Internal Environment and Homeostasis Flashcards Preview

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Flashcards in Internal Environment and Homeostasis Deck (34)
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1
Q

What percentage of the body is fluid (approximately)?

A

60%

2
Q

How is body fluid divided?

A

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
Q

Describe the basic composition of blood.

Approximately how much blood is there in the body?

A

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

Approximately 5L (7% of body weight).

4
Q

Describe the composition of ECF.

Approximately how much is there in the body?

A

Made up of:

  • Plasma (in blood) ~3L
  • Interstitial fluid (in spaces between cells) ~11L
  • Approximately 14L (20% of body weight)
5
Q

What is the difference between plasma and interstitial fluid?

A

Proteins

6
Q

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

A

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
Q

Describe the composition of ICF.

Approximately how much is there in the body?

A
  • ICF is separated from ECF by membranes highly permeable to water but impermeable to most electrolytes.
  • ~28L (40% of body weight)
8
Q

What is the ion concentration of potassium in ICF?

A

140mM

9
Q

What is the ion concentration of sodium in ICF?

A

15mM

10
Q

What is the ion concentraion of chloride in ICF?

A

5mM

11
Q

What is the ion concentration of potassium in ECF?

A

5mM

12
Q

What is the ion concentration of sodium in ECF?

A

140mM

13
Q

What is the ion concentration of chloride in ECF?

A

110mM

14
Q

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

A

Concentration of dissolved substances in the water

15
Q

Describe osmosis

A

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
Q

What is the osmolality of a fluid?

A

Osmoles / Kg

A measure of the number of osmotically active particles per kg

17
Q

What is the osmolarity of a fluid?

A

Particles / L

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

18
Q

Describe tonicity

A

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
Q

Describe isotonic ECF and ICF

A

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

20
Q

Describe hypertonic ECF and ICF

A

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

21
Q

Describe hypotonic ECF and ICF

A

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
Q

Some solutes can permeate the cell membrane.

What is an iso-osmotic solution?

A

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

23
Q

Some solutes can permeate the cell membrane.

What is a hyper-osmotic solution?

A

A solution with a higher osmolarity than usual ECF

24
Q

Some solutes can permeate the cell membrane.

What is a hypo-osmotic solution?

A

A solution with a lower osmolarity than usual ECF

25
Q

How is homeostasis maintained?

A

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
Q

Describe an open loop system

A
  • No feedback
  • Could result in runaway reactions
  • Controller → Controlled component → Output
  • The output is not influenced by the resulting conditions
27
Q

Describe a closed loop system

A
  • 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
Q

What is negative feedback?

A

Return to set point

29
Q

What is positive feedback?

A

Moves away from set point

30
Q

What is feedforward?

A

A response is generated in anticipation of a change

31
Q

Describe hunting in a negative feedback system

A
  • Negative feedback conrolls the system within limits
  • Over time, the process of hunting takes place within a safe limit, around a set point.
  • The depth and extent of hunting depends upon the properties of the elements of the feedback system.
  • The set point may be altered at times of metabolic or physiologic stress.
32
Q

Describe the body’s response to infection

A
  • Often, temperature increase (fever)
    • Results from increase in temperature set point
  • Bacteria / waste products phagocytosed by leukocytes (WBC)
  • Progens (cytokines) released
  • Binds at hypothalamus
  • Change in set point
33
Q

Describe the negative feedback control of arterial blood pressure

A
34
Q

What is gain?

A
  • The degree of effectiveness of the negative feedback control system
    • Gain = correction / error