Body Fluid Compartments

Question 1

What is the distribution of water in the body compartments?

Answer 1

total body water (TBW) is 3/5 of body weight; ICFV is 2/3 of TBW and ECFV is 1/3 TBW; Interstitial fluid is 3/4 ECFV and Plasma or Intravascular fluid is 1/4 ECFV

Question 2

What body compartment does blood fall into? How can the proportions be calculated?

Answer 2

ECFV in plasma and ICFV inside the cells in the blood; ICFV proportion of the blood is provided by the hematocrit, HCT= cell volume/blood volume

Question 3

How are body fluid compartment sizes measured?

Answer 3

Volume= amount/concentration; use the indicator dilution principle, V1C1=V2C2 at equilibrium

Question 4

What indicators or markers are used to measure the different compartments?

Answer 4

TBW- D2O, ECFV= Inulin, Sodium, Sucrose, Mannitol, Plasma Volume= Evan’s Blue and Albumin, RBC Volume= chromium or RBCV=BV-PV

Question 5

Which body fluid compartments cant be measured? How are they calculated?

Answer 5

ICFV= TBW vol. - ECFV; ISFV= ECFV - PV

Question 6

What are complications in measuring body fluid compartments?

Answer 6

marker used, lean body mass, age increase in babies decrease in elderly, sex- varies with women during menstruation, nutritional status= low albumin, diseases= affect permeability

Question 7

What are the electrolyte levels in the plasma? Bicarbonate? Protein?

Answer 7

Na= 136-145 mEq/L, K= 3.5-5.0 mEq/L, Cl= 100-106 mEq/L, HCO3= 24-28 mEq/L, Protein= 16 mEq/L

Question 8

What is the potassium level in Intracellular fluid?

Answer 8

140 mEq/L

Question 9

What is the biggest difference between interstitial fluid and plasma?

Answer 9

albumin is in the plasma

Question 10

What are the general observations with solute distribution within the body fluid compartments?

Answer 10

main solutes in each compartments are electrolytes, in each compartment total positive=total negative, total # equivalents varies from compartment to compartment, plasma contains more protein than interstitial fluid and also contains more cations to maintain electroneutrality

Question 11

What things affect osmosis?

Answer 11

permeability of the membrane to solute in intracellular and interstitial fluid, concentration gradients of solutes in intracellular and interstitial fluids, and the pressure gradient across the cell membrane

Question 12

What is normal osmolality? Isotonic? Hypotonic? Hypertonic?

Answer 12

300mOsm; Isotonic is osmolality = blood plasma, Hypotonic is osmolality< plasma, Hypertonic is osmolality > plasma

Question 13

What happens to the fluid compartments have added salt? Salt loss?

Answer 13

ECF increases and draw H2O from ICF, Osm of both increase; decrease in ECF volume and increase in ICF volume, Osm of both decrease

Question 14

What is the equation for net fluid movement?

Answer 14

starling forces - starling landis equation: Net fluid movement= Kf { (Pc-Pt) - (Pi c - Pi t)} ; Kf= filtration coefficient, Pc= Hydrostatic pressure in capillary, Pt= hydrostatic pressure of fluid in interstitial space, Pi c= oncotic pressure of plasma proteins (colloid osmotic pressure), Pi t= oncotic pressure of proteins in the interstitial fluid

Question 15

How does the body primarily control ECF volume?

Answer 15

sodium regulation; increased intake causes increased ECF which leads to an increase in Excretion of Na in the kidney which decreases ECF (negative feedback)

Question 16

What systems are involved in ECF volume regulation?

Answer 16

GFR, renin angiotensin/ aldosterone system, ADH, ANP, Natriuretic hormone, Proximal Tubule reabsorption, Redistribution of GFR and RBF, Renal Nerves Intrarenal physical factors, and other known humoral agents

Question 17

What factors affect GFR and therefore sodium excretion and therefore ECF volume?

Answer 17

GFR= Puf x Kf; Puf= (Pgc - Pt) - (PiGC - Pit))

Question 18

What is glomerulotubular balance?

Answer 18

when there is an increase in GFR there is a responsive increase in tubular reabsorption of filtrate due to higher than normal colloid pressure in peritubular cap which promotes more fluid reabsorption, body is trying to minimize hemodynamic changes

Question 19

What role does the renin angiotensin aldosterone system play in regulation of ECF?

Answer 19

Angiotensin II causes increase in release of aldosterone from adrenal glands, also potent direct stimulator of PT NaCl and H2O reabsorption, stimulates thirst, NaCl appetite and Vasopressin through CNS; all lead to retention of H2O and NaCl

Question 20

Where is aldosterone synthesized and what is its mechanism of action?

Answer 20

zona glomerulosa of adrenal cortex, increase sodium reabsorption in CD (principle cells and ENaC) also increases potassium secretion, metabolized in the liver

Question 21

What affect does ADH or vasopressin have on ECF?

