Epithelial/Connective Tissues and Integumentary System - Vocabulary

Epithelial Tissue: Roles, Features, and Examples

• Primary job: protection of the body. Acts as a barrier between the inside and outside and helps keep outside stuff out and good stuff in.
  • Protection against physical damage, pathogens, and chemicals.
  • Also involved in selective permeability (deciding what moves in and out).
• Skin as a barrier
  • Highly protective and water resistant due to keratin in epidermal cells.
  • Keratinocytes produce keratin; as skin cells migrate toward the surface, keratin becomes harder and more impenetrable.
  • Water loss is a bigger issue than water entry; keratin helps prevent water loss.
  • UV protection: built-in protection helps shield deeper skin layers from UV damage; damage reaching the basal layer can cause DNA damage and abnormal cell replication.
• Epithelial tissue functions summarized
  • Barrier/protection (primary)
  • Absorption (e.g., nutrients in the digestive tract; senses in olfactory region)
  • Secretion (glands; production and release of substances)
  • Excretion (getting substances out of the body via processes like sweating)
  • Sensation (receptors as part of epithelial-associated structures)
• Simple columnar epithelium and absorption
  • Structure: simple layer of tall cells (one cell layer thick; columnar shape).
  • Location: common in absorption regions like the digestive tract.
  • Microvilli: tiny hair-like projections on the apical surface that increase surface area to absorb nutrients efficiently.
  • Benefit of a single layer: substances can pass through quickly into the bloodstream.
• Secretion and glands
  • Secretion: epithelial cells can secrete substances; associated with glands.
  • Glands: specialized cells that push substances out of a tissue.
  • Sweat glands (in the skin) secrete sweat through ducts to the surface for temperature regulation.
• Is secretion the only way to remove substances from the body?
  • Not the only way. Epithelial and other tissues can contribute to excretion via the skin (sweat) as well as other routes.
  • Exocrine glands release secretions into ducts that leave the body; endocrine glands release products directly into the bloodstream.
• Endocrine vs Exocrine glands (illustrative points)
  • Endocrine glands: products secreted into blood vessels, directly entering the bloodstream.
  • Exocrine glands: products secreted into a duct or onto a surface, leaving the body.
  • Exocrine glands require a larger space and more complex tissue than a single cell layer; not usually present in a single-layer epithelium.
• Blood vessel walls and simple layers
  • The walls of blood vessels are a single layer of epithelial-like cells (endothelium) separating blood from the interstitial space.
  • Gas exchange example: oxygen passes from lungs through a single epithelial layer into the interstitial space, then into the bloodstream through another single-layer capillary wall.
  • This illustrates how simple epithelia enable selective permeability for substances (e.g., CO₂ out, O₂ in).
• Question recap: Is there a specific epithelia type that secretes? (brief answer)
  • Not a single specific type; endocrine vs exocrine gland presence depends on tissue thickness and space.
  • Stratified epithelia are more likely to contain glands due to greater thickness and space.
• Olfactory epithelium and sensation (example)
  • The blue structures in the provided image depict epithelium involved in smell; identified as simple columnar epithelium (one layer; taller than wide).
  • Simple columnar epithelium is well-suited for absorption, including absorbing odorant molecules for interpretation by the brain.
• Simple columnar epithelium in sensation and absorption
  • Absorptive function can extend to olfactory and gustatory regions where a simple layer supports efficient transfer of substances to receptors.
• Epithelial tissue and sensory input
  • Epithelial tissues often contain receptors for input (temperature, pain, pressure) and feed information to the nervous system.
  • Skin contains receptors for temperature, pressure, and pain; nasal cavity contains specialized receptors for smell.
• Tongue epithelial composition (contextual question)
  • The tongue is a mix of tissues (epithelial and muscular); absorptive cells are likely simple columnar, but the tongue contains multiple tissue types.
• Quick quiz guidance (primary function emphasis)
  • Primary function of epithelial tissue: protection.
• Transition to connective tissues: overview
  • Connective tissues differ greatly in appearance and content (blood, lymph, adipose, cartilage, bone).
  • Despite their varied forms, they are united by the ability to connect, support, transport, or share information.
  • The category includes fluids (blood, lymph), fat storage (adipose), cartilage, and bone; all serve connective roles.
• Connective tissue as protective tissue
  • Physical protection: adipose tissue cushions and insulates; cartilage absorbs shock; bones protect organs (e.g., skull and rib cage).
  • Immune protection: blood and lymph transport white blood cells; these cells identify and disable invaders.
• Transportation and transport systems
  • Blood and lymph transport substances around the body; red blood cells carry oxygen to tissues; the circulatory and lymphatic systems act as highways for movement and exit routes (pee, defecation, sweat).
