Anatomy and Physiology: Cellular and Tissue Levels of Organization

Comprehensive practice flashcards covering cell structure, membrane transport, organelles, gene expression, cell division, histology, and tissue repair based on Gerard Tortora and Bryan Derrickson's Principles of Anatomy and Physiology.

How is a biological tissue defined, and what are the four primary tissue classes in the human body?

A tissue is a group of cells that usually share a common embryonic origin and function together to carry out specialized activities. The four primary classes categorized by structure and function are epithelial tissue, connective tissue, muscular tissue, and nervous tissue.

What are the key structural distinctions between epithelial tissue and connective tissue regarding cell arrangement and matrix abundance?

Epithelial tissue features many cells tightly packed together into sheets with little to no extracellular matrix, is avascular, and has high mitotic activity. Connective tissue consists of relatively few scattered cells widely dispersed within a large amount of extracellular matrix and is typically highly vascularized (except for cartilage and tendons).

What type of intercellular junction is depicted in this diagram, composed of strands of transmembrane proteins sealing adjacent plasma membranes?

Tight junctions; they consist of web-like strands of transmembrane proteins that fuse the outer surfaces of adjacent plasma membranes together to seal off passageways between cells.

What structural components make up an adhering junction (zonula adherens)?

Adhering junctions consist of a dense layer of proteins called plaque on the inside of the plasma membrane, microfilaments (actin) of the cytoskeleton, transmembrane glycoproteins called cadherins that join adjacent cells, and an extensive adhesion belt encircling the cell.

Which specific cell junction is illustrated here, featuring intermediate filaments of keratin anchored into a protein plaque with cadherins linking the cells across the intercellular space?

Desmosome; it utilizes plaque and transmembrane glycoproteins (cadherins) linked to intermediate filaments composed of keratin to prevent epidermal and cardiac cells from separating under tension.

What type of cell junction is shown here anchoring a cell's basal surface to the underlying extracellular basement membrane?

Hemidesmosome; it resembles half of a desmosome and anchors intermediate filaments (keratin) within the cell to the basement membrane using transmembrane glycoproteins called integrins.

What cellular junction is depicted here, allowing direct chemical and electrical communication between cells via hollow protein cylinders?

Gap junction; it consists of fluid-filled tunnels called connexons (composed of transmembrane proteins called connexins) that bridge the narrow intercellular space between adjacent cells.

What two distinct layers constitute the basement membrane of epithelial tissue?

The basal lamina (secreted by the epithelial cells, containing collagen, laminin, and glycoproteins) and the reticular lamina (closer to underlying connective tissue, containing collagen fibers produced by connective tissue fibroblasts).

What anatomical locations and functions characterize simple squamous epithelium, and what are its two specialized regional names?

It consists of a single layer of flat cells suited for filtration, diffusion, and secretion. It is called endothelium when lining the cardiovascular and lymphatic systems, and mesothelium when forming the superficial epithelial layer of serous membranes in the thoracic and abdominopelvic cavities.

Where is simple cuboidal epithelium located, and what primary physiological roles does it serve?

It covers the ovary surface, lines the anterior capsule of the eye lens, forms pigmented epithelium on the posterior retina, and lines kidney tubules and small glandular ducts. Its primary functions are secretion and absorption.

What structural adaptations distinguish nonciliated simple columnar epithelium from ciliated simple columnar epithelium?

Nonciliated simple columnar epithelium possesses microvilli on its apical surface and interspersed goblet cells to facilitate secretion and absorption along the gastrointestinal tract. Ciliated simple columnar epithelium contains apical cilia that beat in unison to propel mucus, foreign particles, or oocytes in the respiratory tract and uterine tubes.

Why is pseudostratified columnar epithelium designated with the prefix 'pseudo-'?

All cells are attached to the basement membrane in a single layer, but because cell nuclei reside at varying depths and not all cells extend to the apical surface, the tissue presents a false multilayered or stratified appearance when viewed in section.

