Osmoregulation and Excretion

Osmoregulation and Excretion Water Balance • • • • • • Osmoregulation is the management of the body’s water and solute content. Specialized epithelial cells called transport epithelium are essential to osmoregulation. Nitrogenous waste has the greatest effect on osmoregulation. Enzymes remove nitrogen from macromolecules to form a toxic molecule called ammonia. Many species convert ammonia to urea or uric acid. Endotherms typically produce more nitrogenous wastes Ammonia, Urea, and Uric Acid • • • • • Ammonia is very soluble in water, therefore it is most common waste product of aquatic species. Because of ammonia’s toxicity it can not be transported in large volumes. Mammals, many amphibians, and marine fishes excrete urea, produced in the liver. Urea has low toxicity, but conversion of ammonia to urea costs energy. Land snails, insects, birds, and many reptiles excrete uric acid. • Animals excrete uric acid as a solid which is expensive to produce. Osmoregulation costs energy • • • • • • Solution separated by a membrane differ in osmotic pressure or osmolarity. Osmoconformers do not actively adjust to surroundings. An osmoregulator must control its internal molarity, which allows them to inhabit a variety of habitats. Energy costs depend on the external environment. Stenohaline animals cannot tolerate changes in external osmolarity. Euryhaline animals can survive under fluctuations, e.g. American shad. How do Fish Osmoregulate? • Marine fishes constantly lose water across their gills and produces little urine? • • • • • Sharks remove salt and excrete the waste as feces. Fresh water animals constantly lose salt and gain water from diffusion. Marine fishes constantly drink water and excrete ions and water with little amounts of urine. Some aquatic invertebrates produce a protective shell around the cell during dry periods. Terrestrial adaptations include: a waxy cuticle, protective shells, and diurnal behavior. How do most Excretory Systems produce urine? • • • • Body fluids must first be collected and then adjusted. During filtration the transport epithelium membrane retains cells and proteins, called filtrate. Flatworms have system called protonephridia which are a network of tubes leading to the nephridiopores from the dead-end branch called flame bulb. Metanephridium is a system of tubes with internal openings that collect fluids in earthworms. How do most Excretory Systems produce urine? • • • Terrestrial insects have malpighian tubules that remove nitrogenous wastes from hemolymph and transport to the digestive tract to pass through the rectum as a solid. The kidneys of vertebrates function in excretion and osmoregulation. The kidneys have a dense network of capillaries associated with tubules and ducts that carry urine out of the tubules of the kidney to ureter. Nephrons and Associated Blood Vessels are Functional Unit of the Kidneys? • • • • • • Each kidney is supplied with blood from a renal artery and renal vein. Urine exits the kidney through a ureter that drains into the urinary bladder. Urine is expelled through the urethra. The neprhon consists of a single long tubule and a ball of capillaries called the glomerulus. Bowman’s capsule surrounds the glomerulus. Each human kidney has a million nephrons. A Closer Look at Blood Filtration? • • • • • The proximal tubule reabsorbs most of the salt and water from the filtrate as well as other valuable nutrients. The Descending limb of the Loop of Henle reabsorbs water from the filtrate. In the ascending limb of the Loop of Henle salt diffuses out of the tubule. The distal tubule is important in regulating K and NaCl of body fluids. The collecting duct carries the filtrate to the renal medulla and actively reabsorbs NaCl. Hormone Regulation of the Kidneys • • • Antidiuretic hormone is produced by the hypothalamus stimulates cells in the distal and collecting tubules to reabsorb water in response to increasing blood osmolarity. Another system is activated by blood pressure and involves the hormone aldosterone which acts on the distal tubules to reabsorb more water and Na. Another hormone inhibits other mechanisms to reduce NaCl reabsorption.