Session 4: Fluid compartments and homeostatic mechanisms

Question 1

Define physiology in broad terms.

Answer 1

• Physiology explains the physical and chemical factors that are responsible for the origin, development, and progression of life.
• Each type of life has its own functional characteristics

Question 2

Expand on the concept of physiology to human physiology.

Answer 2

• It is an attempt to explain the specific characteristics and mechanisms of the human body that make it a living being.
• Physiology enables us to live.

Question 3

Define the concept of an internal environment inside the human body.

Answer 3

• About 60% of the human body is fluid
• The ECF makes up about 1/3 of fluid in the body
• The ECF is referred to as the internal environment
  (Milieu Interieur)
  
  • it’s in constant motion & mixed between blood and
    tissue fluids through diffusion
• Cells are able to live, grow and perform specialized
  functions as long as proper [ ] of O2, glucose, ions,
  amino acids are present.

Question 4

What is the need of a physiological man?

Answer 4

A standardized man to which we can compare

Question 5

What are the parameters for the physiological man?

Answer 5

• Ave. 70kg adult male

* Total body water = +- 60% of the bodyweight; about 42L

Question 6

What are the homeostatic mechanisms for a female?

Answer 6

45% solids
55% fluids
1/3 ECF
2/3 ICF
20% Plasma
80% Interstitial fluid

Question 7

What are the homeostatic mechanisms of a male?

Answer 7

40% solids
60% fluids
** the rest is the same

Question 8

Name and quantify 6 fluid compartments as found in the physiological man.

Answer 8

TBF- 42L

• ICF- 28L
• ECF- 14 L
  
  • IVF (plasma) - 3L
  • ISF (tissue fluid) - 11L
  • Transcellular fluid - 1-2L

Question 9

What 3 factors does TBF depend on?

Answer 9

1. Age
2. Obesity
3. Gender

Question 10

Briefly explain the indicator-dilution principle

Answer 10

The volume of a fluid compartment can be measured by placing an indicator substance in the compartment and allow it to disperse evenly throughout the fluid, then analyze to what extent the substance becomes diluted

• Conservation of mass principle applies
  [ ] = mg/ml
  V = ml

Question 11

Name 3 requirements necessary for a substance to qualify as an indicator for fluid volume determinations.

Answer 11

1. indicator disperses evenly
2. indicator only disperses in the compartment being measured
3. indicator does not metabolize

Question 12

Discuss the influence of age on TBF.

Answer 12

Age: older, % TBF decreases (due to increase in % fat which decreases H20%)
* in premies and newborns, TBF = 70-75%

Question 13

Discuss the influence of sex on TBF.

Answer 13

Women usually have more body fat than men, so have lower TBF

Question 14

Discuss the influence of obesity on TBF.

Answer 14

Obesity = less H2O% bc there’s more fat%

Question 15

Explain the constant mixing principle of interstitial fluid.

Answer 15

• Plasma is non-cellular
• Exchanges substances continuously w/ ISF thru pores
  of capillary membranes
• Pores are highly permeable to almost all solutes of
  ECF
• ECF and ISF are constantly mixing so plasma and ISF
  have about the same composition except for proteins.

Question 16

Define hematocrit.

Answer 16

Fraction of blood composed of red blood cells, as determined by centrifugation. ( Packed Red Blood Cell Volume)

Question 17

Give the normal hematocrit values for men and women.

Answer 17

Men: 0.40 / 40%
Women: 0.36 / 36%

The difference is due to testosterone which stimulates growth.

Question 18

Note the intra- and extracellular aspects of blood and explain the concept of compartmentalization by means of the hematocrit.

Answer 18

Blood consists of ECF and ICF, which then consists of plasma, wbc and rbc.

about 4% of plasma remains entrapped amongst cells so about only 96% of the measured is true hematocrit.

Question 19

Define homeostasis.

Answer 19

Maintenance of nearly constant conditions in the internal environment despite variations in the external environment.

Question 20

Explain what a homeostatic mechanism is.

Answer 20

Mechanism to maintain the internal systems of the body at equilibrium despite variations in the external environment.
Example: maintains fluid, temp., etc

Question 21

List three homeostatic mechanisms of the body and discuss the contribution of each towards homeostasis.

Answer 21

1. Musculoskeletal system: provides locomotion in order to obtain food
2. Respiratory system: ensures that the required O2 is diffused into the blood and CO2 is excreted
3. Nervous system: controls many internal organ functions, i.e pumping of the heart and secretion of glands