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Lauralee Sherwood Hillar Klandorf Paul Yancey Chapter 12 Excretory Systems Sections 12.1-12.4 Kip McGilliard • Eastern Illinois University 12.1 Evolution of Excretory Systems Functions of the excretory systems • Maintenance of proper internal levels of inorganic solutes • Maintenance of proper plasma water volume • Removal of waste • Maintenance of osmotic balance 12.1 Evolution of Excretory Systems Evolution of basic excretory organs • Simple aquatic animals depend on diffusion and membrane transporters • More complex aquatic animals evolved specialized excretory tissues with transport epithelia • Larger aquatic and all terrestrial animals evolved specialized tubules lined with transport epithelia 12.1 Evolution of Excretory Systems Nitrogenous wastes • Result from the metabolism of proteins and nucleic acids • Choice of primary nitrogen waste correlates with water availability • Ammonia • Most aquatic animals that breathe water (ammonotely) • Diluted to nontoxic concentrations • Urea • Most terrestrial animals (ureotely) • More expensive metabolically, less toxic than ammonia • Uric acid • Insects, reptiles and birds (uricotely) • Most expensive metabolically, highly insoluble 12.1 Evolution of Excretory Systems Cellular proteins Hydrolysis Ingested proteins Amino acids Growth + maintenance Retention (osmolyte) Glutamine Catabolism of excess HCO3– HCO3– Ammonia Retention (osmolyte) Urea Uric acid Retention (buoyancy) Excreted Excreted Excreted Figure 12-1 p559 Hydrolysis Cellular proteins Ingested proteins Amino acids Growth + maintenance Retention Glutamine Catabolism of excess HCO3– HCO3– Ammonia Retention Urea Retention Uric acid Excreted Excreted Excreted Stepped Art Fig. 12-1, p.559 12.1 Evolution of Excretory Systems Transporting salt and water across epithelial layer • Na+/K+ ATPase pump on basolateral membrane lowers Na+ concentration inside the cell by pumping Na+ into the ECF • Na+ enters cell from apical side by diffusion through ENaC channel • Cl– is attracted out of the cell through CIC or CFTR channels by the charge gradient produced by Na+ efflux • Increased extracellular solute concentration attracts water across basolateral membrane 12.1 Evolution of Excretory Systems Lumen Tubular cell Na+ channel or cotransport carrier CFTR or ClC channel Interstitial fluid Capillary Basolateral Na+ /K + pump 1 Lateral space 2 Figure 12-3a p562 Lumen Proximal tubular cell Interstitial fluid Capillary Osmosis AQP-1 water channel 3 AQP-1 water channel Hydrostatic pressure Osmosis 1 4 2 Figure 12-3b p562 ANIMATION: Tubular reabsorption To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 12.2 Renal Excretory Organs: Overview Basic processes taking place in renal tubules • Filtration • Water and small solutes pass through a barrier while cells and large molecules remain behind • Secretion • Transport epithelia move specific solutes into the tubule lumen for excretion • Reabsorption • Transport epithelia move specific solutes and water back into the body from the lumen • Osmoconcentration • Water is removed from the lumen, leaving solutes behind, producing a more concentrated excretory fluid 12.2 Renal Excretory Organs: Overview Secretion Reabsorption Blood flow Filtrate Filtration Osmoconcentration Urine (c) The four basic renal processes (shown for a vertebrate): filtration, secretion, reabsorption, and osmoconcentration Figure 12-3c p563 12.2 Renal Excretory Organs: Overview Techniques for studying renal excretory systems • Isolated perfused tubule • Perfusion studies • Patch clamp • Microelectrode • Plasma clearance 12.2 Renal Excretory Organs: Overview Types of renal organs • Protonephridia • Blind end ducts project into body cavity • Ultrafiltration driven by cilia moving fluid outward • Mesonephridia and metanephridia • • • • Ultrafiltration driven by fluid pressure Requires a circulatory system Mesonephric tubules in aquatic vertebrates Metanephric tubules in terrestrial animals • Malpighian tubules • Filtration driven by active secretion of ions • Arthropods 12.2 Renal Excretory Organs: Overview Flame cell Protonephridial network Conducting tubule Nucleus Cilia Fenestration Nephridiopores Nephridiopore Figure 12-5a p566 Urine Excretory pore Bladder Eye Antennal gland Antenna End-sac Labyrinth— site of H2O