Fluids, Electrolytes, and Acid-Base Imbalance PDF

Fluids, Electrolytes, and Acid-Base Imbalance  An Introduction Water is the principal and essential constituent of the body. The total body water (TBW) under normal conditions: In young men, it is about 60% of body weight and decreases to 50% in old age. In young women, it is...

Fluids, Electrolytes, and Acid-Base Imbalance  An Introduction Water is the principal and essential constituent of the body. The total body water (TBW) under normal conditions: In young men, it is about 60% of body weight and decreases to 50% in old age. In young women, it is approximately 50% and decreases to 40% in elderly women. In obese people: obesity produces further decreases in body water, sometimes reducing these levels to values as low as 30% to 40% of body weight in adults, because adipose cell contains about10% of water while the skeletal muscle cell contains about 75%. In full-term infants, body water is about 75% to 80% of body weight and is even greater in premature infants. So, TBW varies with sex, age and weight.  The electrolytes Definition of Electrolytes are substances that dissociate in solution to form charged particles, or ions. E.g. a sodium chloride (NaCl) molecule dissociates to form a positively charged Na+ ion and a negatively charged Cl− ion. Particles that do not dissociate into ions such as glucose and urea are called nonelectrolytes. The positively charged ions are called cations because they were attracted to the cathode of the cell. The negatively charged ions are called anions because they were attracted to the anode of the cell. Electrolytes found in your body include: Sodium,  Body fluids and electrolytes functions Body fluids and electrolytes play a role in:- 1. Transport gases, nutrients, and wastes. 2. Help to generate the electrical activity needed to power body functions. 3. Regulating your body’s temperature and pH levels. 4. Regulating the osmotic pressure in cells. 5. Maintaining the function of muscle (Contraction of muscles) and nerve cells (Sending nerve impulses)  Compartmental Distribution of Body Fluids Fluids and electrolytes are present:- 1. The intracellular fluid (ICF) compartment (In body cells) : It is the largest compartment, containing approximately two-thirds of the body water in healthy adults and approximately 40% of total body weight. 2. The extracellular fluid (ECF) compartment (all the fluids outside the cells): It is one-third of body water, approximately 20% of total body weight. ECF includes: A) The interstitial compartment (in the tissue spaces between the cells): it is approximately 15% of ECF. B) The vascular compartment (plasma in blood vessels) it is approximately 4% of ECF. Compartmental Distribution of Body Fluids  Compartmental Distribution of Body Fluids Thus, the body of a normal male weighing 70 kg contains approximately 42 litres of water. [ 70*(60/100)= 42 L]  Distribution of the cations &anions The concentration of cations and anions is different in ICF & ECF. In ICF, the main cations are (K+) and (Mg++) and the main anions is (PO4- ). ICF has low concentration of (Na+) and (Cl-) and (HCO3-). In ECF (The interstitial compartment and vascular compartment), the main cations are sodium (Na+) and calcium (Ca+) and the main anions are (Cl-) and (HCO3-). ECF has low concentration of K+.  Why the plasma and interstitial fluids have very similar composition of electrolytes? ◻ Plasma and interstitial fluids have very similar composition with Na+ as the main cation and Cl- and HCO3- as the main anions. ◻ The blood plasma and interstitial fluid, are separated from each other by capillary wall which is freely permeable to water but does not allow free passage of macromolecules of plasma proteins resulting in higher protein content in the plasma. Concentrations of Extracellular and Intracellular Electrolytes in Adults  Gains and Losses of water ◻ The main source of water gain is through oral intake and metabolism of nutrients. ◻ The largest loss of water occurs through the kidneys, with lesser amounts being lost through the skin, lungs, and gastrointestinal tract.  Mechanisms of Regulation of body water There are two main physiologic mechanisms that assist in regulating body water:- 1. Thirst is primarily a regulator of water intake. 2. Antidiuretic Hormone (ADH) is a regulator of water output. Both mechanisms respond to changes in extracellular osmolality and volume.  Antidiuretic Hormone (ADH) ADH (vasopressin) is formed primarily in the supraoptic nucleus and to a lesser extent in the paraventricular nucleus of the hypothalamus. It is then transported down and stored in secretory granules in the posterior pituitary, where it can be released into the blood. The function of ADH is to cause the body to retain water and constrict blood vessels. ADH levels are controlled by extracellular volume and osmolality. Osmoreceptors are sensory neurons located in the hypothalamus sense changes in extracellular osmolality and stimulate the production and release of ADH. Stretch receptors (baroreceptors) are sensory nerve endings located in the walls of blood vessels that are stimulated by changes in arterial pressure and aid in the regulation of ADH release. ADH initiates its physiological actions by combining with a specific receptor (vasopressin receptors: V1 & V2)