Epithelial Cell Polarity and Specializations

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Questions and Answers

What is the primary function of the apical domain in epithelial cells?

  • Transport of ions, molecules, and water (correct)
  • Cell communication
  • Heat generation
  • Storage of nutrients

Which of the following is NOT a structure associated with the apical domain?

  • Mitochondria (correct)
  • Cilia
  • Microvilli
  • Stereocilia

Where is germinal epithelium primarily found in males?

  • In the seminiferous tubules of the testis (correct)
  • In the pancreas
  • In the prostate gland
  • In the abdominal cavity

What do microvilli mainly enhance in epithelial cells?

<p>Surface area for absorption (B)</p> Signup and view all the answers

Which type of epithelium functions as sensory receptors?

<p>Sensory epithelium (B)</p> Signup and view all the answers

What structural feature distinguishes stereocilia from cilia?

<p>Stereocilia are rigid and contain a core of actin filaments. (C)</p> Signup and view all the answers

What is the primary function of the cilia in the respiratory system?

<p>To perform rhythmic bending movements for moving mucus. (D)</p> Signup and view all the answers

Which component is crucial for the movement of cilia through its ATPase activity?

<p>Microtubule-associated protein dynein. (B)</p> Signup and view all the answers

Kartagener's syndrome results in which of the following conditions?

<p>Hereditary defects in ciliary dynein leading to lung infections. (D)</p> Signup and view all the answers

What distinguishes the basolateral domain of epithelial cells?

<p>It serves primarily for active transport of ions and secretion. (D)</p> Signup and view all the answers

Flashcards

Germinal Epithelium

Epithelial cells with specialized functions, like producing sperm or ova in the testes or ovaries.

Sensory Epithelium

Epithelial cells that act as sensory receptors, detecting stimuli like taste, sound, or light.

Apical Domain

The side of an epithelial cell facing the lumen or open space.

Microvilli

Finger-like projections on the apical surface of some epithelial cells, increasing surface area for absorption.

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Epithelial Cell Polarity

Cell membrane specialization in which different regions of the cell have different structures and functions.

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Stereocilia

Non-motile, long microvilli found only in the epididymis. They are rigid due to their core of actin filaments and increase surface area for absorption.

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Cilia

Long, motile apical cell processes with a rhythmic bending movement. They contain a core of microtubules arranged in a 9+2 pattern, powered by dynein.

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Kartagener's Syndrome

A genetic disorder affecting cilia. People with this syndrome are susceptible to respiratory infections and male sterility.

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Basal Domain

The region of the cell membrane contacting the basement membrane, which provides structural support and anchors the cell.

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Basal Enfolding

Finger-like infoldings of the basal plasma membrane in some epithelia. They increase surface area for ion transport and are rich in mitochondria.

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Study Notes

Epithelial Cell Polarity and Specializations

  • Epithelial cells adapt structurally to perform specific functions
  • Specialized forms of epithelium exhibit unique functions (e.g., germinal epithelium differentiates into sperm/ova; sensory epithelium contains receptors for taste, hearing, and vision)
  • Cell membrane specializations correlate to function
  • Structural abnormalities in cell membrane specialization can lead to clinical disorders

Apical Domain

  • The apical domain faces the lumen
  • Functions in ion transport, molecule transport, and water transport
  • Contains ion channels, carrier proteins, ATPase, glycoproteins, hydrolytic enzymes, and aquaporins.
  • Includes microvilli, stereocilia, cilia, and flagella (sperms)

a. Microvilli

  • Small finger-like projections increasing surface area for absorption
  • Contain microfilaments for rigidity (e.g., intestinal and kidney cells)

b. Stereocilia

  • Long, non-motile microvilli, found in the epididymis
  • Increase surface area

c. Cilia

  • Long, motile projections with a 9 + 2 microtubule arrangement
  • Use ATPase-driven dynein for rhythmic bending
  • Found in respiratory system (e.g., trachea) and oviducts

Clinical Significance of Cilia

  • Kartagener's syndrome: defects in ciliary dynein lead to infertility and lung infections

Basolateral Domain

  • Includes lateral and basal plasma membranes
  • Junctional specializations, receptors for hormones/neurotransmitters
  • Rich in ion channels, Na+/K+ ATPase, and sites for secretion
  • Includes basal enfoldings, hemidesmosomes, and basal lamina.

Basal Lamina

  • Lies between epithelium and underlying connective tissue
  • Composed of glycoproteins (laminin, collagen type IV)
  • Anchors basal cells to connective tissue

Hemidesmosomes

  • Half-desmosomes attaching basal cells to the basal lamina
  • Keratin tonofilaments connect to cytoplasmic plaques
  • Transmembrane linker proteins (e.g., integrins) bind to basal lamina proteins (laminin, type IV collagen)

Clinical Significance

  • Metaplasia: transformation of one epithelium type to another—loss of function
  • Carcinomas: malignant tumors arising from epithelia
  • Tumour classification upgrades if basal lamina is crossed

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