Module 11: Excretory System PDF

MODULE 11: EXCRETORY SYSTEM EDROICO MARI B. BRILLANTE, MD OSMOREGULATION OSMOREGULATION OSMOREGULATION Based largely on balancing the uptake and loss of water and solutes The driving force for movement of solutes and water is a concentration gradient of one or more solutes across the p...

MODULE 11: EXCRETORY SYSTEM EDROICO MARI B. BRILLANTE, MD OSMOREGULATION OSMOREGULATION OSMOREGULATION Based largely on balancing the uptake and loss of water and solutes The driving force for movement of solutes and water is a concentration gradient of one or more solutes across the plasma membrane Physiological systems of animals operate in a fluid environment Relative concentrations of water and solutes must be maintained within fairly narrow limits OSMOREGULATION OSMOSIS Process by which water enters and leaves cells OSMOREGULATION OSMOLARITY Unit of measurement for solute concentration Expressed in moles of solute per liter of solution Human blood: 300 mOsm/L Seawater: 1000 mOsm/L OSMOREGULATION OSMOLARITY The solute concentration of a solution determines the movement of water across a selectively permeable membrane OSMOREGULATION OSMOLARITY If two solutions are iso-osmotic: water molecules will cross the membrane at equal rates in both directions No net movement of water by osmosis OSMOREGULATION OSMOLARITY If two solutions differ in osmolarity: the net flow of water is from the hypo-osmotic to the hyper-osmotic solution OSMOREGULATION OSMOREGULATORY CHALLENGES AND MECHANISMS Osmo-conformers o Consisting only of some marine animals, are iso-osmotic with their surroundings and do not regulate their osmolarity o All osmo-conformers are marine animals o No tendency to gain or lose water since internal osmolarity is same as its environment OSMOREGULATION OSMOREGULATORY CHALLENGES AND MECHANISMS Osmoregulators o Expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment OSMOREGULATION MARINE ANIMALS Most marine invertebrates are osmo-conformers Many marine vertebrates and some marine invertebrates are osmo-regulators Marine bony fishes are hypo- osmotic to seawater They balance water loss by drinking large amounts of seawater and eliminating the ingested salts through their gills and kidneys OSMOREGULATION FRESHWATER ANIMALS Constantly take in water by osmosis from their hypo-osmotic environment They lose salts by diffusion and maintain water balance by drinking almost no water and excreting large amounts of dilute urine Salts lost by diffusion are replaced in foods and by uptake across the gills OSMOREGULATION ANIMALS THAT LIVE IN TEMPORARY WATERS Some aquatic invertebrates in temporary ponds lose almost all their body water and survive in a dormant state This adaptation is called anhydrobiosis OSMOREGULATION LAND ANIMALS Adaptations to reduce water loss are key to survival on land Body coverings of most terrestrial animals help prevent dehydration Desert animals get major water servings 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 ENERGETICS OF OSMOREGULATION Osmoregulators must expend energy to maintain osmotic gradients The amount of energy differs based on: o How different the animal’s osmolarity is from its surroundings o How easily water and solutes move across the animal’s surface o The work required to pump solutes across the membrane OSMOREGULATION TRANSPORT EPITHELIA IN OSMOREGULATION Epithelial cells specialized for moving solutes in specific directions Typically arranged into complex tubular networks Ex. Nasal glands of marine birds, which remove excess sodium chloride from the blood OSMOREGULATION AN ANIMAL’S NITROGENOUS WASTES REFLECT ITS PHYLOGENY AND HABITAT Animals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acid Toxicity: o Ammonia (NH3) > Urea > Uric acid Energy expenditure in conversion of: o Ammonia < Urea < Uric acid EXCRETORY PROCESSES EXCRETORY PROCESS EXCRETORY SYSTEMS Regulate solute movement between internal fluids and the external environment Most produce urine by refining a filtrate derived from body fluids EXCRETORY PROCESS EXCRETORY SYSTEMS Key functions of most excretory systems o Filtration § Filtering of body fluids o Reabsorption § Reclaiming valuable solutes o Secretion § Adding non-essential solutes and wastes to the filtrate o Excretion § Processed filtrate containing nitrogenous wastes is released from the body EXCRETORY PROCESS SURVEY OF EXCRETORY SYSTEMS Systems that perform basic excretory