Download
1 / 53
650 likes | 1.15k Views
Osmoregulation. Osmoregulation – the active regulation of the osmotic pressure of an organism’s fluids to maintain homeostasis of the organism’s water content Osmotic pressure (of a solution) – a measure of its tendency to take in water by osmosis
E N D
Osmoregulation • Osmoregulation – the active regulation of the osmotic pressure of an organism’s fluids to maintain homeostasis of the organism’s water content • Osmotic pressure (of a solution) – a measure of its tendency to take in water by osmosis • Osmosis – the diffusion of water across a semi-permeable membrane • Always occurs from a more dilute solution to a less dilute solution • Higher concentration of solutes more osmotic pressure
Osmoregulation • To maintain osmotic balance, the extracellular compartment of ananimal’s body must be able to take water from, and excrete excess water, into the environment • Exchanges of water and inorganic ions (electrolytes) between the body and the external environment occurs across specialized epithelial cells, and, in most vertebrates, through a filtration process in the kidneys
Osmoregulation kidney
Osmoregulation • Homeostasis maintains a constant level of ions in extracellular fluids • Na+ - major cation • Cl- – major anion • Ca+2, Mg+2, and K+ – also very important
Osmoregulation • Hypertonic solution – cell loses water (and shrinks); more solutes in solution relative to cell • Isotonic solution - no net water movement; equal number of solutes relative to cell • Hypotonic solution - cell gains water (expands); fewer solutes relative to cell REMEMBER, HIGHER CONCENTRATION OF SOLUTES INCREASES OSMOTIC PRESSURE AND THE TENDENCY TO TAKE IN WATER BY OSMOSIS
Osmoconformers • In most marine invertebrates, the osmolarity of their blood fluids is the same as that of their external environment, seawater • That is, their extra-cellular fluids are isotonic to their external environment • NO tendency for water to leave or enter the body • An organism in osmotic equilibrium with its environment is called an osmoconformer
Osmoconformers Adapted from Potts and Parry 1964 as cited by J. Levinton 2009
Osmoregulators • An organism that actively discharges water (in a hypotonic environment) or takes in water (in a hypertonic environment) is called an osmoregulator • Osmoregulators can maintain a relatively constant blood osmolarity despite differences in concentration of solutes in the surrounding environment
Osmoregulators • Examples… • Freshwater vertebrates have much higher solute concentration in their body fluids than in the surrounding water (increase solutes increases osmotic pressure; increased tendency to take in water) • Freshwater vertebrates must prevent water from entering their bodies as much as possible and actively transport ions back into their body
Osmoregulators • More examples… • Most marine vertebrates are hypotonic to their environment; these animals are in danger of losing water by osmosis • Marine vertebrates must retain water and eliminate excess ions via their kidneys and gills • They retain water by drinking seawater (yum!)
Osmoregulators • Even more examples… • Terrestrial vertebrates have a higher concentration of water than in the air in their surrounding environment; these animals tend to lose water to the air by evaporation from the skin and lungs • These animals evolved osmoregulatory/urinary systems to retain water
Nitrogenous Wastes • In many animals, the removal of water and ions is coupled with the removal of wastes generated by metabolism • Amino acids (proteins) and nucleic acids are nitrogen-containing molecules • When proteins and nucleic acids are metabolized (catabolized for energy or converted into carbohydrates or lipids), they become nitrogenous wastes, that must be eliminated from the body
Nitrogenous Wastes: Ammonia • Nitrogenous wastes are toxic to the body and must be removed • Ammonia is formed in the liver by the metabolism of amino and nucleic acids • Ammonia is very toxic to cells and must be present only in very dilute concentrations • Bony fish drink seawater (marine) or have excess water to remove (freshwater) and therefore have very dilute urine, and so excrete ammonia safely
Nitrogenous Wastes: Urea • Urea and uric acid are less toxic to the organism, and are eliminated by cartilagenous fish, adult amphibians and mammals • Urea is water-soluable and so can be excreted in large amounts in the urine • Urea is also synthesized in the liver; takes energy to convert from ammonia
Nitrogenous Wastes: Uric Acid • Uric acid is also less toxic, but is NOT water-soluable • Birds, reptiles and insects excrete uric acid • Uric acid does not require large amounts of water to be excreted • Uric acid is that “special something” you find on your windshield; forms a pasty, white material • Costs more to generate uric acid than urea, but conserves water!
