1. Basement membrane

2. • Many years ago before the advent of
electron microscopy the light microscopy
showed that at the interface between
connective tissue and other tissues there
is a narrow layer of cell-free matrix.
• This was given the name, basement
membrane

3. • It normally contains:
• Glycoproteins
• Glycosaminoglycans
• Type IV collagen
• Reticular fibers

4. • Most commonly the basement membrane
is present at the intersurfaces of
epithelium and connective tissue
• The term derives from the fact that the first
basement membranes to be recognized
were those lying underneath the basal
cells of surface epithelia.

6. • Basement membrane can be
demonstrated easily histochemically with
the light microscope.
• Glycoproteins and polysaccharides give a
positive periodic acid-Schiff reaction, and
• the reticular fibers can be revealed with
silver stain.

7. • Basement membrane is non cellular.
• It is a homogeneous sheet of extra-cellular
material present under the basal surface
of epithelial cells,
• around muscles, nerves, capillaries, and
fat cells.

8. • So basement membrane can be defined
as sheet-like structure of extra-cellular
matrix that acts as interface between the
supporting tissue (connective tissue) and
parenchymal tissue or cells (epithelium,
muscle cells, nerves, capillaries,
adipocytes or fat cells)

9. • It is typically stained strongly by
carbohydrates with PAS method, and for
collagen with van Gieson’s stain.
• It is also stained intensely with silver
techniques but is relatively poorly
demonstrated with eosin in H and E
preparations.

11. • Electron microscopy modified this view, as
it was found that the basement membrane
is composed of two quiet distinct
components:
• Basal Lamina
• Reticular lamina

12. • The term "basal lamina" is usually used
with electron microscopy, while the term
"basement membrane" is usually used
with light microscopy.

13. • The structure known as the basement
membrane in light microscopy refers to the
stained structure anchoring an epithelial
layer.
• This encompasses the basal lamina
secreted by epithelial cells and typically a
reticular lamina secreted by other cells.

14. • Basal lamina cannot be distinguished
under the light microscope, but under the
higher magnification of an electron
microscope, the basal lamina and lamina
reticularis are visibly distinct structures.

15. • Basal lamina is thin (about 80 nm thick)
sheet-like finely fibrilar layer. Its thickness
varies from 40 nm to 120 nm.
• It is a layer of filamentous proteins and
proteoglycans.
• It is associated closely to the cell surface.

16. • The main components of basal lamina
are:
• Type IV collagen
• Glycoproteins laminin and entactin
• Proteoglycans

18. • Reticular lamina contains larger fibrils and
glycosaminoglycans of extra-cellular
matrix.
• It underlies basal lamina and is rich in
reticular fibers.
• It is continuous with the connective tissue
proper and it is synthesized by connective
tissue.

20. • Basal lamina consists of an electron
dense membrane called lamina densa,
about 30–70 nm in thickness, and an
electron lucent zone called lamina lucida.

21. • The Lamina Densa, which is made up of
type IV collagen fibers; perlecan (a
heparan sulfate proteoglycan) coats these
fibers
• The Lamina Lucida is made up of laminin,
integrins, entactins, and dystroglycans.

22. • Lamina densa and lamina lucida together
make up basal lamina.

24. • Basement membrane consists of basal
lamina and underlying network of reticular
collagen (type III) fibrils.
• It is 30 nm in diameter and 0.1–2
micrometer in thickness.

25. • This type III collagen is of the reticular
type, in contrast to the fibrillar collagen
found in the extracellular.
• In addition to collagen, this supportive
matrix contains intrinsic macromolecular
components.

26. • Lamina Reticularis attached to basal
lamina with anchoring fibrils (type VII
collagen fibers) and microfibrils (fibrilin) is
collectively known as the basement
membrane.

28. • Basal lamina consists of a fibrilar layer
called lamina densa which is separated
from the plasma membrane of the
adjacent cell by a narrow electron-lucent
zone, lamina lucida.
• Lamina densa is 20 nm to 50 nm thick.

29. • In epidermis lamina lucida is crossed by
integral plasma membrane proteins and
keratinocyte hemidesmosomes are
anchored into lamina densa.

30. • Basal laminae are of almost similar forms
but their thickness and molecular
composition vary between different
tissues.
• Even between crypts and villi of small
intestine the basal laminae are different.

31. • In Descemet’s membrane of cornea, the
basal lamina is much thicker.
• Here the regular type IV collagen is
replaced by type VIII collagen.

32. • The basal lamina of neuromuscular
junctions contains a haparan sulphate
proteoglycan called agrin.
• Agrin plays a part in the clustering of
muscle acetylcholine receptors in the
plasma membrane at these junctions.

33. • Basal lamina serves to anchor the
overlying epithelial cells and it is produced
by these epithelial cells.

34. • I kidney glomerular basal lamina is
unusual in having a lucent zone on both
sides of lamina densa.
• Here these lucent zones are lamina rara
interna and lamina rara externa (laminae
rarae interna and externa).

35. • In some tissues, the basal lamina
separates two layers of cells and there are
no intervening typical connective tissue
elements (reticular lamina).
• So actually two basal laminae directly join
each others and basal lamina becomes
thick. Sometimes this is also called
basement membrane.

