11.3 The kidney and osmoregulation
Understanding:
- Animals are either osmoregulators or
osmoconformers
- The Malpighian tubule system in insects and the
kidney carry out osmoregulation and removal of
nitrogenous wastes
- The composition of blood in the renal artery is
different from that in the renal vein
- The ultrastructure of the glomerulus and
Bowman’s capsule facilitate ultrafiltration.
- The proximal convoluted tubule selectively
reabsorbs useful substances by active transport
- The loop of Henle maintains hypertonic
conditions in the medulla
- The length of the loop of Henle is positively
correlated with the need for water conservation
in animals
- ADH controls reabsorption of water in the
collecting duct
- The type of nitrogenous waste in animals is
correlated with evolutionary history and habitat.
Applications:
- Consequences of dehydration and
over hydration
- Treatment of kidney failure by
hemodialysis or kidney transplant
- Blood cells, glucose, proteins and
drugs are detected in urinary tests
Nature of science:
- Curiosity about particular
phenomena: investigations were
carried out to determine how
desert animals prevent water loss
in their wastes
Skills:
- Drawing and labeling a diagram of
the human kidney
- Annotation of diagrams of the
nephron.
Responses to osmolarity changes
Osmolarity = solute concentration of a solution
Osmoregulators = maintain a constant internal solute
concentration no matter what environment they are in.
Osmoconformers = internal solute concentration is
always the same as the environment.
One of the main roles of the kidney = osmoregulation
Draw and label a human kidney –
Rules!
Shape should be roughly oval with a concave side to which the
renal artery and vein are attached
Clearly indicate the cortex shown at the edge of the kidney –
1/5 of the entire width of the kidney
Medulla should be shown inside the cortex, with pyramids
Renal pelvis should be shown on the concave side of the kidney,
and should drain into the ureter
The renal artery should have a smaller diameter than the renal
vein
Annotating a nephron
Nephrons are basic functional units of the kidney
Tube with a wall consisting of one layer of cells that
substances cross to leave the body
Annotating a nephron
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Blood vessels
- Afferent arteriole
- Glomerulus
- Efferent arteriole
- Peritubular capillaries
- Vasa recta
- Venules
Label all onto
your nephron
Then describe
what each part
does
Role of the kidney
Osmoregulation and excretion
Remove substances from the
blood that are not needed or
are harmful
Composition of renal artery
entering kidney is very
different from the renal vein
leaving the kidney
Role of the kidney
Higher amounts in the renal
artery:
- Toxins
- Substances that have not been
fully metabolized by the body
- Nitrogenous waste (urea)
- Excess water
- Excess salt
- Oxygen (used in respiration)
- Glucose (used in respiration)
Capillaries
High pressure in capillaries means that plasma is
forced out through the capillary wall to form tissue
fluid
Glomerulus
High pressure in capillaries
Capillary walls very permeable
(fenestrations = small holes)
Volume of fluid force out here
is 100 time greater than in
other areas of the body
Glomerular filtrate in the
Bowman’s capsule
Glomerulus
Ultrafiltration means
that particles are
separated due to size.
Large molecules cannot
fit through the capillary
walls
Proteins and blood cells
are retained in the
blood
Structure of the glomerulus
1. Fenestrations
2. Basement membrane
3. Podocytes
What do each of these do?
Structure of the glomerulus
1. Fenestrations
Between cells in wall of capillaries – 100nm in diameter –
allow fluid to escape but not blood cells.
2. Basement membrane
Covers and supports wall of capillaries. Made of negatively
charged proteins which form a mesh. Prevents plasma
proteins from filtering out. (Second filter)
3. Podocytes
Inner wall of Bowman’s capsule. Wrap around capillaries in
glomerulus. Very narrow gaps prevent small molecules being
filtered out. (Third filter)
Proximal Convoluted Tubule
Glomerular filtrate flows into the proximal
convoluted tubule from Bowman’s capsule.
The volume is several times the total volume of
fluid in the body
Usually about 180dm3
Contains:
• 1.5kg of salt
• 5.5kg of glucose
180dm3 = 180 litres
1.5kg salt
5.5kg glucose
Actual urine produced per day
180 litres
1.5 litres
Reabsorption
Most of the glomerular filtrate must be reabsorbed
Occurs in the first part of the nephron - proximal
convoluted tubule
Reabsorption
By the end of the proximal convoluted tubule all
glucose and amino acids, 80 percent of water, sodium
and other minerals have been reabsorbed.
Sodium
Chloride Ions
Glucose
Water
How are these moved out of the filtrate?
Reabsorption
Sodium – Active transport (also provides energy)
Chloride ions – Diffusion (due to gradient caused by
sodium)
Glucose – Transport proteins (Energy provided by
sodium transport)
Water – Osmosis (Down concentration gradient
caused by ions above)
The Loop of Henle
Creates a
gradient of
solute
concentration
in the
medulla
Countercurrent Multiplier System
Fluid flows in opposite directions (counter current)
Causes a steep solute gradient (Multiplier)
The Loop of Henle
Descending limb
• Permeable to water
• Impermeable to sodium ions
• Water drawn out
Until the filtrate reaches the same solute concentration as
the interstitial fluid.
Ascending limb
• Impermeable to water
• Pumps out sodium ions using proteins
The Loop of Henle
Length of Loop of Henle is positively correlated with
the need for water conservation in animals
Longer loop of Henle = more water volume reclaimed
(animals in dry habitats)
Distal convoluted tubule
Filtrate is now hypotonic as it has a lower solute
concentration that normal body fluids.
Walls have low permeability to water.
If blood solute concentration is too low, little water is
reabsorbed in this area, and more urine is produced.
ADH
If blood solute concentration is too high, pituitary
gland secretes antidiuretic hormone (ADH)
Causes the walls of the distal convoluted tubule and
collecting duct to become much more permeable to
water.
Most of the water is reabsorbed.
Nitrogenous waste
Break down of amino acids and nucleic acids =
nitrogenous waste (ammonia)
Highly alkaline (can alter pH balance) and toxic
(reactive)
Marine organisms
Release waste
directly as ammonia
as it is easily diluted
in the environment
Terrestrial organisms
Expend energy
to convert
ammonia to
the less toxic
forms of urea
or uric acid
Terrestrial organisms
Urea requires water
to be expelled
Uric acid does not
require as much
water (means birds
do not have to carry
it which is good for
flight)
Research
What is dehydration? How is it caused? What are the
consequences?
What is overhydration? How is it caused? What are the
consequences?
What is urinalysis?
Describe the two treatment options for kidney failure:
- Hemodialysis
- Kidney transplant