Chapter 44: Osmoregulation & Excretion Chapter...Chapter 44: Osmoregulation & Excretion 1....
Transcript of Chapter 44: Osmoregulation & Excretion Chapter...Chapter 44: Osmoregulation & Excretion 1....
Chapter 44:
Osmoregulation & Excretion
1. Osmoregulation
2. Nitrogenous Wastes
3. Excretory Processes
4. Hormonal Control ofOsmoregulation & 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
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 from higher to lower concentration: Solutes Water
Selectively permeablemembrane
Net water flow
Hypoosmotic side:• Lower solute
concentration• Higher free H2O
concentration
Hyperosmotic side:• Higher solute
concentration• Lower free H2O
concentration
The side with higher [solute] will gain
water and the side with lower [solute]
will lose water.
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 stenohalineand 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
Gain of waterand salt ionsfrom food
Excretionof saltionsfrom gills
Osmotic waterloss throughgills and otherparts ofbody surface
Excretion of salt ions andsmall amounts of water inscanty urine from kidneys
SALT WATER
Gain of waterand salt ionsfrom drinkingseawater
Water
Salt
Key
• ingest sea water
• reduce the amount of water excreted in the urine
• excrete excess salt from gills and kidneys
Osmoregulation in Freshwater Fish
(b) Osmoregulation in a freshwater fish
Gain of waterand some ionsin food
FRESH WATER
Uptakeof saltionsby gills
Osmotic watergain throughgills and otherparts ofbody surface
Excretion of salt ionsand large amounts ofwater in dilute urinefrom kidneys
Water
Salt
Key
Freshwater fish are hyperosmotic to sea water and thus will gain water and lose salt. To counter this freshwater fish:
• excrete large amounts of water from the kidneys
• uptake salt in the gills
• 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
Transport Epithelia in Osmoregulation
Nasal salt gland
Capillary
Secretory tubule
Transportepithelium
Secretory cell of
transport epithelium
Vein Artery Lumen ofsecretorytubule
Saltions
Bloodflow
Saltsecretion
Nostril with saltsecretions
Central duct
2. Nitrogenous Wastes
uric acid
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:
ammonia
1. rapid elimination from the body
2. conversion to the less toxic nitrogen compounds urea or uric acid
urea
Proteins Nucleic acids
Nitrogenousbases
Aminoacids
Amino groups
Most aquaticanimals, includingmost bony fishes
Mammals, mostamphibians,sharks, somebony fishes
Many reptiles(including birds),
insects, landsnails
Ammonia Urea Uric acid
• most aquatic animals can rapidly eliminate ammonia into the surrounding water
• 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
CapillaryFiltration
Excretorytubule
Reabsorption
Secretion
Excretion
Filtra
teU
rine
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Excretory Systems in General
Excretory systems get rid of nitrogenous waste and osmoregulate through a series of general steps:
FILTRATION – removal of soluble portion of body fluid to form crude filtrate
REABSORPTION – reclaiming water and valuable solutes
SECRETION – transferring additional wastes to the filtrate
EXCRETION – elimination of urine from body
Protonephridia
Tubules ofprotonephridia
INTERSTITIALFLUID
Cilia
Tubule
Flamebulb
Capcell
Tubulecell
Opening inbody wall
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
• found in flatworms
Metanephridia
Metanephridia are excretory organs in segmented worms (annelids), and some arthrophods and molluscs:
Coelom Capillarynetwork
Components of a
metanephridium:
Collecting tubule
Internal opening
Bladder
External opening
• 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
Digestive tract
HindgutRectumIntestine
Malpighiantubules
Midgut(stomach)
Salt, water, andnitrogenous
wastes
Feces and urineTo anus
Rectum
Reabsorption
Malpighiantubule
HEMOLYMPH
Malpighian Tubules
In most insects & other terrestrial arthropods, excretion occurs via Malpighian tubules:
• nitrogenous & other wastes are transferred to Malpighian tubules connected to the gut
• waste then passes out of body through the anus
Kidneys
Posteriorvena cava
Excretory Organs
Renal arteryand vein
Aorta
Ureter
Urethra
Urinarybladder
Kidney
Renalcortex
Kidney Structure
Renalmedulla
Renalartery
Renalvein
Ureter
Renal pelvis
• kidneys are the main excretory organs in vertebrates
20
0 µ
m
Afferent arteriolefrom renal artery Glomerulus
Bowman’scapsule
Proximaltubule
Peritubularcapillaries
Distaltubule
Efferentarteriolefrom glomerulus
Branch ofrenal vein
Descendinglimb
Ascendinglimb
VasarectaCollecting
duct
Blood vessels from a human kidney.Arterioles and peritubular capillariesappear pink; glomeruli appear yellow.
