Osmoregulation Part 3

Question 1

What are different types of Nephridia?

Answer 1

1. Primitive Kidney
2. Protonephridia
3. Metanephridia
4. Filtration-reabsorption systems

Question 2

What are Protonephridia?

Answer 2

Found in flatworms and rotifers, it’s a network of closed tubules throughout the body. Interstitial fluid filters into lumen at flame bulb, some tubule cells might modify ion concentration.

Question 3

What does Protonephridia do in Freshwater flatworms?

Answer 3

Mainly osmoregulation, most waste diffuses out of body or into gastrovascular cavity.

Question 4

What does Protonephridia do in Parasite flatworms?

Answer 4

Found in isotonic environment, mainly excretion of nitrogenous waste.

Question 5

What are Metanephridia?

Answer 5

Found in most annelids, many mollusks, arthropods. It filtrates coelomic fluid by taking small solutes and waste. The tubules reabsorb NaCl and other solutes using active transport. It deals with osmoregulation and nitrogenous wastes.

Question 6

What are osmoregulatory organs involved in?

Answer 6

Nitrogen waste excretion.

Question 7

What is the problem with nitrogen waste?

Answer 7

It’s the leftover of the metabolism of proteins and nucleic acid (produces NH3; ammonia), it’s toxic. Nitrogen waste affects intracellular pH and affects the cell membrane (substitute for K+ in Na+/K+ ATPase -> [K+] depeletion). It uncouples oxidative phosphorylation, abolishing the H+ gradient across the inner mitochondrial membrane, changing the membrane potential.
Nitrogen waste also increase glumate synthesis, which is a neurotransmitter, which effects CNS processes.

Question 8

What occurs with an accumulation of nitrogen waste?

Answer 8

An accumulation of NH3 would result in convulsion, coma, and death. This is why it must be excreted.

Question 9

Why is nitrogen waste difficult to excrete?

Answer 9

NH3 is very soluble, and excretion would require large quantities of water. Animals have evolved different strategies for excretion, based on water availability.

Question 10

How do most aquatic animals excrete nitrogen waste?

Answer 10

Through ammonia, with the use of a lot of water and little energy.

Question 11

How do mammals, amphibians, sharks, and some bony fishes excrete nitrogen waste?

Answer 11

Through Urea, which uses an average amount of energy and water (compared to ammonia and uric acid).

Question 12

How do birds, insects, reptiles, and land snails excrete nitrogen waste?

Answer 12

Through uric acid, which uses a lot of energy and little water.

Question 13

What is Ammonia?

Answer 13

Excreted by ‘Ammonotelic animals’, it is very soluble in water and toxic at low concentrations. It easily permeates membranes (NH3 is membrane permeable, NH4+ is not). Not all aquatic animals, but most, excrete ammonia.

Question 14

How do invertebrates excrete ammonia?

Answer 14

It diffuses out of the body surface and into surrounding water.

Question 15

How do fish excrete ammonia?

Answer 15

It is excreted out of gills and (to a more minor degree) from kidneys.

Question 16

What is Urea?

Answer 16

Excreted by ‘Ureotelic animals’, it is less toxic than ammonia and can be tolerated in a more concentrated form. It required the animal to sacrifice less water, and uses less energy to create.

Question 17

What is Uric Acid?

Answer 17

Excreted from ‘Uricotelic animals’, it is an adaption done due to limited availability of water. It is used for shelled eggs in vertebrates, and is excreted by land snails, insects, birds, and many reptiles.
It is 1,000 times less soluble than NH3, and precipitates. It’s non toxic but requires more energy, and is form of storage excretion.