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PHGY 209 > Body fluids > Flashcards

Body fluids Flashcards

1
Q

What is homeostasis?

A

The relative dynamic constancy of the internal environment

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2
Q

What is the difference between the internal environment and the external environment in the body?

A

IE: where the cells are located and must remain relatively constant/ balanced
EE: varies in terms of pressure, temperature, etc

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3
Q

Who is the father of physiology and what are his main observations?

A

Claude Bernard said that
1. The environment surrounding individual cells is vastly different from the external environment
2. The internal environment remains RELATIVELY CONSTANT under conditions of HEALTH

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4
Q

What is responsible for maintaining homeostasis in the body?

A

Organ systems [and their functional activities] maintain homeostasis and detects changes in order to adjust

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5
Q

What happens if homeostasis is not maintained?

A

Normal function is disrupted and disease occurs

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6
Q

What is the most abundant body fluid? what proportion of the body does it make up?

A

Water. It can make up anywhere between 45%-70% of total body mass depending of age, body composition, etc.

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7
Q

Name 2 reasons why body water is important at the micro scale.

A

It is…
1. Where metabolic reactions take place
2. The medium in which solutes are dissolved

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8
Q

Name 6 larger scale reasons why body water is important to the functioning of the individual

A
  1. Regulate body temperature
  2. Lubricate joints
  3. Moistens tissues [mouth, eyes, nose]
  4. Protection of organs
  5. Dissolves minerals and other nutrients to make them accessible to the body
  6. Carries nutrients and oxygen to cells
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9
Q

Name the main 5 sources of body water, whether they are high or low in body water percentage and if they vary significantly between individuals.

A

High in body water: Skin, muscles and organs (all have around 70-80%
Low in body water: Bone (25%) and Fat (10%)
Fat varies significantly between individuals

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10
Q

Explain why body water as a proportion of mass varies so much between individuals.

A

While solids in the body do not vary much between individuals adipose tissue does. Since it is low in water, individuals with more fat have a lower proportion of total body water than individuals with less fat.

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11
Q

Does body water vary among individuals? Explain why or why not.

A

Body water as a proportion of total body mass varies among individuals because the amount of fat they have will increase or reduce the proportion of water in their bodies.
However, water content as computed as a fraction of lean body mass, meaning with fat excluded, does not vary significantly among (similar) individuals.

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12
Q

Who is the physiological reference individual?

A

A 21 year old, white male with a 70 kg weight.

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13
Q

Name 3 factors that affect water content in the body and explain the trends they cause.

A

Age: Newborns have low amounts of fat and therefore a high body water %. As a child ages they add fat, decreasing their body water %. As we age, tissues become drier because we lose muscle mass in favour of connective tissue, which is drier. So as we get older, the proportion of body water goes down.

Sex: After puberty, females deposit more fat than males in the breast and buttocks region, leaving them with a lower body water proportion than males.

Weight: An overweight individual will have more fat and therefore a lower proportion of body water.

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14
Q

What is the formula to calculate the absolute amount of water an individual has in their body?

A

Absolute amount of water = (mass (kg) x % water)/100 = ?? kg = ?? L

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15
Q

Would you expect a female to have a higher or lower absolute amount of water in her body than male? Why?

A

She would have less water, since females have a higher proportion of fat.

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16
Q

Why is it important to know how much total body water we have?

A

It is necessary to properly administer water-soluble medication.

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17
Q

If you want to administer a water soluble medication in a proportion of 10 mg/7 kg to a 70 kg male with 60% body water, what concentration of medication will end up in his system?

A

Amount of water in his body: 70 kg x 0.60 = 42 L = 42,000 ml water
Amount of medication: 70 mg/7 kg x 70 kg = 100 mg medication
Final concentration: 100 mg/42,000 mL = 0.0024 mg/mL

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18
Q

The water in our body is in a state of dynamic constancy. Explain how this is the case.

A

The amount of body water must remain constant to stay in good health, but there is water turnover every day through exchanges with both the internal and external environment.

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19
Q

How do individuals remain in water balance?

A

Their intake of fluids must equal their output of fluids.

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20
Q

Name our major sources of water intake and explain them.

A

Oral fluid: drinking water
Oral intake as food: intake of the water that is in food
Oxidative water from metabolism: production of 6 molecules of water as a byproduct for every molecule of glucose broken down to produce energy

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21
Q

What is the difference between a sensible and an insensible OUTPUT of water? Give two examples of each.

A

A sensible loss of water is when we can feel/are conscious off the loss. For example, urination and defecation.

An insensible loss of water is when we are not aware of the loss and cannot feel it. For example, water loss of exhalation and through the skin.

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22
Q

What is the difference between obligatory and facultative water loss?

A

Obligatory water loss is the minimum amount of water that needs to be lost every day for the water to remain healthy. This loss will take place regardless of water intake.
Facultative water loss takes care of any excess water that needs to be excreted through the kidneys (urination), allowing us to remain in water balance. The quantity lost varies with intake.

