Urinary System Renal Structure

Intraglomerular mesangial cells

Are located between the endothelial cells of the glomerular capillaries and cover the capillary surfaces not covered by podocyte processes

Filtration Membrane Barrier

Made up of Fenestrated capillary endothelium, the Glomerular basement membrane, GBM, and Slit diaphragm between pedicles

Renal Corpuscle

Made up of glomerulus and glomerular capsule Has a vascular pole (V) and tubular (urinary, U) pole

Cortical collecting tubule

Major site for regulation of potassium excretion by the kidney Those in the juxtamedullary nephrons arch upward. Merge to form Small, straight, cortical Collecting ducts that progressively become Larger, straight, cortical collecting ducts

Renal lobe

(pyramid, cortex, & renal column): site of urine production 12-15 renal pyramids Contains Thin descending and ascending limbs of Henle, Connecting and collecting tubules and collecting ducts, Blood vessels

Medullary collecting duct

A continuation of cortical collecting ducts that extend through the medulla; the final concentration of urine occurs in this region terminal component of the nephron in which vasopressin-sensitive passive water reabsorption occurs Larger, straightermedullary collecting ducts that merge further to form papillary ducts (of Bellini)

Renal Lobule

A cortical lobule (or renal lobule) is a part of a renal lobe. It consists of the nephrons grouped around a single medullary ray, and draining into a single collecting duct. Consists of the straight tubules of the nephrons grouped around a single medullary ray, and draining into a common collecting duct

Mesangial glomerulonephritis

Also called Type I membranoproliferative GN Light microscope demonstrate Proliferation of mesangial cells Large, hypercellular glomeruli, with a "lobular" appearance and increased mesangial matrix and compression of capillaries Infiltrating leukocytes and parietal epithelial crescents are present in many cases Immunofluorescence technique reveals Deposition of immune complex in the mesangium and Activation of complement pathways The glomerular capillary wall often shows a "double-contour" caused by "duplication" of the thickened basement membrane and the inclusion within it of processes of cells extending into the peripheral capillary loops Mode of presentation Nephrotic syndrome occurring in older children or young adults, but usually with nephritic component manifested by hematuria or, more insidiously, as mild proteinuria Course of the disease slowly progressive but unremitting ~ 50% develop chronic renal failure within 10 years

Medullary rays

Base of renal pyramid, where parallel bundles of straight tubules extend into the cortex and alternate with regions of convoluted tubules and renal corpuscles (RC) in the cortex Located at the center of a renal lobule

Renal cortex

Between the renal capsule and the renal medulla In the adult, it forms a continuous smooth outer zone Forms projections called Cortical columns that extend between the pyramids Contains The Renal corpuscles, Proximal convoluted tubules (Have a short straight part that enters the renal medulla), Distal convoluted tubules, Distal tubule the thick straight part ascending from the loop of Henle back into the cortex, Cortical connecting tubules and collecting tubules, and Blood vessels Collectively, the cortex receives over 10 times more blood than the medulla

Extraglomerular mesangial cells

Called lacis cells, are adjacent to the macula densa, the afferent arteriole, and the efferent arteriole

Renal blood supply

Blood enters each kidney through the Renal artery to the Segmental arteries into the Lobar arteries which divide into 2 interlobar arteries. Interlobar arteries lie between pyramids and dichotomize into Arcuate arteries Arcuate arteries feed into the Interlobular arteries that run in the cortex Interlobular arteries feed into the Afferent glomerular arterioles and some terminal branches provide the Perforating radiate arteries which supply the renal capsule Afferent arterioles divide to form a tuft of capillaries, the glomerulus, closely associated with the renal (Bowman's) capsule

Descending vasa recta

Branch into peritubular capillary networks in the medulla, and then return as ascending vasa recta In the medulla they are structured into bundles in close association with the loops of Henle and collecting ducts.

