Histology and Cell Concepts Flashcards

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Tissues

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Collections of cells that are similar in structure and perform a similar function. Tissues have characteristic arrangements and extracellular matrix (ECM) components that relate to their roles in the body. Studying tissues is called histology.

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Histology

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The study of tissues and how their cellular structure relates to function. Histology uses staining and microscopic examination to identify tissue types and diagnose structural adaptations. It emphasizes cell arrangement, shapes, nucleus characteristics, and extracellular components.

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Epithelial

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Tissue that covers surfaces and lines cavities, resting on a basement membrane and supported by connective tissue. It is avascular but highly regenerative and functions in protection, absorption, filtration, excretion, and secretion. Classification is by arrangement (simple vs stratified) and shape (squamous, cuboidal, columnar).

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Simple squamous

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A single layer of flat, scale-like cells specialized for rapid diffusion and filtration. It lines blood vessels and alveoli in the lungs where exchange of gases and small molecules is required. The thinness minimizes diffusion distance.

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Simple cuboidal

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A single layer of cube-shaped cells with roughly equal dimensions that function in secretion and absorption. Common locations include kidney tubules and glandular ducts. These cells often have a central, spherical nucleus.

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Simple columnar

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A single layer of tall, rectangular cells specialized for absorption and secretion, often containing microvilli or goblet cells. This epithelium lines most of the digestive tract and contributes to nutrient uptake and mucus production. The elongated shape reflects absorptive function.

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Stratified squamous

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Multiple layers of cells with flat cells at the surface that protect underlying tissues from abrasion and dehydration. Keratinized forms (with surface keratin) are found in the epidermis for waterproofing, while non-keratinized forms line moist surfaces like the mouth and esophagus. The layered arrangement provides mechanical protection.

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Pseudostratified columnar

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A single layer of columnar cells of varying heights that appears stratified because nuclei are at different levels. Often ciliated and containing goblet cells, it secretes and propels mucus, as seen in the respiratory tract and nasal cavity. All cells contact the basement membrane despite the layered appearance.

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Transitional

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A stratified epithelium specialized for distention and recoil, with surface cells that change shape depending on stretch. It lines the urinary bladder and parts of the urinary tract, allowing expansion as the bladder fills. The apical cells appear dome-shaped when relaxed and flattened when stretched.

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Connective tissue

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Tissues that protect, support, and bind other tissues, characterized by relatively few cells embedded in an extensive extracellular matrix (ECM). ECM components include protein fibers (collagen, elastic, reticular) and ground substance, and vascularity varies by type. Examples include bone, cartilage, adipose, and blood.

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Collagen fibers

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Thick, strong protein fibers in the ECM that provide tensile strength and resist stretching. They are abundant in tendons, ligaments, and bone matrix. Collagen organization (parallel vs. haphazard) influences tissue mechanical properties.

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Dense regular

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Connective tissue with parallel bundles of collagen fibers and fibroblasts, adapted to resist unidirectional tensile stress. It forms tendons and ligaments where strength along a single axis is required. The organized fiber arrangement limits stretch in other directions.

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Adipose

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A specialized connective tissue composed mainly of adipocytes that store lipids for energy, provide insulation, and cushion organs. It is commonly found in the hypodermis, around the heart, and in the abdominal cavity. The large lipid droplet compresses the cytoplasm and nucleus to the cell periphery.

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Cartilage

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A tough, flexible connective tissue with chondrocytes housed in lacunae and an avascular matrix. It resists compression and provides smooth joint surfaces, structural support, or flexibility depending on type. Major types include hyaline, fibrocartilage, and elastic cartilage.

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Hyaline cartilage

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A glassy, smooth cartilage that provides support with some flexibility and forms the articular surfaces of joints, costal cartilages, and the nasal septum. Its matrix is rich in collagen type II and gives a low-friction surface for joint movement. It is the most common cartilage type.

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Bone

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A hard, calcified connective tissue with a mineralized matrix and abundant collagen that provides structural support, protection, and a reservoir for calcium. Bone is highly vascularized and houses osteocytes in lacunae. It also supports hematopoiesis in marrow cavities.

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Muscle tissue

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Tissue specialized for contraction and force generation, categorized as skeletal (voluntary, striated, unbranched), cardiac (involuntary, striated, branched), and smooth (involuntary, non-striated, unbranched). Each type has unique cellular features aligned to its function. Muscle tissue is essential for movement and organ function.

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Epidermis

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The outer epithelial layer of the skin composed of stratified squamous keratinized epithelium that is avascular and regenerative. It contains keratinocytes, melanocytes, dendritic cells, and Merkel cells, and varies between thin skin (4 layers) and thick skin (5 layers). The epidermis provides a barrier against dehydration, abrasion, and infection.

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Keratinocytes

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The predominant epidermal cell type that produces keratin, a structural protein that waterproofs and protects the skin. These cells arise in the basal layer and migrate superficially while undergoing keratinization and eventual desquamation. Their turnover enables epidermal regeneration.

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Melanocytes

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Pigment-producing cells in the epidermis that synthesize melanin to protect underlying tissues from UV radiation. Melanin is transferred to keratinocytes and contributes to skin color and photoprotection. Melanocyte number is relatively constant, but activity varies among individuals.

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Hair bulb

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The expanded base region of a hair follicle located below the skin surface that contains the hair matrix and papilla. The papilla supplies capillaries and signals for hair growth, while the matrix contains actively dividing cells that produce the hair shaft. The bulb is essential for hair production and cycling.

