Human Body Water Content and Fluid Compartments

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Questions and Answers

What is the body water content in infants?

73% or more

What is the water content of adult males?

60%

What does water content decline to in old age?

45%

What causes the drop in water content related to those of old age?

Fat and muscle loss Signup and view all the answers

What happens to the brain's thirst center in old age?

It declines Signup and view all the answers

What is the average total body water content in adults?

40 L Signup and view all the answers

What is the least hydrated of all tissue types?

Adipose tissue Signup and view all the answers

What are the two main fluid compartments in the body?

Extracellular fluid compartment (ECF) Signup and view all the answers

What is intracellular fluid (ICF)?

Fluid inside cells that accounts for 2/3 of total body fluid Signup and view all the answers

What is the average amount of plasma in the body?

3 L Signup and view all the answers

What is interstitial fluid?

Fluid found in the spaces between cells, accounting for 12 L Signup and view all the answers

What is also considered part of interstitial fluid (IF)?

Lymph, CSF, humors of the eye, synovial fluid, serous fluid, and gastrointestinal secretions Signup and view all the answers

What is the universal solvent?

Water Signup and view all the answers

What are substances dissolved in water called?

Solutes Signup and view all the answers

How are solutes classified?

Electrolytes Signup and view all the answers

What are mostly organic molecules?

Nonelectrolytes Signup and view all the answers

Do nonelectrolytes dissociate (break apart) in water?

False Signup and view all the answers

What are examples of nonelectrolytes?

Glucose, lipids, creatinine, and urea Signup and view all the answers

Do nonelectrolytes create charged particles?

False Signup and view all the answers

What dissociates into ions in water?

Electrolytes (inorganic salts, all acids and bases, and some proteins) Signup and view all the answers

What do ions conduct?

Electrical current Signup and view all the answers

Electrolytes have a greater osmotic power than what?

Nonelectrolytes Signup and view all the answers

What do electrolytes have a greater ability to cause?

Fluid shifts Signup and view all the answers

NaCl --> Na+ + Cl-

Electrolyte; 2 particles Signup and view all the answers

MgCl2 --> Mg2+ + 2Cl-

Electrolyte; 3 particles Signup and view all the answers

Glucose --> glucose

Nonelectrolyte; 1 particles Signup and view all the answers

Each fluid compartment has a distinctive pattern of electrolytes.

True Signup and view all the answers

What is the electrolyte content of ECF?

Similar except for higher protein and lower Cl- Signup and view all the answers

What is the major cation in ECF?

Na+ Signup and view all the answers

Study Notes

Body Water Content

Infants have 73% or more water due to low body fat and bone mass.
Adult males have 60% water.
Adult females have 50% water due to higher fat content and less skeletal muscle mass.
In old age, water content declines to 45% due to fat and muscle loss.
The brain's thirst center also declines in old age.
Average total body water content in adults is 40 L.
Adipose tissue is the least hydrated tissue type.

Fluid Compartments

Two main fluid compartments: Intracellular fluid (ICF) and Extracellular fluid (ECF).
ICF: Fluid inside cells; accounts for 2/3 of total body fluid.
ECF: Fluid outside cells; accounts for 1/3 of total body fluid.
Average plasma volume: 3 L.
Interstitial fluid: 12 L in spaces between cells; includes lymph, cerebrospinal fluid, eye humors, synovial fluid, serous fluid, and gastrointestinal secretions.

Solutes in Body Fluids

Solutes are dissolved substances in water.
Solutes are classified as electrolytes or nonelectrolytes.
Nonelectrolytes: Primarily organic molecules; do not dissociate in water (e.g., glucose, lipids, creatinine, urea).
Electrolytes: Inorganic salts, acids, bases, and some proteins; dissociate into ions in water and conduct electrical current. Electrolytes have greater osmotic power and cause more significant fluid shifts than nonelectrolytes. (e.g., NaCl, MgCl2)

Electrolyte Concentrations

ECF: Higher Na+ and Cl- concentrations; similar electrolyte contents in interstitial fluid and plasma except for higher protein and lower Cl- content in plasma.
ICF: Higher K+ and HPO42- concentrations; lower Na+ and Cl- concentrations. More soluble proteins are present in ICF than in plasma.

Water Balance

Water intake must equal water output (~2500 ml/day).
Water intake: Primarily from ingested foods and beverages; a small amount from metabolic water (water of oxidation).
Water output: Urine (60%), insensible water loss (skin and lungs), perspiration, and feces.
Osmolality: Concentration of solute particles per kilogram of water (maintained around 280-300 mOsm).
Increased osmolality stimulates thirst and ADH release; decreased osmolality inhibits ADH release.

Thirst Regulation

The hypothalamic thirst center is the driver for water intake.
Osmoreceptors in the hypothalamus detect changes in ECF osmolality and activate the thirst center.
Triggers for thirst include increased plasma osmolality (1-2%), dry mouth, decreased blood volume/pressure, and angiotensin II or baroreceptor input.
Inhibitory signals for thirst include drinking, stomach/intestinal stretch receptor activation.

ADH Regulation

ADH (antidiuretic hormone) release is proportional to water reabsorption in the collecting ducts.
Decreased ADH leads to dilute urine and decreased body fluid volume.
Increased ADH leads to concentrated urine and increased body fluid volume.
Osmoreceptors sense ECF solute concentration to regulate ADH levels.
Blood volume/pressure changes also trigger ADH release.

Electrolyte Balance

Electrolyte balance primarily refers to salt balance (also includes acids, bases, and some proteins).
Salts control fluid movements, provide minerals for excitability, secretory activity, and membrane permeability.
Salts enter the body through ingestion and metabolism, and leave via perspiration, feces, urine, and vomit.
Sodium (Na+) is the most abundant cation in ECF.
Changes in Na+ levels affect plasma volume, blood pressure, and ECF/IF volumes.

Sodium Regulation

Na+ balance, linked to blood pressure and volume control; regulated via neural and hormonal controls.
Aldosterone is the primary kidney hormone regulating Na+ levels (has slow effects, hours to days).
Triggers for aldosterone release are the renin-angiotensin-aldosterone mechanism.
Atrial natriuretic peptide (ANP) decreases blood pressure and volume, reducing Na+, ADH, renin, and aldosterone production. ANP increases Na+ and water excretion and promotes vasodilation.
Cardiovascular baroreceptors trigger sympathetic nervous system responses to decrease blood volume/pressure if elevated.

Potassium Regulation

Potassium (K+) is crucial for resting membrane potential (RMP) in neurons and muscle cells, especially cardiac muscle.
Hyperkalemia (increased ECF K+) reduces RMP, decreasing excitability.
Hypokalemia (decreased ECF K+) causes hyperpolarization, reducing responsiveness.
K+ shifts in and out of cells opposite in direction with H+ to maintain cation balance.

Hormonal Influences on Electrolyte Balance

Estrogen increases NaCl reabsorption ("similar" to aldosterone), leading to water retention in the menstrual cycle and pregnancy.
Progesterone decreases Na+ reabsorption and promotes Na+ and water loss.
Glucocorticoids (cortisol) increase Na+ reabsorption, promoting edema.

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Description

This quiz explores the distribution of water in the human body across different life stages and gender. It reviews the concepts of intracellular and extracellular fluid compartments, alongside the role of solutes in body fluids. Test your knowledge on the hydration levels of infants, adults, and the elderly.