Transcript homeostasis and excretion [3]

Osmoregulation and
Excretion:
Sections 44.2,44.3, and
44.5 w/ some IB Topics
Deanna, Stephanie, & Christen
Nitrogenous Wastes

Breakdown products of proteins and nucleic acids

Ammonia: very soluble, highly toxic, tolerable only at low
concentrations; excreted b/c animal needs access to lots of
water; aquatic species; readily lost by diffusion across body
surface / thru gills to surrounding H2O

Urea: terrestrial animals (b/c less access to water for ammonia
release); “produced in the vertebrate liver by a metabolic cycle
that combines ammonia w/ CO2; 100,000x less toxic than
NH3; disadvantage: must expend energy to produce urea from
NH3

Uric Acid: relatively nontoxic; in insects, land snails, reptiles,
birds; largely insoluble in water & excreted as semi-sold paste
w/ lil water loss; adv for animals w/ lil water access but lots of
energy to produce (so lots of ATP needed)
Proteins
Nucleic acids
Nitrogenous bases
Amino acids
Pg. 927
–NH2
Amino groups
Most aquatic
animals, including
most bony fishes
Many reptiles
(including
birds), insects,
land snails
Mammals, most
amphibians, sharks,
some bony fishes
O
H
C
O
Ammonia
C
O
NH2
Urea
C
C
C
N
C
NH2
NH3
HN
N
N
H
H
Uric acid
O
Influence of Evolution and
Environment on Nitrogenous Wastes


Depends upon an animal’s evolutionary history and
habitat – esp availability of water
Mode of reproduction affected which kind


Adjusting to environment


Shelled egg vs. shell-less egg or mammalian embryo
Ex: certain tortoise changes from urea to uric acid when
temp increases and water less available
Amount produced depends on ‘energy budget’ –
type of food

Ex: endotherms eat more food so more wastes
IB Syllabus!
Arrows
pointing to
the IB slides
in this
presentation.
11.3.9: Explain the presence of glucose
in urine of untreated diabetic patients

Glucose is often present in the urine of
untreated diabetic patients. This is because
the glucose concentration of blood rises
much higher than 90 mg per 100 ml, so the
pumps in the proximal convoluted tubule
can’t reabsorb all the glucose that is filtered
out into the glomerulus.
11.3.8: Explain the differences in concentration of
proteins, glucose and urea between blood plasma,
glomerular filtrate and urine.
Comparison of Fluid in the Kidney
Content (mg per 100mg of blood)
Blood in
renal artery
Urine
Glomerular
filtrate
Blood in
renal veins
Glucose
90
0
90
90
Urea
30
2000
30
24
Proteins
740
0
0
740

Remember
drawing this
from
yesterday?
The next
slide helps
explain in
more detail.
11.3.4: Explain the process of ultrafiltration,
including blood pressure, fenestrated blood
capillaries, and basement membrane.




Function of glomerulus is production of filtrate from blood by
ultrafiltration
Blood plasma escape through walls of capillaries [remember
video?], but in glomerulus 20% escapes (more than usual)
Why this happens:
 Blood pressure very high b/c efferent arteriole is narrower than
afferent arteriole
 Capillaries in the glomerulus are fenestrated (porous)
 These pores are large enough to let any molecules through, but
on the outside of the capillary wall is a basement membrane
composed of a gel of glycoprotein. It lets all substances in the
blood plasma through except plasma proteins.
The fluid produced by ultrafiltration is collected by the Bowman’s
capsule and flows on into the proximal convoluted tubule.
11.3.7: Explain the roles of the loop of Henle,
medulla, collecting duct and ADH (vasopressin) in
maintaining the water balance of the blood. (pg102)
Survey of Excretory Systems - Intro


Various excretory mechanisms have evolved
in animals for the purpose of osmoregulation
and for the removal of toxins.
Toxins include by-products of cellular
metabolism, such as the nitrogen wastes.
Contractile Vacuoles


Found in the cytoplasm of various protists,
such as paramecia and amoebas.
These vacuoles accumulate water, merge
with the plasma membrane, and release the
water to the environment.
Flame Cells






Aka protonephridium
Flatworms.
Network of dead-end tubules
lacking internal openings. The
cells are distributed along a
branched tube system that
permeates the flatworm.
Body fluids are filtered across the
flame cells whose internal cilia
move the fluids through the tube
system.
Wastes (water and salts) are
excreted from the tubule system
through pores that exit the body.
Tubules reabsorb most solutes
before the urine exits the body so
the urine is dilute.







