Osmoregulation and Disposal of Metabolic Wastes Chapter 47

Osmoregulation and Disposal of Metabolic Wastes Chapter 47

Learning Objective 1 • How do the processes of osmoregulation and excretion contribute to fluid and electrolyte homeostasis?

Fluid-Electrolyte Homeostasis • Osmoregulation • • • active regulation of osmotic pressure of body fluids maintains fluid and electrolyte homeostasis Excretion • process of ridding body of metabolic wastes

Learning Objective 2 • Contrast the benefits and costs of excreting ammonia, uric acid, or urea

Nitrogenous Wastes • Ammonia (toxic) • • Urea (less toxic) • • • excreted mainly by aquatic animals synthesis requires energy excretion requires water Uric acid (less toxic) • excreted as semisolid paste (conserves water)

Nitrogenous Wastes

Amino acids Nucleic acids Deamination Ammonia Keto acids Purines Urea 15 steps cycle Ammonia Urea Uric acid More energy needed to produce More water needed to excrete Fig. 47 -1, p. 1013

Amino acids Nucleic acids Deamination Ammonia Keto acids Purines Urea 15 steps cycle Ammonia Urea Uric acid More energy needed to produce More water needed to excrete Stepped Art Fig. 47 -1, p. 1013

Learning Objective 3 • Compare osmoconformers and osmoregulators

Osmoconformers • Most marine invertebrates • Salt concentration of body fluids varies with changes in sea water

Osmoregulators • Some marine invertebrates • • especially in coastal habitats Maintain optimal salt concentration despite changes in salinity of surroundings

KEY CONCEPTS • Osmoregulation is the process by which organisms control the concentration of water and salt in the body so that their body fluids do not become too dilute or too concentrated

Learning Objective 4 • Describe protonephridia, metanephridia, and Malpighian tubules • Compare their functions

Nephridial Organs • Help maintain homeostasis • • • by regulating concentration of body fluids osmoregulation excretion of metabolic wastes

Protonephridia • Tubules with no internal openings • • in flatworms and nemerteans Interstitial fluid enters blind ends • flame cells (cells with brushes of cilia) • • Cilia propel fluid through tubules • Excess fluid exits through nephridiopores

Protonephridia

Flame cells Protonephridial network Nephridiopores Excretory tubule Flatworm Fig. 47 -2 ab, p. 1014

Nucleus Cytoplasm Cilia (“flame”) Movement of interstitial fluid Excretory tubule Fig. 47 -2 c, p. 1014

Metanephridia • Tubules open at both ends • • Fluid from coelom moves through tubule • • in most annelids and mollusks needed materials reabsorbed by capillaries Urine exits body through nephridiopores • contains wastes

Metanephridia

Tubule Anterior Posterior Gut Funnel Septum Nephridiopore Capillary network Fig. 47 -3, p. 1014

Malpighian Tubules 1 • Extensions of insect gut wall • • Tubule cells actively transport uric acid from hemolymph into tubule • • blind ends lie in hemocoel water follows by diffusion Contents of tubule pass into gut

Malpighian Tubules 2 • Water and some solutes reabsorbed in rectum • Malpighian tubules effectively conserve water • contribute to success of insects as terrestrial animals

Malpighian Tubules

Gut Malpighian tubules Waste Hindgut Rectum Midgut Water and needed ions Fig. 47 -4, p. 1014

KEY CONCEPTS • Excretory systems have evolved that function in both osmoregulation and in disposal of metabolic wastes

Learning Objective 5 • Relate the function of the vertebrate kidney to the success of vertebrates in a wide variety of habitats

The Vertebrate Kidney • Excretes nitrogenous wastes • Helps maintain fluid balance by adjusting salt and water content of urine

Adaptation to Habitats • Freshwater, marine, terrestrial habitats • • different problems for maintaining internal fluid balance, excretion of nitrogenous wastes Structure and function of vertebrate kidney • adapted to various osmotic challenges of different habitats

KEY CONCEPTS • The vertebrate kidney maintains water and electrolyte balance and excretes metabolic wastes

Learning Objective 6 • Compare adaptations for osmoregulation in freshwater fishes, marine bony fishes, sharks, marine mammals, and terrestrial vertebrates

Freshwater Fishes • Take in water osmotically • excrete large volume of hypotonic urine

Water gain by osmosis Loses salt by diffusion Drinks no water Salt uptake by gills Kidney with large glomeruli Large volume of hypotonic urine Fig. 47 -5 a, p. 1015

Marine Bony Fishes • Lose water osmotically • Compensate by drinking sea water and excreting salt through their gills • Produce only a small volume of isotonic urine

