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Epithelial Tissues and Glandular Epithelium (Lecture Video Notes)

Simple Squamous Epithelium

  • Definition: a single layer of flat, thin cells. Simple means one layer; squamous means flat. When viewed from the top, cells resemble floor tiles. Nucleus is usually in the middle.
  • Key terms:
    • Simple: 1 layer
    • Squamous: flat cells
    • Endothelium: simple squamous epithelium lining heart and blood vessels
    • Mesothelium: simple squamous epithelium lining the thoracic and abdominal cavities
  • Locations in the human body:
    • Endothelium lining heart and blood vessels
    • Alveolar epithelium lining air sacs in the lungs
    • Mesothelium lining thoracic and abdominal cavities
  • Functions:
    • Rapid absorption or secretion in sites of exchange
    • Controls vessel permeability (as a lining for vessels)
    • Reduces friction when lining vessels
  • Visual/structural notes:
    • From the top: plasma membrane, nucleus, cytoplasm (looks like floor tiles)
    • Side view: fragile, often closely associated with underlying connective tissue (basement membrane) and adjacent tissues
  • Lab-related tips:
    • Lab three, four, and five involve drawing tissues; best sources for drawing guidance are the textbook or lecture PowerPoint
    • For identification, expect using high-quality images (not just PowerPoint stock images) to avoid ambiguity
  • Quick recap cue:
    • One cell layer thick, flat, central nucleus; endothelium and mesothelium are classic examples; functionality tied to rapid exchange and reduced friction

Simple Cuboidal Epithelium

  • Definition: a single layer of cube-shaped cells; nucleus is typically central
  • Key terms:
    • Simple: 1 layer
    • Cuboidal: 1 layer, cube-shaped cells
  • Common locations in the body:
    • Ovaries (if present)
    • Kidneys
    • Lining of ducts (e.g., thyroid gland ducts and pancreatic ducts)
  • Functions:
    • Secretion and absorption
  • Visual cues:
    • Cube-shaped cells with a central nucleus; basement membrane beneath; single layer on slide
  • Lab/examples discussed:
    • Sweat glands and thyroid gland sections show simple cuboidal epithelium in secretory and ductal regions
    • A note on labeling: when identifying tissues, use the full name (e.g., "Simple Cuboidal Epithelium"); partial names (e.g., just "Cuboidal") receive deductions
  • Important distinctions:
    • In glandular contexts, these cells can form ducts or secretory portions
    • One layer thick in the slide; underlying connective tissue provides the blood supply (epithelium is avascular)
  • Visual details to remember:
    • In some gland diagrams, you’ll see basal surface anchored to connective tissue and a lumen in ducts

Simple Columnar Epithelium

  • Definition: a single layer of tall, column-like cells; nucleus tends to be oval and positioned closer to the bottom (basal region)
  • Shape/placement:
    • Columnar cells are taller than they are wide
    • Nuclei typically near the bottom/middle of the cell
  • Variants:
    • Non-ciliated simple columnar epithelium: often found in the digestive tract (stomach to anus)
    • Ciliated simple columnar epithelium: found in the uterus and fallopian tubes; cilia help propel ovum along the tract
  • Surface modifications:
    • Goblet cells: secret mucus to lubricate and protect the surface; mucus reduces friction in GI tract
    • Microvilli: may be present (peach-fuzz appearance) to increase surface area for absorption
    • Cilia: longer, hair-like projections that beat in coordinated waves to move substances across the surface
  • Functional notes:
    • Non-ciliated: secretion and absorption are primary functions
    • Ciliated: propulsion of mucus and egg movement in reproductive tract
  • Goblet cells specifics:
    • Goblet cells are mucus-secreting cells found in the epithelium
    • Mucus provides lubrication and protective barrier in mucus-secreting surfaces
  • Microvilli vs. cilia distinctions:
    • Cilia: longer and more hair-like
    • Microvilli: shorter, resemble peach fuzz
  • Diagram/visual cues:
    • Goblet cell: clear mucus-filled area (mucus in secretory vesicles) within the cytoplasm
    • Microvilli: dense, brush-like apical surface
  • Lab context:
    • You may be asked to identify goblet cells and distinguish microvilli from cilia in microscope images

Pseudostratified Columnar Epithelium

  • Definition: “false stratified” epithelium that appears to have multiple layers but actually a single layer; all cells rest on the basement membrane
  • Why it looks stratified:
    • Nuclei are located at varying heights across cells, giving an illusion of multiple layers
    • Some cells do not extend all the way to the apical surface
  • Key features:
    • All cells attach to the basement membrane
    • Nuclei distribution is irregular, creating the pseudo-stratified appearance
  • Common locations:
    • Respiratory tract: nasal cavity, trachea, bronchi (cilia often present; mucus produced by goblet cells)
  • Functional role:
    • Traps inhaled particles and pathogens using goblet cells and mucus
    • Cilia move mucus toward the pharynx for expectoration or swallowing
  • Special notes on ciliation and goblet cells:
    • Some pseudostratified epithelia are ciliated and mucus-secreting (goblet cells)
  • Lab observations:
    • When identifying, observe the irregular nuclei positions and basement membrane attachment; ciliations and goblet cells help confirm respiratory tract epithelium

