case 4: Post-Streptococcal Glomerulonephritis (PSGN)

Question 1

Lactate Dehydrogenase (LDH)

Answer 1

• LDH – present in most cells, the highest levels found in the cells of the liver, cardiac & skeletal muscles, kidneys, lungs, and in blood cells.
  Function? (anaerobic respiration)
• When tissues are damaged, LDH is
  released into the blood
• A higher-than-normal level in plasma
  may indicate:
  – Heart attack
  – Stroke
  – Liver, kidney, muscle damages
  – Other tissue damages
• each glucose molecule thru glycolysis in the presence of O2 net product/gain is 2 ATP, co factor 2 NAD+
• absence of O2, pyruvate converted to lactate by lactate dehydrogenase, reduced form of NADH can be oxidized to 2 NAD+ which can be put back into glycolysis to produce 2 ATP at a time
• too much lactate in tissue (muscle) glycolysis cannot occur anymore,
• in order to continue glycolysis, lactate dehydrogenase is needed, is present in every animal cell

Question 2

Erythrocyte Sedimentation Rate

Answer 2

• The rate (RBC sed rate) at which RBCs sediment in 1 hr
• A non-specific measure of inflammation
  – Anticoagulated blood is place in an upright Westergren tube
  – The rate of RBC sedimentation is measured in mm/hr
• An inflammatory process (infection or injury) -> certain proteins (from the liver or immune cells) cause RBCs to stick together -> form rouleaux -> settle faster

higher sedimentation rate

Question 3

C-Reactive Protein (CRP)

Answer 3

• Chemical properties
  – CRP is synthesized by the liver in response to factors released by macrophages and adipocytes
  – The levels of CRP increases during acute inflammation
• CRP binds to cell surface of damaged cells or some bacteria
  – -> Activates complement system -> increase antibody functions & increase phagocytosis by macrophages -> increase destruction of bacteria
• CRP contributes to atherosclerosis progression by exerting pro- inflammatory effects, modulating the innate immune response & activating the complement system, promoting platelet activation, thrombus formation, vascular remodeling, and angiogenesis

levels indicate whos at risk of heart attacks

Question 4

Diagnosis

Answer 4

• Acute inflammation – based on leukocytosis with neutrophilia, increase in RBC sedimentation rate, plasma CRP level,
  decrease in plasma levels of C3, CH50
• Increased titer of anti-streptolysin-O Ab indicates the acute inflammation is due to streptococcal infection
• Increase in lactate dehydrogenase indicates that there is tissue damage (kidney, tonsil, other lymphoid tissue)
• Urine analysis suggests an acute post-Streptococcal glomerulonephritis (PSGN), a type of post-infectious glomerulonephritis
• Acute PSGN – caused by group A beta hemolytic streptococci and follow upper airway infections (pharyngitis or tonsillitis)

Question 5

Renal Blood Flow – Magnitude

Answer 5

• Kidneys – 200 gm each, 400 gm total = 0.6% of body wt, highest blood flow rate per unit of tissue
• Renal blood flow – ~22% of cardiac output at rest
  – Renal tissue – 4 mL/min/gm
  – Skin – 0.03 mL/min/gm
  – Skeletal m. – 0.2 mL/min/gm
  – Brain – 0.6 mL/min/gm
• Why is the renal perfusion rate so
  high?
  – For kidneys to work properly, the glomerular filtration rate (GFR) must be maintained at high rate
  – GFR is dependent on renal blood flow
• metabolize and get rid of toxic material

Question 6

Structure of Kidneys – Gross View

Answer 6

• Kidney – outer cortex and inner medulla
  – Outer cortex – contains many capillaries
  – Medulla – renal pyramids (7 in humans) separated by renal columns, minor & major calyces renal pelvis ureters
  – Renal artery → interlobar artery → arcuate a. → interlobular a. → afferent arteriole → glomerulus (1st capillary network) → efferent arteriole → peritubular capillary (2nd capillary network) → venous blood

