osmoregulation and disposal of metabolic wastes chapter 51

Question 1

Excretion

Answer 1

-Ridding body of metabolic wastes, ions and harmful substances
-Metabolic waste products
-Water—lost from respiratory surfaces and kidneys CO2—most abundant waste, lungs
-Nitrogenous waste—from breakdown of amino acids (deamination
of amino acids)NH2NH3 (ammonia)and nucleic acids

Question 2

Osmoregulation and Disposal of Metabolic Wastes

Answer 2

Osmotic regulation or osmoregulation:

Keeping water and ions in balance between extracellular and intracellular compartments

Question 3

Osmolarity and Osmotic Balance

Answer 3

Important ions
Sodium (Na+) is the major cation in extracellular fluids
Chloride (Cl–) is the major anion
Divalent cations, calcium (Ca2+) and magnesium (Mg2+), the monovalent cation K+, as well as other ions, also have important functions and are maintained at constant levels

Question 4

Osmotic pressure
Measure of a solution’s tendency to take in water by osmosis
Osmolarity
Number of osmotically active moles of solute per liter of solution
Tonicity
Measure of a solution’s ability to change the volume of a cell by osmosis

Answer 4

Osmoconformers
Organisms that are in osmotic equilibrium with their environment
Among the vertebrates, only the primitive hagfish are strict osmoconformers
Sharks and relatives (cartilaginous fish) are also isotonic
All other vertebrates are osmoregulators
Maintain a relatively constant blood osmolarity despite different concentrations in their environment—allows them to exploit a wide variety
of ecological niches

Question 5

Freshwater vertebrates
Hypertonic to their environment—tendency to gain water
Have adapted to prevent water from entering their bodies, and to actively transport ions back into their bodies
Marine vertebrates
Hypotonic to their environment—tendency to lose water
Have adapted to retain water by drinking seawater and eliminating the excess ions through kidneys and gills

Answer 5

Terrestrial vertebrates
Higher concentration of water than surrounding air
Tend to lose water by evaporation from skin and lungs
Urinary/osmoregulatory systems have evolved in these vertebrates that help them retain water

Question 6

Osmoregulatory Organs

Answer 6

In many animals, removal of water or salts is coupled with removal of metabolic wastes through the excretory system
A variety of mechanisms have evolved to accomplish this
Single-celled protists and sponges use contractile vacuoles and diffusion
Other multicellular animals have a system of excretory tubules to expel fluid and wastes

Question 7

Invertebrates
Flatworms
Use protonephridia which branch into bulblike flame cells
Open to the outside of the body, but not to the inside
Earthworms
Use nephridia
Open both to the inside and outside of the body

Answer 7

Insects
Use Malpighian tubules
Extensions of the digestive tract
Waste molecules and K+ are secreted into tubules by active transport
Create an osmotic gradient that draws water into the tubules by osmosis
Most of the water and K+ is then reabsorbed into the open circulatory system through hindgut epithelium

Question 8

Nitrogenous Wastes

Answer 8

When amino acids and nucleic acids are catabolized, they produce nitrogenous wastes that must be eliminated from the body

Question 9

First step—deamination of amino acidsNH2 combined
with H+ to form ammonia (NH3) in the liver toxic
–ammonia by diffusion from gills—bony fishes and amphibian tadpoles
–urea—cartilaginous fishes, adult amphibians and mammals—water soluble
–uric acid—water conserving (insects, reptiles, birds)
water-insoluble—costs most energy, but saves most water

Answer 9

Mammals also produce uric acid, but from degradation of purines, not amino acids
Most have an enzyme called uricase, which convert uric acid into a more soluble derivative called allantoin
Humans lack this enzyme
Excessive accumulation of uric acid in joints causes gout

Question 10

Evolution of the Vertebrate Kidney

Answer 10

Terrestrial vertebrates must conserve water
Only birds and mammals can make a hypertonic (concentrated) urine
Very efficient kidneys

Question 11

Evolution of the Vertebrate Kidney

Answer 11

Made up of 1 million filtering units – nephrons—microscopic functioning unit of the kidney—filters blood and produces urine
		nephron
			1.  glomerulus
			2.  Bowman’s capsule
			3.  renal tubule
				proximal convoluted tubule
				loop of Henle
				distal convoluted tubule

Question 12

Glomerulus—filtrate goes into Bowman’s
capsule proximal convoluted tubulelar fluid, then into the filtrate in the tubular system
loop of Henledistal convoluted tubule
collecting ducturinerenal pelvisureter
urinary bladderurethra

Answer 12

Nephron works bydifferential permeability of tubules

salt gradient established in renal medulla

Question 13

The Mammalian Kidney

Answer 13

Each kidney receives blood from a renal artery
Produces urine from this blood
Urine drains from each kidney through a ureter into a urinary bladder
Urine is passed out of the body through the urethra

Question 14

Divided into an outer renal cortex and inner renal medulla
Within the kidney, the mouth of the ureter flares open to form the renal pelvis
Receives urine from the renal tissue

Answer 14

Nephronurinecollecting ductsrenal pelvisureterurinary

bladderurethra

Question 15

Two types of nephrons:
Juxtamedullary nephron—have long loops that dip deeply into the medulla
Important in concentrating the urine and conserving water

