ZOO 14 – Osmoregulation and Excretion

Osmoregulation

Animals must maintain appropriate levels of solutes and water in their tissues in order to function

Osmoregulation

regulation of water volume and salt concentration inside the animal body

Osmoregulation

at the cellular level, the cell membrane regulates entry and exit of molecules

Hypotonic

_____________ environment - cell bloats beyond its normal size

Isotonic

_______________ environment – cell maintains its shape

Hypertonic

________________ environment – cell shrinks as the net movement of water is out of the cell

Osmoconformers

Type of animals based on their osmotic regulation

match their body’s osmolarity to their environment

Osmoconformers

Type of animals based on their osmotic regulation

Most marine invertebrates

Osmoregulators

Type of animals based on their osmotic regulation

control levels of most of the ions in extracellular fluids,

Osmoregulators

Type of animals based on their osmotic regulation

employing a combination of ion absorption and excretion strategies

Stenohaline

Salinity tolerance of aquatic animals

tolerate a narrow range of salinity (freshwater or marine)

Euryhaline

Salinity tolerance of aquatic animals

tolerate a wide range of salinity

Excretion

• CO₂

• Nitrogenous wastes

____________

• Removal of metabolic wastes

  • _______ - removed during exhalation (external respiration)

  • _____________ – from breakdown of cellular proteins

Excretion

• Requires water → plays a role in osmoregulation

• Type of metabolic waste dependent on the animal’s habitat

Ammonia

Nitrogenous wastes

Highly toxic and requires plenty of water

Ammonia

Nitrogenous wastes

Most bony fishes and many aquatic animals

Ammonia

Nitrogenous wastes

Excreted through gills and diluted by surrounding water

Urea

Nitrogenous wastes

Mammals, sharks and adult amphibians

Urea

Nitrogenous wastes

Less toxic than ammonia; can be concentrated to conserve water and eliminated in urine

Urea

Nitrogenous wastes

Requires energy to be converted from ammonia in the liver

Uric Acid

Nitrogenous wastes

Insects, reptiles, and birds

Uric Acid

Nitrogenous wastes

Can be combined with little water to form a paste

Uric Acid

Nitrogenous wastes

Requires more ATP to be produced

Sponges (porifera), cnidarians, echinoderms

Osmoregulatory and excretory structures

These phyla possess no excretory organs

Sponges (porifera), cnidarians, echinoderms

Osmoregulatory and excretory structures

These phyla have nitrogenous wastes diffuse into the surrounding isosmotic water

Contractile vacuoles

Osmoregulatory and excretory structures

Freshwater sponges and Hydra possess _____________

Contractile vacuoles

Osmoregulatory and excretory structures

Expel excess water gained by osmosis

Nephridia

Most common type of invertebrate excretory organ

Nephridia

Tubular structures designed to maintain appropriate osmotic balance

• Protonephridia (sing. Protonephridum)

• Metanephridia (sing. Metanephridium)

Nephridia

Two types:

• _________________ – closed at the inner end

• _________________ – open at both ends

• Protonephridia (sing. Protonephridum)

• Metanephridia (sing. Metanephridium)

Name the two types of nephridia that reabsorb valuable solutes and remove nitrogenous wastes

Protonephridia

Type of invertebrate excretory organ

Flatworms and rotifers

Protonephridia

Type of invertebrate excretory organ

Each branch terminates in a “flame cell”

Protonephridia

Type of invertebrate excretory organ

Fluid enters the system through the flame cells

Protonephridia

Type of invertebrate excretory organ

Wastes expelled through nephridiopores and diffuse across body surface

Metanephridia

Type of invertebrate excretory organ

Annelids and mollusks

Metanephridia

Type of invertebrate excretory organ

Fluid swept into the tubule through a ciliated funnel-like opening, the nephrostome.

nephrostome

In the Metanephridia Fluid is swept into the tubule through a ciliated funnel-like opening, the _________.

