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Proximal tubule Distal tubule

Filtrate

CORTEX

Loop ofHenle

OUTERMEDULLA

INNERMEDULLA

Key

Active transport

Passive transport

Collectingduct

NutrientsNaCl

NH3

HCO3 H2O

K

H

NaCl

H2O

HCO3

K H

H2O

NaCl

NaCl

NaCl H2O

Urea

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The filtrate then flows from

distal tubule to collecting duct The collecting duct carries the

filtrate through the medulla to

the renal pelvis

The transport of the nephron

and collecting duct processes the

filtrate

Forming the urine that is excretethrough urinary system

Collecting Duct

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How does this mechanism help to conserve water?

The collecting duct, passes through the medulla of the

kidney.

Permeable to water

In the inner medulla, duct becomes permeable to urea

- contribute to high osmolarity of interstitial fluid in themedulla.

water can be drawn out by osmosis, into theconcentrated interstitial fluid in the medulla.

Collecting Duct

TAKE NOTE: The more concentrated the tissue fluidthe more water can be drawn out and the moreconcentrated the urine can be.

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Proximal tubule Distal tubule

Filtrate

CORTEX

Loop ofHenle

OUTERMEDULLA

INNERMEDULLA

Key

Active transport

Passive transport

Collectingduct

NutrientsNaCl

NH3

HCO3 H2O

K

H

NaCl

H2O

HCO3

K H

H2O

NaCl

NaCl

NaCl H2O

Urea

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9. 3. 2 d)

Water Regulation By ADH

\

- Describe the regulation of blood watercontent

- Explain the regulation of Na+ reabsorption

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a) Concepts

The kidney play central role in the regulation of the

water content of the body or osmoregulation.

The water content of the blood is monitored byosmoreceptorcells in the hypothalamus

these cells produce antidiuretic hormone, ADH

Water Regulation by ADH

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ThirstHypothalamus

ADH

Pituitarygland

Osmoreceptors in

hypothalamus triggerrelease of ADH.

STIMULUS:Increase in bloodosmolarity (forinstance, after

sweating profusely)

Homeostasis:Blood osmolarity

(300 mOsm/L)

i) Low intake of water in the blood

Water content of the blood is lower than normal- causing the blood volume to decrease.

-concentration of salts dissolved in the blood

becomes greater, increasingthe bloodosmolarity

Osmoreceptor in hypothalamus are sensitive tothis changes

stimulate the posterior of the pituitary torelease MORE ADH into the blood

Water Regulation by ADH

When the water content in blood is BELOW normal

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i) Low intake of water

When ADH reaches the kidney, its main targets are thecollecting duct

makes the collecting duct wall more permeable towater

The resulting increase in water reabsorption

And concentrate the urine

Water Regulation by ADH

When the water content in blood is BELOW normal

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Small volumes of concentrated urine are

produced

helps to stop the solute concentration of the

blood from becoming too high

Lowers blood osmolarity back toward the set

point

Water Regulation by ADH

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ThirstHypothalamus

ADH

Pituitarygland

Osmoreceptors inhypothalamus trigger

release of ADH.

STIMULUS:Increase in bloodosmolarity (forinstance, after

sweating profusely)

Homeostasis:Blood osmolarity

(300 mOsm/L)

Drinking reducesblood osmolarity

to set point.

H2O reab-sorption helps

prevent furtherosmolarityincrease.

Increasedpermeability

Distaltubule

Collecting duct

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ii. High intake of water

Water content of the blood is higher than normal, the bodyfluids begin to dilute, causing the blood volume to increase.

- concentration of salts in the blood becomes less, causing adecrease in osmotic pressure.

Osmoreceptorin hypothalamus are sensitive to this osmoticchange and stimulate the posterior lobe of the pituitary to

release LESS ADH

ADH makes the collecting duct wall less permeable to water

Water Regulation by ADH

When the water content in blood is ABOVE

normal.

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less water reabsorption at collecting duct

Large volumes of diluted urine are produced

Water Regulation by ADH

Continue.

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9. 3. 2 e) Regulation of NA+

Reabsorption by aldosterone

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a) Concepts

Plasma sodium level is controlled by hormonealdosterone.

It is secreted by the cortex region of the adrenalgland.

Aldosterone stimulates the distal tubule toincrease sodium reabsorptionand K+ secretionthereby maintains the balance of salt in the bodyfluids.

Osmoregulation of mineral ionsby aldosterone

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A decrease in blood sodium

Leads to a decrease in blood volume (less water enters the bloodby osmosis). --reduces blood pressure.

Decreasing in pressure and volume stimulates a adrenal gland torelease aldosteron

Aldosteron increase the rate of reabsorption of sodium ions andsecretion of potassium ion from the distal convoluted tubules.

- fewer sodium ions are lost in the urine, and more are retained

in the blood.

- causes more water to enter the blood by osmosis, raising itsvolume and hence its pressure.

Osmoregulation of mineral ions by aldosterone

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Summarize regulation of water by ADH

Low intake of water

(Increase blood osmolarity)

Osmoreceptor in hypothalamus

Posterior of pituitary gland

secrete ADH

Collecting duct

Permeable to water (Increase in

water reabsorption)

Small volume of concentrated urine

produced

High intake of water

(Reduce blood osmolarity)

Osmoreceptor in hypothalamus

Posterior of pituitary gland

secrete ADH

Collecting duct

Less permeable to water ( less

water reabsorption )

Large volume of dilute urine

produced

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Summarize regulation of Na+ by aldosterone

Decrease in blood sodium

(low blood pressure and volume)

Adrenal gland secrete

aldosterone

Distal tubule

Inrease the rate of sodium

reabsorption

More water enter the blood by

osmosis