Renal sinus

Central area of the kidney that includes the calyces, renal pelvis, renal vessels, fat, nerves, and lymphatics Contains Intrarenal part of renal pelvis with 7 - 13 minor calyces and 2 -3 major calyces, Segmental and lobar branches of the renal artery and Perirenal fat Is lined by the renal fibrous capsule which is continuous with the adventitia of minor renal calyces

Alport syndrome features

Children with persistent hematuria, usually microhematuria, is the most common and earliest sign of Alport syndrome Proteinuria, edema, hypertension Progressive, high frequency sensorineural hearing loss Not improved by kidney transplantation Eyes abnormality Abnormal shaped lens Retinal thinning, perimacular flecks Difficulty with central vision, even loss of vision

Interlobular veins

Collect blood from stellate veins. Joined by venous ends of peritubular capillary plexus to the Ascending vasa recta and drain into Arcuate veins

Stellate veins

Collect blood from the most superficial zone of renal cortex and Fibrous renal capsule Drain into Interlobular veins

Acute glomerulonephritis (GN)

Comprises a specific set of renal diseases in which an immunologic mechanism triggers swelling and proliferation of glomerular tissue that can result in damage to the Capillary endothelium, Mesangium, and Basement membrane The immune response is often triggered by an infection or other disease Is defined as the sudden onset of Hematuria, proteinuria, and red blood cell (RBC) casts in the urine Often accompanied by Hypertension, edema, azotemia, and renal salt and water retention Involves Structural and Functional changes Proliferation of Capillary glomerular endothelial cells leads to Swelling of the endothelium and leakage of erythrocytes. Hematuria and the reduction of blood flow through the kidney causes decreased GFR and Elevated BUN, Salt and water retention leading to Edema and Hypertension

Renal Cortex and Medulla

Cortex is outer and lighter in color medulla is internal and darker in color Are made up of Nephrons 1.3 million in each kidney A Collecting tubular system made up of Collecting tubules and Collecting ducts

Bowman's capsule

Cup-shaped structure in the upper end of a nephron that encases the glomerulus A double-walled epithelial cup consisting of a Parietal layer of simple squamous epithelium continuous with Proximal convoluted tubule at the urinary pole, roughly opposite to the vascular pole, and a Visceral layer, which is composed of highly specialized epithelial cells called Podocytes

Membranous nephropathy

Deposition of antigen-antibody complexes on basement membrane causing a leaky BM

Large straight cortical collecting ducts

Enter the renal medulla and become the Medullary collecting ducts

Capsular space

Filed with fluid that under pressure moves from the capillary circulation and across the filtration membrane barrier

Kidneys

Filter blood from the renal arteries and produce urine as waste Are bean-shaped organs covered by a thin, fibrous CT capsule Consists of Hilum and Renal sinus

Pedicels

Finger-like projections of podocytes surrounding glomerular capillaries; interdigitate to form a filtration membrane Also adhere closely to the basal lamina that separates the endothelial layer of the fenestrated glomerular capillaries from the visceral layer of the glomerular capsule

Renal Efferent arterioles

From juxtamedullary nephrons Branch into thin blood vessels and the descending vasa recta Have a smaller diameter that afferent arterioles. Consequently, they offer greater resistance and contributes to maintaining high blood pressure in the glomerular capillary bed

Nephrotic syndrome

Group of clinical signs and symptoms caused by excessive protein loss in urine. Causes structural and functional abnormality of BM Proteinuria Hypoalbuminemia Edema Lipids are increased in serum and pass into urine Usually no red cells or decreased GFR

Urinary System

Includes 2 kidneys, 2 ureters, bladder, and urethra

Causes of Acute GN

Infectious Causes: Nephritogenic strains of group A beta-hemolytic streptococcus in ~ 10% of persons with pharyngitis and 25% in those with skin infections Staphylococci, Syphilis, mononucleosis, measles, rubella, mumps, and hepatitis B and C viruses Non-infectious Causes: IgG-immunoglobulin A [IgA] nephropathy, Membranoproliferative glomerulonephritis, Vasculitis, Polyarteritis nodosa, Wegener granulomatosis, and Systemic lupus erythematosus

Renal Medulla

Inner portion of the kidney 12-15 renal pyramids Apex of 2-3 renal pyramids form a renal papilla

Hilum of the kidney

Is a concave depression in its medial border where branches of the renal artery and nerves enter into the renal sinus and where renal vein, lymph vessels and renal pelvis leave the kidney

