Osmoregulation and Excretion

Osmoregulation Balances the uptake and loss of water and solutes of the body Species maintain water balance in 2 ways Osmoconformer Isoosmotic with environment Marine animals Osmoregulator Controls internal osmolarity independent of the environment Can live in environments that are otherwise uninhabitable

Adaptations of Osmoregulation Marine animals Osmoconformers must actively transport certain solutes Osmoregulators Some drink seawater to offset water loss, gills and kidneys are used to rid themselves of salt Sharks maintain a high urea to keep large amounts of salt from entering. Excess is excreted Freshwater animals Drink almost no water and excrete large amounts of dilute urine; salts replenished by eating

Adaptations of Osmoregulation Temporary waters Animals enter a state of dormancy when waters dry up Land animals Body coverings help to prevent dehydration; take in water and solutes by drinking and eating; water is produced via cellular respiration

Nitrogenous Wastes There are a variety of nitrogenous wastes. Animals excrete the nitrogenous waste that best fits its need for water and the availability of energy. Ammonia Very toxic; animals need access to large amount of water; most common in aquatic species Urea Produced in the vertebrate liver; low toxicity; less water needed; animals must expand energy to produce urea from ammonia Uric Acid Relatively nontoxic; does not readily dissolve in water; excreted as a semisolid paste; little water loss

Excretory Systems Systems must be able to handle: filtration, reabsorption, secretion and excretion Excretory systems will vary widely, but are based on a tubular theme

Excretory Systems Protonephridia A system of dead-end tubules connected to external openings; each branch is capped with a flame bulb which hold cilia – these function in filtration Includes flatworms, rotifers, some annelids, mullosc larvae, and lancelots Function in osmoregulation and the excretion of nitrogenous wastes

Excretory Systems Metanephridia Excretory organs that open internally to the coelom with the opening surrounded by a ciliated funnel. The cilia push the fluid into the collecting tubule and eventually into a bladder where it can be released In worms, each segment consists of 2 metanephridia and both are immersed in the coelomic fluid and surrounded by capillary network. The capillary network works to return solutes that have been reabsorbed. Most annelids (such as earthworms) Function in osmoregulation and excretion of nitrogenous wastes

Excretory Systems Malpighian Tubules Extend from dead-end tips immersed in hemolymph to openings in the digestive tract Filtration does not occur. Transport epithelium lining the tubules secretes solutes and nitrogenous wastes from the hemolymph to the lumen which also draws water via osmosis. Most solutes and water are reabsorbed in the rectum. Nitrogenous waste is excreted in the form of uric acid. Insects and terrestrial arthropods Function in osmoregulation and removal of nitrogenous wastes

Excretory Systems Kidneys Kidneys are made of highly organized tubules that are associated with capillaries. These tubules will carry urine out of the kidneys and eventually out of the body Functions in both osmoregulation and excretion Site of ultrafiltration – filtration occurs according to size, shape and charge of particles Pores, the basement membrane and podocytes work to accomplish this In vertebrates and some chordates

Mammalian Excretion Blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule Permeable to water and small solutes salts, glucose, amino acids, vitamins, nitrogenous waste Filtrate will then pass into the regions of the nephron Proximal tubule, loop of Henle, and distal tubule Filtrate then passes into the collecting duct where it then can be drained via the ureter

Mammalian Excretion Only mammals and some birds have a loop of Henle In humans 85% of nephrons are cortical 15% of nephrons are juxtamedullary This allows mammals to make urine that is hyperosmotic to the body and allows for water conservation Capillaries are associated with the nephrons to aid in reabsorption The vasa recta and loop of Henle form a countercurrent system that allows for greater effeciency

Adaptations of the Vertebrate Kidney Mammals Juxtamedullary nephrons with varying sizes of loops of Henle Dryer environments give rise to L.O.H.s that are much longer/deeper into the nephron Birds and other reptiles L.O.H. does not extend as far in birds, but conserve water by producing uric acid Other reptiles only have cortical nephron, but are able to reabsorb water via the cloaca. Many also excrete uric acid

Adaptations of the Vertebrate Kidney Freshwater fish and amphibians Conserve salts by reabsorbing ions Amphibians vary between environments. May conserve water or conserve solutes depending on current conditions Marine Bony Fish Do not have distal tubule and many are also missing or have small glomeruli. Filtration rates are low. Main function is to rid excess and unneeded ions

Hormones Antidiuretic hormone (ADH) aka vasopressin Controls the amount of water in urine. An increase in ADH secretion will cause more water to be reabsorbed by the body (less dilute urine). A decrease in ADH will have the opposite effect.