Stratified Epithelium

  • Definition: epithelia composed of two or more cell layers; more protective and durable than simple epithelia
  • Location and purpose:
    • Typically found in areas subject to wear and tear (e.g., skin, oral cavity, esophagus)
  • Subtypes:
    • Stratified Squamous Epithelium
    • Keratinized vs Non-keratinized
  • Stratified Squamous Epithelium (general concepts):
    • Youngest cells at the bottom; cells migrate toward the surface and die as they move away from the blood supply in the underlying connective tissue
    • The oldest surface cells become layers of dead or keratin-filled cells
  • Keratinized vs Non-keratinized:
    • Keratinized:
    • Contains keratin protein; cells on the surface are dead and filled with keratin
    • Found in the skin, hair, nails; provides toughness and water-repellency
    • Stratum corneum is the outermost dead keratinized layer
    • Non-keratinized:
    • Lacks keratin; remains moist
    • Found in moist regions such as the mouth, esophagus, vagina, anus, and pharynx
  • Visual cues:
    • Keratinized: dried-looking surface with a clear dead layer (stratum corneum)
    • Non-keratinized: moist, living surface cells without a keratin coating
  • Pap smear context:
    • Cervical screening (Pap test) collects epithelial cells from the cervix to detect precancerous changes (dysplasia) or cancer
    • Dysplasia indicates abnormal cells that may progress to cancer if left unchecked
  • Ethical and health relevance:
    • Pap smears are a critical screening tool for cervical cancer prevention; HPV infection is a major risk factor; regular screening can enable early intervention

Transitional Epithelium

  • Definition: a stratified epithelium with the ability to stretch and change appearance
  • Location:
    • Urinary system: urinary bladder and ureters
  • Appearance changes with bladder filling:
    • Empty bladder: cells resemble cube-shaped (cuboidal) forms
    • Full bladder: topmost layers flatten out as the epithelium stretches
  • Functional significance:
    • Highly stretchable to accommodate fluctuations in urine volume
    • Provides a barrier while allowing distension
  • Lab relevance:
    • Not required for the lab exam in this course, but may appear on the lecture exam

Glandular Epithelium

  • Definition: epithelial tissue specialized for secretion
  • Two main gland categories:
    • Endocrine glands: secrete products (hormones) directly into the bloodstream
    • Exocrine glands: secrete products into ducts or lumens of hollow organs or onto surfaces (e.g., sweat, mucus)
  • Examples mentioned:
    • Endocrine: thyroid gland, pituitary gland, adrenal gland
    • Exocrine: sweat glands, sebaceous glands, mucous glands in the mouth and intestines
  • Structural notes:
    • Glandular epithelium comprises cells that produce and secrete substances
    • Secretions may be carried in ducts or released into tissues or blood
  • Lab imagery and interpretation:
    • Sweat gland cross-section: visible lumen, secretory units lined by cuboidal epithelium
    • Thyroid gland: thyroid follicles lined by cuboidal epithelium; hormones stored in colloid within follicles (storage within the gland)
  • Thyroid storage detail:
    • Thyroid hormones can be stored for long periods; the slide notes mention approximately a hundred-day supply stored within the gland, reflecting the importance of thyroid hormones for life
  • Naming guidance (lab exam tip):
    • Always provide the full three-part name for most epithelia (Layer/Organization, Shape, Epithelium type), e.g., "Simple Cuboidal Epithelium"
    • Transitional epithelium is an exception with two parts in its name; partial names will be marked down

General Notes and Lab Tips

  • Epithelial tissue characteristics:
    • Epithelial tissues are avascular; they rely on diffusion from the underlying connective tissue blood supply
    • The basement membrane anchors epithelial tissue to connective tissue
    • Unlike epithelium, connective tissue contains blood vessels
  • Anatomical context and exam prep:
    • Expect to identify big-picture differential features between epithelial tissue types (shape, layering, location, and functions)
    • Be able to describe where each tissue type is found in the human body
    • Expect to interpret both labeled diagrams and microscope photos (distinguishing features like goblet cells, microvilli, cilia, and basement membranes)
  • Study strategy tips mentioned by the instructor:
    • For lab exams, anticipate seeing award-winning, unambiguous images to minimize misidentification
    • Drawing practice is emphasized; use textbook or lecture slides as drawing references
    • The upcoming labs will include filling out tables with tissue names, locations, and functions
  • Ethical/health context:
    • Pap smear discussion highlights cervical cancer screening, HPV association, and the importance of regular screening for early detection and intervention
  • Quick reference concepts to memorize:
    • Endothelium = simple squamous lining of blood vessels and heart
    • Mesothelium = simple squamous lining of body cavities (thoracic and abdominal)
    • Goblet cells = mucus-secreting cells found in several epithelia, particularly in GI and respiratory tracts
    • Basal surface vs. apical surface: basal surface anchors to connective tissue; apical surface faces the lumen or external environment
    • Keratinization provides toughness and water resistance; non-keratinized surfaces remain moist (e.g., mucosal linings)