Basal lamina of GBM

Is composed of a network of type IV collagen and laminin, with associated heparan sulfate proteoglycans Functions as a size and charge (due to heparan sulfate proteoglycans) barrier Is the critical barrier between the fenestrated capillary endothelium and the capsular space Blocks passage of large proteins

Renal tubules

Kidney site of urine formation; water, sugar, salt reabsorption Consists of Proximal convoluted tubule Proximal straight tubule Loop of Henle Distal straight tubule Distal convoluted tubule Connecting tubule

Minimal change disease

Most common cause of nephrotic syndrome in children Also known as lipoid nephrosis or nil disease In children its the most common cause of nephrotic syndrome Usually idiopathic In adults its less common Usually secondary to Drug use (especially NSAIDs) Viral infection Allergic reaction Hematologic cancers (especially Hodgkin lymphoma) Histologic change is seen only by electron microscope Swelling, loss of foot process is caused by a cytokine released by T cells Causes Loss of polyanionic charge Leaky BM Proteinuria, mainly albumin Diagnosis Based on clinical findings

Diabetic nephropathy

One of the most significant long-term complications in terms of morbidity and mortality for individual patients with diabetes Major histologic changes in the glomeruli Mesangial cells expansion is directly induced by hyperglycemia, via increased matrix production or glycation of matrix proteins Thickening of the BM 3-5 times provides demarcation of lamina lost and Leaky BM Glomerular sclerosis is caused by intraglomerular hypertension, induced by dilatation of the afferent renal artery or from ischemic injury induced by hyaline narrowing of the vessels supplying the glomeruli EM reveals Kimmelstiel-Wilson nodules which are large, circular, acellular accumulations within areas of increased solid spaces of the tuft Sclerosis or hyalinization Indicates irreversible injury End stage renal disease Glomerular tuft appears as an acellular hylanized mass

Papillary ducts (of Bellini)

Open into the cribiform area at the apex of the renal pyramid and deliver urine into the minor renal calyces

Arcuate veins

Receives blood that drains from the interlobular veins, and feeds into the interlobar veins that unite to form the Renal veins that drain into the IVC. The veins draining the kidneys have no segmental organization like the arteries

Acute nephritic syndrome

Refers to a group of disorders that cause swelling / inflammation of the renal glomeruli, renal tubules, or interstitial renal tissue

Alport syndrome

Refers to a group of inherited, heterogeneous disorders involving the GBM and frequently affecting the cochlea and eye as well Caused by mutations in type IV collagen genes compromising the structure of the basal lamina of the GBM Abnormal filtration of proteins out of blood alters the glomerular homeostasis resulting in GBM thickening and impairment of macromolecular selective permeability and subsequent glomerular sclerosis, interstitial fibrosis, and renal failure Diagnosis confirmed by either the presence of splitting or lamellation of the GBM on electron microscopy Pathogenetic mutation in the genes encoding for the alpha-5 chains of type IV collagen, or pathogenic mutations in the genes encoding for the alpha-3, alpha-4 of type IV collagen of the basement membranes

Mesangial cells

Resemble vascular pericytes in having contractile properties and producing components of an external lamina Are both intraglomerular and extraglomerular May "unclog" and recondition the glomerular basement membrane by phagocytosing and removing accumulated filtration residues such as protein aggregates Also play a role in modulating blood flow by contracting in response to angiotensin stimulation (thereby decreasing blood flow) Extend contractile processes along capillaries that help regulate blood flow in the glomerulus. Some processes appear to pass between endothelial cells (EC) into the capillary lumen (asterisks) where they may help remove or endocytose adherent protein aggregates including antibody -antigen complexes abundant in many pathological conditions

Connecting tubule

Short, last part of each nephron Links each nephron to a collecting tubule. From several nephrons merge to form Small diameter Cortical collecting tubules in the cortical medullary rays

Slit diaphragms

Span adjacent pedicels and bridge the slit-like pores Are modified and specialized tight junctions composed of nephrins, glycoproteins and proteoglycans Block passage of small proteins

Nephron

The tubular excretory unit of the kidney. Comprised of: Renal corpuscle Renal tubules Connecting tubule Collecting tubule Collecting Ducts

Podocytes

These cells form a porous membrane surrounding the endothelial cells of the glomerulus. Form cellular extensions that branch into foot like processes called Pedicels