Renal Part 2c

Question 0

Distal delivery is what percent of the filtered load of H2O? and NaCl?

Answer 0

10% of both H20 and NaCl

Question 1

Distal nephron consists of what?

Answer 1

Distal convoluted tubule + collecting tubule (cortical –> papillary)

Question 2

Distal transport of H2O is regulated by what hormone?

Answer 2

Antidiuretic hormone (ADH)
(Increase ADH --> Increase H2O reabsorption --> Decreased H20 Excretion)

Question 3

What regulates distal nephron transport of NaCl?

Answer 3

Aldosterone

Increased Aldosterone –> Increased NaCl reabsorption –> Decreased NaCl excretion

Question 4

In the presence of what hormone is the collecing tubule permeable to water?

Answer 4

ADH

Question 5

A favorable osmotic gradient in collecting tubule (tubular fluid –> interstitium) promotes what?

Answer 5

Water reabsorption there by generating a small volume of concentrated (hypertonic) urine: ANTIDIURESIS

Question 6

In the absence of ADH, the collecting tubule is permeable or impermeable to water?

Answer 6

Impermeable to water

Question 7

What is occurring during diuresis in collecting tubule?

Answer 7

Reabsorption of some NaCl in the distal nephron continues to dilute the tubular fluid resulting in excretion of a large volume of hypotonic urine

Question 8

Reabsorption of water by the collecting tubule system is dependent on the presence of what?

Answer 8

Water channels (aquaporins) in the luminal membrane

Question 9

ADH stimulates insertion of pre-existing ________________ into the luminal membrane

Answer 9

AQP-2 channels (aquaporins)

Question 10

What aquaporin channels are constitutively expressed in the basolateral membrane?

Answer 10

AQP-3 channels. AQP-2 are the channels that can be moved by action of ADH to the luminal side of the membrane

Question 11

T or F, All nephron segments express basolateral aquaporins

Answer 11

True

Question 12

How many isoforms of aquaporins are differentially distributed along the nephron?

Answer 12

3

Question 13

What would explain water impermeability of the ascending limb?

Answer 13

Lack of luminal aquaporins

Question 14

The cortical collecting tubule reabsorbs what? and secretes what?

Answer 14

Reabsorbs sodium

Secretes potassium

Question 15

ALdosterone controls reabsorption of Na+ by: (3)

Answer 15

1. Increased number of luminal membrane Na+ channels
2. Increased Na+-K+-ATPase (de novo synthesis of pumps)
3. Increased Krebs cycle enzyme synthesis (thus more ATP) –> increased ATPase activity

Question 16

Aldosterone and cortisol have similar affinity for what receptor?

Answer 16

Mineralocorticoid receptor

Question 17

How are higher circulating levels of cortisol prevented from affecting Na+ reabsorption?

Answer 17

By 11B hydroxysteroid dehydrogenase type 2

Question 18

Mutations in 11B hydroxysteroid dehydrogenase type 2 can lead to what?

Answer 18

NaCl retention and hypertension

You can no longer suppress the actions of cortisol

Question 19

What does Parathyroid Hormone stimulate in distal tubule?

Answer 19

Calcium reabsorption

Question 20

Increased PTH –> Increased Ca2+ reabsorption in the distal tubule due to stimulation of:

Answer 20

1. Ca2+ ATPase

2. Na-Ca2+ exchanger on the basolateral membrane

Question 21

Step 1 of countercurrent multiplication

Answer 21

1. Reabsorption of NaCl by the ascending limb; retention in interstitium

Question 22

Step 2 of countercurrent multiplication

Answer 22

1. reabsorption of NaCl by ascending limb; retention in interstitium
2. reabsorption of H20 by the descending limb; removal by vasa recta

Question 23

Step 3 of countercurrent multiplication

Answer 23

1. reabsorption of NaCl by the ascending limb; retention in interstitium
2. reabsorption of H2O by the descending limb ; removal by vasa recta
3. isotonic fluid from proximal tubule into loop; hypertonic fluid into the ascending limb

Question 24

T or F, Cortical/outer medullary collecting tubule reabsorbs urea

Answer 24

False, it cannot reabsorb urea

Question 25

T or F, As tubular fluid flows into inner medullary collecting tubule, high urea concentration promotes passive reabsorption into interstitium

Answer 25

True

Question 26

Does ADH promote permeability of inner medullary collecting tubule to urea?

Answer 26

Yes

Question 27

With a decrease in ADH, do you excrete more or reabsorb more urea?

Answer 27

You excrete more urea. Without the permeability of the inner medullary collecting tubule, urea does not get reabsorbed and is excreted into urine. This tends to happen when you are hydrated

Question 28

T or F, Plasma ADH levels control medullary interstitial urea but not NaCl concentrations

Answer 28

False, it controls both

Question 29

Medullary blood supply essential for: (2)

Answer 29

1. Nutrient supply | 2. Removal of reabsorbed H20 and NaCl

Question 30

Does the plasma flowing out of the medulla have a higher osmolality or lower osmolality than when it entered?

