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Regulating the Internal Environment Animals need to regulate: 1. Water/solute concentration of body fluids – Body fluids-total amount of fluids in the body • Intracellular-amount of fluids found inside the cells, blood cells, and other tissue • Extracellular-amount of fluids found outside of the cells – Plasma-extracellular fluids found in the circulatory system – Interstitial fluid-fluids found between the cells outside the circulatory system 2. 3. pH temperature • The excretory system is a regulatory system that helps to maintain homeostasis within the body • Homeostasis is the dynamic constancy of the internal environment • The excretory system eliminates wastes and functions in osmoregulation. • Osmoregulation is the control of salt and water balance • Osmoconformers – Do not actively adjust their internal osmolarity • Osmoregulators – Animals whose body fluids are not isotonic with the external environment must manipulate solute concentrations in their body fluids Osmoregulation involves: 1. Osmosis-diffusion of H2O across a membrane due to a concentration gradient • remember, hyper/hypo/isotonic 2. Excretion- process of an organism ridding their bodies of metabolic wastes. This process also helps regulate Salt Balance. Animals have to get rid of nitrogen • The metabolism of proteins and nucleic acids produces toxic by-products ammonia • Ammonia: – a small and very toxic molecule – can be transported and excreted only in a very dilute solution • Many animals convert ammonia to urea (mammals and amphibians) or uric acid (birds and reptiles), which are much less toxic, but require ATP to produce Maintaining Extracellular Fluid • Urinary/Excretory system: – keeps volume and composition of extracellular fluid within tolerable ranges – regulates solute movement between internal fluids and the external environment • interacts with the digestive, respiratory, and circulatory systems to fulfill these tasks Urinary System Interactions food, water intake oxygen intake DIGESTIVE SYSTEM nutrients, water, salts RESPIRATORY SYSTEM oxygen elimination of carbon dioxide carbon dioxide CIRCULATORY SYSTEM URINARY SYSTEM water, solutes elimination of food residues rapid transport to and from all living cells elimination of excess water, salts, wastes Aquatic animals: -excrete ammonia which can readily cross membranes and then be flushed from the body 1. Many Marine invertebrates - lack a specialized excretory system, most waste diffuses across a membrane. The sea is an isotonic solution so salt balance is no problem EXCEPT if the organism is put in fresh water or a hypotonic solution. The animal most likely will lose salts and fluids and die 2. Marine fish - their body fluids are diluted (or hypotonic) in comparison to their environment (sea water) -Marine fish tend to lose water to their environment -Compensation 1. Marine fish drink water to replace H2O loss 2. Gills secrete ammonia not urine Gain of water and salt ions from food and by drinking seawater Excretion of salt ions from gills Osmotic water loss through gills and other parts of body surface Excretion of salt ions and small amounts of water in scanty urine from kidneys Osmoregulation in a saltwater fish 3. Fresh water fish – their body fluids are concentrated (or hypertonic) in comparison to their environment - Fresh water fish tend to gain water from their environment - Compensation - almost never drink H2O - Fish excrete a dilute urine, therefore keeping more salts in the body Osmotic water gain through gills and other parts of body surface Uptake of water and some ions in food Uptake of salt ions by gills Osmoregulation in a freshwater fish Excretion of large amounts of water in dilute urine from kidneys Terrestrial animals: **must fight desiccation (drying out) -compensation 1. drinking H2O 2. food with H2O 3. H2O is a by product respiration -Mammal and amphibians form Urea and finally urine -Birds and reptile form uric acid which is insoluble and less H2O is needed for excretion. Also will not toxify embyos in eggs. Proteins Nucleic acids Amino acids Nitrogenous bases —NH2 Amino groups Most aquatic animals, including most