Human Physiology and Cell Transport

Flashcards defining core concepts of human physiology, body fluids, cellular membrane structures, and membrane transport mechanisms.

Physiology

The science that deals with the function of different parts of the body that keeps the human alive.

Homeostasis

Keeping the internal environment constant, which is essential for life and maintained when all body systems are healthy.

Total Body Water (TBW)

Body water accounting for $60\%$ of total body weight.

Extracellular Fluid (ECF)

Fluid outside cells that constitutes $20\%$ of body weight, divided into plasma ($5\%$) and interstitial fluid ($15\%$).

Plasma

Fluid inside blood vessels, constituting $5\%$ of body weight as part of the extracellular fluid.

Interstitial Fluid

Fluid between cells, constituting $15\%$ of body weight as part of the internal environment.

Intracellular Fluid (ICF)

Fluid inside cells, accounting for $4\%$ of body weight.

Cell Membrane

A thin elastic lipoprotein structure about $7.5\text{--}10\,mm$ thick, composed of $42\%$ lipids, $55\%$ proteins, and $3\%$ carbohydrates.

Lipid Bi-layer Structure

Consists of a peripheral spherical phosphate part that is hydrophilic at the outer and inner surfaces, and a central linear fatty acid chain part that is hydrophobic in the center.

Integral Proteins

Cell membrane proteins spanning the whole thickness of the membrane that act as channels, carriers for active transport, enzymes, and receptors.

Peripheral Proteins

Cell membrane proteins located on the inner surface that act as enzymes or controllers of intracellular function.

Glycocalyx

Membrane carbohydrates (glycoprotein or glycolipid) on the outer surface of the membrane that give a negative charge to the cell surface, aid in cell adhesion, act as receptors, and serve as part of the cell identification code in immune mechanisms.

Passive Transport (Diffusion)

Transport across a membrane that requires no energy, may or may not need a carrier, and occurs with an electrochemical gradient.

Simple Diffusion

A type of diffusion that needs no carrier (e.g., $O_2$ and $CO_2$ transport), has no transport maximum, shows no competitive inhibition, and is less sensitive to temperature.

Facilitated Diffusion

A type of diffusion that needs a carrier (e.g., transport of glucose and more amino acids), has a transport maximum, shows competitive inhibition, and is more sensitive to temperature.

Active Transport

Transport across a membrane that needs energy, needs a carrier, and occurs against an electrochemical gradient.

Primary Active Transport

Active transport involving direct release of energy where the carrier has ATPase activity (e.g., $Na^+-K^+$ pump, Calcium pump, and Hydrogen ion pump).

Secondary Active Transport

Active transport involving indirect release of energy where the carrier has no ATPase activity, utilizing energy from primary active transport on the other side.

Co-transport

A form of secondary active transport where two substances move in the same direction, such as Sodium-glucose and Sodium-amino acid transport.

Counter-transport

A form of secondary active transport where two substances move in opposite directions, such as Sodium-hydrogen and Sodium-calcium counter transport.

Exocytosis

Active transport by which large molecules move near the cell membrane in vesicles, attach to it, rupture the membrane, and extrude contents outside the cell.

Endocytosis

Active transport to the inside of the cell, which is the reverse of exocytosis.

Phagocytosis

'Cell eating'; endocytosis of solid particles.

Pinocytosis

'Cell drinking'; endocytosis of fluid particles.

Factors Increasing Diffusion

Concentration gradient of the substance, temperature, surface area of diffusion membrane, number of protein channels, and lipid solubility of the substance.

Factors Decreasing Diffusion

Thickness of the diffusion membrane and molecular weight of the diffusion substance.

Leak Channels

Ion channels that are always opened without gates, such as sodium leak channels (with negative charge inside) and potassium leak channels (with no charge).

Ligand Gated Channels

Gated ion channels that open by binding with a chemical substance.

Voltage Gated Sodium Channel

A voltage-gated channel that has an activation gate outside and an inactivation gate inside, opening and closing rapidly.

Voltage Gated Potassium Channel

A voltage-gated channel that has only one gate inside, opening and closing slowly.