Transcript Homeostasis – steady state of physiological

Osmoregulation &
Excretion
Kevin Kwan
Jeffery Khou
Jessica Dai
Jason Yiu
Introduction to Osmoregularity and Excretion
•The physiological systems of animals operate within a
fluid environment
•The relative concentration of water and solutes must be
maintained
•Metabolism presents organisms with the problem of
waste disposal thus animals use two key homeostatic
processes:
- Osmoregulation – how animals regulate
solute concentrations and balance the gain
and loss of water
- Excretion – how animals get rid of nitrogencontaining waste products of metabolism
Homeostasis – steady state of physiological condition of
the body
Osmosis and -osmotic
•All animals face the central problem of
osmoregularity. The rates of the uptake and loss
of water must balance. This is done with the help
of osmosis.
-Osmosis:diffusion or movement of water
across a selectively permeable
membrane
•Osmolarity happens when two solutions,
separated by a membrane, differ in osmolarity.
-Osmolarity: total solute concentration
expressed as molarity, or moles of solute
per liter of solution
Osmosis and –osmotic cont.
•Different terms relating to osmolarity:
-Isoosmotic: refers to two solutions of the same
molarity that are separated by a selectively
permeable membrane. There is no net
movement of water between the solutions,
although water molecules are continually
crossing the membrane at equal rates in both
directions
-Hyperosmotic: refers to the solution that has
the greater concentration of solutes
-Hypoosmotic: refers to the solution that has
the more dilute solution
•Thus, when the osmolarities of solutions differ, water
flows by osmosis from a hypoosmotic solution to a
hyperosmotic solution
Osmotic Challenges
•There are two basic solutions to the problem of balancing water gain
with water loss. One is to be an osmoconformer.
- Osmoconformer: an animal that does not actively
adjust its internal osmolarity. The internal osmolarity
is the same as that of its environment. There is no
tendency to lose or gain water, and they often live in
water with stable composition, so as to keep a
constant internal osmolarity.
Another is to be an osmoregulator.
-Osmoregulator: an animal that must control its own
osmolarity because its own body fluids are not
isoosmotic with its outside environment.
If the environment is hypoosmotic, an osmoregulator must discharge
extra water.
If the environment is hyperosmotic, an osmoregulator must take in
water to offset osmotic loss.
•Nonetheless, osmoregulation costs energy depending on the
difference between its osmolarity and its surroundings.
Osmotic Challenges cont.
•Most animals, though, are stenohaline animals:
-Stenohaline: animals (osmoconformers/
osmoregulators) that cannot tolerate
substantial changes in external
osmolarity.
In contrast, some are:
-Euryhaline: animals (certain
osmoconformers/ certain
osmoregulators) that can survive large
fluctuations in external osmolarity.
Osmoregulation and adaptation and water balance
•Marine Animals, Freshwater Animals, Animals of
Temp Waters, Land animals
•Most marine invertebrates are
osmoconformers. But, the concentration of
its specific solutes differ from each other.
Thus, even an osmoconformer regulates its
internal composition of solutes. The ocean
is a strongly dehydrating environment
because it is much saltier, thus:
Marine animals: drink large amount of
seawater; gills dispose sodium chloride;
kidney disposes excess calcium,
magnesium, and sulfate ions or uses the
rectal gland and feces to excrete salt and
water slowly enters the body by osmosis
and food.
•Freshwater animals constantly gain water
and lose salts, thus:
Freshwater animals: Excrete large amount
of dilute urine, salts are replenished by food
and by uptake across the gills.
Osmoregulation and adaptation and water balance cont.
•Animals that live in temporary waters can withstand huge
fluctuations of moisture in their environments.
