midterm lecture study guide

Plasma Membrane

A flexible yet sturdy barrier consisting primarily of a phospholipid bilayer that surrounds and contains the cytoplasm of the cell; also called the plasmalemma.

Integral Proteins

Membrane proteins that extend into or through the lipid bilayer; also referred to as transmembrane proteins.

Peripheral Proteins

Membrane proteins that are not embedded in the lipid bilayer but are attached loosely to polar heads of lipids or to integral proteins on the inner or outer surface of the membrane.

Electrochemical Gradient

The combined influence of a concentration gradient (difference in chemical concentration across a membrane) and an electrical gradient (difference in charge/ion concentration across a membrane).

Simple Diffusion

A passive transport process in which a substance moves down its concentration gradient through the lipid bilayer without the assistance of membrane transport proteins.

Facilitated Diffusion

A passive transport process in which transmembrane proteins functioning as channels or carriers assist polar or highly charged solutes to move down their concentration gradient through the lipid bilayer.

Osmosis

The passive net movement of a solvent (water in living systems) through a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration until equilibrium is reached.

Hypotonic Solution

A solution that has a lower solute concentration and higher water concentration than the cytosol of a cell, resulting in net movement of water into the cell and causing it to swell or burst.

Hypertonic Solution

A solution that has a higher solute concentration and lower water concentration than the cytosol of a cell, resulting in net movement of water out of the cell and causing it to shrink.

Primary Active Transport

An active process in which energy derived directly from the hydrolysis of ATP changes the shape of a carrier protein pump to move substances across a membrane against their concentration gradient, such as the $Na^+/K^+$ ATPase pump moving $3\,Na^+$ out and $2\,K^+$ into the cell.

Secondary Active Transport

Coupled active transport in which the kinetic energy of an ionic concentration gradient (such as $Na^+$ or $H^+$) established by primary active transport drives other substances against their own concentration gradients.

Antiporters

Carrier proteins involved in secondary active transport that move $Na^+$ (or $H^+$) and another substance in opposite directions across the plasma membrane, such as exporting $Ca^{2+}$ or $H^+$ from cells.

Symporters

Carrier proteins involved in secondary active transport that move $Na^+$ (or $H^+$) and another substance in the same direction across the plasma membrane, such as importing glucose or amino acids into cells.

Receptor-Mediated Endocytosis

A highly selective vesicular active transport process in which ligand-receptor complexes trigger the infolding of a clathrin-coated pit to form a vesicle importing specific ligands such as LDLs or transferrin.

Phagocytosis

A form of endocytosis ('cell eating') in which a cell binds and engulfs a solid particle (such as bacteria, viruses, or aged/dead cells) using pseudopods to form a phagosome.

Bulk-Phase Endocytosis (Pinocytosis)

A form of endocytosis ('cell drinking') in which droplets of extracellular fluid and dissolved solutes are brought into the cell by the nonselective infolding of the plasma membrane to form a vesicle.

Exocytosis

An active transport process in which membrane-enclosed secretory vesicles fuse with the plasma membrane and release their contents (such as neurotransmitters, hormones, and digestive enzymes) into extracellular fluid.

Transcytosis

An active vesicular process that moves a substance entirely through a cell via endocytosis on one side followed by exocytosis on the opposite side, common for transporting substances like antibodies across endothelial cells.

Cytoskeleton

A cytoplasmic network composed of three protein filament types—microfilaments, intermediate filaments, and microtubules—that maintains cell shape, organizes cell contents, and drives cellular movements.

Centrosome

An organelle consisting of a pair of centrioles and pericentriolar matrix containing tubulins, which are utilized for microtubule formation and mitotic spindle growth.

Cilia and Flagella

Motile surface projections anchored to a basal body containing $20$ microtubules; cilia propel fluids across a cell's surface, whereas a flagellum moves an entire cell.

Ribosome

An organelle composed of large and small subunits containing ribosomal RNA (rRNA) and proteins, found free in the cytosol or attached to rough ER, that conducts protein synthesis.

