Fluid compartments and fluid homeostasis Flashcards
Compare locations of ICF and ECF; describe various body fluid compartments; discuss sources and regulation of water and solute gain and loss; explain how fluids move between compartments
What is the % split of solids and fluids in males?
40% solids, 60% fluids
What is the % split of solids and fluids in females?
45% solids, 55% fluids
What is the fractional split of ICF and ECF in humans?
2/3 ICF and 1/3 ECF
What is the % split of ICF between interstitial fluid and blood plasma in humans?
80% interstitial fluid, 20% blood plasma
What is the name for the general barrier which separates ICF from interstitial fluid?
The plasma membrane
Selectively permeable barrier with active transport pumps for some ions
What is the name for the general barrier which separates interstitial fluid from blood plasma?
Blood vessel walls
Thin and ‘leaky’ to allow water and solute exchange
Which type of blood vessel has walls thin enough to allow the exchange of water and solutes between blood plasma and interstitial fluid?
Capillaries
What is another name for intracellular fluid?
Cytosol
What are the two standards for a body being in fluid balance?
- Required amounts of water and solutes are present
- Water and solutes are correctly proportioned among the various compartments
Which has the higher water content: adipose tissue or skeletal muscle tissue?
Skeletal muscle tissue (∼65% water)
Adipose tissue is <20% water
Why is fluid balance closely related to electrolyte balance?
Osmosis is the primary means of water movement between interstitial fluid and ICF - concentration of solutes determine the direction of water movement
How do the kidneys support fluid balance?
Varying the concentration of urine to ensure the right balance between water and solutes in the body
List the three methods of water gain in order from largest to smallest contribution
- Ingested liquids
- Ingested foods
- Metabolic water
List the four main forms of water loss in order from largest to smallest losses
- Urine
- Perspiration
- Water vapour in exhalation
- Faeces
In which region of the brain is the thirst centre found?
Hypothalamous
What are the four main stimuli of the thirst centre?
- Increased blood osmolarity - MAIN
- Decreased blood volume
- Decreased blood pressure
- Dry mouth
What is the technical definition of dehydration?
Reduction in total body water
A decrease in volume and increase in osmolarity of body fluids
What is the major hormone which regulates water loss?
Antidiuretic hormone (ADH)
also known as vasopressin
Where is ADH produced?
The hypothalamous
Where is ADH stored?
The posterior pituitary gland
What are the five organic substances found in body fluids?
- Glucose
- Amino acids/proteins
- Fatty acids
- Hormones
- Enzymes
Name and describe the three levels of fluid spacing
- First spacing - normal distribution of fluids
- Second spacing - abnormal accumulation of interstitial fluid (oedema)
- Third spacing - abnormal fluid accumulation where it is not easily exchanged with ECF e.g. ascites
What is the difference between dehydration and hypovolaemia?
Dehydration is a loss of total body water causing hypertonicity whereas hypovolaemia is an abnormally low blood volume
What three routes of sodium loss and can cause hypovolaemia?
Bonus for a non-sodium related cause
Sodium losses via:
1. GI e.g. vomiting, diarrhoea
2. Skin e.g. excessive sweating or burns
3. Renal e.g. renal disease or diuretics
OR
Haemorrhages
What are three medical causes of hypervolaemia?
- IV therapy
- Renal sodium retention in heart failure
- Renal sodium retention in renal failure
What is the effect on the amount of water in urine of each of the three main hormones involved in maintaining water balance?
- ADH - reduces loss of water in urine
- Aldosterone - reduces loss of water in urine
- ANP - increases loss of water in urine
By what mechanism does ADH reduce urinary water loss?
Promotes insertion of water-channel proteins in collecting ducts of the kidneys to increase water reabsorption in to the blood
By what mechanism does aldosterone reduce urinary water loss?
Promotes Na⁺ reabsorption in to the blood which leads to greater water reabsorption by osmosis
By what mechanism does ANP increase urinary water loss?
Promotes increased urinary excretion of Na⁺ which leads to greater water loss by osmosis
