The human body has the ability to maintain a constant internal environment so that every organ and cell is provided the perfect conditions to perform its functions. This is called homeostasis. There is no organ system for this function. However, every organ plays a role in maintaining a constant internal environment. For example the lungs are responsible for the supply of oxygen to cells. The liver is to maintain a constant level of glucose and amino acids, and so on..

Temperature Regulation:

A healthy human should have a body temperature of 37°C.  If the body temperature drops below 37°C, metabolic reactions become slower because molecules move slower and have less kinetic energy. If the temperature rises above 37°C, the enzymes of the body begin to get denatured and metabolic reactions will be much slower.

Sometimes, the temperature of the area you are at is low enough to decrease your body temperature. Sometimes it is high enough to raise your body temperature. This is why the body has the ability to control its body temperature. Our skin is responsible for this process.

The Human Skin:

The skin is an organ that coats your entire body. The skin is made up of two layers, the Epidermis and the dermis.

The epidermis’s main function is to protect the dermis which contains most of the structures, and protect the body from ultra-violet rays. The surface of the epidermis is made of tough, dead cells.

The dermis contains many useful structures. Hairs, sweat and sebaceous glands, sense receptors and erector muscles are responsible for controlling the body temperature. Blood vessels transport oxygen and nutrients to the cells of the skin.

A healthy body is continuously gaining and losing heat. Metabolic reactions like respiration release a lot of heat energy, muscular activity increase the metabolic rate and release more heat energy. The body can also gain temperature from the surroundings like the sun or by eating hot food. Heat is lost by the body through exposed skin by conduction. If there is sweat or water on the skin, it will absorb body heat to evaporate which drops the temperature. All these factors are normal however, but it is considered dangerous when the body temperature keeps on dropping or rising severely.

Cooling Down the Body:

When the body is overheated, the body takes several actions to drop it by trying to lose heat in several ways:

  • Vasodilation: this action causes the body to lose heat quickly. It involves widening the lumen of blood vessels of the skin, this increases blood flow and rate of heat loss. The vessels are also brought near the surface of the skin to reduce the distance heat has to travel to escape.
  • Sweating: Sweat glands near the skin begin to secret sweat on the surface of the skin through the pores. This sweat acts as a heat consumer to absorb the body heat and use it in evaporation. The activity of sweat glands is increased when the temperature of the body rises.
  • Hairs lie flat: The muscle erectors of the hairs relax making the hairs lay flat of the skin. When the hairs are erect, they trap air in the gaps between them, this acts as an insulation and prevents heat loss. But when the hairs are flat, less air is trapped between them so there is no insulation and more heat can be lost.

Heating Up the Body:

When the body temperatures drop, the body takes several actions to regulate its temperature by insulation to prevent heat loss and producing heat energy:

  • Vasoconstriction: this causes the blood vessels to become narrower to reduce heat loss. They also sink deep into the skin to increase the distance heat has to travel to escape thus reducing heat loss.
  • Shivering: the muscles in the limbs start to contract and relax rapidly, thus increasing the rate of respiration and amount of heat energy released by it.
  • Hairs become erect: muscle erectors contract and make the hairs erect and stand up vertically trapping air in the gaps between them. This acts as insulation to reduce heat loss.

How the Body Senses Change in internal environment:

When the body’s internal temperature changes the temperature of the blood changes with it. When the blood flows through the brain, a part of it called the hypothalamus detects the drop or rise in temperature. The brain then starts sending electrical impulses to the rest of the body so that it works on heating or cooling its self.

This process is called Negative Feedback. Negative feedback is not for change in temperature only though, it is for any change in the internal temperature including the blood glucose level.

Regulating Blood Glucose Level:

For blood glucose level however, the pancreas is the organ which monitors its level not the hypothalamus. When the blood flows through the pancreas, the pancreas detects the level of glucose in it. If it is higher than normal, the pancreas secretes a hormone called insulin. Insulin flows in the blood till it reaches the liver. When it reaches the liver, insulin hormone will make it convert excess glucose in the blood into glycogen and store it in the liver cells. When the blood glucose level becomes normal, the pancreas will stop secreting insulin so that the liver stops converting glucose. If the blood glucose level decreases below normal, the pancreas secretes another hormone called glucagon. When glucagon reaches the liver, it makes the liver convert the glycogen it made from excess glucose back into glucose and secrete it into the blood stream so that the blood glucose level goes back to normal. When this happens the pancreas stops secreting glucagon.

Normal Blood Glucose Level: 80-100 mg per 100cm3.