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1. RENAL HISTO-PATHOLOGY (II)
m
NORMAL KIDNEY
ELECTRON MICROSCOPY
Mohammed Abdel Gawad

2. Lecture References
2
 Text Books:
 Fundamental of Renal Pathology
 Comprehensive Clinical Nephrology
 Websites:
(Links are available on www.nephrotube.blogspot.com):
 Histology at SIU SOM
 WebPath
 Visual Histology
 Zoomified Histology
 Renal Pathology Tutorial

3. OBJECTIVES
3
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

4. OBJECTIVES
4
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

5. 5
EM of a cast of
several glomeruli

6. 6
Extensions of
the podocyte
cell (pedicels)
wrap around the
capillary system
of the glomeruli

7. 7
Renal
Corpuscle
 RBC = red blood cell in capillary lumen
 fm = filtration membrane
 p = nucleus of podocyte
 e = nucleus of capillary endothelium
 B = nucleus of Bowman's capsule epithelium
 Collagen appears in the interstitial space below the
basement membrane of Bowman's capsule

8. Renal Corpuscle
8

9. OBJECTIVES
9
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

10. Glomerular Filtration Membrane
10

11. Glomerular Filtration Membrane
11

12. Glomerular Filtration Membrane
12

13. Glomerular Filtration Membrane
13

14. Glomerular Filtration Membrane
14 A. The endothelial cells of the glomerulus;
 1. pore (fenestra) (50-100 nm)
 B. Glomerular basement membrane:
 1. lamina rara interna
 2. lamina densa
 3. lamina rara externa
 C. Podocytes:
 1. enzymatic and structural protein
 2. filtration slit (30-40 nm)
 3. slit diaphragm:
 composed of nephrin, P-cadherin, FAT1,
NEPH1-3, and podocin.
 These proteins mediate slit diaphragm
connection to the actin cytoskeleton of the
foot processes.
 How these molecules interact with each
other to establish a size-selective porous
membrane is unknown.

15. Glomerular Filtration Membrane
15

16. OBJECTIVES
16
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

17. Podocyte
17
 PP = primary processes
 FP = foot processes

18. Podocyte
18
 EM of triangular shaped podocyte with its many terminal end feet (foot processes)
touching the basement membrane (dark) which is shared on its other surface by
endothelium of a capillary.
 The abluminal membrane (i.e., the soles of podocyte processes) contains specific
transmembrane proteins that connect the cytoskeleton to the GBM.

19. OBJECTIVES
19
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

20. Glomerular Basement Membrane
20
 The bulk of the basement membrane is the lamina densa.
 The thickness of the glomerular basement membrane lamina densa is about 5-6
times thicker than the lamina lucida externa in this particular electron micrograph.
The lamina lucida externa thickness is a useful landmark that can be used to assess
the normal thickness of the glomerular basement membrane.
 Another internal reference point for basement membrane thickness is an intact foot
process. If you average the width of intact foot processes and then turn that 90
degrees, that is about the normal thickness of the laminar densa.
 The glomerular basement membrane in adults measures approximately 340 to 360
nanometers (nm) in thickness and is significantly thicker in men than in women.

21. Glomerular Basement Membrane
Structure
21
 Formed of:
 Major components: Collagen type IV, laminin, and proteoglycans (predominantly heparan
sulfate).
 Also: type V, VI collagen, In addition, nidogen, entactin and fibronectin are present.
 Type IV collagen:
 3 α-peptide chains (α3, α4, α5 chains)
 consists of triple helix with globular non collagenous domain (NC1) at its C-
terminal.
 Laminin 11 consists of α5, 2 and 1 chains
 Abnormalities:
 Mutation in α-peptide chains → no proper helix Alport’s Syndrome
 Antibodies against type IV collagen in kidney → anti GBM disease

22. Glomerular Filtration Membrane
22
Charge & Size Selective Barriers
 The heparan sulphate proteoglycans of the glomerular
basement membrane are negatively charged.
 The surface of both epithelial (luminal membrane & slit
diaphragm) and endothelial cells are also anionically charged
because of sialoglycoproteins (podocalyxin in epithelia &
endothelial cells, podocendin in epithelial cells|) in the cellular
coats.
 Both of these negatively charged structures are responsible for the
charge selective barrier to filtration of capillary contents.
 Endothelial pores & filtration slits allow filtration of water and
small substances, is known as the size selective barrier.

23. Glomerular Filtration Membrane
23
Charge & Size Selective Barriers
Charge selective barrier
Size selective barrier

24. Glomerular Filtration Membrane
Size Selective Barriers
24
The crucial structure accounting for
the size selectivity of the filtration
barrier appears to be the slit
diaphragm.
Uncharged macromolecules up to
an effective radius of 1.8 nm pass
freely through the filter.
Larger components are more and
more restricted and are totally
restricted at effective radii of more
than 4 nm.
Plasma albumin has an effective
radius of 3.6 nm; without the repulsion
from the negative charge, plasma
albumin would pass through the filter
in considerable amounts.

25. OBJECTIVES
25
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

26. Mesangium
26

27. Mesangium
27
 The layer of interdigitating podocyte processes and the glomerular basement membrane (GBM)
do not completely encircle the capillary.
 At the mesangial angles (arrows), both deviate from a pericapillary course and cover the
mesangium.
 Mesangial cell processes, containing dense bundles of microfilaments (MF), interconnect the
GBM and bridge the distance between the two mesangial angles.

