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Homeostasis (Higher)
 
Control of Body Temperature | Removal of Toxic Waste Products
 

Control of Body Temperature

Homeostasis is the control of internal body conditions so that body processes can work efficiently.

Control of body temperature is called thermoregulation.

Normal body temperature is 37ºC.  This is the temperature at which enzymes work best.

The thermoregulatory centre in the brain has receptors to monitor the temperature of the blood flowing through it.  Receptors in the skin send impulses to the centre about skin temperature.


If body temperature is too high:

If body temperature is too low:
  • Blood vessels in the skin dilate (get wider) so more blood flows to the surface of the skin. 
  • Blood vessels in the skin constrict and narrow so less blood flows to the surface of the skin.
  • Sweat is produced, which cools the body as it evaporates. 
  • Muscles shiver.  They need more energy so respire more and some energy is released as heat.

More water and salts, in the form of ions, are lost by sweating when it is hot.  These have to be replaced by taking drinks and food.

 

Removal of Toxic Waste Products

Carbon dioxide is the toxic waste product of respiration.  This is removed from the body through the lungs when we breathe out.  Some water is also lost this way.

Urea is a toxic waste produced in the liver when excess amino-acids are broken down.

It is transported in the bloodstream to the kidneys to be excreted in urine.

Urine is temporarily stored in the bladder.

The kidneys produce urine by ultrafiltration of the blood into the kidney tubules, then selectively reabsorbing useful substances like glucose and some water and dissolved ions back into the blood.

Urine contains water, urea and some salts in the form of ions.  It should not contain protein or glucose.  Protein molecules are too large to be filtered out of the blood and all the glucose is reabsorbed back into the blood from the kidney tubules.

Protein in the urine indicates kidney disease and glucose in the urine indicates diabetes.

The concentration of the urine depends on how much water is in the blood.  On hot days, when a lot of water has been lost by sweating, a small volume of concentrated urine is produced.

If there is too little water in the blood the pituitary gland releases the hormone ADH.

ADH causes the kidneys to reabsorb more water, so more concentrated urine is produced.

If the water content of the blood is high less ADH is released so less water is reabsorbed and dilute urine is produced.