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Homeostasis Case Study

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The conditions inside our body must be very carefully controlled if the body is to function effectively. Homeostasis is the maintenance of a constant internal environment. The nervous system and hormones are responsible for this. One example of homeostasis is the concentration of carbon dioxide in the blood being carefully controlled. Here are some of the other internal conditions that are regulated: Body temperature

This is controlled to maintain the temperature at which the body’s enzymes work best, which is usually 37°C. Blood sugar level

This is controlled to provide cells with a constant supply of glucose for respiration. It is controlled by the release and storage of glucose, which is in turn controlled by insulin. Water content

This is controlled to protect cells by stopping too much water from entering or leaving them. Water content is controlled by water loss from: the lungs – when we exhale
the skin – by sweating
the body – in urine produced by the kidneys
Negative feedback

Homeostatic control is achieved using negative feedback mechanisms: if the level of something rises, control systems reduce it again if the level of something falls, control systems raise it again Regulating body temperature

The human body is designed to function most efficiently at 37ºC. If you become too hot or too cold, there are ways in which your body temperature can be controlled. Too hot

When we get too hot:
Sweat glands in the skin release more sweat. The sweat evaporates, removing heat energy from the skin. Blood vessels leading to the skin capillaries become wider – they dilate – allowing more blood to flow through the skin, and more heat to be lost. Too cold

When we get too cold:
Muscles contract rapidly – we shiver. These contractions need energy from respiration, and some of this is released as heat. Blood vessels leading to the skin capillaries become narrower – they constrict – letting less blood flow through the skin and conserving heat in the body. The skin

The hairs on the skin also help to control body temperature. They lie flat when we are warm, and rise when we are cold. The hairs trap a layer of air above the skin, which helps to insulate the skin against heat loss. The hypothalamus is the part of the brain which monitors the body’s temperature. It receives information from temperature-sensitive receptors in the skin and circulatory system. The hypothalamus responds to this information by sending nerve impulses to effectors to maintain body temperature. For example, if we become too cold, the hair erector muscles contract. This raises the skin hairs and traps a layer of air next to the skin. Skin hairs lying flat and upright

Skin hairs lie flat when we are hot and stand upright when we are cold Negative feedback mechanisms control body temperature. They include the amount of: shivering (rapid muscle contractions release heat)

sweating (evaporation of water in sweat causes cooling)
blood flowing in the skin capillaries
Vasoconstriction and vasodilation

The amount of blood flowing through the skin capillaries is altered by vasoconstriction and vasodilation. Too coldToo hot
ArteriolesGet narrowerGet wider
Blood flow in skin capillariesDecreasesIncreases
Heat loss from skinDecreasesIncreases
These diagrams show the processes that take place when vasoconstriction and vasodilation occur. Diagram looks like a capital A. The horizontal is shunt vessel. Nerve impulses come from the hypothalmus and the arteriole become constricted whilst the shunt vessel dilates, little heat is lost. Vasoconstriction – a response to being too cold

Diagram looks like a capital A. The horizontal is shunt vessel. Nerve impulses come from the hypothalmus and the arteriole becomes dilated whilst the shunt vessel narrows. A lot of heat is lost. Vasodilation – a response to being too hot

Regulating blood glucose

Glucose is needed by cells for respiration. It is important that the concentration of glucose in the blood is maintained at a constant level. Insulin is a hormone – produced by the pancreas – that regulates glucose levels in the blood. Action of insulin

Low glucoseHigh glucose
Effect on pancreasInsulin not secreted into the bloodInsulin secreted into the blood Effect on liverDoes not convert glucose into glycogenConverts glucose into glycogen Effect on blood glucose levelIncreasesDecreases

The diagram shows how this works:
Too much glucose. Pancreas produces insulin, body cells absorb glucose, blood glucose reduced. Normal levels, insulin not produced by pancreas, less glucose absorbed, blood glucose remains same. iabetes

Diabetes is a condition in which the blood glucose levels remain too high. It can be treated by injecting insulin. The extra insulin causes the liver to convert glucose into glycogen, which reduces the blood glucose level. There are two types of diabetes – Type 1 and Type 2. Type 1 diabetes

Type 1 diabetes is caused by a lack of insulin. It can be controlled by: monitoring the diet injecting insulin
An insulin kit including needles and blood glucose meter
People with Type 1 diabetes have to monitor their blood sugar levels throughout the day. Their levels of physical activity and their diet affect the amount of insulin needed. They can help to control their blood glucose level by being careful with their diet (eating foods that will not cause big spikes in their blood sugar level) and by exercising (which can lower blood glucose levels due to increased respiration in the muscles). Type 2 diabetes

Type 2 diabetes is caused by a person’s body becoming resistant to insulin. It can be controlled by diet and exercise. There is a link between rising levels of obesity and increasing levels of Type 2 diabetes. Graph showing prevalence of diabetes in percentage in relation to mean body weight in kg between 1990 and 2000. The graph shows an increase in diabetes as mean body weight increases Changes in obesity and Type 2 diabetes

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