Control Mechanisms

Here is the information we used for the control mechanisms assignment.  Remember to include enough information to cover the dot points set out in the assignment sheet.

Dehydration
Water makes up over two-thirds of the healthy human body. It is essential for lubricating the joints and eyes, aiding digestion, flushing out waste and toxins and keeping skin healthy.
Dehydration occurs when the normal water content of your body is reduced, upsetting the delicate balance of minerals (salts and sugar) in your body fluid. Many of your body's cells depend on these minerals being maintained at the correct levels to function properly.

Some of the early warning signs that you are dehydrated are feeling thirsty and lightheaded and having concentrated, strong-smelling urine. The body works less efficiently with even a relatively low level of fluid loss.

How it happens

Dehydration is generally caused by not drinking enough fluid or by losing fluid and not replacing it.
You can lose fluid through vomiting or diarrhoea (for example, if you have gastroenteritis), through sweating (for example, if you have a fever or are exercising in hot conditions) or through urinating too frequently (for example, if you have diabetes).
Drinking too much alcohol can also cause dehydration, which is the main symptom of a hangover.

Types of dehydration

There are two types of dehydration:

• Isotonic dehydration is when you lose water and salt in the same proportion as the water and salt in the fluid surrounding your cells. It is the type of dehydration most often caused by diarrhoea.
• Hypernatraemic dehydration usually happens in infants or children. 'Hypernatraemic' means high levels of salt in the blood, so hypernatraemic dehydration is when a child loses relatively more water than salt, for example when they have watery diarrhoea or excessive vomiting. 

At-risk groups

People who are particularly at risk from dehydration are:

• babies and infants, because they have a low body weight and are sensitive to even small amounts of fluid loss
• older people, because they may be less aware of becoming dehydrated and the need to keep drinking fluids
• people with a long-term condition, such as diabetes or alcoholism
• athletes, because of the amount they sweat

Heatstroke
Heatstroke happens when a person’s core temperature rises above 40°C (104°F). Cells inside the body begin to break down and important parts of the body stop working.
Symptoms of heatstroke can include mental confusion, hyperventilation (rapid shallow breathing) and loss of consciousness.
Heatstroke is a medical emergency. If left untreated, it can cause multiple organ failure, brain damage and death.

Types of heatstroke

There are two main types of heatstroke:

• classic heatstroke, and
• exertional heatstroke.

Classic heatstroke

Classic heatstroke usually affects the elderly, babies and people with chronic health conditions. It develops during unusually hot weather, such as a heatwave.

Exertional heatstroke

Exertional heatstroke usually affects young, active people doing strenuous physical activity for a long time in the heat. For example, cases of exertional heatstroke have occurred in:

• athletes,
• people serving in the military, and
• fire-fighters.

How common are heat exhaustion and heatstroke?

It is hard to tell exactly how common heat exhaustion is, as many people who get it do not go to their GP for treatment.
Heatstroke is rare in England, but during a heatwave the death rate among the elderly is much higher than usual.

Outlook

If a person with heat exhaustion is taken quickly to a cool place and given plenty of water to drink, they should begin to feel better within half an hour and experience no long-term complications. Without treatment, they could develop heatstroke.
Heatstroke is very serious and should be treated immediately. Treatment involves quickly cooling down the body to lower the core temperature.
If treated swiftly, 90% of people with heatstroke survive. If not, the survival rate is as low as 20% among vulnerable people such as the elderly.

Controlling blood sugar

Insulin

Insulin is secreted by the beta cells of the pancreas in response to high blood sugar, although a low level of insulin is always secreted by the pancreas.  After a meal, the amount of insulin secreted into the blood increases as the blood glucose rises.  Likewise, as blood glucose falls, insulin secretion by the pancreatic islet beta cells decreases.

In response to insulin, cells (muscle, red blood cells, and fat cells) take glucose in from the blood, which ultimately lowers the high blood glucose levels back to the normal range.

Glucagon

Glucagon is secreted by the alpha cells of the pancreas when blood glucose is low.   Blood glucose is low between meals and during exercise.  When blood glucose is high, no glucagon is secreted from the alpha cells.  Glucagon has the greatest effect on the liver although it affects many different cells in the body.  Glucagon's function is to cause the liver to release stored glucose from its cells into the blood.  Glucagon also the production of glucose by the liver out of building blocks obtained from other nutrients found in the body, for example, protein.

Levels

Blood glucose is normally maintained between 70 mg/dl and 110 mg/dl.  Blood glucose levels below 70mg/dl,  denote the situation of "hypoglycemia".   Although blood glucose levels of 110mg/dl can be normal, this is only the case if a meal has been taken within 2 to 3 hours.  A blood glucose level of 180mg/dl or more, is termed "hyperglycemia."  Diagnosis is made if blood glucose levels are above 200mg/dl after drinking a sugar-water drink (glucose tolerance test). 

Hypothermia

Hypothermia is classified as a temperature below 35°C (96°F).
Watch out for the 'umbles': stumbles, mumbles, fumbles and grumbles. These are symptoms that show a gradual reduction in coordination of muscles and movement, and a falling level of consciousness.
Symptoms progress as the person's temperature drops:

• Initially, involuntary shivering, loss of complex motor skills (but still able to walk and talk), shutdown of blood vessels in the hands and feet.
• As temperature falls below 35°C (95°F), violent shivering, impaired consciousness, loss of fine-motor coordination, especially in the hands, slurred speech, illogical behaviour, loss of emotional cognition - an 'I don't care' attitude.
• As core temperature falls below 34°C (92°F), the effects becomes life threatening, shivering become intermittent and then stops, the person curls into the foetal position, muscles become rigid, pupils dilate, pulse rate drops.
• By 30°C (86°F) the person looks dead. Although still alive, they're in a state known as the 'metabolic icebox', breathing becomes shallow and erratic, consciousness is lost and the heart becomes vulnerable to deadly arrhythmias.

Shivering is one of several symptoms that can be used to assess hypothermia. If the person is able to stop themselves shivering, their hypothermia is only mild. If it can't be stopped voluntarily, the person has moderate to severe hypothermia.
Another quick test is to assess higher brain functioning by asking the person to count backwards from 100 in multiples of nine. This sort of cerebral ability is soon lost as temperature falls.
A sign of severe hypothermia is loss of the pulse at the wrist, a result of the circulation shutting down.
The basic principles are to stop heat loss and preserve the heat the person has, and provide body fuel to generate more heat. If a person is shivering, they can warm themselves at a rate of 2°C an hour.
Put on additional layers of clothing and replace wet clothes with dry. Get them moving to increase their activity and ensure their surroundings are as warm and still as possible.
Provide food, initially as hot liquids. Carbohydrates provide a rapid source of energy while fats can provide a prolonged source of fuel. Add warmth with a fire or heater, or by body-to-body contact.