Chapter 44: Osmoregulation
and Excretion
Overview: A Balancing Act
• Animals must maintain water and solute
concentration within certain limits.
– An extreme external environment can greatly impact
the the water to solute levels of an organism.
• Osmoregulation: how animals regulate solute
concentrations and balance the gain and loss of
water.
Overview: A Balancing Act
• Metabolism presents organism with problems
of waste disposal.
– The breakdown of nucleic acids and proteins have
a very toxic product of ammonia. Many animals
have adapted to meet these physiological
challenges
• Excretion: How animals dispose of nitrogencontaining waste products from metabolism.
Osmoregulation
• Balances the uptake and loss of water and
solutes.
Osmosis
• Water enter and leaves cells through the
process of osmosis.
• The difference in osmolarity (total solute
concentration expressed in moles) of two
solutions determines where the water is
moving.
Osmotic Challenges
• The Osmotic challenges an animal faces
depends on how it deals with its internal
osmolarity.
– Osmoconformer: An animal that does not need to
actively adjust its internal osmolarity because they
match the conditions of their environment.
– Osmoregulator: An animal that does not share the
same osmolarity with its environment and has the
need to adjust its internal concentrations.
• Osmoregulation requires an expense of
energy since active transport is used to
manipulate solute concentration in an
organisms cells.
Animal tolerance to change in
osmolarity
• Most animals are said to be either Euryhaline
or Stanohaline
• Euryhaline can live in environments of great
fluctuation in solute concentration.
• On the other hand, stanohaline cannot.
• Both can be either osmoconformers or
osmoregulators.
Osmoregulation adaptations in aquatic
life
• Marine Animals
– These animals are broken up into Osmoregulators and
Osmoconformers.
– Most invertebrate marine animals are Osmoconformers
– Some invertebrates and all vertebrates are Osmoregulators
• Many vertebrates like the bony fish are hypoosmotic to salty sea
water and take in solutes.
• Freshwater Animals
– These osmoregulatory animals are hyperosmotic
to their environment.
– Their body fluids are much more concentrated
then their freshwater habitat.
– Freshwater Animals adapted to there environment
by having a decrease in solute concentration from
their salt-water relatives.
• Animal living in temporary waters
– Some aquatic invertebrates like the tartigrade
(water bear) can lose almost all of their body
water and still survive.
– Tatrigrades have grown the adaptation known as
anhydrobiosis, which is living without water.
– The Tatrigade can live with reduced water weight
of 85%-2% for a decade.
Osmoregulation adaptation in
terrestrial animals
• Many land animals eat moist foods and use
metabolic water (water produced from
cellular respiration) to maintain water levels.
• Desert Animals have many adaptations and
strategy to conserve water
– Waxy cuticles
– Live nocturnally to reduce evaporation and take
advantage of the moist atmosphere
– Use large amounts of metabolic water
Transport Epithelia
• The composition of the cellular cytoplasm is usually
managed by an internal body fluid that surrounds the cells.
• Transport Epithelia are cells that control solute movement
through our internal body fluids.
– Solutes leaving or entering the body must pass through the
selectively permeable membrane of the Transport Epithelia.
Animal’s nitrogenous wastes reflect
phylogeny and habitat
• The type and amount of an organism’s waste products has a
lot to do with the animal’s water balance
• The most common nitrogenous waste product is the
extremely toxic ammonia (NH3).
Forms of Nitrogenous Waste
• Ammonia
– Ammonia can only be tolerated at low levels and
need a lot of water to dilute it.
• This is why ammonia excretion is very common in
aquatic life.
– Invertebrates can have ammonia released
throughout their whole body surface.
• Urea
– A combination of CO2 and ammonia that is formed
in the liver.
– 100,000 times less toxic then ammonia
– Disadvantage is that it takes sufficient energy to
create Urea through the liver’s metabolic
processes.
– Mammals, sharks, bony fish, amphibians, sharks
and turtles use Urea.
• Uric Acid
– Used by Insects, land snails, reptiles, and birds
– Relatively non-toxic
– Insoluble and is efficient for animals with little
water and/or a relatively dry environment.
– However, Uric Acid is the most energy insufficient
nitrogenous waste to produce.
Influence of Evolution and
Environment on Nitrogenous Wastes
• Uric Acid started to be naturally selected for
because soluble nitrogenous wastes could
dangerously accumulate in the embryo.
• Environmental factors
– Temperature: Higher the temperature, the less
water is available to dilute the waste
– Energy Available: How much and what kind of
food an organism eats
Diverse Excretory systems are
variations on a tubular theme
• Excretory Systems: controls fluid movement
between internal fluids and external
environment.
