1. Regulation of Body Fluid: Regulation of Water

Question 1

What must the thick ascending limb maintain between the tubular fluid and the interstitium at any point along its length?

Answer 1

200mOsmol/kg H20

Question 2

What is the maximum osmolality at the tip of the loop of henle?

Answer 2

1200-1400mOsmol/kg H2O

Question 3

What is the state of the fluid when it leaves the loop of henle and enters the distal convoluted tubule?

Answer 3

100mOsmol/kg H2O, HYPOTONIC solution meaning the cells will swell in this solution

Question 4

The first step in the coutnercurrent multiplier is when the tubular fluid enteres the descending limb from the PCT and is isotonic (PCT is always 300mosm). Before the gradient is established, the medullary interstitial fluid concenctration is?

Answer 4

300mosm everywhere

Question 5

The second step of the countercurrent: thick ascending NaKClCl transporter pumps NaCl into the meduallary interstitium until there is a 200 mOsm difference, this causes?

Answer 5

The fluid in the medullary interestitium will then become hypertonic, more concentrated, leading to water from the thin descending limb to permeating into the interstitium

Question 6

In the 3rd step, water passivle moves until it is at equilibrium with the interestitium. The fluid in the ascending loop of H becomes more concentrated due to?

Answer 6

more water going into the interstitium to equilibriate, ascending LoH is at 200 and interstitium and descending are at 400mosm

Question 7

The same steps are repeated over and over again with the descending limb progessively getting more hypertonic until it reaches 1200-1400mosm. What about the fluid before leaving the ascending loop?

Answer 7

the fluid is hypotonic at about 100mosm before entering the DCT, about 1/3 of the original osmolaltity

Question 8

The vasa recta supplies blood to the medulla, and is HIGHLY permeable to solute and water. The ability for it to maintain the gradient is flow dependent, if there is an increase in blood flow, it dissipates the medulary gradient causing medullary washout. What happens if there is a increase in blood flow?

Answer 8

decreases salt and solute transport by nephron segments in the medulla reducing the ability to concerntrate the urine

Question 9

Urea is recycled when concentrated urine needs to be formed or when there are high levels of ADH. With high levels of ADH, reabsorption of water from the distal tubule and cortical collecting tubule increases, increasing the tubular fluid of concentration of Urine. What does urea then do when ADH is present?

Answer 9

Via the UTA1 and UTA3 transporters in the inner medullary collecting duct, urea diffuses into the medullary interstitium which diffuses into the LoH through UTA2 , concentrating the urea

Question 10

There are two things that create the medullary interstitial gradient. One: the combination of aquaporin channels and absence of tight junctions in the thin limb provides pathway for H2O to move w/o sodium following. Two:?

Answer 10

The anatomic arrangements of the LoH and collecting ducts which increases the osmolality as the loop dips deeper into the medulla

Question 11

What is the location of the the two large neurons in the hypothalamus which synthesize ADH?

Answer 11

supraoptic and paraventricular nuclei of the hypothalamus

Question 12

When the supraoptic and paraventricular nuclei are stimulated by increased osmolarity and other things, a nerve impulse passes down the nerve endings, doing what?

Answer 12

changing their membrane permability and increasing calcium entry. (ADH is stored in the secretory vesicles of the nerve endings, occurs within minutes)

Question 13

Osmoreceptors are sensitive to small changes (1-2%) which releases ADH and stimuates thirst. Which usually occurs first?

Answer 13

ADH released and then thirst activated

Question 14

The late distal tubule and collecting ducts have two cell types including the principle cells and the intercalated cells. What do the principle cells reabsorb and secrete?

Answer 14

Reabsorb Na+, Cl-, H2O and secretes K+

Question 15

Principle cells reabsorbs Na via NaKATPase, H2O via ADH, which increases permeability via AQP2 in the apical membrane in the late DCT and CD. How is K+ secreted here?

