Lecture 6 - Water and Ionic Balance Kidney Function (29.2)
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What is osmotic pressure?
A measure of the total concentration of solutes in a solution.
what does osmotic pressure determine?
direction of water movement
In what direction does water move during osmosis?
From an area of lower osmotic pressure toward an area of higher osmotic pressure.
Why does water move toward the side with more dissolved solutes?
The side with more dissolved particles has a higher osmotic pressure
What does isosmotic mean?
Two solutions have the same osmotic pressure.
What does hyperosmotic mean?
solution with higher osmotic pressure
What does hyposmotic mean?
solution with a lower osmotic pressure
low osmotic pressure = _____ solute concentration
low
high osmotic pressure = _____ solute concentration
high
How can two isosmotic solutions differ in ionic composition?
They can have the same total osmotic pressure but different concentrations of ions.
How do the body fluids of freshwater animals compare with freshwater?
Their body fluids are hyperosmotic to the surrounding freshwater.
What happens to water in a freshwater fish?
constantly diffuses into tissues
What happens to Na⁺ and Cl⁻ in freshwater fish?
constantly diffuse out
How do freshwater fish remove excess water?
They produce large amounts of dilute urine.
How do freshwater fish replace Na⁺ and Cl⁻ that are lost to the environment?
They actively transport the ions back into the body.
What type of osmotic regulator is a freshwater fish?
A hyperosmotic regulator.
How do most marine invertebrates compare osmotically with seawater?
isotonic with seawater
What is an Osmotic conformer?
An animal whose body-fluid osmotic pressure approximately matches its environment.
How do marine bony fish compare osmotically with seawater?
They are hyposmotic to seawater.
What happens to water in a marine bony fish?
Water tends to leave the fish by osmosis.
What happens to salts in marine bony fish?
Excess ions enter by diffusion
How do marine bony fish replace the water they lose?
They drink seawater.
Where are excess ions removed in marine bony fish?
Mainly through the intestine and gills.
marine bony fish are known as...
hypoosmotic regulators
How do the osmotic problems of freshwater and marine bony fish differ?
Freshwater fish gain water and lose salts while marine fish lose water and gain salts.
What do freshwater and marine bony fish have in common physiologically?
Both use energy for active ion regulation.
Why do many seabirds, marine lizards, and sea turtles experience high salt intake?
Their marine foods contain large amounts of salt.
What are salt glands?
Specialized organs outside the kidneys that excrete excess salt.
What does the term extrarenal mean?
Outside the kidneys.
What energy source allows salt glands to excrete concentrated salt?
ATP.
some fish migrate between ______ and ______
rivers and oceans
Where do salmon begin early development?
Freshwater.
Where do salmon complete much of their growth?
The ocean.
Where do salmon return to reproduce?
Freshwater.
What type of osmotic regulator is a salmon in freshwater?
A hyperosmotic regulator.
What type of osmotic regulator is a salmon in seawater?
A hyposmotic regulator.
Which hormone promotes the transition toward seawater physiology in salmon?
Cortisol
What effect does cortisol have on salmon gills?
chloride cells in gills pump salts out
Which hormone promotes freshwater physiology in salmon?
Prolactin
What effect does prolactin have on salmon gills?
chloride cells reverse to pump salts in
How does salinity tolerance vary among osmoconformers?
Some tolerate only narrow salinity ranges, while others tolerate wider ranges.
Which Osmotic conformer example tolerates a relatively broad range of salinity?
Mussels.
some coastal invertebrates are _______ _______
osmotic regulators
What is an osmoregulator?
An animal that maintains a relatively constant internal osmotic pressure despite environmental changes.
Which coastal invertebrate is an example of an osmotic regulator?
The blue crab.
What metabolic processes produce nitrogenous wastes?
Metabolism of proteins and nucleic acids.
What environmental factor strongly influences which nitrogenous waste an animal excretes?
Water availability.
What are the three major nitrogenous wastes?
Ammonia, urea, and uric acid.
Which animals commonly excrete ammonia?
Most aquatic animals that breathe water.
How toxic is ammonia compared with urea and uric acid?
