From PPT-Water, Acid/Base, and Electrolyte Balance

Vocabulary flashcards covering body fluid compartments, daily water balance, the renin-angiotensin-aldosterone system (RAS), major electrolytes, and acid-base regulation.

Fluid Compartments

The distinct liquid spaces of the human body comprising intracellular fluid ($63\%$) and extracellular fluid ($37\%$), which includes interstitial fluid, plasma, lymph, and transcellular fluid.

Intracellular Fluid (ICF)

The portion of total body water enclosed by the cell membranes of body cells, making up approximately $63\%$ of total body water.

Extracellular Fluid (ECF)

All fluid located outside of body cells, making up approximately $37\%$ of total body water and divided into interstitial fluid, plasma, lymph, and transcellular fluid.

Transcellular Fluid

A specialized subcompartment of extracellular fluid that includes synovial fluid, aqueous and vitreous humors, cerebrospinal fluid (CSF), and glandular secretions.

Osmosis (in Fluid Balance)

The primary passive process by which water moves between body cells and extracellular spaces, typically regulated by ions actively pumped across cell membranes.

Total Body Water

The total volume of water in the body, averaging about $40\,\text{liters}$ in a human; it comprises approximately $60\%$ of body weight in men (due to greater muscle mass) and $50\%$ in women (due to higher adipose content).

Water of Metabolism

Water synthesized internally as a byproduct of anabolic reactions, accounting for $250\,\text{mL}$ ($10\%$) of average daily water intake.

Average Daily Water Intake

The typical daily volume of water ingested and produced ($2,500\,\text{mL}$), supplied by beverages ($1,500\,\text{mL}$ or $60\%$), moist food ($750\,\text{mL}$ or $30\%$), and water of metabolism ($250\,\text{mL}$ or $10\%$).

Average Daily Water Output

The typical daily volume of water eliminated ($2,500\,\text{mL}$), lost through urine ($1,500\,\text{mL}$ or $60\%$), skin and lungs ($700\,\text{mL}$ or $28\%$), sweat ($150\,\text{mL}$ or $6\%$), and feces ($150\,\text{mL}$ or $6\%$).

Macula Densa Cells

Specialized cells in the juxtaglomerular apparatus (JGA) of the kidney that detect decreasing blood volume and respond by releasing epinephrine into adjacent tissues.

Granular Cells

Cells of the juxtaglomerular apparatus (JGA) that are stimulated by epinephrine to secrete the enzyme renin into the bloodstream.

Renin

An enzyme secreted into the bloodstream by granular cells of the JGA that catalyzes the conversion of angiotensinogen into angiotensin I.

Angiotensin-Converting Enzyme (ACE)

An enzyme originating from the lungs and kidneys that catalyzes the conversion of angiotensin I into active angiotensin II.

Angiotensin II

A potent vasoconstrictor produced in the renin-angiotensin system that increases blood pressure and stimulates the release of ADH from the pituitary gland and aldosterone from the adrenal cortex.

Antidiuretic Hormone (ADH)

A nonapeptide hormone (composed of 9 amino acids and also known as vasopressin) released by the pituitary gland that promotes water retention and concentrates urine.

Aquaporins

Water channel proteins that insert into the membranes of distal nephron tubules and collecting ducts in response to ADH, allowing water to exit filtrate and return to capillaries.

Aldosterone

A steroid hormone secreted by the adrenal cortex that activates $\text{Na}^+/\text{K}^+$ pumps in distal tubules and collecting ducts, causing $\text{Na}^+$ diffusion into capillaries so water follows osmotically.

Alcohol (Diuretic Effect)

A chemical substance that acts as a diuretic by directly inhibiting the release of antidiuretic hormone (ADH) from the pituitary gland.

Caffeine (Diuretic Effect)

A chemical substance that acts as a diuretic by inhibiting the renal reabsorption of sodium ions ($\text{Na}^+$).

Electrolyte

Any molecule that dissociates into ions (charged atoms) when dissolved in water.

Sodium ($\text{Na}^+$)

The major cation that makes up $90\%$ of all ions in extracellular fluid, functions in water balance, muscle contraction, and nerve impulse transmission, and consumes over $50\%$ of daily caloric intake to pump.

Potassium ($\text{K}^+$)

A vital bodily electrolyte whose primary listed physiological function is the transmission of nerve impulses.

Calcium ($\text{Ca}^{2+}$)

An essential electrolyte required for muscle contraction and intracellular communication.

Hydrogen Ion ($\text{H}^+$)

A cation whose flow drives the ATP synthase enzyme to generate cellular energy and whose concentration defines the acidity and pH of body fluids.

Chloride ($\text{Cl}^-$)

An essential anion responsible for maintaining the proper osmolarity of body fluids.

Acid

Any substance that releases hydrogen ions ($\text{H}^+$) when in an aqueous solution, causing the pH of the solution to decrease.

pH Scale

A logarithmic measurement scale of acidity and alkalinity where moving up or down by one unit corresponds to a tenfold ($10\times$) change in hydrogen ion concentration.

Carbonic Acid

An acid formed during aerobic glucose metabolism when produced carbon dioxide ($\text{CO}_2$) combines with water, serving as a major internal source of $\text{H}^+$ ions.

Lactic Acid

An acid generated as an end product of anaerobic glucose metabolism that contributes hydrogen ions ($\text{H}^+$) to body fluids.

Bicarbonate Buffer System

A primary physiological chemical buffer system that minimizes shifts in blood pH by reversibly binding or releasing hydrogen ions ($\text{H}^+$).

Respiratory Center (Medulla)

The neural control center in the medulla that monitors blood $\text{CO}_2$ levels and accelerates the respiratory rate as $\text{CO}_2$ rises to expel more gas and lower blood $\text{H}^+$ levels.

Renal Excretion of $\text{H}^+$

The active secretion of excess $\text{H}^+$ by peritubular capillaries into kidney tubules, where it is bound and trapped for elimination in urine.

Ammonium ($\text{NH}_4^+$)

An ion produced when ammonia ($\text{NH}_3$) secreted by kidney tubule cells binds to $\text{H}^+$; because it cannot diffuse out of the tubules, it is trapped and excreted in the urine.