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Questions and Answers
What percentage of total body weight does Total Body Water (TBW) represent for a male adult?
Which of the following is NOT a main function of body water?
In which fluid compartment is cerebrospinal fluid (CSF) found?
What is the primary cation found in intracellular fluid (ICF)?
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Which of the following fluids would be classified as interstitial fluid?
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What is the main role of the ionic difference between extracellular fluid (ECF) and intracellular fluid (ICF)?
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What is the calculated TBW for an adult male weighing 70 kg?
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Which of the following anions is NOT found in high concentrations in extracellular fluid?
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What is the primary function of extracellular fluid (ECF) in the body?
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What is the term for an abnormal increase of total body water?
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Which of the following variables is NOT homeostatically regulated?
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Why is it important to maintain a nearly constant internal environment?
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What type of feedback mechanism promotes changes in the variable rather than opposing them?
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Which component is NOT a factor that is regulated for homeostasis?
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What is the setpoint for human body temperature in degrees Celsius?
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What is the role of negative feedback in homeostatic control systems?
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Study Notes
Body Water
- Total Body Water (TBW) represents about 60% of total body weight.
- TBW varies with age, sex, and body composition.
- Infants: 73%
- Male adults: 60%
- Female adults: 40-50%
- Older adults: 45%
Functions of Body Water
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Main Functions:
- Solvent for various substances.
- Transports substances within the body.
-
Other Functions:
- Provides shape and form to cells.
- Regulates body temperature.
- Lubricates joints.
- Cushions body organs (e.g., cerebrospinal fluid for the central nervous system).
Fluid Compartments
-
Extracellular Fluid (ECF):
- Plasma: Fluid component of blood.
- Interstitial fluid: Fluid surrounding cells.
- Transcellular fluid: Fluid within specific body cavities, including:
- Cerebrospinal fluid
- Intraocular fluid
- Pleural fluid
- Peritoneal fluid
- Synovial fluid
- Digestive secretions
- Intracellular fluid (ICF): Fluid within cells.
Body Water Distribution
- Total Body Water (TBW) is distributed among the intracellular, interstitial, and plasma fluid compartments.
- In a 70 kg adult male, TBW is approximately 42 liters.
- Interstitial fluid surrounds and bathes cells.
- Transcellular fluid fills spaces between epithelial linings.
Composition of Body Fluids
-
Cations (mmol/l):
- Plasma: High in sodium (Na+)
- Interstitial fluid: High in sodium (Na+)
- Intracellular fluid: High in potassium (K+)
-
Anions (mmol/l):
- Plasma: High in chloride (Cl-) and bicarbonate (HCO3-)
- Interstitial fluid: High in chloride (Cl-) and bicarbonate (HCO3-)
- Intracellular fluid: High in phosphate (HPO4-)
- There are special mechanisms maintaining the ionic differences between ECF and ICF, which play crucial roles in neuronal signaling and muscle contraction.
- ECF provides essential nutrients and ions for cell function.
- ECF continuously circulates throughout the body, transported in blood vessels and diffusing through capillary walls.
Normal Daily Inputs and Outputs
-
Input (mL):
- Drinks: 1500 mL
- Food: 750 mL
- Metabolic water: 350 mL
- Total Input: 2600 mL
-
Output (mL):
- Urine: 1500 mL
- Faeces: 100 mL
- Lungs: 400 mL
- Skin: 600 mL
- Total Output: 2600 mL
Water Balance
- Water balance: Input equals output.
- Dehydration: Abnormal reduction in body fluid volumes.
- Overhydration: Abnormal increase in total body water.
Homeostasis
- Homeostasis is the maintenance of a relatively constant internal environment (a dynamic steady state).
- The internal environment is primarily represented by the extracellular fluid.
- Homeostasis is achieved through constant adjustments in response to changes in the internal environment.
Components of Homeostatic Control Systems
- Homeostatic control systems operate by negative feedback, where the action taken opposes the change in the variable.
- Negative feedback helps maintain a steady state by keeping the variable around the set point.
Water Balance
- Water balance is a critical aspect of homeostasis.
Positive Feedback
- Positive feedback reinforces or amplifies the change in a variable.
- It does not typically promote homeostasis and can lead to a potentially dangerous vicious cycle.
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Description
This quiz explores the concept of Total Body Water (TBW), its significance in body composition, and the various compartments of body fluids. It covers the essential roles of body water in transporting substances, regulating temperature, and providing support to organs. Test your knowledge on the crucial aspects of body water in human physiology.