Cortical nephron—have shorter loops

Answer 15

The kidney has three basic functions
Filtration
Fluid in the blood is filtered out of the glomerulus into the tubule system as filtrate
Reabsorption
Selective movement of solutes out of the filtrate back into the blood via peritubular capillaries
Secretion
Movement of substances from the blood into the extracellular fluid, then into the filtrate in the tubular system

Question 16

Blood is carried by an afferent arteriole (larger diameter) to the glomerulus
Blood is filtered as it is forced through porous capillary walls
Filtered out of blood by size—not selective
Leaves glomerulus via efferent arteriole (smaller
diameter)

Answer 16

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Question 17

Osmoregulatory Organs

Answer 17

Filtration
Filters the blood under pressure (hydrostatic pressure) through the glomerulus (filtration)filtrate
Filtrate contains many small molecules (glucose, amino acids, vitamins), in addition to water and waste products
Filtrate enters Bowman’s capsule

Question 18

Reabsorption
Bowman’s capsuleproximal convoluted tubuledown the medulla and back up into cortex in the loop of Henle

Most of these nutrient molecules and water in the filtrate are reabsorbed back into the blood
Selective reabsorption provides great flexibility—depending on the vertebrate and habitat, they reabsorb molecules that are especially valuable in particular habitats—colonize many diverse habitats

Answer 18

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Question 19

Reabsorption

Answer 19

Approximately 2000 L of blood passes through the kidneys each day
180 L of water leaves the blood and enters the glomerular filtrate
Most of the water and dissolved solutes that enter the glomerular filtrate must be returned to the blood by reabsorption
Water is reabsorbed by the proximal convoluted tubule, descending loop of Henle, and collecting duct

Question 20

The Mammalian Kidney

Answer 20

After leaving the loop, the fluid is delivered to a distal convoluted tubule in the cortex
Drains into a collecting duct
Merges with other collecting ducts to empty its contents, now called urine, into the renal pelvis

Question 21

Secretion
Blood components that are not filtered drain into an efferent arteriole, which empties into peritubular capillaries
Secretion of waste products involves transport across capillary membranes into kidney tubules into the filtrate

Answer 21

Kidneys also regulate electrolyte balance in the blood by reabsorption and secretion
K+, H+, and HCO3–

Question 22

Transport in the Nephron

Answer 22

Proximal Convoluted tubule

Reabsorption of glucose and amino acids is driven by active transport
Maximum rate of transport
Glucose remains in the urine of untreated diabetes mellitus patients

Question 23

Proximal convoluted tubule
Reabsorbs virtually all nutrient molecules in the filtrate, and two-thirds of the NaCl and water
Because NaCl and water are removed from the filtrate in proportionate amounts, the filtrate that remains in the tubule is still isotonic to the blood plasma

Answer 23

Loop of Henle
Creates a gradient of increasing osmolarity from the cortex(less salt) to the medulla (more salt)
Actively transports Na+, and Cl– follows from the ascending loop
Creates an osmotic gradient
Allows reabsorption of water from descending loop and collecting duct
Two limbs of the loop form a countercurrent multiplier system
Creates a hypertonic renal medulla

Question 24

Distal convoluted tubule and collecting duct
Filtrate that enters is hypotonic
Hypertonic interstitial fluid of the renal medulla pulls water out of the collecting duct and into the surrounding blood vessels
Permeability controlled by antidiuretic hormone (ADH)
Kidneys also regulate electrolyte balance in the blood by reabsorption and secretion
K+, H+, and HCO3–

Answer 24

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Question 25

Excretion

Answer 25

Major function of the kidney is elimination of a variety of potentially harmful substances that animals eat and drink
In addition, urine contains nitrogenous wastes, and may contain excess K+, H+, and other ions that are removed from blood
Kidneys are critically involved in

Question 26

Hormones Control Osmoregulation

Answer 26

Kidneys maintain relatively constant levels of blood volume, pressure, and osmolarity
Also regulate the plasma K+ and Na+ concentrations and blood pH within narrow limits
These homeostatic functions of kidneys are coordinated primarily by hormones

Question 27

Antidiuretic hormone (ADH)
Produced by the hypothalamus and secreted by the posterior pituitary gland
Stimulated by an increase in the osmolarity of blood (low blood volume)
Causes walls of distal tubule and collecting ducts to become more permeable to water
Aquaporins
More ADH increases reabsorption of water
Makes a more concentrated urine

Answer 27

Aldosterone
Secreted by the adrenal cortex
Stimulated by low levels of Na+ in the blood
Causes distal convoluted tubule and collecting ducts to reabsorb Na+
Reabsorption of Cl– and water follows
Low levels of Na+ in the blood are accompanied by a decrease in blood volume
Renin-angiotensin-aldosterone system is activated

Question 28

Atrial natriuretic hormone (ANH)
Opposes the action of aldosterone in promoting salt and water retention
Secreted by the right atrium of the heart in response to an increased blood volume
Promotes the excretion of salt and water in the urine and lowering blood volume

Answer 28

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