Water loss by osmosis Gains salts by diffusion Drinks salt water Salt excreted through gills Kidney with small or no glomeruli Small volume of isotonic urine Fig. 47 -5 b, p. 1015

Sharks and Other Marine Cartilaginous Fishes • Retain large amounts of urea • • allows them to take in water osmotically through their gills Excrete large volume of hypotonic urine

Water gain by osmosis Salt-excreting gland Salts diffuse in through gills Some salt water swallowed with food Kidney with large glomeruli— reabsorbs urea Large volume of hypotonic urine Fig. 47 -5 c, p. 1015

Marine Mammals • Ingest sea water with their food • produce concentrated urine

Terrestrial Vertebrates • Must conserve water • • adaptations include efficient kidneys Endotherms • • have a high metabolic rate produce large volume of nitrogenous wastes

LIVER Wastes produced ALL CELLS Hemoglobin breakdown Breakdown of nucleic acids Cellular respiration Deamination of amino acids Wastes Uric acid Bile pigments Water Carbon dioxide Urea Organs of excretion KIDNEY Excretion Urine DIGESTIVE SYSTEM Feces SKIN LUNGS Exhaled air Sweat containing water vapor and carbon dioxide Fig. 47 -6 b, p. 1016

KEY CONCEPTS • Freshwater, marine, and terrestrial animals have different adaptations to meet the challenges of these diverse environments

Learning Objective 7 • Describe (or label on a diagram) the organs of the mammalian urinary system • Give the functions of each

The Urinary System • Principal excretory system in mammals • Mammalian kidneys produce urine • • • passes through ureters to urinary bladder for storage Urine is released from the body (urination) • through the urethra

Human Urinary System

Adrenal gland Right kidney Left renal artery Right renal vein Left kidney Inferior vena cava Abdominal aorta Ureteral orifices Right and left ureters Urinary bladder Urethra External urethral orifice Fig. 47 -7, p. 1017

Kidney Structure 1 • Renal cortex • • Renal medulla • • • outer portion of kidney inner portion of kidney contains 8 to 10 renal pyramids Renal pyramids • tip of each pyramid is a renal papilla

Kidney Structure 2 • Urine flows into collecting ducts • • which empty through a renal papilla into the renal pelvis (funnel-shaped chamber) Nephrons • • functional units of kidney each kidney has more than 1 million

Internal Kidney Structure

Renal pyramids (medulla) Capsule Renal cortex Renal medulla Renal artery Renal vein Renal pelvis Ureter Internal structure of the kidney. Fig. 47 -8 a, p. 1018

Juxtamedullary nephron Distal convoluted tubule Cortical nephron Capsule Renal cortex Proximal convoluted tubule Glomerulus Bowman’s capsule Artery and vein Loop of Henle Renal medulla Collecting duct Papilla Juxtamedullary and cortical nephrons. Fig. 47 -8 b, p. 1018

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Learning Objective 8 • Describe (or label on a diagram) the structures of a nephron (including associated blood vessels) • Give the functions of each structure

Nephron Structure • Each nephron consists of • • a cluster of capillaries (glomerulus) surrounded by a Bowman’s capsule that opens into a long, coiled renal tubule Renal tubule consists of • • • proximal convoluted tubule loop of Henle distal convoluted tubule

Types of Nephrons • Cortical nephrons • • • located mostly within cortex or outer medulla have small glomeruli Juxtamedullary nephrons • • • extend deep into medulla have large glomeruli and long loops of Henle important in concentrating urine

Blood Vessels 1 • Blood flows • • from small branches of renal artery to afferent arterioles to glomerular capillaries into an efferent arteriole

Blood Vessels 2 • Efferent arteriole • • delivers blood into peritubular capillaries that surround the renal tubule Blood leaves kidney through renal vein

Nephron Structure

Proximal tubule Bowman's capsule Glomerulus Efferent arteriole Afferent arteriole Peritubular capillaries Distal tubule Collecting duct From renal artery To renal vein (a) Location and basic structure of a nephron. Loop of Henle To renal pelvis Fig. 47 -9 a, p. 1019

Distal tubule Bowman's capsule Proximal tubule Podocyte Glomerular capillaries Afferent arteriole Juxtaglomerular apparatus Efferent arteriole Distal tubule (b) Cutaway view of Bowman’s capsule. Fig. 47 -9 b, p. 1019

KEY CONCEPTS • The nephron is the functional unit of the vertebrate kidney

Learning Objective 9 • Trace a drop of filtrate from Bowman’s capsule to its release from the body as urine

Urine Production • Filtration • • Reabsorption • • of plasma of needed materials Secretion • of potassium, hydrogen ions into renal tubule

