Fluid and Acid-Base Balance

A complete set of vocabulary flashcards covering fluid compartments, osmolarity, water and salt balance, BP regulation, and acid-base homeostasis based on Chapter 15 lecture notes.

Balance Concept

The requirement that substances added to the body ($input$ through ingestion or metabolic production) must equal substances removed from the body ($output$ through excretion or metabolic use) to maintain ECF homeostasis.

Positive Balance

A state where the gains of a substance exceed its losses.

Negative Balance

A state where the losses of a substance exceed its gains.

Intracellular Fluid (ICF) Compartment

The major fluid compartment comprising two-thirds of total body water.

Extracellular Fluid (ECF) Compartment

The fluid compartment comprising one-third of total body water, subdivided into plasma ($20$% of ECF) and interstitial fluid ($80$% of ECF).

Blood Vessel Walls

The physical barrier between plasma and interstitial fluid.

Cellular Plasma Membranes

The physical barrier between ECF and ICF.

Total Body Fluid Volume

Approximately $42$ liters, representing $60$% of body weight.

ECF Volume Regulation

The process of maintaining salt balance to ensure long-term regulation of blood pressure.

ECF Osmolarity Regulation

The process of maintaining water balance to prevent cells from swelling or shrinking.

Baroreceptor Reflex

A short-term control measure for blood pressure; it increases cardiac output and total peripheral resistance when BP is low, and decreases them when BP is high.

Salt Balance Inputs and Outputs

Ingestion is the only input; output occurs via sweat, feces, and primarily urine.

ECF Hypertonicity

A condition where a deficit of free $H_2O$ leads to concentrated solutes and high ECF osmolarity, causing cells to shrink due to osmosis.

Diabetes Insipidus

A cause of ECF hypertonicity resulting from a lack of vasopressin ($ADH$).

ECF Hypotonicity

A condition where an excess of free $H_2O$ leads to dilute solutes and low ECF osmolarity, causing cells to swell due to osmosis.

ECF Isotonic

A state where ECF volume increases but osmolarity remains unchanged, such as during the administration of $0.9$% $NaCl$.

Vasopressin (Anti-diuretic hormone)

A hormone made by the hypothalamus and released from the posterior pituitary that causes water reabsorption in the kidneys, leading to decreased urine output and increased ECF volume.

Acid-Base Balance

The precise regulation of free hydrogen ion concentration ($[H^+]$) in body fluids.

Acidosis

A condition where blood pH falls below $7.35$, leading to depression of the central nervous system.

Alkalosis

A condition where blood pH rises above $7.45$, leading to overexcitability of the central nervous system.

Three Sources of $H^+$ in the Body

1. Carbonic acid formation ($CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$). 2. Inorganic acids from nutrient breakdown. 3. Organic acids from metabolism.

Chemical Buffer Systems

The first line of defense against changes in $[H^+]$, acting immediately to bind or yield free $H^+$ without removing them from the body.

H2CO3:HCO3- Buffer Pair

The primary chemical buffer system of the Extracellular Fluid (ECF).

Protein Buffer System

The primary chemical buffer system of the Intracellular Fluid (ICF).

Hemoglobin Buffer System

The buffer system responsible for buffering $H^+$ generated from metabolically produced $CO_2$ during transit between tissues and lungs.

Phosphate Buffer System

An important urinary buffer system that can switch a $H^+$ for a $Na^+$.

Respiratory Mechanism of pH Control

The second line of defense against pH changes; it regulates $H^+$ by controlling the rate of $CO_2$ removal, acting within minutes.

Renal Mechanism of pH Control

The third line of defense against pH changes; it requires hours to days to compensate by adjusting $H^+$ excretion, $HCO_3^-$ conservation, and ammonia secretion.

Respiratory Acidosis

A pH imbalance below $7.35$ arising from an increase in $[CO_2]$ usually caused by hypoventilation.

Respiratory Alkalosis

A pH imbalance above $7.45$ arising from a decrease in $[CO_2]$ usually caused by hyperventilation.

Metabolic Acidosis

A pH imbalance below $7.35$ characterized by a decrease in $[HCO_3^-]$.

Metabolic Alkalosis

A pH imbalance above $7.45$ characterized by an increase in $[HCO_3^-]$.

Normal Blood pH Range

$7.35 - 7.45$.

Normal $CO_2$ Range

$35 - 45$ ($<35$ indicates alkalosis; $>45$ indicates acidosis).

Normal $HCO_3^-$ Range

$22 - 26$ ($<22$ indicates acidosis; $>26$ indicates alkalosis).