bony fishes Ammonia Mammals, most amphibians, sharks, some bony fishes Urea Many reptiles (including birds), insects, land snails Uric acid Ammonia • Animals that excrete nitrogenous wastes as ammonia need lots of water • They release ammonia across the whole body surface or through gills Urea • The liver of mammals and most adult amphibians converts ammonia to less toxic urea • The circulatory system carries urea to the kidneys, where it is excreted Uric Acid • Insects, land snails, and many reptiles, including birds, mainly excrete uric acid • Uric acid is largely insoluble in water and can be secreted as a paste with little water loss Excretory Processes • Most excretory systems produce urine by refining a filtrate derived from body fluids • Key functions of most excretory systems: – Filtration: pressure-filtering of body fluids – Reabsorption: reclaiming valuable solutes – Secretion: adding toxins and other solutes from the body fluids to the filtrate – Excretion: removing the filtrate from the system Protonephridia: Flame-Cell Systems - flatworms • A protonephridium is a network of dead-end tubules lacking internal 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 LE 44-10 Nucleus of cap cell Cilia Interstitial fluid filters through membrane where cap cell and tubule cell interdigitate (interlock) Tubule cell Flame bulb Protonephridia (tubules) Tubule Nephridiopore in body wall Metanephridia • Each segment of an earthworm has a pair of open-ended metanephridia • Metanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretion LE 44-11 Coelom Capillary network Bladder Collecting tubule Nephridiopore Nephrostome Metanephridium Malpighian Tubules • In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation • Insects produce a relatively dry waste matter, an important adaptation to terrestrial life LE 44-12 Digestive tract Rectum Hindgut Intestine Midgut (stomach) Malpighian tubules Feces and urine Salt, water, and nitrogenous wastes Anus Malpighian tubule Rectum Reabsorption of H2O, ions, and valuable organic molecules HEMOLYMPH The Vertebrate Excretory System • Kidneys (function in both excretion and osmoregulation), ureters, urinary bladder, urethra, renal artery, renal vein • Also… – Lungs: excrete carbon dioxide – Skin: excretes water, salts, and a small amount of urea (in sweat) Water Gains and Losses Water Gains • Absorption from gut • Metabolism Water Losses • Urination • Cell secretions • Sweating • Water in feces Solute Gains and Losses Solute Gains • Absorption from gut Solute Losses • Urinary excretion • Cell secretions • Respiration • Respiration • Sweating • Metabolism Controlling Water Gain & Loss • Urinary excretion provides the most control over water loss • Concentration of urine can be varied Components of Urinary System • Pair of kidneys • Pair of ureters • Urinary bladder • Urethra • Anytime you see the terms “nephr” or renal it has something to do with the kidneys Urinary Excretion • Urine flows from each kidney to a ureter • Ureters deliver urine to bladder • Contraction of the smooth muscle of the bladder forces urine out of the body into the urethra • Skeletal muscle surrounds urethra; allows voluntary control of urination Function of Kidneys • Filter water, mineral ions, wastes from the blood • Adjust filtrate concentration and return most to blood • Remaining water and solutes in filtrate constitute urine Structure of Kidney • Renal capsule surrounds kidney • Two regions – Outer renal cortex – Inner renal medulla • Renal pelvis collects urine and funnels it to ureter Figure 42.4a Page 747 Posterior vena cava Renal artery and vein Kidney Renal medulla Renal cortex Renal pelvis Aorta Ureter Urinary bladder Urethra Ureter Excretory organs and major associated blood vessels JuxtaCortical medullary nephron nephron Afferent arteriole Glomerulus from renal Bowman’s capsule artery Proximal tubule Peritubular capillaries Renal cortex Collecting duct 20 µm Renal medulla To renal pelvis Nephron Section of kidney from a rat Kidney structure SEM Efferent arteriole from glomerulus Distal tubule Branch of renal vein Descending Loop limb of Henle Ascending limb Collecting duct Vasa recta Filtrate and blood flow Nephron • Functional unit of the kidney Bowman’s capsule (red) distal tubule • Each consists of a renal tubule and associated collecting duct proximal tubule loop of Henle capillaries Figure 42.4c Page 747 Humans - There are over 1,000,000 nephrons in each kidney. 1,100-1,200 L of blood flows through the kidneys each day. -blood is delivered via an efferent arteriole to a capillary bed called the glomerulus. -The blood leaves the glomerulus via the afferent arteriole forming a second capillary bed called the peritubular capillaries that surrounds the nephron. --The blood then leaves the nephron via the a venule. - Urine Formation Hormone action Filtration Tubular secretion Tubular reabsorption Excretion Figure 42.5 Page 748 Leaky Glomerular Capillaries • Glomerular capillaries have large pores • Fluid leaks from glomerular capillaries into kidney tubules Renal corpuscle (Bowman’s capsule + glomerular capillaries) Figure 42.5 Page 748 Filtration Rate Varies • Increased blood pressure increases glomerular filtration • Flow volume to kidneys changes in response to neural, endocrine, and local changes Most Filtrate Is Reabsorbed • Each day, about 180 liters of filtrate flows out of glomerulus into tubules • 1 to 2 liters excreted • Most filtrate is reabsorbed into blood peritubular capillaries Tubular Reabsorption • Ions move from the filtrate in tubule lumen into the interstitial fluid • Sodium ions are actively pumped out of the proximal tubule into the interstitial fluid • Chloride ions follow; they are passively transported Tubular Reabsorption • Ion flow creates an osmotic gradient; it is saltier outside the tubule than inside • Water flows down the osmotic gradient, from the tubule lumen into the interstitial fluid • Peritubular capillaries pick up the water and ions from the interstitial fluid Amino acids, vitamins, proteins, and glucose are reabsorbed in the PCT. Tubular Reabsorption interstitial fluid filtrate in tubule Na+ Na+ Na+ Cl- Na+ Na+ Na+ H2O peritubular capillary sodium pump Figure 42.6 Page 749 Tubular Secretion • The opposite of reabsorption • Molecules are transported out of the peritubular capillaries, through tubule cells, and into the filtrate • Eliminates H+ ions, metabolites, and toxins Proximal tubule NaCl Nutrients HCO3– K+ H2O H+ NH3 Distal tubule H2O NaCl K+ HCO3– H+ CORTEX Descending limb of loop of Henle Filtrate H2O Salts (NaCl and others) HCO3– H+ Urea Glucose; amino acids Some drugs Thick segment of ascending limb NaCl H2O OUTER MEDULLA NaCl Thin segment of ascending limb Key Collecting duct Urea NaCl Active transport Passive transport INNER MEDULLA H2O Osmolarity of interstitial fluid (mosm/L) 300 300 100 300 100 CORTEX Active transport H2O H2O NaCl 400 NaCl 300 300 400 400 H2O 200 H2O Passive transport OUTER MEDULLA H2O NaCl H2O NaCl H2O INNER MEDULLA H2O 400 600 H2O H2O NaCl 900 NaCl NaCl H2O 600 H2O Urea 700 H2O Urea 900 H2O Urea 1200 1200 600 1200 Urine Formation Hormone action Filtration Tubular secretion Tubular reabsorption Excretion Figure 42.5 Page 748 • http://www.biologymad.com/resources/kidney.swf Regulation of Kidney Function • The osmolarity of the urine is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys Hormones: 1.Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney making urine more concentrated and conserving water – Acts on collecting ducts; makes walls more permeable to water Osmoreceptors in hypothalamus Thirst Hypothalamus Drinking reduces blood osmolarity to set point ADH Increased permeability Pituitary gland Distal tubule STIMULUS The release of ADH is triggered when osmoreceptor cells in the hypothalamus detect an increase in the osmolarity of the blood H2O reabsorption helps prevent further osmolarity increase Collecting duct Homeostasis: Blood osmolarity 2. The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis controlling blood pressure and volume • If low blood volume or low blood pressure: a) Aldosterone - Stimulates reabsorption of sodium (H2O follows) in the Distal Convoluted Tubule , increasing blood volume and therefore pressure b) Kidneys can also secrete an enzyme (resin) which is converted to Angiotensin which helps control blood