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Blood Vessels Associated with the Nephrons • Each nephron supplied with blood by an
afferent arteriole
• branch of renal artery
• divides into glomerular capillaries
• capillaries converge as they leave glomerulus
• forming an efferent arteriole
• The vessels divide again
• Forming the peritubular capillaries
• surround the PCT and DCT
• Vasa recta
• Capillaries that serve the loop of
Henle
• vasa recta and loop of Henle
• funcBon as countercurrent system
• Blood flows in opposite direcBon
of filtrate
Blood Vessels Associated with the Nephrons
From Blood Filtrate to Urine: A Closer Look
• Proximal Convoluted Tubule (PCT)
• ReabsorpBon of ions, water, and
nutrients
• Molecules transported
• acBvely and passively
• From filtrate into intersBBal
fluid then capillaries
• Some toxic materials
• secreted into the filtrate
• filtrate volume decreases
2
• Descending Limb of the Loop of Henle
• ReabsorpBon of water conBnues
• through aquaporin proteins
• Movement is driven by
• High osmolarity of the
intersBBal fluid
• HyperosmoBc to the
filtrate
• filtrate becomes increasingly
concentrated
From Blood Filtrate to Urine: A Closer Look
• Ascending Limb of the Loop of Henle
• Salt diffuses from tubule into
intersBBal fluid
• but not water
• No aquaporins present
• Completely impervious
to water
• Filtrate becomes increasingly
dilute
From Blood Filtrate to Urine: A Closer Look
• Distal Convoluted Tubule (DCT)
• Regulates K+ and NaCl
concentraBons of body fluids
• controlled movement of ions
contributes to pH regulaBon
From Blood Filtrate to Urine: A Closer Look
3
• CollecCng Duct
• Carries filtrate through
medulla to renal pelvis
• Water reabsorbed from filtrate
• some salt and urea
• Filtrate becomes more
concentrated
• Urine hyperosmoBc to body
fluids
From Blood Filtrate to Urine: A Closer Look
Fig. 44-‐15
Key
Active transport Passive transport
INNER MEDULLA
OUTER MEDULLA
H2O
CORTEX
Filtrate
Loop of Henle
H2O K+ HCO3–
H+ NH3
Proximal tubule NaCl Nutrients
Distal tubule
K+ H+
HCO3–
H2O
H2O
NaCl
NaCl
NaCl
NaCl
Urea
Collecting duct
NaCl
Solute Gradients and Water ConservaBon Summary
• Urine
• Much more concentrated than blood
• loops of Henle and collecBng ducts
• responsible for osmoBc gradient
• concentrates urine
• NaCl and urea
• Contribute to osmolarity of intersBBal fluid
• causes reabsorpBon of water
• concentrates the urine
Key
Active transport Passive transport
INNER MEDULLA
OUTER MEDULLA
H2O
CORTEX
Filtrate
Loop of Henle
H2O K+ HCO3 –
H+ NH3
Proximal tubule
NaCl
Nutrients
Distal tubule
K+ H+
HCO3 –
H2O
H2O
NaCl
NaCl
NaCl
NaCl
Urea
Collecting duct
NaCl
4
The Two-‐Solute Model (NaCl & Urea) • PCT
• Filtrate volume decreases
• osmolarity remains same
• Countercurrent mulCplier system
• loop of Henle
• Maintains high salt concentraBon in kidney
• acBve transport of NaCl
• In thick ascending limb of LoH
• Thin limb loses NaCl by diffusion
• Allows formaBon of concentrated urine
• allows vasa recta to supply nutrients to kidney
• without interfering with osmolarity gradient
• Due to counter flow of blood in vasa recta
Key
Active transport Passive transport
INNER MEDULLA
OUTER MEDULLA
CORTEX H2O
300 300 300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of interstitial
fluid (mOsm/L)
400
600
900
1,200
Key
Active transport Passive transport
INNER MEDULLA
OUTER MEDULLA
CORTEX H2O
300 300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of interstitial
fluid (mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
• collecBng duct
• Conducts filtrate through
osmolarity gradient
• Cortex to outer medulla to
inner medulla
• More water exits filtrate by
osmosis
• Urea diffuses out of collecBng
duct
• In inner medulla
The Two-‐Solute Model
Key
Active transport Passive transport
INNER MEDULLA
OUTER MEDULLA
CORTEX H2O
300 300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of interstitial
fluid (mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
1,200
300
400
600
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
Urea
Urea
Urea
Fig. 44-‐16-‐1
Key
Active transport Passive transport
INNER MEDULLA
OUTER MEDULLA
CORTEX H2O
300 300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of interstitial
fluid (mOsm/L)
400
600
900
1,200
5
Fig. 44-‐16-‐2
Key
Active transport Passive transport
INNER MEDULLA
OUTER MEDULLA
CORTEX H2O
300 300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of interstitial
fluid (mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
Fig. 44-‐16-‐3
Key
Active transport Passive transport
INNER MEDULLA
OUTER MEDULLA
CORTEX H2O
300 300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of interstitial
fluid (mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
1,200
300
400
600
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
Urea
Urea
Urea
PLAY
Mammals
• The juxtamedullary nephron
• Contributes to water
conservaBon
• in terrestrial animals
• Mammals that inhabit dry
environments
• Have long loops of Henle
• While those in fresh water
have relaBvely short loops
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Birds and Other RepBles • Birds
• shorter loops of Henle
• Even in juxtamedullary nephrons
• conserve water by excreBng uric acid
• instead of urea
• excreted as a paste
• Fairly non-‐water soluble
• Other repBles have only corBcal nephrons
• No juxtamedullary nephrons
• But also excrete uric acid
Uptake of water and some ions in food
Uptake of salt ions by gills
Osmotic water gain through gills and other parts of body surface
Excretion of large amounts of water in dilute urine from kidneys
(b) Osmoregulation in a freshwater fish
Freshwater Fishes and Amphibians
• Freshwater fish
• Conserve salt in DCT’s
• Excrete large volumes of dilute
urine
• Amphibian
• kidney funcBon similar to freshwater
fish
• conserve water on land
• by reabsorbing water from the
urinary bladder
Excretion of salt ions from gills
Gain of water and salt ions from food
Osmotic water loss through gills and other parts of body surface
Excretion of salt ions and small amounts of water in scanty urine from kidneys
Gain of water and salt ions from drinking seawater
(a) Osmoregulation in a saltwater fish
Marine Bony Fishes • Marine bony fish
• HypoosmoBc compared with their environment
• excrete very lible urine
• Urea lost through skin and gills
• Fewer and smaller nephrons than fresh water fish
• No DCT
• Divalent ions secreted to proximal tubule
• Ca2+, Mg2+, SO42-‐
7
Thirst
Drinking reduces blood osmolarity
to set point.
