Chapter 12 Excretory Systems Sections

Name: Chapter 12 Excretory Systems Sections
Uploaded: 2017-07-14T12:29:49+00:00
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Description: Chapter 12 Excretory Systems Sections

Chapter 12 Excretory Systems Sections 12.1-12.4

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 2

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 3

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 4

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Hydrolysis Cellular proteins Ingested proteins Amino acids
Growth + maintenance Retention (osmolyte) Glutamine Catabolism of excess HCO3– HCO3– FIGURE General overview of nitrogen metabolism and excretion in animals. The three main nitrogen excretory products are highlighted in colored boxes. See main text for details. Ammonia Retention (buoyancy) Retention (osmolyte) Urea Uric acid Excreted Excreted Excreted Figure 12-1 p559

Hydrolysis Cellular proteins Ingested proteins Amino acids Growth +
maintenance Retention Glutamine Catabolism of excess HCO3– Uric acid Urea HCO3– Ammonia Retention Retention Excreted Excreted Excreted Stepped Art Fig. 12-1, p.559

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 8

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channel or cotransport carrier
Lumen Tubular cell Interstitial fluid Capillary Na+ channel or cotransport carrier Basolateral Na+ /K + pump 1 FIGURE Properties of transport epithelia and tubular excretory organs. (a) Salt absorption by a waterproof epithelium. (1) Basolateral Na+/K+ ATPase pumps increase Na+ externally, which (2) draws Cl− by electric charge through ClC and/or CFTR channels. (b) Fluid absorption by a water-permeable epithelium in a well-supported model ﬁrst proposed by Peter Curran and John Macintosh in This has the same steps 1 and 2, but also (3) H2O is drawn across osmotically through aquaporins by the NaCl buildup in lateral spaces between cells. H2O is not drawn from the capillary because it is permeable to NaCl (recall that osmosis requires nonpermeable solutes). (4) H2O and Cl− may also move paracellularly. See main text for other details. CFTR or ClC channel 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 FIGURE Properties of transport epithelia and tubular excretory organs. (a) Salt absorption by a waterproof epithelium. (1) Basolateral Na+/K+ ATPase pumps increase Na+ externally, which (2) draws Cl− by electric charge through ClC and/or CFTR channels. (b) Fluid absorption by a water-permeable epithelium in a well-supported model ﬁrst proposed by Peter Curran and John Macintosh in This has the same steps 1 and 2, but also (3) H2O is drawn across osmotically through aquaporins by the NaCl buildup in lateral spaces between cells. H2O is not drawn from the capillary because it is permeable to NaCl (recall that osmosis requires nonpermeable solutes). (4) H2O and Cl− may also move paracellularly. See main text for other details. 4 2 Figure 12-3b p562

ANIMATION: Tubular reabsorption
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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 13

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Secretion Reabsorption Blood flow Filtrate Filtration
Osmoconcentration FIGURE 12-3, CONT’D Properties of transport epithelia and tubular excretory organs. (c) Schematic of the principal functions of a tubular renal organ, such as the vertebrate nephron: ﬁltration, secretion, and reabsorption. Insect, avian, and mammalian tubules may also osmoconcentrate urine. Urine (c) The four basic renal processes (shown for a vertebrate): filtration, secretion, reabsorption, and osmoconcentration Figure 12-3c p563

Techniques for studying renal excretory systems Isolated perfused tubule Perfusion studies Patch clamp Microelectrode Plasma clearance 16

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 17

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Protonephridial network Nucleus Conducting tubule Cilia
Flame cell Protonephridial network Nucleus Conducting tubule Cilia Fenestration Nephridiopores Nephridiopore FIGURE Protonephrida and metanephridia. (a) General schematic for the organization of the protonephridia in a triclad ﬂatworm Dendrocoelum and the detailed structure of a single protonephridium and its ﬂame cell. (b) The head region of a crustacean and the location and arrangement of the metanephridial antennal gland (green gland). Figure 12-5a p566

Fluid flow and filtration as fluid flows across the end-sac
Urine Bladder Excretory pore Eye Antennal gland Antenna Fluid flow and filtration as fluid flows across the end-sac End-sac FIGURE Protonephrida and metanephridia. (a) General schematic for the organization of the protonephridia in a triclad ﬂatworm Dendrocoelum and the detailed structure of a single protonephridium and its ﬂame cell. (b) The head region of a crustacean and the location and arrangement of the metanephridial antennal gland (green gland). Labyrinth— site of H2O reabsorption 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 21