What is the structural and functional difference between keratinized and nonkeratinized stratified squamous epithelium?

Keratinized stratified squamous epithelium forms the dry, tough, superficial layer of the skin (epidermis) packed with the protective protein keratin. Nonkeratinized stratified squamous epithelium lines moist internal surfaces (such as the mouth, esophagus, vagina, and tongue) to provide defense against abrasion without drying out.

What unique physical property defines urothelium (transitional epithelium), and where is it located?

It has variable morphology: rounded, cuboidal apical cells in a relaxed state that flatten into a squamous appearance when distended. This allows hollow organs of the urinary system (urinary bladder, ureters, portions of urethra) to stretch without rupturing.

What is the fundamental difference between endocrine glands and exocrine glands?

Endocrine glands are ductless and release their chemical messengers (hormones) directly into interstitial fluid to diffuse into the bloodstream. Exocrine glands discharge their secretions through ducts onto the surface of a covering or lining epithelium.

Which three functional mechanisms of exocrine glandular secretion are illustrated in panels (a), (b), and (c)?

(a) Merocrine secretion (secretions synthesized on ribosomes and packaged by Golgi are released via exocytosis without cell damage, e.g., salivary glands); (b) Apocrine secretion (apical portion of cell pinches off with secretory product, e.g., mammary glands); (c) Holocrine secretion (mature cell ruptures entirely, releasing product and dying, e.g., sebaceous oil glands).

What are the three types of protein fibers embedded in the extracellular matrix of connective tissue?

Collagen fibers (strong, flexible bundles of collagen protein; the most abundant protein in the human body), elastic fibers (composed of elastin and fibrillin, providing stretch and recoil), and reticular fibers (thin, branching networks of collagen and glycoproteins providing stroma in organs).

What distinct functional roles do fibroblasts, macrophages, and mast cells play in connective tissue?

Fibroblasts are large, flat cells that secrete protein fibers and ground substance; macrophages develop from monocytes and destroy bacteria and cellular debris via phagocytosis; mast cells produce histamine along blood vessels during inflammation to dilate vessels and combat microbes.

How do hyaline cartilage, fibrous cartilage (fibrocartilage), and elastic cartilage differ in structure and mechanical strength?

Hyaline cartilage contains fine collagen in a glassy, bluish-white resilient gel (weakest cartilage; found at articular bone ends and fetal skeleton); fibrocartilage has thick, visible bundles of collagen fibers without perichondrium (strongest cartilage; found in intervertebral discs and pubic symphysis); elastic cartilage contains a threadlike network of elastic fibers (provides strength, elasticity, and shape retention; found in the auricle of the ear and epiglottis).

What microscopic structural units compose compact bone versus spongy bone tissue?

Compact bone is organized into repeating cylindrical units called osteons (haversian systems) containing concentric lamellae, lacunae housing osteocytes, radiating canaliculi, and a central haversian canal. Spongy bone consists of an open lattice of slender columns called trabeculae with intervening spaces filled with red bone marrow.

What are the two major components of blood, and what are the specific formed elements?

Blood consists of a liquid extracellular matrix called blood plasma and formed elements: red blood cells (erythrocytes) that transport gases, white blood cells (leukocytes) that carry out phagocytosis and immune responses, and platelets (thrombocytes) essential for blood clotting.

What are the four primary types of body membranes and their characteristic locations?

Mucous membranes line body cavities opening directly to the exterior (digestive, respiratory tracts); serous membranes line closed internal ventral cavities and cover enclosed viscera (pleura, pericardium, peritoneum); cutaneous membrane is the skin covering the external body surface; synovial membranes line freely movable joint cavities and lack an epithelial layer.

How do skeletal, cardiac, and smooth muscle tissues differ in striations, cell shape, nuclei number, and control?

Skeletal muscle consists of long, cylindrical, striated, multinucleated fibers under voluntary control; cardiac muscle consists of branched, striated, single-nucleated fibers joined by intercalated discs under involuntary control; smooth muscle consists of spindle-shaped, nonstriated, single-nucleated cells under involuntary control.