Loop ofHenle
Renalmedulla
Renalcortex
Corticalnephron
Juxtamedullarynephron
Nephrons – the Function Unit of the Kidney
Nephron Structure
200 µ
m
Afferent arteriolefrom renal artery Glomerulus
Bowman’scapsule
Proximaltubule
PeritubularcapillariesDistal
tubule
Efferentarteriolefrom glomerulus
Branch ofrenal vein
Descendinglimb
Ascendinglimb
VasarectaCollecting
duct
Blood vessels from a human kidney.Arterioles and peritubular capillariesappear pink; glomeruli appear yellow.
Loop ofHenle
Glomerulus & Bowman’s Capsule
• the crude filtrate
produced
contains salts,
glucose, amino
acids, vitamins,
nitrogenous
wastes, & other
small molecules
Fluid from the blood leaks from the glomerulus into Bowman’s capsule:
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
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 hypoosmoticrelative 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
Proximal tubule1
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Distal tubule
Descending limbof loop of Henle
Thick segmentof ascendinglimb
Thin segmentof ascendinglimb
Collectingduct
CORTEX
OUTERMEDULLA
INNERMEDULLA
Active transport
Passive transport
Interstitialfluid
Filtrate
Salts (NaCl and others)
H2O
HCO3
H+
Urea
Glucose, amino acids
Some drugs
H2O
NH3H+
K+H2OHCO3
NaCl Nutrients
NaCl
H2OHCO3
K+ H+
NaCl
NaCl
H2ONaCl
Urea
3
Summary of Nephron Function
300300
300
300
400400
600 600
900900
1,200
1,200
mOsm/L
H2O
H2O
CORTEX
OUTERMEDULLA
ActivetransportPassivetransport H2O
H2O
H2O
H2O
H2OINNERMEDULLA
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
Urea
Urea
Urea
NaCl
600
1,200
400
300
200
400
700
100
100
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
Blood osmolarityincreases
(such as aftersweating profusely).
NORMALBLOOD OSMOLARITY
(300 mOsm/L)
Collectingduct
Distaltubule
Hypothalamusgenerates thirst.
Posteriorpituitary
ADH
Osmoreceptorsin hypothalamustrigger releaseof ADH.
Drinking ofwater
H2O reabsorption
Hypothalamus
Antidiuretic Hormone
• antidirutichormone or ADH (aka vasopressin) released by the posterior pituitary gland stimulates greater water reabsorption in the kidney blood when osmolarityincreases due to dehydration
…more on ADHADHreceptor
ADH
cAMPSecondmessenger
COLLECTINGDUCT CELL
LUMENCollectingduct
Proteinkinase A
Storagevesicle
Aquaporinwaterchannel
Exocytosis
H2O
H2O
• the effect of ADH is to increase the number of aquaporin water channels on the apical surface of collecting duct epithelial cells
• this results in more water reabsorption from the collecting duct to the interstitial fluid
Renin-Angiotensin-Aldosterone System (RAAS)NORMAL
BLOOD PRESSUREAND VOLUME
Blood pressure or
blood volume drops
(for example, due to
dehydration or blood loss).
Distaltubule
Sensors inJGA detectdecrease.
Juxtaglomerularapparatus (JGA)
JGAreleasesrenin.
Renin
Liver
Angiotensinogen
Angiotensin II
Angiotensin I
ACE
Adrenal glandArterioles constrict.
Aldosterone
Na+ and H2O are reabsorbed.• the RAAS is a
complex hormonal feedback system that increases water reabsorption in the kidney in response decreased blood pressure
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Atrial natriuretic peptide (ANP) inhibits renin release when blood pressure rises.