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Histology > Epithelium Lecture > Flashcards

Epithelium Lecture Flashcards

1
Q

Types of Tissue

A

1) Epithelium
2) Connective Tissue
3) Muscle
4) Nerve

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2
Q

Types of Connective Tissue

A

1) CT Proper
2) Cartilage
3) Bone
4) Blood

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3
Q

Location of Epithelium

A

1) Cover exterior body surfaces
2) Line cavities
3) Line tubular organs
4) Cover external surfaces of organs
5) Line vascular system
6) Line ducts

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4
Q

Characteristics of Epithelium

A

1) Typically have a free surface
2) Form a sheet by adhering to adjacent cells by junctional complexes and adhesion molecules
3) Rest on basal lamina
4) Exhibit polarity: apical, basal, and lateral
5) AVASCULAR

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5
Q

Functions of Epithelium

A

1) Absorption
2) Secretion
3) Excretion
4) Protection
5) Contraction
6) Transport of material

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6
Q

What is a basal lamina?

A
  • It is like a rug

- Helps glue the epithelium to the connective tissue

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7
Q

How to classify Epithelial Tissue?

A
  • number of layers
  • cell shape
  • THEN modifications
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8
Q

“Number of Layers” Classification

A
  • Simple (one layer thick)
  • Stratified (two or more layers)
  • Pseudostratified (looks more than one, but all cells rest on basal lamina)
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9
Q

“Shape” Classification

A
  • Squamous (thin, flat cells)
  • Cuboidal (cell that is the same width as height; square)
  • Columnar (tall and thin; rectangle)
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10
Q

Types of Modifications

A

1) Keratinized, non-keratinized
2) Cilia
3) Microvilli
4) Stereocilia
5) Goblet cells

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11
Q

Types of Epithelia

Without Modifications

A
  • Simple Squamous
  • Simple Cuboidal
  • Simple Columnar
  • Stratified Squamous Keratinized
  • Stratified Squamous Non-keratinized
  • Stratified Cuboidal
  • Stratified Columnar
  • Pseudostratified Columnar
  • Transitional [Urothelium]
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12
Q

Simple Squamous

A
  • Flat cell
  • Shaped like a pancake
  • Thin from side
  • Large from surface
  • Flat nucleus
  • Endothelium: lines blood vessels and other vascular structures
  • Mesothelium: covers organ surfaces
  • Kidney (pariteal surface of Bowman’s, thin segment of loop of Henle)
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13
Q

Simple Cuboidal

A
  • Square cells
  • Height = width
  • Found in glands
  • Found in kidney tubules
  • Nuclear location: middle or bottom of cell
  • Thyroid gland
  • Kidney proximal convoluted tubule (brush border), distal convoluted tubule (basal striations), collecting ducts, collecting tubules
  • Eyes (lens surface, corneal endothelium)
  • Gland ducts in so many locations, kidney ducts and tubules
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14
Q

Simple Columnar

A
  • Rectangular cells
  • Tall and thin cells
  • In many organs from digestive to female reproductive
  • USUALLY has apical modifications; microvilli or cilia
  • Often will have goblet cells present
  • Nuclear location: middle, bottom
  • Gallbladder
  • Gland ducts in many locations
  • Surface lining of the stomach/large and small intestines, uterus, and endocervix
  • Ciliated in oviducts (fallopian tubes), lungs (small bronchi and bronchioles)
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15
Q

Stratified Cuboidal

A
  • found in the ducts of glands
  • salivary glands (large ducts)
  • sweat gland ducts
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16
Q

Pseudostratified Columnar

A
  • Rectangular-ish cells
  • Tall and thin cells
  • Looks like someone shook a simple columnar epi.
  • USUALLY have apical modifications; stereocilia, cilia
  • May have goblet cells present
  • Nuclear location: varies; which makes it confusing
  • Ciliated in trachea and large bronchi
  • Lines Eustachian tube
  • Stereocilia in epididymis and vas deferens
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17
Q

Stratified Squamous

A
  • flat cells on top
  • Skin epidermis (keratinized )
  • Non keratinized (corneal epithelium, esophagus, exocervix, oral cavity lining)
18
Q

Transitional Epithelium

A
  • Puffy round cells on top
  • Cells small at the bottom
  • Epi is found in the urinary system
  • Allows distention for urine
  • Urinary system (from renal calyx to proximal urethra)
19
Q

Stratified Columnar

A

Large ducts of glands, urethra (male)

20
Q

Basal Lamina

A
  • Epithelial cells secrete majority of components
  • Components: Collagens (Type 4 at least 50%, Type 3, and Type 7)
  • Type 4 forms scaffold of basal lamina
  • Type 3 and 7 anchor basal lamina to underlying connective tissue
  • Type 3 is of non-epithelial origin
  • Laminin: MAG that polymerizes on basal surface and interacts with Type 4 collagen to make a sheet like structure
  • Fibronectin: MAG participates in binding integrins
21
Q

Basement Membrane

A

basal lamina + fibroreticular lamina

22
Q

Anchoring junctions

A

sites of adhesion; secure cells to the basal lamina or ECM

23
Q

Focal Adhesions

A

Integrin-associated adhesions that anchor intracellular actin filaments to fibronectin of ECM of BM

24
Q

Hemidesmosomes

A
  • strong anchoring junction found in tissues subjected to abrasion and shearing forces (skin)
  • Integrin-associated adhesion that anchors intracellular intermediate filaments to collgen type 4 and laminin in ECM of BM
25
Q

What is the takeaway from these anchoring junctions?