functions vary widely among animal groups: o Protonephridia o Metanephridia o Malpighian tubules o Kidneys EXCRETORY PROCESS PROTONEPHRIDIA A network of dead-end tubules connected to external openings The smallest branches of the network are capped by a cellular unit called a flame bulb These tubules excrete a dilute fluid and function in osmoregulation EXCRETORY PROCESS METANEPHRIDIA Consist of tubules that collect coelomic fluid and produce dilute urine for excretion Function in excretion and osmoregulation Each segment of an earthworm has a pair of open-ended metanephridia EXCRETORY PROCESS MALPIGHIAN TUBULES Remove nitrogenous wastes from hemolymph in insects and other terrestrial arthropods Function in osmoregulation Insects produce a relatively dry waste matter, mainly uric acid, an important adaptation to terrestrial life Some insects can also take up water from the air EXCRETORY PROCESS KIDNEYS The excretory organs of vertebrates, function in both excretion and osmoregulation The numerous tubules of kidneys are highly organized Also includes ducts and other structures that carry urine from the tubules out of the kidney and out of the body EXCRETORY PROCESS EXCRETORY PROCESS THE NEPHRON IS ORGANIZED FOR STEPWISE PROCESSING OF BLOOD FILTRATE The filtrate produced in Bowman’s capsule contains o Salts o Glucose o Amino acids o Vitamins o Nitrogenous wastes o Other small molecules EXCRETORY PROCESS FROM BLOOD FILTRATE TO URINE Proximal tubules o Reabsorption of ions, water, and nutrients takes place in the proximal tubule EXCRETORY PROCESS FROM BLOOD FILTRATE TO URINE Descending Limb of Loop of Henle o Reabsorption of water continues through channels formed by aquaporin proteins o Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate o The filtrate becomes increasingly concentrated EXCRETORY PROCESS FROM BLOOD FILTRATE TO URINE Ascending Limb of Loop of Henle o Salt but not water is able to diffuse from the tubule into the interstitial fluid o The filtrate becomes increasingly dilute EXCRETORY PROCESS FROM BLOOD FILTRATE TO URINE Distal Tubule o Regulates the K+ and NaCl concentrations of body fluids o The controlled movement of ions (H+ and HCO3-) contributes to pH regulation EXCRETORY PROCESS FROM BLOOD FILTRATE TO URINE Collecting Duct o Carries filtrate through the medulla to the renal pelvis o Task: reabsorption of solutes and water o Urine is hyperosmotic to body fluids EXCRETORY PROCESS ADAPTATIONS OF THE VERTEBRATE KIDNEY TO DIVERSE ENVIRONMENTS Variations in nephron structure and function equip the kidneys of different vertebrates for osmoregulation in various habitats Mammals o That inhabit dry environments have long loops of Henle o Those in fresh water have relatively short loops Birds o Have shorter loops of Henle than mammals do, but conserve water by excreting uric acid instead of urea Reptiles o Excrete nitrogenous waste as uric acid o Other reptiles have only cortical nephrons but reabsorb water from wastes in the cloaca EXCRETORY PROCESS ADAPTATIONS OF THE VERTEBRATE KIDNEY TO DIVERSE ENVIRONMENTS Freshwater fishes o Conserve salt in their distal tubules and excrete large volumes of very dilute urine Amphibians o Kidney function is similar to freshwater fishes o Conserve water on land by reabsorbing water from the urinary bladder Marine bony fishes o Are hypo-osmotic compared with their environment o Their kidneys have small glomeruli and some lack glomeruli entirely o Filtration rates are low, and very little urine is excreted EXCRETORY PROCESS HOMEOSTATIC REGULATION OF THE KIDNEY A combination of nervous and hormonal controls manages the osmoregulatory functions of the mammalian kidney These controls contribute to homeostasis for blood pressure and blood volume EXCRETORY PROCESS ANTIDIURETIC HORMONE (ADH) OR VASOPRESSIN Osmoreceptor cells in the hypothalamus monitor blood osmolarity and regulate release of ADH from the posterior pituitary When osmolarity rises above its set point, ADH release into the blood stream increases Binding of ADH receptors leads to a temporary increase in the number of aquaporin proteins in the membrane of collecting duct cells This reduces urine volume and lowers blood osmolarity EXCRETORY PROCESS  THANK YOU! REFERENCE: Campbell NA, Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV. 2021. Biology: a global approach (12th ed.). Pearson Education Ltd. England. https://www.bioexplorer.net/divisions_of_biology/zo ology/