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
cycle 15 steps
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
cycle 15 steps
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. 47-2ab, p. 1014
Nucleus
Cytoplasm
Cilia (“flame”)
Movement of
interstitial fluid
Excretory tubule
Fig. 47-2c, 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. 47-5a, 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. 47-5b, 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. 47-5c, 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. 47-6b, 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. 47-8a, p. 1018
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.
Fig. 47-8b, p. 1018
Insert “Human kidney”
kidney_anatomy_v2.swf
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
Loop of
Henle
To
renal
pelvis
(a) Location and basic structure of a nephron.
Fig. 47-9a, p. 1019
Distal tubule
Bowman's capsule
Proximal tubule
Podocyte
Glomerular
capillaries
Afferent
arteriole
Afferent arteriole
Juxtaglomerular
apparatus
Efferent arteriole
Distal tubule
(b) Cutaway view of Bowman’s capsule.
Fig. 47-9b, 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
H2O; URINE
CONCENTRATED
Distal tubule
Collecting duct
Renal artery
Renal vein
Capillaries
To renal pelvis
Loop of Henle
Fig. 47-10, p. 1020
Insert “Structure of the
glomerulus”
glomerulus.swf
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
Bowman's capsule
Glomerulus
Afferent arteriole
Efferent arteriole
Fig. 47-11a, p. 1021
Blood cells restricted
from passing through
Red blood cell
Capillary
pores
Endothelial cell of
capillary
Nucleus
Podocyte
Filtration
slits
Foot processes
Fig. 47-11b, 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
Insert “Tubular
reabsorption”
tubular_reabsorption_m.swf
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
Bowman's capsule
Afferent
arteriole
Distal tubule
Proximal tubule
Efferent
arteriole
NaCl H2O
Filtrate
CORTEX
H2O
NaCl
NaCl
H2O
NaCl
MEDULLA
Collecting
duct
H2O
H2O
Descending
limb
NaCl
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
Distal tubule
Bowman's capsule
Afferent
arteriole
Proximal tubule
300
100
300
100
200
Efferent
arteriole
CORTEX
Filtrate
300 100
300
300
400 200
400
400
600 400
600
600
600
Collecting
duct
Interstitial
fluid
1200
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
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)
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, 7ADH secretion 3Posterior pituitary
is inhibited.
and osmotic pressure
secretes ADH.
Collecting
duct
decreases.
Nephron
H2O H2O
H2O
H2O
Kidney
H2O
5 Water reabsorption
H2O
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