Download 4/2/2015 Osmoregulation & Excretion Chapter 44:

4/2/2015
Chapter 44:
Osmoregulation & Excretion
1. Osmoregulation
2. Nitrogenous Wastes
3. Excretory Processes
4. Hormonal Control of
Osmoregulation & Excretion
1. Osmoregulation
Balancing Uptake & Loss of Water, Solutes
Osmoregulation is the process of balancing the uptake and
loss of water as well maintaining solute concentrations
within acceptable levels:
• the key factor in this balance is
osmosis, the diffusion of water
from high to low concentration
across a semi-permeable
membrane
1
4/2/2015
Osmosis & Osmolarity
Differences in osmolarity (the total solute concentration) across a
membrane permeable only to the water will result in osmosis – the
diffusion of water
Selectively permeable
from higher to lower
membrane
Solutes
Water
concentration:
The side with higher
[solute] will gain
water and the side
with lower [solute]
will lose water.
Hyperosmotic side:
Hypoosmotic side:
Higher solute
concentration
• Lower free H O
2
concentration
•
•
•
Lower solute
concentration
Higher free H2O
concentration
Net water flow
Osmolarity & Aquatic Animals
Some aquatic animals such as marine invertebrates are
osmoconformers that are isoosmotic with their surroundings and
thus don’t regulate their osmolarity. However most are
osmoregulators that expend energy to regulate their osmolarity.
• most aquatic animals are stenohaline
and cannot tolerate large fluctuations
in the osmolarity of their environment
• some animals such as salmon and bull
sharks are euryhaline and can survive
large fluctuations in the osmolarity of
their environment
Osmoregulation in Marine Fish
Marine bony fish are hypoosmotic to sea water and thus will lose
water and take in excess salt. To counter this bony fish:
(a) Osmoregulation in a marine fish
• ingest sea water
Gain of water
and salt ions
from food
• reduce the amount of water
excreted in the urine
• excrete excess salt from gills
and kidneys
Excretion
of salt
ions
from gills
Osmotic water
loss through
gills and other
parts of
body surface
Key
SALT WATER
Gain of water
and salt ions
from drinking
seawater
Water
Salt
Excretion of salt ions and
small amounts of water in
scanty urine from kidneys
2
4/2/2015
Osmoregulation in Freshwater Fish
Freshwater fish are hyperosmotic to sea water and thus will gain
water and lose salt. To counter this freshwater fish:
(b) Osmoregulation in a freshwater fish
Gain of water
and some ions
in food
Uptake
of salt
ions
by gills
Osmotic water
gain through
gills and other
parts of
body surface
• excrete large amounts of
water from the kidneys
Key
Water
Salt
• uptake salt in the gills
FRESH WATER
Excretion of salt ions
and large amounts of
water in dilute urine
from kidneys
Transport Epithelia in Osmoregulation
Nostril with salt
secretions
• transport epithelia
are cell layers
specialized for
moving solutes in
specific directions
typically arranged
in tubular networks
such as the nasal
glands of marine
birds to excrete
excess salt
Secretory cell of
transport epithelium
Vein Artery
Lumen of
secretory
tubule
Nasal salt gland
Capillary
Secretory tubule
Salt
ions
Transport
epithelium
Blood
Salt
flow secretion
Central duct
2. Nitrogenous Wastes
3
4/2/2015
Forms of Nitrogenous Waste
All animals produce nitrogenous waste in the form of ammonia
(NH3) due to the break down of proteins and nucleic acids.