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Solute secretion into the Malpighian tubule
Midgut H2O follows by osmosis K+ CI– H2O reabsorption H2O Urine— semi-solid Head Solute reabsorption FIGURE Malpighian tubules. (a) The arrangement of these tubules in a typical insect. First, K+ ions are transported into the proximal end of the tubule, drawing Cl− in by charge attraction and then water by osmosis. The tubule fluid is further modified as it travels distally in the tubule; in the rectum, large amounts of water are reabsorbed. (b) Countercurrent flow between the Malpighian tubule and hindgut in some desert insects, with osmolarities shown in mOsm. In these animals, the tubules bend posteriorly to lie against the rectum. Unlike in other insects, the side of the tubule facing the hemolymph is waterproof so that K+ and Cl− transported into the tubule without water following osmotically can accumulate to high levels (e.g., 4,000 mOsm). This in turn draws water osmotically from the nonwaterproof rectum, concentrating the fluid leaving the anus Thorax Figure 12-6a p567

Perinephric membrane Leptophragmata Hemolymph 750 KCI KCI KCI 300
Malpighian tubule 4,000 FIGURE Malpighian tubules. (a) The arrangement of these tubules in a typical insect. First, K+ ions are transported into the proximal end of the tubule, drawing Cl− in by charge àttaction and then water by osmosis. The tubule fluid is further modified as it travels distally in the tubule; in the rectum, large amounts of water are reabsorbed. (b) Countercurrent flow between the Malpighian tubule and hindgut in some desert insects, with osmolarities shown in mOsm. In these animals, the tubules bend posteriorly to lie against the rectum. Unlike in other insects, the side of the tubule facing the hemolymph is waterproof so that K+ and Cl− transported into the tubule without water following osmotically can accumulate to high levels (e.g., 4,000 mOsm). This in turn draws water osmotically from the nonwaterproof rectum, concentrating the fluid leaving the anus 300 Perinephric space 2,500 H2O H2O From midgut To anus 800 Rectal lumen <2,500 Figure 12-6b p567

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 25

12.4 Vertebrate Urinary Systems and Extrarenal Organs
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 26

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Renal artery Renal vein Kidney Inferior vena cava Aorta Ureter
FIGURE Urinary system components in two vertebrates. (a) Location of the components of the human male urinary system. The pair of kidneys form the urine, which the ureters carry to the urinary bladder. Urine is stored in the bladder and periodically emptied to the exterior through the urethra. (b) Longitudinal section of a human kidney. The kidney consists of an outer, granular-appearing renal cortex and an inner, striated renal medulla. The renal pelvis at the medial inner core of the kidney collects urine after it is formed. (c) The long, thin mesonephric kidneys of a ﬁsh lie under the spine. Ureter Urinary bladder Urethra Figure 12-7a p569

Renal cortex Renal medulla Renal pyramid Renal pelvis
FIGURE Urinary system components in two vertebrates. (a) Location of the components of the human male urinary system. The pair of kidneys form the urine, which the ureters carry to the urinary bladder. Urine is stored in the bladder and periodically emptied to the exterior through the urethra. (b) Longitudinal section of a human kidney. The kidney consists of an outer, granular-appearing renal cortex and an inner, striated renal medulla. The renal pelvis at the medial inner core of the kidney collects urine after it is formed. (c) The long, thin mesonephric kidneys of a ﬁsh lie under the spine. Renal pelvis Figure 12-7b p569

Gas bladder Kidney Ureter Urinary bladder Stomach
FIGURE Urinary system components in two vertebrates. (a) Location of the components of the human male urinary system. The pair of kidneys form the urine, which the ureters carry to the urinary bladder. Urine is stored in the bladder and periodically emptied to the exterior through the urethra. (b) Longitudinal section of a human kidney. The kidney consists of an outer, granular-appearing renal cortex and an inner, striated renal medulla. The renal pelvis at the medial inner core of the kidney collects urine after it is formed. (c) The long, thin mesonephric kidneys of a ﬁsh lie under the spine. Urinary bladder Stomach Figure 12-7c p569

