Unit 2 Human Anatomy

Role of water in synovial fluid

Acts as a lubricant to reduce friction during the movement of body joints.

Role of water in pleural fluid

Provides lubrication between pleural membranes, enabling the lungs to expand and recoil smoothly during breathing.

Synovial fluid

A thick, viscous fluid that fills the interior cavity of a movable joint to cushion and lubricate motion.

Pleural fluid

A lubricating substance located between the visceral and parietal layers of the pleura in the thorax.

Heat sink

A substance or object that absorbs and dissipates thermal energy without undergoing a corresponding increase in its own temperature.

Mechanism of evaporative cooling via sweat

Thermal energy from the body breaks hydrogen bonds holding water molecules together, allowing water to vaporize and carry away heat.

Hydrogen bond

A weak dipole-dipole attraction between a hydrogen atom covalently bound to one electronegative atom and a second electronegative atom.

Mixture

A physical combination of two or more distinct substances, each of which retains its own chemical identity.

Compound

A chemical substance composed of two or more different elements held together by chemical bonds.

Solution

A homogeneous liquid mixture in which a solute is completely dissolved into molecules within a solvent.

Solvent vs. solute

The solvent is the dissolving liquid medium, whereas the solute is the substance that dissolves within it.

Dehydration synthesis (condensation reaction)

A chemical reaction where one reactant loses $-H$ and another loses $-OH$, forming a covalent bond while releasing a molecule of water ($H_2O$).

Hydroxyl group

A functional group composed of $-OH$, commonly found in organic compounds such as alcohols.

Hydrolysis

A chemical reaction that consumes a molecule of water by splitting it into $H^+$ and $OH^-$, breaking a bond within a compound.

Body water percentage across human life stages

Ranges from about $75\%$ in infants to $45\%$ in elderly individuals, averaging $50\%$ in adult females and $60\%$ in adult males.

Intracellular fluid (ICF)

The fluid contained within all cells by their plasma membranes, comprising roughly $55\%$ of total body water.

Two primary constituents of extracellular fluid (ECF)

Blood plasma (accounting for approximately $16\%$ of ECF) and interstitial fluid (accounting for roughly $80\%$ of ECF).

Interstitial fluid

The extracellular fluid that occupies microscopic spaces between tissue cells outside of blood vessels.

Blood plasma

The liquid matrix of blood that travels through vessels to deliver formed elements, clotting factors, antibodies, electrolytes, nutrients, and wastes.

Selective permeability

The property of a barrier or membrane that allows specific molecules to cross while restricting the passage of others.

Cerebrospinal fluid (CSF)

The central nervous system circulatory fluid produced by ependymal cells filtering blood within the choroid plexus.

Lymph fluid

Excess interstitial fluid collected and returned to the blood via lymphatic vessels, carrying leukocytes, proteins, and lipids.

Dominant electrolytes in intracellular fluid (ICF)

High concentrations of potassium ($K^+$), phosphate ($HPO_4^{2-}$), magnesium ($Mg^{2+}$), and cellular proteins.

Dominant electrolytes in extracellular fluid (ECF)

High concentrations of sodium ($Na^+$) and chloride ($Cl^-$), along with bicarbonate ($HCO_3^-$).

Six primary functional electrolytes in the human body

Sodium ($Na^+$), potassium ($K^+$), chloride ($Cl^-$), bicarbonate ($HCO_3^-$), calcium ($Ca^{2+}$), and phosphate ($HPO_4^{2-}$).

Acid

A chemical substance that dissociates in aqueous solution to release hydrogen ions ($H^+$), which are single protons.

Strong acid vs. weak acid

A strong acid (such as $HCl$) ionizes completely in solution to liberate all of its $H^+$, whereas a weak acid only partially dissociates.

Base

A substance that releases hydroxide ions ($OH^-$) in solution or accepts free hydrogen ions ($H^+$).

Potential of hydrogen (pH)

A measure of the concentration of free hydrogen ions in solution, where values below $7$ are acidic and values above $7$ are alkaline.

Normal physiological blood pH range

$7.35$ to $7.45$.

Phosphate buffer system in the blood

Composed of sodium dihydrogen phosphate ($NaH_2PO_4$, weak acid) and sodium monohydrogen phosphate ($Na_2HPO_4$, weak base).

Bicarbonate to carbonic acid ratio in normal blood

$20:1$ when arterial blood pH is maintained within the standard homeostatic range.

Effect of elevated blood $CO_2$ on blood pH

Excess $CO_2$ combines with $H_2O$ to form carbonic acid ($H_2CO_3$), dissociating into $H^+$ and lowering blood pH.