Body Fluids Flashcards
what is an electrolyte balance
an electrolyte is a substance that separates into cations and anions when dissolved in water to produce an electrically conducting solution
name the list of electrolytes
- Sodium
- Potassium
- Calcium
- Magnesium
- Chloride
- Hydrogen phosphate HPO42-
- Hydrogen carbonate HCO3-
What does an electrolyte balance effect
it affects the volume and distribution of fluid in the body
describe the types of body fluid
- Intracellular fluid – fluid within the cell
- Extracellular fluid – fluid outside the cell – made up of interstitial fluid, and plasma
- Interstitial fluid
- Plasma
what makes up intracellular fluid
- plasma and interstitial fluid
What is the total amount of extracellular fluid
14L
20% of body weight
what is the total amount of intracellular fluid
28L
40% of body weight
what is the total volume of fluid in the body
42L
60% of body weight
what is the total volume of interstitial fluid
10.5 L
3/4 of ECG surrounding the cells
what is the total volume of plasma fluid
3.5L, approx 1/4 of ECF: fluid that is inside the blood vessel
what is the total volume of red blood cells
1.5L
what is the total volume of blood
5L
what is blood made out of
plasma
red blood cells
what is the volume of cells in the intracellular fluid other than red blood cells
26.5L
how many litres does transecellular fluid make up
approx. 5% (1 L) of ECF contained within spaces surrounded by epithelial cells for example synovial fluid in joints
what separates the intracellular fluid and the interstitial fluid
- Between intracellular and interstitial fluid then the fluid passes through the cell membrane
what separates the interstitial fluid and plasma
- Through the interstitial fluid and plasma, it has to pass from the capillary endothelium
describe the normal electrolyte composition
- ECF is high in sodium and chlorine and low in potassium
- ICF is high in potassium and low in sodium and chlorine
- sodiums are on the outside and potassium is on the inside of the cell
what determines the movement of water between two compartments
- Osmotic pressure difference: determined by the concentration of solute particles
- Hydrostatic pressure difference: produced by pumping action of the heart
what transports water into and out of the cell
osmosis
describe the process of osmosis
- Water molecules pass through the cell membrane from an area of low solute concentration to high solute concentration
- Water is transported into and out of the cell by osmosis
- Separated by a semipermeable membrane which is permeable to water but not to solute
what opposes the movement of water across a membrane
- The movement of water across the membrane can be opposed by applying a hydrostatic pressure to the solution
what is the pressure just sufficient enough to oppose called
- The pressure is just sufficient to oppose the uptake of water is called osmotic pressure of that solution
what is the osmotic pressure related to
- The osmotic pressure is related to the number of particles present in a solution
what is osmolality
A measure of the number of osmotically active particles in solution
describe the measure of osmolality
this is a measure of the osmoles (Osm) of solute per kilogram of solvent (Osm/kg) or osmol/kg
describe the measure of osmolarity
Osmolarity is the number of osmoles (Osm) of solute per L of solution/ osmol/L or Osm/L
what are the sources of intracellular osmolarity
- Charged macromolecules such as proteins and carbohydrates and their counter ions
- Smaller metabolites (these are the result of metabolism) and their counter ions
- Small inorganic ions “ donnan effect” macromolecules and metabolites attract these small inorganic ions into the cell this is the donnan effect
what is intracellular osmolarity
this is when the cells interior intracellular fluid drives the passage of water
what is the donnan effect
macromolecules and metabolites attract these small inorganic ions into the cell this is the donnan effect
what happens if the cell does not control osmolarity
- If the cell does not control osmolarity solutes will concentrate inside the ell, therefore there is a higher concentration of water outside the cell compared to inside so water enters the cell and the cell swells and eventually bursts this is called lysis
how do animal and bacterial cells control intracellular osmoregularity
- Animal cells and bacterial control intracellular osmoregularity by actively pumping out inorganic ions so that their cytoplasm contains a lower total concentration of inorganic ions than the extracellular fluid thereby compensating for their excess of organic solutes
what is ATPase
it is a sodium potassium pump
describe what ATPase do
- Most important primary active transporter
- Uses energy of ATP to pump sodium and potassium into the cell
- Counteracts the Donnan effect and stops small inorganic ions being attracted into the cell by pumping them out
- pump that will actively transport 3 sodium molecules outside the cell and 2 potassium molecules inside the cell
how is ATPase inhibited
- Can be inhibited with toxins the sodium rises and the potassium falls
- The pump is electrogenic so controlling sodium and potassium concentration and cell volume
- Contributes to the cell membrane voltage
what is tonicity
Tonicity is the effective osmolarity and it is this that determines the cell volume
- The ability of an extracellular solution to make water move into or out of a cell by osmosis is known as its tonicity
what is an isotonic solution
same number of osmotically active particles no water loss or gain
what is a hypertonic solution
more osmotically active particles, osmotic water loss and cells shrink and crenate
describe a hypotonic solution
fewer osmotically active particles, osmotic water gain, cells swell and burst which is lysis
what is tonicity determined by
- Tonicity is determined by the concentration of those solutes that do not enter the cell
what is tonicity equal to
- It is equal to the sum of the concentrations of the solutes which have the capacity to exert an osmotic force across a membrane