Osmoreceptors in hypothalamus trigger
release of ADH.
Increased permeability
Pituitary gland
ADH
Hypothalamus
Distal tubule
H2O reab- sorption helps prevent further
osmolarity increase.
STIMULUS: Increase in blood
osmolarity
Collecting duct
Homeostasis: Blood osmolarity
(300 mOsm/L)
(a)
Exocytosis
(b)
Aquaporin water channels
H2O
H2O
Storage vesicle
Second messenger signaling molecule
cAMP
INTERSTITIAL FLUID
ADH receptor
ADH
COLLECTING DUCT LUMEN
COLLECTING DUCT CELL
AnBdiureBc Hormone • Osmolarity of urine
• Regulated by nervous and
hormonal control
• of water and salt reabsorpBon
• AnCdiureCc hormone (ADH)
(vasopressin)
• Increases water reabsorpBon in
DCT and collecBng ducts
• An increase in osmolarity triggers the
release of ADH
• to conserve water
• When above 300mOsm/L
• MutaBon in ADH producBon causes severe dehydraBon
• Results in diabetes insipidus
• Large volumes of dilute urine
• Alcohol is a diureBc
• inhibits the release of ADH
AnBdiureBc Hormone
PLAY
The Renin-‐Angiotensin-‐Aldosterone System
• Renin-‐angiotensin-‐aldosterone system
(RAAS)
• Part of complex feedback circuit
• funcBons in homeostasis
• drop in blood pressure near glomerulus
• Causes juxtaglomerular apparatus
(JGA)
• to release the enzyme renin
• triggers the formaBon of
angiotensin II
8
• Angiotensin II
• Raises blood pressure and decreases blood flow to kidneys
• Through vasoconstricBon
• SBmulates release of the hormone aldosterone
• Causes retenBon of salt
• Increases blood volume and pressure
• As water follows salt
The Renin-‐Angiotensin-‐Aldosterone System
Fig. 44-‐21-‐1
Renin
Distal tubule
Juxtaglomerular apparatus (JGA)
STIMULUS: Low blood volume or blood pressure
Homeostasis: Blood pressure,
volume
Fig. 44-‐21-‐2
Renin
Distal tubule
Juxtaglomerular apparatus (JGA)
STIMULUS: Low blood volume or blood pressure
Homeostasis: Blood pressure,
volume
Liver
Angiotensinogen
Angiotensin I
ACE
Angiotensin II
9
Fig. 44-‐21-‐3
Renin
Distal tubule
Juxtaglomerular apparatus (JGA)
STIMULUS: Low blood volume or blood pressure
Homeostasis: Blood pressure,
volume
Liver
Angiotensinogen
Angiotensin I
ACE
Angiotensin II
Adrenal gland
Aldosterone
Arteriole constriction
Increased Na+ and H2O reab-
sorption in distal tubules
HomeostaBc RegulaBon of the Kidney
• ADH and RAAS
• Both increase water reabsorpBon
• But only RAAS will respond to a decrease in blood volume
• Atrial natriureCc pepCde (ANP)
• Opposes the RAAS
• released in response to increase in blood volume and pressure
• Inhibits the release of renin
You should now be able to:
1. DisBnguish between the following terms: isoosmoBc, hyperosmoBc, and hypoosmoBc; osmoregulators and osmoconformers; stenohaline and euryhaline animals
2. Define osmoregulaBon, excreBon, anhydrobiosis
3. Compare the osmoregulatory challenges of freshwater and marine animals
4. Describe some of the factors that affect the energeBc cost of osmoregulaBon
10
5. Describe and compare the protonephridial, metanephridial, and Malpighian tubule excretory systems
6. Using a diagram, idenBfy and describe the funcBon of each region of the nephron
7. Explain how the loop of Henle enhances water conservaBon
8. Describe the nervous and hormonal controls involved in the regulaBon of kidney funcBon
You should now be able to:
