Transcript Water balance

Control of The
Internal
Environment
Water Gain and Water Loss

Mammals gain and lose water in several ways.

Over the course of the day water gain is equal to
water loss.

This is known as osmoregulation

Osmoregulation – regulation of water content in
mammals.
Water Gain and Water Loss
GAIN
LOSS
Drinking
Sweat
Food
Urine
Chemical reactions
e.g. respiration
Faeces
Breathing
If water gain is equal to
water loss, what is the
value of X?
X = 300cm3
Urinary system
The system responsible
for osmoregulation is
called the urinary
system.
urethra
Part
Function
Kidney
Filtration of blood.
Reabsorption of important
substances.
Bladder
Stores urine.
Ureter
Transports urine from kidney
to bladder
Urethra
Carries urine from bladder to
external environment.
Renal artery
Carries unpurified blood into
the kidney.
Renal vein
Carries purified blood away
from the kidney.
Urea

Urea is made in the liver.

Urea is made by breaking down excess amino acids
(remember that this process is known as
deamination!)

Urea is transported to kidney in the blood by the
renal artery.

Urea is removed from the body as urine.
Filtration By The Kidney
Blood enters the kidney via the renal artery (red) and
leaves via the renal vein (blue)
The kidney

Main organ of osmoregulation.

3 main functions:
Filtration of blood
 Reabsorption of useful materials e.g.
glucose, water, amino acids and some
salts
 Production of urine

Structure of the kidney

The renal artery which contains
unpurified blood enters the kidney and
divides into many tiny branches.

The blood in each tiny branch is filtered in
a special filtering unit called a nephron.
Structure of the kidney

Each kidney is made up of about 1 million tiny
filtration units called NEPHRONS

Nephrons filter the blood and then reabsorb the
useful substances.
Kidney
The start of the
nephron – where
blood is filtered
The Nephron – A Filtration Unit
Bowman’s
capsule
Glomerulus
Collecting
duct
Blood
capillaries
The Role of the Nephron

The nephron reabsorbs useful
substances such a glucose back
into the blood vessels.

Tiny blood vessels then join up
as they leave the kidney. This
forms the renal vein.

The renal vein carries purified
blood back to the body.
Structure of the Nephron

Renal artery divides into about
a million tiny branches.

Each branch leads to a
glomerulus (a tiny knot of
blood capillaries).

The glomerulus is surrounded
by a cup-shaped Bowman's
capsule which leads to a long
tubule.
Renal artery
Knot of blood
capillaries called
a GLOMERULUS
The glomerulus
sits inside a cupshaped
BOWMAN’S
CAPSULE
Filtration

Blood vessels that enter the glomerulus are wider than
those that leave.

Blood inside these vessels are under pressure (being
squeezed).

This means that only the small molecules in blood are
squeezed out of the tiny spaces in the capillary wall and
collect in the Bowman's capsule.

This liquid is now called glomerular filtrate.

Blood cells and plasma proteins are too big to fit through
the pores so remain in the blood.
Reabsorption By Kidney

All glucose and variable
amounts of water, amino
acids and salts are
reabsorbed back into the
blood

No urea is reabsorbed –
expelled as urine (excess
water dilutes urea)

Water is absorbed again by
collecting duct
Summary Table of Filtration
in the Kidney Nephron
Filtered Out Of The
Blood
Not Filtered Out Of The
Blood
Water
Blood Proteins
Glucose
Red Blood Cells
Salts and Urea
White Blood Cells
Excretion By The Kidney

Urine is a nitrogenous waste product.
It must be removed from the body
because it is toxic

Urea must be excreted as urine so
that urea can be removed from the
body
Osmoregulation in
Freshwater Fish
Freshwater Fish

Freshwater fish gain water by osmosis

Examples of freshwater fish are pike, perch and
sticklebacks

Freshwater fish have a water balance problem as
they take in too much water

Freshwater fish have many, large glomeruli to filter
the water quickly
Gills also absorb salts
that the fish needs
Freshwater
enters mouth
Water enters gills
by osmosis
There is a lower water
concentration inside the
fish than outside, so water
moves in by osmosis
A large volume
of dilute urine is
produced
Marine (saltwater) Fish

Marine fish lose water by osmosis

Examples of freshwater fish are haddock, herring and cod

Water flows out of the gills because the water concentration of
the salty sea water is lower than the water concentration inside
the fish

To get round this problem, marine fish have to drink a lot of sea
water and filter it to absorb the water

Excess salt is pumped out of the fish via the gills

Marine fish have few, small glomeruli to filter the water slow
Loses water by osmosis as
there is a higher water
concentration inside the
fish than outside
Sea water
Excess salts are excreted
from the gills
A small volume of
concentrated urine is
produced
Top Tip!
You should be aware that the
situations for the freshwater and the
marine water fish is the exact opposite
problems. If you know one well, you
should be able to work out the other!
Receptors and Effectors

Any changes from the normal point is
picked up by special cells called
receptors

Receptors are specialised cells that
detect changes in the internal
environment
Receptors and Effectors

For the correction to be carried out,
receptor cells pass on the message about
this change to effectors, which carry out
corrective mechanisms

Effectors are cells or organs that
respond to messages from receptors by
producing a corrective mechanism
Factor
Receptor
Cells
Effector
Cell or
Organ
Negative Feedback
Control

Negative feedback control is a process
by which changes to conditions in the
internal environment are returned to
normal
Controlling Water
Concentration
hypothalamus
Pituitary
Gland
Controlling Water
Concentration

A part of your brain called the hypothalamus
contains osmoreceptors that detect the
concentration of water in the blood

If the water concentration of the blood is too low,
the osmoreceptors trigger a hormone to be
released into the blood called ANTIDIURETIC
HORMONE (ADH)

ADH acts by increasing the permeability of the
nephron tubules to water
Low Water Concentration
In the Blood

If you are feeling dehydrated, the
concentration of water in the blood
is low

Osmoreceptors detect this and send
out more ADH to allow more water
to be reabsorbed from the nephrons
back into the blood

This allows the concentration of
water to return to normal

Little urine is produced
High Water Concentration
In the Blood

If you have drunk a lot of water,
your blood is full of water

Osmoreceptors detect this and
send out less ADH to allow less
water to be reabsorbed from the
nephrons back into the blood

This allows the concentration of
water to return to normal

A lot of urine is produced
NORMAL
WATER
CONTENT OF
BLOOD
NORMAL
WATER
CONTENT OF
BLOOD
HIGH WATER
CONTENT OF
BLOOD
THE HYPOTHALAMUS
DETECTS THE HIGH
WATER CONTENT
VERY LITTLE ADH IS
RELEASED INTO THE
BLOOD STREAM
NORMAL
WATER
CONTENT OF
BLOOD
LOW WATER
CONTENT OF
BLOOD
THE
HYPOTHALAMUS
DETECTS THE LOW
WATER CONTENT
LOTS OF ADH IS
RELEASED INTO
THE BLOOD
STREAM
Role of ADH
Water content of
blood too low
Salt eaten or
much sweating
Brain releases
much ADH
Too much
water drunk
Water content of
blood normal
High volume of
water passes
into blood
High volume of
water reabsorbed
by kidney
Small volume of
concentrated urine
passed to the bladder
Water content of
blood too high
Brain releases
little ADH
Low volume of
water passes
into blood
High volume of dilute
urine passed to the
bladder
Low volume of
water reabsorbed
by kidney