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36.1 Animal Excretory Systems
All of these functions are important to good health.
Compare and contrast the excretory organs of animals.
osmoregulation is an important part of maintaining homeostasis in animals.
Excess nitrogen must be excreted when the breakdown of nitrogen-containing molecule results in excess nitrogen.
When the body breaks down amino acids to generate energy or convert them to food, they must be removed because they are not needed, and they may be toxic at high levels.
This excess nitrogen can be removed from the body in the form of ammonia, urea, or uric acid.
Carbon chains and amino groups are the result of the breakdown of proteins.
The carbon chains can be used as an energy source, but they have to be removed from the body.
NH3 is formed by the addition of a third hydrogen ion.
This reaction doesn't require a lot of energy.
Ammonia can be a nitrogenous excretory if enough water is available to wash it from the body.
Most fishes and other aquatic animals excrete Ammonia when they are in direct contact with the water of the environment.
mammals and sharks excrete their main nitrogenous waste.
Ammonia is much more toxic than urea and can be excreted in a concentrated solution.
An advantage for animals with limited access to water is the elimination strategy.
The production of urea requires the expenditure of energy because it is produced in the liver by a set of energy-requiring enzymatic reactions.
In this cycle, carrier molecules take up carbon dioxide and ammonia and release urea.
Uric acid is synthesised by a long, complex series of enzymatic reactions that requires more energy than urea synthesis.
Uric acid isn't very toxic and it isn't verysoluble in water.
Uric acid can be concentrated more readily than urea, so poor solubility is an advantage.
insects, reptiles, and birds excrete ric acid.
The water is reabsorbed into the large intestine, where it is refluxed into the cloacal contents.
uric acid is found in bird feces.
Eggs are completely enclosed and contain the embryo of a reptile or bird.
The production of insoluble, relatively nontoxic uric acid is good for shelled embryos because nitrogenous waste is stored inside the shell until hatching.
The evolutionary advantages of uric acid production outweigh the disadvantage of energy expenditure needed for its synthesis.
Humans have the ability to produce uric acid because of the breakdown of excess purine and pyrimidine nucleic acids in the diet.
The watersalt balance of the body is regulated by tubular excretory organs.
The planarians, flatworms that live in fresh water, have two strands of branching excretory tubules that open to the outside of the body.
The beating of flame-cell cilia propels fluid out of the body.
The system is believed to work in ridding the body of excess water and excreting waste.
Two or more tracts of branching tubules run the length of the body and open to the outside.
The flame cells are at the ends of the side branches.
Before being released to the outside, urine can be temporarily stored in the bladder.
Each beating of cilia has a different composition.
There is a network of capillaries surrounding the tubule.
The earthworm excretes a very small amount of urine.
An earthworm can excrete a volume of urine equal to 60 percent of its body weight.
Uric acid is actively transported from the surrounding hemolymph into these tubules, and water follows a salt gradient established by active transport of K+.
Uric acid leaves the body through the anus when water and other useful substances are reabsorbed at the rectum.
The insects that live in water reabsorb little water when they eat large quantities of moist food.
In dry environments, insects excrete a semisolid mass of uric acid.
Other arthropods have different names for their excretory organs.
In aquatic crustaceans, nitrogenous waste can be removed by moving it across the gills.
The fluid is modified before it leaves the tubules and comes from the surrounding blood.
The amount of urine excretion is regulated by the amount of salts in the tubules.
Coxal glands are spherical sacs.
The waste is collected from the surrounding blood and discharged through several pairs of appendages.
The kidneys are the most important parts of the body.
Maintaining the balance between water and salts is one of the functions performed by the kidneys.
The body systems, such as the skeletal, nervous, and muscular systems, are affected by Na+, Ca2+, K+, and PO - 4.
There are a number of different types of metabolic waste in urine.
The amount of urine produced by an animal varies depending on factors such as water and salt intake.
The total concentration in the blood of sharks, rays, and skates is less than in the water.
Their blood is almost isotonic to seawater, because they pump it full of urea, and this molecule gives their blood the same tonicity.
Excess salts are released by the rectal glands.
The marine environment is high in salts, which causes it to be hypertonic to the blood of fishes.
Some groups invaded the sea after the common ancestor of marine fishes evolved in fresh water.
The sea washes over the fishes' gills.
The average amount of water a marine fish swallows is 1% of their body weight every hour.
It is equivalent to a human drinking 700 liters of water every hour.
The habit of getting water by drinking causes these fishes to get salt.
They transport excess salt into the surrounding water at the gills.
The kidneys conserve water and the marine fishes produce a small amount of isotonic urine.
The osmotic problems of freshwater fishes and their environment are very similar to those of marine fishes.
The gills and the body surface are where freshwater fishes get their water.
The fishes never drink water.
They transport salts across the gills.
They eliminate excess water by making large quantities of urine.
Each day, they discharge a quantity of urine equal to one-third of their body weight.
The development of a kidneys that could produce a concentrated urine was an important evolutionary adaptation that allowed animals to survive on land.
There is a need for water in desert mammals, such as the kangaroo rat, as well as in animals that drink water.
Dehydration is a threat to all animals, especially those that live in a desert.
During the day, the rats stay in a cool burrow to conserve water.
The kangaroo rat's nose has a surface that captures water from exhaled air.
On cold winter mornings, exhaled air is full of condensation, which is why you can see it.
The ability of the kangaroo rat to form a very hypertonic urine is a major adaptation that allows it to conserve water.
The loop of the nephron in a kangaroo rat is much longer and more efficient than in most other animals, which is why the rat is able to do this.
The fecal material produced by kangaroo rats is almost completely dry.
Most animals need to drink water at least occasionally to make up for the water lost from the skin and respiratory passages.
The kangaroo rat is so adapted to conserve water that it can survive by using water derived from cellular respiration, and it never drinks water.
There are a variety of ways in which the kangaroo rat reduces water loss.
Birds and mammals are good at saving water because they evolved on land.
Some of these animals have adapted to living near the sea.
They can drink water.
We don't know how whales get rid of extra salt, but we do know that their kidneys are huge.
The kidneys of some marine animals are not efficient enough to excrete all the excess salt.
Some animals living in highsalt environments have developed specialized glands for excreting salts.
The salt from the blood is transported into the glands where it can be removed as a concentrated solution.
Sea birds have salt-excreting glands near their eyes.
The salty solution that is produced by the glands goes down grooves on their beaks until it drips off.
In sea snakes and marine turtles, the salt glands are used to remove excess salt from the tongue.
The nervous system regulates the work of these glands.
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