Metanephridia

Type of invertebrate excretory organ

Surrounded by a network of blood vessels that assist in reabsorption of water and valuable materials such as salts, sugars, and amino acids

Arthropod excretory organs

Antennal, maxillary, and coxal glands

Arthropod excretory organs

probably originated from nephridia and are homologous with each other

Arthropod excretory organs

lack an open nephrostome and function by filtration through a closed filtration membrane

Arthropod excretory organs

Hemolymph pressure forces fluids, ions, and small molecules through the filtration membrane and into the tubule system

Antennal glands

Aquatic crustaceans excrete ammonia through this gland in their gills

Antennal glands

_________________ gland removes excess water and reabsorbs ions while discharging other nitrogenous wastes

Antennal glands

Also known as green glands in arthropods

Coxal glands

Gland common among arachnids (spiders, scorpions, ticks, and mites)

Coxal glands

Wastes are discharged through pores on one to several pairs of appendages near the proximal segment (coxa) of the leg

Malpighian tubules

Excretory (network of) organs Found in insects and myriapods

Malpighian tubules

Not nephridial in origin; derived from the gut

Malpighian tubules

Involves the active transport of potassium ions into the tubules from surrounding hemolymph

Malpighian tubules

Uric acid and water move into tubules via osmosis

• Water and ions reabsorbed in the rectum

From the graph, the crab keeps its internal (blood) salinity relatively constant even as the external water salinity changes → this means it osmoregulates.

Because estuaries fluctuate widely in salinity (5–25 ‰) and the crab tolerates this wide range, it is euryhaline.

So the correct interpretation is:

• A — They are euryhaline ✔

• C — They osmoregulate in those salinities ✔

Therefore D (A and C) is correct.

Correct answer: C. Metanephridium

Clams (bivalves) possess metanephridia, also called kidneys in mollusks.
You can even see it labeled as “Kidney” in the diagram.

Here’s why the other options are incorrect:

• A. Ctenidia → These are gills, not excretory organs.

• B. Protonephridium → Found in flatworms/larvae, not adult mollusks.

• D. Antennal gland → Found in crustaceans.

• E. Malpighian tubules → Found in insects and some arachnids.

So the excretory organ in clams = Metanephridium.

Correct answer: A. Marine sharks tend to gain water

Because:

• Marine sharks are slightly hyperosmotic to seawater (due to high urea + TMAO).

• Water moves from lower osmolarity → higher osmolarity.

• So seawater is slightly hypoosmotic relative to the shark’s internal fluids.

➡ Water naturally enters the shark’s body by osmosis.

This is why:

• Sharks do not drink seawater like bony fish.

• They produce very dilute urine to get rid of the excess water.

So the correct answer is A.

The statement that is NOT TRUE for adult frog kidneys is:

C. They have loops of Henle

Explanation:

• Adult frogs (amphibians) have opisthonephric kidneys → so B is true.

• Their kidneys are made of nephrons → A is true.

• Their nephrons contain glomeruli → D is true.

• BUT amphibians do not have loops of Henle; only mammals have them.
  Frogs cannot produce hyperosmotic urine for this reason.

✅ Correct answer: C

The correct answer is:

E. B and C

Why?

Alcohol is a diuretic, meaning it inhibits ADH (antidiuretic hormone).
Less ADH → kidneys reabsorb less water → more urine is produced.

So:

• B is true: You produce more urine.

• C is true: Excess water loss → risk of dehydration.

Therefore, the correct combination is:

✅ E. B and C

• Lose water through:

  • evaporation

  • urine

  • feces

• Gain water via:

  • food

  • metabolic

Water Balance in Terrestrial Vertebrates

• Terrestrial vertebrates evolved physiological mechanisms to avoid desiccation

• Lose water through:

  • _________ from the respiratory and body surfaces

  • excretion in ________

  • elimination in _______

• Gain water via:

  • Consuming water in _______

  • drinking water when available

  • retaining __________ water

Mucus

Integument as an osmotic barrier

an extracellular secretion of mucopolysaccharides, lipids, and proteins

Mucus

Integument as an osmotic barrier

Hydrophobic barrier

Mucus

Integument as an osmotic barrier

Lines vertebrate lungs and amphibian skin to reduce water loss

Stratum corneum in skin

Integument as an osmotic barrier

Keratinized to minimize desiccation

• skin; kidneys

Salt and water balance in frogs

• Water enters the highly permeable _____ and excess is excreted by __________.

