Homeostasis- controlling internal temperature


The term homeostasis is derived from two Greek words:

Words Homeo stasis
Meaning Unchanging Standing

Homeostasis is defined as the maintenance of constant internal environment

It is an organism’s internal environment that needs to stay the same in order to continue metabolic reactions at the same rate.

Importance of Homeostasis

  • Helps your cells work at optimum rate
  • Ensures that enzymes work most efficiently
  • Ensures that the cells aren’t damaged by absorbing or losing too much water by osmosis
  • Ensures that there is enough fuel in reserve for respiration

Controlling body temperature

  • Warm blooded animals (Mammals and Birds) keep their body temperature constant, despite of the fluctuations in environmental conditions.
  • They are Homoeothermic or endothermic.
  • Endothermic means that the animals get their heat energy within themselves.
  • On the other hand, a poikilotherm is an organism whose internal temperature varies rapidly.

Poikilothermic animals include:

  1. Fish
  2. Amphibians
  3. Reptiles
  4. Large number of invertebrates

The skin

Skin Homeostasis

  • Epidermis is on the outside. This has a layer which is always forming new cells through cell division.
  • The new cells gradually move towards the surface, become flat, and develop keratin.
  • The outermost layer of epidermis is made up of flat dead cells, which are continuously worn away by friction and are called the cornified layer.
  • Epidermis also contains a pigment called melanin, which gives a black colour to the skin and absorbs harmful UV radiation
  • The epidermis folds inwards, forming a hair follicle, surrounded by sebaceous glands which secrete an oily liquid called sebum.
  • Sebum keeps the skin soft and supple.
  • The dermis contains sweat glands.
  • Sweat travels through the sweat duct and evaporates to regulate the internal body temperature.
  • Blood vessels and nerve endings make us aware of pain, pleasure and temperature.
  • A layer of fat known as the adipose tissue acts as insulation.

When body temperature drops below 37oC

  • Muscles work- heat is generated and distributed all over the body by quick action of muscles
  • Metabolism may increase
  • Hair stands up and in human erector muscles leads to Goosebumps.
  • In hairy animals, thick layer of hair acts as an insulator

When body temperature shoots above 37oC

  • Hair lies flat
  • erector muscles relax
  • Sweat gland secretes sweat (so that sweat evaporates and cools the body down)


  • If the body temperature rises:
  • The arteriole supplying sweat gland dilates, bringing more blood, so the gland can make more sweat.
  • Arterioles supplying the capillaries dilate, bringing more blood to the capillaries.
  • More blood is brought to the surface capillaries where, it can lose heat.


  • If the body temperature falls:
  • Arterioles and capillaries in the skin constrict, so not much blood flows through them

Negative feedback

A mechanism used in homeostasis, in which a change in a parameter brings about actions that push it back towards normal.

For example, when the body temperature rises, information about the temperature change is sent to the hypothalamus which in turn sends signals to the effectors to decrease this change.

It is termed ‘feedback’ as the information about the effects of cooling the body are fed ‘back’ to it and ‘negative’ as it is compelled to ‘stop’ doing these changes in order to stop overcooling.

Control of blood glucose concentration

  1. Cells need a steady supply of glucose to allow them to respire. Without this they cannot release energy.
  2. Too much glucose in the blood is not good either, as it can cause water to move out of the cell and into the blood by osmosis.
  3. The control of blood glucose concentration is carried out by the pancreas and liver.
  4. Islets of Langerhans (Pancreatic cells) make two hormones called insulin and glucagon.
  5. These hormones help the liver to control the amount of glucose in the blood.
  6. Insulin has the effect of lowering blood sugar
  7. Glucagon has the effect of increasing the blood sugar
  8. Food with lot of glucose increases the concentration in the blood; insulin is released into the blood.
  9. When insulin reaches the liver, it causes the liver to absorb glucose from the blood.
  10. Some is used for respiration and some is stored as glycogen
  11. If the blood sugar concentration falls too low, the pancreas secrete glucagon
  12. Liver cells break down glycogen to glucose and release it into the


When the blood glucose concentration of the body fails to function, the person with such a condition is said to have diabetes.

Type 1 diabetes is a condition caused when the WBCs destroy our own pancreatic cells that produce insulin.

This condition leads to a state where the blood glucose concentration does not fall.

If the person has had a high glucose diet, he may suffer from hyperglycaemia.

The symptoms of hyperglycaemia:

  1. The person feels unwell
  2. The person has a dry mouth
  3. Blurred Vision
  4. The person feels very thirsty
  5. Heart rate increases
  6. Breathing rate increases

If the person has a low glucose diet, the blood glucose concentration falls. As not much glycogen has been built up in the liver due to the absence of insulin, the person suffers from hypoglycaemia.

The cells do not have enough glucose to release through respiration in this condition.

The symptoms of hypoglycaemia:

  1. The person feels very tired
  2. The person shows confusion
  3. The person shows irrational behaviour
  4. The person becomes unconscious

Checking Blood Glucose concentration:

Blood glucose concentration can be monitored using:

  1. A simple sensor: which needs to be dipped in the person’s blood
  2. A urine dipstick: Urine must not contain any glucose in a normal person’s urine. But in a diabetic’s urine, the kidneys fail to absorb all the glucose and thus glucose is present in it.

Treating Type 1 diabetes

People with type 1 diabetes often need to inject insulin in order to control their blood sugar concentration



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