When the glucose level in the blood increases above normal levels:

Step 1

Glucose levels in the blood increase above normal levels

Step 2

The pancreas is stimulated

Step 3

to secrete insulin into the blood

Step 4

Insulin travels in the blood to the liver

Step 5

where it stimulates the conversion of excess glucose to glycogen which is then stored

Step 6

The glucose level in the blood now decreases

Step 7

and returns to normal

When the glucose level in the blood decreases below normal levels:

Step 1

Glucose levels in the blood decrease below normal levels

Step 2

The pancreas is stimulated

Step 3

to secrete glucagon into the blood

Step 4

Glucagon travels in the blood to the liver

Step 5

where it stimulates the conversion of stored glycogen to glucose

Step 6

The glucose level in the blood now increases

Step 7

and returns to normal

When the CO₂ level in the blood increases above normal levels:

Step 1

CO₂ levels in the blood increase above normal levels

Step 2

Receptor cells in the carotid artery in the neck are stimulated

Step 3

To send impulses to the medulla oblongata in the brain

Step 4

Medulla oblongata stimulates breathing muscles (intercostal muscles and diaphragm) and heart

Step 5

Breathing muscles contract more actively - increases the rate and depth of breathing. The heart beats faster.

Step 6

More CO₂ is taken to and exhaled from the lungs

Step 7

The CO₂ level in the blood returns to normal

When the blood has less water than normal:

Step 1

Blood has less water than normal

Step 2

The hypothalamus is stimulated

Step 3

and sends impulses to the pituitary gland  to secrete more ADH

Step 4

ADH travels in the blood to the kidneys

Step 5

ADH increases the permeability of the collecting ducts and the distal convoluted tubules of

the kidney

Step 6

More water is re-absorbed and passed to the surrounding blood vessels

Step 7

The water level in the blood returns to normal

When the blood has more water than normal:

Step 1

Blood has more water than normal

Step 2

The hypothalamus is stimulated

Step 3

and sends impulses to the pituitary gland  to stop secreting ADH/to secrete less ADH

Step 4

No ADH/less ADH travels in the blood to the kidneys

Step 5

The collecting ducts and the distal convoluted tubules of the kidney become less permeable to water

Step 6

Less water is re-absorbed and passed to the surrounding blood vessels. More water is now lost

Step 7

The water level in the blood returns to normal

When the salt level in the blood decreases:

Step 1

The salt level in the blood decreases

Step 2

Receptor cells in the afferent and efferent arterioles of the kidney detect the low salt level

Step 3

The adrenal gland is stimulated

Step 4

into secreting more aldosterone

Step 5

Aldosterone increases the re-absorption of sodium ions from the renal tubules in the kidney into the

surrounding blood vessels

Step 6

The salt level in the blood vessels increases

Step 7

and returns to normal

When the salt level in the blood increases:

Step 1

The salt level in the blood increases

Step 2

Receptor cells in the afferent and efferent arterioles of the kidney detect the high salt level

Step 3

The adrenal gland is stimulated

Step 4

to stop secreting aldosterone/to secrete less aldosterone

Step 5

This decreases the re-absorption of sodium ions from the renal tubules in the kidney into the

surrounding blood vessels

Step 6

The salt level in the blood vessels decreases

Step 7

and returns to normal