Question 7

Structure of Kidneys – Nephrons

Answer 7

• Nephrons – the basic functional unit to form urine
• 1. Renal tubular components
     – Nephron tubule – glomerular capsule → proximal convoluted tubule (PCT) → loop of Henle (LOH) (desc. & asce. limbs) → distal convoluted tubule (DCT) → collecting duct (CD) → calyx
     – Loop of Henle & medullary collecting ducts are located in medulla
• 2. Renal vascular components (glomeruli and peritubular capillary network)

Question 8

Glomerular Filtration

Answer 8

• Forces that cause glomerular filtration
  of plasma → ultrafiltrate
  – Formed under hydrostatic P of blood (major, due to BP) & colloid osmotic P of glomerular filtrate (minor) (push fluid going through pores into glomerular space/bowmans capsule, then to renal tubule, proximal tubule, loop of henle, distal tubule, collecting duct)
  – Countered by:
  * Hydrostatic P of glomerular filtrate
  * The colloid osmotic P of plasma proteins
  – Net filtration pressure is +10 mm Hg (pushing fluid from lumen of capillary into glomerular space)
  – Glomerular filtration rate (GFR; ml/min)
  * Volume of filtrate produced by both kidneys each minute ~115 in women; 125 in men
  * < 90 ml/min – lower kidney function

Question 9

Glomerulus – Functional Analogies

Answer 9

• Filter paper – filtration barrier
• Glomerulus – a blood filtering device, large pores
• Structure of a balloon and a fist

Question 10

Renal Corpuscle

Answer 10

• Glomerular (Bowman’s) capsule – surrounds glomerulus (capillary tufts) by 2 layers (visceral & parietal)
  – Visceral layer – forms part of filtration barrier
  – Parietal layer – line by squamous epithelia cells; does not function in filtration, acts like a funnel (inside glomerular capsule)
  – Glomerular space is between the two layers
• Renal corpuscle – glomerulus + capsule + glomerular space

Question 11

The Glomerulus

Answer 11

• The glomerulus – capillary network (glomerular tuft) + mesangial cells + epithelial cells (podocytes) etc.
• The glomerulus is the interface between blood and the outside world (thru lumen of renal tubules)
• All renal blood flow passes through a glomerulus for filtration

Question 12

Glomerulus Capillary – Fenestrae

Answer 12

• Glomerulus capillary –fenestrated capillary
  – Endothelium have large pores (fenestrae), 50-100 nm in diameter
  – 100-400x more permeable to
  plasma H2O & solutes (electrolytes, glucose etc.) than capillaries of skeletal muscle
  – Small enough to prevent RBCs (6-8 micro m), platelets (~2 micro m), WBCs, and large proteins from passing through pores

Question 13

Glomerulus Capillary – Visceral Layer

Answer 13

• Visceral layer of glomerular capsule:
  – Made of podocytes
  – Epithelial cells with foot processes or pedicels
  – Rest on outer layer of basement membrane
  – Pedicel interdigitate, like fingers
  * Primary processes & secondary processes
  – Slits – space between adjacent pedicel (pore is ~30 nm wide ), form a secondary size-selective
  barrier

Question 14

Glomerular Capillary – Basement Membrane

Answer 14

• Basement membrane (basal lamina):
  – A meshwork of collagen & glycoprotein fibers in a gel-like matrix
  – Limits the passage of all plasma proteins except the smallest ones
  – The main size-selective barrier

Question 15

The Glomerular Filtration Barriers

Answer 15

1. Fenestrated glomerular capillary endothelium – prevents large proteins from passing through
2. The glomerulus basement membrane – contains a negative charge mainly due to heparan sulfate
3. Podocytes (visceral epithelial cells) – contain intercellular junctions that prevent further protein loss