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23
Q

Are insensible perspiration and sweating the same? Give 3 reasons why or why not.

A

No. They are not the same because:
1. IP consists of the release of pure water, while sweat contains electrolytes (salt)
2. IP takes place over the entire skin surface (not just sweat glands), while sweating occurs only through sweat glands
3. IP is continuous, while sweating is activated by heavy work or high temperatures

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24
Q

When an individual is in water balance, what proportion of the body weight is turned over in adults and infants? What accounts for the difference?

A

3-4% of total body weight in adults and 10% of body weight in infants. It is much higher in infants because they have a higher surface to mass ratio than adults, meaning that the water molecules are more easily released.

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25
Q

Why shouldn’t you give water to newborns?

A

They are very susceptible to water loss because of their high surface to mass ratio and because their electrolyte concentration can easily be diluted, since their kidneys are developing and cannot process very much water.

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26
Q

Name 2 reasons why it is important to maintain a constant body water volume.

A
  1. It helps maintain solute concentrations
  2. It helps maintain normal blood volume and pressure
    These both ensure that an adequate amount of oxygen reaches tissues.
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27
Q

What are the two ways in which water balance can be thrown off?

A

You can have a negative water balance if water loss > water intake
or
water intoxication if water intake > water loss.

28
Q

Name the 5 ways in which a negative water balance could happen.

A
  1. Reduced intake
  2. Excessive loss from gut
  3. Excessive sweating
  4. Excessive loss in expired air
  5. Excessive loss in urine
29
Q

Name the 2 ways in which water intoxication can occur.

A
  1. Excessive intake [kidneys get overwhelmed]
  2. Renal system failure
30
Q

Between a 70 kg male, a 70 kg female, and a 70 kg elderly person, who would you expect to require the biggest and the smallest dose of water-soluble medication? Why?

A

Since the male has more water, he would require the biggest dose of medication to have the same concentration of medications

31
Q

What percentage of body mass consists of water for the standard reference individual?

A

60% of body mass

32
Q

State the major compartments and subcompartments that make up body water.

A

2 major compartments: intracellular fluid (ICF), extracellular fluid (ECF)
ECF is subdivided into 2 major subcompartments and 2 minor subcompartments:
- Plasma (major)
- Interstitial fluid (ISF) (major)
- Lymph (minor)
- Transcellular fluid (minor)

33
Q

What proportion of total body water and total body mass do intracellular fluid and extracellular fluid make up (for the standard reference individual)?

A

ICF occupies 2/3 of total body water. Since total body water makes up 60% of body mass, ICF is 40% of body mass. ECF occupies 1/3 of total body water and therefore 20% of total body mass.

34
Q

What is the difference between intracellular fluid and extracellular fluid?

A

Intracellular fluid is all the fluid inside the cells of the body and extracellular fluid is the fluid that is moving around between cells of the body.

35
Q

In an individual with 42 L of body water total, how many litres of intracellular fluid and extracellular fluid are in their body?

A

ICF = 2/3 of total body water, so 2/3 of 42 = ~28 L
ECF = 1/3 of total body water, so 1/3 of 42 = ~14 L

36
Q

What is plasma?

A

Plasma is the fluid medium in which blood cells are suspended.

37
Q

What are the components of blood? How can we isolate them?

A

The three components of blood are red blood cells (erythrocytes), the buffy layer (consisting of white blood cells and platelets), and plasma. To isolate these things, we have to centrifuge blood.

38
Q

What is hematocrit (Ht)?

A

It is the percentage of blood volume that is occupied by red blood cells, also known as the packed cell volume. It can be thought of as the height of the erythrocyte column in centrifuged blood.

39
Q

What is the formula to calculate hematocrit?

A

Height of erythrocyte column/height of whole blood column

40
Q

How can the hematocrit value be used?

A

It can be used to calculate how much of the blood is composed of plasma. Plasma (% of blood) = 100% - hematocrit (%)

41
Q

What is the normal hematocrit value?

A

Around 45%

42
Q

What is the percent breakdown (% body mass) of the different compartments of extracellular fluid?

A

Of the 20% of body mass occupied by extracellular fluid, 15% is interstitial fluid and 5% is plasma.

43
Q

What is interstitial fluid?

A

It is the fluid that moves between cells in the body, making it the true “milieu interieur”.

44
Q

In a 70 kg male with 60% body water, how much interstitial fluid and plasma does he have?

A

0.6 x 70 kg = 42 L of body water total
ISF: 0.15 x 42 = 10.5 :
Plasma; 0.05 x 42 = 3.5 L

45
Q

Explain the interaction between the fluid in the capillaries, lymphatic system, and interstitial space.