ANIMATION: Human kidney

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 32

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 33

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 34

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Distal tubule Collecting duct Overview of Functions of Parts of a Nephron Proximal tubule 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 Juxtaglomerular apparatus Efferent arteriole Afferent arteriole Bowman’s capsule 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 Glomerulus Artery Vein Cortex Medulla FIGURE Nephrons in vertebrate kidneys. (a) A schematic representation of a nephron in a mammal, with both tubular and vascular components. (b) Schematic representations of the tubular components of nephrons from a shark (dogﬁ sh Squalus acanthias), a teleost or bony ﬁsh (eel Anguilla anguilla), and an amphibian (mudpuppy Necturus maculosus). Combined vascular/tubular component • Juxtaglomerular apparatus —produces substances involved in the control of kidney function Peritubular capillaries Loop of Henle To renal pelvis Figure 12-8 p570

ANIMATION: Urine formation

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 38

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+ 39

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Proximal tubule segment I Proximal tubule segment II
Neck Proximal tubule segment I Glomerulus Proximal tubule segment II FIGURE Schematic representations of nephrons from the major classes of vertebrates showing the major tubule segments. See main text for details. Collecting duct Distal tubule (a) Marine elasmobranch Figure 12-9a p573

Proximal tubule segment I
Neck Proximal tubule segment I Proximal tubule segment II Collecting tubule Collecting duct FIGURE Schematic representations of nephrons from the major classes of vertebrates showing the major tubule segments. See main text for details. (b) Marine glomerular teleost Figure 12-9b p573

Proximal tubule segment II
Collecting duct Collecting tubule FIGURE Schematic representations of nephrons from the major classes of vertebrates showing the major tubule segments. See main text for details. (c) Marine aglomerular teleost Figure 12-9c p573

Proximal tubule segment I Proximal tubule segment II
Neck Proximal tubule segment I Proximal tubule segment II Intermediate segment Distal tubule Collecting duct FIGURE Schematic representations of nephrons from the major classes of vertebrates showing the major tubule segments. See main text for details. (d) Freshwater glomerular teleost Figure 12-9d p573

Neck Proximal tubule Distal tubule Intermediate segment
Collecting duct FIGURE Schematic representations of nephrons from the major classes of vertebrates showing the major tubule segments. See main text for details. (e) Amphibian Figure 12-9e p573

Neck Proximal tubule Intermediate segment Collecting duct
FIGURE Schematic representations of nephrons from the major classes of vertebrates showing the major tubule segments. See main text for details. Distal tubule (f) Nonavian reptile Figure 12-9f p573

(g) Bird, reptilian-type
Proximal tubule Distal tubule Collecting duct FIGURE Schematic representations of nephrons from the major classes of vertebrates showing the major tubule segments. See main text for details. (g) Bird, reptilian-type Figure 12-9g p573

Descending thin limb of Henle’s Loop
Distal tubule Proximal tubule Collecting duct Descending thin limb of Henle’s Loop FIGURE Schematic representations of nephrons from the major classes of vertebrates showing the major tubule segments. See main text for details. Ascending thick limb of Henle’s Loop (h) Bird, mammalian-type and mammal Figure 12-9h p573

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 49

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 50

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 51

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Central vein (efferent)
Afferent vein Collecting duct Central vein (efferent) Arterial supply Reptilian-type nephron Capillary plexus Short loop mammalian-type nephron Long loop mammalian-type nephron FIGURE Avian urinary systems. (a) The kidney, showing its organization into lobes with short “reptilian”-type and long “mammalian”-type nephrons. (b) The hindgut, showing retrograde ﬂow of urine from the ureter into the coprodaeum and colon Medullary cone Ureteral branch Ureter Figure 12-10a p575

Ureteral urine Ureteral urine
Proctodaeum Colon Caecum Ureteral urine Coprodaeum Ureteral urine FIGURE Avian urinary systems. (a) The kidney, showing its organization into lobes with short “reptilian”-type and long “mammalian”-type nephrons. (b) The hindgut, showing retrograde ﬂow of urine from the ureter into the coprodaeum and colon Urodaeum Cloaca Bird Figure 12-10b p575

INSERT FIG on page 576 55

Salt gland Ducts Lobe Central canal
FIGURE The salt glands of a gull. Central canal Figure p576

Chapter 12 Excretory Systems Sections

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