what is tonicity influenced by
- Influenced only by solutes that cannot cross the membrane as only these exert an effective osmotic pressure
- Solutes able to freely cross the membrane do not affect tonicity because they will always be in equal concentrations on both sides of the membrane such as urea
describe the hydrostatic pressure within the body,
- Hydrostatic pressure differences and osmotic forces regulate fluids transport across the walls of the capillaries
Water is driven out the capillary by several forces - Capillary hydrostatic pressure – pumps out of capillary
- Interstitial fluid hydrostatic fluid - pumps in
- Osmotic force due to plasma protein concentration – pumps in
- Osmotic force due to interstitial fluid protein concentration – pumps out
how is the hydrostatic pressure created
produced by the pumping action of the heart
what are colloids
large molecular weight particles that are present in a solution
describe colloids
- They are solutes that contribute to the total osmotic pressure of a solution
- In plasma the plasma proteins are the colloids that are present
- They are reffered to a colloid osmotic pressure
what can small solute do
can pass freely across most capillary walls into the ISF
what are the rules of water control in the body
- Water cross cell membrane easily
- Intracellular osmolality must equal extracellular osmolality
- Extracellular osmolality is effectively determined by the ECF (sodium ion)
- ECF(sodium) determines ICF volume
- Osmoreceptor control of osmolality is sensitive and powerful so ECF (sodium) is held constant
- Total body solute is relatively constant
describe the water intake in the body
90% is food and drink and metabolism is 10% (fluids, food, oxidation)
describe the water losses in the body
(insensible, sweat, respiration and faeces) 30% lungs and skin, 10% sweat and faeces, urine 60%
describe plasma proteins moving across the capillary wall
- Plasma proteins which are too large to move freely across the capillary wall do not enter the ISF
what happens if there is a greater concentration of plasma proteins
- Therefore there is a greater concentration of plasma proteins in intravascular compartments than in the ISF this sets up a osmotic pressure difference, Colloid osmotic pressure (COP) tends to pull the fluid back into the capillary
whats the obligatory water loss
- The volume of water required for daily urinary excretion of metabolic waste products is known as obligatory water loss
- The minimal amount of fluid loss from the body that can occur
describe the amount of urine that is lost a day
500ml
describe the kidney and what its responsible for
homeostatic control mechanisms that regulate the urinary excretion of sodium and water this maintains overall fluid balance
what are the two hormones that regulate blood osmolarity
- Sodium is reabsorbed in the distal convoluted tubule regulated by the hormone aldosterone
- Water is reabsorbed primarily in collecting duct regulated by the ADH also known as vasopressin
describe the nephron that filters plasma to form urine
- Filtrate
- 120ml/min
- 7.2 L/Hour
- Greater than 170 litres per day, 99% of filtrate is reabsorbed
- 2 litres of urine is generated
what are the disorders associated with a decrease in extracellular osmolarity
- Hyponatremia
- Decrease in plasma electrolytes sodium
- Many conditions including congestive heart failure, liver and kidney failure and pneumonia can have an associated hyponatremia
- It can also be caused by overhydration from drinking too much water (excessive thirst= polydipsia)
- Osmotic shift can cause water to enter cells and make them swell
- Particularly dangerous in the brain where it can cause convulsions, coma and death
what are the disorders associated with an increase in extracellular osmolarity
- Hypernatremia
- Elevated plasma electrolytes
- Hypernatremia – often associated with dehydration
- Extreme dehydration has important clinical implications and can lead to cell shrinkage
describe the ADH pathway
- ADH release is triggered when osmoreceptor cells in the hypothalamus detect an increase in the osmolarity of the blood
- this causes the osmoreceptors in the hypothalamus to release ADH from the posterior pituitary gland
- this causes the collecting duct to become more permeable and water reabsorption further prevents osmolarity increase and this maintains homeostasis
- if you are thirsty drinking reduces blood osmolarity to a set point
describe how the blood volume is regulated
- stimulus; the juxtaglomerular apparatus responds to low blood volume or blood pressure (such as due to dehydration or loss of blood)
- this causes renin to be produced
- this causes angiotensinogen to be produced which makes angiotensin II
- which can either cause arteriole constriction or the adrenal gland to produce aldosterone and this causes increased sodium and water reabsorption in the distal tubules leading to normal blood pressure and volume
what is plasma
- Plasma is a yellow component of blood that holds blood cells into suspension
what is interstitial fluid (ISF)
- this is the fluid that surrounds cells but is outside the blood vessels
- oxygen nutrients, cellular waste and chemical messengers all pass through the ISF
what is trans-cellular fluid
- another compartment of ECF
- small and ignored when doing body fluid calculations
Name some examples of trans-cellular fluid
- cerebrospinal fluid
- peritoneal fluid
- synovial fluid
what happens in intracellular fluid
- it is where chemical reactions inside a cell take place
define the osmotic pressure
- osmotic pressure is the amount of pressure required in order to stop osmosis occurring down its potential gradient
when does a colloid osmotic pressure form
this forms when plasma proteins are too large to pass through the capillary wall membrane
what is hydrostatic pressure
- this is pressure that is produced by the heart that occurs when fluid is being pushed against a wall
why is sodium seen as a nonpenetrating substance in tonicity
because it is pumped out via sodium and potassium ATPase pumps at the same rate that it enters
