1. Body fluids Flashcards
To preserve the cell there is a need to regulate: (4)
- Fluid and water volume
- The concentration of electrolytes and nutrients
- pH
- Temperature
1 mole (mol) =
= 6.02 x 10^23 particles
= molecular weight (MW) of a substance in gram
How is concentration expressed?
Concentration is usually expressed as the number of moles per litre (mol/l or mol.l‐1
Diffusion: (3)
- Molecule movement is from high concentration to low concentration, down a concentration gradient
- Particles tend to distribute themselves evenly within a solution
- Size of the molecule and temperature affect the speed of diffusion
Lipid-soluble substances can diffuse across the ____ _____, but polar substances cannot.
lipid bilayer
Molecules will move by diffusion down a concentration or electrochemical gradient if any of the following apply: (3)
- The molecules are lipid‐soluble
- The molecules are small enough to pass through the membrane’s pores (channels formed by membrane proteins)
- There is a membrane carrier to assist movement
How do you move substances across the cell membrane against a concentration or electrochemical gradient? (2)
If energy is required for the movement of a substance across a membrane it is known as ACTIVE TRANSPORT
Energy for the process is supplied by either:
* The hydrolysis of ATP to ADP (primary active transport)
* Coupling the movement of one substance moving up a concentration gradient to another moving down a concentration (secondary active transport)
What are the types of active transport mechanisms? (3)
How are transport proteins named?
The transport proteins are named according to what they transport e.g. the sodium ATPase pump transports sodium ions primarily.
Why are the sodium glucose-linked transporter and sodium amino acid-linked transporters important?
The sodium glucose linked transporter and sodium amino acid linked transporters are
important for absorption of sodium and amino acids from the GIT and reabsorption in the
kidneys.
A significant proportion of our ______ _______ is used in activity of the sodium‐potassium ATPase pump.
basal metabolism
Difference between simple diffusion and carrier-mediated diffusion:
Transcellular vs Paracellular:
Other ways in which substances move in and out of cells:
– Endocytosis and exocytosis
What is endocytosis?
Endocytosis of particulate material is through phagocytosis. For example when neutrophils
engulf bacteria. Endocytosis of fluids is termed ‘pinocytosis’.
What is crystalloid osmotic pressure?
Osmotic pressure exerted by electrolytes is termed crystalloid osmotic pressure
What is oncotic pressure?
Osmotic pressure due to proteins is called colloidal or oncotic pressure. In plasma, albumin synthesised by the liver is a major contributor to oncotic pressure in the
capillaries.
What is the difference between osmolarity and tonicity? (2 vs 3)
Relative to cells/body fluids, other fluids can be: (3)
- Isotonic: Similar concentration
- Hypotonic: Less concentrated
- Hypertonic: more concentrated
Osmolarity vs Osmolality:
Osmolarity = number of osmoles/litre solvent
Osmolality = number of osmoles/kg solvent
Effects of tonicity on cells:
Calculate the osmolarity of normal/physiological saline (0.9% NaCl).
Show your calculation (note: dissociation coefficient of NaCl 0.92)
Physiological or normal saline is isotonic and has a concentration of _____ NaCl which is the equivalent of an osmolarity of about _____.
0.9%
285 m0sm/l
In the body, fluid is either:
within cells (____) or outside (surrounding cells) (____)
ICF
ECF
The total body water is divided into two major compartments:
That which is inside cells contributes 2/3 total body water. The remaining 1/3 is outside cells.
The fluid outside cells is further subdivided into:
plasma, interstitial and transcellular compartments.
How can transcellular fluid volume be altered?
Transcellular fluid volume can be altered quite quickly and is variable in volume. For example, the fluid in the GIT can be rapidly increased by drinking a large
volume of fluid. Emptying the urinary bladder can also decrease the ECFV quite rapidly.
How is total body fluid measured by? (2)
- Dye dilution technique
- Bioimpedance
How are Body fluid compartment volumes distributed?
What are Starling’s forces?
What is Capillary hydrostatic pressure (Pc )?
Capillary hydrostatic pressure (Pc ) pushes fluid out of the capillary.
What is Interstitial hydrostatic pressure (Pi )?
Interstitial hydrostatic pressure (Pi ) pushes fluid into of the capillary.
What is Interstitial oncotic pressure (i)?
Interstitial oncotic pressure (i) draws fluid into the interstitial space.
What is Capillary oncotic pressure (c)?
Capillary oncotic pressure (c) draws fluid into the capillary.
What does this diagram depict?
The figure above summarises the major sources of water in the body. Water produced by metabolism has not been included. The figure also shows how water is lost from the body. In some instances pathological conditions such as diarrhoea and vomiting can cause significant losses.
What are some factors affecting body water?
It is important to note that when a sample is taken to assess the clinical chemistry of an individual, normally blood samples are taken. Plasma/blood then serves as a _____ ______.
reference point
What is the function of sweat?