Ammonia is quite toxic and thus must be handled in 1 of 2 ways:
1. rapid elimination from the body
2. conversion to the less toxic nitrogen
compounds urea or uric acid
ammonia
urea
Proteins
Nucleic acids
• most aquatic animals can
rapidly eliminate ammonia into
the surrounding water
Nitrogenous
bases
Amino
acids
Amino groups
Most aquatic
animals, including
most bony fishes
Ammonia
Mammals, most
amphibians,
sharks, some
bony fishes
Urea
uric acid
Many reptiles
(including birds),
insects, land
snails
Uric acid
• mammals, amphibians and
some aquatic animals expend
energy to convert ammonia to
urea which requires more water
for excretion than uric acid
• reptiles, birds & insects convert
ammonia to uric acid which is
more energetically expensive
than urea but requires little
water to be excreted
3. Excretory Processes
4
4/2/2015
1
Capillary
Filtration
Filtrate
Excretory systems get rid of nitrogenous
waste and osmoregulate through a series
of general steps:
Excretory
tubule
2
Excretory Systems in General
Reabsorption
FILTRATION – removal of soluble portion of
body fluid to form crude filtrate
REABSORPTION – reclaiming water and
3
Secretion
valuable solutes
Urine
SECRETION – transferring additional wastes
to the filtrate
4
Excretion
EXCRETION – elimination of urine from body
Protonephridia
Protonephridia are a simple type of excretory system consisting
of networks of dead-end tubules that excrete a dilute waste fluid
into excretory tubules:
• flame bulbs with cilia
move fluid through
perforated cap cells that
filter out waste into
excretory tubules
Tubules of
protonephridia
INTERSTITIAL
FLUID
Cilia
Cap
cell
Tubule
cell
Flame
bulb
Tubule
• found in flatworms
Opening in
body wall
Metanephridia
Metanephridia are excretory organs in segmented worms
(annelids), and some arthrophods and molluscs:
Coelom
Components of a
metanephridium:
Collecting tubule
Internal opening
Bladder
External opening
Capillary
network
• blood filtrate collects in the
coelom and is transferred
via cilia into a collecting
tubule
• reabsorption & secretion
across the tubule results in
a dilute urine that is
released out of the body
5
4/2/2015
Malpighian Tubules
Digestive tract
Rectum
Intestine
Midgut
(stomach)
Salt, water, and
nitrogenous
wastes
Hindgut
Malpighian
tubules
To anus
Feces and urine
In most insects & other
terrestrial arthropods,
excretion occurs via
Malpighian tubules:
• nitrogenous & other
wastes are transferred to
Malpighian tubules
connected to the gut
Malpighian
tubule
Rectum
Reabsorption
• waste then passes out of
body through the anus
HEMOLYMPH
Kidneys
Excretory Organs
• kidneys are
the main
excretory
organs in
vertebrates
Posterior
vena cava
Renal artery
and vein
Kidney
Kidney Structure
Renal
cortex
Renal
medulla
Renal
artery
Renal
vein
Aorta
Ureter
Ureter
Urinary
bladder
Renal pelvis
Urethra
Nephrons – the Function Unit of the Kidney
Afferent arteriole
from renal artery Glomerulus
Bowman’s
capsule
Nephron Structure
Cortical
nephron
Proximal
tubule
Collecting
duct
Branch of
renal vein
Renal
cortex
Descending
limb
Vasa
recta
Loop of
Henle
Ascending
limb
200 µm
Distal
tubule
Efferent
arteriole
from
glomerulus
Juxtamedullary
nephron
Peritubular
capillaries
Renal
Blood vessels from a human kidney.
medulla
Arterioles and peritubular capillaries
appear pink; glomeruli appear yellow.
6
4/2/2015
Afferent arteriole
from renal artery
Glomerulus & Bowman’s
Capsule
Glomerulus
Bowman’s
capsule
Proximal
tubule
Peritubular
capillaries
Distal
tubule
Fluid from the blood leaks from the
glomerulus into Bowman’s capsule:
Efferent
arteriole
from
glomerulus
Branch of
renal vein
Descending
limb
Vasa
recta
Loop of
Henle
Ascending
limb
200 µm
Collecting
duct
Blood vessels from a human kidney.
Arterioles and peritubular capillaries
appear pink; glomeruli appear yellow.
