LO 19 Flashcards
Describe average body water
- References to “average” body water volume based on a healthy, nonobese, 70-kg male
- Water is 60% of body weight in males; 50% in females
- Volume averages 40 L in a 70-kg male (154 pounds)
Why does total body water vary?
- Total body weight of individual- Large variation
- Fat content of body - The more fat the less water (adipose tissue is low in water content)
- Gender - Female body has about 10% less water than male body; Related to reproduction
- Age - In a newborn infant, water may account for 80% of total body weight; In older adults, water per pound of weight decreases (muscle tissue —high in water—replaced by fat, which is lower in water)
- The percentage of body water decreases rapidly during the first 10 years of life.
List the fluid from least to most in the body: plasma, interstitial, intracellular
- Plasma (approx 3L)
- Interstitial (approx 12L)
- Intracellular (25L)
What percent of total water content are extracellular fluid and intracellular fluid
- Extracellular - 34%
- Intracellular - 66%
Describe extracellular fluid (ECF)
- Outside of cells
- Called internal environment of body
- Surrounds cells and transports substances to and from
- 3 types - Plasma (Liquid part of whole blood); Interstitial fluid (Surrounds the cells); Transcellular fluid (Lymph, joint fluids, cerebrospinal fluids, eye humors)
Describe intracellular fluid (ICF)
- Inside cells
- Largest fluid compartment
- The cytosol within cells
- Gives structure and support to cell organelles
- Serves as solvent to facilitate intracellular chemical reactions for chemical metabolism
Describe the mechanisms that maintain fluid balance
- Sources of fluid intake - Liquids we drink, water in food, and metabolic water (produced by cells as byproduct)
- Sources of fluid output - Water vapor in breath, sweating, urine, and water in feces, tear loss
- Three main factors affect plasma, IF, and ICF volumes: Regulating fluid output; Regulating fluid intake; Exchanging fluid among compartments and around the body
What happens if the water content of the body changes?
- Cellular activities are jeopardized
- We must maintain a normal volume and composition in the extracellular fluid (ECF) and the intracellular fluid (ICF) via homeostasis
What are the sources of fluid intake?
- Liquids we drink (60%)
- Water in foods we eat (30%)
- Water from breakdown of foods (10%)
- Average adult needs about 2,500 ml (10 cups) of fluid per day!
How does the body regulate fluid intake?
When fluid is lost salivary secretion is decreased, dry mouth feeling, motivated to drink water, fluid balance restored
How does the body regulate fluid output?
- Fluid output, mainly urine volume, adjusts to fluid intake
- 3 main factors for controlling volumes of plasma, IF and ICF:
1. Concentration of electrolytes in ECF (Important concept: Water ‘follows’ sodium)
2. Capillary blood pressure
3. Concentration of proteins in blood
Describe electrolytes
- Compounds that dissociate in a water solution into separate particles called ions e.g. ordinary table salt (NaCl 🡪 Na+ and Cl-)
- Can conduct electrical current
- Fluid balance is largely regulated by electrolytes
Describe ions
The dissociated particles of an electrolyte that carry an electrical charge (positive or negative)
List the important positively charged ions (cations)
- Sodium (Na+)
- Potassium (K+)
- Calcium (Ca++)
- Magnesium (Mg++)
List the important negatively charged ions (anions)
- Chloride (Cl–)
- Bicarbonate (HCO3–)
- Phosphate (HPO4-)
- many proteins
Each body fluid compartment has different levels of the various important ions, which helps ____________
Control water & electrolyte balance between them
Describe the balance of ions in extracellular fluid
ECF (plasma + IF): Sodium (Na+) & Chloride (Cl–)
Describe the balance of ions in intracellular fluid
ICF: Potassium (K+), Phosphate (HPO4- -) and negatively charged proteins
What are the functions of the important elements and ions in the body?
- Iron 🡪 hemoglobin
- Iodine 🡪 thyroid hormones
- Potassium (K+) 🡪 nerve conduction
- Bicarbonate (HCO3-) 🡪 acid-base balance
- Calcium (Ca++) 🡪 bone formation, blood clotting, muscle contraction
- Chloride (Cl-) 🡪 HCl production
How does sodium impact fluid volume?
- Electrolytes influence the movement of water among the 3 fluid compartments of the body.
- ECF electrolyte concentration affects fluid volumes.
- “Where sodium goes, water soon follows”
What body secretions contain Na+?
- Saliva
- Gastric secretions
- Bile
- Pancreatic juices
- Intestinal secretions
___________ is the most abundant & important cation of plasma and is the chief method of fluid regulation in the kidneys
Sodium (Na+)
How do aldosterone and sodium interact?
Aldosterone (from adrenal cortex) increases Na+ reabsorption in kidney tubules, this increases water reabsorption and in turn increases ECF
Why are saline IVs given in cases of severe blood loss
- increases the amount of Na+ in blood
- fluid/water will move from IF to plasma
- blood volume increases
- blood pressure stabilizes
_________ is when the amount of Na+ in IF increases above normal
Edema
_________ are depressions in swollen subcutaneous tissue that do not rapidly refill
Pitting edema
Describe Antidiuretic Hormone (ADH)
- Released from posterior pituitary gland to increase kidney tubule reabsorption of sodium and water from tubular urine back into blood
- This function increases ECF (and total body fluid) by decreasing urine volume (Figure 19-5)
Describe the regulation of fluid intake
- ECF electrolyte concentration influences ECF volume
- Increase in ECF directly increases ECF volume, this Increases the movement of water out of ICF and by increasing ADH secretion, which decreases urine volume
Describe the exchange of fluid by blood
- Capillary blood pressure pushes water out of blood, into interstitial fluid
- Oppositely blood plasma protein (BPP) concentration pulls water into blood from interstitial fluid
- Hence, these two forces regulate plasma and interstitial fluid volume under usual conditions
Describe Blood Plasma Proteins (BPP)
- Act as a ‘water-holding’ or ‘water-pulling’ force - Hold water in blood and Pull water into blood from IF
- Decrease in concentration of BPP results in less water ‘pulled’ into blood from IF
- IF volume varies more than plasma volume
- The two forces of capillary blood pressure and the concentration of blood plasma proteins regulate plasma and IF volume under ‘normal’ conditions
Describe dehydration
- Total volume of body fluids less than normal
- Interstitial fluid volume shrinks first, and then if treatment is not given, ICF volume and plasma volume decrease
- Dehydration occurs when fluid output exceeds intake for an extended period
- Loss of skin elasticity (turgor) is a clinical sign of dehydration
Describe overhydration
- Total volume of body fluids greater than normal
- Overhydration occurs when fluid intake exceeds output
- Various factors may cause this (e.g., giving excessive amounts of intravenous fluids or giving them too rapidly may increase intake above output)
- Water intoxication may result from rapidly drinking large volumes of water or giving hypotonic solutions to persons unable to dilute and excrete urine normally
- The danger of overhydration is that it puts a heavy burden on the heart.
