Osmoregulation & Excretion (BIOL 204 Lecture 35) PDF

 Learning Objectives What is osmolarity? Discuss the relationships among isoosmotic, hypoosmotic, and hyperosmotic solutions Distinguish between osmoconformers and osmoregulators Discuss the energetics of osmoregulation Distinguish between ammonia, urea, and uric acid in t...

 Learning Objectives What is osmolarity? Discuss the relationships among isoosmotic, hypoosmotic, and hyperosmotic solutions Distinguish between osmoconformers and osmoregulators Discuss the energetics of osmoregulation Distinguish between ammonia, urea, and uric acid in terms of toxicity and cost of production Discuss the production of urine in mammals  Animal Physiology Homeostasis – maintenance of internal environment regardless of external environment Fluctuations above or below a set point detected by a sensor serve as a stimulus, which triggers a response to return body to set point  Osmoregulation Physiological systems of animals operate in a fluid environment – concentrations of water and solutes must be balanced Osmoregulation controls solute concentrations and balances water gain and loss; excretion rids the body of nitrogenous and other waste products  Osmoregulation Water enters and leaves cells by Osmosis Osmolarity (solute concentration of a solution) determines the movement of water across a selectively permeable membrane – Isoosmotic – equal osmolarity; water molecules will cross the membrane at equal rates in both directions – Hypoosmotic – low osmolarity; water moves out of cell – Hyperosmotic – high osmolarity; water moves into cell Osmosis  Osmoregulation Osmoconformers – isoosmotic with their surroundings and do not regulate their osmolarity Osmoregulators – expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment  Osmoregulation in Marine Animals (a) Osmoregulation in a marine fish Most marine invertebrates Gain of water Excretion of salt Osmotic water loss through are osmoconformers; and salt ions from food ions from gills gills and other parts of many marine vertebrates body surface are osmoregulators Key Marine bony fishes are hypoosmotic (lower SALT WATER Gain of water Excretion of salt ions and concentration) to seawater and salt ions from drinking small amounts of water in scanty urine from kidneys – Balance water loss by seawater drinking large amounts of Figure 44.4 seawater and eliminating the ingested salts through their gills and kidneys  Osmoregulation in Freshwater Freshwater animals (b) Osmoregulation in a freshwater fish Uptake Osmotic water constantly take in water by Gain of water and some ions of salt ions gain through gills and other osmosis from their in food by gills parts of body surface hypoosmotic environment Water balanced by drinking almost no water and excreting large amounts of Excretion of salt ions and large amounts of dilute urine FRESH WATER water in dilute urine from kidneys Salts lost by diffusion are Figure 44.4 replaced in foods and by uptake across the gills  Osmoregulation on Land Adaptations to reduce water loss are key to survival on land Body coverings of most terrestrial animals help prevent dehydration  Osmoregulation on Land Other adaptations – kangaroo rats concentrate their urine (produce urine 12-15x more concentrated than blood plasma; ~4x in humans)  Osmoregulation on Land Desert animals get major water savings from simple anatomical features and behaviors such as a nocturnal lifestyle Land animals maintain water balance by eating moist food and producing water metabolically through cellular respiration  Osmoregulation on Land Camels – tolerate a 7˚C rise in body temperature, reducing the amount of water lost from sweat. They can lose 25% of their water and still survive  Energetics of Osmoregulation Osmoregulators must expend energy to maintain osmotic gradients The amount of energy differs based on – How different the animals osmolarity is from its surroundings – How easily water and solutes move across the animal’s surface – The work required to pump solutes across the membrane  Energetics of Osmoregulation Osmoregulators must expend energy to maintain the osmotic gradients that cause water to move in or out. They do so by using active transport to manipulate solute concentrations in their body fluids (hemolymph or blood)  Energetics of Osmoregulation Transport epithelia are epithelial cells specialized for moving solutes in specific directions They are typically arranged into complex tubular networks that lead to the external environment (kidneys, salt