Page 127 - Biology_Form_3

Biology for Secondary Schools

and salt loss through sweating. In hot Osmoregulation is primarily controlled
climates or during physical exertion, the by two hormones; Antidiuretic Hormone
body sweats more to cool down, leading (ADH) and Aldosterone hormone.
to a higher loss of fluids and electrolytes.
On the other hand, cooler conditions reduce ADH
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sweating, helping to maintain a more stable ADH, also known as vasopressin, is
fluid balance. Additionally, diet has a produced by the hypothalamus and stored
direct impact on the body’s water and salt in the pituitary gland. It plays a crucial
levels. Consuming hydrating foods like role in water conservation. When the body
watermelon and cucumber helps boost body experiences dehydration, osmoreceptors
water content, while eating salty foods or in the hypothalamus detect an increase in
foods high in sodium raises the salt levels in blood osmotic pressure. Osmoreceptors in
body fluids, which can influence the body’s the hypothalamus of the brain are stimulated
ability to maintain fluid balance. and send the information to the pituitary

gland to release ADH into the bloodstream.
Physical activity is another key factor, as When it reaches the kidneys, ADH causes
intense physical exertion leads to increased the membrane of distal convoluted tubules
sweating, which results in the loss of both and collecting ducts to be more permeable
water and electrolytes such as sodium. to water. The higher permeability of the
During periods of physical strain, the membrane increases the reabsorption of
body’s fluid balance can become disrupted
if adequate hydration is not maintained. water into the bloodstream. This returns
Furthermore, certain health conditions, such the water balance to normal.
as diabetes, can affect the body’s ability
to regulate fluid balance. In diseases like When the osmotic pressure of the blood and
diabetes, excessive urination due to high tissue fluid falls due to the large intake of
blood sugar levels leads to increased fluid water, the pituitary gland is less stimulated.
loss, which can result in dehydration if not This results into the reduced secretion of
properly managed. Overall, maintaining a ADH into the bloodstream. Therefore, the
healthy balance of salt and water is crucial water permeability of the membrane of
for optimal body function. Moreover, distal convoluted tubules and collecting
understanding the factors that influence ducts decreases. Hence less water will be
this balance is essential for good health. reabsorbed resulting in excretion of large
amount of dilute urine.
Mechanisms of osmoregulation
Task 5.6 Aldosterone
When the osmotic pressure in the blood
Search from the library and internet falls due to a low concentration of salt
sources animations about mechanism ions, particularly sodium and chloride
of osmoregulation. Watch the animations ions, another hormone called aldosterone
and prepare a summary. is released from the adrenal glands into

120 Student’s Book - Form Three

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