Things to know for REN

Question 1

What is the relationsip between input and output

Answer 1

INput must generally equal Output

Question 2

How do we get water into the body

Answer 2

Drinking
Food
Metabolism

Question 3

How do we lose water

Answer 3

• Lungs: exhaling
• skin: sweatin
• bowels: low volume losses cuz large bowel reabsorbs water
• kidneys can change urinary output in a variety of different ways

Question 4

What is a fluid

Answer 4

fluid is a substance that deforms under a shear stress.

physiology, the important fluids are those in which water, or a fat/lipid, are the solvent.

Question 5

What are the body fluid compartments

Answer 5

• Intracellular water (inside cells)
• Interstitial water: filling the space between cells, amongst the extracellular matrix
• Fat
• Plasma (blood)
• Transcellular fluid: separated from the extracellular fluid by a membrane usually lined by epithelial barrier (e.g. CSF, peritoneal fluid, aqueous humor)
  
  • CSF is different compared interstitial fluid

Question 6

Give examples of transcelluar compartments

Answer 6

• Peritoneal Space: Can greatly expand (used therapeutically during peritoneal dialysis)
• CSF:protected by the Blood-Brain Barrier (endothelial cells joined by tight junctions; with a role for glia)
• Pleural cavity
• Sinovial fluid

Question 7

How do we measure body fluid

Answer 7

You would inject a substance which is known to distibute in the compartment

and from that work out the volume of distribution

can measure plasma: by using deuterium or tritium to replace the normal hydrogen in water

can label protiens, for example evans blue

can measure extracelluar fluid: thiosulfate, insulin (problem can pass intracellualry)

Question 8

What are the general concentrations of ions in the body fluids

Answer 8

K+-> high intracelluar, low extracelluar

Cl-: high extracelluar, low intracelluar

Na+: high extracelluar low intracelluar

Question 9

How much is the usual body osmolality

Answer 9

285mOsm kg-1

Question 10

How does calcium float around in the body

Answer 10

50% is bound to albumin
the other half is free floating in the plasma

free calcium more biologically active

Question 11

What would happen to the total calcium conc during liver failure

Answer 11

albuimn conc will fall (liver makes albumin)
then the total calcium concentration would fall

Question 12

How do we calculate free calcium

Answer 12

Ca corrected= Ca total +0.020 (40-albumin)

Question 13

What is an osmole

Answer 13

number of molecules that a compound dissociates into when dissolved in solution

100 mmol of NaCl -> 200 mOsm in solution, because it dissociates into Na+ and Cl-.

Question 14

What is meant my osmolality

Answer 14

number of osmoles per unit mass of the solvent
(Osm.kg-1)

Question 15

What is meant by osmolarity

Answer 15

number of osmoles per unit volume of the solution (Osm.l-1)

Question 16

What is meant by osmotic pressure

Answer 16

is a force that drives water movement that is proportional to osmoloaity

high water potential is the same as low osmotic pressure

this means the more salts you have in solution, the more water that moves towards

Question 17

What is meant by “two solutions are isoosmotic”

Answer 17

they share the same osmolality

Question 18

What is meant by istonic

Answer 18

when theres no net fluid movement

Question 19

What is the main osmotic potential in the caps caused by

Answer 19

proteins

force caused by proteins called oncotic pressure as well

Question 20

What drives water movment in caps

Answer 20

hydrostatic pressure and oncotic pressure

Question 21

Can you give an example of osmotic pressure chnages

Answer 21

Albumin is a protein is plasma
a fall in albumin can be caused by
liver failure (decreased production)
renal failure (increased protein loss)

Question 22

What can happen if theres a fall in plasma proteins

Answer 22

• plasma protein can no longer keep water in circulation
• so onoctic pressure falls, so water will move out
• so water will acculamae in intersital spaces
  
  • For example pulmonary, peripheral (Oedema, ascites)

Question 23

Where is odema a problem

Answer 23

in the brain

Question 24

How can a brain odemema be corrected

Answer 24

we can use mantitol
- it is a stable sugar alchol
- it is inetced intravasuclarlly so it increases the plasma osmolality
- increases osmotic pressure, so water moves back into circluation
- pulls water from intracellaur and transcualleu aplces
- which helps decreases intracranial haemmoraghe

Modern use: inhaled for cystic fibrosis management

it is also an osmotic diuretic because causes water to move out of the kidneys