Building tissues from cells Flashcards
Describe what a tissue is ?
Collections of similar cells and the material surrounding them-
its classification is based on structure of cells, composition of extracellular matrix, functions of the cells of that particular tissue
Name four types of tissue
epithelial
connective
muscle
nervous
Describe epithelia tissue
exist as sheets
they line the body surface (epidermis )
they line almost all internal cavities
they rest on the basement membrane
depends on diffusion for nutrients- blood vessels never pass through epithelium- always beneath epithelium usually connective tissue
Describe the basement membrane
it is extracellular matrix- DENSE- it contains the largest proteins in the body which cross link with each other to form a mesh work.
Epithelia cells attach themselves to the basement membrane by specialised function.
NB if tumours are to come me static they have to penetrate basement membrane
How are epithelial cells classified
Cell Shape
Layer Structure
Surface Specialisation
Location and Function
Name the different types of shapes
squamous
cuboidal
columnar
Name the different layer structure
Simple
Pseudostratified
stratified
Name the different surface specialisations
Cilated
Brush Borders
Keratanized
Name the different location and functions
eg. respiratory, transitional
How do glands originate?
Almost all originate from imaginations of epethilium- hence why they retain the epithelial organisation
Name the two types of epithelial glands
Exocrine- secrete to free surface eg. sweat glands
Endocrine- secrete to blood stream
How do exocrine glands form?
1) the solid mass of epithelial remain attached
2) These cells then become specialised into secretory cells and excretory ducts
There can be different types of glands eg different number/types of branches and coils
EPITHELIAL CELLS NEVER BREAK THROUGH BASAL LAMINA
How do endocrine glands form?
1) the solid mass of epithelial cells detach off
2) These then become specialised into cords of glandular cells.
Immature cells send signals to bring capillaries towards it
EPITHILIAL CELLS NEVER BREAK THROUGH BASAL LAMINA
Name the three types of mechanisms of exocrine secretion
Merocrine
Apocrine
Holocrine
Merocrine
Vesicles open onto the surface of the cell and the secretory product is discharged from the cell - ie normal exocytosis
Aprocrine
Part of the apical (top half of the cell) cytoplasm of the cell break up- larger vesicles
the cell then regrows that part
eg. sweat glands, memory glands, prostate gland
Holocrine
The breakdown and discharge of entire secretory cell
eg. sebaceous glands of the skin
What is the role of junctions
Keeps epithelial sheets tightly bound
Allows for the remaining of functional integrity of cells’ selective barriers/communication
What are are the three types of anchoring junctions?
desmosome
hemidesomosome
adherens
Describe the desmosome
Strongest type of junction- connects to adjacent cells
the junctions are linked by Intermediary filaments
facilitates the bending of cell sheets
Describe the hemidesmosome
Like the desmosome-the junctions are linked by Intermediary filaments
connects the base of the epithelia cell to the basement membrane-
facilitates the bending of cell sheets
Describe Desmonal Proteins
There are two types- desmoglein and desmocolin. Both of these are attached to the IF
the desmogelin of one cell binds homophilically to the desmogelin of the adjacent cell- this promotes adhesion
The strength is emphasised by the fact that the linker proteins do cluster firming a mesh- dense
Describe the Adherens junction
It maintains the shape of the cell.
Cadherin dimers of one cell binds homophillically with partner of the neighbouring cel
These dimers are linked by actin filaments which are rigid and stretch across the cell from adherens junction to adherent junction
eg. columnar epitheliar cells
Name the two types of non-anchoring proteins
Tight and Gap
Tight-
prevents the exchange of material from passing between 2 cells- acts as a seal to the inter membrane space
Brings the plasma membranes of the 2 adjacent cells so close that nothing can fit through them- NO GLUCOSE/NO AA/NO IONS
eg upper part of the digestive track has higher glucose so it diffuses into the epethilal cells but you don’t want movement of water out of the epithelial cells
NB the seal can be relaxed thanks to cell signalling
the two proteins involved are Claudin and occulin which bind to their respective opposite proteins on the adjacent cell
Gap
very small small bridges between cytoplasm allowing exchange of materials between cytoplasm of neighbouring cells-
composed of 6 connexins to form a connexon. The hole in the middle is continuous. Allows small molecules to pass through this hole.
This helps calibration of molecules along cells despite the relative position of the cell compared to blood vessel
What happens if the conexins are not aligned
the channel is closed
