Human Physiology Quiz on Body Water and Fluid

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Questions and Answers

What percentage of body weight does total body water represent in a typical adult?

20%

15%

40%

60% (correct)

Which ion is the main cation found in extracellular fluid (ECF)?

Ca++

K+

Na+ (correct)

Mg++

How much volume does intravascular plasma contribute to the total body water in an average adult?

11 L

5 L

14 L

3 L (correct)

What is the approximate osmolality of extracellular fluid?

300 mOsm/L Signup and view all the answers

Which of the following is NOT considered a component of the extravascular fluid?

Intravascular plasma Signup and view all the answers

What happens to the ICF volume when a hypertonic NaCl solution is injected?

ICF volume decreases, causing cells to dehydrate. Signup and view all the answers

Which of the following ions contributes most significantly to the cation composition of the ICF?

K+ Signup and view all the answers

What is the effect of a hypotonic NaCl solution on the cells?

Cells swell and may rupture due to excess water intake. Signup and view all the answers

Which of the following statements best describes the impact of isotonic solution injection?

It mainly increases ECF volume and can lead to edema. Signup and view all the answers

What is the primary reason for the lower pH in ICF compared to ECF?

Lower concentration of bicarbonates (HCO3-). Signup and view all the answers

What is the plasma volume calculated from an injected dye amount of 30 mg with a concentration of 0.01 mg/ml?

3000 ml Signup and view all the answers

Which characteristic of Evans blue dye makes it suitable for measuring plasma volume?

It is not adsorbed to red blood cells. Signup and view all the answers

Which method of measuring plasma volume is considered more accurate?

Isotope method Signup and view all the answers

What is the daily water intake through the oral route in milliliters?

1500 ml Signup and view all the answers

What is the primary source of exogenous water gain in the body?

Beverages consumed Signup and view all the answers

In normal conditions, which route accounts for the highest daily loss of body water?

Urine Signup and view all the answers

How much metabolic water is typically produced in the body per day?

200 ml Signup and view all the answers

During which conditions could urine output reach as high as 20 liters per day?

High water intake Signup and view all the answers

What primarily stimulates the thirst center in the hypothalamus?

Decreased blood pressure Signup and view all the answers

Which of the following is NOT a mechanism that increases thirst sensation?

Decreased osmolarity of fluids Signup and view all the answers

Where is the antidiuretic hormone (ADH) released from?

Posterior pituitary gland Signup and view all the answers

What physiological condition would lead to the activation of the thirst center due to hypertonicity?

Increased solute concentration in blood Signup and view all the answers

Which of the following correctly describes insensible perspiration?

It occurs through diffusion and is not related to sweat glands. Signup and view all the answers

Which statement about peripheral mechanisms of thirst is accurate?

They result in stimulation via the vagus nerve. Signup and view all the answers

Which fluid losses mentioned do NOT increase significantly with severe diarrhea?

Skin perspiration Signup and view all the answers

Study Notes

Course Information

Faculty: Medicine
University: Helwan National University
Academic Year: 2024-2025
Year: 1
Semester: 1
Module: Blood and Body Fluids (BLF) 103

Body Fluid and Water Balance - Objectives

Students will be able to identify the distribution of water in the body.
Students will be able to compare and contrast extracellular fluid (ECF) and intracellular fluid (ICF).
Students will be able to identify the fluid exchange between ECF and ICF.
Students will be able to determine the volumes of specific body fluid compartments.
Students will be able to list water gain and water loss.
Students will be able to describe the control of water balance.
Students will be able to describe the forces involved in the formation and drainage of tissue fluid.

Introduction

In young adult males, body water constitutes 60% of body weight (approximately 42 liters in a 70 kg individual).
This percentage varies based on age, sex, and obesity.
In older individuals, there is a decrease in the percentage of body water due to increased fat.
Females typically have a slightly lower percentage of body water than males due to higher body fat content.
Obese individuals have a lower body water percentage (45%).
Body fat is relatively free of water.

