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Ch. 14 Part 5
Loop of Henle, Distal Convoluted
Tubule, Collecting Duct,
Osmoregulation
Loop of Henle Review
• Found in 1/3 of all
nephrons in kideny
• Begins in Cortex of
Kidney and Dips into
Medulla of Kidney
• Two Parts:
• Descending LOH
• Ascending LOH
• Function:
• To create a very high
concentration of Na+
and Cl- ions in tissue
fluid of medulla,
enabling water to be
reabsorbed from fluid
in collecting duct as it
flows through medulla
• Enables concentrated
urine production
• Ensures water is
conserved in body and
not released in urine
• Prevents dehydration
Ascending Loop of Henle
Loop of Henle Reabsorption
Descending Loop of Henle
•
•
•
•
Permeable to Water
Permeable to Na+ and Cl- ions
Filtrate flows down DLOH
Water moves OUT of LOH into tissue
fluid via OSMOSIS
• Na+ and Cl- in medulla tissue fluid
diffuse INTO DLOH (down their
conc.grad.)
• Bottom of LOH
• Filtrate contains LESS water and LOTS
of Na+ and Cl- ions (lower water
potential)
• Longer loops = more concentrated
filtrate becomes in LOH
•
•
•
•
Impermeable to water
Permeable to Na+ and Cl- ion
Permeable to Urea
Cells ACTIVELY TRANSPORT Na+ and
Cl- ions OUT of Filtrate in LOH and
INTO tissue fluid in medulla
• Decreases water potential in tissue fluid
• Increases water potential of filtrate fluid
inside of ascending ALOH
• High concentrations of Na+ and Cl- build
up near bottom of LOH (between DLOH
and ALOH)
• As filtrate moves UP ALOH, filtrate
becomes less concentrated with Na+ and
Cl- (it has been losing them the whole
way up)
• Still removed b/c higher portions of ALOH
are found in the medulla that has less
concentrated tissue fluid (near top of
medulla, close to cortex)
• Concentration of Na+ and Cl- inside ALOH
is never drastically different from
concertation of ion sin tissue fluid
Counter-Current Multiplier
• Mechanism used in the Loop of
Henle
• Created by have the DLOH and
ALOH run side by side
• Fluid flows down in DLOH
• Current goes down
• Fluid flows up in ALOH
• Current goes up
• Enables maximum concentration
of solutes to build up inside and
outside the tube at the bottom
of the LOH
Urea in Loop of Henle
and Collecting Duct
• Ascending LOH and Collecting Ducts
PERMEABLE to UREA
• Urea has diffused into tissue fluids
• High concentrations on UREA in Medulla
tissue fluid
• Collecting Duct dips into medulla
• Some Urea diffuses back out of collecting
duct and INTO medulla tissue fluid
(increasing solutes, lowering water
potential)
• Water flows OUT of collecting duct by
OSMOSIS
• Water is reabsorbed into tissue fluid
• Happens until water potential of medulla
tissue fluid is equal to water potential of
urine(may be greater than water potential in
blood)
• Controlled by ADH
•
Anti-diuretic hormone (more on this later)
• Some urea remains in collecting duct and
is excreted in urine
Reabsorption in the Distal
Convoluted Tubule (DCT) and
Collecting Duct
• First part of DCT
• Functions same as ALOH
• Na+ and Cl- actively
pumped out
• Second Part of DCT
• Functions same as
collecting duct
• Na+ ions are actively
pumped from filtrate
fluid IN tubule TO tissue
fluid INTO peritubular
capillaries
• K+ ions ACTIVELY
TRANSPORTED INTO
tubule
• Rate of ions pumping in
and out varies
• Regulates concentration
of ions in blood
Animal Adaptations
• Mammals can produce highly
concentrated urine to conserve
water
• Increase thickness of medulla of
kidneys = more concentrated urine
(more water reabsorbed by tissues)
• Deep LOH with ascending LOH that
have lots of Na+-K+ pumps
• Cytoplasm has lots of mitochondria
(lots of ATP to pum Na+)
• Human concertation of urine = 4x
that of our blood plasma
• Desert rodents concertation of
urine = 20 x that of their blood
plasma
Osmosregulation
• Control of water potential of body fluids
• Important part of homeostasis
• Involves:
• Hypothalamus
• Osmoreceptors sensory neurons
