Introductory Physiology: Body Fluids, Cell Structure, and Cell Junctions

Vocabulary flashcards covering introductory human physiology concepts, fluid compartments, cellular organelles, plasma membrane structure, and intercellular junctions based on lecture notes.

Physiology

The study of how living things work, explaining the physical and chemical processes that keep an organism alive.

Anatomy

The study of organismal structure and physical appearance (what body parts look like).

Homeostasis

The maintenance of a nearly constant internal environment within an organism.

Negative Feedback Loop

A primary homeostatic control mechanism that reverses a change in a variable to return it to its set point.

Intracellular Fluid (ICF)

Fluid located inside cells, accounting for $40$% of total body weight ($\neq 28\,L$ in a $70\,kg$ adult) and enriched in $\text{K}^+$, $\text{Mg}^{2+}$, phosphate, and proteins.

Extracellular Fluid (ECF)

Fluid located outside cells, accounting for $20$% of total body weight ($\neq 14\,L$ in a $70\,kg$ adult), enriched in $\text{Na}^+$, $\text{Cl}^-$, $\text{Ca}^{2+}$, and $\text{HCO}_3^-$.

Interstitial Fluid

The main subcomponent of extracellular fluid that directly bathes cells, comprising approximately $11\,L$ in an adult.

Plasma

The liquid component of blood within the extracellular fluid compartment, comprising approximately $3\,L$ in an adult.

Transcellular Fluid

A specialized extracellular fluid volume ($1 - 2\,L$) comprising cerebrospinal fluid (CSF), intraocular fluid, digestive juices, and fluid in pericardial, pleural, peritoneal, and joint spaces.

Protoplasm

The collective material inside the cell membrane, consisting of the cytoplasm and nucleus.

Fluid Mosaic Model

Model describing the cell membrane as a lipid bilayer (7.5 - 10 nm thick) with proteins floating in it that can move laterally.

Glycocalyx

An outer cell membrane coating formed by carbohydrate chains attached to lipids and proteins, responsible for cell identification, recognition, and protection.

Extracellular Matrix (ECM)

A watery gel filled with protein fibres occupying the space between cells, facilitating diffusion of nutrients and waste while holding cells together.

Collagen

The most abundant protein in the body; strong, non-stretchy fibers in the extracellular matrix that provide tensile strength to tissues.

Elastin

A rubber-like extracellular matrix protein that stretches and recoils, prominent in lungs, skin, and arteries.

Fibronectin

An extracellular matrix protein that promotes cell adhesion; its concentration is reduced in certain cancer cells to facilitate metastasis.

Desmosomes

Adhering cell junctions that act like spot-welds or rivets to hold cells together under mechanical stretch across a gap of approximately $20\,nm$.

Tight Junctions

Impermeable cell junctions that join outer cell membranes at kiss sites like a zip-lock seal to block intercellular movement of substances.

Gap Junctions

Communicating junctions consisting of protein tunnels that connect adjacent cell cytoplasms to permit passage of small ions and molecules ($\text{MW} < 1000$).

Connexon

A protein hemichannel composed of $6$ connexin subunits that aligns with a corresponding connexon on a neighboring cell to complete a gap junction pore ($\neq 2\,nm$ wide).