Human Body Composition Flashcards
1
Q
2 major fluid compartments of the body
A
Intracellular fluid (ICF) Extracellular fluid (ECF)
2
Q
2 subcompartments of the ECF
A
Intravascular
Interstitial (extravascular)
3
Q
Percent of body weight occupied by water in an average man
A
60%
4
Q
Percent body weight occupied by ICF
A
40%
5
Q
Percent body weight occupied by ECF
A
20%
6
Q
Percent body weight occupied by water in old age
A
50%
7
Q
Percentage of ECF water in the interstitial compartment
A
75 - 80%
8
Q
Percentage of ECF water in the vascular compartment
A
20 - 25%
9
Q
Name of fluid in the intravascular compartment
A
Plasma
10
Q
Via which compartment does water enter and leave the body?
A
Intravascular compartment
11
Q
What determines the volume of water that ends up in a given compartment?
A
Osmotic pressure (the number of osmotically active particles within) Intravascular hydrostatic pressure
12
Q
Define an osmole
A
The number of osmotically active particles in a solution
13
Q
Define an osmotically active particle
A
A dissolved molecule (solute) that cannot penetrate through a water-permeable membrae
14
Q
Semi-permeable membrane separating the ECF and ICF
A
Cell membrane
15
Q
4 naturally occurring molecules that can freely penetrate cell membranes
A
Oxygen
Carbon dioxide
Water
Urea
16
Q
Solute composition of the ICF
A
Sodium and chloride = very low
Potassium, magnesium and phosphate = very high
Protein = very high (approx. 200 g/L)
17
Q
Solute composition of the ECF
A
Sodium = high (140 mmol/L) Chloride = high (105 mmol/L) Potassium = very low (4 mmol/L) Protein = very low (relative to ICF)
18
Q
Semi-permeable membrane separating the interstitial and intravascular compartments of the ECF
A
Capillary wall
19
Q
2 components of the bloodstream
A
Fluid (plasma)
Cells (blood cells)
20
Q
What do the capillaries retain in their lumen (despite being porous)
A
Blood cells
High molecular weight proteins
21
Q
One of the main reasons why capillaries retain high molecular weight proteins
A
To create an osmotic pressure to counter-balance the hydrostatic pressure that would otherwise force plasma water out of them into the interstitial compartment and deplete the intravascular compartment
22
Q
Approximate hydrostatic pressure inside the capillaries relative to the arterial pressure
A
Considerably less than half (but far from zero)
23
Q
Pressure in the interstitial compartment
A
Approximately zero
24
Q
Define colloid oncotic pressure
A
Inward directed osmotic pressure (in the capillaries)
25
WHat exerts the colloid oncotic pressure?
The concentration difference of high molecular weight proteins across the capillary wall
26
Main high molecular weight protein in the capillary responsible for the colloid oncotic pressure
Albumin
27
Define the hematocrit
Content of blood occupied by red blood cells (40% normally)
28
Percentage of blood occupied by plasma
60%
29
Most acutely critical body compartment
Intravascular compartment
30
Purpose of the interstitial compartment in terms of water balance
Buffer to minimize volume fluctuations in the intravascular compartment (since it is a zero pressure system)
31
Speed of equalization between the ECF sub-compartments' osmolarity and why
Rapid (minutes) because the ECF's main osmoles (sodium and chloride) permeate easily through the capillary wall
32
Speed of equalization between the ECF and ICF osmolarity and why
Long (hours) because it occurs as a result of water shifts alone
33
Standard osmolarity of all fluid compartments at equilibrium
300 mOsm/L
34
Normal serum sodium concentration
140 mmol/L
35
Importance of serum sodium concentration measurement
Indication of osmolarity in all of the fluid compartments
36
What fluid does the intracellular compartment contain
Water inside the body's cells (mostly skeletal muscle cells)
37
Anatomic correspondence of the intracellular compartment
Body cell mass (BCM)
38
Reason why the volume of the ICF compartment is large
1) A lot of cells in the body
| 2) These cells exert a strong osmotic pressure
39
Why do the cells of the body exert a strong osmotic pressure?