Question 16

Movement Across Capillary Wall

Answer 16

• Small molecules (< 5,000 MW)
  – Through intercellular cleft and pores (readily)
• Examples – water, electrolytes, glucose, amino acids
  – Some (lipid soluble) permeate cell membrane as well
• Example – cortisol (MW 362) and halothane (MW 197)
• Example – chloramphenicol (MW 323)
• Mid-sized molecules (5,000 – 30,000 MW)
  – Through pores
  – Some large lipid soluble molecules might permeate cell membrane (uncommon)
• Organic molecules (toxins, pharmacologic agents)
• Macromolecules (> 30,000 MW)
  – Normally retained in capillaries
• Example – albumin and immunoglobulins

Question 17

Basic Nephron Processes

Answer 17

• Basic nephron processes
  – Glomerular filtration
  – Tubular reabsorption
  – Tubular secretion
  – Tubular synthesis (NH3)
• Renal handling of any substance – Ask 4 questions:
  – Is it filtered? Is it reabsorbed? Is it secreted? Is it produced or degraded?

Question 18

Factors Affecting Filtration

Answer 18

1. Molecular weight & size
   – Molecular weight
   – Diameter size – substances < 8 nm can pass through barriers
   water and glucose and insulin can easily be filtered, hemoglobin less is filtered, albumin cannot be filtered
2. • Fenestrae are covered by negatively charged glycocalyx
     * Glomerular basement membrane are filled with a matrix with negative charge
     * Podocytes contain a negative surface coat
     * → Proteins with negative (anonic) charge (eg. albumin) are repelled
     - cationic can easily go through barrier
3. • The glomerular mesangial cells
     – Produce mesangial intercellular matrix to provide structural support for glomerulus
     – Contain myofilaments → can contract like smooth muscle
     * Contraction of myofilaments → decrease
     glomerular surface area
     * Relaxation of myofilaments → increase glomerular surface area
     – increase Blood glucose level → increase oxidative stress → advanced glycosylation
     end products → thickening of glomerular basement → glomerulosclerosis & fibrosis → diabetic nephropathy
     – Antigen-IgG complexes may lead to activation of cytokines by mesangial cells → inflammation → decrease glomerular surface area
     - when squeezed, goes from round shape to flat shape which changes surface area

Question 19

Filtration – Summary

Answer 19

• Three filtration barriers
  – 1st filtration barrier – endothelial cells (70 nm radius pores)
  – 2nd filtration barrier – basement membrane (negatively charged)
  – 3rd filtration barrier – podocytes (pedicels)
• Normally the glomerular ultrafiltrate (filtrate)
  – Is free of blood cells
  – Has very low protein concentration, the filtered proteins are reabsorbed by renal epithelial cells → no proteins in urine
• Hematuria & proteinuria
• Glomerular filtration is a bulk-flow process
  – Both useful & waste substances are filtered
  together

Question 20

Glomerulus Filtration

Answer 20

• Driven by high hydrostatic pressure of the blood
• Highly permeable to water and small molecules (electrolytes, glucose & amino acids)
• Highly selective – albumin is kept in plasma → colloid osmotic P
• About 1/4 of plasma entering glomerular capillary bed is filtered into Bowman’s space

Question 21

Acute Glomerulonephritis

Answer 21

• Acute glomerulonephritis (GN) – a set of renal diseases in which immunologic mechanism triggers inflammation & proliferation of
  glomerular tissue that can results in
  – Antibody + antigen = immune complex
  – → Deposition of plasma-soluble immune complexes in glomeruli
  – → Activation of the classical pathway of complements
  – → Inflammation → glomerular damage to the basement membrane,
  mesangium, or capillary endothelium

Question 22

Acute Post-Streptococcal GN – Background

Answer 22

• Acute post-streptococcal glomerulonephritis (PSGN) is the archetype of acute glomerulonephritis
• PSGN appears 1-4 weeks after a streptococcal infection of
  pharynx or skin
• Most cases occurs in children 5-15 years old; patients 40 years
  of age (10%); more common in males (2:1 male-to-female)
• > 95% eventually recover with conservative therapy (a self-
  limiting disease)
• Associated with Group A β-hemolytic streptococci strains
• The incidence of post-streptococcal GN in the US & other
  developed countries has fallen, while GN associated with post-
  staphylococcal infection has risen

