Regulation of Body fluid volume

Body water content varies with

Age, sex & adipose tissue

Water content in infants

80% Total body weight

water content in males

60% TBW

water content in females

50% TBW

What does the low women water content reflect

Higher body fat & Smaller amount of skeletal muscle

Why do infants have 80% water TBW

Low body fat, low bone mass

Water content throughout life

Declines in old age to 45% TBW

Total body water in liters

40 L (60% TBW)

Water occupies 2 main fluid compartments:

-Intracellular fluid (ICF) - 2/3
-Extracellular fluid (ECF) - 1/3

volume of water in Intracellular fluids

40% TBW (25 liters)

volume of water in extracellular fluids

20% TBW

Intracellular fluid is contained in

cells

2 major subdivisions of extracellular fluids

Plasma & lymph (Fluid portion of blood)
Interstitial fluid (Fluid in spaces between cells)

Volume of interstitial fluid (part of extracellular fluid)

12L (80% of ECF)

Volume of Plasma (part of extracellular fluid)

3L (20% of ECF)

Total ECF volume in liters is

12L (interstitial) + 3L (plasma) \= 15

Other ECF (Transcellular fluid) is found in

CSF
Eye humors
Synovial fluid
Serous fluid
GI secretions

Water moves according to

osmotic gradients

Composition of body fluids

Solutes + solvent (water)

Solutes in body fluids are mainly

Electrolytes & Non-electrolytes

Electrolytes solutes in body fluids

Inorganic salts
Acids
Bases
Some proteins

Non-electrolyte solutes in body fluids

Glucose
Lipids
Creatinine
Urea

Osmotic power of electrolytes

Greater osmotic power than non electrolytes

Inorganic salts in intracellular fluids

Low sodium & Chloride
Potassium --\> Chief cation
Phosphate --\> Chief Anion

chief cation of intracellular fluid

Potassium (K+)

Chief anion of intracellular fluid

Phosphate

Inorganic salts in extracellular fluids

Similar to intracellular
+ High protein content of plasma

Chief cation of extracellular fluids

Sodium

Major anion in extracellular fluids

Chloride (Cl-)

What determines the chemical & physical reactions of fluids

Electrolytes

Sodium & potassium concentrations in extra & intra cellular fluids are

nearly opposite

how do potassium & sodium enter & leave cells

ATP-dependent sodium-potassium pumps

Water Balance Equation

Water input (entering body) \= Water output (leaving body)

Sources of water input

-Ingested foods & fluids
-Water produced from metabolic processes

water output is controlled by

variations in urine volume usually linked to sodium reabsorption

Water output is \= to

Water intake + metabolic water production

Sources of Water Loss in the Body

-Vaporization out of lungs
-Lost in perspiration
-Urine production
-Feces

Pathological loss of water in body

-Vascular bleeding (H2), Na+)
-Vomiting (H2O, H+)
-Diarrhea (H2O, HCO3-)

How does change in fluid volume affect blood pressure?

Sodium retention or water reabsorption \>
Increased blood volume \>
Increased venous return \>
Increased Stroke volume \>
Increased Cardiac output \>
Increased Blood pressure

Sensors for body water balance in body

-Osmoreceptors
-Thirst center
-Volume receptors
-High pressure baroreceptors

Osmoreceptors are located in

hypothalamus

Where is the thirst center located?

hypothalamus

Where are volume receptors

Atria

Where are high pressure baroreceptors located?

Carotid sinus and Aortic arch

What is the driving force for water intake

Thirst mechanism

What % increase in plasma osmolarity excites the hypothalamic thirst center

2-3 %

How are hypothalamic thirst center neurons stimulated?

-Osmoreceptors lose water by osmosis to hypertonic ECF
-Angiotension 2
-Baroreceptor inputs

what controls water output

Changing urine volumes

when is small, concentrated urine produced

Large amounts of water are lost

when is large, diluted urine produced

Water intake is excessive

What is the main factor that determines the distribution of total body water between ICF & ECF

ECF Na+

Changes in electrolyte balance

causes water to move from one compartment to another --\> which alters blood volume and blood pressure and can impair the activity of cells

Why is regulation of water balance & Na+ balance needed

Changes in electrolyte balance causes water to move from one compartment to another --\> which alters blood volume and blood pressure and can impair the activity of cells

How is sodium ion balance linked to ECF volume & Blood pressure regulation?