Ammonia is highly toxic.
Why can many aquatic animals safely excrete ammonia?
It is highly water-soluble and can be easily diluted
Which nitrogenous waste requires the greatest amount of water for safe excretion?
Ammonia.
Which animals commonly excrete urea?
Most terrestrial animals.
How does the toxicity of urea compare with ammonia?
Urea is less toxic.
What metabolic disadvantage does urea have compared with ammonia?
more metabolically expensive
Which 3 animals commonly excrete uric acid?
Insects, reptiles, and birds.
Which nitrogenous waste is the most energetically expensive to produce?
Uric acid.
Why is uric acid useful in dry environments?
It is highly insoluble
Which nitrogenous waste conserves the greatest amount of water?
Uric acid.
What tradeoff exists among ammonia, urea, and uric acid?
Greater water conservation usually requires greater metabolic energy.
How would you rank the three wastes from most to least water required?
Ammonia → urea → uric acid.
What are the four basic renal processes?
Filtration, secretion, reabsorption, and osmoconcentration.
What is filtration?
Water and small solutes cross a barrier while cells and large molecules remain behind.
What is filtrate?
Fluid that has passed through the filtration barrier into the renal tubule.
What is secretion?
Selective movement of substances from the blood/body into the renal tubule for excretion
in secretion, what moves the specific solutes into the tubule lumen for excretion?
transport epithelia
What is reabsorption?
Movement of solutes and water back into body from the tubule lumen
How do secretion and reabsorption differ?
Secretion moves substances into the tubule; reabsorption moves them out of the tubule and back into the body.
How does filtration differ from secretion?
Filtration broadly passes small substances through a barrier, while secretion selectively transports specific substances.
What is osmoconcentration?
Removal of water from lumen and leaves solutes behind.
What effect does osmoconcentration have on the tubular fluid on the lumen?
It makes the excretory fluid more concentrated.
What are protonephridia?
Renal organs found in simple invertebrates.
What is unusual about the ducts of protonephridia?
They have blind ends projecting into the body cavity.
What drives ultrafiltration in protonephridia?
Cilia movement of fluid outward
What drives ultrafiltration in mesonephridia and metanephridia?
Fluid pressure.
Why is a circulatory system important for pressure-driven renal filtration?
The circulatory system supplies the pressure needed to drive fluid through filtration barriers.
Where are mesonephric tubules commonly found?
Aquatic vertebrates.
Where are metanephric tubules commonly found?
Terrestrial animals.
What process drives filtration or fluid formation in Malpighian tubules?
Active secretion of ions.
Which animals use Malpighian tubules?
Arthropods.
What organs form urine in vertebrates?
The kidneys.
Where are the kidneys located?
On the dorsal side of the abdominal cavity.
What vessel carries blood into a kidney?
The renal artery.
What vessel carries blood away from a kidney?
The renal vein.
What tubes carry urine away from the kidneys?
Ureters.
Where do the ureters empty in mammals, fish and amphibians?
Into the urinary bladder.
What is the function of the urinary bladder?
Storage of urine.
Where may ureters empty in reptiles and birds?
Into the hindgut.
What structure carries urine from the bladder to the outside?
The urethra.
What urinary pathway should you memorize?
Kidney → ureter → bladder → urethra → outside.
What is a nephron?
The smallest functional unit of the kidney.
Approximately how many nephrons are found in one human kidney?
About one million.
What two major components make up a nephron?
A tubular component and an associated vascular component.
What structures make up the vascular component of a nephron?
1. Afferent arteriole
2. glomerulus
3. efferent arteriole
4. peritubular capillaries
What is the function of the afferent arteriole?
It carries blood toward the glomerulus.
What is the glomerulus?
A small, tangled cluster of capillaries where plasma is filtered.
What kind of fluid does the glomerulus filter into the nephron?
A protein-free plasma
What is the function of the efferent arteriole?
It carries blood away from the glomerulus.
What are peritubular capillaries?
Capillaries surrounding renal tubules that exchange substances with tubular fluid.
What is the nephron vascular sequence?
Afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries.