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Topic 11.3 - Kidneys
Excretion is the removal of
metabolic waste products
from the body. It is the
jobs of kidneys to clean the
bloodstream which supplies
pathways and carries waste
from tissues.
Urea is a common waste
product that must be
removed. It is a waste
product of amino acid
deamination.
11.3.1
11.3.U9 The type of nitrogenous waste in animals is correlated with evolutionary history and habitat.
http://www.bio.miami.edu/dana/dox/nitrogenouswaste.html
Mammals metabolize ammonia into a molecule called urea.
Much of metabolic waste is in the form of Nitrogen
Reptiles and birds go one step further, packaging their nitrogenous waste as uric acid. It requires more metabolic energy to make than urea, but is less toxic, and requires very little water to flush from the body.
Animals such as fish and amphibians, which have constant access to waterflush their nitrogenouswaste primarily as ammonia.
Terrestrial animals, however, because they have less access to water, have been under selective pressure to "repackage" their toxic ammonia as less toxic molecules which can be flushed with less water
http://science.kennesaw.edu/~jdirnber/Bio2108/Lecture/LecPhysio/44_08NitrogenousWastes_L.jpg
11.3.U1 Animals are either osmoregulators or osmoconformers.
Osmoconformers maintain an internal conditions that are equal to osmolarity of their environment.
Minimizing the osmotic gradient minimizes the water movement in and out of cells. A disadvantage is that internal conditions may be sub- optimal.
Most Osmoconformers are marine invertebrates, e.g. starfish.
Osmoregulators tightly regulate their body osmolarity, which always stays constant, irrespective of their environment.
Kidneys play a large role in osmoregulation by regulating the amount of water reabsorbed. A disadvantage is that osmoregulation costs the animal ATP.
Osmoregulators are much more common in the animal kingdom, e.g. bony fish.
Osmoregulation in saltwater fish Osmoregulation in freshwater fish
https://en.wikipedia.org/wiki/Osmoregulation#Regulators_and_conformers
11.3.U2 The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal of
nitrogenous wastes.
#Malpighian tubules are longer and more convoluted than shown in this simplified illustration, they extend into the body cavity, where they are surrounded by hemolymph.
http://biology-forums.com/index.php?action=gallery;sa=view;id=1281
*Hemolymph is a fluid (analogous to the blood) that circulates in the interior of the insect’s body remaining in contact with the tissues.
The removal of nitrogenous waste and osmoregulation in insects by the Malpighian tubule
*
#
11.3.1
Anatomy of a Kidney
11.3.2
• Renal artery = carries blood into each kidney
• Renal vein = drains blood from the kidneys
• Ureter = carries away urine that has collected in the
renal pelvis
• Medulla = contains
loops of Henle,
maintains salt/water
balance in body
• Cortex = contains
Bowman’s bodies
and nephrons
11.3.2
Anatomy of a Kidney
11.3.2
Kidneys are made up of over a million filtering units called
nephrons. Structures in a nephron include…
11.3.3
Nephron Structure
• Glomerulus = capillary bed that filters substances from the blood
• Bowman’s Capsule =
capsule surrounding
glomerulus
• Tubule that extends from
Bowman’s capsule that
includes:
– proximal convoluted
tubule
– loop of Henle
– distal convoluted tubule
• Capillary bed that surrounds
the previous tubule.11.3.3
Malphigian Body
efferent
arteriole
afferent
arteriole
Bowman’s Capsule
glomerulus basement
membrane
beginning of
proximal
convoluted tubule
11.3.3
Within the Malphigian body, the afferent arteriole carries
blood into glomerulus and the efferent drains it back out.
The efferent diameter is smaller than the afferent, which
creates a higher than normal blood pressure within the
glomerulus.
efferent
arteriole
afferent
arteriole
11.3.3
Ultrafiltration describes the process by which substances are
filtered through the glomerulus under the unusually high
blood pressure caused by the afferent/efferent flow.