• Monitor water potential of blood
• Posterior pituitary gland
• Kidney
ADH
• Anti-diuretic hormone
• “Diuresis” = production of dilute urine (release of water)
• ADH stops urine from being dilute by stimulating reabsorption of
water
• Peptide hormone made of 9 amino acids
• Hypothalamus detects changes in water potential of blood
• Using OSMORECPTOR sensory neurons
• Detect decrease in water potential and send nerve impulse to stimulate
Posterior Pituitary Gland
• Secreted by posterior pituitary gland
• Target cells: cells of the collecting duct of nephron in kidney
• Function of ADH: REDUCE water loss in urine by making kidney
reabsorb as much water as possible
• Stops dilute urine from being made
• Creates MORE aquaporins in Collecting duct so more water can leave collecting
duct, go into tissue fluid and be reabsorbed by peritubular capillaries
Decrease in Water Potential in
Blood
• Decrease in water
potential below SET
POINT is detected by
osmoreceptors in
hypothalamus
• Nerve impulses sent
along neurons that end
at posterior pituitary
gland
• Impulses stimulate
posterior pituitary gland
to release ADH into
blood capillaries and
travel all over body
Effects of ADH on Kidney
• Collecting ducts allow reabsorption of water
(OUT of nephron and into
medulla/tissuecapillaries)
• ADH molecules BIND to receptor proteins on
cell surface membranes of collecting duct cells
• Makes collecting duct more permeable to water by
INCREASING number of aquaporins
• Aquaporins -water permeable channels in cell surface
membrane of collecting duct cells
• Binding of ADH to receptor proteins on cell
membrane activate ENZYMES inside of cell
• Activates series of enzyme controlled reactions that end
in final product: ACTIVE PHOSPHORYLASE ENZYME
• PHOSPHORYLASE causes vesicles in cytoplasm of cell
(vesicles contain aquaporins in their membrane) to begin
moving towards cell membrane (review Golgi body
modifications to proteins)
• Vesicles fuse with cell membrane, thus increasing the
number of aquaporins
• Water can now freely move through the membrane
DOWN water potential gradient, into concentrated tissue
fluid peritubular capillaries  blood plasma
• Fluid flows through
collecting duct
• Fluid in collecting duct =
HIGH water potential
• Tissue fluid in medulla =
LOW water potential
• Water leaves collecting duct
cells
• Fluid in collecting duct
becomes more concentrated
• Increase of water in blood
• This is due to reabsorption of
water due to release of ADH
• Volume of fluid flowing into
bladder will be less = more
concentrated urine (less
dilute)
Effects of Lots of Water in Body
• Water potential in blood INCREASES
• Osmoreceptors in hypothalamus detect
increase
• Osmoreceptors are no longer stimulated
• Neurons in posterior pituitary gland no
longer stimulated to release ADH
• No ADH being secreted
• Aquaporins in cell membrane of collecting
duct cells move OUT of membrane and
become vesicles in the cytoplasm again
• Takes 10-15 minutes for this to happen
• Not immediate
• Collecting duct becomes impermeable to
water
• Lots of water flowing in fluid in collecting
duct = increased volume into bladder =
DILUTE urine
• Ensures maintenance of water potential
Response to decrease in ADH
• Collecting duct cells do NOT respond immediately to
decrease in ADH secretion by posterior pituitary gland
• ADH already in blood needs to be broken down
• Half of ADH is blood is destroyed every 15-20 minutes
• Eventually ADH stops arriving at collecting duct cells
• No attachment to receptor proteins
• Aquaporins removed and become vesicles in cytoplasm
again
• 10-15 minutes
Alcohol and ADH
• Alcohol affects the pituitary gland
• Reduces secretion of ADH
• No ADH attaching to receptors on collecting duct cells = no aquaporins =
impermeable to water = water stays in collecting duct with urine (NO water
reabsorption as filtrate moves through collecting duct)
• Dilute urine
• Dehydration