reabsorption Fluid flow and filtration as fluid flows across the end-sac Nephridial canal— site of ion reabsorption Figure 12-5b p566 12.3 Insect Malpighian Tubules Structure of Malpighian tubules • Blind end epithelial ducts • One cell layer thick • Project into hemolymph from the hindgut Filtration by ion secretion • Secrete K+ (and often Na+) into tubule lumen using a proton pump (V-ATPase, secondary active transport) • Electrical gradient attracts Cl– into lumen through CIC channels • Water from hemolymph moves into tubular fluid by osmosis through aquaporins 12.3 Insect Malpighian Tubules Solute secretion into the Malpighian tubule Malpighian tubule Midgut H2O follows by osmosis + CI– K H2O H2O reabsorption Urine— semi-solid Head Solute reabsorption Thorax Figure 12-6a p567 Perinephric Hemolymph 750 membrane Leptophragmata KCI 300 300 From midgut KCI Malpighian tubule 4,000 Perinephric space 2,500 H2O 800 KCI H2O Rectal lumen <2,500 To anus Figure 12-6b p567 12.3 Insect Malpighian Tubules Secretion and reabsorption in Malpighian tubules • Osmotic movement of water creates bulk flow down the tubule • Organic wastes (e.g. uric acid) are secreted into the tubule by transporters Antidiuresis and diuresis take place in the hindgut • Tubule empties an isosmotic fluid into the gut • Osmoconcentration involves active transport of ions from hindgut followed by osmosis • Diuresis involves active transport of ions without water uptake • Regulated by antidiuretic and diuretic hormones 12.4 Vertebrate Urinary Systems and Extrarenal Organs Vertebrate urinary systems • Kidneys are the urine-forming organ • Paired organs on dorsal side of abdominal cavity, one on each side of the vertebral column • Blood is supplied by renal artery, exits via renal vein • Urine drains into two ureters • Ureters empty into urinary bladder (in fish, amphibians, mammals), which stores the urine, or hindgut (in reptiles and birds) • Bladder empties to the outside through the ureter 12.4 Vertebrate Urinary Systems and Extrarenal Organs Renal artery Renal vein Inferior vena cava Urinary bladder Kidney Aorta Ureter Urethra Figure 12-7a p569 Renal cortex Renal pyramid Renal medulla Renal pelvis Figure 12-7b p569 Gas bladder Kidney Ureter Urinary bladder Stomach Figure 12-7c p569 ANIMATION: Human kidney To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 12.4 Vertebrate Urinary Systems and Extrarenal Organs Regions of the kidney • Renal cortex -- outer • Renal medulla -- inner • Medulla is divided into renal pyramids in larger mammals • Renal pelvis -- drainage area in center of kidney Nephron is the smallest functional unit of the kidney • 1 million nephrons in human kidney • Consists of a tubule and associated vascular component 12.4 Vertebrate Urinary Systems and Extrarenal Organs Vasculature of the nephron • Afferent arteriole supplies each nephron • Glomerulus is a ball-like knot of capillaries in renal cortex -- site of filtration of the blood • Efferent arteriole exits the glomerulus • Peritubular capillaries surrounding the tubules supply the renal tissue with blood and exchange materials with the tubular fluid 12.4 Vertebrate Urinary Systems and Extrarenal Organs Functional parts of the renal tubule • Bowman’s capsule -- glomerular filtration • Proximal tubule -- tubular reabsorption and secretion • Loop of Henle -- osmoconcentration • Descending limb plunges into medulla • Ascending limb returns to cortex • Distal tubule -- reabsorption/secretion and osmoconcentration • Collecting duct -- osmoconcentration • Empties into renal pelvis • Juxtaglomerular apparatus -- sensor in osmoregulation and blood pressure regulation 12.4 Vertebrate Urinary Systems and Extrarenal Organs Distal tubule Collecting duct Proximal tubule Juxtaglomerular apparatus Efferent arteriole Afferent arteriole Bowman’s capsule Glomerulus Artery Vein Cortex Medulla Peritubular capillaries Overview of Functions of Parts of a Nephron Vascular component • Afferent arteriole —carries blood to the glomerulus • Glomerulus —a tuft of capillaries that filters a protein-free plasma into the tubular component • Efferent arteriole —carries blood from the glomerulus • Peritubular capillaries —supply the renal tissue; involved in exchanges with the fluid in the tubular lumen Tubular component • Bowman’s capsule —collects the glomerular