Rough Endoplasmic Reticulum

A membranous network studded with ribosomes and continuous with the nuclear envelope that synthesizes glycoproteins and phospholipids for insertion into membranes, cellular organelles, or for exocytosis.

Smooth Endoplasmic Reticulum

A membranous tubular network lacking ribosomes that synthesizes fatty acids and steroids, inactivates or detoxifies drugs, removes phosphate groups from glucose-6-phosphate, and stores and releases $Ca^{2+}$ in muscle cells.

Golgi Complex

An organelle consisting of $3\text{ to }20$ flattened membranous saccules organized into cis (entry), medial, and trans (exit) faces that modifies, sorts, and packages proteins received from the rough ER.

Lysosome

A membrane-enclosed vesicle derived from the Golgi complex that contains approximately $60$ digestive and hydrolytic enzymes to digest endosomal cargo, worn-out organelles (autophagy), or entire cells (autolysis).

Peroxisome

A small vesicle containing oxidases and catalase that oxidizes amino acids and fatty acids while detoxifying harmful substances like hydrogen peroxide and associated free radicals.

Proteasome

A tiny barrel-shaped structure containing proteases that destroys unneeded, damaged, or faulty proteins by hydrolyzing them into small peptides.

Mitochondrion

An organelle bounded by external and internal membranes, cristae, and a matrix; serves as the primary site of aerobic cellular respiration to generate ATP and plays an early role in apoptosis.

Transcription

The nuclear process catalyzed by RNA polymerase in which genetic information encoded in DNA is copied onto a complementary strand of RNA (mRNA, rRNA, or tRNA).

Translation

The cytoplasmic process occurring at ribosomes in which the nucleotide sequence of an mRNA molecule is read to direct the assembly of a specific sequence of amino acids into a protein.

Mitosis

Nuclear division in somatic cells that distributes two identical sets of chromosomes into two separate nuclei through prophase, metaphase, anaphase, and telophase.

Meiosis

A two-stage reproductive cell division ($\text{Meiosis I}$ and $\text{Meiosis II}$) that involves synapsis, tetrad formation, and crossing-over, producing four haploid ($n$) gametes from a diploid ($2n$) parent cell.

Tissue

A group of cells that usually share a common embryonic origin and function together to carry out specialized activities.

Tight Junctions

Cell junctions consisting of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to prevent substances from passing between cells.

Adhering Junctions

Cell junctions containing a dense plaque of proteins joined to microfilaments (actin) of the cytoskeleton and anchored across the intercellular space by transmembrane glycoproteins called cadherins, forming adhesion belts.

Desmosomes

Plaque-containing cell junctions that span the intercellular space using cadherins and link to intermediate filaments (keratin), preventing cells from detaching under tension in tissues like the epidermis and cardiac muscle.

Hemidesmosomes

Cell junctions resembling half a desmosome that anchor the basal surface of epithelial cells to the basement membrane using transmembrane glycoproteins called integrins attached internally to intermediate filaments (keratin).

Gap Junctions

Cell junctions formed by transmembrane proteins called connexins that assemble into tiny fluid-filled tunnels called connexons, enabling ions and small molecules to diffuse directly between adjacent cells.

Basement Membrane

A thin extracellular layer consisting of a basal lamina produced by epithelial cells and an underlying reticular lamina produced by connective tissue cells, providing an attachment base for epithelia.

Simple Squamous Epithelium

A single layer of flat cells resembling a tiled floor with a central nucleus; functions in filtration, diffusion, and secretion (designated as endothelium in the cardiovascular/lymphatic systems and mesothelium in serous membranes).

Simple Cuboidal Epithelium

A single layer of cube-shaped cells with centrally located, spherical nuclei; lines kidney tubules and small ducts of glands, where it performs secretion and absorption.

Nonciliated Simple Columnar Epithelium

A single layer of column-like cells with oval nuclei near their bases, featuring microvilli at the apical surface and mucus-secreting goblet cells; lines the gastrointestinal tract to lubricate passages and absorb nutrients.