Answer 30

Higher osmolality

Question 31

T or F, Exiting plasma flow rate will be lower than that entering the medulla (vasa recta)

Answer 31

False, It will be higher

Question 32

What is the only water output that can be precisely controlled?

Answer 32

Urine output

Question 33

Maximum Diuresis:

Answer 33

Urine volume: 20-25 L/day | Urine Osmolality: 50-75 mOsm/kg

Question 34

Maximum ANTIDIURESIS:

Answer 34

Urine volume: 0.5 L/day | Urine Osmolality: 1200-1400 mOsm/kg

Question 35

Where is ADH synthesized? | Where is it stored?

Answer 35

in neural cell bodies located in supraoptic and paraventricular nucleii of hypothalamus - Transported down axon, stored in nerve terminals in posterior pituitary

Question 36

Which method of ADH secretion regulation is most sensitive?

Answer 36

Changes in plasma osmolarity (hypothalamic osmoreceptors) - Increases in plasma osmolarity will increase secretion of ADH so that the tubule will become more permeable and therefore reabsorb water

Question 37

The lesser sensitive method to regulating ADH secretion is through what?

Answer 37

Volume receptors: Plasma volume (baroreceptors) | Changes in plasma volume will affect ADH secretion

Question 38

T or F, Increase in osmolality = Decrease in urine volume

Answer 38

True

Question 39

What are some causes of Syndrome of Inappropriate ADH secretion (SIADH)

Answer 39

Head trauma, encephalitis, meningitis ADH secreting tumors (lung, pancreas) Drug-induced (nicotine, morphine, chemotherapeutic agents)

Question 40

What is the effect of Syndrome of Inappropriate ADH secretion (SIADH)?

Answer 40

Increase in ADH, Increase in H2O reabsorption --> Hyponatremia Decrease in serum Na --> Decrease in Plasma osm --> influx of H2O (into brain cells) --> Coma

Question 41

What is the cause of Diabetes Insipidus (D.I.)

Answer 41

1. Hypothalamic (CENTRAL) D.I. --> decrease of production or release of ADH 2. Nephrogenic D.I. --> Renal unresponsiveness to ADH

Question 42

What may cause nephrogenic D.I.?

Answer 42

- Mutations in the ADH receptor - Impaired synthesis/translocation of aquaporins - Drugs (lithium, tetracyclines); hypokalemia

Question 43

What is the effect of Diabetes Insipidus

Answer 43

Lower ADH --> Lower H2O reabsorption --> Hypernatremia | Higer serum Na --> Higher plasma osm --> efflux of H2O (out of brain cells) --> Coma

Question 44

What is Free Water clearance?

Answer 44

Represents the amount of distilled water that must be added to or removed from urine to create an isotonic fluid

Question 45

What is the use for Free Water Clearance?

Answer 45

It provides a non-invasive assessment of diluting efficiency of the thick ascending limb

Question 46

T or F, ECF volume is directly related to total body sodium (chloride)

Answer 46

True

Question 47

ECF volume being directly related to total body sodium is due to what: (3)

Answer 47

1. H2O shifts extracellular intracellular 2. Effects on ADH secretion, thus distal nephron H2O reabsorption 3. Effects on thirst

Question 48

How do kidneys maintain constant ECF volume?

Answer 48

by adjusting NaCl excretion to match NaCl intake

Question 49

How much of filtered load of sodium is excreted?

Answer 49

1% or less of filtered load

Question 50

Na excretion is primarily regulated by the action of what?

Answer 50

Aldosterone on the cortical collecting tubule

Question 51

Aldosterone regulates the excretion of approximately how much percentage of the filtered load of sodium?

Answer 51

5%

Question 52

Aldosterone controls reabsorption of Na+ by: (3)

Answer 52

1. Increased number of luminal membrane Na channels 2. Increase Na-K-ATPase 3. Increased Krebs cycle enzyme synthesis (more ATP)--> ATPase activity

Question 53

Total body Na changes sensed as changes in?

Answer 53

Effective circulating volume (ECV)

Question 54

The effective circulating volume (ECV) is monitored by what?

Answer 54

Baroreceptors - Cardiac atria, pulmonary vasculature - carotid sinus, aortic arch, juxtaglomerular apparatus

Question 55

Rate limiting step in aldosterone release from adrenal cortex?

Answer 55

Renin (enzyme) release by kidney (Renin --> Angiotensin to Angiotensin I -> Converting enzyme from lungs converts Angiotensin I to Angiotensin II --> Angiotensin II to adrenal cortex --> Adrenal cortex releases Aldosterone to kidney)

Question 56

Renin-angiotensin-aldosterone system can be pharmacologically controlled at several points: (4)

Answer 56

1. Renin inhibitors 2. ACE (angiotensin converting enzyme) inhibitors 3. Angiotensin II receptor antagonists 4. Aldosterone receptor antagonists

Question 57

Renin is secreted by what cells?

Answer 57

Granular cells of the afferent arteriole

Question 58

SUSTAINED increases in aldosterone secretion results in what?

Answer 58

Relatively transient Na retention - Increase in Aldosterone --> Increase ECV --> Increase blood pressure - This results in Pressure natriuresis and Pressure diuresis (Aldosterone Escape)