Cell Membrane & Tissue Types: Key Concepts for Biology

Cell Membrane / Plasma Membrane

Surrounding layer of all living cells in multicellular organisms that provides a protective barrier and regulates which materials pass in or out.

Fluid Mosaic Model

A structure composed primarily of a stacked phospholipid bilayer that is extremely pliable.

Mosaic

The lipid bilayer is 'peppered throughout' with various proteins.

Selectively Permeable

Allows only substances meeting certain criteria (like relatively small, nonpolar materials) to pass through unaided.

Amphipathic

A molecule that contains both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.

Phospholipids

Amphipathic molecules, having a polar, hydrophilic phosphate head and nonpolar, hydrophobic lipid tails.

Integral Protein

Permanently embedded in the membrane and usually spans the entire membrane.

Channel Proteins

Allow specific materials (e.g., ions) to pass in or out of the cell.

Concentration Gradient

Difference in concentration of a substance across a space.

Diffusion

Movement of particles from an area of higher concentration to an area of lower concentration.

Passive Transport

Uses the substance's own kinetic energy and does not require the expenditure of chemical energy (like ATP hydrolysis) from the cell.

Simple Diffusion

Small, nonpolar molecules slip between the lipid tails of the cell membrane, moving down their concentration gradient.

Facilitated Diffusion

Used for substances that cannot cross the lipid bilayer due to their size, charge, and/or polarity (e.g., glucose, ions, amino acids).

Carrier-mediated Facilitated Diffusion

Molecules like glucose bind to specialized carrier proteins that change shape to allow the molecules into the cell.

Channel-mediated Facilitated Diffusion

The use of a protein that acts as a channel through which an ion or small polar molecule moves down its concentration gradient.

Hypertonic

Higher concentration of solutes than another solution.

Crenation

Red Blood Cells will shrivel as water leaves the cell via osmosis.

Hypotonic

Lower concentration of solutes than another solution.

Active Transport

Movement of substances across the membrane that requires energy from the hydrolysis of adenosine triphosphate (ATP hydrolysis).

ATP Hydrolysis

The chemical breakdown of ATP that releases energy.

Sodium-Potassium Pump

An example of active transport powered by ATP hydrolysis.

Endocytosis

Cell ingesting material by enveloping it in a portion of its cell membrane and then pinching off that portion to form an independent, intracellular vesicle or vacuole.

Phagocytosis

'Cell eating,' the endocytosis of large particles.

Pinocytosis

The cell takes in small particles in fluid.

Receptor-mediated Endocytosis

A selective process where external receptors bind a specific ligand, which then triggers the cell to endocytose the ligand in a coated vesicle.

Exocytosis

Cell exporting material out of the cell using vesicular transport.

Osmosis

Diffusion of water through a semipermeable membrane down its concentration gradient.

Isotonic

solution that has a solute concentration equal to another solution

Red Blood Cells

Cells in an isotonic solution will maintain their normal shape and volume, with water diffusing into and out of the cell at equal rates.

Primary Active Transport

active transport that directly uses the energy from ATP hydrolysis to move a substance across the membrane, typically against concentration gradient.

Peripheral Protein

protein that is temporarily adhered to the membrane, typically on the inner or outer surface of the lipid bilayer, but can also be attached to an integral protein.

Connective Tissue

protection, support, and integration of all body parts.

Areolar Tissue

A type of Loose Connective Tissue that fills spaces between muscle fibers, wraps nerves and blood vessels, and supports organs.

Adipose Tissue

A type of Loose Connective Tissue mainly of specialized cells (adipocytes) that stores fat for energy and provides insulation.

Dense Connective Tissue

subcategory of connective tissue proper characterized by a predominance of thick fibers over ground substance.

Dense Regular Connective Tissue

Fibers (collagen) are packed into parallel bundles, providing great tensile strength and resistance to stretching in one direction.

Dense Irregular Connective Tissue

Fibers (collagen) are organized into a random, interwoven mesh-like pattern, providing strength in all directions.

Collagen Fiber

Protein fibers composed of the most abundant protein in the body, collagen, providing flexibility yet possessing great tensile strength to resist tearing.

Cartilage

supportive connective tissue with collagenous fibers in a firm matrix of chondroitin sulfates, providing support and flexibility.

Chondrocyte

cells embedded in the cartilage matrix responsible for producing and maintaining it.

Bone

A supportive connective tissue with a mineralized matrix.

Cancellous/Trabecular/Spongy Bone

Bone tissue that has an open, lattice-like structure of bony processes called trabeculae, found in the interior of bones.

Blood

A Fluid Connective Tissue consisting of erythrocytes, leukocytes, and platelets suspended in a liquid extracellular matrix (plasma).

Apical

free, exposed surface of an epithelial cell that faces the body exterior or a lumen (internal cavity).

Basal

bottom edge of an epithelial cell that is attached to the underlying connective tissue.

Basement Membrane

A thin layer that anchors the epithelial cells at their basal surface to the underlying connective tissue.

Basal Lamina

Layer of the basement membrane that is secreted by the epithelial cells themselves.

Cilia

Microscopic, hair-like extensions on the apical surface of some epithelial cells that move rhythmically to sweep materials (like mucus and dust) across the cell surface.