Answer 21

ADH secretion will change based on ECF osmotic pressure and volume, ADH promotes reabsorption of water in CD which would increase ECF volume

Question 22

How does ANF or ANP affect ECF volume?

Answer 22

are granules released with increased atrial stretch, which can be expected to be accompanied with ECF expansion causes sodium excretion rapidly but does not last long, inhibits ENaC in CD

Question 23

What other Natriuretic factors are there and how do they function?

Answer 23

BNP- hypothalamic factor blocks Na-K-ATPase; Renal Medullary Factor, EDLS (from Adrenal or Kidney), Urodilatin (ANP like), C-type NP; all work to decrease sodium reabsorption

Question 24

What factors work on the proximal tubule to effect reabsorption thereby effecting ECF volume?

Answer 24

starling forces of peritubular capillaries- hydrostatic pressure in peri. cap., oncotic pressure of plasma in peri. cap., RIHP, oncotic pressure of fluid in interstitial compartment

Question 25

How is GFR and RBF redistributed to effect ECF volume and in what situations?

Answer 25

blood flow shifts from outer cortex to inner cortex during hemorrhage or decreased cardiac output (heart failure), decrease in sodium excretion occurs; it is believed the inner cortical nephrons are salt retaining whereas the outer are salt losing

Question 26

What effect do the renal nerves have the kidney and what areas?

Answer 26

vasoconstriction- mostly afferent arteriole via alpha adrenergic receptors, renin release via beta adrenergic receptors, tubular action (PT and TAL) direct reabsorption of NaCl

Question 27

What paracrine hormones affect volume homeostasis? How?

Answer 27

Prostaglandins, dopamine, and kinins all decrease reabsorption

Question 28

What humoral agents affect ECF volume? How?

Answer 28

estrogen and insulin increase reabsorption, parathyroid hormone decreases reabsorption

Question 29

What happens in heart failure to the ECF volume?

Answer 29

increase in SNS to increase contractility to increase CO and increase retention of fluid via increase Ang II and ADH to increase CO; this is the compensated stage

Question 30

What happens in congestive heart failure to the ECF volume?

Answer 30

decreased CO need to increase NaCl and water; because decreased CO there is decreased BP; more retention; now fluid retention is a problem, need to treat with a diuretic

Question 31

What disease states are salt retaining states?

Answer 31

cirrhosis- cant breakdown aldosterone, NaCl retaining remains active; Nephrosis- can’t excrete Na+

Question 32

What is dilute urine?

Answer 32

less than 300mOsm

Question 33

What is concentrated urine?

Answer 33

above 300 mOsm, can be 500-1200, normally 600-800

Question 34

Where is ADH synthesized? Where is ADH stored?

Answer 34

nerve cell bodies of the supraoptic nuclei and paraventricular nuclei in the hypothalamus, migrate down the axons to be stored in the axon terminals in the posterior pituitary

Question 35

What signals the release of ADH? How?

Answer 35

signals from volume receptors in capacitance vessels and right atria, increased ECFV osmolality (Cells near SON and PVN) when they shrink due to changes in osmolality they send signal to the SON and PVN to release more ADH (osmoreceptors), and in response to Ang. II; effects rate of firing in SON and PVN which increases/decreases accordingly the release of ADH

Question 36

Of the stimuli which is ADH most sensitive to Osmolality or Volume?

Answer 36

osmolality only need 1-2% change, volume needs 15-20% change

Question 37

What is free water clearance?

Answer 37

calculated as difference between urine flow and osmolar clearance CH2O = V- Cosm

Question 38

What is osmolar clearance>

Answer 38

ml/min of plasma completely cleared of osmotically active solute; Cosm = Uosm x V/ Posm

Question 39

What is osmotic diuresis? Provide examples.

Answer 39

filtered solutes that become trapped or cant be reabsorbed, this causes water to remain in tubule producing diuresis, characterized by large amounts of urine high in solutes; glucose and mannitol, eventually increase ADH response

Question 40

Alterations in sodium balance are manifested as changes in what?

Answer 40

ECF volume; volume depletion or volume expansion

Question 41

Alterations in water balance manifest as changes in what?

Answer 41

Plasma osmolarity and are measured as changes in Pna; Hypernatremia- deficit of H2O relative to salt or Hyponatremia- excess of H2O relative to salt

Question 42

What are classic cuases of Hyponatremia and hypernatremia?

Answer 42

SIADH (excessive ADH secretion, retain water in excess, Hyponatremia) and Diabetes Insipidus (neurogenic- failure in prod. or secretion or nephrogenic- unresponsive, large volume of dilute urine, hypernatremia)

Question 43

What factors can be altered to cause DI?

Answer 43

may or may not be producing or releasing ADH, countercurrent system may not be establishing molar gradient in inner medulla, collecting ducts and distal tubules unable to respond to ADH, lack of establishing osmolar gradient- low urea from low protein diet, tubular problem, or increased flow through vasa recta diluting the gradient