Lecture 5

Levels of organization

The hierarchical structure of the body: chemical → cell → tissue → organ → organ system → organism.

Homeostasis

The maintenance of a relatively stable internal environment despite changing external conditions.

Negative feedback

Regulation where the response opposes the change in a physiological variable.

ECF

Extracellular fluid, divided into plasma and interstitial fluid.

ICF

Intracellular fluid, that comprises about two-thirds of total body water.

Plasma membrane

A lipid barrier that surrounds every cell, defining the boundary between ICF and ECF.

Muscle tissue

Tissue type that contracts to produce force and movement.

Nervous tissue

Tissue type that provides rapid electrical signaling for control and communication.

Epithelial tissue

Tissue type that covers surfaces, lines cavities, and forms glands.

Connective tissue

Tissue type that provides support, energy storage, and connects other tissues.

Organ

A structure composed of two or more tissue types working together.

Organ system

A group of organs that share a common purpose.

Ion gradient

Differences in ionic concentrations across the plasma membrane.

Selective permeability

The property of the plasma membrane that allows some substances to cross more easily than others.

Simple diffusion

The process by which substances move from a high concentration to a lower concentration without energy.

Fick's law

A law that describes the factors affecting the rate of diffusion: gradient, area, permeability, and thickness.

Tonicity

A measure of a solution based on its effect on cell volume.

Hypotonic solution

A solution with a lower concentration of nonpenetrating solutes than the cell, causing the cell to swell.

Isotonic solution

A solution with equal concentration of solutes as the cell, resulting in no net change in cell volume.

Hypertonic solution

A solution with a higher concentration of nonpenetrating solutes than the cell, causing the cell to shrink.

Osmosis

The net diffusion of water across a selectively permeable membrane.

Endocytosis

The process of uptake of material into a cell through vesicles.

Exocytosis

The process of releasing material from a cell via vesicles.

Aquaporins

Protein channels that facilitate the transport of water across the plasma membrane.

Carrier-mediated transport

Transport of substances across a membrane via specific carrier proteins.

Facilitated diffusion

Passive transport process utilizing carrier proteins without energy expenditure.

Active transport

Transport process that requires energy to move substances against their gradient.

Primary active transport

Transport using ATP directly to move ions against their concentration gradient.

Secondary active transport

Uses the gradient established by primary active transport to move other substances.

Tight junctions

Specialized connections between epithelial cells that restrict passage of substances.

Desmosomes

Cell junctions that mechanically link adjacent cells together.

Gap junctions

Communicating junctions that allow ions and small molecules to pass between cells.

Fluid-mosaic model

Description of the plasma membrane structure, emphasizing fluidity and diversity of membrane proteins.

Cell adhesion molecules (CAMs)

Membrane proteins that help cells stick to each other and to the extracellular matrix.

Extracellular matrix (ECM)

A network of proteins and carbohydrates outside of cells that provides structural and biochemical support.

Plasma ionic composition

The balance of ions in the plasma, typically high in Na⁺ and low in K⁺.

Intracellular ionic composition

The balance of ions inside the cells, typically high in K⁺ and low in Na⁺.

Saturation

Condition in which all available transport proteins are occupied by the substrate.

Competition

Occurs when two substances compete for the same transport protein.

Sodium-potassium pump

An ATP-using pump that moves Na⁺ out of and K⁺ into the cell.

Proton pump

A transporter that moves protons across a membrane, often using ATP.

Corneal edema

Swelling of the cornea due to excess fluid accumulation, treated with hypertonic solutions.

Fuchs dystrophy

A corneal disease caused by endothelial cell loss, leading to fluid build-up.

Carbonic anhydrase inhibitors

Drugs that reduce intraocular pressure by inhibiting aqueous humor secretion.

Blood-retinal barrier

A selective barrier composed of tight junctions that prevent unwanted substances from entering the retina.

Inherited cataract

A lens opacity caused by genetic mutations affecting gap junction proteins.

Muscle mass contraction

Coordinated contraction of muscle cells facilitated by gap junctions.

Fluid barrier

Function of the plasma membrane that maintains distinct internal and external environments.

Local concentration gradient

Difference in concentration of a substance between two areas.

Permeability

The ability of a membrane to let substances pass through it.

Volume constant

Condition where the volume of a cell remains unchanged due to osmosis.

Nutrient diffusion

The movement of nutrients from the extracellular fluid into the cell.

Waste removal

The process by which waste products move from inside a cell to the extracellular fluid.

Lipid bilayer

The structure formed by two layers of phospholipids that make up the plasma membrane.

Signal transduction

The process by which a cell responds to chemicals in its environment via receptors.

Membrane potential

The voltage across a cell's plasma membrane due to ion separation.

Skeletal muscle

Muscle tissue responsible for voluntary movements.

Cardiac muscle

Involuntary muscle found only in the heart.

Smooth muscle

Involuntary muscle found in walls of hollow organs.

Nutrient extraction

Process of obtaining essential materials from the extracellular fluid.

Substance transport

Movement of molecules across a cellular membrane.

Hydrophobic core

The central region of the lipid bilayer that repels water-soluble molecules.

Cell signaling

Communication between cells that governs basic cellular activities.

Ionic barriers

Mechanisms that maintain difference in ion concentrations across cell membranes.

Metabolic function

Biochemical processes within cells necessary for life.

Electrolyte balance

The proper proportion of ions in the body for normal physiological function.

Physiological variable

Any parameter in the body that can change, such as temperature or glucose levels.

Cellular energy

The energy required by a cell to perform necessary functions.

Chemical signaling

Communication based on the release of signaling molecules.

Glycoproteins

Proteins with attached carbohydrates that play a role in cell recognition.

Transport proteins

Proteins that assist in the movement of ions and other solutes across a membrane.

Cytoskeletal machinery

Structural network within the cytoplasm that helps with transport processes.

Ion channels

Proteins that allow specific ions to pass through the membrane.

Transmembrane potential

The voltage difference across a biological membrane.

Fluid balance

A state where the intake and output of fluids are equal.

Aqueous humor

Fluid produced by the eye that maintains intraocular pressure.

Stress responses

Physiological reactions to changes in the internal or external environment.

Cellular osmoregulation

Cellular mechanisms to maintain homeostasis of fluid balance.

Metabolic homeostasis

Maintenance of stable metabolic functions in response to external changes.