(Anhydrobiosis: survival in a dormant state when one habitat
dries up) Their habitats may dry up, thus:
Animals that live in temporary water (and hydrobiotic
animals): utilize large amounts of sugar (trehalose)
•Land animals face the threat of desiccation as a major
regulatory problem, thus
Land animals: utilize adaptations that reduce water loss
such as body coverings, some are nocturnal, drinking and
eating moist food and by using metabolic water, and simple
anatomical features
Countercurrent heat exchange
•Four processes that account for heat exchange:
conduction (direct transfer of heat), convection
(transfer of heat by movement of liquid or air
against the body), radiation (the emission of
electromagnetic waves produced by something
containing heat), evaporation (loss of heat from
the surface of a liquid that is losing some of its
molecules as gas).
•Circulation aids in heat exchange: it alters the
amount of blood flowing to the skin; increased
blood flow usually results in vasodilation
(increase in diameter of superficial blood vessels)
causing more blood flow, thus heat transfer.
Vasoconstriction reduces the blood flow and heat
loss by decreasing the diameter of the blood
vessels.
Countercurrent heat exchange cont.
•Countercurrent heat exchange involves a
special arrangement of arteries and veins
•The countercurrent heat exchange conserves
heat by arteries that carry warm blood which
circulate through limbs, which come into
contact with veins that convey blood in the
opposite direction. This arrangement
facilitates heat transfer from arteries to veins
along the entire length of the blood vessel.
•Examples of how an ectotherm maintains
higher than expected temperature: behavioral
adaptations (seek ideal environments),
physiological adaptations (vasoconstriction).
Countercurrent heat exchange cont.
•How feedback mechanism regulates temperature
(and diagram): nerve cells that control
thermoregulation, concentrated in the
hypothalamus, contain a thermostat that responds
to change in body temperature above/below a set
point by activating mechanisms that promote heat
loss/gain (located in the skin).
Others are cold receptors and respond by
inhibiting heat loss mechanisms and activate heatsaving ones (vasoconstriction, erection of fur,
heat-generating mechanisms).
In response to elevated temperatures: shuts down
heat-saving mechanisms, promotes cooling
(vasodilation, sweating, panting)
Transport Epithelia
•The ultimate function of
osmoregulation is to maintain
composition of cellular cytoplasm, by
managing the composition of the
internal body fluid that bathes the cells
(insects and other animals with an
open circulatory system: hemolymph;
vertebrates with closed circulatory
system: interstitial fluid)
•Transport epithelium: layer or layers of specialized epithelial cells that
regulates solute movements, essential components of osmotic regulation/
metabolic waste disposal
•Seagulls and high salt diet: The nasal glands secrete a fluid much saltier
than that of ocean water so even if the bird drinks ocean water, the net gain
is water. Salt glands empty it via a duct into the nostrils and the salty
solution either drips off the tips of the beak or is exhaled in a fine mist.
Nitrogenous waste
•Metabolic waste in general: must be
dissolved in water, type and quantity have
a large impact on water balance
•Different types of waste:
-Ammonia: soluble but tolerated
at very low concentrations
-Urea: low toxicity, combination of
ammonia and carbon dioxide and
high concentrations
-Uric Acid: relatively non toxic,
insoluble in water, semi-solid
paste with very little water loss
Nitrogenous waste cont.
•The kinds of nitrogenous waste depend on
the animal’s evolutionary history and habitat
(influence). If there is minimal water, uric acid
rather than urea may be the favored waste
products because it needs less water to be
produced. Also, different waste products are
a result with different forms of reproductions.
For some animals such as tortoises, if temperature changes and goes
up, or if water becomes less available, uric acid will be produced, for
example, in place of urea. Evolution determines the limits of
physiological organisms and organisms make physiological adjustments
within these evolutionary constraints. It is also dependent on the energy
budget, which is affected by the food in the habitat.
Excretory Process
•First, body fluid is collected, involving filtration
through selectively permeable membranes (filtrate)->
selective reabsorption-> secretion-> excretion.
-Filtration: blood or other body fluids
are exposed to filtering device of
selectively permeable membranes of
transport epithelia
-Selective reabsorption: excretory systems
use active transport to reabsorb valuable
solutes (glucose, certain salts, amino acids)
-Secretion; solutes are removed from
animal body fluids and added to the
filtrate
-Excretion: disposal of nitrogencontaining waste products of
metabolism
Excretion cont.