28. Mesangial Cells
28
 The interface between glomerular capillaries & mesangium

29. Mesangial Cells
29

30. Mesangial Cells
30

31. Mesangial Cells
31
 Mesangial cells are modified smooth muscle cells, and are continuous with the
vascular smooth muscle cells in the hilar arterioles
 Mesangial cells are quite irregular in shape with many processes extending from
the cell body toward the GBM .
In these processes, dense assemblies of microfilaments are found that contain
actin, myosin, and α-actinin.
The processes are attached to the GBM either directly or through the interposition of
microfibrils.
 Mesangial cells have numerous functions:
 have a contractile capability and can tug on the edges of the capillaries and
thus control blood flow through the glomerulus,
 production of extracellular matrix,
 secretion cytokines, inflammatory and other active mediators,
 phagocytosis.
 There is a route for trafficking of debris through the mesangium that begins in
the subendothelial zone and enters the mesangium and then passes through
physiologic if not actual channels through the matrix to the hilum.

32. Mesangial Matrix
32
 Formed of: a dense network of elastic microfibrils:
 A large number of common extracellular matrix proteins have
been demonstrated within the mesangial matrix, including:
 several types of collagens (IV, V, and VI)
 several components of microfibrillar proteins (fibrillin and
the 31-kd microfibril-associated glycoprotein).
 The matrix also contains several glycoproteins (fibronectin is
most abundant) as well as several types of proteoglycans.

33. OBJECTIVES
33
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

34. PCT vs DCT
34
PCT DCT
 DCT is shorter than the PCT segment and has no apical
brush border.

35. PCT vs DCT
35
 Proximal convoluted tubule is equipped  In contrast to the proximal tubule, the apical
with a brush border and a prominent surface is amplified only by some stubby
vacuolar apparatus in the apical cytoplasm microvilli.
(a prominent lysosomal system responsible
for the reabsorption of macromolecules
polypeptides and proteins).
 The rest of the cytoplasm is occupied by a  The epithelium is, exhibiting extensive
basal labyrinth consisting of large basolateral interdigitation of the cells and
mitochondria associated with basolateral great density of mitochondria in all nephron
cell membranes. portions

36. PCT vs DCT
36
 Proximal and distal convoluted tubules. Distal has no brush border.
Peritubular capillaries lie in the connective issue between tubules.

37. 37
Proximal
Convoluted
Tubules
(PCT)
 Higher EM of proximal tubule with its brush border (arrow).

38. Proximal Convoluted Tubules (PCT)
38
 Note basement (basal) lamina and the great infolding of the cell membrane. These
folds, plus the many mitochondria lying in them, tend to give the cytoplasm a striated
look in light microscopy. The many folds also provide increased cell surface for
passage of absorbed fluid and ions into t he peritubular capillary below.

39. Proximal Convoluted Tubules (PCT)
39

40. OBJECTIVES
40
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

41. Loop of Henle
41
 Thick limb: simple cuboidal epithelium with an apical brush border.
 Thin limb: loosing its brush border and turning into a simple squamous epithelium.

42. Loop of Henle – Thin Limb
42
 The thin limb of the loop of Henle has a similar appearance
as blood capillaries.

43. Loop of Henle – Hairpin Turn
43

44. Loop of Henle & Collecting Ducts
44
 Cross section through the inner stripe of the outer medulla. A descending thin limb
of a long loop (DL), the medullary thick ascending limbs (AL), and a collecting duct
(CD) with principal cells (P) and intercalated cells (IC) are shown. C, peritubular
capillaries; F, fibroblast.

45. OBJECTIVES
45
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

46. Collecting Ducts
46
 In the inner medulla cross section, thin descending and ascending limbs
(TL), a collecting duct (CD), and vasa recta (VR) are seen.

47. Collecting Duct Cells
47
Principal cell (CD cell) of a medullary collecting duct.
 The apical cell membrane bears some stubby microvilli covered by a
prominent glycocalyx.
 The basal cell membrane forms invaginations. Note the deep tight junction.

48. Collecting Duct Cells
48
Intercalated cells type A
 Note the dark cytoplasm (dark cells) with many mitochondria
 Apical microfolds.
 Note: Type A cells have been defined as expressing H+-ATPase at their
luminal membrane; they secrete protons. Type B cells express the H+-
ATPase at their basolateral membrane; they secrete bicarbonate ions and
reabsorb protons

49. OBJECTIVES
49
 Renal Corpuscle
 Glomerular Filtration Membrane
 Podocyte
 Glomerular Basement Membrane
 Mesangium
 PCT vs DCT
 Loop of Henle
 Collecting Ducts
 Juxtaglomerular Apparatus

50. Juxtaglomerular Cells
50
 Afferent arteriole near the vascular pole. Several smooth muscle cells are
replaced by granular cells (GC) containing accumulations of renin granules.

51. Juxtaglomerular Cells
51
 EM photo showing dark particles, which are secretory granules in the
cytoplasm of juxtaglomerular cells. These cells are modified smooth muscle
cells and secrete the hormone renin.

52. Macula Densa
52
 The cells have prominent nuclei and lateral intercellular spaces.
 Basally, they attach to the extraglomerular mesangium (EGM).

53. 53
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54. 54
Gawad