filtrate • Proximal tubule —uncontrolled reabsorption and secretion of selected substances occur here • Loop of Henle —establishes an osmotic gradient in the renal medulla that is important in the kidney’s ability to produce urine of varying concentration • Distal tubule and collecting duct — variable, controlled reabsorption of Na+ and H2O and secretion of K+ and H+ occur here; fluid leaving the collecting duct is urine, which enters the renal pelvis Combined vascular/tubular component • Juxtaglomerular apparatus —produces substances involved in the control of kidney function Loop of Henle To renal pelvis Figure 12-8 p570 ANIMATION: Urine formation To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 12.4 Vertebrate Urinary Systems and Extrarenal Organs Fish urinary systems • Elasmobranches are isosmotic or hyperosmotic relative to seawater • Retain urea and trimethylamine oxide (TMAO) as major osmolytes • Rectal gland in hindgut excretes a hypertonic fluid high in NaCl 12.4 Vertebrate Urinary Systems and Extrarenal Organs Fish urinary systems • Marine bony fishes are hypo-osmotic • Drink seawater to reverse water loss through the gills • Gills actively transport NaCl outward and excrete nitrogenous waste • Kidneys remove excess divalent ions • Freshwater bony fishes are hyperosmotic • Take in water through gills and mouth • Excrete a large volume of highly dilute urine • Gills take in NaCl and excrete NH3 and NH4+ 12.4 Vertebrate Urinary Systems and Extrarenal Organs Neck Glomerulus Proximal tubule segment I Proximal tubule segment II Collecting duct Distal tubule (a) Marine elasmobranch Figure 12-9a p573 Neck Proximal tubule segment I Proximal tubule segment II Collecting tubule Collecting duct (b) Marine glomerular teleost Figure 12-9b p573 Proximal tubule segment II Collecting duct Collecting tubule (c) Marine aglomerular teleost Figure 12-9c p573 Neck Proximal tubule segment I Proximal tubule segment II Intermediate segment Distal tubule Collecting duct (d) Freshwater glomerular teleost Figure 12-9d p573 Neck Proximal tubule Distal tubule Collecting duct Intermediate segment (e) Amphibian Figure 12-9e p573 Neck Proximal tubule Intermediate segment Collecting duct Distal tubule (f) Nonavian reptile Figure 12-9f p573 Proximal tubule Distal tubule Collecting duct (g) Bird, reptilian-type Figure 12-9g p573 Distal tubule Proximal tubule Collecting duct Descending thin limb of Henle’s Loop Ascending thick limb of Henle’s Loop (h) Bird, mammalian-type and mammal Figure 12-9h p573 12.4 Vertebrate Urinary Systems and Extrarenal Organs Amphibian urinary systems • Demonstrate the transition to life on land • Lungs cannot excrete nitrogenous wastes nor regulate NaCl • Kidneys maintain a constant ECF • Metanephric nephrons in adult amphibians resemble mesonephric ones in freshwater fish with urea excretion added • Urinary bladder serves as a temporary water reservoir in case of dehydration • Arginine vasotocin (AVT) triggers water uptake through aquaporins in the bladder wall 12.4 Vertebrate Urinary Systems and Extrarenal Organs Reptile urinary system • Nephrons resemble aquatic vertebrates • Ureters carry urine in liquid or semisolid form into the cloaca • Lack a loop of Henle to help conserve water • Uric acid is the primary nitrogenous waste • Cloaca and lower intestine can reabsorb water • Nasal salt glands secrete a highly salty fluid 12.4 Vertebrate Urinary Systems and Extrarenal Organs Avian urinary system • Resembles reptiles • Some mammalian-type nephrons with loops of Henle further concentrate the urine • Uric acid crystals are covered with protein coats to form urate balls • Marine birds have nasal salt glands located near the eyes • Contain blind-end tubules lined with active salt secreting cells • Excrete excess salt out of nasal passages 12.4 Vertebrate Urinary Systems and Extrarenal Organs Afferent vein Collecting duct Central vein (efferent) Arterial supply Reptilian-type nephron Capillary plexus Short loop mammalian-type nephron Long loop mammalian-type nephron Medullary cone Ureteral branch Ureter Figure 12-10a p575 Ureter Proctodaeum Colon Ureteral urine Caecum Coprodaeum Ureteral urine Urodaeum Cloaca Bird Figure 12-10b p575 12.4 Vertebrate Urinary Systems and Extrarenal Organs INSERT FIG 12-11 on page 576 Salt gland Ducts Lobe Central canal Figure 12-11 p576