• Storage in connective tissue
  • Adipose tissue stores excess energy as fat for future use; energy reserves help survive periods without external energy sources.
• Repair and regeneration in connective tissue
  • Fibroblasts produce collagen, forming the internal scaffolding that supports tissue structure and aids repair from the inside out.
• Immune defense in connective tissue
  • Blood and lymph contain platelets and white blood cells that detect invaders and defend the body.
• Quick recap: primary functions of connective tissue
  • Primary cluster of functions: transportation, energy storage, repair/regeneration, and immune defense; all contribute to protection and homeostasis.
• Connective tissue review: quick check
  • Even though protection is a common thread, connective tissues provide multiple distinct primary functions depending on the tissue type.
• Integumentary system: quick overview
  • The theme for this module: protection.
  • The integumentary system acts as a barrier, protecting the body from physical damage, UV radiation, and chemical exposure.
• Keratin and keratinocytes
  • Keratinocytes produce keratin, which provides strength and waterproofing.
  • Keratin contributes to the waterproof barrier of the skin and helps prevent water loss.
• UV protection and DNA safety
  • The skin’s barrier protects deeper layers from UV radiation; if UV reaches the basal layer, DNA damage can occur, leading to abnormal cell replication.
• What if keratin production is impaired?
  • If keratin production is reduced, skin loses toughness and waterproofing, increasing water loss and possibly increasing permeability to potentially harmful substances.
• Thermoregulation in the skin
  • Vasodilation: dilation of superficial vessels increases blood flow and aids sweating to dissipate heat, cooling the body.
  • Vasoconstriction: constriction of superficial vessels reduces heat loss and keeps blood near the core to maintain core temperature.
• Sensation in the skin
  • The skin contains receptors for temperature, pain, and pressure, enabling the brain to respond to environmental changes and potential harm.
• Epithelial tissue: excretion vs secretion (definitions)
  • Secretion: getting substances out of a cell.
  • Excretion: getting substances out of the body entirely.
  • Sweat glands are a major excretory pathway through the skin (excretion via sweat; components often include water, urea, and salts like sodium).
  • Sweat composition can vary with state: rest, exercise, anxiety, medications; different byproduct patterns can appear in sweat.
• Vitamin D synthesis pathway (skin to bone health)
  • UV exposure converts 7-dehydrocholesterol in the skin to Vitamin D$_3$ (calciferol).
  • In the liver, Vitamin D$_3$ is converted to Calcidiol (25-hydroxyvitamin D).
  • In the kidneys, Calcidiol is converted to Calcitriol (1,25-dihydroxyvitamin D).
  • Calcitriol increases calcium absorption in the gut, supporting bone health and reducing the need to pull calcium from bones.
  • Pathway representation:
    ext{7-dehydrocholesterol}
    ightarrow{ ext{UV}} ext{Vitamin D}3
    ightarrow{ ext{liver}} ext{Calcidiol} ightarrow{ ext{kidneys}} ext{Calcitriol}
  • Calcitriol effect: ext{Calcitriol}
    ightarrow ext{↑} ext{Ca}^{2+} ext{absorption}
    ightarrow ext{bone health maintenance}.
• Primary function of the integumentary system (summary)
  • The overarching primary function is protection (barrier against physical damage, UV radiation, and chemical exposure).
• Lab worksheet guidance and study tips (optional, as provided in lecture)
  • Two charts available: epithelium and connective tissue; there is not a single correct function box—you can note multiple legitimate functions for a tissue type (e.g., simple squamous can be described as protective and permeable/absorptive in context).
  • Location and function can have multiple valid examples; be prepared to list several locations and functions for each tissue type.
  • The integumentary worksheet last page is recommended for studying vitamin D conversion steps and reinforcing the key concepts; filling the blanks there helps ensure readiness for the quiz.
• Quick study pointers from the lecture
  • Always focus on the primary function first (epithelial: protection; connective: protection plus transport/storage/repair/immune defense).
  • Remember the governance of barrier tissues: protection, selective permeability, and sensation.
  • Recognize the three-step vitamin D pathway and its impact on calcium homeostasis and bone health.
  • Distinguish endocrine vs exocrine gland products and where they are released.
  • Keep the concepts of vasodilation and vasoconstriction in the context of thermoregulation and skin function.
• Final takeaway theme for today
  • Tissues and the integumentary system are organized around a central purpose: protection. Each tissue type achieves protection in its own way—physically, chemically, immunologically, metabolically, and via sensory feedback.
• If you have questions, bring them to the next session or ask during office hours. The module three content builds on these foundations and will connect to the upcoming exam content.