Body Water and Its Functions

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Questions and Answers

What percentage of total body weight does Total Body Water (TBW) represent for a male adult?

40%

60% (correct)

73%

50%

Which of the following is NOT a main function of body water?

Transport

Regulation of pH levels (correct)

Shape and form to cells

Solvent

In which fluid compartment is cerebrospinal fluid (CSF) found?

Intracellular fluid

Plasma

Interstitial fluid

Transcellular fluid (correct)

What is the primary cation found in intracellular fluid (ICF)?

Potassium (K) Signup and view all the answers

Which of the following fluids would be classified as interstitial fluid?

Fluid surrounding the cells Signup and view all the answers

What is the main role of the ionic difference between extracellular fluid (ECF) and intracellular fluid (ICF)?

It plays a role in neuronal signaling and muscle contraction. Signup and view all the answers

What is the calculated TBW for an adult male weighing 70 kg?

42 L Signup and view all the answers

Which of the following anions is NOT found in high concentrations in extracellular fluid?

Phosphate (HPO4) Signup and view all the answers

What is the primary function of extracellular fluid (ECF) in the body?

To provide essential nutrients and ions for cells Signup and view all the answers

What is the term for an abnormal increase of total body water?

Overhydration Signup and view all the answers

Which of the following variables is NOT homeostatically regulated?

Environmental humidity Signup and view all the answers

Why is it important to maintain a nearly constant internal environment?

For proper functioning of living cells Signup and view all the answers

What type of feedback mechanism promotes changes in the variable rather than opposing them?

Positive feedback Signup and view all the answers

Which component is NOT a factor that is regulated for homeostasis?

Muscle mass Signup and view all the answers

What is the setpoint for human body temperature in degrees Celsius?

37 oC Signup and view all the answers

What is the role of negative feedback in homeostatic control systems?

To maintain steady state around the set point Signup and view all the answers

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

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.