Fenestrations (gaps) between the glomerulus cells create a path
of low resistance out into the Bowman’s capsule.
11.3.4
The basement membrane of the Bowman’s capsule acts a
filtration barrier and prevents blood cells and large plasma
proteins from passing through.
Podocytes form the inner
membrane of the Bowman’s
capsule. The interdigitation
of their extensions create
gaps for filtrates to pass
through, but not large
molecules.
Cells, proteins and other
molecules remain in blood
and leave in efferent arteriole.11.3.4
11.3.4
11.3.4
Some of the filtrate that leaves the glomerulus/Bowman’s
capsule are necessary for the body and so need to be
reabsorbed. This occurs in the proximal convoluted tubule.
Substances that leave the lumen
of the tubule are returned to the
blood by way of the peritubular
capillary bed.
The wall of the tubule are one
cell thick and contain microvilli
that increase the surface area for
reabsorption. They contain
both active and passive
transport channels.
11.3.6
Salt ions move into the tubule cells via active transport and
water follows as a result of osmosis.
All glucose molecules are reabsorbed in a fully functioning
nephron, which can only occur via active transport.
11.3.6
11.3.6
Osmoregulation is the control is the control of water balance
of the blood, tissue or cytoplasm of an organism.
The amount of water eliminated each day depends on factors
including:
- Amount of water ingested - Perspiration rate
-Ventilation rate (water exhaled)11.3.5
After the proximal convoluted tube, the remaining water and
solutes enter the descending portion of the loop of Henle.
The first section is
relatively permeable to
water but not ions, so
solute conc. rises.
The ascending portion
is relatively impermeable
to water and permeable
to ions, which are
pumped into the
intercellular fluid.11.3.7
The loop of Henle extends into the medulla, so it has a higher
ion concentration (hypertonic) as compared to fluids in the
tubules and collecting ducts.
This decreases the
overall volume of
the filtrate, but also
results in
reabsorption of
water in the
collecting ducts.
11.3.7
Next, the filtrate enters the distal convoluted tube where the
solute concentration is fine-tuned before entering the
collecting duct. At this point, the water concentration is high.
11.3.7
The water permeability of the
collecting duct depends on the
presence/absence of
antidiuretic hormone (ADH),
which is secreted by the
posterior lobe of the pituitary
gland.
Osmoreceptors detect blood
osmolarity (solute
concentration) and trigger
ADH release when osmolarity
increases (less water).
11.3.7
High osmolarity / low water levels induce ADH secretion,
which increases the water permeability of the collecting duct.
The water is then enters the peritubular capillaries and returns
to the bloodstream.
Low osmolarity prevents ADH secretion, which maintains the
collecting ducts water impermeability.11.3.7
11.3.7
11.3.7
Throughout the excretion process, the concentration of
various molecules changes (proteins, glucose and urea).
Molecule
Amount blood
plasma
(mg / 100 mL)
Amount in
glomerular
filtrate
(mg / 100 mL)
Amount in
urine
(mg / 100 mL)
Proteins >700 0 0
Glucose >90 >90 0
Urea 30 30 >1800
11.3.8
• Proteins are too large to cross through the fenestrations and
basement membrane in the glomerulus / Bowman’s capsule
and so remain in the blood plasma through the efferent
arteriole.
• Glucose is able to pass through the basement membrane
and become part of the glomerular filtrate. When it reaches
the proximal convoluted tube, it is reabsorbed into the
bloodstream through the peritubular capillaries.
• Urea passes through the glomerular fenestrations/basement
membrane and is not reabsorbed in the loop of Henle or
proximal/distal convoluted tubes. Its concentration is
magnified in urine due to water reabsorption in the
collecting duct.
11.3.8
When an individual has diabetes, blood-glucose levels are not
properly regulated by the hormones insulin/glucagon. High
levels of glucose in the blood (hyperglycaemia).
Glucose becomes part of the glomerular filtrate, but due to
high levels they can not be actively transported out fast
enough. This results in glucose being present in urine.11.3.9
11.3.7
Recommended