Different excretory systems:
•Protonephridia: Flame-Bulb System
Flatworms utilize
protonephidium: a network
of dead-end tubules lacking
internal opening.
•Metanephridia:
It is another type of tubular
excretory system; has
internal openings that collect
body fluids.
•Malphighian tubules:
A type of tubular excretory
system in which organs in
insects and other terrestrial
arthropods remove
nitrogenous wastes and also
function in osmoregulation.
Excretion cont.
Metanephridia of
Earthworm
Excretion cont.
Malpighian Tubules of insects
Nephron and Associated Structures
Structure and Function of the Nephron:
-nephron: functional unit of the vertebrate
kidney
-renal cortex: outer part of a mammalian kidney
-renal medulla: inner part of a mammalian
kidney
-glomerulus: single long tubule and a ball of
capillaries
- Bowman’s capsule: blind end of a tubule that
forms a cup-shaped swelling surrounding the
glomerulus.
80% of the nephrons in the human kidney are
cortical nephrons and they have reduced loops
of Henle. Juxtamedullary nephrons are about
20% and have well-developed loops that extend
deeply into the renal medulla.
Excretion cont.
Renal Medulla
The relationship of the
Posterior Vena cava
vein
Renal cortex
Kidney
kidney and the circulatory Renal artery and
Aorta
Renal pelvis
Ureter
system: The kidneys
Urinary Bladder
Ureter
Urethra
produce urine and regulate
the composition of the
Bowman’s capsule
Cortical nephron
Glomerulus
Juxtamedullar
Afferent arteriole
blood. The urine is
Proximal tubule nephron
from renal artery
Peritubular capillaries
conveyed to the urinary
Efferent arteriole from
Renal cortex
Distal tubule
bladder via the ureter and glomerulus
Branch of
to the outside via the
renal vein
Collecting duct
urethra. Branches of the
Descending
Renal medulla
limb
aorta, retinal arteries, Loop of Henle Ascending
limb
convey blood to the
Vasa recta
kidneys; renal veins drain
blood from the kidneys into
the posterior vena cava.
Nephron and Associated Structures
Filtration of the Blood: It occurs as blood
pressure forces fluid from the blood in the
glomerulus into the lumen of the Bowman’s
capsule. It contains a variety of substances
including nitrogenous wastes.
Pathway of the filtrate: (Blood filtrate to Urine)
proximal tubule-> Descending limb of the loop
of Henle-> Ascending limb of the loop of Henle> Distal tubule-> Collecting duct-> renal pelvis> drained by ureter
Blood Vessels Associated with the Nephrons
Afferent arteriole: supplies blood
to each Nephron
Efferent arteriole: formed by the
capillaries that converge as they
leave the glomerulus
Peritubular capillaries: formed
by vessels subdividing
Vasa recta: capillaries that serve
the loop for Henle
Solute Gradients and Water Conservation
•The cooperative action and
precise arrangement of the loops of
Henle and the collecting ducts are
responsible for the concentration of
urine
•The nephrons, especially the
loops of Henle, consume energy to
produce a region of high osmolarity
in the kidney, which extract water
from the filtrate.
How the human kidney concentrates urine
Regulation of Kidney Function
One of the most important aspects of the mammalian
kidney is its ability to adjust both the volume and
osmolarity of urine depending on the animals’ water
and salt balance and rate of urea production.
•Filtrates starts at the Bowman's capsule which then leads
to the proximal tubule, the filtrate starts at an osmolarity of
300 mosm/L.
•In the proximal tubule, a large amount of water and salt
is reabsorbed, which decreases the volume of the filtrate,
because both water and NaCl is lost, osmolarity remains
the same.
•As the filtrate flows from the cortex to the outer medulla,
in the descending limb of the loop of Henle, water leaves
the tubule by osmosis. Osmolarity increases, and the
highest osmolarity of NaCl occurs here, at 1,200 mosm/L.
•As it rounds the curve and starts to ascend the next limb,
which is only permeable to salt, not to water.
