body fluid homeostasis Flashcards
ICF
intracellular fluid; fluid within all cells
ECF:
- extracellular fluid, fluid outside of cells
- made up of plasma and interstitial fluid
2 components of ECF
- plasma, also known as intravascular fluid
- interstitial fluid, which is found in the interstitial space located between cells and tissues.
Lymph, synovial, intestinal, biliary, hepatic, pancreatic, CSF, sweat, urine, pleural, peritoneal, pericardial, and intraocular fluids are all
ECF
___% of body is water
60
intracellular fluid is ___% of BW
40
extracellular fluid is ___% of BW
20
interstitial; 15% BW
intravascular (plasma); 5% BW
Dogs have a total blood volume of ____ml/kg
80-90
Cats have a total blood volume of ____ml/kg
60-70
cell membranes permeable to
- Water and gases
- Urea
and permeable via facilitated diffusion/active
transport - Ions
- Small hydrophilic molecules
Channel proteins
provide a narrow channel for ions to pass through. This allows passage of ions down their
concentration and electrical gradient (passive)
Carrier proteins
can physically bind to a substance on one side of the membrane, and release it on the other
Large molecules can only cross cell membrane via
endocytosis, or exocytosis
water is in osmotic _____
equilibrium
Colloids
very large molecules such as proteins and starches
osmotic pressure
amount of pressure that would have to be applied to a solution to prevent pure water - the solvent - from passing through a semi-permeable
membrane into the solution
primary mechanism by which water is transported into and out of cells.
osmosis
3 mechanisms that regulate movement of water and solutes between extracellular and intracellular fluid spaces in the body
1) large molecules like proteins cannot diffuse out of cell; influences osmotic pressure
2) ion transport via active and passive transport
3) positively charges attracts negatively charged ions
Crystalloids
fluids with electrolytes and small molecules, can move between all 3 compartments (intravascular space, interstitial space intracellular space)
colloids
fluids with large molecules
Stay in intravascular space, generating colloid osmotic pressure
advantages and disadvantages of crystalloids
- Cheap
- Accessible
- Short half life
- Larger volume required for resuscitation
advantages and disadvantages of colloids
- Longer half life
- Smaller volume required to expand intravascular volume
- Expensive
- Risk of allergic reaction
how is movement between compartments controlled
Endothelial cells
essentially selective filters. They regulate the passage of gases, fluids, as well as various molecules across their cell membranes. Different organs have different types of endothelium, some are leaky and some are very tightly bound
Homeostasis
Maintenance of relatively constant internal environment (“same state”) for optimal function
what does homeostasis require
Consistent monitoring: Feedback
Capacity to make changes and adjust internal environment: Integrated endocrine and neural response
Defence against external environment: Microbes andTemperature
negative feedback pathways
- Used to maintain a constant value = “set point”
- Increase or decrease from set point detected → corrective mechanism
- System controlled by negative feedback constantly oscillates about set point
- An efficient homeostatic system minimises the size of oscillations
every day water is lost from body in what ways
- Urine
- Sweat
- Faeces
- Milk
- Eggs
- Respiration
Factors affecting both the intake and output of water include
- Age
- Sex
- Obesity
- Climate
- Habits
- Level of physical activity
High fluid intake =
high fluid output
Osmolality vs Osmolarity
Osmolality - amount of solutes in the solvent (mass)
Osmolarity is per volume of solution (given in osmoles per litre (osmol/L)) – osmotic concentration
Plasma osmolarity/osmolality is important for
keeping proper electrolytic balance in the blood stream
Improper electrolyte balance can lead to
dehydration, alkalosis, acidosis or other life-threatening changes.
Antidiuretic hormone (vasopressin)
controls the amount of water the body retains from the kidney
Osmoregulation
Active regulation of the osmotic pressure of an organism’s body fluids
Maintains fluid balance and electrolyte concentrations
____ play a large role in osmoregulation
Controlled by _____
kidneys
hypothalamus
how does brain control osmoregulation
- Contains osmoreceptor cells which detect changes in osmolarity of blood passing through brain
- Hypothalamus controls thirst and produces ADH (vasopressin)
Osmolarity must be regulated to prevent loss of
water from cells
cells need to maintain constant
volume
how do cells Respond to swelling or shrinkage
by activating membrane transport/metabolic processes
What is the approximate amount of intracellular fluid in a dog that weighs 20 kg?
8 L
What percentage of a cat’s total body weight is in the intravascular space (plasma)?
5%
When a cell is immersed in a hypertonic solution, what happens to the cell volume?
The cell volume decreases, and the cell shrinks
Which of the following statements is INCORRECT regarding the movement of water and solutes between the extracellular and intracellular fluid spaces?
A.
Ions are transported
B.
Large protein molecules are unable to diffuse out of the cell, which influences osmotic pressure
C.
The cell membrane is impermeable to water
D.
There is a charge difference across the cell membrane
C.
The cell membrane is impermeable to water
When delivering fluids to rehydrate a patient, what type of fluid will stay within the intravascular space?
Colloids
