Topic 8 - Osmoregulation | I - An Intro to Animal Metabolic Waste Management

animal life is challenged under what?

changing environmental conditions

homeostatic control systems

compensate for changing conditions and maintain the internal environment within the relatively narrow limits that cells can tolerate

osmoregulation

the regulation of water and ion balance

excretion

helps maintains the body’s water and ion balance while ridding the body of metabolic wastes

thermoregulation

the control of body temperature

living cells contain ___, are surrounded by ___, and constantly exchange ___ with their environment 

water (3x) 

What surrounds the cells of the simplest animals?

water of the external environment directly surrounds cells 

What surrounds the cells of complex animals?

aqueous extracellular fluid (ECF)

In animals with a circulatory system, what does ECF include?

interstitial fluid and blood plasma

osmolarity

total solute concentration of a solution

osmoles

measurement of osmolarity, the number of solute of molecules and ions (in moles) per liters of solution 

osmolarity of body fluids in humans and other mammals

300 mOsm/L

hyperosmotic

describing the solution with the higher osmolarity than the other solution

hypoosmotic

describing the solution with a lower osmolarity than the other solution

isosmotic

when the solutions on either side of a membrane have the same osmolarity

For metabolic stability, animals must keep their fluids and ECFs….

isosmotic

osmoconformers

the osmolarity of cellular and extraocular solutions matches that of the environment 

osmoregulators

use control mechanisms to keep the osmolarity of cellular and ECF the same, but at levels that may differ from the osmolarity of surroundings 

How do animals regulate osmolarity?

by removing certain substances from body fluids and releasing them into the environment 

What do animals excrete?

H⁺ ions, nitrogenous products of metabolism (NH₄), and breakdown products of toxins and poisons

What is the excretion of ions and metabolic products accompanied by?

water excretion, water acts as a solvent for these molecules 

Why might animals that take in large amounts of water also excrete water?

to maintain osmolarity 

What carries out excretion and osmoregulation?

microscopic tubules formed from transport epithelium

Where are the tubules immersed in body fluids?

at the proximal end 

Where are the tubules open to the body exterior?

the distal end 

What moves ions and molecules in and out of the tubules and how? What does it depend on?

transport proteins by either active or passive transport; depends on the substance and its concentration gradient 

What are the 4 steps in the tubule function?

1) filtration

2) tubular reabsorption

3) tubular secretion 

4) excretion 

fliltration  

the nonselective movement of water and solutes, but not large molecules such as proteins, through the proximal end of tubules and into the spaces between cells

tubular reabsorption

important molecules (e.g. glucose and amino acids) and ions are transported by the transport epithelium back to the ECF and eventually to the blood as the filtered solution moves through the excretory tubule 

tubular secretion

a selective process in which specific small molecules and ions are transported from the ECF and blood to the tubules

excretion (tubule function)

fluid (urine) containing waste materials is released to the environment from the distal end of the tubule (in some animals, waste fluids are concentrated into a solid or semisolid form)

What does the metabolism of ingested foods produce, and what is this product used for?

metabolic water that is used in chemical reactions and is involved in physiological processes (excretion)

What are the nitrogenous products of the breakdown of proteins, amino acids, and nucleic acids excreted as?

ammonia, urea, uric acid, or a combo of these substances

particular molecule or combo of molecules depends on a balance among toxicity, water, conservation, and energy requirements 

Why must ammonia be excreted or converted into something else?

because it is soluble in water and highly toxic 

What is the only way that ammonia can be excreted? Who is this possible for?

only in dilute solutions; possible only in animals with a plentiful supply of water (i.e. aquatic invertebrates, teleost, and larval amphibians)

What do mammals, most amphibians, some reptiles, some marine fishes, and some terrestrial invertebrates do with ammonia?

combine it with HCO₃^- and convert it to urea

urea

a soluble and relatively nontoxic form of ammonia

How much water does urea require for excretion?

only 10% as much water as ammonia 

What do terrestrial invertebrate, reptiles, and birds form instead?

uric acid

uric acid

nontoxic and insoluble form of ammonia; precipitates in water as a crystal and can be excreted as a concentrated paste

Compare uric acid to ammonia

uric acid requires more energy, but it contains 4 times as much N as ammonia

How much water does uric acid excretion conserve?

conserves about 99% of the water need to excrete the same amount of N in ammonia

most invertebrates are osmoconformers or osmoregulators?

osmoconformers; the osmolarity of the intercellular and extracellular fluid are equal to that of the seawater (1,000 mOsm/L)

All freshwater invertebrates are osmoconformers or osmoregulators?

osmoregulators