– Key to homeostasis
– Disposes metabolic wastes and controls the
composition of body fluids by adjusting the
amount of solute lost.
– http://www.youtube.com/watch?v=chhNaLi9P3E
Excretory processes
1. Filtration: Water and solutes (the filtrate) are
forced through a selectively permeable
membrane of many capillaries into the excretory
tubule.
2. Reabsorption: The transport epithelium finds
valuable substances of the filtrate and sends
them back to their bodily fluids.
3. Secretion: More toxins and excess ions were
added to the substances in the excretory tubule.
4. Excretion: The filtrate exits the body.
Types of Excretory Systems
• Protonephridia: Flame-Bulb Systems
– A network of dead end tubules that do not have internal openings.
– Water is provided from the Flame-Bulb and travels to the tubules. The
water is released into the outside world through openings known as
nephridiopores
– Tubules release for diluted urine.
• Metanephridia
– Internal openings that obtain body fluids
– Metanephridia are found in most annelids.
– Useful solutes are reabsorbed and nitrogenous
wastes are excreted.
– Also produce very diluted urine to balance the
water influx.
• Malpighian Tubules
– Insects and terrestrial anthropods
– Nitrogenous wastes are removed from
hemolymph.
– The is a key adaptation to conserve water for
terrestrial life through waste matter and feces
• Vertebrate Kidneys:
– Thrive in both osmoregulation and excretion
Nephrons and associated blood
vessels are the functional units of
the mammalian kidney
• A pair of mammal kidneys are responsible for
water balance and and salt regulation.
• Renal artery: The blood vessel that brings
blood to the kidney.
– Renal vein drains the blood.
• Urine travels from the two ureters in the
kidney to a urinary bladder and through the
urethra.
Structure and Function of the Nephron
and Associated Structures
Renal cortex and Renal Medulla are made of microscopic excretory
tubules and their blood vessels.
• The nephron is the functional area of the
kidney that includes one long tubule and a
cluster of cappillaries known as the
glomerulus.
• Filtration of the Blood
– The filtration of small molecules is non-selective
• Pathway of the Filtrate
– The filtrate travels through three segments of the
nephron
• Proximal tubule, the loop of Henle, distal tubule, and
finally the filtrate empties into the collecting duct.
• Nephron and collecting duct lined by a transport
epithelium that enables the filtrate to make urine.
• Blood Vessels Associated with the Nephrons
– Afferent arteriole: a type of renal artery that
subdivides into the capillaries of the glomerulus
– All nephrons take blood from an afferent arteriole.
– When capillaries leave the glomerulus and
converge to form an efferent arteriole. This
subdivides to create peritubular capillaries.
– The tubules and capillaries do not exchange
materials directly.
From Blood Filtrate to Urine
1. Proximal tubule- Secretion and reabsorbtion manipulate
the volume and composition of the filtrate.
–
A majority of the water and NaCl from the original filtrate is
reabsorbed
2. Reabsorbtion of water continues to occur. The filtrate
shifts to the descending limb of the loop of Henle.
3. Salt diffuses out of the permeable tubule into the
interstitial fluid.
4. Distal tubule: Regulates the balance in concentration of
K+ and NaCl.
5. Collecting Duct: The Filtrate is finally carried through
the medulla to the renal pelvis
The mammalian kidney’s ability to
conserve water is a clear terrestial
adaptation
• Urine can be filled with a diluted solute because then the organism will
not have too much water loss.
• Conserving water successfully Is very advantageous for terrestrial
organisms.
Solute Gradients and Water
Conservation
• Nephrons consume energy and produce a region of high
osmolarity.
• Filtrate flows from cortex to medulla and water leaves the
tubule through osmosis
The 1200 mos/ml enlarges
the amount NaCl that is
diffused out of the tubule
The Counter Current Multiplier System
• This system deals with the loop of Henle
• It keeps a high salt concentration in the
kidney, so urine is tightly compact with solute.
Regulation of Kidney Function
• Water in the kidney can be regulated by nervous
and hormonal control
• Antiuretic hormone: Increases water
reabsorption which as a result, reduces urine
volume.
• Renin-angiotensin-aldosterone system (RAAS):
This a complex feedback circuit that heavily
contributes to an organisms homeostasis.
• Atrial Natriuretic Factor-This has an opposing
process of the RAAS.
• All three factors create a system of checks and
balances that let the kidney properly control
– Osmolarity
– Salt concentration
– Volume
– Blood Pressure
Diverse adaptations of the vertebrate
kidney
• Different nephron structures can supply
species with osmoregulation that match up
with their environment.
Works Cited
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