Intro to Medical sciences and Homeostasis 2

Question 1

What are homeostatic reflexes represented by?

Answer 1

Reflexes (automatic responses we don’t think about) - may be neural and or hormonal

Question 2

What do these homeostatic reflexes maintain?

Answer 2

Can be simple or complex.

O2 and CO2 levels, water and ion balance, blood pressure and blood volume, nutrient levels and more….

Question 3

How much body weight does water make up?

Answer 3

~ 60%

Question 4

Why is homeostatic maintenance of water crucial?

Answer 4

Water affects the concentration of everything else in the body (water gets/has access to everywhere so affects conc of everything)

Question 5

On average how much water do you gain and lose a day?

Answer 5

2.5 litres for both

Whet we gain we must lose. What we lose we must replace.

Question 6

What happens if you gain more water than you lose?

Answer 6

swell up, bloated.

Question 7

What happens if you lose more water than you gain?

Answer 7

shrivel up like a prune

Question 8

Which processes are regulated in order to maintain water balance?

Answer 8

Input regulated by thirst mechanism.

Output regulated by kidney function (urinary losses)

Question 9

Are other process regulated to maintain water balance?

Answer 9

Some processes that ALTER water balance are also regulated but their control isn’t aimed at maintaining water balance eg. sweating is controlled as a part of temp regulation, so possible conflict between water and temp regulation.

Question 10

Where is the water in our body?

Answer 10

Split between 3 compartments: 
1. Intracellular fluid (ICF)
2. Interstitial fluid (fluid component between cells)
3. Plasma (fluid component of blood)  
ISF and plasma = Extracellular fluid ECF

Question 11

Is ECF important?

Answer 11

The body can survive only as long as the composition of the ECF is maintained in a state compatible with the survival of its individual cells i.e. composition of the ECF is very, VERY important.

Question 12

What do “normal” values refer to?

Answer 12

average 70kg 21 year old male

Question 13

What is the capillary wall permeable to?

Answer 13

Everything but plasma proteins and blood cells

Question 14

What is the difference between ISF and plasma?

Answer 14

Plasma proteins and blood cells.

Very similar apart from plasma contains plasma proteins which can’t cross capillary wall into ISF

Question 15

Total body water is 42L - describe how it splits between 3 compartments in figures

Answer 15

Plasma - 3L
ISF - 11L
so ECF = 14L 
ICF = 28 L
Twice as much ICF as ECF.

Question 16

What is the ratio of ICF to ECF for water or a drug that freely crosses the membrane?

Answer 16

1/3 ECF : 2/3 ICF

Question 17

What is plasma?

Answer 17

The fluid component of blood.

Question 18

What is the dilution principle?

Answer 18

c=m/v so v=m/c

Question 19

What Compartments can be measured directly using the Dilution Principle?

Answer 19

1. Plasma Volume (PV)
2. Extracellular Volume (ECF)
3. Total Body Water (TBW)
   other compartments measured indirectly