Water balance Flashcards
What determines the plasma volume that perfuse organs?
Amount of water in the blood
What is hyperosmolality?
Too little water
What are the symptoms of hyperosmolarity?
Diarrhea
Vomiting
Negative water balance
Reduced water volume
Increased blood viscosity
Headache
Cramps
What are the symtoms of hyposmolality?
Low serum sodium levels
Headache
Vomiting
Confusion
Seizures
Coma
Muscle weakness
How much water is lost by insensible losses?
0.5 - 1L
What are insensible losses?
Non-urine losses
Sweating, breathing, faeces
How much water is lost in the urine a day?
1.5 L
What is the recommended volume of water that should be taken in during a day?
2 - 2.5 L
Through consumption of food and drink
What is the percentage of water in the body?
60%
What percentage of body water is found in the cells?
40% inside the cells - intracellular fluid
What percentage of body water is found between cells?
15% in between cells - interstitial fluid
What percentage of body water is found in blood plasma and lymph?
5%
Is water distribution between intracellular and extracellular compartments interchangeable?
Yes
What regulates the movement of water to and from the intracellular compartment?
Osmotic pressure
What is the major solute determining osmotic pressure in the intracellular compartment?
Potassium
What is the major solute determining osmotic pressure in the extracellular compartment?
Sodium
What is the plasma oncotic pressure?
Pressure exerted by plasma proteins that cannot move across capillary walls
What are the forces that determine the water distribution in the vascular compartment?
Oncotic pressure
Hydrostatic pressure
What does the hydrostatic pressure do to water distribution?
Pushes water out of the vascular space
What does the oncotic pressure do to water distribuyion?
Draws water into the vascular space
What happens to the blood pressure in high plasma protein levels?
High blood pressure
What is plasma oncotic pressure?
Pressure exerted by plasma proteins that cannot move across capillary walls
What are examples of specialised structures maintains perfusion of vital organs?
Baroreceptors in the aortic arch and carotid sinus
Osmoreceptors in the hypothalamus
JG cells in the kidney
Where are baroreceptors found?
In the aortic arch and carotid sinus
Where are the osmoreceptors found?
In the hypothalamus
Where are the JG cells found?
In the kidney
What do baroreceptors react to?
Changes in vascular tone and cardiac output
What do baroreceptors do to maintain homeostasis?
Cause volume changes
What do osmoreceptors in the hypothalamus react to?
Thirst
Vasopressin release
What do osmoreceptors do to maintain homeostasis?
Causes osmolality changes
What do JG cells in the kidney react to?
Salt and water reabsorption
Renin-angiotensin system
What do JG cells in the kidney do to maintain homeostasis?
Cause pressure changes
What is the effective circulating volume?
Part of the extracellular volume in the arterial system perfusion the organs
What is the average effective circulating volume of a 70 kg person?
700 ml
What maintains the effective circulating volume?
Total body sodium
Main extracellular solute holding water
Control of sodium balance through renal excretion is key to control circulating volume
TRUE or FALSE
TRUE
Pathogenesis of heart failure
Reduced blood pressure induces fluid retention by the kidneys and expansion of the extracellular compartment
Effective circulating volume is low
Water is in the same volume but in the wrong place - should be in the vascular space, not extracellular compartment
During heart failure, the decreased volume of water in the vascular space arises since the total body water is decreased
TRUE or FALSE
FALSE
The volume of water in the body is normal, just in the wrong compartment
What is water immersion?
Bathing in cold water after exercise
Why is water immersion beneficial?
Increases the pressure of the body and causes blood to go from the legs to the heart
What does water volume do to circulating volume and urine output?
Increases them
What are the benefits of water immersion?
Induces natriuresis by inducing vasopressin release
Induces diuresis
What is natriuresis?
Decrease in sodium concentration in the extracellular space
More sodium lost in the urine
Why is the induction of diuresis helpful?
Increases volume of water lost in conditions of water and salt retention
What is diuresis?
Increased urine output
