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Human Epithelial Biology > Structure of Epithelia > Flashcards

Structure of Epithelia Flashcards

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1
Q

What are the fundamental similarities in physiology between the kidney, gut and lung?

A 
Systemic BP
CO2 balance and excretion
Acid-base Balance
O2 sensing
Fluid Secretion
Fluid Absorption
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2
Q

What are the general characteristics of the epithelium?

A

Cells are packed into sheets
Cells form apical and basolateral domains which are oriented the same way throughout
Cells attach to a thin, fibrous basement membrane
Epithelia line surfaces of cavities and structures throughout the body - also form glands
Sheets lack blood vessels but contain nerves

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3
Q

How are the organs of the body formed in development?

A

Epithelia act in conjunction with mesenchyme

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4
Q

How might epithelia be classified?

A

Cell shape - cuboidal, columnar, squamous
Organisation in sheet - single, stratified, pseudo-stratified
Specialised forms - ciliated, neuronal connections, mucus secretion

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5
Q

Name the types of epithelium in the alveolus

A

AV type 1 - sqaumous - surface area for gas exchange
AV type 2 - cuboidal - fluid secretion, surfactant secretion, stem cell for AV type 1
Endothelium - squamous - gas exchange, capillary wall

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6
Q

Where are neuroepithelial bodies in the lung and what is their function?

A

At the junction of the upper airways. Have chemosensing function regulating O2 in the airway and breathing rate

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7
Q

What is the function of the epithelium in the Kidney nephron and collecting duct?

A

Ion transport
Fluid Homeostasis
Hormone Secretion
Acid- base Balance

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8
Q

What is the type and function of the epithelium in the Gut villus?

A

Simple, columnar with goblet cells.

Ion transport, fluid homeostasis, mucus and digestive enzyme secretion, nutrient absorption

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9
Q

Why is polarity crucial for function?

A

Gives direction to the transport of ions
Specialisation of function at one end of cell or the other
Supports formation of complex architectural shapes

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10
Q

How might loss of polarity lead to lung disease?

A

Flu -> disorganised ion transport -> oedema

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11
Q

How might loss of polarity lead to cancer?

A

cell detachment -> metastasis -> reorganisation as tumour

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12
Q

What is the adherens junction?

A

cell-cell recognition site where primitive contacts are made through homophillic E cadherin interactions.

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13
Q

What makes up the Adherens Junction?

A

E-cadherin
a, b, y, p120 catenins
F-actin

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14
Q

What is essential for E-cadherin homodimerisation and how many binding sites are there for this?

A

4 binding sites for Ca2+

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15
Q

Where are the catenins found?

A

on the COOH carboxy terminus of E-cadherin

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16
Q

What is the function of p120?

A

Interacts with cell membrane and E-cadherin to regulate cell junction type

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17
Q

What is the function of a-catenin?

A

Forms a homodimer that anchors actin filaments to the membrane and pulls cells together in shape

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18
Q

What is the function of b-catenin?

A

Released from E-cadherin by proteolysis in the absence of homodimerisation or degradation and acts as a nuclear signal to stimulate loss of polarity and cell growth

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19
Q

What is y-catenin also known as?

A

plakoglobin

20
Q

What is the function of y-catenin?

A

alters the cell junction type and is common to desmosomes

21
Q

What is the function of F-actin?

A

forms supporting belt structure around inner cell membrane and supports transition into cuboidal structure and recruits other cytoskeletal elements i.e. tubulin

22
Q

Where do tight junctions form?

A

Apical side of the Adherens Junction

23
Q

What is the tight junction?

A

Creates an impermeable barrier that blocks paracellular movement of molecules between cells and acts as a fence between apical and basolateral membranes

24
Q

What is the basic unit of a tight junction?

A

the occludin

25
Q

What are the zona occuldens?

A

proteins that anchor cytoskeletal proteins actin and tubulin to the tight junction complex

26
Q

What sort of structures might tight junctions support?

A

microvilli, cilia

27
Q

Give an example of how tight junction permeability is regulated?

A

Glucose Transport
SGLT1 stimulates NHE3
Rise in NHE3 activity increases H+ extrusion and alkalinises the cytoplasm
Alkalinisation activates MLCK causing actin ring contraction and TJ opening
Paracellular nutrient uptake rate increases as transepithelial resistance falls

28
Q

How are the apical and basolateral membranes distinguished by the tight junction?

A

Par3 recruits PTEN to the tight junction which enriches PIP2 to the apical membrane
PI3K localises to the adherens junction which enriches PIP3 in the basolateral membrane

29
Q

What is the function of desmosomes?

A

to form loose junctions between cells enabling cell shape to distort without tearing due to mechanical strain

30
Q

Where are desmosomes most common?

A

in cells exposed to stretch (lung) and shear (vasculature)

31
Q

What are the key proteins of the desmosome?

A

desmoglein and desmocollin

32
Q

What are the proteins which anchor desmoglein and desmocollin?

A

plakoglobin and plakophillin heterodimers

33
Q

What does desmoplakin bind?

A

desmin, the cytoskeletal protein to the desmosome complex

34
Q

What is the gap junction formed from?

A

hexamers of connexin proteins

35
Q

What is the function of the gap junction?

A

function as channels that connect the cytoplasms of two cells and establish Planar Cell Polarity

36
Q

How are the connexin hemi-channels connected?

A

EC connexin loops

37
Q

What is the basement membrane essential for?

A

cell metabolism, survival, proliferation, migration

38
Q

What is the basement membrane?

A

ECM underlying all epithelia connecting cells to connective tissue and providing structural support

39
Q

What are the major components of the basement membrane?

A

Laminin - primary organiser of BM proteins
Integrins - expressed on basolateral side of cell. bind to laminin
Collagens and Fibronectin - chicken-wire-like meshwork that gives BM its tensile strength
Nidogen and Perlecan - link laminin to collagen and fibronectin

40
Q

What forms the lamina lucida?

A

Integrins

41
Q

What forms the lamina densa?

A

Laminin

42
Q

What connects laminin to collagen and fibronectin?

A

nidogen and perlecan

43
Q

What cellular process might lead to cancer in epithelia?

A

degradation of E-Cadherin releasing b-catenin which enters nucleus and increases cell growth by activating LEF-1/TCF driven expression of cell cycle genes

44
Q

How does gluten activate an autoimmune response?

A

gluten stimulates zonulin secretion from gut epithlium which opens TJ
gluten enters blood stream and promotes immune response which degrades gut epithlial barrier and exacerabates T cell recruitment

45
Q

What is hypermobility syndrome?

A

mutation in the collagen gene disrupts epithelial adhesion to the basement membrane resulting in hyperflexible joints and polarity loss esp. in the lung

Human Epithelial Biology (20 decks)

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