Physiology Lo: Water Excretion, Na, K, Ca Balance

Front 1

How does the kidney conserve water by producing a more concentration urine?

Back 1

by countercurrent multiplication in the loop of Henle which creates hyperosmotic medullary interstitial that provides the osmotic force for water reabsorption from the lumen of the collecting duct under appropriate condition to concentrate the urine.

Front 2

Principle of countercurrent system

Back 2

A system with two parallel and adjacent tubes separated by a membrane of finite permeability and within which the flow of the fluid is in the opposite direction

Front 3

What component of the kidney is considered a countercurrent exchanger?

Back 3

vasa rectae

Front 4

What is a countercurrent exchanger?

Back 4

A passive system, producing equilibrating effect at
each horizontal level between two adjacent tubes with opposing flow, therefore it helps intensify as well as maintain pre-existing vertical gradient

Front 5

True or false: a countercurrent exchanger can create a gradient by itself.

Back 5

False; by itself it cannot create any gradient

Front 6

__ can both generate and maintain the gradient that it creates.

Back 6

Countercurrent multiplier

Front 7

What is a countercurrent multiplier?

Back 7

possesses energy source to generate a horizontal
concentration gradient between two adjacent tubes. This horizontal gradient is then multiplied vertically along the length of the tube as the fluid flows through

Front 8

What component of the kidney is a countercurrent multiplier?

Back 8

loop of Henle

Front 9

What is the net result of "single effect" multiplication?

Back 9

development of a vertical concentration gradient
along the length of the U-tube (both inside the descending tube and its surrounding) with the highest concentration existing at the bend of the Utube.

Front 10

The proximal tubule is __ to salts and water.

Back 10

highly permeable

Front 11

The descending limb of loop of Henle is __ to salts and __ to water.

Back 11

relatively impermeable; very permeable

Front 12

The ascending limb of the loop of Henle has very __ permeability but is permeable to __.

Back 12

low water; salts

Front 13

The distal tubule and collecting duct are permeable to __.

Back 13

salts

Front 14

The distal tubule and collecting duct have low water permeability in the absence of __ but permeable to water in the presence of it.

Back 14

ADH

Front 15

Countercurrent multiplication in the loop of Henle causes what two things?

Back 15

1. Fluid in ascending limb of loop of Henle to become progressively diluted
2. An osmotic gradient (highest concentration at papilla tip) to be established both within the descending limb of Henle as well as in the medullary interstitium

Front 16

If you have a low circulating level of ADH urine is __. If you have a high circulating level of ADH urine is __ and the distal nephron becomes permeable to water.

Back 16

hypo-osmotic (dilute), hyperosmotic (concentrated)

Front 17

For urine to become concentrated, there must be
what two things?

Back 17

medullary osmotic gradient and functional ADH system

Front 18

Deposition of urea in the medullary interstitium

Back 18

High medullary urea occurs through medullary recycling of urea. Urea helps establishing medullary osmotic gradient with less energy expenditure

Front 19

True or false: Since only the inner medullary segments of the loop of Henle and collecting duct are permeable to urea, urea is present in the interstitium only in the inner medulla when it recycles from inner medullary collecting duct lumen back to the loop of Henle lumen

Back 19

true

Front 20

Most of the water in the tubule lumen of distal nephron is reabsorbed into __ in the cortex when ADH is present.

Back 20

peritubular capillaries

Front 21

Vasa recta

Back 21

picks up water (reabsorbed from loop of Henle and distal nephron in the presence of ADH) and helps equilibrating
solutes (sodium, chloride, other salts, organic solutes, urea) within medullary interstitium.

Front 22

Role of vasa recta

Back 22

In addition to its normal capillary role, transporting oxygen and nutrients to the renal medullary cells, the vasa recta, the capillary loop that parallels the loop of Henle, helps maintain medullary osmotic gradient.

Front 23

The site for regulation of water balance is at the __ where the amount of water reabsorbed is independent of sodium reabsorption and varies directly with amount of circulating ADH

Back 23

distal nephron (collecting ducts)

Front 24

Source of ADH

Back 24

Synthesized in hypothalamus and stored in posterior
pituitary until released

Front 25

Plasma osmolality

Back 25

It is an inverse function of water content in body fluid
compartments, therefore change in plasma osmolality directly correlates with change in water balance.

Front 26

Increases in plasma osmolality above a threshold value increases the amount of __ released via
stimulation of hypothalamic osmoreceptors

Back 26

ADH

Front 27

Increases in __ with resulting increases in BP inhibit ADH release via action of left atrial baroreceptors. Decreased __ results in disinhibition of this pathway, allowing more ADH to be released

Back 27

blood volume

Front 28

Sites of ADH action on water permeability

Back 28

late distal tubules and collecting ducts

Front 29

Mechanism of ADH action

Back 29

making the luminal membranes of distal nephron
permeable to water through activation of adenylate cyclase which, by a sequence of events, finally results in the insertion of water channels into the luminal membrane

Front 30

Diabetes insipidus

Back 30

condition in which a person excretes large amount of very dilute urine but otherwise normal
-may be central (hypothalamus - no ADH) or nephrogenic in origin (distal nephron is not responding to ADH, or no medullary gradient).

