Download Clinical biochemistry (1) water balance

CLINICAL BIOCHEMISTRY
Lecture No 1
Water balance, Osmolality,
Electrolytes,pH and Blood gases
Electrolytes
Internal environment
• In medical usage the
term electrolytes is
applied to any of the four
ions in plasma Na+ , K+ ,
Cl- and Hco3- that exert
the greatest influence
upon water balance and
acid-base relationship.
• This refer to the
concentration of ions
and other constituents
in the body fluids it also
include pH.
Homeostasis
Osmolality
 The maintenance of the  Is a measurement of
steady state in the body
the of dissolved
and a relatively constant
particles ( ions and
concentration of ions ,pH
undissolved molecules
and osmotic pressure in
such as glucose or
protein) per unit of
the various body fluid.
water.
Osmotic pressure
Active Transport
 When two compartments of
different osmolality are
separated by semipermeable
membrane that allows any
small molecules to pass
through it, the osmotic
pressure represent the
hydrostatic pressure that
would have to be applied to
the compartment of higher
osmolality to prevent water
passage into it from the
lower one.
 Active transport is the
transport of ions or
molecules a cross a cell
membrane against a
concentration gradient , it
involves energy-linked,
enzyme reaction, because
energy in form of ATP is
usually required.
Body water
Water is found both inside and outside cells and can be
divided into main two spaces or compartments :
intracellular (water within cells) and extracellular (water
outer of cells). The extracellular water can be interstitial
fluid between cells and plasma.
 The body water is about 60% of total body weight.
 In many illnesses the water
and electrolyte balance is
severely disturbed because of
heavy fluid and electrolyte
losses caused by :
- Vomiting
- Diarrhea
- excessive urination
- fistulas ( ‫) ناسور‬
Electrolytes distribution
 Na+ is the principal cation of extracellular fluid 92 %
 Cl- is the principal anion of extracellular fluid 67%
Sodium Na+
normal range (136-145meq/L) or 136-145mmol/L
Hypernatremia
1. Sever dehydration
2. Hyperadrenalism (Cushing's
syndrome)
3. Comatose diabetics
4. Hypothalamic injury
interfering with thirst
mechanism
5. Nasogastric feeding
6. Diabetes insipidus
(deficiency of antidiuretic
hormone)
Hyponatremia
1. Large loss of gastrointestinal
secretion (diarrhea, intestinal
fistulas)
2. Acidosis of diabetes mellitus
3. Addison's disease(depressed
secretion of aldosterone and
corticosteroids)
4. Renal disease malfunction
(salt-losing nephritis)
Potassium K+
normal range (3.8-5.4meq/L) or 3.8-5.4mmol/L
Hyperkalemia
Hypokalemia
Anoxia and acidosis
Decrease output of urine
Shock or circulatory failure
Decrease production of
aldosterone
5. Chronic renal insufficiency
1. Increase loss of potassium
(vomiting, diarrhea,
gastrointestinal fistulas)
2. Long-term therapy with diuretics
3. Certain carcinomas that secrete
ACTH (adrenocorticotropic
hormone) cause a lowering of
serum potassium
1.
2.
3.
4.
Chloride Clnormal range (98-108meq/L) or 98-108mmol/L
Increased concentration
Decreased concentration
1. Dehydration
2. Certain type of renal tubular
acidosis
3. Over breathing (respiratory
alkalosis) following
stimulation of the respiratory
center by some drugs,
hysteria, anxiety or fever
1. Metabolic acidosis
2. Uncontrolled diabetes
3. In renal disease (impaired
glomerular filtration
4. Prolonged vomiting
5. Salt-losing nephritis
6. Metabolic alkalosis (Hco3increases and Cl- decreases)
Chloride ClCerebrospinal fluid(CSF)
Normal range 120-132 meq/L
The concentration of
chloride decreases in cases
of bacterial meningitis
Urine chloride
The amount of urinary
chloride varies greatly with
the intake. An adult eating
an average diet may excrete
from 110-250 meq/L.
Blood buffer systems
When carbohydrates, fats and proteins are catabolized, the
hydrogen atoms of the carbon chains are converted to H+ .
The H+ is transported with an electron chain along a chain
of coenzymes in mitochondria (the respiratory chain)
Bicarbonate/Carbonic Acid buffer System
• The most important buffer system in plasma
because of the high concentration of HCO3- and the
readiness with which H2CO3 may be increase
through lung activity and decrease by blowing off
CO2 .Carbonic anhydrase (carbonic dehydratase)
• The increased HCO3- in blood cells is followed by
diffusion of HCO3- into plasma, accompanied by
passage of Cl- into the erythrocytes to maintain ionic
balance. Supplies about 95% of the buffering
capacity.
Hemoglobin buffer system
 Hemoglobin (Hb), the protein present in high
concentration in red blood cells, bind to oxygen in the
lungs and releases it in the tissues.
 The oxygenated form of Hb is much stronger acid than
the deoxygenated form. The reaction take place
 This buffer buffer system accounts for about 30% of the
buffering capacity of the whole blood.
Phosphate buffer system
 The phosphate buffer system is a minor component of
the total blood buffer system, but it does play an
important role in the elimination of H+ in urine.
 In the plasma at pH 7.4, 80% of the phosphate in form
of HPO4-- , but in an acid urine the bulk of it exist as
H2PO4- .
Compensation of acid-base disturbance
 Plasma protein can also accept H+ to a minor extent and
therefore serve as a buffer.
 Disturbance s in blood pH are usually compensated to
greater or lesser extent by appropriate responses of
respiratory and renal systems.
 The direction of the changes in values of the acid-base
parameter in various state of imbalance are summarized
above.
 Blood gases : pH, pCO2 and pO2
 the normal values of acid-base and blood gas shown above
(pO2 the partial pressure of oxygen)