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? How do the processes of osmoregulation and excretion contribute to fluid and electrolyte homeostasis?

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

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

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

Nitrogenous Wastes

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

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

Learning Objective 3 Compare osmoconformers and osmoregulators Compare osmoconformers and osmoregulators

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

Osmoregulators Some marine invertebrates Some marine invertebrates especially in coastal habitats especially in coastal habitats Maintain optimal salt concentration despite changes in salinity of surroundings 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 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 Describe protonephridia, metanephridia, and Malpighian tubules Compare their functions Compare their functions

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

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

Protonephridia

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

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

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

Metanephridia

Fig. 47-3, p Tubule Anterior Posterior Gut Funnel SeptumNephridiopore Capillary network

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

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

Malpighian Tubules

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

KEY CONCEPTS Excretory systems have evolved that function in both osmoregulation and in disposal of metabolic wastes 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 Relate the function of the vertebrate kidney to the success of vertebrates in a wide variety of habitats

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

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

KEY CONCEPTS The vertebrate kidney maintains water and electrolyte balance and excretes metabolic wastes 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 Compare adaptations for osmoregulation in freshwater fishes, marine bony fishes, sharks, marine mammals, and terrestrial vertebrates

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

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

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

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

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

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

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

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

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

KEY CONCEPTS Freshwater, marine, and terrestrial animals have different adaptations to meet the challenges of these diverse environments 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 Describe (or label on a diagram) the organs of the mammalian urinary system Give the functions of each Give the functions of each

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

Human Urinary System

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

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

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

Internal Kidney Structure

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

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

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

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

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

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

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

Nephron Structure

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

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

KEY CONCEPTS The nephron is the functional unit of the vertebrate kidney 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 Trace a drop of filtrate from Bowman’s capsule to its release from the body as urine

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

Urine Production

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

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

Filtration Membrane

Fig a, p Glomerulus Bowman's capsule Afferent arteriole Efferent arteriole

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

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

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

Reabsorption 2 Tubular transport maximum (Tm) Tubular transport maximum (Tm) maximum rate at which a substance can be reabsorbed 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 Hydrogen ions, certain other ions, and some drugs are actively transported into renal tubule to become part of urine

Water, Ion and Urea Movement

Fig , p Bowman's capsule Proximal tubule Distal tubule Afferent arteriole Efferent arteriole Filtrate NaCl MEDULLA NaCl CORTEX NaCl Collecting duct H2OH2O NaCl Urea Descending limb Ascending limb Loop of Henle H2OH2O H2OH2O H2OH2OH2OH2O

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

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

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

Urine Concentration

Fig , p Bowman's capsule Proximal tubule Distal tubule Afferent arteriole Efferent arteriole CORTEX Filtrate MEDULLA Interstitial fluid Collecting duct 1200 Loop of Henle

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

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

Regulation by ADH

Fig , p Fluid intake is low. Receptors in the hypothalamus 2Blood volume decreases, and osmotic pressure increases. Posterior pituitary ADH secretion is inhibited. Posterior pituitary secretes ADH. Blood volume increases, and osmotic pressure decreases Collecting duct Nephron H2OH2O Kidney 5Water reabsorption increases. Collecting ducts become more permeable. 4 Lower urine volume H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O

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

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

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