BIOL 005B Lecture Notes - Lecture 19: Osmoregulation, Osmotic Concentration, Cryptobiosis
BIOL 005B Lecture 19: Osmoregulation
●Osmoregulation regulates solute concentrations and balances the gain and loss of water
○Freshwater animals show adaptations that reduce water uptake and conserve
solutes
○Desert and marine mammals face reduced water loss and avoid excess solutes
●Excretion is the disposal of nitrogen containing metabolites and other waste products
●Osmolarity: Some Terms
○Cells require a balance between osmotic gain and loss of water
○Osmolarity, the solute concentration of a solution, determines the movement of
water across a selectively permeable membrane
○If two solutions are isosmotic, the movement of water is equal in both directions
○If two solutions differ in osmolarity, the net flow of water is from the hyposmotic
to the hyperosmotic solution
○Osmolarity is measured as: L solvent
# of moles solute
■You should think of this as the number of particles that can move in a
solution; they give the solution its osmotic potential (Osml/L)
●Osmoregulation balances the uptake and loss of water and solutes
○Osmoregulation is based largely on controlled movement of solutes between
internal fluids and the external environment
■Remember: Solutes will move down their “own” concentration gradient
●The concentration of each molecule will be the same
●Water will follow the concentration gradient of particles if possible
○Osmotic Challenges
■Only some marine animals are osmoconformers
●They are isosmotic with their surroundings and do not regulate
their osmolarity
●Euryhaline animals can tolerate a great deal of change
■Osmoregulators expend energy to control water uptake and loss in a
hyperosmotic or hyposmotic environment
●Animals that can not tolerate substantial changes are stenohaline
○Marine Animals
■Most marine invertebrates are osmoconformers
■Most marine vertebrates are osmoregulators
■Marine bony fishes are hyposmotic
to sea water
●They lose water by osmosis and gain salt by diffusion and from
food
●They balance water loss by drinking seawater and excreting salts
○Freshwater Animals
■Freshwater animals constantly take in water by osmosis from their
hyposmotic environment
■They lose salts by diffusion and maintain water balance by excreting large
amounts of dilute urine
■Salts lost by diffusion are replaced in foods and by uptake across the gills
○Animals That Live in Temporary Waters
■Some aquatic invertebrates in temporary ponds lose almost all their body
water and survive in a dormant state
●This adaptation is called anhydrobiosis
○Land Animals
■Land animals drink water, eat moist foods and use metabolic water (water
from the process of metabolism)
■Desert animals obtain major water savings from simple anatomical
features and behaviors such as a nocturnal lifestyle
●An animal’s nitrogenous wastes reflect its phylogeny and habitat
○The type and quantity of an animal’s waste products may greatly affect its water
balance
○Among the most important wastes are nitrogenous breakdown products of
proteins and nucleic acids
○Some animals convert toxic ammonia (NH3) to less toxic compounds prior to
excretion
●Diverse excretory systems are variations on a tubular theme
○The kinds of nitrogenous wastes excreted depend on an animal’s evolutionary
history and habitat
○Thus, the amount of nitrogenous waste is coupled to the animal’s energy budget
○Excretory systems regulate solute movement between internal fluids and the
external environment
○Excretory Processes
■Most excretory systems produce urine by refining a filtrate derived from
body fluids
●Key functions of most excretory systems:
○Filtration: pressure-filtering of body fluids
○Reabsorption: reclaiming valuable solutes from the filtrate
TO the blood or body fluids
○Secretin: adding toxins and other solutes from the body
fluids to the filtrate
○Excretion: removing the filtrate from the system
○A prototypical excretion unit
■Collect fluids
■Modify composition of fluids (Passive and Active Transport
)
■Expulsion of excretory fluid from body
○Kidneys
■Kidneys are the organs of excretion and osmoregulation in vertebrates
●In mammals, paired kidneys are the principal site of water balance
and salt regulation
○Structure of the Mammalian Excretory System
■Each kidney is supplied with blood by a renal artery and drained by a renal
vein
■Urine exits each kidney through a duct called the ureter
Document Summary
Osmoregulation regulates solute concentrations and balances the gain and loss of water. Freshwater animals show adaptations that reduce water uptake and conserve solutes. Desert and marine mammals face reduced water loss and avoid excess solutes. Excretion is the disposal of nitrogen containing metabolites and other waste products. Osmolarity: some terms water across a selectively permeable membrane. Cells require a balance between osmotic gain and loss of water. Osmolarity , the solute concentration of a solution, determines the movement of. If two solutions are isosmotic , the movement of water is equal in both directions. If two solutions differ in osmolarity, the net flow of water is from the hyposmotic to the hyperosmotic solution. You should think of this as the number of particles that can move in a. Osmoregulation balances the uptake and loss of water and solutes solution; they give the solution its osmotic potential (osml/l)