pressure by causing arterioles to constrict Homeostasis: Blood pressure, volume Increased Na+ and H2O reabsorption in distal tubules STIMULUS: The juxtaglomerular apparatus (JGA) responds to low blood volume or blood pressure (such as due to dehydration or loss of blood) Aldosterone Arteriole constriction Adrenal gland Angiotensin II Distal tubule Angiotensinogen JGA Renin production Renin Thirst • Osmoreceptors detect changes • Activate thirst center in hypothalamus and ADH-secreting cells • Angiotensin II acts on brain to promote thirst and ADH secretion 3. Another hormone, atrial natriuretic factor (ANF), opposes the RAAS • The walls of the atria of the heart release ANF in response to increase in blood volume and pressure. • ANF inhibits the release of rennin from the JGA and inhibits NaCl reabsorption by the collecting ducts Variation in Urinary Systems • Structure of vertebrate urinary systems varies in details • Adapted to particular habitats • Freshwater fish must deal with continuous influx of water by osmosis • Marine fish must deal with continuous loss of water Length of Loop of Henle • Longer loop of Henle allows an organism to produce a very steep osmotic gradient and the more water that is conserved or retained by the body • Kangaroo rats have very long loops of Henle. Kidney Disorders • Glomerulonephritis – Infection of glomeruli leads to chronic inflammation that damages kidney • Kidney stones – Uric acid and calcium salts settle out of urine, form hard deposits that can lodge in ureter or urethra Renal Failure • Both kidneys are damaged to the point where they are nonfunctional • Fatal if not treated • Dialysis is used to restore normal solute balances temporarily • Transplant is only way to fully restore function Acid-Base Balance • Kidneys work in concert with buffering systems to keep pH in normal range • Normal range is 7.37 to 7.43 • Normal metabolism produces an excess of H+ Buffer Systems • Weak acid and weak base that can reversibly bind and release ions • Bicarbonate-carbon dioxide buffer system can neutralize excess H+ Regulating Blood pH (1) • Involves secretion of H+ and reabsorption of HCO3- (bicarbonate) • HCO3- in filtrate combines with H+ to form carbonic acid (H2CO3) • H2CO3 becomes CO2 and H2O, which are reabsorbed into blood from filtrate Regulating Blood pH (2) • In blood, HCO3 dissociates to form HCO3- and H+ • The H+ can be secreted into proximal tubule, while the HCO3- remains in blood, thus increasing blood pH • H+ can also combine with K+ or ammonia and leave body in urine Core Temperature • Internal temperature of an animal’s body • Must be maintained within a narrow range for normal enzyme function – Human body temp is 37C or 98.6F on average • Heat gains and losses must be kept in balance THERMOREGULATION • Thermoregulation – homeostatic process where body temperature is maintained • VASOCONSTRICTION & VASODILATION – making blood vessels smaller or larger to shunt blood to areas of the body ENDOTHERM METHODS • Shivering – involuntary muscle contraction that generates heat • Goose bumps – muscles at base of hairs raise hairs off of skin creating a pocket of warmer air near skin • Sweating – water evaporating removes heat energy from the skin • Panting – loss of body heat as water evaporates from moist surfaces of resp. tract (birds, dogs, bears) Maintaining Temperature • Peripheral thermoreceptors in skin • Thermoreceptors deeper in body • Feed input to hypothalamus • Hypothalamus sends messages to effectors by way of nervous system Response to Heat Stress • Peripheral vasodilation • Sweating • Panting Response to Cold • Peripheral vasoconstriction • Pilomotor response –moving the hairs • Shivering response • Nonshivering heat response Fever • Part of response to tissue damage • Hypothalamus resets body thermostat at higher temperature • Moderate fever can promote healing and need not be suppressed ECTOTHERM METHODS • CONDUCTION – direct transfer of heat between molecules of objects in contact (lizard on a hot rock) • CONVECTION – transfer of heat by movement of air or liquid past a surface – blood moving heat from extremities to the core • RADIATION – sun • EVAPORATION – cooling effect