Renal Histo-Pathology (II) - Normal Kidney Electron Microscopy
RENAL HISTO-PATHOLOGY (II) m NORMAL KIDNEY ELECTRON MICROSCOPY Mohammed Abdel Gawad
Lecture References2 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
6 Extensions of the podocyte cell (pedicels) wrap around the capillary system of the glomeruli
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 Bowmans capsule epithelium Collagen appears in the interstitial space below the basement membrane of Bowmans capsule
Glomerular Filtration Membrane14 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.
Podocyte18 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.
Glomerular Basement Membrane20 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.
Glomerular Basement Membrane Structure21 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
Glomerular Filtration Membrane22 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.
Glomerular Filtration Membrane Size Selective Barriers24The crucial structure accounting forthe size selectivity of the filtrationbarrier appears to be the slitdiaphragm.Uncharged macromolecules up toan effective radius of 1.8 nm passfreely through the filter.Larger components are more andmore restricted and are totallyrestricted at effective radii of morethan 4 nm.Plasma albumin has an effectiveradius of 3.6 nm; without the repulsionfrom the negative charge, plasmaalbumin would pass through the filterin considerable amounts.
Mesangium27 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.
Mesangial Cells28 The interface between glomerular capillaries & mesangium
Mesangial Cells31 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.
Mesangial Matrix32 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.
PCT vs DCT34 PCT DCT DCT is shorter than the PCT segment and has no apical brush border.
PCT vs DCT35 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
PCT vs DCT36 Proximal and distal convoluted tubules. Distal has no brush border. Peritubular capillaries lie in the connective issue between tubules.
37 Proximal Convoluted Tubules (PCT) Higher EM of proximal tubule with its brush border (arrow).
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.
Loop of Henle & Collecting Ducts44 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.
Collecting Ducts46 In the inner medulla cross section, thin descending and ascending limbs (TL), a collecting duct (CD), and vasa recta (VR) are seen.
Collecting Duct Cells47 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.
Collecting Duct Cells48 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
Juxtaglomerular Cells50 Afferent arteriole near the vascular pole. Several smooth muscle cells are replaced by granular cells (GC) containing accumulations of renin granules.
Juxtaglomerular Cells51 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.
Macula Densa52 The cells have prominent nuclei and lateral intercellular spaces. Basally, they attach to the extraglomerular mesangium (EGM).
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