Osmoregulation
Maintaining water balance
Today’s goals!
• Understand the negative feedback system for
water balance in vertebrates (the kidney).
• Analyse some data (osmolarity).
• Identify structural, physiological and
behavioural adaptations to conserve water.
Negative feedback system-1
1. Blood pressure decreases
2. Receptors in the hypothalamus detect an increase
in blood solutes (!!LESS WATER!!)
3. The hypothalamus releases vasopressin via
pituitary gland
4. Vasopressin (hormone) is released into the blood
and travels to the kidney
5. Loop of Henley in the kidney reabsorbs more water
from the urine
6. Blood pressure increases
Negative feedback loop-2
1. Hypothalamus detects increase in blood
solutes (!!LESS WATER!!!)
2. Hypothalamus creates a thirst sensation
3. Animal drinks water
4. Blood pressure rises
Negative feedback loop-3
1. Blood pressure falls
2. Pressure sensitive receptors in the kidney detect
this decrease
3. Kidney releases renin
4. Renin causes adrenal glands to release
aldosterone
5. Aldosterone causes the tubules in the kidney to
absorb sodium ions water follows and is
reabsorbed by the body
6. Blood pressure rises
What to remember about the kidney!
• After blood is filtered, the kidney plays a part
regulating water content of the blood
• 2 ways
– Directly causing re-absorption of water into the
blood (vasopressin)
– Indirectly causing absorption of water into the
blood by releasing sodium ions (causing water to
follow by osmosis)
Next
• Wednesday we will spend some time on the
adaptations of different groups of organisms
– Single celled organisms
– Birds
– Reptiles
– Amphibians
– Plants
– And more!!!!
Activity
• Complete activity 10.2, examining the data to
answer questions 1-6
VIDEO (YAY!!!)
• Life in cold blood