-Neural
-Hormonal

Neural regulation of sodium balance

Systemic baroreceptors

Hormonal regulation of sodium balance

Renin-angiotensin system
Aldosterone
Atrial natriuretic peptide
Glucocorticoids
Estrogen
Progesterone

Regulation of fluid volume is done by

Kidneys
ADH
Renin-angiotensin-aldosterone system
Aldosterone
ANP

Fluid balance is maintained by

-Thirst mechanism
-Antidiuretic hormone ADH
-Aldosterone

Thirst mechanism (Fluid balance maintain)

-Located in hypothalamus
-Osmoreceptors sense internal environment (fluid volume & concentration) & promote fluid intake

ADH (Fluid balance maintain)

-Controls amount of fluid leaving body in urine
-Promote reabsorption of water into blood from renal tubules

Aldosterone (Fluid balance maintain)

-Determines reabsorption of sodium ions & water from renal tubules --\> conserve fluid in body

What hormones controls amount of water lost in urine

ADH

Osmoreceptors-ADH feedback

Increased blood osmolarity --\> stimulate hypothalamic osmoreceptors --\> stimulate ADH --\> Thirst, Stimulate DCT & collecting duct --\> Increased water reabsorption --\> Reduced urine volume & Increased Na+:H2O in urine

Where is Atrial natriuretic peptide (ANP) made & released

Atrium of heart (as response to stretch \= elevated blood volume)

How does ANP reduce blood pressure & blood volume

By inhibiting:
-Events that promote vasoconstriction
-Na+ & water retention

Who is ANP levels elevated in

patients with congestive heart failure who have increased blood volume in atria

Hypercolemia (excess fluid volume) INHIBITS

ADH
Aldosterone
Thirst
\==\>
Increased urination & dilute urine

Hypocolemia (deficient fluid volume) STIMULATES

Thirst
ADH
Aldosterone
\==\>
Decreased urination & concentration urine

Water balance disorders include

Dehydration
Overhydration
Edema

Dehydration is

Water loss exceeds water intake
Body is in negative fluid balance

Causes of dehydration

Vomiting and diarrhea
Excessive sweating with loss of sodium and water
Diabetic ketoacidosis
Loss of fluid, electrolytes, and glucose in the urine
Insufficient water intake in older adults or unconscious persons
Use of concentrated formula in infants
Hemorrhage
Sweating

Signs & symptoms of dehydration

Extreme thirst
Dry mouth
Swollen tongue
Less urination
Headache
Fatigue
Bad breath
Dizziness
Palpitation

Consequences of dehydration

Hypovolemic shock & loss of electrolytes

Other names for overhydration

Water intoxication
Hyper-hydration
Water poisoning

Causes of overhydration

Drink too much
Decreased body ability to excrete water

Overhydration is difficult to happen ...

normally

who is overhydration common with

people whose kidneys do not excrete urine normally
Eg. People with disorder of the heart, kidneys or liver

What is edema

Abnormal accumulation of fluid in the interstitial space, leading to tissue swelling

What is edema caused by?

Anything that increases flow of fluids out of bloodstream or hinders their return

Factors that accelerate flow of fluid out of bloodstream

-Increased blood pressure
-Increased capillary permeability
-Incompetent venous valves
-Localized blood vessel blockage
-Congestive heart failure
-Hypertension
-High blood volume

What does hindered fluid return usually reflect?

Imbalance in colloid osmotic pressures

What is low levels of plasma proteins called

Hypoproteinemia

Consequences of hypoproteinemia

Forces fluids out of capillary beds at arterial ends --\> Fluids fail to return at venous end

What does hypoproteinemia result from

Protein malnutrition
Liver disease
Glomerulonephritis

What do blocked (or surgically removed) lymph vessels cause

Leaked proteins to accumulate in interstitial fluid --\> Exert increasing colloid osmotic pressure --\> Draws fluid from blood

Increased capillary permeability could be due to

Inflammation
Bacterial infection
Burns