A

The blood (plasma) flows through the capillaries and exits into the interstitial space, where it becomes interstitial fluid. Some interstitial fluid reenters the capillaries. Excess fluid gets picked up by the lymphatic system, at which point it becomes lymph (lymph does not exit at this point again - drains into the chest later).

46
Q

Explain what the lymphatic system is (briefly).

A

It is a network of terminal tubules that form larger lymphatic vessels, which themselves form lymphatic ducts. These ducts drain into the large veins in the chest.

47
Q

What proportion of the ECF does lymph volume make up?

A

About 1-2% of the ECF volume.

48
Q

What is trancellular fluid?

A

It is an aggregate of fluid found in specific areas of the body, secreted by specific epithelial cells and with specialized functions depending on the body part.

49
Q

Give 3 examples of trancellular fluid.

A
  1. Intraocular fluid (in the eye)
  2. Cochlear fluid (in the ear)
  3. Synovial fluid (in joints)
50
Q

What proportion of the ECF does transcellular fluid make up? How significant is transcellular fluid in the body as a whole?

A

It makes up less than 1-2% of the ECF volume. While it does not contribute significantly to overlal water, however, it is very important in local function.

51
Q

How does the total body fluid volume and the relative distribution of compartments vary within an individual (not over a long period of time)?

A

They both remain constant to remain in good health. That being said, there is always water movement between the compartments.

52
Q

What method is used to determine body fluid compartment volumes in an individual?

A

The indicator dilution method.

53
Q

Describe the 5 steps of the indicator dilution procedure

A
  1. Introduce a known quantity (Q) of indicator into the vein
  2. Allow time to equilibrate
  3. Remove known volume of blood, and centrifuge to obtain plasma
  4. Measure concentration (c) in unit volume of plasma
  5. Calculation V = Q/c
54
Q

Name 4 considerations when choosing an indicator for the indicator dilution process.

A
  1. Must be non-toxic
  2. Must be able to diffuse and distribute itself evenly throughout the compartments being measured
  3. It must induce no changes in the distribution of water between compartments (i.e. reduce permeability somewhere)
  4. Must be easy to measure
55
Q

If you want to measure the volume of total body water using the indicator dilution method, describe the key property of the indicator that must be chosen.

A

The indicator must be able to cross the capillary wall (dividing the plasma and the rest of the ISF) and the cell membrane to be able to get into both the whole ECF and the ICF.

56
Q

Given that you inject 50 ml of D2O into a man and find that, after some time, its concentration is 0.001 ml/ml plasma.
a) What body fluid compartments are we calculating for?
b) How much of that fluid is present in the man?

A

a) Total body water, because D2O can cross both the plasma membrane and the cell membrane.
b) 50/0.001 = 50,000 ml = 50 L

57
Q

If we want to measure only extracellular fluid volume using the indicator dilution method, what key property must the indicator have?

A

We need an indicator that can cross the plasma membrane into the interstitial fluid, but not cross the cell membrane into the intracellular fluid.

58
Q

If we wanted to measure the plasma volume using the indicator dilution method, what is the key property that the indicator would need?

A

The indicator would have to be unable to pass through the capillary wall or the cell membrane.

59
Q

What factors are not taken into consideration by the indicator dilution method calculation that would have to be taken into account in a clinical setting?

A

Fluid leaving the body by metabolism or excretion.

60
Q

How do you determine the volume of the intracellular fluid using the indicator dilution method? What key properties must the indicator have?

A

You can’t measure intracellular fluid directly. You have to first measure extracellular fluid, which requires an indicator that can pass through the capillary wall but not the cell membrane. Then, you would measure total body water using an indicator that can pass through both barriers. You would then find the difference between these two results to get the ICF.

61
Q

How do you measure the interstitial fluid volume using the indicator dilution method? What key properties must the indicator have? Give examples of possible indicators.

A

It cannot be directly measured. First, you would need to measure the total extracellular fluid volume using an indicator that can pass through the capillary wall but not the cell membrane. You would then have to calculate the volume of plasma using an indicator that can pass through neither barrier. You would then take the difference to find the interstitial fluid volume.

62
Q

If someone’s total plasma volume = 3L and their Hematocrit (Ht) = 40%, what is their total blood volume?

A

Plasma occupies 100-40 = 60% of the blood. 3 L = 60% of the blood, so (100x3)/60 = 5 L total.

63
Q

Explain the main ways in which the ICF and ECF vary in ionic composition.

A

ICF is high in potassium and magnesium and low in sodium and chloride.ECF is high in sodium and chloride and low in potassium.

64
Q

What is the difference in composition between interstitial fluid and plasma?

A

There are more or less the same except that plasma contains more proteins.

65
Q

How can extracellular fluid by artificially simulated if an individual needs their fluids replaced? Why does this work?

A

It can be simulated with a 0.9% NaCl solution, called physiological saline. This works because extracellular fluid is naturally high in Na and Cl.

PHGY 209 (5 decks)

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