Epithelial Tissue Flashcards
Where are epithelial tissues found?
They line hollow cavities, tubes, ducts, and hollow organs, cover body surfaces, and form glands.
What are the three main functions of epithelial tissue?
- Selective barrier for substance movement. 2. Secretion of substances. 3. Protection from abrasion.
What are the three surfaces of epithelial cells?
Apical, lateral, and basal surfaces.
What are the five types of cell junctions in epithelial tissue?
Tight junctions, adherens junctions, desmosomes, gap junctions, and hemidesmosomes.
What proteins form tight junctions?
Claudins and occludins.
What is the function of tight junctions?
They prevent movement of ions and proteins between cells, maintaining cell polarity.
What is the function of adherens junctions?
Prevent cell separation due to tension forces (e.g., in the gut).
What proteins are involved in adherens junctions?
Cadherins span the gap, linking to catenins, which connect to actin microfilaments.
What is the main function of desmosomes?
They resist shearing forces and prevent cell separation, especially in cardiac and skin cells.
What proteins are involved in desmosomes?
Cadherins link to keratin intermediate filaments.
What is the function of gap junctions?
chemical/electrical cell communication, especially in cardiac tissue.
What proteins form gap junctions?
Connexins (six connexins form a connexon/hemichannel).
What is the function of hemidesmosomes?
They attach epithelial cells to the basement membrane.
What proteins are involved in hemidesmosomes?
Keratin (in the cytoplasm) binds to integrins, which connect to laminin in the basement membrane.
What are the two layers of the basement membrane?
- Basal lamina (secreted by epithelial cells, contains collagen, laminin, proteoglycans, glycoproteins). 2. Reticular lamina (secreted by fibroblasts in connective tissue, contains fibronectin and collagen).
What are three functions of the basement membrane?
- Structural support for epithelium. 2. Surface for epithelial migration during wound healing. 3. Physical barrier against malignant melanoma invasion.
Why is epithelial tissue avascular?
It lacks blood vessels; nutrients and waste exchange occur via diffusion through the basement membrane.
What are the two main types of epithelial tissue?
- Covering epithelium (covers surfaces, lines cavities). 2. Glandular epithelium (secretes substances).
How is covering epithelium classified?
By cell shape (squamous, cuboidal, columnar, transitional) and layering (simple, stratified, pseudostratified).
What are the functions of the different epithelial cell shapes?
Squamous: Diffusion. Cuboidal: Secretion & absorption. Columnar: Secretion & absorption. Transitional: Stretch.
What are the functions of simple vs. stratified epithelia?
Simple: Secretion, absorption, filtration. Stratified: Protection.
Where is simple squamous epithelium found?
Endothelium (cardiovascular & lymphatic vessels), mesothelium (serous membranes), alveoli (lungs), kidney (filtration barrier), inside the eye.
What is the function of stratified squamous epithelium?
Protection against mechanical/chemical stress and microorganisms.
What are the two types of stratified squamous epithelium and where are they found?
Keratinized: Skin (waterproof & abrasion-resistant). Non-keratinized: Mouth, throat, esophagus, vagina, anus.
What is the function of simple cuboidal epithelium?
Secretion & absorption.
Where is simple cuboidal epithelium found?
Pancreatic ducts, thyroid secretory chambers, kidney tubules, ovary surface, pigmented retina epithelium.
What is the function of stratified cuboidal epithelium?
Protection, absorption, and secretion.
Where is stratified cuboidal epithelium found?
Esophageal glands, adult sweat glands, male urethra.
What is the function of simple columnar epithelium?
Secretion and absorption (more organelles for secretion).
What are the two subtypes of simple columnar epithelium?
Non-ciliated (with microvilli for absorption) and ciliated (with cilia for movement).
Where is non-ciliated simple columnar epithelium found?
GI tract (stomach → anus), gallbladder, ducts of glands.
What is the function of ciliated simple columnar epithelium?
Moving mucus/foreign objects (e.g., mucociliary escalator) and oocytes.
Where is ciliated simple columnar epithelium found?
Bronchioles, spinal cord, fallopian tubes, brain ventricles, sinuses.
What is the function of pseudostratified columnar epithelium?
Protection, secretion, and movement (if ciliated).
What are the two subtypes of pseudostratified columnar epithelium?
Ciliated (with goblet cells) - in upper airways. Non-ciliated (no goblet cells) - in male urethra, epididymis, large gland ducts.
What is the function of stratified columnar epithelium?
Protection & secretion.
Where is stratified columnar epithelium found?
Urethra, conjunctiva (eye), esophageal glands, anal mucosa membrane.
What is the function of transitional epithelium?
Stretching (e.g., urinary bladder).
How does transitional epithelium change shape?
Relaxed state: Stratified cuboidal appearance (rounded cells). Stretched state: Squamous shape.
What is the function of glandular epithelium?
Secretion of substances into ducts, surfaces, or blood.
What is the difference between exocrine and endocrine glands?
Exocrine: Secretes into ducts (local effects). Endocrine: Secretes into blood (systemic effects).
What are examples of exocrine and endocrine glands?
Exocrine: Salivary glands, sweat glands, pancreas. Endocrine: Pituitary, thyroid, parathyroid, pineal gland, pancreas.
What is the function of goblet cells?
Secrete mucin, which forms mucus.
How are exocrine glands classified based on duct structure?
Simple (single duct, does not divide) vs. Compound (branched ducts).
How are exocrine glands classified based on secretory portion shape?
Tubular (straight or coiled) vs. Alveolar/Acinar (sac-like).
What are the three types of exocrine secretion?
Merocrine (exocytosis, e.g., sweat glands). Holocrine (cell ruptures, e.g., sebaceous glands). Apocrine (apical part pinches off, e.g., mammary glands).
Why does pseudostratified epithelium look multilayered?
All cells are attached to the basement membrane, but not all reach the apical surface, making the nuclei appear at different heights/looking like multiple layers.
