Epithelium

characteristics

• arranged side by side
• covers external and internal surfaces( liked skin, peritoneum)
• lines tubes( blood vessels)

Structures

1.Lateral circumference

Tight junction

- aka zona occludents
- very tightly packed prevent fluid leakage from lumen

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Adherence junction

• gives shape to cell
• attached to actin ( micro filaments)

Desmosomes

• aka macula densa
• attached to intermediate filaments
• cell to cell adhesion
• desmocolin and desmoglein transmembrane proteins

Gap junction

• porins exchange nutrients between cells

2. basal surface

Hemidesmosomes

• Integrin as transmembrane proteins attaching to lamina desa
• attached of cell to Basement membrane

Bullous impetigo

Problem in Hemidesmosomes binding to Basement membrane

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Basement membrane

graph LR
  X{under electron microscope} -->|Basementmembrane is | Y[Basal lamina];
  A[Basal lamina] --> |Lighter| B[lamin lucida ];
  A -->|darker| C[Lamina densa];
  A -->|irregular| D[Lamina reticularis];

1. lamina lucida

   • integrins attach to hemi-desmosomes inside the cell

2. Lamina densa

   • integrins attach to Collagen 4

3. Lamina reticularis

   • collagen 4 is attached to collagen 3 secreated by firbroblasts

Epithelial cell modifications

graph LR
    A{Epithelial cell} ==>|modification| B[Apical surface ];
    B ==> B1[Cilia];
    B ==> B2[micro-villi];
    B ==> B3[stereoili];
    A ==>|Total cell modification| C[Secretion];
    C ==> C1[Endocrine];
    C ==> C2[Exocrine]
    C1 ==>|multiple secretory cells| C1a[Multi-secretory cell];
    C1 ==>|one secretory cell| C1b[ single cell];
    C2 ==>|multiple secretory cells| C2a[Multi-secretory cell];
    C2 ==>|one secretory cell| C2b[ single cell aka Globlet cell];
    A ==>|Others| D[keratin production];

Apical Surface

	Micro villi	Cilia	Stereocili
Made up	Microfilaments (actin)	Microtubes (9)2	branched microfilaments
Use	Absorption	waving movement	Absorption
Location	GI for absorption	Lungs clearing mucus	Epididyemis,ear

Ciliary Dyskinesia

1. Kartnger Syndrome = Absent motor protein dynein => - Mucus in lungs not cleared - Fallopion Tube

Total cell modifications

Secretions

graph TD
    A(Epithelial cell layer ) ==>  B(invagination);
    B ==> C( secretions from apical);
    C ==> D{exocrine gland};
    B ==> E(secretion from basal surface);
    E ==> F(into blood vessel);
    F ==> G{endocrine gland};
    Z[multiple cell secretion ] ==> Y[multicell secretory gland];
    X[Single cell secretion] ==> V[single secretory gland eg:Globlet cell];

Keratin

- Multiply and deposits (keratin) type of intermediate filament 
- Prevent mechanical stress