Ciliated Simple Columnar Epithelium

A single layer of ciliated columnar cells with basal oval nuclei; lines uterine tubes and bronchioles where coordinated ciliary beating moves mucus, trapped particles, or oocytes.

Pseudostratified Columnar Epithelium

An epithelium that appears multi-layered because cell nuclei lie at varying levels, although all cells are anchored to the basement membrane in a single layer; ciliated varieties line airways of the upper respiratory tract.

Stratified Squamous Epithelium

A tissue containing two or more cellular layers with flat apical cells and cuboidal/columnar basal cells; occurs as keratinized (epidermis of skin) for abrasion/water-loss resistance or nonkeratinized (mouth, esophagus, vagina) for moist protection.

Urothelium (Transitional Epithelium)

A stratified epithelium with variable cell morphology (large and rounded when relaxed, flat and squamous when stretched) lining the urinary bladder, ureters, and urethra to accommodate expansion without rupture.

Endocrine Gland

A ductless gland whose secretions (hormones) enter interstitial fluid and diffuse into the bloodstream to regulate metabolic and physiological activities throughout the body.

Exocrine Gland

A gland that releases secretory products into ducts that empty onto the surface of a covering or lining epithelium, such as skin or the lumen of a hollow organ.

Merocrine Secretion

A mode of exocrine secretion where secretory products packaged into vesicles by the Golgi complex are released from the cell via exocytosis without cellular damage (e.g., salivary glands).

Apocrine Secretion

A mode of exocrine secretion where secretory products accumulate at the apical portion of the cell, which then pinches off from the rest of the cell to release the secretion (e.g., mammary glands).

Holocrine Secretion

A mode of exocrine secretion in which a mature cell accumulates secretory product, ruptures, and dies to become the secretion itself, with lost cells replaced by cell division (e.g., sebaceous oil glands).

Extracellular Matrix (ECM)

The material located in spaces between connective tissue cells, composed of protein fibers (collagen, elastic, reticular) and a ground substance consisting of water and organic molecules.

Fibroblasts

Large, flat, branching cells that migrate through connective tissue and secrete extracellular fibers as well as ground substance.

Hyaline Cartilage

The most abundant cartilage type in the body, containing prominent chondrocytes in lacunae within a resilient bluish-white gel extracellular matrix; surrounded by perichondrium (except at articular surfaces and growth plates).

Fibrous Cartilage

The strongest and most rigid cartilage type, composed of chondrocytes scattered among prominent, thick bundles of collagen fibers and lacking a perichondrium; located in the pubic symphysis and intervertebral discs.

Elastic Cartilage

A flexible cartilage containing chondrocytes positioned in a threadlike network of elastic fibers within the matrix, enveloped by perichondrium; maintains the shape of structures such as the epiglottis and auricle.

Mucous Membrane (Mucosa)

An epithelial membrane lining body cavities that open directly to the exterior (digestive, respiratory, reproductive, and urinary tracts), consisting of an epithelium and an underlying areolar connective tissue layer called the lamina propria.

Serous Membrane (Serosa)

An epithelial membrane lining body cavities that do not open directly to the exterior (pleura, pericardium, peritoneum), composed of areolar connective tissue covered by mesothelium that secretes lubricating serous fluid.

Synovial Membrane

A membrane lining freely movable joint cavities that lacks an epithelial layer, composed of synoviocytes and areolar connective tissue that secretes lubricating synovial fluid.

Skeletal Muscle Tissue

A voluntary muscular tissue composed of long, cylindrical, striated, multinucleated fibers with peripheral nuclei, typically attached to bones by tendons to provide motion and heat production.

Cardiac Muscle Tissue

An involuntary muscular tissue restricted to the heart wall, composed of branched, striated fibers with a central nucleus, connected end-to-end by intercalated discs containing desmosomes and gap junctions.

Smooth Muscle Tissue

An involuntary muscular tissue composed of nonstriated, spindle-shaped fibers with a single central nucleus, located within the walls of hollow organs, blood vessels, and airways to regulate motility and constriction.