• the crude filtrate
produced
contains salts,
glucose, amino
acids, vitamins,
nitrogenous
wastes, & other
small molecules
The Proximal Tubule
proximal tubule
The following occurs in the
proximal tubule:
• reabsorption of water, minerals
& nutrients (e.g., glucose)
• some toxins are secreted into
the tubule
• these activities result in a more
concentrated filtrate
The Descending Loop of Henle
descending limb of the Loop of Henle
The following occurs in the
descending limb of the Loop of Henle:
• reabsorption of water by diffusion
through aquaporin channels
• interstitial fluid is hyperosmotic
relative to filtrate
• further concentrates filtrate
7
4/2/2015
The Ascending Loop of Henle
ascending limb of the Loop of Henle
The following occurs in the
ascending limb of the Loop of Henle:
• reabsorption of salt ions
• interstitial fluid is hypoosmotic
relative to filtrate
• filtrate becomes more dilute
The Distal Tubule
distal tubule
The following occurs in the
distal tubule:
• Na+, K+ & Cl- and other ions are
transported in or out of the filtrate
to maintain osmotic balance
• H+ and HCO3- ions are
transported in or out of filtrate
to maintain pH balance
The Collecting Duct
collecting duct
The following occurs in the
collecting duct:
• reabsorption of water and
valuable solutes
• resulting urine is conducted to
the renal medulla on its way to
the renal pelvis and ureter
8
4/2/2015
1 Proximal tubule
H+
H2O
NaCl
K+
NH 3
NaCl
H2O
OUTER
MEDULLA
NaCl
3 Thin segment
of ascending
limb
NaCl
Active transport
Passive transport
300
OUTER
MEDULLA
INNER
MEDULLA
Urea
H2O
mOsm/L
100
300
100
Active
transport
Passive
transport
5 Collecting
duct
INNER
MEDULLA
300
CORTEX
H+
3 Thick segment
of ascending
limb
2 Descending limb
of loop of
Henle
H2O
Salts (NaCl and others)
HCO3
H+
Urea
Glucose, amino acids
Some drugs
HCO 3
Interstitial
fluid
CORTEX
Filtrate
Summary of
Nephron
Function
4 Distal tubule
NaCl Nutrients
K+
HCO3
H2O
NaCl
H2O
H2O
400
H2O
H2O
NaCl
200
NaCl
600
NaCl
H2O
NaCl
H2O
900 NaCl
H2O
NaCl
1,200
300
300
400
400
H2O
400
700
H2O
NaCl
H2O
NaCl
H2O
600
600
1,200
1,200
H2O
Urea
H2O
Urea
H2O
Urea
900
Osmolarity in the
Cortex vs Medulla
The osmolarity of the
interstitial fluids
surrounding the
nephron increases from
cortex to medulla.
This gradient is responsible for
the passive transport of water
and solutes in various sections
of the nephron.
4. Hormonal Control of
Osmoregulation & Excretion
9
4/2/2015
Antidiuretic Hormone
Osmoreceptors
in hypothalamus
trigger release
of ADH.
Hypothalamus
Hypothalamus
generates thirst.
Posterior
pituitary
• antidirutic
hormone or ADH
(aka vasopressin)
released by the
posterior pituitary
gland stimulates
Drinking of
water
greater water
reabsorption in the
kidney blood when
osmolarity
increases due to
dehydration
Distal
tubule
ADH
Blood osmolarity
increases
(such as after
sweating profusely).
Collecting
duct
H2O reabsorption
NORMAL
BLOOD OSMOLARITY
(300 mOsm/L)
ADH
receptor
LUMEN
ADH
cAMP
…more on ADH
Collecting
duct
COLLECTING
DUCT CELL
• the effect of ADH is to
increase the number of
aquaporin water channels on
the apical surface of
collecting duct epithelial cells
Second
messenger
Protein
kinase A
Storage
vesicle
Exocytosis
Aquaporin
water
channel
• this results in more water
reabsorption from the
collecting duct to the
interstitial fluid
H2O
H2O
Renin-Angiotensin-Aldosterone System (RAAS)
and H O are
5 Nareabsorbed.
+
• the RAAS is a
complex hormonal
feedback system
that increases
water reabsorption
in the kidney in
response
decreased blood
pressure
Atrial natriuretic peptide
(ANP) inhibits renin release
when blood pressure rises.
4
2
Aldosterone
Adrenal gland
NORMAL
BLOOD PRESSURE
AND VOLUME
Blood pressure or
blood volume drops
(for example, due to
dehydration or blood loss).
Arterioles constrict.
3
Angiotensin II
ACE
Angiotensin I
2
Distal
tubule
JGA
releases
renin.
1
Sensors in
JGA detect
decrease.
Renin
Angiotensinogen
Liver
Juxtaglomerular
apparatus (JGA)
10