Epithelia 2025 Flashcards
(46 cards)
Q: What are the five main functions of epithelial tissues?
Protection – Acts as a barrier against physical, chemical, and biological threats.
Transport – Enables transepithelial movement of substances.
Absorption – Takes in nutrients from the external environment.
Sensing – Detects environmental stimuli via specialized cells.
Secretion – Releases substances to maintain homeostasis.
Q: What are the key characteristics of epithelial tissues?
High cellularity – Densely packed cells.
Polarity – Distinct apical, lateral, and basal domains.
Attachment – Anchored to each other and the basement membrane.
Avascularity – No blood vessels; relies on diffusion.
High regeneration – Rapid cell turnover and repair
How are epithelial tissues classified by layers?
Simple – One layer (e.g., for absorption/secretion).
Stratified – Multiple layers (e.g., for protection).
Pseudostratified – Appears layered, but all cells touch the basement membrane.
Transitional – Specialized for stretching (e.g., bladder).
Q: How are epithelial tissues classified by shape?
Squamous – Flat and thin.
Cuboidal – Cube-shaped.
Columnar – Tall and column-like.
What are the six extracellular links in epithelial tissues?
Tight Junctions – Seal cells together; regulate paracellular transport.
Adherens Junctions – Transmit mechanical tension; first to form.
Desmosomes – Provide strong adhesion via intermediate filaments.
Gap Junctions – Allow exchange of ions and small molecules.
Hemidesmosomes – Anchor cells to the basement membrane using integrins.
Focal Adhesions – Connect actin cytoskeleton to ECM; involved in signaling and movement.
What are the two main pathways for transepithelial transport?
Transcellular – Solutes pass through the cell via apical and basolateral membranes.
Paracellular – Solutes pass between cells through tight junctions.
Q: What are the two types of transcellular transport?
Passive transport – No energy required; moves substances down their gradient.
Active transport – Requires energy; moves substances against their gradient.
Q: What is passive transcellular transport?
A: Movement of molecules down their concentration or electrochemical gradient without energy input.
Q: What are examples of passive transport mechanisms?
Simple diffusion – Small, non-charged molecules (e.g., O₂, CO₂).
Facilitated diffusion – Uses channels or carriers for larger or charged molecules (e.g., glucose via GLUT, water via aquaporins).
Q: What is active transcellular transport?
A: Movement of molecules against their gradient using energy.
Q: What are the two types of active transport?
Primary active transport – Direct use of ATP (e.g., Na⁺/K⁺ ATPase).
Secondary active transport – Uses energy from another gradient (e.g., SGLT uses Na⁺ gradient to transport glucose).
Q: How does the Na⁺/K⁺ ATPase work?
Pumps 3 Na⁺ out and 2 K⁺ into the cell using ATP.
Maintains low intracellular Na⁺ and high K⁺, creating an electrochemical gradient.
Q: Why is the Na⁺/K⁺ ATPase important for epithelial transport?
It creates the Na⁺ gradient that powers secondary active transport systems like SGLT.
Q: How does the sodium-glucose cotransporter (SGLT) function?
Uses the Na⁺ gradient to transport glucose into the cell against its concentration gradient.
This is an example of secondary active transport.
Q: What are the main cell types in the conducting respiratory epithelium?
Ciliated cells – Move mucus toward the esophagus.
Goblet cells – Secrete mucus (Muc5ac, Muc5b) to trap particles.
Basal cells – Stem cells that regenerate other epithelial cells.
Club (Clara) cells – Secrete CCSP; act as secondary stem cells.
Neuroendocrine cells (NEC) – Secrete neuropeptides; regulate breathing.
Tuft cells – Detect harmful substances; secrete cytokines.
Ionocytes – Regulate pH via ion transport.
Deuterosomal cells – Progenitors of ciliated cells.
Q: What are the two main alveolar epithelial cell types and their functions?
Type I (ATI) cells – Thin, squamous cells for gas exchange; cover 95% of alveolar surface.
Type II (ATII) cells – Cuboidal cells that secrete surfactant and regenerate ATI cells.
Q: What is the role of dynein in cilia movement?
Dynein is a motor protein that enables the whip-like, coordinated movement of cilia, which propels mucus toward the esophagus for clearance.
Q: What is the function of surfactant in the alveoli?
Surfactant, secreted by ATII cells, reduces surface tension at the air-liquid interface, preventing alveolar collapse—especially in smaller alveoli.
Q: What protein is a key component of surfactant?
Surfactant Protein C (SP-C) – crucial for reducing surface tension and maintaining alveolar stability.
Q: What causes cystic fibrosis and how does it affect the lungs?
Mutations in the CFTR gene impair chloride transport, leading to thick, sticky mucus that causes airway obstruction, infection, and inflammation.
Q: How does asthma affect the respiratory epithelium?
Goblet cell hyperplasia – Excess mucus production.
Overexpression of MUC5AC – Increased mucin synthesis.
Loss of junction proteins – Reduced tight, adherens, and gap junctions.
Q: What is a common allergen that triggers respiratory epithelial responses?
House dust mite allergen – Can lead to inflammation and allergic responses in the airway epithelium.
Q: What are the five main types of intestinal epithelial cells and their functions?
Enterocytes – Absorb nutrients; most abundant (80–95%).
Goblet cells – Secrete mucus (mainly Muc2) for protection.
Paneth cells – Secrete antimicrobial peptides and support stem cells.
Enteroendocrine cells – Release hormones (e.g., motilin, somatostatin) to regulate gut function.
Stem cells – Located in crypts; regenerate all epithelial cell types.
Q: How are epithelial cells eliminated from the intestinal layer?
Through epithelial cell extrusion, a process mediated by adherens junctions that:
Transmit mechanical tension to neighboring cells
Re-establish cell-cell contact after extrusion
Maintain barrier integrity and homeostasis
Occurs via apoptotic, oncogenic, or live-cell extrusion
