1. Lesson 1: Biology Unit 2, Water Regulation in Vertebrates
Thursday, 9th
August, 2012.
Class duration: 70 mins
Class setting: Science laboratory
Materials: None
Learning intention:
To understand the physiological the adaptions in mammals that assist them to maintain water balance.
Time
(mins)
Teacher activity Student activity
5 Introduce myself, mark the roll.
20 Introduce topic, and teach the process of water
regulation in mammals.
Vasopressin
Listen, answer questions, copy definitions and
diagrams from the board.
10-15
mins?
Tell students to get into groups of 2-3, and teach
each ot her.
Drawing/teaching
15 Revision mind-map cut and paste activity (work
in pairs)
Cutting and pasting steps into the mindmap.
10 Check answers as a class (page 329) Checking their answers.

2. Lesson 1: Biology Unit 2, Water Regulation in Vertebrates
Thursday, 9th
August, 2012.
Class duration: 70 mins Class setting: Science laboratory Materials: Projector
Learning intention:
To understand the physiological the adaptions in mammals that assist them to maintain water balance.
Teacher activity
Introduce topic:
Physiological Adaptions for Maintaining Water Balance in Vertebrates
Break down the meaning of the topic:
Physiological: In relation to the scientific study of the processes and functions of a living organism.
Adaptions: Any genetically controlled features that may assist survival and reproduction of organisms in
their specific environments.
Vertebrates: Animals distinguished by the possession of a backbone (including mammals, marsupials, birds,
reptiles, amphibians, and fish).
The physiological adaptions for maintaining water balance in MAMMALS
1. Does anybody know which organ controls water balance of the body for all vertebrates?
Ans: Kidneys
2. What is the function of the kidneys?
Ans: To eliminate nitrogenous wastes from the body while ensuring water balance.
3. Why is it important to maintain water balance (osmoregulation)?
Ans: To stabilize the internal environment of the body (homeostasis). That’s why kidneys are
important. We would only survive for a few days without them.
Osmoregulation is associated with the maintenance of blood pressure.
Increase water (in body) = increase blood pressure
“Osmoregulation is associated with the maintenance of blood pressure.” … HOW?
Two significant compounds (hormones) are involved:
- Antidiuretic hormone (ADH) a.k.a. Vasopressin
- Renin
Vasopressin (Antidiuretic hormone, ADH) is a hormone found in most mammals (including humans).
*Show diagram of the brain*

3. Produced in the hypothalamus, and released by the pituitary gland.
*Draw diagram on the board. Students copy this.*
- Vasopressin is produced by neurosecretory cells in the hypothalamus of the brain.
- There are cells in the hypothalamus called osmoreceptors.
- Neurosecretory cells are activated when osmoreceptors in the hypothalamus detect an increase in
blood solutes…
1. When there is a rise in blood solutes (increase of osmolarity), is there an increase or decrease of
water in the blood? Ans: there is a decrease in water concentration in the blood.
2. What could cause the decrease of water concentration in the blood? Ans: insufficient intake of
water, excessive sweating, diarrhoea.
- Neurosecretory cells release vasopressin. Vasopressin flows through the axons of the
neurosecretory cells to the posterior pituitary gland, where it is released into the bloodstream (or
stored).
- Vasopressin is transported through
the bloodstream to the kidneys, where it increases the permeability of distal tubules and collecting
ducts to water.
What does this mean? “increased permeability to water”?
What does “permeable” mean? Ans. Allows fluids to go through (i.e. more water).
So the distal tubules and collecting ducts (in the kidneys) become more permeable to water, allows water
to pass through. So there is an increase of water being reabsorbed by these areas…
With the reabsorption of water from the kidneys, our bodies would now contain sufficient water. Then
what would happen to the concentration of blood solutes (increase or decrease)?
Ans. Fall/decrease… blood becomes more diluted, and concentration of blood solute decreases
If there is a decrease in the concentration of blood solutes (osmolarity), what would happen to the
levels of vasopressin in our blood?
Ans: Decrease, because Vasopressin is released when there is a decrease in blood solutes.
THIS IS CALLED “NEGATIVE FEEDBACK”.
How do you feel when you don’t have enough water in your body? Ans. THIRSTY!!!
Why? Because osmoreceptors generate a sensation of thirst when they detect a rise in blood solutes!
Increased drinking also acts as a feedback mechanism leading to reduced secretion of Vasopressin.
If water is being reabsorbed from the kidneys and back into our bloodstream, what would happen to
our urine?
Ans. Become more concentrated, less water/less urine, yellow in colour.
Concentration
of solutes in
blood
(osmolarity)
Detected by
osmoreceptors
in the
hypothalamus
Increased production
of vasopressin in
neurosecretory cells
and flow to posterior
pituitary
Increased release of
vasopressin from the
posterior pituitary
into the bloodstream
Increased
permeability of
distal nephron
tubules to water
Increased
water
reabsorption
from nephron
tubules
Blood pressure
increased
(vessels
constricted)
Decreased
production of
vasopressin in
neuroscretory cells
Negative
Feedback
mechanism
Creates
sensation of
thirst
Increased
intake of water
Increased production
of vasopressin in
neurosecretory cells
and flow to posterior
pituitary
Increased release of
vasopressin from the
posterior pituitary
into the bloodstream
Decreased
production of
vasopressin in
neuroscretory cells
Increased production
of vasopressin in
neurosecretory cells
and flow to posterior
pituitary
Increased release of
vasopressin from the
posterior pituitary
into the bloodstream
Decreased
production of
vasopressin in
neuroscretory cells
Increased production
of vasopressin in
neurosecretory cells
and flow to posterior
pituitary
Increased release of
vasopressin from the
posterior pituitary
into the bloodstream
Decreased
production of
vasopressin in
neuroscretory cells
Concentration
of solutes in
blood
(osmolarity)
Detected by
osmoreceptors
in the
hypothalamus
Increased
water
reabsorption
from nephron
tubules
Blood pressure
increased
(vessels
constricted)
Negative
Feedback
mechanism
Creates
sensation of
thirst
Increased
intake of water
Increased
permeability of
distal nephron
tubules to water
Concentration
of solutes in
blood
(osmolarity)
Detected by
osmoreceptors
in the
hypothalamus
Increased
water
reabsorption
from nephron
tubules
Blood pressure
increased
(vessels
constricted)
Negative
Feedback
mechanism
Creates
sensation of
thirst
Increased
intake of water
Increased
permeability of
distal nephron
tubules to water
Concentration
of solutes in
blood
(osmolarity)
Detected by
osmoreceptors
in the
hypothalamus
Increased
water
reabsorption
from nephron
tubules
Blood pressure
increased
(vessels
constricted)
Negative
Feedback
mechanism
Creates
sensation of
thirst
Increased
intake of water
Increased
permeability of
distal nephron
tubules to water