What are the two principal classes of cells in nervous tissue, and what are their respective functions?

Neurons (composed of a cell body, dendrites, and an axon) generate and propagate electrical action potentials to transmit signals; neuroglia do not generate impulses but protect, support, and nourish neurons.

What physiological characteristic defines excitable cells such as neurons and muscle fibers?

Electrical excitability: the ability to respond to specific stimuli by generating and conducting electrical action potentials across their plasma membranes through voltage-gated ion channels.

What sequential stages occur during tissue repair following an injury?

Repair begins with inflammation and vasodilation to form a blood clot and protective scab; next, the clot is replaced by delicate pink granulation tissue that contracts to bring wound margins together; finally, parenchymal cells regenerate or fibroblasts lay down collagen in fibrosis to form scar tissue.

What is Systemic Lupus Erythematosus (SLE), and what are its prominent clinical presentations?

An autoimmune inflammatory disorder of connective tissues occurring predominantly in nonwhite women during childbearing years. Classic findings include a characteristic butterfly rash across the bridge of the nose and cheeks, chronic inflammation, fatigue, painful joints, and patchy hair loss.

According to the fluid mosaic model, what components make up the plasma membrane bilayer, and what is the role of cholesterol?

The plasma membrane is an amphipathic lipid bilayer composed of phospholipids, cholesterol, and glycolipids studded with integral and peripheral proteins. Cholesterol molecules insert between phospholipids to stabilize membrane structure and decrease membrane fluidity.

What are the six major functional categories of plasma membrane proteins?

Ion channels (selective pores), carriers/transporters (change shape to move solutes), receptors (bind specific ligands), enzymes (catalyze intra- or extracellular reactions), linkers (anchor cytoskeletal filaments or join cells), and cell-identity markers (glycoproteins like MHC proteins that identify self-cells).

Which molecular classes can freely diffuse across the lipid bilayer, and which require transport proteins?

Small, nonpolar, uncharged hydrophobic molecules ($O_2$, $CO_2$, $N_2$, fatty acids, steroids) and small uncharged polar molecules (water, urea) diffuse directly through the lipid bilayer. Ions ($Na^+$, $K^+$, $Ca^{2+}$, $Cl^-$) and large polar solutes (glucose, amino acids) require transmembrane protein channels or carriers.

What five physical factors determine the rate of simple diffusion across a membrane?

Steepness of the concentration gradient, temperature, mass of the diffusing substance, surface area available for diffusion, and diffusion distance.

What is the primary operational difference between channel-mediated and carrier-mediated facilitated diffusion?

Channel-mediated diffusion moves small ions through a specific aqueous pore (often gated open or closed) down their concentration gradient without binding-induced conformational cycles. Carrier-mediated diffusion involves a solute binding to a specific transporter site, which induces a conformational change in the protein to release the solute on the other side.

How is osmosis defined, and what determines osmotic pressure?

Osmosis is the net movement of solvent (water) through a selectively permeable membrane from an area of higher water concentration (lower solute) to lower water concentration (higher solute). Osmotic pressure is the pressure exerted by the non-diffusible solute particles on the solution side proportional to their concentration.

What morphological changes happen to a red blood cell placed in isotonic, hypotonic, and hypertonic solutions?

In an isotonic solution ($0.9\%\,NaCl$), cell volume remains unchanged. In a hypotonic solution, water moves inside by osmosis, causing the cell to swell and burst (hemolysis). In a hypertonic solution, water exits the cell, causing it to shrink and crinkle (crenation).

If a red blood cell containing $0.9\%\,NaCl$ is placed into a $2\%\,NaCl$ solution, what is the tonicity of the solution and what happens to the cell?

The $2\%\,NaCl$ solution is hypertonic relative to the cell; water flows down its concentration gradient out of the cell into the hypertonic solution, causing the red blood cell to undergo crenation (shrinkage).

