Homeostasis and Excretion

Chapter 44

Presentation by: Imani Phillips, Stephanie Riley, and Jamie Chavez

Osmoregulation and Excretion

• Osmoregulation: how animals regulate solute concentrations and balance the gain and loss of water

• Excretion: how animals get rid of the nitrogen-containing waste products of metabolism

Osmosis• Osmolarity: total solute concentration expressed

as molarity or moles of solute per liter of solution– Unit of measurement: milliosmoles per liter(mosm/L)

where 1 mosm/L = a total solute concentration of 10-3 M

– Osmolarity of human blood= 300 mosm/L while osmolarity of seawater= 1000 mosm/L

• When tow solutions differ in osmolarity,– The one with greater concentration of solutes is

hyperosmotic

– The more dilute solution is hypoosmotic

• When two solutions separated by a selectively permeable membrane have the same osmolarity they are said to be isoosmotic

2 Basic Solutions to the Problem of Balancing Water Gain with

Water Loss

• Osmoconformers: – Available only to marine animals that

mostly live in water that has a very stable composition

– Does not actively adjust its internal osmolarity

• Osmoregulators:– An animal that must control its internal

osmolarity because its body fluids are not isoosmotic with the outside environment

Energy Cost of Osmoregulation

• Osmoregulators must expend energy to maintain the osmotic gradients that cause water to move in or out

• Energy Cost depends on

– how different an animal’s osmolarity is from its environment

– how easily water and solutes move across the animal’s surface

– how much work is required to pump solutes across the membrane

• Adaptations also help to reduce the energy cost by reducing the amount of water lost

– ex: many animals that live in the desert are nocturnal. This reduces water loss by taking advantage of lower temperature and higher relative humidity of night air.

Transport Epithelia• Is a layer or layers of specialized epithelial cells

that regulate solute movements • Moves specific solutes in controlled amounts in

specific directions

Nitrogenous Wastes• When proteins and nucleic acids are broken apart for

energy or converted to carbohydrates or fats, enzymes remove nitrogen in the form of ammonia which is very toxic

• The amount of nitrogenous waste produced is tied to the energy budget because it strongly depends on how much and what kind of food the animal eats

Endo-

therms

VS.

Ecto-

therms

Preda-

tores

VS.

Herbi-

vores•Produce energy at high rates

•Eats less than most endo-therms

•Gains energy from dietary proteins

•Relies on lipids & carbohydrates as energy sources

So Endotherms>Ectothermsin producing nitrogenous wastes

So Predators>Herbivores in producing nitrogenous wastes

Forms of Nitrogenous WastesAmmonia Urea Uric Acid

•Ammonia excretion is most common to aquatic species because

– there needs to be lots of access to water

– its toxicity only makes it possible to be excreted in large volumes of very dilute solutions

•In many vertebrates, ammonia release occurs across the whole body surface

•Excreted by most terrestrial animals and many marine species•Low toxicity•Can store urea at high concentrations•Urea-excreting animal requires much less water•Animals must expend energy to produce it from ammonia

•Excreted by insects, land snails, and many reptiles•Relatively nontoxic•Largely insoluble in water •Can be excreted as semi-solid paste with very little water loss•Even more energetically expensive to produce than urea•Needs ATP for synthesis from ammonia