Fluid balance Flashcards
Discuss how fluid is gained by the body (including average daily values).
Gains water:
1. Thirst- Driving force for water intake (governed by the hypothalamic thirst centre) or by consuming moist foods (2250 ml/day).
2. Production of metabolic water- Either in the electron
transport chain during aerobic respiration (when O accepts H) or in dehydration synthesis (250
ml/day)
Total water gain is 2500 ml/day.
Identify the fluid compartments of the body.
TBW (total body water) is divided into ICF (
Intracellular fluid) and ECF.
ECF is divided into the plasma and interstitial fluid.
There is also transcellular fluid (synovial, peritoneal, pericardial, and intraocular space, as well as the cerebrospinal fluid) = specialized ECF.
Describe the electrolyte composition of extracellular fluid and intracellular fluid.
The major positive ion of the extracellular fluid is sodium, and the major negative ion is chloride.
The major positive ion of the intracellular fluid is potassium, and the major negative ions are protein and phosphates.
Outline the role of thirst, antidiuretic hormone and aldosterone in fluid homeostasis.
8.5 Identify the following as examples of disrupted fluid and electrolyte balance: oedema, shock, water intoxication, vomiting and diarrhoea.
Disrupted fluid and electrolyte balance:
- Oedema =. Interstitial fluid retention
- Shock = severe blood/fluid loss.
- Water intoxication = Too much water in cells, causing cells to swell.
- Vomiting and Diarrhoea = causes loss of fluids.
9.1 Outline how the interplay between hydrostatic and osmotic pressures at each end of the capillary results in the formation and re-uptake of interstitial fluid.
The reuptake of interstitial (tissue) fluid is done through the osmotic pressure of the blood, which is higher than the hydrostatic pressure in the capillary.
At the arteriole end, the blood osmotic pressure is lower than the hydrostatic pressure, and the net movement of substances is outside the blood cells.
9.2 Identify oedema as an accumulation of excess interstitial fluid and indicate possible causes.
Oedema is excess fluid within the tissue (interstitial). Often resulting in tissue swelling and is often due to blockage in the lymphatic system or when the lymphatic system cannot drain.
Outline the circulation of lymph from the lymph capillary back into the general circulation.
Lymph capillaries have walls that only work one way to let fluid in. As lymph capillaries collect interstitial fluid from tissues, the pressure in the lymph capillaries grows. This increasing pressure moves the lymph fluid forward toward the heart.
Describe the role of the renin-angiotensin-aldosterone system in the control of blood volume and pressure.
Negative feedback loop:
Low blood volume/pressure > Kidney releases renin > releasing angiotensinogen and angiotensin > causing the adrenal cortex to release aldosterone > leading to more absorption of salts and therefore more water > returning to normal levels.
Discuss how fluid is lost by the body (including average daily values).
Avenues of loss include:
1. In urine produced by kidneys (1500 ml/day)
2. Through the skin, sensible perspiration (200 ml/day)
3. Insensible losses through the skin and lungs (700 ml/day)
4. In feces (100 ml/day)
Total water loss is 2500 ml/day (gain and loss balances).
What percentage of body weight is TBW (total body water), ICF, ECF, Interstitial Fluid, and plasma?
TBW is 60% of body weight (40 L).
ICF is 40% of body weight.
ECF is 20% of body weight.
Interstitial fluid is 15% of body weight and Plasma is 5% of body weight.
What are the clinical signs of dehydration?
Weight loss
Hypotension
Tachycardia
Sticky oral mucus and dry tongue
Low urine production (oliguria)
Neurological disturbances (extreme cases)
What are the clinical signs of fluid overload/retention?
Weight gain
Hypertension (High BP)
Oedema
Neurological disturbance (extreme cases)
What are the 4 functions of the ions formed when electrolytes break apart?
- Control the osmosis of water between fluid compartments.
- Help maintain acid–base balance.
- Involved in nerve conduction and muscle contraction.
- Serve as cofactors for optimal activity of enzymes.
What is intracellular fluid?
Fluid Within cells
