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Ch. 36 - Excretory Systems & Body Fluid Regulation. Body Fluid Regulation. An excretory system regulates body fluid concentrations. It does this by: •Retaining or eliminating certain ions & water Dependent upon concentration of mineral ions such as: Na + , Cl - , K + , & HCO 3 -
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Body Fluid Regulation • An excretory system regulates body fluid concentrations. It does this by: • •Retaining or eliminating certain ions & water • Dependent upon concentration of mineral ions such as: Na+, Cl-, K+, & HCO3- • Water can enter the body through: • Drink, food & metabolism • Water can leave the body through: • Evaporation, feces formation, excretion (urine)
Osmoregulation • When there are differences in osmolarity (solute concentration) between two regions, water tends to move from regions with the greatest water concentration into regions with the lowest water concentration • Thus, water moves to the region with the highest amount of ions • Marine Environment = high in salts -Promotes osmotic loss of water & gain of ions by animals • Fresh Water Environment = low in salts -Promotes osmotic gain of water & loss of ions by animals •Terrestrial Environments -Animals tend to lose both water and ions to environment
Body Fluid Regulation • Marine Invertebrates • Like mollusks (squid) & arthropods (lobsters) • Have body fluids that are ~ isotonic to seawater • These organisms have little difficulty maintaining normal salt and water balance (osmotic balance) • Thus, they have no special mechanisms
Body Fluid Regulation • Cartilaginous fishes (Elasmobranchs) • Like sharks & rays • Have body fluids that are ~ isotonic to seawater • These organisms have little difficulty maintaining normal salt and water balance (osmotic balance) • They do NOT have the same amount of mineral ions as seawater like the marine invertebrates • Instead, their blood contains a high concentration of urea (a nitrogen waste product). This level would be toxic to other vertebrates but is not to these fish.
Body Fluid Regulation • Bony Marine Fishes • Body fluids of bony fishes have less salt than the surrounding seawater. Thus they are hypotonic to their surroundings. • They continually lose water through their gills & thus risk dehydration • Must constantly drink seawater to compensate • The excess salt intake is counteracted by actively transporting salt ions out into seawater through the gills • They produce small amounts of isotonic urine
Body Fluid Regulation • Freshwater Bony Fishes • The body fluids of freshwater bony fishes are hypertonic to fresh water but not as concentrated as seawater • Water tends to rush into their bodies through gills. • They never drink water • Eliminate excess water by producing large quantities of dilute, hypotonic, urine • This causes them to lose salt, so they actively transport salts into the blood through their gills
Body Fluid Regulation • Terrestrial animals • •Lose water through excretion, respiration, sweat & feces • •Most must drink water to make up for loss. (Exception is kangaroo rat) • Some reduce excretory loss by excreting nitrogen as relatively insoluble uric acid • Marine birds & reptiles drink seawater & need to excrete excess salts. They have salt glands located above each eye • Certain animals, camels & kangaroo rats, also have a highly convoluted nasal passage with a mucous membrane surface
Nitrogenous Waste Products • Catabolism of amino acids and nucleic acids results in nitrogenous wastes since the NH2 has to be removed (deamination) • There are 3 forms that may be excreted: • 1. Ammonia (NH3) • Little or no energy needed to create • It is very toxic; needs a great deal of water to wash it from the body • High solubility in water permits it to be excreted directly by many aquatic animals • Excreted by bony fishes, marine invertebrates & aquatic amphibians whose gills & skin are in direct contact with water
Nitrogenous Waste Products • 2. Urea • Terrestrial animals must convert ammonia to urea or uric acid since they don’t have a watery environment • Much less toxic than ammonia • Requires the expenditure of energy. Liver changes ammonia into urea by adding CO2 • Excreted by terrestrial amphibians and mammals • Can be excreted in a moderately concentrated solution • Urea allows water to be conserved but there is still a loss of significant water • Thus, most amphibians & mammals must drink water
Nitrogenous Waste Products • 3. Uric Acid • Not very toxic • Requires large amounts of energy to produce • Relatively insoluble in water; leads to water conservation • Uric acid requires much less water per unit of nitrogen excreted • Allows invasion of drier habitats far from standing water • Excreted by reptiles, birds & insects, -Especially good in desert areas - Also very useful for egg-laying animals. Insoluble wastes are stored in shell until hatching & don’t poison the embryo inside
Organs of Excretionin Invertebrates • Various mechanisms have evolved in different animal groups to cope with fluid balance. • Flame Cells in Planarians • Set of tubules & bulblike flame cells rid body of excess water & wastes • Nephridia in Earthworms • In every segment of body there is a pair of these excretory structures that creates urine from blood in surrounding capillaries. • Malpighian Tubules in Insects • Long thin tubes attached to gut. Uric acid leaves through anus.