Answer 15

K+ is uptaken from the blood via NaKATPase, and then passed down its gradient throuhg the Kchannel into the lumen urine

***Aldosterone increases this process of K+ excretion and Na+ reabsorption

Question 16

Intercalated cells reabsorb K+ and secrete H+ how?

Answer 16

Via aldosterone, which stimulates the H+ATPase in the intercalated cells (along with what it does in the priciple cells)

Question 17

Steroid aldosterone causes an increase in the number of ENaC (epithelial Na Channels) located on the apical side transporting more Na into the cell to be reabsorbed. If more Na is reabsorbed via the NaK ATPase, what does this mean for K+?

Answer 17

K+ will increase in the lumen and more will be excreted d/t increase in aldosterone.

Question 18

There are four main ways aldosterone is activated.

1. Rise in plamas K+ directly stimulates adrenal cortex to increase its output of aldosterone. What are the other 3?

Answer 18

2. A decline in K+ plasma reduces aldosterone secretion
3. decrease in plasma Na stimulates aldosterone secretion via RAAS system
4. Increased aldost promotes simulatneous Na reabs. and K+ secretion*****

Question 19

AQP2 is in the apical membrane of the medullary CD and DCT. When present due to ADH/vaspressin/AVP, they do what?

Answer 19

An increase in AQP2 would lead to an increase in reabsorption of H2O, creating a more concentrated urine. Vice versa if there was a decrease in AQP2 d/t decreased or absent ADH

Question 20

What are the steps of our body responding to increased osmolality?

Answer 20

When concentration is increased, signals to the hypothalamic osmoreceptors, secreted ADH which travels to kidneys where stimulates AQP2 and thirst, which increases reabsorption of H2O, increase urine concentration and excretes extra solute

Question 21

What are the steps for our body to respond to decreaseed osmolarity?

Answer 21

Osmoreceptors in the supraoptic and paraventricular nuclei of the hypothalamus trigger cessation of release of ADH so collecting tubules remain impermeable to water, increasing dilution of urine and excreting more H2O to get concentration back to normal

Question 22

An adequately hydrated person has a osmolarity of 275 to 295 while a dehydrate person would have a osmolarity of >300. What are the simple rules for ADH?

Answer 22

Overhydrated = ADH inhibited
Dehydrated= ADH released

Question 23

Diabetes insipidus has 2 types. The first type is failure to produce ADH from posterior pituitary due to head trauma, infections, or congenital- central neurogenic diabetes insipidus. What is the second type?

Answer 23

Inability of the kidneys to respond to ADH: Nephrogenic diabetes insipidus

Question 24

In central diabetes, the distal tubular segments cannot reabsorb H2O, resulting in a large volume of dilute urine (15L/day). What is the main treatment for this disease besides water restriction?

Answer 24

Demospressin (analog of ADH) which acts on V2 receptors to increase water permeability in late distal tubule and CD.
restores urine back to normal, stronger concentration

Question 25

In nephrogenic diabetes, normal levels of ADH are present but renal segments do not respond d/t failure of countercurrent to form a hyperosmotic interstitium (diuretics can do this) or failure of distal/collecting tubules to respond to ADH. What is seen and what drugs can cause this?

Answer 25

Large volumes of dilute urine, causing dehydration.

Seen with lithium (depressive disorder medication) and tetracyclines (antibiotic) that impair the ability of the distal nephron to respond to ADH

Question 26

Central and nephrogenic can be distinguished by adminstrating desmopressin. What would be seen after the administration that would suggest nephrogenic diabetes insipidus?

Answer 26

Seeing a lack of decrease in urine volume and an increase in urine concentration within 2 hours

Question 27

SIADH= Syndrome of Inappropriate antidiuretic hormone. When this occurs, there is an increase in ADH, leading to an increase in H20 reabsorption, disturbing fluid and electrolyte balance. When the ECF increases, what four things occurs?

Answer 27

1. reduces plasma osmolarity
2. Dilutional hyponatremia
3. Decreased aldosterone secretion
4. Elevated GFR

Question 28

What do the four factors of SIADH lead to and how would the patient present?

