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6. List the factors that determine body water content and describe the effect of each factor.

Age - starts at 73% in infancy - declines to about 45% in elderly,

Body mass - skeletal muscle is 75% h2o so more muscle = more water,

Body fat - Adipose is least hydrated tissue 10%.


7. Indicate the relative fluid volume of the fluid compartments of the body.

ICF - 40% of weight/25L,

ECF 20% of weight/15L (IF = 80%, Plasma = 20%)

Also, major anion in ICF is phosphate, chloride in ECF.


Water is ? % of body weight?



7. Indicate the relative solute composition of the fluid compartments of the body.

Na+ - 90% ECF (split between IF/plasma),

K+ - 98% ICF,

Ca2+ - 99% bone


8. Contrast the overall osmotic effects of electrolytes and nonelectrolytes.

Electrolytes - dissociate in water to ions, can carry a charge. Inorganic salts, acids, bases, some proteins.

Non-electrolytes - Do not dissociate in water, do not carry a charge. Most organic molecules, (glucose, urea.)

Electrolytes have much greater osmotic power than nonelectrolytes because each electrolyte dissociates into 2 or more ions.

Because water moves from an area of lesser osmolity to greater, electrolytes have the greatest ability to shift water.


Electrolyte concentrations are expressed in?



9. Describe factors that determine fluid shifts in the body.

Anything that changes solute concentration in any compartment leads to net water flows.

Substances must pass through both the plasma and IF to reach ICF (exchanges occur continuously.)

Protein free plasma is forces out of the blood by hydrostatic pressure and almost completely reabsorbed due to colloid osmotic pressure of plasma proteins.

Movement of water between IF and ICF involses osmotic flow that is equal in both directions.

Ion fluxes between IF and ICF are restricted, but movement of gases, nutrients and wastes typically occur in one direction.


How does water enter the body?

Ingested foods 30% and liquid 60%, cellular metabolism 10% ("metabolic water".)


How does water leave the body?

Sensible: Feces 4%, Sweat 8%, Urine 60%

Insensible: losses via skin and lungs 28%


How much water to remain properly hydrated?

2500ml in, 2500 out. Input must equal output.


Obligatory water loss

Occurs regardless of the state of hydration because of insensible water loss and 500ml of urine needed to get rid of nitrogenous waste.


Faculative water loss

Controlled water loss that is dependent on state of hydration and is hormonally regulated in DCT/CD


Which five hormones that are involved in regulating fluid output.

ADH - secretion is promoted/inhibited by hypothalamus in response to changes in the solute concentration of ECF/large BV or BP changes/vascular baroreceptors.

Angio II - stimulates hypothalamus and post pit/ADH.

Aldosterone - save salt and water will follow.

ANP/BNP - increases urine output to ↓ BV and BP

(ADH is most important of these)


Fluid imbalance with constant osmolarity:

Hemorrhage, sever burns, chronic vomit, decreased fluid loss thru kidneys.


Fluid imbalance with changes in osmolarity:

(fluid loss/gain that is not isotonic/isosmotic) Dehydration - due to profuse sweating, ect, water output exceeds input.

Water intoxication/hypotonic hydration - result of renal insufficiency or excessive H2O quickly. Leads to cerebral edema/lysis of neurons.

Edema - accumulation of fluid in IF from ↑ HP/permeability.
Hypoproteinemia - Tissue edema because of protein deficient plasma.


**C+C Na+ K+ Ca2+

Loc ECF 90% ICF 98% Bone 99%

RMP/AP(depolarization) Na+/K+ ATPase Osmolarity
RMP/AP(repolarization) Na+/K+ ATPase Osmolarity in ICF
Musc cont/blood clot/2nd messenger/enzyme co-factor/nerve conduct

Regulation RAAS/ANP Aldosterone Parathyroid/calcitriol/Calcitonin

Imbalance 135-145 3.5-5.5 mEq/L 9-11 mg/100ml


Summary of the regulation of ECF volume and ECF osmolarity

Why important
Long term reg of BP
Prevent fluid shifts in ECF/ICF

If not reg

↑BV = ↑BP/↓BV = ↓ BP

↑osmolarity = fluid from ICF to ECF (crenation) ↓ osmolarity = fluid shift from ECF to ICF (cell lysis)

Mech of Regulation



Ionic compounds containing cations other than H+ and anions other than hydroxal/OH-. Ie. NaCl


Electrolyte balance usually refers to?

Salt balance in the body.

Salts are important in controlling fluid movements and provide minerals for excitability, secretory activity and membrane permeability.

Most important: Na+, K+, Ca2+


Why is sodium critical to salt balance?

Due to its abundance - 90% of ECF, 280 of ECF solute concentration (total 300).

Most important cation in regulation of fluid/electrolyte balance.


Mechanisms involved in regulating sodium balance, blood volume, and blood pressure?

Aldosterone via raas.

Targets prinicpal cells, last 1/3 of DCT and portion of CD.

Affects BV and BP because salt follows water.

Raas is triggered by symp stimulation, ↓ filtrate osmolality, ↓ BP.

If Na+ absorption ↑, K+ secretion ↑.



Hypo - more difficult for hyperpolarized neurons/muscles to fire APs. Danger: Cardiac/respiratory arrest.

Hyper - more dangerous because depolarization of excitable tissue makes the more excitable initially. Cells are unable to repolarize and become less excitable. Danger: Cardiac/respiratory arrest.


Structure/function - Urinary

1. Aff/Eff diameter
Smaller eff helps maintain pressure in glomerulus

2. PCT - microvilli on apical surface
↑ surface area, ↑ reabsorption

3. DCT/CD has principal cells
Allow for modifications of aquaporins/Na+-K+ pumps via aldosterone and ADH

4. Double capillary beds
Allows a second chance for exchanges

5. JG app - Afferent arteriole and DCT are modified at point of contact with macula densa and granular cells.
Allows for communication about what is happening at the end of the system (macula densa/DCT) to the beginning of the system (granular cells/aff art) and changes can be made.


Structure/function - Respiratory

1. Nasal conchae shape
↑ surface area and air turbulence - more particulates are trapped in mucus

2. Stroma of the lung is mostly elastic CT
Allows for recoil in expiration

3. innervation/smooth musc of bronchioles
Allows for bronchioconstriction

4. Ciliated epithelium in larynx/trachea
Propels mucus and trapped particle upward

5. Type II cells
Keep alveoli open