Excretory Organs in Animals Flame Cells in Planaria Malpighian tubules in Ant Nephridia in Earthworms
Urinary System in Humans • Human kidneys • Located on either side of vertebral column, just below the diaphragm • Each connected to a tube called a ureter • Ureters conduct urine from the kidney to the urinary bladder • Urine leaves bladder through tube called the urethra • In males, the urethra passes through the penis & shares functions with reproductive system • In females, there is no connection between excretory & reproductive systems
Functions of Human Kidneys • The kidneys have various functions: • Removal of urea from blood into urine • Regulation of water balance • Elimination of excess molecules • Regulation of ionic balance (Na+, Cl-, H+, K+, etc.)
Kidneys • The parts of the kidney: • 1. Renal cortex • Outer region with granular appearance • 2. Renal medulla • Inside of cortex; cone-shaped renal pyramids • 3. Renal pelvis • Hollow-chambered innermost part of the kidney
Nephrons • Each kidney composed of over 1 million tubular nephrons • Each nephron is composed of several parts: • Glomerular capsule (Bowman’s capsule) • Glomerulus • Proximal convoluted tubule • Loop of Henle • Distal convoluted tube • Collecting duct
Nephrons • Each nephron has its own blood supply: • Aortabranches off to renal artery which branches into • renal arterioles which branch into an afferent arteriole which divides to form the • glomerular capillary bed (glomerulus) (bed #1) • Glomerulus drains blood into efferent arteriole which branches into • A second capillary bed, the peritubular capillary bed (bed #2) • The capillaries lead to venules which join the • The renal vein which brings blood back to vena cava
Urine Formation • Urine production requires three distinct processes: • Glomerular filtration in glomerular capsule • Tubular reabsorption at the proximal convoluted tubule • Tubular secretion at the distal convoluted tubule
Glomerular Filtration • Occurs at glomerulus & Bowman’s capsule • Blood pressure forces large percentage of molecules to move out of capillaries of glomerulus & into the Bowman’s capsule. Walls of glomerulus are 100 times more permeable than most capillaries in body. • Water, nutrients, salts & urea move out of blood & into capsule and end up in tubules of nephron • Plasma proteins & blood cells are too large & remain behind in the blood that flows into efferent arteriole • Fluid in capsule is now called filtrate. 180 liters produced per day.
