Role of Water in Living Tissues

Flashcards covering the distribution, functions, sources, losses, and regulatory mechanisms of water in the human body based on Dr. P. C. Eze's lecture notes.

Who is the author of the lecture on the role of water in living tissues?

DR P. C. EZE

What is the average percentage of total body weight accounted for by water in an adult man?

$$60\%$$

For a man weighing $70\,kg$, what is the estimated total body water content?

About $42\,liters$

What is the constant percentage of water in lean body mass in mammals?

$$73\%$$

How does the water content of adipose tissue (body fat) compare to lean body mass?

Adipose tissue is only about $10\%$ water.

What is the typical range of water as a percentage of body weight in newborn babies compared to the elderly?

It varies from $75\%$ in newborns to $50\%$ in the elderly.

What organ has the highest water percentage ($83\%$) according to the distribution list?

Blood and Kidney

What is the water percentage of the skeleton (bone)?

$$22\%$$

How is total body water divided between the intracellular and extracellular compartments for a $70\,kg$ man?

Intracellular accounts for $40\%$ ($28\,L$) and Extracellular accounts for $20\%$ ($14\,L$).

What are the two sub-categories of extracellular fluid?

Intravasular (plasma) and Extravascular (interstitial and transcellular).

What are examples of transcellular fluid (the "Third space")?

Git fluid, cerebrospinal fluid, peritoneal fluid, and ocular fluid.

How is metabolic water produced in the body?

By the oxidation of hydrogen-containing substrates or energy-yielding nutrients.

Which energy-yielding nutrient produces the most water per gram of oxidation?

Lipids

What is the estimated metabolic water production for a sedentary person?

Approximately $250$ to $350\,ml/day$

What percentage of total fluid intake is typically represented by drinking water and beverages?

$$70\text{-}80\%$$

What are the four primary ways the body loses water?

1. Insensible water losses, 2. Fecal water losses, 3. Sweat production, and 4. Urinary water losses.

What are the components of insensible water loss?

Water lost from skin evaporation and through breathing.

What is the normal volume of fecal water loss in healthy adults?

About $200\,mL/d$

Which water loss mechanism is considered the largest for healthy, non-exercising adults and is tightly controlled to regulate fluid balance?

Urinary water losses

What is the main physiological stimulus for the sensation of thirst?

An increase in plasma osmolality.

What is the normal threshold for plasma osmolality that stimulates the release of ADH?

About $280\,mOsmol/kg\,H_2O$

Where is Anti-Diuretic Hormone (ADH) synthesized and stored?

Synthesized in the hypothalamus and stored in the posterior pituitary gland.

How does ADH affect the kidneys to conserve water?

It increases the permeability of the distal tubules and collecting ducts to water, causing increased water reabsorption.

Besides ADH, what other hormones are involved in body water regulation?

Aldosterone and Atrial natriuretic peptide.