• salt; salt; skin

Salt and water balance in frogs

• Must compensate for _______ loss by actively absorbing ________ from the water through their _______

• urinary bladder

Salt and water balance in frogs

• Urine flows into the ___________ where salts are reabsorbed

Desert animals

• At risk of dehydration

• Conserve water by excreting highly concentrated urine and minimizing evaporation from lungs and skin

Desert animals

Gain water from food but mostly from metabolic water

• salt glands

Marine birds and reptiles

• Have __________ to pump excess salt

Vertebrate kidneys

Osmoregulatory and excretory organ of vertebrates

Archinephros

Kidneys form embryologically from tissue that extends the length of the body cavity

_______________: Kidney found in embryo of hagfish; this is the inferred ancestral condition of the vertebrate kidney

_______________: Functional kidney in adult hagfish, a few bony fish species, and embryonic fishes and amphibians; fleeting existence in embryonic reptiles, birds, and mammals

First kidney to appear in all vertebrate embryos

• Located anteriorly in the body

_______________: Transient function in embryonic lampreys, fishes, amphibians, reptiles, birds, and mammals

• functional kidney of embryonic amniotes (reptiles, birds and mammals)

kidney made up of an increased number of nephrons, usually dozens to hundreds

Kidney that Allowed vertebrates to face the rigorous osmoregulatory and excretory demands of freshwater and terrestrial environments

_______________: Functional kidney of adult lampreys, fishes, and amphibians

Kidney Comprised of mesonephros and metanephros

_______________: Functional adult kidney of amniotes (reptiles, birds, and mammals)

Kidney More caudally located and more compact

• increased number of nephrons, (thousands to millions)

Kidneye Drained by a new duct, the ureter,

• Old archinephric duct was relinquished to the male reproductive system for sperm transport

ureter

In the metanephros, the kidney is drained by a new duct, called the ________,

Nephron

Functional unit of vertebrate kidneys

Renal cortex

Outer portion of kidney

Renal cortex

Contains the renal corpuscles and tubules (glomerular filtration)

Renal medulla

Split into renal pyramids

Renal medulla

Contains the loop of Henle and collecting ducts (maintain salt and water balance in blood)

Renal pelvis

Dilated portion of the ureter

Urine Formation

1. Filtration

   • Small molecules move across glomerular wall because of blood pressure

   • Filtrate is protein-free, otherwise same composition as blood plasma

2. Reabsorption

   • Salts and nutrients actively reabsorbed from convoluted tubules

3. Secretion

   • Removes ammonia, uric acid, hydrogen ions, creatinine and penicillin which are secreted into convoluted tubules

Urine Formation

1. ____________

   • Small molecules move across ____________ because of blood pressure

   • Filtrate is protein-free, otherwise same composition as blood plasma

2. ____________

   • Salts and nutrients are actively reabsorbed from ____________

3. ____________

   • Removes ammonia, uric acid, hydrogen ions, creatinine, and penicillin which are secreted into ____________

• permeable

• impermeable; permeable

Kidneys concentrate urine to maintain salt-water balance

• Loop of Henle has a descending and ascending limb

  • Descending limb – _________ to water

  • Ascending limb – _________ to water, __________ to salt ions

countercurrent multiplication

Kidneys concentrate urine to maintain salt-water balance

Solute concentration increases near the inner renal medulla because of _________________

anti-diuretic hormone (ADH)

Kidneys concentrate urine to maintain salt-water balance

Collecting duct can be made more porous to reabsorb water by the ______________ hormone

• Make urine concentrated