Tubular Reabsorption • Takes place when substances move across the walls of the tubules into the peritubular capillaries. • Kidneys produce only about 1-2 liters of urine per day 99% of water must be reabsorbed into blood or humans would die of dehydration • 100% of glucose is reabsorbed into blood or we could die of starvation Plentiful carrier molecules actively reabsorb glucose through walls of tubules. In diabetes mellitus, abnormally large amounts of glucose are in blood & cannot be completely reabsorbed. • 99% of salts are reabsorbed into blood
Tubular Reabsorption • How does tubular reabsorption occur? 1. Proximal convoluted tubule • Na+ is actively transported out of tubule & back into peritubular capillaries Cl- follows passively Water then follows by osmosis. ~60-70% of salt & water are thus reabsorbed right away. - Nutrients, like glucose & amino acids, are returned to blood here - Filtrate is now isotonic to blood in surrounding capillaries & to the fluids in the surrounding kidney tissues
Tubular Reabsorption • 2. Descending Loop of Henle • This side of loop is permeable to water & NOT permeable to salts -Water will leave the descending limb along its entire length due to an increasing concentration gradient in the surrounding kidney tissues (more on how this was created soon) -By the time the filtrate reaches the bottom of the loop of Henle, it is very concentrated in solutes -Much of the water that was in the filtrate has now been reabsorbed back into the blood
Tubular Reabsorption • 3. Ascending Loop of Henle • This side of loop is impermeable to water & permeable to salts -Salt passively diffuses out of the lower portion of the ascending loop -The upper portion actively transports Na+ out of the loop tubule & into the surrounding kidney tissues -Less & less salt is available for transport as the fluid moves up the ascending loop. • An osmotic concentration gradient is set up within the tissues of the renal medulla. ***This allows the increasing amount of water to diffuse out of the descending loopwhich is permeable to H2O***
Tubular Reabsorption • The innermost portion of inner medulla has the highest concentration of solutes -Due to the leakage of urea from the lower portion of ascending loop of Henle • Countercurrent Multiplier Mechanism • •The combined effects of: • 1. the active transport of salts from the ascending limb • 2. the leakage of urea from lower end of ascending loop 3. and the passive transport of water out of the descending loop • set up an increasing solute concentration gradient from the renal cortex down to the medulla
Tubular Reabsorption • Countercurrent Multiplier Mechanism (continued) • •As water diffuses out of descending limb the remaining fluid in the tubule encounters outside kidney tissues of an even higher concentration • •So water continues to flow out of the descending limb all the way to the bottom. • •This maximizes the amount of water that can be diffused out of the filtrate at this point. • *** The longer the loop of Henle, the greater the concentration gradient will become & the more concentrated the urine that can be produced*** • The kangaroo rat has an extremely long loop of Henle which allows it to produce almost no urine & thus conserve so much water it usually doesn’t drink water in the desert
Tubular Reabsorption • 4. Distal Convoluted Tubule • The fluid that enters this tubule is actually hypotonic compared to the renal cortex surrounding it -The distal tubule is now permeable to water again -Salts are actively transported out of this tubule -Water will follow passively by osmosis • Fluid that exits the distal tubule is isotonic to surrounding cortex tissue
Tubular Reabsorption • 5. Collecting Duct (Tubule) • The fluid that enters this tubule is actually isotonic compared to the renal cortex surrounding it -This tubule goes down through the renal medulla once again through the same increasing concentration gradient as the loop of Henle -Tubule is usually permeable to water; but not to salt -Water will flow out passively by osmosis as tubule passes through the concentration gradient • Fluid becomes hypertonic to blood plasma by the time it reaches the renal pelvis
Tubular Secretion • Tubular secretion is the second way that substances are removed from blood & added to filtrate • •Excess ions and other substances like uric acid, ammonia, creatinine, histamine & penicillin move from the capillaries into the tubules, most often at the distal convoluted tubule • ●The body can get rid of substances like drugs & other foreign substances in this step. • -This is how athletes get caught when they are taking steroids & have to produce urine to be tested
Urine Formation and Homeostasis • Humans are capable of excreting hypertonic urine • As water flows down the collecting duct towards the renal medulla it is going through the external concentration gradient & the filtrate will continue to lose water to blood capillaries as long as the collecting tubules are permeable to water. • Permeability of collecting duct can be changed: • The hormone, antidiuretic hormone (ADH), produced by the posterior lobe of the pituitary gland, regulates the permeability of collecting duct
Urine Formation and Homeostasis • How does ADH work? • When ADH is present, more water will be reabsorbed into blood capillaries from tubule -This will tend to occur when you are slightly to greatly dehydrated & need to conserve water -A decreased amount of urine will be formed & its color will be a darker yellow • When ADH is NOT present, the collecting tubules become impermeable to water & it does not reabsorb the water into capillaries (alcohol & caffeine can cause this) -This will tend to occur when you drank a lot of water & need to get rid of the excess water -An increased amount of urine will be formed & its color will be a lighter yellow
