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Flashcards in Internal Environment and Homeostasis Deck (34)
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1

What percentage of the body is fluid (approximately)?

60%

2

How is body fluid divided?

Divided into compartments:

  • Approximately 70% of body fluid is within cells - ICF
  • Approximately 30% of body fluid is outwith cells - ECF
  • Compartments are spearated by membranes

3

Describe the basic composition of blood.

Approximately how much blood is there in the body?

Contains both ECF (plasma) and ICF (fluid in RBC).

Approximately 5L (7% of body weight).

4

Describe the composition of ECF.

Approximately how much is there in the body?

Made up of:

  • Plasma (in blood) ~3L
  • Interstitial fluid (in spaces between cells) ~11L
  • Approximately 14L (20% of body weight)

5

What is the difference between plasma and interstitial fluid?

Proteins

6

Why is there a higher conentration of proteins in plasma than interstitial fluid?

Plasma and interstitial fluid exchange substances through highly permeable capillary membranes, but:

  • Most proteins are too big to permeate the membrane so they are maintained in a higher concentration in plasma than in interstitial spaces. 

7

Describe the composition of ICF.

Approximately how much is there in the body?

  • ICF is separated from ECF by membranes highly permeable to water but impermeable to most electrolytes.
  • ~28L (40% of body weight)

8

What is the ion concentration of potassium in ICF?

140mM

9

What is the ion concentration of sodium in ICF?

15mM

10

What is the ion concentraion of chloride in ICF?

5mM

11

What is the ion concentration of potassium in ECF?

5mM

12

What is the ion concentration of sodium in ECF?

140mM

13

What is the ion concentration of chloride in ECF?

110mM

14

What determines the rate of osmosis (ie the net movement of water)?

Concentration of dissolved substances in the water

15

Describe osmosis

The process by which molecules of water pass through a semipermeable membrane from a less concentrated solution to a more concentrated one. 

 

Water molecules move randomly, so there is always some water movement in both directions in physiologic systems. 

16

What is the osmolality of a fluid?

Osmoles / Kg

 

A measure of the number of osmotically active particles per kg

17

What is the osmolarity of a fluid?

Particles / L

 

A measure of the number of osmotically active particles per litre.

18

Describe tonicity

The mechanical effects (eg on a cell) in terms of shrinkage or swelling caused by placing a cell in a solution of impermeant osmotically active particles. 

19

Describe isotonic ECF and ICF

Water concentration in ECF and ICF is equal; solutes cannot leave or enter; cell volume stays the same.

20

Describe hypertonic ECF and ICF

A cell in a solution with low water concentration and high concentration of impermeant particles; water diffuses out; the cell shrinks. 

21

Describe hypotonic ECF and ICF

A cell in a solution with high water concentration and lower concentration of impermeant particles; water diffuses into the cell; the cell swells (bursts).

22

Some solutes can permeate the cell membrane.

 

What is an iso-osmotic solution?

Solution with the same osmolarity as the cell, regardless of whether the solute can permeate the cell.

23

Some solutes can permeate the cell membrane.

What is a hyper-osmotic solution?

A solution with a higher osmolarity than usual ECF

24

Some solutes can permeate the cell membrane.

 

What is a hypo-osmotic solution?

A solution with a lower osmolarity than usual ECF

25

How is homeostasis maintained?

By control systems

  • Within cells
    • Genetics
  • Within / between tissues / organs / systems
    • Nervous system - quick response, short duration
    • Endocrine system - longer response, longer duration
  • Most control systems use negative feedback

26

Describe an open loop system

  • No feedback
  • Could result in runaway reactions
  • Controller → Controlled component → Output
  • The output is not influenced by the resulting conditions

27

Describe a closed loop system

  • Output of the system feeds back and influences the controller
  • Controller → Controlled component → Output → Sensor → Feedback → Controller
  • The output is influenced by the resulting conditions

28

What is negative feedback?

Return to set point

29

What is positive feedback?

Moves away from set point

30

What is feedforward?

A response is generated in anticipation of a change