glands in birds, sea turtles, etc.) Nostril with salt secretions Secretory cell of transport epithelium Vein Artery Secretory tubule Nasal salt gland Capillary Secretory tubule Transport Salt epithelium ions Blood Salt flow secretion Central duct Figure 44.6  Energetics of Osmoregulation Others forcefully eject excess salts  Excretion Excretion: ridding the body of toxic metabolites (ammonia) produced from breaking down nitrogenous (nitrogen-containing) molecules (mostly proteins and nucleic acids) and other metabolic waste products  Excretion Nitrogenous wastes – Some animals convert Proteins Nucleic acids Figure 44.7 toxic ammonia (NH3) to less toxic Amino acids Nitrogenous bases compounds prior to excretion; each differ Amino groups in toxicity and energy costs of producing them Ammonia Urea Uric acid Ammonia Extremely toxic (needs to be kept at low concentrations) Excretion of ammonia requires access to lots of water They release ammonia across the whole body surface Urea Less toxic than ammonia Produced in liver in vertebrates; circulatory system takes it to kidneys Energetically expensive, but requires less water to excrete than ammonia  Proteins Nucleic acids Figure 44.7 Uric Acid Amino acids Nitrogenous bases Nontoxic, but Amino groups does not dissolve readily in water Very energetically expensive, but Most aquatic Mammals, most Many reptiles animals, including amphibians, (including birds), can be excreted most bony fishes sharks, some insects, land bony fishes snails as a paste with little water loss Ammonia Urea Uric acid  Excretion – Ammonia is toxic, need lots of H2O to excrete – Urea is less toxic, low H2O to excrete – Uric acid, non-toxic, ~no H2O to excrete  Excretion Hydrostatic pressure (blood pressure in many animals) drives a process of filtration  Excretion Protonephridia are found in flatworms, some annelids, mollusc larvae, and lancelets  Excretion Most annelids (e.g., earthworms), have metanephridia: excretory organs that collect fluid directly from the coelom. A pair are found in each segment of an annelid.  Excretion Insects and other terrestrial arthropods have organs called Malpighian tubules that remove nitrogenous wastes and that also function in osmoregulation  Excretion Kidneys used in osmoregulation and excretion – Filters blood and generates urine Found in vertebrates and some other chordates  Kidneys The tubules of kidneys are closely associated with a network of capillaries. Ducts carry urine from tubules out of the kidneys.  Kidney in Mammals Kidney important for homeostasis (endocrine and urinary systems) Filters blood for nitrogenous waste Contains ~1 million excretory tubules called nephrons – long tubule and capillary ball (glomerulus) Kidneys Nephron is the functional unit of the kidneys Nephron  Kidney in Mammals Nephron 3 Processes: 1) Filtration – occurs as blood pressure forces fluid from blood in glomerulus to Bowman’s capsule  Kidney in Mammals Nephron 3 Processes: Bowman’s Capsule 1) Filtration – occurs Glomerulus as blood pressure forces fluid from Formation blood in glomerulus of urine to Bowman’s capsule Blood with waste Proximal Tubule  Proximal Tubule Distal Tubule Nephron 3 Processes: 2) Reabsorption – water and minerals Bowman’s Capsule (e.g., NaCl) actively and passively transported to blood (occurs in proximal Collecting Duct tubule, loop of Henle, distal tubule) Loop of Henle To Ureter  Proximal Tubule Distal Tubule Nephron 3 Processes: 3) Secretion – H and K ions transported to Bowman’s Capsule tubules (occurs in proximal and distal tubules) Collecting Duct Loop of Henle To Ureter  Kidney in Mammals Filtrate becomes urine as it flows through the nephron and collecting duct Figure 44.15  Kidney in Mammals Countercurrent multiplier system – actively transports NaCl to regulate osmolarity Figure 44.16  Kidneys Cortical nephron: most nephrons, short, filter wastes Juxtamedullary nephron: long, conserve water, regulate ion concentrations  Kidneys relative abundance of juxtamedullary nephrons varies between different mammals  Summary It is more energy efficient for osmoconformers compared to osmoregulators, which must regulate their osmolarity Ammonia is toxic, requires little energy, but lots of water. While urea is less toxic, requires little water, but lots of energy. In contrast, uric acid is non-toxic, requires very little-to-no water, but requires the most energy. Within the nephrons of the kidneys, filtration, reabsorption, and secretion all occur to remove wastes and produce urine