The function of sweat is primarily for evaporative cooling. Therefore the body tries for conserve electrolytes when using the water for evaporation.
Sweat is therefore hypotonic compared to plasma.
What is the function of Cerebrospinal fluid?
In adults, normal CSF has two-thirds glucose
concentration of serum
CSF/serum = 0.6
< 0.4-0.5 = hypoglycorrachia
What is the cause of hypoglycorrachia? (3)
- impairment of glucose membrane transporters
- Increased neural anaerobic metabolism
- meningitis
Synovial membrane (synoviocytes) produce _____.
Transcellular ________.
fluid
compartment
What is the function of synovial fluid? (4)
-Lubrication (↓ Friction)
-Support
-Nutrients
-Shock absorber
What are the features of synovial fluid? (2)
-Clear
-Low fibrinogen so normally doesn’t clot
If:
Input = Output = _________
Input > Output = __________
Input < Output = _________
Euhydration
Overhydration
Dehydration
Water deficit —–>
thirst + decreased urine formation
Water excess ——>
Increased urine formation
What does the hydration of an individual refer to?
Hydration refers to the TBW in an individual.
When we consider hydration we also need to look at the electrolyte concentration of the body water.
What is euhydration?
Euhydration is the normal state of hydration with a plasma osmolarity of 280‐290 mOsm/l.
Whenever there is a reduction in TBW, the individual is said to be ________.
When TBW is greater than normal, the individual is said to be _______.
dehydrated
overhydrated
How does the regulation of body water take place?
How does the regulation of Na+ (and water) and K+?
What is Oedema?
Oedema ‐ the pathological accumulation of fluid in the extracellular compartments, mainly in the interstitial spaces.
How do Starling’s forces affect Oedema? (2)
- The balance between capillary filtration and reabsorption is determined by Starling’s forces
- Lymph flow can be affected by blockage or damage.
How does increased capillary hydrostatic pressure cause oedema?
The first cause is an increase in capillary hydrostatic pressure. This Starlings force ‘pushes’ fluid out of the capillary. Any condition which increases capillary hydrostatic pressure can end up causing oedema.
Typical examples include deep vein thrombosis and congestive heart failure.
How does decreased capillary oncotic (colloidal) pressure cause oedema?
The second cause of oedema is a reduction in capillary oncotic (colloidal) pressure. This Starling’s force normally ‘pulls’ or retains water in the capillaries. When there is a reduction in protein in blood, less fluid is pulled back from the interstitial space and less is retained in the capillary, so it accumulates in the interstitial space causing oedema
What diseases does decreased plasma capillary oncotic pressure cause?
This commonly occurs in protein-malnourished children who have a reduced capacity to
synthesise plasma proteins such as albumin in the liver. Liver failure is also an important cause of oedema. Failure to absorb dietary protein from the GIT due to conditions such as coeliac disease and
Tropical sprue also cause oedema. Abnormal loss of protein through the GIT and kidneys is also an important cause of low capillary oncotic pressure. In some parts of the world hookworms can also cause a low plasma oncotic pressure.
How does the blockage of lymphatic vessels cause oedema?
The third physiological cause of oedema is blockage of lymphatic vessels. The lymphatics drain approximately 10% of the fluid from the interstitial spaces. When the
lymphatics are blocked due to neoplasia (cancer), damage of the lymphatic drainage system during surgery or parasites which enter the lymphatics, the drainage via lymph is reduced.
How does increased capillary membrane permeability affect oedema?
The fourth major physiological cause of oedema is when there is an increase in interstitial fluid oncotic/colloidal pressure. This scenario arises when the capillary membranes are damaged resulting in the leaking of plasma protein into the interstitial spaces. The
interstitial proteins pull fluid from the capillaries and also retain it in the interstitial spaces, resulting in oedema. Allergic reactions and inflammation or trauma are common causes of increased capillary permeability.
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Other signs of dehydration: (3)
- ↑ Plasma osmolarity
- ↓ Blood pressure
- ↑ Haematocrit
In children especially in developing countries, dehydration is a common cause of morbidity
and mortality. It mainly occurs due to loss of fluid through profuse ______ and _____. Loss of fluid due to heavy sweating eg hard labour on a hot day or heavy prolonged exercise is also another common cause of dehydration. Dehydration ______ skin elasticity/turgor. Please note that the fontanelle is _____ in adults.
diarrhoea
vomiting
decreases
absent
Body fluid changes as a result of: (2)
Oral dehydration therapy: (3)
Estimation of plasma osmolarity:
Plasma osmolarity (m0sm/l) = 2[Na + ] + [glucose] + [urea]
If you are not given [glucose] or [urea] then estimate plasma osmolarity using:
Plasma osmolarity (mOsm/l) = 2[Na + ] + 15
Determine the plasma osmolarity for Patient A.
