biology - keeping internal conditions constant

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  • Created by: eleanor
  • Created on: 30-04-13 16:12

controlling internal conditions


Two examples of things that the body keeps the same are:Homeostasis is how the body keeps conditions inside it the same. Scientists describe it as the maintenance of a constant internal environment.

  • body temperature at 37°C
  • the amount of water inside our body
  • getting rid of waste products e.g. co2, urea 
  • ion content 
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human kidneys

What the kidneys do

As the blood passes through the kidneys, all the small molecules are filtered out of the blood.

This includes molecules of:

  • water
  • salt
  • glucose
  • urea (a waste product from the breakdown of proteins)

The kidneys then reabsorb all of the glucose and as much water and salt as the body needs, putting them back into the blood. This leaves some water and salt, and all of the urea, which is now called urine. The urine passes from the kidneys to the bladder, where it is stored prior to being excreted from the body.

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the kidney


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dialysis- an artificial kidney

  • If a person suffers from kidney failure they can be kept alive by dialysis. 
  • A dialysis machine carries out the same job as the kidneys. the blood flows between partially permeable membranes 
  • Only urea diffuses out of the blood because the glucose and minerals ions are equal. 
  • Then a person will have a kidney transplant if one comes available 
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kidney transplant

  • a transplant is better than dialysis, the dieased kidney is replaced with a healthy one. 
  • a kidney must be a tissue match or it coud be rejected. 
  • the immune is designed to attack anything foriegn in the body, therefore the patient must take drugs to suppress the immune response to prevent rejection 
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controlling body temperature

 Diagram shows cross section of skin when cold, with erect hairs (B) caused by tense hair muscles (A), and reduced blood flow to capillaries (C)  ( Diagram shows a cross section of skin when hot. Hair muscles relax (D) causing hairs to lie flat so that heat can escape. Sweat is secreted (E) from the sweat glands. Blood flow in the capillaries is increased (F) ( too cold 
A - Hair muscles pull hais on end.
B - Erect hairs trap air.
C - Blood flow in capillaries decreases.
too hot 
D - Hair muscles relax. Hairs lie flat so heat can escape.
E - Sweat secreted by sweat glands. Cools skin by evaporation.
F - Blood flow in capillaries increases.

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controlling blood glucose

glucose level   effect on pancreas      effect on liver              effect on glucose level

too high             insulin secreted into      liver converts                            goes down
                          the blood                    glucose into glycogen

 too low             insulin not secreted       liver does not convert                  goes up
                        into the blood                glucose into glycogen  

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treating diabetes


Glucose is a sugar needed by cells for respiration. It is important that the concentration of glucose in the blood is maintained at a constant level. Insulin, a hormone secreted by the pancreas, controls blood sugar levels in the body.

Diabetes is a disorder in which the blood glucose levels remain too high. It can be treated by carefully maintaining a certain diet or injecting insulin. The extra insulin allows the glucose to be taken up by the liver and other tissues, so cells get the glucose they need and blood sugar levels stay normal.

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