Lec. 16: Kidney Regulation of Ion (NaCl) and H20 Balance

Cascade of events leading to increased water reabsorption if Hypothalmus detects high ECF osmolarity? (Baroreceptor *to* Aquaporin)

*1.* Baroreceptors shrink in response to high ECF *2.* CHange in firing rate initiates Hypx to create *ADH* *3.* ADH then moves, and is *secreted* by (or stored) in the posterior pituitary into the blood stream. *4.* ADH enters renal interstitial fluid, and binds to it's *receptor* on the basolateral side of the collecting epithelial cell *5.* Upon reception, intracellular production of secondary messenger *cAMP* is increased *6. cAMP-dependent protein kinase,* in turn, phosphorylates proteins that increase the rate of fusion of vesicles containing AQP2 in the apical membrane *7. Water* can now diffuse through from apical side (AQP2) through basolateral side (AQP3 & 4) to the ECF!

Insufficient ADH leads to

*Diabetes Insipidus.* A disorder of salt and water metabolism marked by intense thirst and heavy urination. *Major symptoms:* *-* Intense thirst, *-* water-electrolyte imbalance, *-* dehydration *-*fatigue *-* bed-wetting *Treatment:* *-* Hormone therapy, *-* Low salt diet

At the medullary U-turn portion of the loop of Henry, the osmolarity between the ECF and tubular lumen is _______

*Isosmotic.*

Ethanol will _____ ADH release, making your urine ________ concentrated, and makes you pee _____ often.

Ethanol will *inhibit* ADH release, making your urine *less* concentrated, and makes you pee *more* often.

Nicotine will _____ ADH release, making your urine ________ concentrated, and makes you pee _____ often.

Nictonine will *stimulate* ADH release, making your urine *more* concentrated; making you pee *less* often.

Extracellular fluid (and volume) is comprised of:

Plasma fluid (volume), & Interstitial fluid (volume).

Receptors/sensors of osmolarity are called ________, and are located in the ________.

REceptors/sensors of osmolarity are called *osmoreceptors,* and are located in the *hypothalamus.* )smoreceptors *expand* when blood plasma has *lower* osmolarity (because osmolarity inside osmoreceptor cell is greater, thus, it takes on water) -- and will *contract* at *higher* Osmolarity of the ECF. (as the receptor will lose H2O as a result of having lowering osmolarity)

Where is ADH produced? What kind of hormone is it?

Supra Optic Nucleus of the Hypothalamus. Secreted into Posterior pituitary via neurosecretory neuron terminals. An antidiruetic, peptide hormone.

The ___________ of the loop of Henle is permeable to water but impermeable to ______, due to the presence of _______ in its tubular wall. Thus water moves across the tubular wall into the medullary space, making the filtrate ________

The *descending limb* of the loop of Henle is permeable to water but impermeable to *solutes*, due to the presence of *Auqaporin 1* in its tubular wall. Thus water moves across the tubular wall into the medullary space, making the filtrate *hypertonic.*

The _________ is impermeable to water because of a lack of ________, but permeable to ________ What ions are being actively transported? This makes the filtrate _______

The *thick ascending loop* is impermeable to water because of a lack of *aquaporins*, but permeable to *solutes* What ions are being actively transported? Na+ & Cl- active transport (also K+) This makes the filtrate *hypotonic*

Macula densa

The cells of the distal tubule at the juxtaglomerular apparatus. They are receptors that monitor filtrate osmolarity ---- as a means of ultimately regulating filtration rate. If a drop is osmolarity is sensed, the macula densa dilates the afferent arteriole (to increase the blood pressure in the glomerulus and thus increase filtration) --and stimulates the juxtaglomerular cells to secrete Renin (to raise systemic blood pressure).

The countercurrent multiplier system creates a ________ interstitial fluid.

The countercurrent multiplier system creates a *hyperosmotic medullary* interstitial fluid.

The fluid at the ________ will have the most NaCl pumped out, so it's osmolarity is _____ than the ECF

The fluid at the *distal tubule* will have the most NaCl pumped out, so it's osmolarity is *lower* than the ECF. (80 mOsm/l) *Because of water being reabsorbed in the proximal convoluted tubule (~65%), and descending loop of Henry (~15%), only about 20% of the filtered watter remains. --This would be the maximum urine flow rate.

The movement of water balances the________ pressure within or across the tubule walls, which maintains ___________ volume.

The movement of water balances the *osmotic* pressure within or across the tubule walls, which maintains *extra cellular fluid* volume. *ECF osmolarity depends on the relative amoutns of water to solutes (mostly NaCl, plus lots of other things at lower concentration)

Baroreceptors & ADH release: Increased MAP will ______ ADH release, which will ________ excretion of water, leading to a _______ volume (venous return), returning MAP to set point.

detect change in MAP. Increased MAP will *decrease* ADH release, which will *increase* excretion of water, leading to a *decrease* in blood volume (venous return), and a decrease in MAP returning to set point.

Urea recycling can cause a buildup of urea in the

renal medulla

Aldosterone

Aldosterone is release by the zona glomerulosa of the adrenal cortex when stimulated by Angiotensin II. Aldosterone acts ton the distal convoluted tubules, and collecting duct of the kidneys to cause a net movement of ions back into the blood---which in turn forces the reabsorption of water. ----this *increase blood volume and blood pressure*

Renin

An enzyme secreted by the juxtaglomerular cells when blood pressure decreases. Renin converts angiotensinogen to angiotensin I.

Angiotensin

A normal blood protein produced by the liver, *Angiotensinogen* is converted to Angiotensin I by Renin (secreted by Juxtaglomerular complex in the kidney when blood pressure falls). Angiotensin I is further converted to angiotensin II by ACE (angiotensin converting enzyme in the lungs and kidney). Angiotensin II is a powerful systemic *vasocontrictor*, and stimulator of *aldosterone* release, both of which result in an increase in blood pressure.

A 100 mMol solution of NaCl, thus would be _____ mOsm. The Osm is _______.

A 100 mMol solution of NaCl, thus would be *200* mOsm. The Osm is moles of solute / liter.

When ________ moves, water follows!

WHen *Na+* moves, water follows! Sodium reabsorption is tightly coupled to passive water reabsorption,

Atrial Natriuretic Peptide

heart; involved in osmoregulation and vasodilation. This 28 amino acid peptide, is synthesized and stord by large eins and the atria. When the chambers of Cardia atria are stretched (expanded ECF volume) ANP is released into the blood. It acts to inhibit Na+ reabsoorption in the in the distal tubules and collecting duct, --- and blocks Aldosterone action. This will lead to an increased Na+ excretion, decrease ECF volume.

Juxtaglomerular Apparatus

in the nephron, --the complex of cells between the distal tubule and the afferent arteriole, which helps regulate blood pressure by secreting *Renin* in response to blood pressure changes in the kidney; located near the glomerulus