Fluid Balance Flashcards
What does ‘fluid balance’ refer to?
the balance between fluid inputs to the body and fluid outputs.
Vital for life and a key aspect of homeostasis - fluid balance = optimum hydration
What happens to percentage of water over a lifespan? and what’s the difference of water mass between males and females?
- percentage of water decreases with age
- less water mass in females due to less muscle in their body (muscles contain water)
Water is the main constituent of the body. What percentage of body mass is water?
50%
What liquids in the body are water based?
plasma, lymph, interstitial fluid, intracellular fluid
Besides being a solvent for substances/chemicals to dissolve and transport in, what other functions does water have in the body?
- thermoregulation
- cushioning
- reduce friction
Describe thermoregulation
evaporation of sweat from the skin and heat loss
Describe cushioning
the cerebrospinal fluid, amniotic fluid that surround the foetus
Give 2 examples of where water is used to reduce friction
- pleura fluid (surrounds the lungs and chest walls)
- synovial fluid (between the bones)
What is dehydration in the body often caused by?
- water lost from interstitial fluid that surrounds the cells in the body’s tissues - dehydration of cells will disable the cell to work effectively
- water lost from the plasma reduces blood volume and can lead to reduction in blood pressure
The body continually loses water. What does the ability to maintain fluid depend on?
our sensation of thirst, our ability to act on this sensation and maintain fluid inputs
Regulation of body water content is through regulating inputs and outputs. What are they mainly regulated by?
- inputs are mainly regulated through thirst mechanism
- outputs are mainly regulated through water loss by the kidney
Name two major fluid compartments of the body
- intercellular fluid volume
- extracellular fluid volume
Where is intercellular and extracellular fluid found?
intercellular - inside the cells
extracellular - outside of the cells
Describe intercellular fluid, what is it formed by and what does it provide?
Constitutes the largest reservoir and bathers the external environment of cells. Formed by filtration of blood plasma through the walls of capillaries. It provides communication between compartment and individual cells, enabling cells to regulate their own intercellular composition.
Extracellular fluid volume: Where is interstitial fluid found?
bathing cells
Extracellular fluid volume: Define plasma volume
fluid with intravascular compartment exists as blood plasma
Blood volume is approximately 5 litres. How many litres of this is plasma?
3 litres
What is osmolarity?
the balance of water to salt in plasma (blood)
What does raised osmolarity mean?
dehydration
What is the role of osmoreceptors and where are they located?
osmolarity is detected by them, i.e. when the blood is dehydrated the osmoreceptors are stimulated by loss of water.
They are in the hypothalamus
What happens with the osmoreceptors detect dehydration?
- signal to thirst centres in brain
- release ADH from posterior pituitary gland and travels in blood to kidneys
- kidneys retain/reabsorb water enabling less dilute urine = increased osmolarity
State the negative feedback loop of osmolarity
high osmolarity, thirst mechanism, ADH release to kidney, kidney retains more water, return osmolarity to low
What regulates blood/plasma volume?
the kidneys, which retain or excrete more of less sodium
What is the result of increased excretion of sodium by the kidneys?
an increased excretion of water by the kidneys (i.e. nuts in a pub make you buy more drinks, increase thirst)
What does increased sodium and water excretion from the kidneys do to blood volume?
decreases it
Kidneys increasing and decreasing blood volume is an important response to:
blood loss
dehydration
physiologically in pregnancy - plasma volume (placenta)
What is the result of decreased excretion of sodium from the kidneys?
causes decreased water loss and enable an increase in blood volume