High concentrations of potassium, magnesium, phosphate and soluble proteins
40
Define a hypotonic solution
Solution that has a relatively low osmolarity
41
Define a hypertonic solution
Solution that has a relatively high osmolarity
42
Effect of putting a cell in a hypotonic environment
Unequal osmotic pressures will drive water into the cell --> swell to a larger volume
43
Effect of putting a cell in a hypertonic environment
Unequal osmotic pressures will drive water out of the cell --> shrink in size
44
Define simple dehydration
A medical condition accompanying hypertonicity of the body's fluid compartments
45
Define relative dehydration
A disproportionately large amount of sodium in relation to the volume of water in the ECF (hyperosmolarity)
46
Define hypernatremia
Abnormally high serum sodium concentration
47
Most frequent cause of simple dehydration
Failure or inability of the patient to drink enough water to compensate for body losses of water
48
Key symptom pointing to relative dehydration
Thirst
49
2 clinical symptoms and signs of moderate dehydration (thirst aside)
Lethargy
| Uneasiness
50
Cause of symptoms in severe dehydration
Shift of water out of brain cells --> shrink them enough to depress consciousness and cause coma and death
51
Water buffer for the ECF compartment
ICF
52
Effect of simple dehydration on ECF osmolarity
Hyperosmolarity
53
Effect of ECF hyperosmolarity on fluid distribution
Shift water from the ICF into the ECF --> protect from drastic depletion
54
Define simple (ECF) volume depletion
A roughly iso-osmolar loss of electrolytes and water from the ECF
55
2 common causes of volume depletion
Severe diarrhea
| Protracted vomiting
56
Intravascular compartment effects of a lowered ECF volume (acutely)
Reduced volume
| Lowered arterial blood pressure
57
Compensatory response to reduced intravascular volume
Increased HR to maintain the rate of blood flow through the circulation
58
Describe the compensatory response in SUBTLE forms of ECF depletion and the importance of this
HR accelerates only upon assuming an upright position. Measurement of BP and HR, first on lying, then upright posture = important diagnostic maneuver
59
Describe the physical manifestation of low venous pressure
Veins that are normally visible, such as jugular veins, become undetectable
60
Describe the contribution to ECF depletion by each of its compartments
Interstitial fluid volume and intravascular volumes decrease together, but most decrease occurs in the interstitial
61
Place in the body to examine the interstitial compartment
Skin
62
Describe the skin of a patient with normal interstitial fluid volume
Juicy
63
Medical term for skin juiciness
Turgor
64
Describe decreased skin turgor
If you pinch up the skin over the deltoid muscle or sternum or a patient who is volume depleted, the pinched up skin will remain tented, like putty, for a few moments
65
Describe the mouth of a person with volume depletion
Small pool of saliva normally present under the tongue disappears
66
Urine excretion under volume depletion
Decreased (compensatory mechanism)
67
2 signs and symptoms of a baby experiencing volume depletion
Dry diaper
| Crying without tears
68
Consequence of blood volume falling >50%
Inability to perfuse organs adequately
69
Define hypovolemic shock
Inability to perfuse organs adequately
70
Earlier stage of shock
Pre-shock
71
Define pre-shock
An important and dangerous intravascular volume depletion (>15% of blood volume)
72
5 symptoms and signs of pre-shock
```
BP very low
HR very fast
Collapsed veins
Reduced (or zero) urine output
Patient feels terrible
```
73
Body's response to severe toxic-inflammatory states
Cytokines and hormones are released from certain cells to make the capillary wall much more permeable to large molecular weight proteins
74
Consequence on serum albumin in the event of toxic-inflammatory states
Albumin can diffuse out of the vascular compartment --> interstitial compartment --> patient's serum albumin concentration decreases dramatically (NOTE: total albumin unchanged in ECF, just redistributed)
75
Reliable indicator of tissue damage and systemic inflammation
Hyperalbuminemia
76
Define over-hydration
Decreased serum sodium per L of plasma
77
When can over-hydration AND hypovolemia occur together?
In a patient who has been experiencing ECF depletion for a long enough time for their body to sense their low ECF volume and respond by sending a thirst signal to induce them to drink more water. Kidney also reabsorbs more free water.
78
Why does the body allow over-hydration to occur in the setting of hypovolemia?