Nitrogeous Wastes: Uric Acid • The insoluability of uric acid is very important to reptiles and birds, which lay eggs • Uric acid accumulates inside egg with developing embryo, but precipitates and crystalizes • Does not interfere with developing embryo; does not dissolve in yolk • Worth the extra cost of production • Gout in humans – deposits of uric acid crystals in joints ; kidney stones; inability to properly make uric acid water soluable
Osmoregulatory Organs • Single-celled organisms use contractile vacuoles to rid wastes (freshwater protozoans are constantly gaining water by osmosis) • Invertebrates use specialized cells and tubules • Flatworms (Platyhelminthes) use protonephridiawhich branch into bulblike flame cells throughout the body • Cilia inside the flame cells draw in fluids from the body; substances then excreted through pores
Osmoregulatory Organs • Earthworms have nephridia - a system of tubules that open to the inside and outside of the body • Fluid enters internal openings called nephrostomes by filtration • Tubules are lined with epithelial cells that reabsorb essential salts
Osmoregulatory Organs • Insects use malpighian tubules • Extensions of the digestive tract • Waste products are transferred into the tubules by active transport • Secretion of K+ creates an osmotic gradient that causes water to enter the tubules by osmosis from the body’s open circulatory system • Most of the water and K is then reabsorbed into the circulatory system via the epithelium of the hindgut, leaving behind only small molecules and waste products to be excreted from the rectum
Mammalian Kidneys • The vertebrate kidney consists of many nephrons, the filtering unit of the kidney • In humans, the kidneys consist of a pair of fist-sized organs located in the lower back • The kidney receives bloom from a renal artery and produces urine • Urine drains from each kidney through a ureter towards the urinary bladder (and into the urethra)
Mammalian Kidneys • The kidney has three basic functions: • Filtration – fluid in the blood is filtered into the tubule system, leaving behind cells and large proteins in the blood and a filtrate composed of water and all of the solutes from the blood • Reabsorption – important solutes, such as glucose, amino acids and inorganic ions, and water are selectively moved out of the filtrate back to the blood (reabsorbed) • Secretion – substances from the blood are moved into the tubule system ‘permanently’ (e.g., toxins)
Mammalian Kidneys: Filtration • Each nephron consists of a long tubule and associated blood vessels • Blood is carried by an affarent arteriole to a tuft of capillaries in the renal cortex, the glomerulus • Blood is filtered in the glomerulus as the blood pressure forces fluid through porous capillary walls • Blood cells and large proteins are too large to enter
Mammalian Kidneys: Filtration • Large amounts of blood plasma, containing water and dissolved molecules enter the nephron tubules in a region known as Bowman’s capsule • Bowman’s capsule envelopes the glomerulus • Blood components that were not filtered drain into an efferent arteriole, which empties into a second bed of capillaries • Filtrate then flows through the loop of Henle (birds and mammals), which dips into the medulla before ascending back into the cortex
Mammalian Kidneys: Filtration • After leaving the loop of Henle, the fluid drains into a collecting duct • Merges with other collecting ducts to empty its contents, now called urine, into the renal pelvis • Filtration is a nonselective process with regard to small molecules • Filtrate initially consists of water, urea, salts, glucose, vitamins, etc.
Mammalian Kidneys: Reabsorption and Secretion • Most of the water and dissolved solutes that enter the glomerular filtrate must be returned to the blood by reabsorption • Reabsorption is the selective transport from the filtrate back to the blood • Sugars, vitamins, organic nutrients, and water are reabsorbed (don’t want to lose!) • Secretion is a very selective process
Mammalian Kidneys: Reabsorption and Secretion • Reabsorption of glucose and amino acids is driven by active transport carriers • LOTS of capillaries surround the loop of Henle to readjust composition of filtrate • Approximately 25x the volume of your body is filtered each day • Aquatic animals have short loops of Henle; desert organisms have longer loops (conserve water!)
Mammalian Kidneys: Reabsorption and Secretion • The function of the loop of Henle is to create a gradient of increasing osmolarity from the cortex to the medulla; allows water to be reabsorbed via osmosis in the collecting duct as it runs down into the medulla past the loop of Henle • The descending and ascending limbs of the loop of Henle differ structurally in regards to their permeability to water • Ascending limb is impermeable to water; descending limb is thin and permeable
Kidneys: Hormonal Control • Kidneys maintain relatively constant levels of blood volume, pressure, and osmolarity • These homeostatic functions of kidneys are coordinated primarily by hormones • Antidiuretic hormone (ADH) is released by the pituitary gland when the solute concentration of the blood rises • Makes the epithelium of the distal tubules and the collecting ducts more permeable to water; stimulates water reabsorption from the collecting duct (no ADH, no reabsorption in collecting duct)
Kidneys: Hormonal Control • Alcohol inhibits ADH, dehydrates the body! • … what a hangover is; the headache results from the dehydration of your organ systems • …why they say to drink water before you go to bed after drinking
Osmotic balance • The kidney appeared first in freshwater fish • Fish, amphibian and reptile kidneys can only produce a hypotonic (or isotonic) urine (no loops of Henle) • Marine bony fish must excrete electolytes and retain water; most monovalent ions are actively transported across gill surfaces; divalent ions excreted in urine (isotonic urine)
Osmotic balance • Freshwater fish must retain electrolytes and keep water out; freshwater fish do NOT drink water and excrete a large volume of dilute urine (hypotonic urine); reabsorb ions across the nephron tubules and actively transport ions across gill surfaces from the water into their blood
Osmotic balance • Marine reptiles eliminate excess salt through salt glands located near the nose or the eye • “crocodile tears” • Marine birds drink seawater and then excrete excess salt through salt glands, which dribble down the beak