Cell Soma / Body

Region of a neuron (nerve cell) that contains the nucleus; also called the perikaryon. The metabolic and information-integration center.

Dendrite

Extensions (processes) of the neuron cell body that function to receive stimuli from other neurons.

Axon

Specialized elongated extension of the neuron that transmits electrical signals away from the cell body toward a cell.

Cardiac Muscle

Excitable muscle tissue found exclusively in the heart that contracts involuntarily to pump blood.

Ground Substance

Major component of the connective tissue matrix, crisscrossed by protein fibers; clear, viscous, colorless fluid, but it can be mineralized and solid, as in bones.

Fibroblast

Most abundant cells in connective tissue, 'fixed cells,' meaning they remain within the connective tissue; produce the fibrous tissue of connective tissue proper.

Elastic Fiber

Protein fibers that contain elastin; when stretched or compressed, they return to their original shape.

Macrophage

A mobile cell found in connective tissue proper that is part of the immune system; a phagocytic cell that engulfs pathogens and rids tissue of cellular debris.

Loose Connective Tissue

Fibers are loosely organized, leaving large spaces in between; acts both to absorb shock and bind tissues together.

Fluid Connective Tissue

Includes blood and lymph; characterized by specialized cells circulating in a watery fluid.

Erythrocyte

A type of specialized cell that circulates in blood.

Lymph

A type of fluid connective tissue that ensures the transport of chemical messengers.

Lacuna

The small space within the cartilage matrix that houses the chondrocytes (cartilage cells).

Hyaline Cartilage

Most common type of cartilage; is both strong and flexible, found in the rib cage and nose, and covers bones at moveable joints.

Fibrocartilage

Tough due to thick bundles of collagen fibers; provides some compressibility and can absorb pressure.

Elastic Cartilage

Provides firm but elastic support.

Epithelial Tissue

Sheets of cells that cover surfaces exposed to the outside world (like skin, airways, digestive tract) and line body cavities; the body's first line of protection and acts as gatekeepers controlling permeability.

Endothelium

Type of epithelium that lines hollow organs and body cavities that do not connect to the body's exterior, such as blood vessels and serous membranes.

Keratin

A protein that fills the dead cells of the upper layer in certain types of stratified squamous epithelium.

Matrix

Substance in which connective tissue cells are dispersed; includes a large amount of extracellular material, with major components being ground substance and protein fibres.

Mesenchymal Cell

Fixed cell that remains within the connective tissue; multipotent adult stem cell that can differentiate into any type of connective tissue cells needed for repair and healing.

Mast Cell

Connective tissue cell that is part of the immune system protecting the body.

Reticular Fibre

Narrow protein fibers arranged in a branching network, produced by reticular cells; found in soft organs such as the liver and spleen.

Anchor

Provide structural support to the parenchyma (functional cells) of soft organs.

Parenchyma

Refers to the functional cells, blood vessels, and nerves of an organ.

Perichondrium

Layer of dense irregular connective tissue that encapsulates the cartilage.

Osteocyte

Bone cells similar to chondrocytes, found within spaces called lacunae.

Pseudostratified Columnar Epithelium

Lines the trachea and much of the upper respiratory tract; appears stratified but is a single layer.

Reticular Lamina

Layer of the basement membrane that is secreted by the underlying connective tissue.

Neuron

The main cells of nervous tissue specialized to transmit and receive impulses.

Neuroglia / Glial Cell / Glia

Characterized as having a simple support role; the word 'glia' comes from the Greek word for glue.

Muscle Fiber

Refers to the cells of muscle tissue.

Skeletal Muscle Cells

Long cylindrical fibres.

Cardiac Muscle Cells

Short, branched fibres (cardiomyocytes).

Smooth Muscle Cells

Short, spindle-shaped fibres.

Supportive Connective Tissue

Hard tissues of the body: cartilage and bone.

Reticular Tissue

Loose Connective Tissue characterized by a mesh-like, supportive framework formed by reticular fibres.

Simple Epithelium

A single layer of cells.

Stratified Epithelium

More than one layer of cells.

Simple Squamous Epithelium

Single layer of thin, flat cells.

Simple Cuboidal Epithelium

Single layer of cube-shaped cells.

Simple Columnar Epithelium

Single layer of tall, column-shaped cells; involved in absorption and secretion.

Stratified Squamous Epithelium

Most common type of stratified epithelium providing protection against wear and tear.

Stratified Cuboidal Epithelium

Rare; has only two layers of cuboidal cells; provides protection.

Stratified Columnar Epithelium

Rare; basal layers are cuboidal, apical layer consists of columnar cells; provides protection and secretion.

Transitional Epithelium

A specialized type of stratified epithelium where the shape of the apical cells changes depending on the stretch of the organ.

Skeletal Muscle

Long, cylindrical muscle fibres (cells) that appear striated; control voluntary movement.

Smooth Muscle

Short, spindle-shaped muscle fibres (cells) that are non-striated.

Anatomical Position

Standing upright, with feet parallel and shoulder-width apart, toes forward; upper limbs held out to each side, palms facing forward.

Anterior / Ventral

Front or direction toward the front of the body.

Inferior / Caudal

Below or lower than another part of the body; specifically means near or toward the tail.

Medial

The middle or direction toward the middle of the body.