L3- Integrating cells into tissues, organs and systems Flashcards
when do cells first coalesce (come together
during embryogenesis
o Spermatozoa penetrates the eggs and they fuse to make a single cell
o Occurs during the first stages of embryogenesis- blastocysts
Cells divide into two distinct types
• Inner cell mass- becomes me
• Trophoblast- becomes placenta
Cells then start to differentiate- becomes embryoblast
what is the fate of the embryo blast?
inner cell mass becomes epiblast
cells around the edge become the hypoblast
epiblast
all cells fo the body come from here (bilaminar disc will form from this)
hypoblast
also forms bilaminar disc- feeds the epiblast
definition of an organ
more than one tissue coming together to fulfil the same function
what 4 factors hold cells together
- cell-cell adhesion molecules
- ECM proteins
- internal-external scaffolding
- close proximity
nerves, lymphatics and blood vessels always found in
connective tissue layer
no nerves found in
epithelium
Connective tissue and epithelial tissue represent two extremes of organisation
- Main difference between them:
Connective tissue
- cells are sparsely distributed
- ECM is plentiful
- matrix rich in fibre polymer
Epithelial tissue
- Cells are tightly bound together into sheets called epithelia
- Extracellular matrix is scant- consisting mainly of a thin mat called the basal lamina, which underlies the epithelium
- Cell are attached to each other by cell-cell adhesions, which bear mechanical stresses
primary cell of connective tissue
mesenchymal stem cells
mesenchymal stem cells
- Can interconvert between several cell types
- Produces lots of extracellular fibres that anchor cells into place or make tissue
mesenchymal stem cells produce
o Fibronectin
o Laminin
o Collagen
epithelia cell sheets line
all cities and surfaces of the body
specialised junctions between epithelial cells help to form a tissue barrier, inhibiting:
Inhibiting movement of water, solutes and cells from one body compartment to another
epithelial cells rest on a
supporting bed of connective tissue
- attaches epithelial layer to other tissues such as muscles
cell adherence systems found on which surfaces
lateral
basal
lateral surface specialisation
- Tight junctions
- Adherens junctions
- Desmosome
- Gap junction
- Cell adhesion molecules (integrin, selectin, CAM)
basal surface specialisation
- Hemi-desmosome
- Focal adhesions
- Integrins
- Proteoglycans
what’s found on the apical surface of epithelial cells
villi and cilia
tight junctions
- near top of the cell
- prevent movement of large molecules into deeper tissue
example of where tight junctions are very important
proximal convoluted tubule
adheren junctions
Tissue stabilising factor and additional transport barrier
- found 1/3rd distance from apical surface
- found in pairs
- formed from intracellular actin filaments
- linked to E-cadherin proteins that cross the intercellular space
desmosomes
provides mechanical strength
- Found half way down the lateral part of the cell
- cbtoketatin fibres intracellularly and E-cadherin inter cellularly
where are desmosomes fond
in tissues that experience intense mechanical stress
o Cardiac muscle, bladder tissue, GI mucosa, epithelia and pregnant uterus