The body permits its fluid compartments to become hypo-osmolar because its survival priority is preservation of the intravascular volume
79
Amount of water that the skin can soak up and release without visible change
2 - 3 kg (10 pounds)
80
The most sensitive way to detect small changes in the ECF volume
Record and follow the patient's weight
81
Characteristic and specific sign of ECF excess
Palpable and usually visible accumulation of fluid within and under the skin (edema)
82
Most dangerous consequence of over-expansion of the total ECF compartment
Intolerable over-expansion of the intravascular compartment
83
4 signs and symptoms of over-expansion of the intravascular compartment
Feeling of distress
Normal (or above-normal) BP
Swollen veins (high venous pressure)
Expanded interstitial compartment (edema)
84
2 commonest settings for ever-expansion of the intravascular compartment
```
Acute RHF
Acute LHF (--> pulmonary edema)
```
85
Define effusion
Abnormal accumulation of fluid in potential spaces of the body (i.e. pleural space or pericardium)
86
Define ascites
Excessive ECF accumulation in the abdomen (peritoneum)
87
Define transudate
An effusion with the chemical composition of normal interstitial fluid (same electrolyte pattern and a LOW protein concentration)
88
Cause of transudates
Pathological expansion of the ECF compartment, developing from an increased outward hydrostatic P, negative interstitial tissue P, and decreased plasma oncotic P
89
Define exudate
Protein-rich and often cell-rich outpouring of inflammatory fluid
90
Cause of exudate
Infection or tissue damage
91
4 anatomic compartments of the human body
Fat
Non-fat soft tissues (body cell mass)
Extracellular fluids
Structural compartment (skeleton and associated connective tissue)
92
Define the body cell mass
Hydrated, metabolically active protein tissues of the body
93
Approximate percent body weight occupied by bones and supporting extracellular ligaments and structural protein
20%
94
Ideal percent of body weight occupied by fat
20% in men
| 30% in women
95
Most variable compartment
Fat
96
Two techniques to determine contribution of pure fat to total body weight
Densitometry
| Measuring total body water (isotope dilution or bioelectrical impedance analysis)
97
Describe densitometry
Measurement of total body fat by relying on different densities of pure fat (0.900 kg/L) and the rest of the body (1.100 kg/L). Every density in between these boundaries corresponds to a unique fraction of fat/total body weight
98
Differentiate between pure fat and the fat seen and felt on a person
Adipose tissue = physical fat, comprised of 85% pure fat and 15% water
99
For precise calculations of body fat loss, what must one consider?
The 15% of body water that accompanies any important change in pure fat
100
Equation for BMI
Weight (kg) / height^2 (m)
101
Conversion from kg to lbs
1 kg = 2.2 lbs
102
Conversion from inches to cm
1 inch = 2.54 cm
103
2 exceptions to BMI
1) Professional athletes and body builders may have an abnormally high muscle mass and low fat, but high BMI
2) ECF compartment expansion or depletion under pathological conditions
104
Define BMI >25
Implies that the body's fat content is greater than normal
105
Define BMI <18 - 20
Implies the body's fat content is below normal
106
Define BMI >30
Association with increasing health risk that increases in rough proportion to the increase in BMI
107
Approximate percent of BCM occupied by skeletal muscle
80%
108
Define the peripheral protein store
Portion of the BCM containing skeletal muscle
109
Approximate percent of BCM occupied by all other non-adipocyte cels of the body (i.e. organs, bone marrow, blood cells)
20%
110
Define the central/visceral protein store
Proteins from the portion of the BCM containing organs, blood cells and bone marrow (non-adipocyte cells that are non-skeletal muscle)
111
When does BCM decrease
Muscle mass loss
112
Define BCM loss of >10 - 15%
Association with reduced strength and a variety of physiological derangements
113
Define BCM loss of >25%
Association with severe disability and an increased risk of death from several possible complications
114
Define BCM loss of >45%
Commonly incompatible with survival
115
Most important way to assess a patient's BCM
Examine their muscle groups
116
Method to measure the rate of change of BCM
Calculate changes in body nitrogen content
117
Percent weight of protein occupied by nitrogen
16%
118
1 g of N lost corresponds to what mass of protein lost?
6.25 g of protein
119
1 g of protein lost corresponds to what mass of normally hydrated lean tissue lost?
5 g
120
Equation for the estimation of daily N output
Urinary urea N excretion : 2 g N (urinary non-urea N) + 2 g fecal N
121
Define sarcopenia
The decrease of muscle mass with age (old people's fat mass tend to increase)