Answer 28

leads to increased sodium excretion and shifting fluid into cells which leads to thirst, dyspnea, vomiting, abdominal cramps, confusion, lethargy, and hyponatremia

Question 29

In SIADH, you see...
Low urinary output
high levels of ADH
Hyponatremia
overhydrated
retain alot of fluid
Excessive thirst
What about Diabetes insipidus? (6)

Answer 29

High urinary output
low levels of ADH
Hypernatremia
Dehydrated
lose too much fluid
excessive thirst

Question 30

Remember that dilution is dependent on the thick ascending limb of loop of henle because solutes (na k cl) are reabsorbed here without water. What else is important to remember about water here?

Answer 30

thick ascending loop is impermeable to water… if you remove solute but not water then the tubule fluid will become more dilute

Question 31

Hyponatremia is an excess of water relative to the solute/Na+ concentration. This leads to urine sodium being less than 20mmol/L and urine osmolality being greater than 300mosm. With water intoxication or low solute intake, what would be expected to occur?

Answer 31

Water intox would cause a urine osmolarity less than 100 and low urine osmolarity

Question 32

Hypernatremia is when there is more solute than free water caused by inadequate water intake. When seen with water depleteion the urine osmolality will be greater than 600-800. What occurs with salt intoxication or diabetes insipidus?

Answer 32

Salt Intox: urine sodium would be very high

Diabetes: less than 300 urine osmolality or less than 100 in nephrogenic

Question 33

Polyuria (excessive urine production) is when you urinate more than 2.5L/day. What are the main causes of this? (4)

Answer 33

diabetes mellitus/insipidus
excess caffeine/alcohol
Kidney disease
diuretics/sickle cell/excessive h2o intake

Question 34

Oliguria (urine less than normal (1-2L/day) is when you urinate 300-500mL/day. What are the main causes of this? (6)

Answer 34

dehydration, blood loss, diarrhea, cardiogenic shock, kidney disease, enlarged prostate

Question 35

Anuria is when you urinate less than 50mL/day and can be caused by (3)?

Answer 35

kidney failure
obstruction-kidney stone
enlarged prostate

Question 36

Polyuria is assocaited with polydipsia (excessive water intake 6L/day). What is water diuresis?

Answer 36

increased water excretion without corresponding increased salt excretion due to increased intake of H2O

Question 37

Solute diuresis is increased water excretion concurrent with increased salt excretion. the primary cause is significant increase in sal present in tubular fluid such as? (3)

Answer 37

IV NaCl
Hyperglycemia
High protein intake

Question 38

What are the four main mechanisms that cause polyuria?

Answer 38

increase fluids
increased GFR
Increased output of solutes
inability in kidney to reabsorb water in DCT

Question 39

how does one calculate urine volume?

Answer 39

total excreted mOsmsolute/day
___________________________ (divided by)
Maximal urine concentrating ability in mOsm/L

Question 40

If less than 0.5L/day of water is excreted then considered Oliguria which is decribes in infants, children and adults as?

Answer 40

infants: <1ml/kg/h
children: <0.5ml/kg/h
adults: <0.125ml/kg/h (?)

Question 41

The rate of free water clearance represents the rate at which solute-free water is excreted by the kidneys. How do you calculate this?

Answer 41

V - Clearance osmolar = CH2O
V= urine flow rate
Clearance osmolar = [U] * V / [P]

Question 42

positive free clearance means excess water is being excreted by the kidney while a negative free clearance indicates excess solutes are being removed from blood and water being conserved. When urine osmo is greater than plasma osmo, what occurs?

Answer 42

free water clearance will be negative indicating water conservation

Question 43

When the ratio of Uosm:Posm is greater than 1, indicates kidneys can concentrate urine. When Uosm:Posm is one, indicates that equal water and solute excreted are same as plasma. What happens when Uosm:Posm is less than one?

Answer 43

U:P<1= kidneys are able to dilute urine, cant concentrate it