Chapter 21 :Water, Electrolyte and Acid-base Balance

Balance -

Osmosis

. Most of the solutes in body fluids are

 "where sodium goes,   ...... 

About 40 liters of water in the body (10.56 gallons)

Body range

Babies -

Men -

Women -

Compartments : (separated by selectively permeable membranes)

Intracellular -

Extracellular -

Interstitial fluid -

Blood plasma -

Extracellular fluids contain more

Blood plasma - more

Intracellular fluid higher conc.

Two major factors that regulate the movement of water between compartments:

Hydrostatic pressure

Osmotic pressure -

Water intake = Water loss:

Average adult takes in about 2,500 ml/day

Sources of water:

Regulation of water intake:

The main regulator of intake is

.Dehydration (as little as 1%) stimulates thirst in 3 ways:

1)

2)

3)

All three stimulate the thirst center in the hypothalamus, which produces the sensation of thirst. (or mistakenly - hunger)

Sources of water loss:

Regulation of fluid loss:

Sweat

ADH -

aldosterone -

ANP -

The amount that moves back into the capillaries depends largely on the concentration of the plasma proteins.

Fluid imbalances:

Dehydration

Since sodium as well as water is lost, rapidly drinking large quanities of water causes

Overhydration can occur if

Edema is

 It can be caused by many imbalances.

ELECTROLYTE BALANCE

An electrolyte is

 Cations are

 anions are

Besides the inorganic electrolytes, body fluids also contain some charged organic molecules. Organic acids, such as lactate, and some amino acids within proteins are anions.

Only a small percentage of the molecules of the fluids in the body are nonelectrolytes, such as glucose and urea.

Functions of electrolytes:

1.

2.

3.

4.

Sodium

Sodium accounts for

Aldosterone

ANP can cause

Potassium

Potassium ions are the most numerous cations in the

Calcium

Calcium levels are controlled by several hormones.

 PTH causes

 Calcitonin from the thyroid gland

Chloride

Chloride ions are the most common

Aldosterone

Bicarbonate

Next to proteins, bicarbonate is the most abundant anion in the

 It is part of the body’s chief buffer, and acts to transport CO₂ in the blood stream.

CO₂ + H₂O ^↔ H₂CO₃ ↔ H⁺ + HCO₃^-

The kidneys are the main regulators of bicarbonate.

Phosphate

PTH causes

 Calcitonin

ACID-BASE BALANCE:

Acid-base balance is particularly important because

Some H⁺ comes into our bodies

Strengths of acids and bases:
Acids and bases that ionize completely are strong acids; those that ionize less completely are weak acids and bases.

    Remember that blood pH needs to stay between

 Since more acids are formed, pH balance is mainly a matter of

    There are three basic mechanisms that the body uses to maintain acid-base balance:

1. Buffer systems
2. Exhalation of carbon dioxide
3. Kidney excretion.

    Buffers are

Bicarbonate buffer system:
   One of the main blood buffer pairs is sodium bicarbonate (NaHCO³) and carbonic acid (H₂CO₃). The addition of a strong acid such as HCl to this buffer system does the following:

HCl + NaHCO₃    H₂CO₃ + NaCl

The carbonic acid does not dissociate completely, and the H⁺ concentration increases to a much smaller degree than if HCl were added without the buffer.

The addition of a strong base :

NaOH + H₂CO₃ NaHCO₃ + H₂O

    Water dissociates very little, and the pH remains nearly the same.
  

1. the carbonic acid in the blood increases
2. the amount of bicarbonate ion in the blood decreases -Blood normally contains 20 X more bicarbonate ion than carbonic acid; if this ratio decreases, the pH drops.
3. The H⁺ concentration increases slightly, but the increase is minimized by the buffer.
4. the pH drops slightly.

H₂CO₃ is the most abundant acid in the body because it is constantly being formed by the buffering of fixed acids ( acids that cannot be expelled by respiration) and by:

CO₂ + H₂O    H₂CO₃   H⁺ + HCO₃^-

The next buffer system is the phosphate buffer system.

H⁺      +     HPO₄^2-                    H₂PO₄^-
    _{monohydrogen phosphate               dihydrogen phosphate}

OH ^- + H₂PO₄^- H₂O + H2PO₄^2-

    The protein buffer system is the most abundant in

Respiratory mechanisms - exhalation of CO₂
An increase in the carbon dioxide level in body fluids increases

 volatile acid.

Also, exhaling too much CO₂ can

The respiratory system is a powerful eliminator of acid, but the

Kidney excretion of H⁺
   

   Buffer systems are the body’ first line of defense

    The respiratory and renal mechanisms are considered to be the body’s secondary defenses because

ACID-BASE IMBALANCES
    Remember that the normal pH range is 7.35 (venous blood) to 7.45 (arterial blood). A pH below this range is considered to be acidosis ( even though the blood is not acidic) and a pH above this range is considered to be alkalosis.
   The body response to acid-base imbalances is called compensation.

The principal effect of acidosis is

Alkalosis causes

Respiratory Acidosis is a carbonic acid excess,

Respiratory Alkalosis is a carbonic acid deficit,

Metabolic Acidosis is a bicarbonate deficit,

Metabolic Alkalosis is a bicarbonate excess