Transcript Osmoregulation and Excretion

OSMOREGULATION
AND EXCRETION
Key Concepts
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Osmoregulation balances the uptake and loss of water
and solutes
An animal’s nitrogenous wastes reflect its phylogeny and
habitat
Diverse excretory systems are variations on a tubular
theme
Nephrons and associated blood vessels are the
functional units of the mammalian kidney
The mammalian kidney’s ability to conserve water is a
key terrestrial adaptation
Diverse adaptations of the vertebrate kidney have
evolved in different environments
Key Words
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homeostasis
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ammonia
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excretion
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filtrate
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uric acid
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ureter
filtration
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renal vein
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glomerulus
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urethra
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loop of Henle
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nephron
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cortical nephrons
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proximal tubule
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collecting duct
peritubular
capillaries
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efferent arteriole
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aldosterone
antidiuretic hormone
(ADH)
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osmoregulation
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urea
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renal cortex
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secretion (selective
reabsorption)
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renal artery
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urinary bladder
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renal medulla
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Bowman's capsule
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distal tubule
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afferent arteriole
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vasa recta
Types of metabolic waste produced by living
systems
1.
2.
3.
4.
Digestive waste
Respiratory waste
Excess water and
salts (through
osmoregulation)
Nitrogenous waste
(through excretion)
Osmoregulation
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Balance of uptake and loss
of water and solutes
Controlled movement of
solutes between internal
fluids and environment
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Osmoconformer
(marine animals isoosmotic
with environment)
Osmoregulator (freshwater,
marine, and terrestrial
animals that adjust internal
osmolarity)
Types of nitrogenous
wastes
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Deamination – protein
and nucleic acid
metabolism
Three main types
differing in terms of:
1.
2.
3.
Toxicity
Amount of water
needed for excretion
Energy needed for
synthesis
300 – 500 mL/gN
1 step rxn
50 mL/gN
4 step rxn
10 mL/gN
15 step rxn
Type of
Organism
Structure
Product of
excretion
Stomata, lenticels
Insoluble crystals
Crystals are kept inside
plant cells
Plants
No excretory organ
Osmoconformers,
isoosmotic with
environment
Cnidarians and
echinoderms
Contractile vacuole
Freshwater protists and
sponges
Other features
Excretory Systems
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Dispose of metabolic wastes
Regulate solute concentrations in the body
Transport epithelia arranged in tubes
4 major processes
1.
2.
3.
4.
Filtration, pressure-filtering of body
fluids producing a filtrate (water, salts,
sugars, amino acids, N-wastes)
Reabsorption, reclaiming valuable
solutes (glucose, salts, amino acids) from
the filtrate
Secretion, addition of larger molecules
like toxins and other excess solutes from
the body fluids to the filtrate
Excretion, the filtrate leaves the system
Type of
Organism
Structure
Flatworms
Flame cells
Unsegmented
roundworms
Protonephridia, closed
network of dead-end tubes
lacking openings
Annelids
Metanephridia, open-ended
network of tubes with internal
openings that collect body
fluids
Product of
excretion
Other features
Type of
Organism
Structure
Molluscs
Nephridia or metaphridia
Crustaceans
Antennal/green gland
Insects
Malpighian tubules and
digestive tract
Product of
excretion
Uric acid
Other features
Type of
Organism
Structure
Product of
excretion
Marine fishes
Gills
Ammonia
Other features
Rectal glands – excrete
excess NaCl
Elasmobranchs (sharks,
skates, rays)
Kidneys
Urea
Freshwater fishes
Gills
Ammonia or urea
Amphibians and
mammals
Kidneys
Urea
Liver converts ammonia to
urea
Reptiles and birds
Kidneys
Uric acid
Salt glands
From Blood Filtrate to Urine: A Closer Look
1
Proximal tubule – secretion and reabsorption
NaCl
HCO3
4 Distal tubule – secretion and reabsorption
Nutrients
H+
H2O
K+
H2O
NaCl
K+
NH3
CORTEX
Filtrate
H2O
Salts (NaCl and others)
HCO3–
H+
Urea
Glucose; amino acids
Some drugs
>> Same concentration of
substances in blood plasma
2 Descending limb
of loop of
Henle – reabsorption
-Permeable to water but not to salt
3
H+
Thick segment
of ascending
limb –
reabsorption
- Impermeable to
water but
permeable to salt
NaCl
H2O
OUTER
MEDULLA
NaCl
3
Thin segment
of ascending
limb
Key
5 Collecting
Duct – permeable to water
but not to salt, bottom portion is
permeable to urea
Urea
NaCl
Active transport
Passive transport
HCO3
INNER
MEDULLA
H2O
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Two solutes: NaCl
and urea, contribute
to the osmolarity of
the interstitial fluid
Cause the
reabsorption of
water in the kidney
and concentrates the
urine
Osmolarity of
interstitial
fluid
(mosm/L)
300
300
100
300
100
CORTEX
NaCl
H2O
Active
transport
300
400
400
600
600
H2O
200
400
300
H2O
NaCl
H2O
H2O
NaCl
H2O
Passive
transport
OUTER
MEDULLA
NaCl
H2O
H2O
400
600
NaCl
H2O
H2O
Urea
NaCl
H2O
700
900
INNER
MEDULLA
H2O
NaCl
900
H2O
Urea
H2O
1200
Urea
1200
1200
Nervous system and
hormones regulate kidney
functions
Osmoreceptors
in hypothalamus
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Antidiuretic hormone (ADH)
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Stimulated by a rise in the
blood’s osmolarity (>300
mosm/L)
Enhances fluid retention by
making the kidneys reclaim more
water
Increases water reabsorption in
the distal tubules and collecting
ducts of the kidney
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
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The renin-angiotensinaldosterone system (RAAS)
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Responds to a loss of salt and
water in the blood
Stimulated by low blood volume
or pressure
Increases water and sodium ion
reabsorption in the proximal
and distal tubules
Leads to an increase in blood
volume and pressure
Opposed by the hormone atrial
natriuretic factor (ANF)
 Released by atria
 Inhibits release of renin
Homeostasis:
Blood pressure,
volume
Increased Na+
and H2O reabsorption in
distal tubules
STIMULUS:
The juxtaglomerular
apparatus (JGA) responds
to low blood volume or
blood pressure (such as due
to dehydration or loss of
blood)
Aldosterone
Arteriole
constriction
Adrenal gland
Angiotensin II
Distal
tubule
Angiotensinogen
JGA
Renin
production
Renin
Some medical aspects concerning the excretory
system
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Urinary tract infection (UTI)
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bacterial infection
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cystitis/pyelonephritis
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treated by antibiotics and prevented through proper hygiene
Kidney stones
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solidified crystals in kidneys or ureters
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Calcium oxalate
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Uric acid
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nephrolithiasis/urolithiasis
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prevention:
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Drinking adequate water
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Proper diet low in protein, N, and Na
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Avoid excess Vitamin C intake
Dialysis
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Hemodialysis
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Peritoneal dialysis