Aka Metanephridia
Unlike previous, has internal openings
Earthworms.
Occur in pairs within each segment of the earthworm. Interstitial fluids
enter through a cilated opening called a nephrostome.
Fluids concentrated as they pass through the collecting tubule which
includes a storage bladder that opens to the outside through a pores.
As urine moves along the tubule, most solutes are reabsorbed and
returned to the blood in the capillaries. Nitrogenous wastes remain and
are excreted outside.
Live in damp soil and absorb water through osmosis. They balance water
influx by making diluted urine.
Nephridia
Malpighian Tubules



Insects and other terrestrial
arthropods.
Tubes attached to the
midsection of the digestive
tract collect body fluids from
the hemolymph that bathe the
cells.
Fluids which include both
nitrogen wastes and materials
to be retained (salts and
water), are deposited to the
midsection.
• As fluids pass near the rectum, most solutes are pumped
back into the hemolymph.
• The nitrogenous wastes are eliminated as nearly dry
matter along with the feces.
Kidney



The last one..
Kidneys.
But you all should be experts on that now.
Teehee.
Regulation of Kidney Functions:
Hormones






These hormones influence osmoregulation by
regulating the concentration of salts in the
urine:
ADH
JGA
Angiotensin II
Aldosterone
ANF
Antidiuretic Hormone (ADH)





Increases the reabsorption of water by the body and
increases the concentration of salts in the urine.
It does this by increasing the permeability of the
collecting duct to water.
Urine becomes more concentrated as water diffuses
out of the collecting duct as the filtrate descends into
the renal pelvis.
Recall its position: Posterior Pituitary
Recall process of Feedback Inhibition
Juxtaglomerular Apparatus
(JGA) to Angiotensin II




Location: near afferent arteriole that supplies blood
to the glomerulus
When blood pressure/volume drops, an enzyme
(renin) aids in producing a peptide called
angiotensin II.
This hormone raises blood pressure by constricting
arterioles, decreasing blood flow to many capillaries,
like in the kidney.
Also stimulates the proximal tubules of the nephrons
to reabosorb more NaCL and water which reduces
the amount of both in the urine.
Aldosterone



This hormone acts on the nephrons’ distal
tubules making them reaborb more sodium
(Na+) and water allowing for further increase
of blood volume/pressure
It does this by increasing the permeability of
the distal tubule and collecting duct to Na+
As a result, more Na+ diffuses out of this
tubule and duct allowing for water to passive
flow.
In summary so far, RAAS



Starting basically from the JGA to
Aldosterone, that whole process is called
RAAS
When blood pressure drops, JGA is released
and aids in rising it again with angiotensin II
and aldosterone.
So, the first hormone ADH and the RAAS
process raise blood pressure. Isn’t this a bit
redundant?
ADH vs RAAS




Both increase water reabsorption, but counter
different osmoregulatory proglems.
ADH is a response to body dehydration.
A loss of both salt and body fluids such as an
injury or severe diarrhea will reduce blood
volume without increasing osmolarity.
This will not induce a change in ADH release
but RAAS will respond by increasing water
and Na+ reabsorption.
Atrial Natriuretic Factor (ANF)





This hormone opposes the former RAAS
Recall renin, the enzyme that helped make
JGA
ANG inhibits the release of renin, inhibits
NaCl reabsorption by the collecting ducts,
and reduces aldosterone release.
This basically lowers blood volume/pressure.
Thus, ADH, RAAS, and ANF is basically a
biological check and balance system
Guess what?!




No more new info! Review if time.
Enjoy your 3 day weekend!
=]
Study away for those exams….=/