Specialization of plasma membrane

this article is on specialization of plasma membrane to read about membrane structure click on this link
CELL MEMBRANE STRUCTURE
Pores in plasma membrane-
In Plasma membrane's structure pores of 0.35 manometer are found. In size that pores are same as Na positive ion's size. only 0.1% surface has pores. there is many models for pore structure on membrane-
1.Structural pores
2.Dynamic pores
3.paving block pores
4.Protein channel pores
5. Ionophore

THE CELL COAT-
Every cell has cell coat which is made of polysaccharides this coat calls glycocalyx.The cell coat is outer layer which present on whole membrane but only absent on tight junctions.  
Structure- this is very mine layer which founds on cell membrane. this is made of mucous- polysaccharides.A fibre protein  FIBRONECTIN also take part in composition of this.
Function-
1.This gives stability to plasma membrane.
2.this works of selective barrier .
3.This controls cells outer micro environment.
4.In intestine it works like a protective layer.
5.Around kidney glomerulai it work life filter and control transfer of molecules.
6. in connective tissue cell coat has HYALURONATE.
7.plasma membrane of erythrocytes has special antigens of different blood groups.
8.A single cell has many types of glaycoprotiens in its cell membrane.

Modifications of cell membrane-

1.Microvilli-the small finger like structure which founds on uutside the plasma membrane call microvilli .microvilli mostly founds in ALIMENTARY CANAL's absorption cells.for example- intestinal cells,hepatic cells,uriniferous tubules. the surface where microvillis are present call Brush border. some cells has very high number of microvilli like intestine's epithelium cells  has 3000 microvillis.When we cut the section of micrlvilli we see a central core in its structure.this canter core is completely covers by cell membrane.cores of microvillis are connected by on the base by many micro filaments web.
function-microvillis are increase the absorption power of cell by grow the surface.
2. Empty areas between microvillis works like sieve.
read about animal physiology on this link-
ANIMAL PHYSIOLOGY
                                           Cell junctions-
these are many types-
1.Tight junctions-oh this outer layer of plasma membrane of two cells connects and block the empty area very tightly so no empty area has left.it stop particles transfer to one to other cell completely.from cell.this stop  pancreas's digestive juice to dissolve in blood.this controls communication of protein and other elements to one to other cell.

2.Gap Junctions-Gap junctions are a means of communication. channel protein of two opposite cells joint together providing channels for sugar,ions,amino acids and other small molecules to pass .every gap junction is made up of specialized protein channels called connexins.

3.PLasmodesmata- They are protoplasmic bridges amongst plant cells which occur in the areas of cell wall pits or pores.

4. Desmosomes-Adjacent membranes possess disc shaped ticking of about 0.5 µm diameter, a number of tonofibrils and trans-membrane linkers embedded in dense intercelluler material. Desmosomes function as spot welds and are hence called spot desmosomes. They occur in epithelia subjected to disruption.

5.Terminal bars- Terminal bars are desmosomes without tonofibrils. Bands of thickening occur on the inner surface of membrane. The bands contain micro filaments and intermediate filaments.