Regulation of Extracellular Fluid Osmolarity and Sodium Concentration

Question 1

Which hormone is a major determining factor in urine concentration?

Answer 1

ADH

Question 2

Increase in OSMOLARITY in the body

Answer 2

• INCREASE ADH
• INCREASE water permeability
• large REABSORPTION of water
• INCREASED concentration of urine
• no marked change in excretion of solutes

Question 3

Osmolarity in proximal tubule

Answer 3

Stays ISOTONIC

Question 4

Osmolarity in loop of Henle

Answer 4

-enters loops being ISOTONIC

**water is reabsorped by OSMOSIS in the DESCENDING segment of the loop of Henle

• thin and think ascending segments are NOT permeable to water!!!
  
  • solutes are ACTIVELY transported out (THICK)
• tubular fluid becomes more DILUTE as it travels up ascending segments

-leaves loop of Henle as a HYPOTONIC solution

Question 5

T/F: renal medulla interstitial fluid is very HYPERTONIC

Answer 5

True

-tubular fluid becomes more concentrated as it travels into the medulla

Question 6

Osmolarity in the distal tubule and collecting ducts

Answer 6

• enters being DILUTE
• later parts:
  
  • additional reabsorption of sodium
• absence of ADH = dilute urine excreted
• presence of ADH = concentrated urine excreted

Question 7

Urine Specific Gravity

Answer 7

• used as a measurement in clinical settings to assess the concentration of urine
  1) high concentration = high specific gravity
  2) low concentration = low specific gravity

Question 8

Basic requirements for forming a concentrated urine

Answer 8

1) HIGH level of ADH

2) HIGH osmolarity in the medulla tissue

Question 9

How do we create a hyperosmotic renal medullary interstitial fluid?

Answer 9

• COUNTERCURRENT MECHANISM
• juxtamedullary nephrons
• vasa recta
• collecting ducts
• molarity of the renal medullary interstitial fluid

Question 10

What is the osmolarity around the papilla of the renal pyramids?

Answer 10

~1200mOsm/L

Question 11

Countercurrent multiplier

Answer 11

the repetitive reabsorption of NaCl by the THICK ASCENDING loop of Henle and continued inflow of new Na+ from the PROXIMAL TUBULE into the loop of Henle

Question 12

Vasa Recta and urine concentration

Answer 12

• Countercurrent exchangers
• minimizes washout of solutes from the interstitium
• preserve the high solute concentration in the renal medulla

Question 13

A high concentration of UREA is found in the…

Answer 13

inner medullary collecting ducts

-diffusion of urea into the renal medulla (facilitated by urea transporters)

Question 14

Thirst

Answer 14

when sodium content increases 2mEq/L above normal there is a desire to ingest fluid

**the THRESHOLD FOR DRINKING

Question 15

Thirst center

Answer 15

• an area along the anteroventral wall of the THIRD ventricle that promotes ADH release also stimulates thirst
• anterolateral in the PREOPTIC NEURONS

Question 16

Factors that increase thirst

Answer 16

• INC plasma osmolarity
• DEC blood volume
• DEC blood pressure
• INC angiotensin II
• a dry mouth

Question 17

Factors that decrease thirst

Answer 17

• DEC plasma osmolarity
• INC blood volume
• INC blood pressure
• DEC angiotensin II
• gastric distension

Question 18

Extracellular fluid volume (ECV)

Answer 18

• determined by intake and output of fluid and sodium

- usually dependent on person’s HABITS

Question 19

Homeostatic state of ECV

Answer 19

• must excrete almost the same amount of sodium that you take in (w/in a few days)
• not much change in extracellular fluid
• ADH
• osmolality and sodium concentration are maintained

Question 20

What happens if ECV can not maintain a steady balance?

Answer 20

• change in BP
• change in circulating hormones
• change in SNS

Question 21

Pressure diauresis

Answer 21

increased blood pressure raising urinary volume excretion

Question 22

Pressure natriuresis

Answer 22

the raise in sodium excretion that occurs with elevated blood pressure

Question 23

T/F: pressure diauresis and pressure natriuresis occur concurrently

Answer 23

True

Question 24

As long as the pressure diauresis mechanism is working the body will be able to handle an increase in fluid and salt intake with LITTLE change to:

Answer 24

• blood volume
• ECF volume
• cardiac output
• arterial pressure

Question 25

What circumstances would change the fact that ECF volume and blood volume are controlled together?