•This loss of water and NaCl maintains the osmolarity of
the interstitial fluid in the kidney.
Hormonal Control of the Kidney by Negative Feedback Circuits
Regulation of Kidney Functions
• One of the most important aspects of the
mammalian kidney is its ability to adjust both
the volume and osmolarity of urine, depending
on the animal’s water and salt balance and the
rate of urea production. This versatility in
osemoregulatory function is managed with a
combination of nervous and hormonal controls.
ADH: antidiuretic hormone - Produced in
the hypothalamus, stored in and released
from the posterior pituitary gland,
osmoreceptor cells monitor the osmolarity of
the blood. If it rises about a set point of 300
mosm/L, more ADH is released into the
bloodstream/reaches kidney. The main
targets are the distal tubules and collecting
ducts where it increases the permeability of
the epithelium to water, amplify water
reabsorption, reduce urine volume and
prevent further increase of blood osmolarity
above the set point. If negative feedbackless ADH. Only gain of additional water in
food/drink can bring osmolarity back. Large
intake of water-> little ADH is released thus
decreases permeability of the distal tubules
and collecting ducts (more urine).
•· JGA: juxtaglomerular apparatus: locate
near the afferent arteriole that supplies
blood to the glomulus. When
pressure/blood volume drops, enzyme
rennin initiates chemical reactions that
convert a plasma protein called
angiotensinogen to a peptide called
angiotensin II-> raises blood pressure by
constricting arterioles, decreasing blood
flow to many capillaries, stimulates proximal
tubules to nephrons to reabsorb more NaCl
and water (raises blood volume/pressure),
stimulation of adrenal glands to release a
hormone called aldosterone (causes
reabsorption of sodium and water,
increasing blood volume/pressure).
·
RAAS: renin-angiotensin-aldosterone
system: part of a complex feedback circuit that
functions in homeostasis, drop in blood
pressure/blood volume triggers renin release
from JGA. In turn, rise in blood pressure/volume
from various actions of angiotensin II/aldsterone
reduce the release of renin.
·
ADH vs RAAS: ADH is a response to an
increase in osmolarity of the blood and lowers
blood sodium ion concentration by stimulating
water reabsorption in the kidney. RAAS
responds to a fall in blood volume/pressure by
increasing water and sodium ion reabsorption.
ANF: atrial natriuretic: a hormone/peptide that
opposes the RAAS. Walls of atria of the heart
release ANF in response to an increase in
blood volume/pressure and inhibits the release
of renin from JGA, NaCl reabsorption by the
collecting ducts, reduces aldosterone release
from the adrenal glands, and lower blood
volume and pressure.
All animals have different habitats, functions
of osmoregulations, physiological machines
(organs) to maintain solute and water
balance and excreting nitrogenous wastes.
EXTRA CREDIT: Amoeba vs. Human
AMOEBA
-water enters amoeba by osmosis
-excess water collects in the
contractile vacuole(contains water
soluble nitrogenous wastes)
-osmoregulation is the main
function of the contractile vacuole
-EXCRETION: when the
contractile vacuole is full and is
ready to burst, it goes to the
surface of the amoeba and uses
energy from the mitochondria to
release all the nitrogenous wastes.
-Then, a new contractile vacuole is
formed and water enters the
amoeba and the same steps
repeat.
^
THAT IS SOOO COOL!!!
O.O xP
EXTRA CREDIT CONT.
OSMOREGULATION:
The way us humans utilize osmoregulation
is we drink fresh water to re-hydrate and
also to balance out the salt and sugar level
in our bodies.
EXCRETION:
Unlike the Amoeba, the excretory process
for human includes filtration, selective
reabsorption, secretion, and excretion, and
they take place respectively. The liquid goes
through the kidney, where absorption and
secretion takes place, and filters out the
unnecessary material, also known as
excretion. Humans cannot take in as much
salt in the body as some animals can,
because our kidney will have to work very
hard to get all the salt out of our body, since
we don’t have other excretory systems in
our body.