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Chapter 44
Osmoregulation and
Excretion
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: A Balancing Act
• Physiological systems of animals operate in a
fluid environment
• Relative concentrations of water and solutes
must be maintained within fairly narrow limits
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Freshwater animals show adaptations that
reduce water uptake and conserve solutes
• Desert & marine animals face desiccating
environments that quickly deplete body water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
This Chapter Discussion Around
1. Osmoregulation (regulatn solute concs &
gain/loss of water)
2. Excretion gets rid of metabolic wastes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 44.1: Osmoregulation
balances the uptake and loss of
water and solutes
• Osmoregulation is based largely on controlled
movement of solutes between internal fluids
and the external environment
Osmosis
• Cells require a balance between osmotic gain
and loss of water
• Various mechanisms of osmoregulation in
different environments balance water uptake
and loss
- isoosmotic- same on both sides of membrane
- hyperosmotic
Water flows from hyperosmotic to hypoosmotic
- hypoosmotic
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Osmotic Challenges
• Osmoconformers = (some marine animals) are
isoosmotic with their surroundings and do not
regulate their osmolarity
• Osmoregulators = expend energy to control
water uptake & loss in a hyperosmotic or
hypoosmotic environment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Most animals are stenohaline; they cannot
tolerate substantial changes in external
osmolarity
• Euryhaline animals can survive large
fluctuations in external osmolarity
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Marine Animals
• Most marine invertebrates are
osmoconformers
• Most marine vertebrates and some
invertebrates are osmoregulators
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Marine bony fishes hypoosmotic to sea water
• They lose water by osmosis and gain salt by
diffusion & from food
• They balance water loss by drinking seawater
• Freshwater animals constantly take in water
from their hypoosmotic environment
• They lose salts by diffusion & maintain water
balance by excreting large amounts of dilute urine
• Salts lost by diffusion are replaced by foods &
uptake across the gills
Land Animals
• manage water budgets by drinking & eating
moist foods & using metabolic water
• Desert animals get major water savings from
simple anatomical features
Transport Epithelia
• Transport epithelia are specialized cells that
regulate solute movement
• They are essential components of osmotic
regulation and metabolic waste disposal
• They are arranged in complex tubular
networks
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Example = salt glands marine birds remove
excess NaCl
Nasal salt gland
Nostril
with salt
secretions
Lumen of
secretory tubule
Vein
Capillary
Artery
Secretory
tubule
NaCl
Transport
epithelium
Direction
of salt
movement
Blood
flow Secretory cell
of transport
epithelium
Central
duct
Secretory cells actively
transport salt from blood into
tubules for secretion
Concept 44.2: An animal’s nitrogenous
wastes reflect its phylogeny and habitat
• The type and quantity of an animal’s waste
products may greatly affect its water balance
• Most impt wastes = nitrogenous bkdwn prodts
of prots & nucl acids
- N waste = ammonia which toxic
Wastes must be
dissolved in H2O for
secretion
Different animals
excrete nitrogenous
wastes in different
forms: ammonia,
urea, or uric acid
Ammonia
• Animals that excrete nitrogenous wastes as
ammonia need lots of water
• They release ammonia across the whole body
surface or through gills
Urea
• Liver of mammals & most adult amphibians
converts ammonia to less toxic urea
• The circulatory system carries urea to the
kidneys, where it is excreted
Uric Acid
• Insects, land snails, and many reptiles,
including birds, mainly excrete uric acid
• Uric acid is largely insoluble in water and can
be secreted as a paste with little water loss
• The kinds of nitrogenous wastes excreted
depend on an animal’s habitat
• The amount of nitrogenous waste is
coupled to the animal’s energy budget
