Transcript 7.6: Water Balance

7.6: Water Balance
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Antidiuretic hormone (ADH): causes the
kidneys to increase water reabsorption
Regulating ADH:
water intake
[blood solute]
blood osmotic pressure and is sensed by
osmoreceptors in the hypothalamus
hypothalamus cells shrink; nerve message is
sent to the pituitary gland to release ADH;
initiates sensation of thirst
ADH is carried to the kidneys and signals the
reabsorption of water
This produces a more concentrated urine
Osmotic Pressure (H2O balance
– Regulating ADH)
• high osmotic pressure = when there is
little water in blood (dehydrated) … this
causes water to rush out of cells to enter
bloodstream.
• A hormone, antidiuretic hormone (ADH),
helps regulate the osmotic pressure of
bodily fluids by causing the kidneys to
increase water reabsorption
Animation: Hormonal
Communication
Communication between
hypothalamus and
pituitary gland.
* ADH secretion triggers
reabsorption of water at the
kidney.
behavioural
change
Osmoreceptors in hypothalamus (brain)
-detect osmotic change
How? (blood:  water =  solutes = shrinkage
of cells in hypothalamus as water leaves)

 hormonal change
Creates the
sensation of thirst
ADH (hormone made in hypothalamus, stored
in pituitary)  Released to the bloodstream
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= drink more
=  osmotic
pressure
ADH to kidneys via blood
= increase in water uptake
How?  makes the usually impermeable
distal tubule and collecting duct permeable to
water
 water is ‘sucked’ out because of high NaCl
concentration in intercellular spaces

= osmoreceptors
swell
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=  in ADH
Kidneys and Blood Pressure
1. low blood volume and low blood pressure
2. sensed by blood pressure receptors in
juxtaglomerular apparatus
3. renin is released to convert angiotensinogen into
angiotensin
4. angiotensin constricts blood vessels and
simulates release of aldosterone from adrenal
gland
5. aldosterone is carried to the kidneys
6. nephrons increase Na+ and H2O reabsorption
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Blood Pressure (Adjusting Blood
Volume)
a hormone aldosterone, produced in the adrenal glands (located
above kidneys), acts on the nephrons to increase Na+ reabsorption.
 water =  blood pressure =  O2 to tissues so…

receptors near glomerulus detect blood pressure change
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= release renin (enzyme) which converts the plasma protein
angiotensinogen into angiotensin (enzyme)
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* angiotensin has 2 roles:
vasoconstriction (constriction of blood vessels)
stimulates the release of aldosterone which increases reabsorption
of NaCl/H2O at the nephron
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 in blood pressure
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pH Balance
• The pH of our body is 7.3  7.5
• Cell respiration releases H+ ions into the blood
which decreases pH
• So… our buffer system:
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H+ + HCO3-  H2CO3  H2O + CO2
• But this removes HCO3- ions so we have to get
more of them
• So… 2 things happen (in different parts of the
kidney) to replace the HCO3-
 CO2 (taken in actively)
HCO3-
(out to blood )
peritubule
capillary
interstitial
fluid
CO2 + H2O  HCO3- + H+
(makes more bicarbonate – sends it back
to blood)
tubule cells
 H+ + HPO42- pee
H+ + NH3  pee
(the H+ ions combine with either
phosphate or ammonia – flushed out in
filtrate)
lumen of
tubule
Section 7.6, pp. 356, #1-8
Kidney Disease
Diabetes Insipidus
• kidneys don't concentrate urine well
Symptoms
• frequent urination
• strong thirst response
Causes
• inadequate production of ________.
• may be caused by head injury or brain tumours.
• Medication containing lithium
Treatment:
• drink large volumes of water
Diabetes Mellitus
• islet cells of the pancreas produce little or no
insulin
Symptoms
• frequent urination
• extreme thirst
• lack of energy
• vision problems
Blood Sugar
Animation: Blood
Sugar Regulation in
Diabetics
Treatment
• insulin replacement therapy
• oral hypoglycemic medication
Bright's Disease (Nephritis)
• grouping of diseases characterized by the
inflammation of the nephrons. One type of
nephritis changes the permeability of the
glomerulus allowing proteins to pass into the
nephron. This causes an increase in urine
production.
Kidney Stones
• caused by the precipitation of mineral solutes
from the blood
• sharp stones can damage tissues
• Extracorporeal shock-wave lithotripsy (ESWL)
breaks stones into smaller fragments that can be
voided through the excretory system
Diabetes inadequate secretion of insulin
Mellitus blood sugar levels rise
you pee out lots of glucose
this messes up the osmotic pressure and more water is
lost = lots of peeing
must drink a lot
Diabetes destruction of ADH producing cells in the
Insipidu hypothalamus (not able to control water reabsorption)
urine output increases
s
you must drink a lot
Bright’s
Disease
“inflammation of the nephron” = altered permeability
lots of characteristics
start peeing out large molecules like proteins
proteins in tubule = osmotic issues = lots more peeing
Kidney
Stones
precipitation of mineral solutes from the blood
Ouch!
some can be destroyed by ultrasound
Dialysis Technology
 the exchange of substances across a
semipermeable membrane
• haeomodialysis  a tube is connected to
a vein and blood is removed from the body
 the blood goes into a dialysis machine
(in the tube) and passes through various
environments(solutions) that remove
toxins from the blood
 essentially a “man made” kidney.
• peritoneal dialysis  pump dialysis fluids into
abdominal cavity (~2 L)
•  the selectively permeable membranes of the
cavity allow toxins to go into the fluid
•  fluid is removed and new fluid pumped in
• wastes diffuse from the plasma into the
peritoneum and is filtered into the dialysis fluid
• accumulated wastes are drained off and
replaced several times a day
• performed at home (2-6 hours)
• neither provide the hormones that kidneys do so
they have to be injected
Kidney Transplant
• 85 % successful
• new kidney is placed lower in the pelvis
and attached to blood vessels and ureter
• old kidney is not removed
• patient must receive immunosuppressant
drugs forever
• Section 7.7, pp. 362, #1-10
• Review: pp. 367, #1-8; pp. 368, #1-13, 15,
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