36. • In the following situations the basal lamina
is very thick
• Glomerular membranes of kidney
• Thin portions of the lung inter-alveolar
septa
• Capsule of the lens of eye
• Anterior limiting membrane (Descemet’s
membrane) in cornea
• Reichert’s membrane in placenta

37. • The thickness of basal lamina may
change in some pathological conditions
such as glomerulonephritis and diabetes.

38. • The most notable examples of basement
membranes is in the glomerular filtration of
kidney, by the fusion of the basal lamina
from endothelium of glomerular capillaries
and the basal lamina of the epithelium of
Bowman’s capsule, and

39. • between the lung alveoli and pulmonary
capillaries, by the fusion of the basal
lamina of the lung alveoli and of the basal
lamina of the lung capillaries, which is
where oxygen and CO2 diffusion happens.

40. • Basal laminae around the muscle fibers
and fat cells are sometimes called external
laminae.
• The singular is external lamina.

41. • The functions of basal laminae are:
• They support and anchor the cells
• They act as selective permeable barrier
between adjacent tissues
• They stabilize and orient the tissue layers

42. • They instructive the adjacent tissues
• They determine the polarity of the
associated tissues
• They determine the rate of cell division
• They guide the growing cell processes
during normal development and tissue
repair

43. • Reticular lamina is always towards the
connective tissue and it is produced by the
connective tissue. It is composed of
bundles of type III filaments embedded in
dense matrix of polysaccharides.
• The high concentration of proteoglycans in
this zone is responsible for the positive
PAS reaction in light microscopic sections.

44. • Reticular lamina is much reduced or
largely absent in the following tissues:
• Around the muscle fibers
• Schwann cells
• Capillary endothelia
• External to reticular lamina, there are thick
fibers of type I collagen.

45. • Basement membrane consists of:
• Basal lamina
• It has following components in sequence
• Lamina lucida or lamina rara interna
• It is electron-lucid layer containing
glycoprotein laminin

46. • Lamina densa
• It is electron-dense layer composed of
type IV collagen
• Lamina lucida or lamina rara externa
• It has similar composition to lamina rara
interna. Some sources do not consider
this a distinct layer

47. • Lamina Reticularis
• The three above layers of the basal lamina
typically sit on top of the reticular lamina,
which is synthesized by cells from the
underlying connective tissue and contains
fibronectin.

49. • The exception is when two epithelial
layers abut one another as in the alveoli of
the lungs and glomeruli of the kidneys, in
which the basal lamina of one epithelial
layer fuses with that of the other

50. • Anchoring fibrils composed of type VII
collagen extend from the basal lamina into
the underlying reticular lamina and loop
around collagen bundles.
• Although found beneath all basal laminae,
they are especially numerous in stratified
squamous cells of the skin.

51. • Basement membrane serves following
functions:
• It serves as a semipermeable membrane.
Epithelial tissue is nourished by diffusion
of food substances from the blood vessels
situated in the underlying connective
tissue.

52. • The primary function of the basement
membrane is to anchor down epithelium
and its loose connective tissue
underneath. It connects the epithelial cells
to the underlying connective tissue and
thus stabilizes the basal ends of the cells.
This function is demonstrated clearly in
epidermis, where the basement
membrane is very well developed.

53. • Basement membrane also has a profound
instructive effect on the adjacent tissues,
determining their polarity, rate of cell
division, metabolism, movements and
repair.

54. • The basement membrane is also essential
for angiogenesis (development of new
blood vessels).
• Basement membrane proteins have been
found to accelerate differentiation of
endothelial cells.

55. • They also act as pathways for migration
and routing of growing cell processes.
This function is seen in the regeneration of
the cells of peripheral nervous system.
• After injury when basal lamina guides the
outgrowth of axons and the establishment
of neuromuscular junctions.

56. • The basement membrane acts as a
mechanical barrier, preventing malignant
cells from invading the deeper tissues.
• Early stages of malignancy that are thus
limited to the epithelial layer by the
basement membrane are called
carcinoma in situ.

57. • In many stratified epithelia, the basal
plasma membrane of the cells is strongly
adherent to the underlying basement
membrane at the sites known as hemi-
desmosomes. As the name implies, only
half of the desmosome is present; only
one cell is participating, the second cell
being represented by the basement
membrane.

58. • Latest view regarding the development of
basement membrane is that almost all
components of basement membrane are
produced by epithelium or muscle rather
than the adjacent connective tissue.

59. • Some diseases result from the poor
functioning of basement membrane.
• The cause can be genetic defects, injuries
by the body's own immune system, or
other mechanisms.

60. • Genetic defects or mutations in the
collagen fibers of the basement
membrane cause Alport syndrome, a form
of renal failure.

61. • A good example of autoimmune disease is
Goodpasture syndrome. Here renal basal
lamina collagen is targeted by
autoantibodies.
• Collagen type IV is autoantigen (target
antigen) of autoantibodies in the
autoimmune disease Goodpasture
syndrome.

62. • A group of diseases stemming from
improper function of basement membrane
zone are united under the name
epidermolysis bullosa.