Urine Production

REABSORPTION AND SECRETION Proximal tubule FILTRATION Bowman's capsule Glomerulus REABSORPTION AND SECRETION REABSORPTION OF H 2 O; URINE CONCENTRATED Distal tubule Collecting duct Renal artery Renal vein Capillaries To renal pelvis Loop of Henle Fig. 47 -10, p. 1020

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Filtration 1 • Plasma filters through glomerular capillaries into Bowman’s capsule • Filtration membrane • • • permeable walls of capillaries filtration slits between podocytes Podocytes • • specialized epithelial cells make up inner wall of Bowman’s capsule

Filtration Membrane

Glomerulus Bowman's capsule Afferent arteriole Efferent arteriole Fig. 47 -11 a, p. 1021

Blood cells restricted from passing through Red blood cell Capillary pores Endothelial cell of capillary Nucleus Podocyte Filtration slits Foot processes Fig. 47 -11 b, p. 1021

Filtration 2 • Filtration is nonselective • • small molecules become part of filtrate glucose, other needed materials, metabolic wastes

Reabsorption 1 • About 99% of filtrate is reabsorbed from renal tubules into blood • Highly selective process • • returns usable materials to blood leaves wastes, excess substances to be excreted in the urine

Reabsorption 2 • Tubular transport maximum (Tm) • maximum rate at which a substance can be reabsorbed

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Secretion • Hydrogen ions, certain other ions, and some drugs are actively transported into renal tubule to become part of urine

Water, Ion and Urea Movement

Afferent arteriole Bowman's capsule Efferent arteriole Distal tubule Proximal tubule Na. Cl H 2 O Filtrate CORTEX H 2 O Na. Cl MEDULLA Collecting duct H 2 O Descending limb Na. Cl Urea Ascending limb Loop of Henle Fig. 47 -12, p. 1022

Urine Concentration 1 • Depends on high concentration of salt and urea in interstitial fluid of kidney medulla • Concentration gradient • • salt most concentrated around bottom of loop of Henle maintained by salt reabsorption from various parts of renal tubule

Urine Concentration 2 • Counterflow of fluid through two limbs of loop of Henle • • • concentrates filtrate moving down descending loop dilutes filtrate moving up ascending loop Water is drawn from filtrate by osmosis • • as it passes through collecting ducts concentrating urine in collecting ducts

Urine Concentration 3 • Vasa recta • • system of capillaries extending from efferent arterioles removes some water that diffuses from filtrate into interstitial fluid

Urine Concentration

Afferent arteriole Distal tubule Bowman's capsule Proximal tubule 300 Efferent arteriole 100 300 100 200 CORTEX Filtrate 300 100 300 400 200 400 600 600 Collecting duct Interstitial fluid 1200 MEDULLA 1200 Loop of Henle Fig. 47 -13, p. 1023

Urine • A watery solution of nitrogenous wastes, excess salts, and other substances not needed by the body

Watch renal processes in action by clicking on the figures in Thomson. NOW.

Learning Objective 10 • Describe the hormonal regulation of fluid and electrolyte balance by antidiuretic hormone (ADH), the renin–angiotensin– aldosterone system, and atrial natriuretic peptide (ANP)

Antidiuretic Hormone (ADH) • Posterior pituitary increases ADH release • • • when body needs to conserve water responds to increase in osmotic concentration of blood (caused by dehydration) ADH increases permeability of collecting ducts to water • • more water is reabsorbed small volume of urine is produced

Regulation by ADH

Receptors in the hypothalamus 1 Fluid intake is low. 2 Blood volume decreases, and osmotic pressure increases. Posterior pituitary 6 Blood volume increases, 7 ADH secretion 3 Posterior pituitary is inhibited. and osmotic pressure secretes ADH. Collecting duct decreases. Nephron H 2 O Kidney H 2 O 5 Water reabsorption H 2 O increases. 4 Collecting ducts become more Lower permeable. urine volume Fig. 47 -14, p. 1024

Renin-Angiotensin-Aldosterone Pathway 1 • When blood pressure decreases • • juxtaglomerular apparatus secretes renin Renin (enzyme) • activates pathway to production of angiotensin II

Renin-Angiotensin-Aldosterone Pathway 2 • Angiotensin II (hormone) • • • constricts arterioles (raises blood pressure) stimulates aldosterone release Aldosterone (hormone) • increases sodium reabsorption (raises blood pressure)

Atrial Natriuretic Peptide (ANP) • When blood pressure increases • • • ANP increases sodium excretion, inhibits aldosterone secretion increases urine output, lowers blood pressure Renin-angiotensin-aldosterone pathway and atrial natriuretic peptide work antagonistically