Answer 25

- INC capillary hydrostatic pressure - DEC plasma colloid osmotic pressure - INC permeability of the capillaries - obstruction of lymphatic vessels

Question 26

T/F: an inhibition of sympathetic activity may help to rapidly eliminate excess fluid and sodium when large amounts are consumed

Answer 26

True

Question 27

What stimulates SNS activity on the kidneys?

Answer 27

an extensive decrease in blood volume (i.e., hemorrhage) - signals kidneys to HOLD ON TO salt and fluid - constriction of renal arterioles -> DEC GFR - increase tubular reabsorption - stim of renin release -> INC angiotensin II and aldosterone -> INC tubular reabsorption

Question 28

T/F: Angiotensin II level generally have a big impact on extracellular fluid or blood volume

Answer 28

FALSE; little impact -Angiotensin II is a powerful controller of SODIUM EXCRETION

Question 29

T/F: a small increase in blood pressure causes an increase in sodium excretion when sodium levels rise

Answer 29

TRUE - due to angiotensin II

Question 30

Salt sensitivity

Answer 30

a little bit of salt will cause a large increase in blood pressure -in these patients, renin secretion can NOT be decreased; NEED higher BP to excrete excess sodium

Question 31

Increased Aldosterone will cause

Answer 31

- INC sodium and water REABSORPTION in the cortical collecting tubules - INC potassium excretion

Question 32

Increased ADH will cause

Answer 32

- INC reabsorption of fluid | - concentrated urine

Question 33

Decreased ADH will cause

Answer 33

- REDUCED reabsorption of fluid | - decreases fluid volume in the body

Question 34

Omsoreceptor-ADH Feedback System

Answer 34

- water defecit - osmoreceptor cells in the Anterior Hypothalamus SHRINK - osmoreceptors cells fire and stimulate the Posterior Pituitary to RELEASE ADH - ADH transported in blood to kidneys - LATE DISTAL TUBULE, CORTICAL COLLECTING TUBULES, and MEDULLARY COLLECTING DUCTS increase water permeability - water reabsorption, and excretion of concentrated urine

Question 35

AV3V region

Answer 35

- anteroventral region of the third ventricle | - signals posterior pituitary to release ADH

Question 36

Arterial baroreceptor reflexes

Answer 36

decreased arterial pressure causes an increase in ADH

Question 37

Cardiopulmonary reflexes

Answer 37

Decreased blood volume causes an increase in ADH

Question 38

Other things that increase ADH secretion

Answer 38

- nausea - hypoxia - drugs (morphine, nicotine, cyclophosphophamide)

Question 39

Inhibitors of ADH

Answer 39

- alcohol - clonidine - haloperidol

Question 40

Mechanisms that increase sodium excretion

Answer 40

1) activation of low pressure receptor reflexes in the right atrium and pulmonary vessels 2) suppression of Angiotensin II 3) Stimulation of natiruretic system 4) Small increase in arterial pressure

Question 41

What happens to ECF and blood volume when there's a leakage of fluid into the interstitium?

Answer 41

INCREASE in ECF blood volume remains same or decreases - kidneys sense a decrease in blood volume - respond by retaining salt and fluid - retained fluid leaks into interstinum (increased edema)

Question 42

What happens to ECF and blood volume during congestive heart failure? (or anything that increases vascular capacity, i.e. pregnancy, vericose veins)

Answer 42

``` INCREASE ECF (200%) INCREASE blood volume (15-20%) ``` - heart reduces ability to pump = decreased output - kidneys retain salt and fluid to normalize pressure - work well; however, extra fluid

Question 43

What happens to ECF and blood volume during Nephrotic Symdrome?

Answer 43

INCREASE ECF blood volume remains the SAME - loss of large amounts of PROTEIN in urine - osmotic pressure in capillaries falls - fluid moves from capillaries to tissues - causes BP to fall - kidneys activate measures to retain water/sodium

Question 44

What happens to ECF and blood volume during Liver Cirrhosis?

Answer 44

INCREASE ECF blood volume remains the SAME - liver cannot synthesize enough plasma proteins - osmotic pressure in capillaries falls - fluid moves from capillaries to tissues - causes BP to fall - kindeys activate measures to retain water/sodium - liver develops fibrous tissue = impedes portal blood flow - raises capillary pressure in the portal vascular bed - leakage of fluid and proteins into the peritoneal cavity