What specific active transport mechanism is depicted here, and how many ions are moved per ATP hydrolyzed?

Primary active transport by the $Na^+/K^+$ ATPase (sodium-potassium pump); it hydrolyzes one molecule of ATP to pump $3\,Na^+$ out of the cell and $2\,K^+$ into the cell against their respective concentration gradients.

What two classes of secondary active transport proteins are illustrated in panels (a) and (b)?

(a) Antiporters, which move $Na^+$ down its electrochemical gradient into the cell while driving another substance ($Ca^{2+}$ or $H^+$) in the opposite direction out of the cell; (b) Symporters, which transport $Na^+$ and a cotransported solute (such as glucose or an amino acid) simultaneously in the same direction into the cell.

What sequential steps occur during receptor-mediated endocytosis of low-density lipoproteins (LDLs)?

1. Binding: LDL particles bind specific cell-surface receptors in clathrin-coated pits; 2. Vesicle formation: membrane invaginates and pinches off as a clathrin-coated vesicle; 3. Uncoating: clathrin proteins detach; 4. Fusion with endosome: LDLs separate from receptors; 5. Recycling: receptors bud off in transport vesicles back to the plasma membrane; 6. Lysosomal degradation: transport vesicles fuse with lysosomes where digestive enzymes break down LDLs.

How do phagocytosis and bulk-phase endocytosis (pinocytosis) differ?

Phagocytosis ('cell eating') is a selective process wherein a cell uses pseudopods to engulf large solid particles (microbes, cellular debris) to form a phagosome that fuses with a lysosome. Bulk-phase endocytosis ('cell drinking') is a nonselective uptake where the plasma membrane invaginates to take up droplets of extracellular fluid and dissolved solutes.

What is the difference between exocytosis and transcytosis?

Exocytosis is the fusion of intracellular membrane-enclosed secretory vesicles with the plasma membrane to release contents into the extracellular fluid. Transcytosis combines endocytosis on one side of a cell with vesicular transport across the cytoplasm and exocytosis on the opposite side (e.g., antibodies traversing endothelial cells).

What are the three structural filaments of the cytoskeleton in order of increasing diameter?

Microfilaments (thinnest, composed of actin; provide mechanical support and generate movement), intermediate filaments (medium diameter, e.g., keratin; stabilize organelle positions and withstand mechanical stress), and microtubules (thickest, hollow cylinders composed of tubulin; determine cell shape and guide organelle and chromosome movement).

What is the structural composition and organizing role of the centrosome?

The centrosome consists of a pair of orthogonally oriented centrioles (each a cylinder of nine microtubule triplets) surrounded by pericentriolar matrix containing tubulin complexes that serve as the organizing center for microtubule assembly and the mitotic spindle.

What internal microtubular arrangement is found in motile cilia and flagella, and how do their movement patterns differ?

Both contain a '$9+2$' array (nine doublet microtubules encircling a central pair) anchored to a basal body. Cilia execute a coordinated back-and-forth movement with an effective power stroke and recovery stroke to move surface fluids; flagella move an entire cell (such as a sperm cell) in undulating, wavelike patterns.

What structural and functional distinctions separate the rough endoplasmic reticulum from the smooth endoplasmic reticulum?

Rough ER is continuous with the nuclear envelope, studded with ribosomes, and synthesizes glycoproteins and phospholipids destined for membranes or exocytosis. Smooth ER lacks ribosomes and contains enzymes to synthesize fatty acids and steroids (e.g., estrogen, testosterone), detoxify drugs, remove phosphate from glucose-$6$-phosphate, and store/release $Ca^{2+}$ in muscle.

What structural organization does the Golgi complex exhibit, and how do proteins progress through its compartments?

It consists of $3\text{ to }20$ flattened membranous sacs called saccules. Proteins enter at the entry (cis) face from rough ER transport vesicles, undergo enzymatic modification (forming glycoproteins, glycolipids, lipoproteins) in the medial saccules, and are sorted and packaged into secretory, membrane, or storage vesicles at the exit (trans) face.

