1 Osmoregulation and ExcretionChapter 44 Osmoregulation and Excretion

2 Overview: A Balancing ActPhysiological systems of animals operate in a fluid environment Relative concentrations of water and solutes must be maintained within fairly narrow limits

3 Freshwater animals show adaptations that reduce water uptake and conserve solutesDesert and marine animals face desiccating (dehydrating) environments that can quickly deplete body water

4 Osmoregulation regulates solute concentrations and balances the gain and loss of waterExcretion gets rid of metabolic wastes

5 Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitatThe type and quantity of an animal’s waste products may greatly affect its water balance Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids

6 This is dependent on their habitat!Proteins Nucleic acids HOW these waste products are excreted depends on how much water an organism needs to maintain homeostasis This is dependent on their habitat! Amino acids Nitrogenous bases —NH2 Amino groups (nitrogenous waste) Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Which organism consumes more energy to get rid of their waste? Which organism needs more water to get rid of their waste? More H2O needed to excrete Ammonia Urea Uric acid More energy needed to excrete

7 Forms of Nitrogenous Wastes: AmmoniaAnimals that excrete nitrogenous wastes as ammonia need lots of water So… they live in an environment where water is abundant. They release ammonia across the whole body surface or through gills Freshwater animals Marine invertebrates

10 Forms of Nitrogenous Wastes: Uric AcidAnimals that excrete uric acid have a critical problem with getting water some time in their lifetime Insects, land snails, and many reptiles, including birds, mainly excrete uric acid Lay eggs with limited supply of water inside the egg. Note: eggshells are impermeable to water so it won’t lose any water, but... Uric acid NH3 NH3 Uric acid Why reptiles/birds evolved to release uric acid instead of ammonia… These organisms share the same orifice for their reproductive, excretory and digestive wastes. In other words, they use the same hole for their pee, poop, and eggs. This means that their eggs were exposed to their nitrogenous waste products. Reptiles/birds that evolved to release ammonia probably contaminated the eggs since the shells are permeable to ammonia. Reptiles/birds that evolved to excrete uric acid did not contaminate the eggs. Non-contaminated egg meant healthy viable offspring, which would survive, and reproduce.  NH3 Uric acid H2O H2O NH3 Uric acid Contamination No Contamination

11 Forms of Nitrogenous Wastes: Uric AcidUric acid is largely insoluble in water and can be secreted as a paste with little water loss

12 The Influence of Evolution and Environment on Nitrogenous WastesThe kinds of nitrogenous wastes excreted depend on an animal’s evolutionary history and habitat The amount of nitrogenous waste is coupled to the animal’s energy budget

13 The Influence of Evolution and Environment on Nitrogenous WastesRemember, there are 3 general wastes products Special cases: Lungfish: make ammonia when there’s a lot of water, urea when pond dries out Aquatic mollusks make ammonia, terrestrial snails make urea ammonia urea uric acid Increasing amount of water

14 Concept 44.1: Osmoregulation balances the uptake and loss of water and solutesOsmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment Cells require a balance between osmotic gain and loss of water Various mechanisms of osmoregulation in different environments balance water uptake and loss Terms to remember: Osmotic pressure: solute “pull” Osmotic potential: water concentration Hyper- , hypo-, iso- tonic solutions

15 Osmotic Challenges Osmoconformers, consisting only of some marine animals, are isoosmotic (isotonic) with their surroundings and do not regulate their osmolarity Osmoregulators expend energy to control water uptake and loss in a hyperosmotic (hypertonic) or hypoosmotic (hypotonic) environment

16 Most animals are stenohaline; they cannot tolerate substantial changes in external osmolarityEuryhaline animals can survive large fluctuations in external osmolarity

17 Marine Animals Most marine invertebrates are osmoconformersMost marine vertebrates and some invertebrates are osmoregulators

18 Marine bony fishes are hypoosmotic to sea waterThey are in a hypertonic environment Constantly lose water (as if they were in a desert) They lose water by osmosis and gain salt by diffusion and from food They balance water loss by drinking seawater Gain of water and salt ions from food and by drinking seawater Osmotic water loss through gills and other parts of body surface [hypotonic] [hypertonic] Excretion of salt ions and small amounts of water in scanty urine from kidneys Excretion of salt ions from gills Osmoregulation in a saltwater fish

19 Transport Epithelia Transport epithelia are specialized cells that regulate solute movement They are essential components of osmotic regulation and metabolic waste disposal They are arranged in complex tubular networks An example is in salt glands of marine birds, which remove excess sodium chloride from the blood Nasal salt gland (acts as a filter) Nostril with salt secretions

20 Freshwater Animals Freshwater animals constantly take in water from their hypoosmotic environment Need: get rid of extra water, keep salts They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine Salts lost by diffusion are replaced by foods and uptake across the gills Osmotic water gain through gills and other parts of body surface Uptake of water and some ions in food [hypotonic] [hypertonic] Uptake of salt ions by gills Excretion of large amounts of water in dilute urine from kidneys Osmoregulation in a freshwater fish

21 Animals That Live in Temporary WatersSome aquatic invertebrates in temporary ponds lose almost all their body water and survive in a dormant state This adaptation is called anhydrobiosis (“life without water”) Hydrated tardigrade Dehydrated tardigrade 100 µm

22 Land Animals Water balance in a kangaroo rat (2 mL/day) balance in a human (2,500 mL/day) gain loss Derived from metabolism (1.8 mL) Ingested in food (0.2 mL) metabolism (250 mL) in food (750 mL) in liquid (1,500 mL) Evaporation (900 mL) Feces (100 mL) Urine Evaporation (1.46 mL) Feces (0.09 mL) (0.45 mL) Land animals manage water budgets by drinking and eating moist foods and using metabolic water

23 Desert animals get major water savings from simple anatomical features4 3 (L/100 kg body mass) Water lost per day 2 1 Control group (Unclipped fur) Experimental group (Clipped fur)