Structure of Epithelia Flashcards
What are the fundamental similarities in physiology between the kidney, gut and lung?
Systemic BP CO2 balance and excretion Acid-base Balance O2 sensing Fluid Secretion Fluid Absorption
What are the general characteristics of the epithelium?
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
How are the organs of the body formed in development?
Epithelia act in conjunction with mesenchyme
How might epithelia be classified?
Cell shape - cuboidal, columnar, squamous
Organisation in sheet - single, stratified, pseudo-stratified
Specialised forms - ciliated, neuronal connections, mucus secretion
Name the types of epithelium in the alveolus
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
Where are neuroepithelial bodies in the lung and what is their function?
At the junction of the upper airways. Have chemosensing function regulating O2 in the airway and breathing rate
What is the function of the epithelium in the Kidney nephron and collecting duct?
Ion transport
Fluid Homeostasis
Hormone Secretion
Acid- base Balance
What is the type and function of the epithelium in the Gut villus?
Simple, columnar with goblet cells.
Ion transport, fluid homeostasis, mucus and digestive enzyme secretion, nutrient absorption
Why is polarity crucial for function?
Gives direction to the transport of ions
Specialisation of function at one end of cell or the other
Supports formation of complex architectural shapes
How might loss of polarity lead to lung disease?
Flu -> disorganised ion transport -> oedema
How might loss of polarity lead to cancer?
cell detachment -> metastasis -> reorganisation as tumour
What is the adherens junction?
cell-cell recognition site where primitive contacts are made through homophillic E cadherin interactions.
What makes up the Adherens Junction?
E-cadherin
a, b, y, p120 catenins
F-actin
What is essential for E-cadherin homodimerisation and how many binding sites are there for this?
4 binding sites for Ca2+
Where are the catenins found?
on the COOH carboxy terminus of E-cadherin
What is the function of p120?
Interacts with cell membrane and E-cadherin to regulate cell junction type
What is the function of a-catenin?
Forms a homodimer that anchors actin filaments to the membrane and pulls cells together in shape
What is the function of b-catenin?
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
What is y-catenin also known as?
plakoglobin
What is the function of y-catenin?
alters the cell junction type and is common to desmosomes
What is the function of F-actin?
forms supporting belt structure around inner cell membrane and supports transition into cuboidal structure and recruits other cytoskeletal elements i.e. tubulin
Where do tight junctions form?
Apical side of the Adherens Junction
What is the tight junction?
Creates an impermeable barrier that blocks paracellular movement of molecules between cells and acts as a fence between apical and basolateral membranes
What is the basic unit of a tight junction?
the occludin