Body Fluids Distribution

Intracellular fluid (ICF) is about ⅔ of total body water (TBW), approximately 28 liters (40% of body weight) in a 70 kg individual.
Extracellular fluid (ECF) is about ⅓ of TBW, approximately 14 liters (20% of body weight) in a 70 kg individual.
- Intravascular fluid (plasma): 3 liters (5% of body weight).
- Extravascular fluid: 11 liters (15% of body weight).
  - Interstitial fluid (ISF, tissue fluid): 11 liters.
  - Transcellular fluids: fluids in the joints, pleura, peritoneum, cerebrospinal fluid, intraocular fluid, etc.
The blood volume in an adult is approximately 5 liters (8% of body weight).

ECF and ICF Composition

ECF:
- Main cation: Na⁺ (142 mEq/L)
- Main anion: Cl⁻ (106 mEq/L)
- Other cations: K⁺ (4 mEq/L), Ca²⁺ and Mg²⁺ (small amounts)
- Other anions: HCO₃⁻ (24 mEq/L), proteins, HPO₄²⁻, SO₄²⁻ (small amounts)
- Non-electrolytes: glucose, cholesterol, urea, uric acid, creatinine, bile pigments, phospholipids
- pH: ~7.4
- Osmolarity: ~300 mOsm/L
ICF:
- Main cations: K⁺ (140 mEq/L), Mg²⁺ (58 mEq/L), Na⁺ (14 mEq/L), Ca²⁺ (small amount)
- Main anions: HPO₄²⁻, proteins (40-45 mEq/L), Cl⁻, HCO₃⁻, SO₄²⁻ (small amounts)
- pH: ~7.0
- Osmolarity: ~300 mOsm/L (similar to ECF)

Fluid Exchange

Fluid continuously exchanges across cell membranes, maintaining similar osmolality in ECF and ICF.
Hypertonic NaCl Injection: Water moves from ICF to ECF, causing cell dehydration and shrinking.
Hypotonic NaCl Injection: Water moves from ECF to ICF, causing cell swelling and potentially rupture.

Fluid Volume Measurements

Using indicator dilution principle:
- Inject a known amount of a substance that will be distributed in the body water.
- Measure the concentration of the indicator in the plasma.
- Calculate the total volume of body water by dividing the injected amount by the concentration in the plasma.
TBW: Uses substances that cross both cell membranes (Deuterium oxide (D₂O), Tritium oxide (H₂O), Aminopyrine).
ECF: Uses substances that do not cross cell membranes (inulin, mannitol).
ICF: Calculated as TBW - ECF.
Interstitial fluid (ISF): Calculated as ECF - plasma volume

Water Balance

The body regulates its water content through a balance of water gain and water loss.
Water Gain:
- Exogenous: from drinking and food (2100 ml/day)
- Endogenous: metabolic processes (200 ml/day)
Water Loss:
- Urinary excretion (1400 ml/day): varies with hydration and climate.
- Skin: (insensible perspiration/sweating)
- Lungs: exhaled air.
- Fecal excretion.

Control of Water Balance

Water Gain Control: Primarily regulated by thirst, an organic sensation triggered by changes in plasma volume or osmolality.
Water Loss Control: Primarily regulated by the antidiuretic hormone (ADH), influencing water reabsorption in the kidneys.
- Stimulated by hypovolemia and hypertonicity.
- Inhibited by hypervolemia and hypotonicty.

Tissue Fluid Formation

Interstitial fluid (ISF) is continuously formed and drained by blood capillaries.
Composition mirrors plasma, excluding large plasma proteins.
Forces influencing fluid movement across capillary walls:
- Capillary blood pressure
- Plasma osmotic pressure (oncotic pressure)
- Interstitial fluid hydrostatic pressure
- Interstitial fluid osmotic pressure

Additional Notes

The numerical values presented in this document are estimations and can vary among individuals.
Specifics such as blood pressure and volumes can differ significantly depending on individual factors such as age, health, and activity level.

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Description

Test your knowledge on the physiological aspects of body water in adults. This quiz covers topics such as the composition of total body water, the effects of different saline solutions on cells, and the characteristics of extracellular and intracellular fluids. Perfect for students studying human physiology or related fields.