Regulation of Extracellular Fluids
• Excretory systems:
The removal from the body of the waste
products of metabolic pathways
Osmoregulation – control of the water
balance of the blood, tissue or cytoplasm
of a living organism.
• Excretion applies to metabolic waste
products that cross a plasma membrane.
• What are some wastes?
• Elimination is the removal of feces.
• Nitrogen wastes are a by product of
• The NH2 (amino group) combines with a
hydrogen ion (proton) to form ammonia
• Ammonia is very toxic and usually is
excreted directly by marine animals.
Terrestrial animals usually need to
• Ammonia is converted to urea, a
compound the body can tolerate at higher
concentrations than ammonia.
• Birds and insects secrete uric acid that
they make through large energy
expenditure but little water loss.
• Amphibians and mammals secrete urea
that they form in their liver. Amino groups
are turned into ammonia, which in turn is
converted to urea, dumped into the blood
and concentrated by the kidneys.
• Terrestrial animals use a variety of
methods to reduce water loss: living in
moist environments, developing
impermeable body coverings, production
of more concentrated urine.
• Water loss can be considerable: a person
in a 100 degree F temperature loses 1 liter
of water per hour.
Vertebrates Have Paired Kidneys p
• The urinary system is
made-up of the
bladder, and urethra.
• You must be able to draw kidney,
nephron, and glomerulus… go to study
guide p 101
• PUT IN DRAWING BOOK
Structure of the Kidney p 101
Renal capsule: a thin
Cortex: lightly colored
Medulla: darker inner
Renal pelvis: funnel
shaped cavity collects
Renal artery and vein
• The functional unit of the excretory system
or urinary system
• The nephron is a long thin tube
• closed at one end
• two twisted regions interspaced with a
long hair pin loop
• ends in a long straight portion and is
surrounded by capillaries
• Nephrons filter 125 ml of body fluid per
minute; filtering the entire body fluid
component 16 times each day.
• In a 24 hour period nephrons produce 180
liters of filtrate, of which 178.5 liters are
reabsorbed. The remaining 1.5 liters forms
The nephron has three functions:
1. Glomerular filtration of water and solutes
from the blood.
2. Tubular reabsorption of water and
conserved molecules back into the
3.Tubular secretion of ions and other waste
products from surrounding capillaries into
the distal tubule.
• Nephron anatomy
• Concentrating Urine - The Mammalian
• Animations and Tutorials
The steps in urine production or
• Blood enters the glomerulus under
• This causes water, small molecules (but
not macromolecules like proteins) and ions
to filter through the capillary walls into the
• This fluid is called nephric filtrate.
• Nephric filtrate collects within the
Bowman's capsule and then flows into the
• Here all of the glucose, and amino acids,
reabsorbed by active transport.
• large volume of the water follows them by
osmosis (80–85% of the 180 liters
deposited in the Bowman's capsules in 24
• As the fluid flows into the descending
segment of the loop of Henle, water
continues to leave by osmosis because
the interstitial fluid is very hypertonic.
• This is caused by the active transport of
Na+ out of the tubular fluid as it moves up
the ascending segment of the loop of
• In the distal tubules, more sodium is
reclaimed by active transport, and still
more water follows by osmosis.
• Final adjustment of the sodium and water
content of the body occurs in the
collecting tubules. (ADH)
• Read this explanation of the process:
Regulating Blood Composition
.concentrations of various ions and other
important substances constant.
.volume of water in your body constant.
. acid/base concentration of your blood
. Removing wastes from your body.
• The kidney does this by a combination of three
• It filters 20 percent of the plasma and non-cell
elements from the blood into the inside of the
nephron (the lumen).
• It reabsorbs the components that the body
needs from the lumen back into the blood.
• It secretes some unwanted components from
the blood into the lumen of the nephron.
• glomerulus, blood plasma (the fluid
component of blood) is forced out of the
capillaries and into the nephron.
• Narrow spaces : proteins and RBC left
• Nephric filtrate
capsule and then
flows into the
• glucose, and amino acids, are
reabsorbed by active transport.
• Filtrate must now travel through a long and
winding tubular pathway, first through the
cortex, or outer portion of the kidney, then
the medulla, the deep portion.
• What happens to some of the substances which
travel down the tubule.
• Pay attention to glucose, water, and salts. You
need to know which is reabsorbed where, and
which requires active transport.
• Concentrating Urine - The Mammalian Kidney
Two major factors influence
• High concentration = more absorption …
up to a limit . There are only so many
transporters for each molecule and they
can only carry so many at a time
• Rate of flow of the filtrate meaning that if
the flow is quick there will be less
• The hypertonic interstitial fluid surrounding the
tubules provides a high osmotic pressure for the
removal of water.
• Transmembrane channels made of a protein
called aquaporin are inserted in the plasma
membrane greatly increasing its permeability to
water. (When open, an aquaporin channel
allows 3 billion molecules of water to pass
through each second.)
• Insertion of these water channels requires
signaling by the antidiuretic hormone
(ADH; also known as arginine
• Animation: Hormonal Communication
• The Mammalian Kidney
• Virtual Anatomy Lab