Front 31

The regulation of __ represents the regulation of ECF volume.

Back 31

total Na content

Front 32

The kidneys maintain sodium balance by __ to match variable intake of sodium.

Back 32

adjusting renal output (sodium excretion)

Front 33

Changes in sodium balance are sensed as changes in volume of the extracellular fluid compartment by __.

Back 33

volume-dependent sensors/receptors (baroreceptors)

Front 34

The portion of the ECF compartment that is sensed by baroreceptors is __.

Back 34

plasma volume (effective circulating volume)

Front 35

Sodium excretion is the results of what two processes?

Back 35

glomerular filtration and tubular reabsorption.

Front 36

__ and __ stimulate the Na+/H+ exchanger and sodium reabsorption in the proximal tubule.

Back 36

Angiotensin II and norepinephrine

Front 37

Aldosterone

Back 37

regulates the final amount of Na+ that is excreted by increasing tubular reabsorption of Na+ by the cortical collecting ducts. This part of the distal nephron is the most important regulatory site for sodium reabsorption

Front 38

The Renin-Angiotensin-Aldosterone System (Na-conserving system: most important regulator of Na+ reabsorption)

Back 38

The release of aldosterone is dependent on the circulating level of angiotensin II, which in turn depends on the availability of the enzyme renin. Therefore the regulation of renin release is the most important and the rate-limiting step in the regulation of renal Na+ reabsorption/excretion.

Front 39

When is renin released?

Back 39

in response to a decrease in ECF volume and/or arterial pressure via 3 mechanisms:
1. Extrarenal baroreceptors (carotid sinus) and intrarenal
baroreceptor mechanism in afferent arterioles sensing the size of the ECF compartment
2. Macula densa mechanism
3. Sympathetic nerve activity in response to signals from baroreceptors

Front 40

Does sympathetic nerve activity increase or decrease Na+ reabsorption?

Back 40

increase

Front 41

Atrial natriuretic peptide

Back 41

released from atria in response to ECF volume expansion (detected by baroreceptor in right atria).
-It increases Na+ excretion, in part, by increasing GFR, by inhibiting Na+ reabsorption in collecting duct, and by inhibiting renin and aldosterone secretion.
-This is the "Na+ losing"system.

Front 42

Pressure natriuresis

Back 42

Increases in arterial pressure can produce a significant increase in sodium excretion without changes in GFR

Front 43

Generalized edema

Back 43

Under these conditions, the body perceives a decrease in the "effective" ECF volume, the volume sensors are stimulated and renal tubular Na+ reabsorption increases despite the initilal normal ECF volume, resulting in Na+ and water retention and subsequent accumulation of fluid in peripheral tissues

Front 44

>90% of filtered K+ is reabsorbed by __ and __ (obligatory reabsorption)

Back 44

proximal tubule and loop of Henle

Front 45

K+ can either be reabsorbed or secreted in the
__. Urinary K+ excretion varies with the amount of K+ secreted by the distal nephron

Back 45

late distal tubule and collecting duct

Front 46

K+ secretion is stimulated by __ in cortical collecting duct.

Back 46

aldosterone

Front 47

The most important regulatory site for potassium

Back 47

distal nephron

Front 48

K+ is accumulated in the cell via the activity of __ and its secretion occurs across luminal membrane via K+ channels (passive -
down electrochemical gradient).

Back 48

Na/K-APPase

Front 49

Factors controlling renal secretion of potassium

Back 49

1. When plasma [K+] increases, K+ secretion will be stimulated because cellular [K+] increases from increased activity of Na/K APPase
2. Increased flow rate of tubular fluid will stimulate K+ secretion due to reduction in luminal [K+] which in turn creates better diffusion gradient for K+ secretion.

Front 50

In the cortical collecting duct, __ is released in response to high plasma [K+] and
stimulates K+ secretion

Back 50

aldosterone

Front 51

99% of the filtered ionized Ca2+ is reabsorbed, with most of the reabsorption occurs in the __.

Back 51

proximal tubule.

Front 52

The major regulatory site for Ca2+ reabsorption
in the nephron is the __, where parathyroid hormone directly stimulates Ca2+ reabsorption when plasma calcium is low.

Back 52

distal convoluted tubule

Front 53

Parathyroid hormone will also stimulate the kidneys to produce the active form of __ which then stimulates intestinal absorption of calcium

Back 53

vitamin D