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 44.3: Diverse excretory systems are
variations on a tubular theme
• Excretory systems regulate solute mvt
between internal fluids & ext environ
• Most excretory systems produce urine by
refining a filtrate derived from body fluids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Excretory Processes
Filtration:
pressure-filtering of body fluids
Reabsorption:
reclaiming valuable solutes
Secretion:
adding toxins & other solutes from
body fluids to the filtrate
Excretion:
removing the filtrate from system
Vertebrate Kidneys
• Kidneys, the excretory organs of vertebrates,
function in both excretion and osmoregulation
Concept 44.4: Nephrons & assoc bld vessels =
functional unit mammalian kidney
• The mammalian excretory system centers on
paired kidneys, which are also major site of
water balance & salt regulation
• Each kidney is supplied with blood by a renal
artery & drained by a renal vein
• Urine exits each kidney through a duct called
the ureter
• Both ureters drain into a common urinary
bladder from which excretion
Animation: Nephron Introduction
Structure and Function of the Nephron and
Associated Structures
• mammalian kidney has 2 regions
– outer renal cortex
– inner renal medulla
• The nephron, the functional unit of the
vertebrate kidney, consists of a single long
tubule and a ball of capillaries called the
glomerulus
Filtration of the Blood
• Filtration occurs as blood pressure forces fluid
from the blood in the glomerulus into the
lumen of Bowman’s capsule
The filtrate in Bowman’s
capsule mirrors the
concentration of solutes
in blood plasma
Pathway of the Filtrate
• From Bowman’s
capsule, the filtrate
passes through
three regions of the
nephron: the
proximal tubule,
the loop of Henle,
and the distal
tubule
• Fluid from several
nephrons flows
into a collecting
duct
Blood Vessels Associated with the Nephrons
• Each nephron is supplied with blood by an
afferent arteriole, a branch of the renal artery
that divides into the capillaries
• The capillaries converge as they leave the
glomerulus, forming an efferent arteriole
• The vessels divide again, forming the
peritubular capillaries, which surround the
proximal and distal tubules
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•
Filtrate becomes urine
as it flows through the
mammalian nephron
and collecting duct
•
Major reabsorbtion in
proximal tubule +
some secretion
•
Reabsorption of water
continues as filtrate
moves into the
descending limb of the
loop of Henle
• In the ascending limb of the loop of Henle, salt
diffuses from the permeable tubule into the
interstitial fluid
• The distal tubule regulates the K+ and NaCl
concentrations of body fluids
• The collecting duct carries filtrate through the
medulla to the renal pelvis and reabsorbs NaCl
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 44-14
Proximal tubule
NaCl Nutrients
HCO3–
K+
H2O
H+
NH3
Distal tubule
H2O
NaCl
K+
HCO3–
H+
CORTEX
Descending limb
of loop of
Henle
Filtrate
H2O
Salts (NaCl and others)
HCO3–
H+
Urea
Glucose; amino acids
Some drugs
Thick segment
of ascending
limb
NaCl
H2O
OUTER
MEDULLA
NaCl
Thin segment
of ascending
limb
Key
Collecting
duct
Urea
NaCl
Active transport
Passive transport
INNER
MEDULLA
H2O
Animation: Bowman's Capsule and Proximal Tubule
Animation: Loop of Henle and Distal Tubule
Animation: Collecting Duct
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 44.5: The mammalian kidney’s
ability to conserve water is a key terrestrial
adaptation
• The mammalian kidney conserves water by
producing urine that is much more
concentrated than body fluids
Regulation of Kidney Function
• The osmolarity of the urine is regulated by
nervous and hormonal control of water and
salt reabsorption in the kidneys
• Antidiuretic hormone (ADH) increases water
reabsorption in the distal tubules and
collecting ducts of the kidney
Animation: Effect of ADH
Osmoreceptors
in hypothalamus
Thirst
Hypothalamus
Drinking reduces
blood osmolarity
to set point
ADH
Increased
permeability
Pituitary
gland
Distal
tubule
STIMULUS
The release of ADH is
triggered when osmoreceptor cells in the
hypothalamus detect an
increase in the osmolarity
of the blood
H2O reabsorption helps
prevent further
osmolarity
increase
Collecting duct
Homeostasis:
Blood osmolarity