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Eccrine glands

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Also called merocrine sweat glands, they are numerous coiled tubular glands that open to the skin surface and secrete sweat by exocytosis. Their secretions are mostly water with salts, vitamin C, antibodies, and metabolic wastes; they function in thermoregulation and waste excretion. Secretion is under sympathetic nervous control.

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Sebaceous glands

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Simple branched alveolar holocrine glands that produce sebum, an oily substance that lubricates and helps protect skin and hair. Sebum has bactericidal properties and prevents excessive drying. These glands typically associate with hair follicles.

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Water

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A polar molecule $H_2O$ with properties essential for life, including high heat capacity, high heat of vaporization, solvent ability, reactivity, and cohesion/adhesion. Water makes up about 60% of body weight and functions as the primary medium for biochemical reactions and transport in body fluids. Its polarity underlies solubility of many biological molecules.

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Solvent

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A liquid in which other substances dissolve; in biology, water is the universal solvent that dissolves many solutes to form aqueous solutions. Solvents allow reactants to meet and reactions to proceed in cells and body fluids. Solubility depends on molecular polarity and interactions with the solvent.

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Hydrophilic

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Describes polar molecules or ions that interact readily with water and dissolve in aqueous solutions. Hydrophilic substances form hydrogen bonds or electrostatic interactions with $H_2O$, facilitating transport in body fluids. Many biological macromolecules and ions are hydrophilic.

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Hydrophobic

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Describes nonpolar molecules that do not interact well with water and tend to aggregate or separate from aqueous solutions. Hydrophobic interactions drive membrane formation and protein folding by minimizing exposure of nonpolar groups to $H_2O$. Lipids are typically hydrophobic.

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Acid

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A substance that donates hydrogen ions ($H^+$) to a solution, thereby increasing $H^+$ concentration and lowering pH. Strong acids dissociate more completely, while weak acids partially dissociate. Acids play roles in digestion and metabolic reactions.

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Base

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A substance that accepts hydrogen ions ($H^+$), decreasing $H^+$ concentration and raising pH. Bases can be strong or weak and are important in maintaining physiological pH and in biochemical reactions. Examples include bicarbonate and many cellular buffers.

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pH

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A logarithmic measure of hydrogen ion concentration that indicates solution acidity or alkalinity. Lower pH values are acidic (higher $H^+$), pH 7 is neutral, and higher pH values are basic (lower $H^+$). Physiological processes require tight pH regulation in body fluids.

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Buffer

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A molecule or system that minimizes pH changes by reversibly releasing or binding $H^+$ to resist sudden shifts. An important blood buffer pair is bicarbonate/carbonic acid, represented as $HCO_3^- + H^+ \leftrightarrow H_2CO_3$, which helps stabilize blood pH during metabolic or respiratory disturbances. Buffers maintain homeostasis by absorbing excess acid or base.

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Osmosis

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The diffusion of water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration. Osmosis changes cell volume and generates osmotic pressure, which can influence cell shape and function. It is essential for fluid balance between compartments.

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Tonicity

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A description of how extracellular solution concentration affects cell volume: isotonic solutions maintain cell volume, hypertonic solutions cause water to exit cells (shrinking), and hypotonic solutions cause water to enter cells (swelling). Tonicity depends on membrane-permeable solutes and has clinical importance for IV fluids. Cells rely on homeostatic mechanisms to preserve isotonic conditions.

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Plasma membrane

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A selectively permeable lipid bilayer (fluid mosaic) composed of phospholipids, cholesterol, proteins, and carbohydrates that separates the cell from its environment. Membrane proteins mediate transport and signaling while carbohydrates provide recognition patterns. The membrane controls material exchange and information flow.

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Mitochondrion

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A double-membraned organelle that produces cellular energy in the form of ATP via oxidative phosphorylation. Mitochondria are abundant in energy-demanding cells and contain their own DNA and machinery for protein synthesis. They also participate in apoptosis and metabolic signaling.

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Cell cycle

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An orderly sequence of stages a eukaryotic cell passes through to grow and divide, including interphase (G1, S, G2) and the mitotic phase (M). Interphase encompasses growth and DNA replication, while M phase includes mitosis and cytokinesis producing daughter cells. Regulation ensures proper DNA replication and division.

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Mitosis

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The process of nuclear division producing two genetically identical daughter nuclei and includes prophase, prometaphase, metaphase, anaphase, and telophase. Chromosomes condense, align at the metaphase plate, sister chromatids separate, and the nuclear envelope re-forms. Cytokinesis divides the cytoplasm to complete cell division.

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Microscope

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An optical instrument used to magnify small specimens; a compound light microscope uses objective and ocular lenses to produce primary and secondary images. Key components include objectives, stage, condenser, focus knobs, and light source, and operation requires proper centering, focusing, and illumination adjustments. Resolution depends on wavelength and numerical aperture.

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Attendance

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Attendance to lab is mandatory and treated like an exam; you must attend or have an approved absence and arrange make-ups for missed work. Missing more than two labs results in failing both lecture and lab sections of the course. Documentation is required for excused absences.

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Lab attire

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Required lab-appropriate clothing includes long pants, a shirt with sleeves, and closed-toed shoes for safety. No food or drink is allowed, and tardiness, disruptive behavior, or cell phone use can lead to dismissal and an unexcused absence. Proper attire minimizes risk during laboratory activities.