptoms

Even though the symptoms of flu seem similar to those of cold, flu makes the affected individual severely ill.  The symptoms of cold and flu occur as a result of the immune response against the invading virus. Viruses causing cold and flu enter the body mainly through the air. Some viruses, like rhinoviruses enter the body by direct contact. Once they are entered to the body, they bind to the specific receptors in the cell membranes of the respiratory tract.  The viruses causing cold and mild flu can only bind to the cells in the upper respiratory tract. But, some viruses such as HINI virus bind to lower respiratory tract and therefore, cause more severe diseases such as pneumonia.

After binding to the cell membrane, the virus enter into the cell and start replicating and producing molecules they require. The host cell identifies these viruses as foreign bodies and release inflammatory mediators (cytokines and chemokines). These mediators goes and act on other cells and start an inflammatory process which finally gives rise to the symptoms.

1) Sneezing and Runny Nose

The inflammatory mediators start an inflammatory process within the respiratory epithelium. As a result the edema develops and the cells start secreting mucus. The produced mucus comes out of the nostril. That is what is experienced as runny nose. It also causes irritation of the nerves which starts the sneezing reflex. The impulses are carried to the sneezing center of the brain, which commands the chest muscles, the diaphragm, the abdominal muscles and the muscles of the larynx to contract. This ultimately results in a violent blowing of air out of the nose. The high velocity of the air carries some of the mucus out along with the viruses. The process finally helps to quicken the healing process by reducing the viral load. But, it also creates a route for the virus to find another host.

2) Chills and Fever

The inflammatory mediators released by the cells go and act on the hypothalamus. Hypothalamus is the centre for thermoregulation. These inflammatory mediators increase the temperature set point.  So, the hypothalamus sends signals to the body to produce more heat. Heat is produced by contraction of the muscles. This finally causes fever. In the same way the patient has chills when the hypothalamus is set to a lower temperature.

3) Sore throat

Viral infection itself and breathing through the mouth damage the epithelium of the throat. This starts an inflammatory process in the throat. The patient feels this as sore throat.

4) Cough

As mentioned above, the infection of the respiratory tract starts an inflammatory process. One of the components of the inflammatory process is excess mucus secretion. This excess mucus is passed in to the throat. The mucus irritates the throat mucosa. This triggers the cough reflex. The violent coughing helps to bring the excess mucus out from the lower respiratory tract and expel them out.

5) Enlargement of the LymphNodes

Lymph nodes are the places where most of the lymphocytes lie. These lymphocytes proliferate and produce antibodies to fight against the invading organisms. This process causes the lymphoid tissues to swell.

6) Generalizes feeling of ill health

The inflammatory mediators released during an attack of flu or cold act on almost all the cells in the body. They alter the normal cellular functions. It finally results in generalized body weakness.

How studying squirrel hibernation helps in transporting organs

Squirrel hibernation is one of the most amazing wonders of the Mother Nature. There is a certain kind of squirrels (ground squirrels) who can undergo hibernation. In the state of hibernation the body temperature is brought down to an extremely lower level. These squirrels undergo this physiological state to survive during extremely cold whether.

These squirrels undergo hibernation in the time of the year where the environmental temperature falls, even down to 0 Celsius. In mammals, the body temperature is kept in a constant level. The body requires optimum conditions to function correctly. Most of the mammals are programmed to keep the optimum temperature by thermoregulations. When the body temperature goes down, the body burns energy from the fat reserves and generates heat. But, this is not possible for these squirrels due to lack of food. During the cold whether, the squirrels are unable to find food. Therefore, they have to survive with whatever the energy they have already stored within their bodies.

The animal body is composed of cells. The survival of the animal depends on the survival of the each and every cell in the body. The integrity of the cell depends on the intracellular and extracellular electrolyte concentrations. These concentrations are kept at their optimum concentrations by the pumps that are present in the cell membrane. These pumps need energy and optimum temperatures to work. These pumps in the ground squirrels differ from those of non-hibernating mammals. Their pumps are able to work at very low temperatures. Therefore, these pumps are able to keep the cells viable even under very low temperatures.

HOW DOES IT HELP IN ORGAN TRANSPORT?

The organs are transported in cold temperatures to keep then viable for a longer period. But at lower temperatures, the pumps may not work properly. The absence of functioning pumps in the cells makes the organs non-viable. But, if the scientists can find the exact kind of electrolyte pumps that work at very low temperatures, then the nature of these pumps can be used to find a way to store organs for a loner period of time so they can be transported to the required area.  

According to Cryo Letters, 2000, pubmed, organs taken from squirrels that were in deep hibernation survived in cold for up to 72 hours. But, the organs from non-hibernating squirrels were able to survive only for24 hours.

If these studies become successful, a way can be found to preserve organs for a longer period of time.