Neurons

Electrically excitable nervous cells consisting of a cell body, dendrites, and an axon that convert stimuli into nerve impulses (action potentials) and conduct them to other cells.

Neuroglia

Non-conductive supporting cells of the nervous system that nourish, protect, and maintain homeostasis for neurons without generating nerve impulses.

Fibrosis

The process of tissue repair that leads to the formation of scar tissue when fibroblasts synthesize collagen fibers and extracellular matrix to replace damaged parenchymal tissue.

Axial skeleton

The division of the skeleton containing 80 bones that lies along the longitudinal axis of the body, including the skull bones, auditory ossicles, hyoid bone, ribs, sternum, and vertebral column.

Appendicular skeleton

The division of the skeleton containing 126 bones, consisting of the bones of the upper and lower extremities plus the girdles that connect the limbs to the axial skeleton.

Long bones

Bones that have a greater length than width and consist of a shaft and variable number of extremities.

Short bones

Cube-shaped bones that are nearly equal in length and width.

Flat bones

Bones composed of two thin layers of parallel plates enclosing a layer of spongy bone tissue.

Irregular bones

Bones with complex shapes that cannot be grouped into long, short, flat, or sesamoid categories.

Sesamoid bones

Small bones shaped like sesame seeds that develop within certain tendons where considerable friction, tension, and physical stress exist.

Sutural bones

Small, extra bone plates located within the sutures between certain cranial bones.

Fissure

A narrow slit between adjacent parts of bones through which blood vessels or nerves pass.

Foramen

An opening or hole in a bone through which blood vessels, nerves, or ligaments pass.

Fossa

A shallow depression located on or within a bone.

Sulcus

A furrow or groove along a bone surface that accommodates a blood vessel, nerve, or tendon.

Meatus

A tubelike opening or passageway penetrating through a bone.

Condyle

A large, rounded protuberance with a smooth articular surface at the end of a bone.

Facet

A smooth, flat, slightly concave or convex articular surface on a bone.

Head (bone)

A rounded articular projection usually supported on a constricted portion, or neck, of a bone.

Crest

A prominent ridge or elongated projection on a bone surface.

Epicondyle

A typically roughened projection situated superior to a condyle.

Line (linea)

A long, narrow ridge or border that is less prominent than a crest.

Spinous process

A sharp, slender projection originating from a vertebra or other bone.

Trochanter

A very large projection found exclusively on the femur.

Tubercle

A variably sized, rounded projection on a bone.

Tuberosity

A variably sized projection that possesses a rough, bumpy surface.

Mandible

The lower jawbone; it is the largest and strongest facial bone and the only movable bone of the skull other than the auditory ossicles.

Paranasal sinuses

Mucous membrane-lined cavities within the frontal, maxillary, sphenoid, and ethmoid bones that serve as voice resonating chambers and increase nasal mucosal surface area.

Fontanels

Unossified mesenchyme regions in a fetus and infant that develop into dense connective tissue between cranial bones, closing by 2 years of age via intramembranous ossification.

Hyoid bone

A U-shaped bone in the anterior neck that does not articulate with any other bone, supporting the tongue and serving as an attachment point for neck and pharynx muscles.

Annulus fibrosus

The outer ring composed of fibrocartilage that encloses each intervertebral disc.

Nucleus pulposus

The inner, soft, highly elastic central structure of an intervertebral disc.

Atlas (C1)

The first cervical vertebra, which supports the head and lacks both a vertebral body and a spinous process.

Axis (C2)

The second cervical vertebra, characterized by a peg-like projection called the dens, which serves as a pivot for head rotation.

True (vertebrosternal) ribs

The first 7 pairs of ribs that connect directly to the sternum through their own individual costal cartilages.

False (vertebrochondral) ribs

Rib pairs 8 through 12 whose costal cartilages attach indirectly to the sternum or lack sternal attachment entirely.

Floating (vertebral) ribs

Rib pairs 11 and 12, which have costal cartilages that do not attach to the sternum at all.