What are the definitions of autophagy and autolysis mediated by lysosomes?

Autophagy is the digestion and recycling of a cell's own worn-out organelles inside an autophagosome fused with a lysosome. Autolysis is the complete self-destruction of an entire cell caused by the simultaneous release of lysosomal digestive enzymes into the cytosol.

What are the biochemical functions of peroxisomes and proteasomes?

Peroxisomes contain oxidases that oxidize fatty acids and amino acids, producing toxic hydrogen peroxide ($H_2O_2$) which is immediately decomposed by catalase into water and oxygen. Proteasomes are barrel-shaped multiprotein complexes containing proteases that degrade unneeded, damaged, or misfolded cytosolic proteins into small peptide fragments.

What structural features characterize a mitochondrion, and what essential functions does it execute?

It consists of an outer mitochondrial membrane, an inner mitochondrial membrane folded into cristae to expand surface area, and an internal fluid-filled matrix. It is the primary site of aerobic cellular respiration to generate ATP and plays an essential early triggering role in apoptosis.

What is the structural hierarchy of DNA packaging within the interphase nucleus?

The double-helix DNA wraps twice around an octamer of histone proteins to form nucleosomes; these coil tightly with linker DNA into a $30\text{-nm}$ chromatin fiber, which loops and folds further into chromatids and visible condensed chromosomes during nuclear division.

What enzyme catalyzes transcription, and what are the roles of introns and exons during pre-mRNA splicing?

RNA polymerase catalyzes transcription from a DNA promoter sequence. Pre-mRNA contains noncoding regions called introns that are excised by small nuclear ribonucleoproteins (snRNPs) and coding regions called exons that are spliced together to produce mature functional mRNA.

What functions do the A, P, and E binding sites of a functional ribosome serve during translation?

The A (aminoacyl) site binds the incoming aminoacyl-tRNA bearing the next amino acid; the P (peptidyl) site holds the tRNA attached to the growing polypeptide chain where peptide bonds form; the E (exit) site temporarily holds the uncharged initiator/carrier tRNA before its ejection into the cytosol.

Which major cell cycle phases are depicted in this diagram, and what primary molecular event defines the S phase?

The somatic cell cycle consists of Interphase ($G_1$ phase, S phase, and $G_2$ phase) and the Mitotic (M) phase. During the S phase (lasting approximately $8\,\text{hours}$), identical replication of cellular DNA occurs.

What characteristic nuclear and chromosomal events occur during prophase, metaphase, anaphase, and telophase of mitosis?

Prophase: chromatin condenses into visible chromosomes, nucleolus and nuclear envelope disintegrate, centrosomes migrate to poles; Metaphase: centromeres of chromatid pairs align at the metaphase plate; Anaphase: centromeres split and sister chromatids separate toward opposite poles; Telophase: chromosomes uncoil into chromatin, nuclear envelopes and nucleoli reform, and the mitotic spindle disassembles.

How does cytokinesis divide the cytoplasm in somatic cell division?

A contractile ring composed of actin microfilaments and myosin forms a cleavage furrow around the center of the cell, which pinches progressively inward until the parent cytoplasm and organelles are partitioned into two identical daughter cells.

What are the two major genetic differences between mitosis and meiosis?

Mitosis consists of a single nuclear division yielding two genetically identical diploid ($2n$) somatic cells. Meiosis consists of two nuclear divisions (Meiosis I and Meiosis II) involving synapsis and crossing-over in Prophase I, producing four genetically variable haploid ($n$) gametes.

How are carcinomas, sarcomas, and the process of tumor angiogenesis defined?

Carcinomas are malignant neoplasms originating from epithelial cells; sarcomas are malignant neoplasms arising from muscle or connective tissues; angiogenesis is the growth of new blood vessel networks stimulated by a tumor to supply its rapid metabolic growth.