Water Flashcards
What portion of adult body water weight is found intracellularly?
2/3
-
Water is an excellent solvent for what?
ionic compounds and solutes such as glucose and AA’s
Children have more water than adults in which compartment?
extracellular
Water weakens what forces?
electrostatic forces and hydrogen bonding between other polar molecules
Water is involved in what type of reactions?
hydrolytic (peptide hydrolysis)
Water is produced in the body by what?
oxidative metabolism of hydrogen-containing substrates
- 300 ml/day
In what 3 ways does water act as a carrier?
- transports nutrients and removes wastes
- allows exchanged between cells, interstitial fluid, and capillaries
- maintains vascular volume and blood circulation
How does water act in thermogenesis?
- waters large heat capacity helps limit body temp fluctuations
- water has large capacity for heat vaporization
- sweating and evaporation allows heat loss
How does water act as a lubricator?
forms lubricating fluid for joints, saliva, gastric, intestinal, genito-urinary, and airway mucus.
How does water act as a shock absorber?
Maintains cellular shape and allows imbibition
What important function does water have for the brain and fetus?
Forms CSF for brain and spinal cord protection and suspends fetus
What is activated with increase in internal body temp?
Activation of sweat glands
How many KJ of heat is lost by evaporation of 1 gram of water?
2.2 KJ
What is sweat compared to plasma or extracellular fluid?
Hypotonic
Intense sweating leads to greater water than electrolyte losses and results in what type of dehydration?
Hypertonic (fluid replacement is more important that salt!!)
The osmotic pressure of extracellular fluid increases when?
When water losses exceed water intake
Is ADH release or the hypothalamic thirst reflex triggered first?
ADH release (1% osmolarity increase)
What is the most important stimulus controlling thirst?
Osmoreceptor input
What is the cornerstone of clinical assessment of hydration status?
Urine and blood assays
High grades of urine color can also indicate what?
Gross hematuria or bilirubin excretion from jaundice
For hydration status, urine osmolarity is inferior to what?
Plasma
What is the most widely used hematological index of hydration?
plasma osmolarity
- greater than 300 mmol/Kg –> dehydration
What can affect bioelectrical imedance analysis?
- alcohol consumption
- diuretics
- menstrual cycle
- ilness
How can total body water be measured?
using deuterium oxide (stable hydrogen isotope)
What are the 3 types of dehydration?
- isotonic - net salt and water loss is equal
- hypertonic - water loss or excess salt
- hypotonic - loss of salt or excess water
Mild dehydration (1-2%) can impair what?
cognitive functions and physical performance
Moderate dehydration (2-5%) can result in what?
- hyperthermia
- reduced SV, CO, BP, and bloof low
- fatigue
How does dehydration impair cognition?
underperfusion of brain and increased stress hormones
Sever dehydration leads to what?
- dizziness, lethargy, irritable
- confusion
- ortho hypotension
- tachycardia
What 3 factors make infants more vulnerable to fluid/electrolyte imbalance?
- high surface-to-body-weight ratio
- limited ability to secrete solutes and concentrate urine
- low ability to express thirst and high metabolic rate
What 6 factors lead to decreased fluid intake and increased fluid
- elderly have less thirst (hypodipsia)
- defects in osmoreceptors, baroreceptors, and central reg mechanisms
- decreased urine concentration, renin activity, aldosterone, and ADH resistance
- reduced access to fluids
- diuretics or laxatives
- fear of incontinence
Drinking to thirst is not advised in what conditions?
- congestive heart failure
- end-stage renal disease
- COPD
What are the short term effects of water consumption?
- increased satiety
- reduced hunger
- increased energy expenditure from water induced thermogenesis
Excess water combined with glycerol creates what?
as osmotic gradient for temporary water retention
What is hyponatremia?
when blood sodium levels fall bellow 135 mmol/L
Hyponatremia causes what?
brain swelling –> seizures, coma, and death
Symptoms of hyponatremia include…
headache, nausea, fatigue, confusion
- these can mimic heat illness (dehydration)