A
  • Integrins form the core of both of these junctions (transmembrane proteins found in the basal cell membrane)
  • Extracellular side of these proteins contain receptors that help bind Type 4 collagen, laminin, fibronectin
26
Q

Junctional Complexes in Lateral Domain

A
  1. Zonula Occludens (Tight junctions): tight seal; zip-lock
  2. Zonula Adherens (Adherens junctions): belt-like; six pack
  3. Macula Adherens (desmosome): spot weld
  4. Gap Junction: pipe between cells; chemically couples cells
27
Q

The order of the junctions

A
  1. Tight junction
  2. Cell-Cell Anchoring Junctions (adherens or desmosomes)
  3. Channel Forming Junction (gap)
28
Q

Zonula Occludens (Tight junctions)

A
  • Acts like a zipper between cells
  • Forms a tight seal between cells
  • Attaches to actin
  • Defines apical vs. basolateral domains of cells
  • Appears as a darkened line to adjacent cells
  • Does not allow material to flow between cells
  • Amount of the seal depends on the tissue type
  • Formed by occludins and claudins
29
Q

Zonula Adherens (sticking together junctions)

A
  • Encircles cells like 6 pack rings/belt
  • Formed by e-cadherin (transmembrane) and Catenin ( intracellular)
  • Cadherin: Calcium Dependent Adhesion
  • Cadherins are Calcium Binding Proteins
  • Calcium is needed for the Cadherins to bind
  • Adheres cells together via actin of terminal web
30
Q

Macula Adherens (desmosomes)

A
  • Spot welds cells together
  • Desmoglein and Desmocollin (cadherins, calcium ion dependent adhesion, calcium binding proteins)
  • Catenin-like = desmoplakin
  • Desmoplakin binds the intermediate filaments
  • **
  • On the TEM, it looks like a black fuzzy caterpillar on each cell. Those fuzzy bits are intermediate filaments (cytokeratin)
31
Q

Gap Junction

A
  • Chemically couples cells (mechanically and electrically)
  • Connexins are the major protein
  • 6 connexins form a connexon
  • Connexons form spots that acts as channels between cells
  • Allows calcium and other ions to pass from cell to cell
  • On TEM, it forms a very dark and thin line
32
Q

Apical Specializations

A
  • Microvilli (non-motile, more like straws)
  • Stereocilia (just very long microvilli)
  • Cilia (motile, sweeping motion like little brooms)
33
Q

Microvilli

A
  • Fingerlike projections of the apical plasma membrane
  • Exaggerated glycocalyx (shows up as PAS + and shows up as HOT HOT pink)
  • Increase surface area
  • Usually absorptive
  • Actin filaments form core
  • Attached to terminal web (actin net)
34
Q

Cilia

A
  • Larger finger-like projections of apical plasma membrane
  • They sweep material along the surface
  • 9+2 arrangement of microtubules = 9 doubles and 2 singles
  • Attached via basal bodies (BB=modified centrioles; 9 triplet microtubules)
35
Q

Stereocilia

A
  • Extra looooonnngggg microvilli
  • Actin core
  • Passive movement by fluid
  • Absorptive
  • Epididymis, vas deferens, inner ear
36
Q

Hair cells

A

stereocilia of inner ear

37
Q

What makes up the glandular epithelium?

A
  • endocrine gland

- exocrine gland

38
Q

Endocrine Glands

A
  • Secrete into blood stream (ENDOthelium)
  • Do not have ducts
  • Hormones are the main endocrine secretions
39
Q

Exocrine Glands

A
  • Secrete directly into the duct
  • Some ducts modify he product
  • Some ducts simply transport the secretion
  • Product can be mucous, serous, or mixture
40
Q

Functional Classification of Glands

A

Merocrine/Eccrine
- secrete via exocytosis
- most common
- plasma membrane is recycled
- secretory product is released; vesicle retained
**
Holocrine
- Whole cell is created
- Cells begin to die as they reach area of secretion
- Best example is the sebaceous gland around hair follicle
**
Apocrine
- portion of the apical membrane and the cytoplasm are secreted
- apical portion pinches off with product inside it
- loss of plasma membrane
- best example is lipid component of milk during lactation

41
Q

Myoepithelial cells

A
  • Contain actin, myosin, and cytokeratins; contractile
  • Difficult to identify on H&E sections
  • Associated with glands
  • Assists with moving secretions from glands
  • “Hugs” glandular elements to squeeze out contents
42
Q

Renewal of Epithelium

A
  • Most epithelial cells have a finite lifespan
  • Skin turns over in 28 days
  • Intestinal lining: 4-6 days
  • Mitotic activity is visible in basal cell layers
  • If injury or inflammation occurs, more mitotic figures are seen
  • Also during dysplasia and neoplasia

Histology (7 decks)

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