Question 23

Acute Post-Streptococcal GN – Symptoms

Answer 23

• Clinical presentation (sudden onset)
  – Edema (80-90% cases), malaise, fever,
  nausea
  – decrease GFR → oliguria
  – Hematuria (coffee-colored urine) → RBC
  casts, dysmorphic RBCs in the urine (macro
  – 30%, micro – 10%)
  – increase Na+ retention → mild to moderate
  hypertension (80% cases). Mechanism?
  increased Na retention in the blood maintains normal osmolarity, because of water body increase, increases the volume of blood plasma /total blood, as blood volume is increased then pressure will be increased
• Serological data
  – Elevated antistreptolysin O (ASO) titers
  – Hypo-complementemia
  – Azotemia (increase blood urea levels, mainly due to decrease GFR. Uremia is the pathological manifestations of severe azotemia)

Question 24

In acute post-Streptococcal glomerulonephritis, why would C3 and CH50 (total hemolytic complement) be reduced?

Question 25

Complement System

Answer 25

• The complement system refers to a series of >20 proteins, circulating in the blood and tissue fluids in inactive forms
• Immune recognition of microbes → activate complement proteins sequentially in an enzyme cascade via three different pathways (classical, alternative & lectin)
• Each complete pathways all lead to the activation of C3
• Activated C3 triggers the lytic pathway → damage bacteria & cell

Question 26

Complement Component 3 (C3)

Answer 26

• The complement system (complement cascade) is part of the innate immunity. It complements the ability of antibody and phagocytic cells to destroy pathogens.
• C3 is produced by immune cells (monocytes, macrophages)
• C3 is the most important and abundant protein in the complement system.
• C3 plays a central role in all 3 complement activation pathways (classical, alternative & lectin pathways)

Question 27

The CH50 Test

Answer 27

• a.k.a. total hemolytic activity, or total complement test
• CH50 test is a complement function assay that measures the
  ability of patient’s serum to lyse Ab-sensitized sheep RBCs via
  complement classical pathway
• CH50 test is a very useful screening tool to rule out or to verify
  suspected genetic complement deficiency disease or
  secondary complement disorder due to other medical
  conditions
• This patient has hypocomplementemia due to activation of the
  complement pathways → blood complements were consumed
  → decrease the ability of serum complements to cause hemolysis of
  Ab-sensitized sheep RBCs → lower titer on CH50 test

we know whether the amount of complement in the blood is higher or lower

lower ch50 (and lower c3?) in the test indicates that inflammation occurs, theres an immune reactin going on

Question 28

Acute PSGN – Pathogenesis

Answer 28

• Acute PSGN – an immune complex-mediated disease, is a type of
  post-infectious glomerulonephritis (PIGN)
• Streptococcus infection → streptococcal neuraminidase alters
  host IgG structure → host produces anti-IgG → forms IgG/anti-IgG
  immune complexes → deposit in glomeruli → WBC (inflammatory
  cells) recruitment → activation of the complement pathways →
  most plasma complements are used in acute phase (esp. C3) →
  hypocomplementemia
• PSGN is a self-limited glomerulonephritis, usually recover
  baseline kidney functions in weeks, resolving hematuria,
  proteinuria, and hypocomplementemia without therapeutic
  intervention
• If not cure → chronic glomerulonephritis or nephrosis

Question 29

Acute Post-Strept. GN – Pathogenesis

Answer 29

• Inflammation → infiltration of inflammatory cells (neutrophils & macrophages) in glomeruli →
  – Swelling & proliferation of endothelial cells
  – Proliferation of mesangial cells & epithelial cells
  – Thickening of the basement membrane
  – Injury in podocytes
  – Hyalinization (sclerosis) indicates irreversible injury

Question 30

Why might the oliguria occur in PSGN (PIGN)?

Answer 30

• Acute PSGN → deposition of Ag-Ab complex in glomeruli → infiltration of inflammatory cells, proliferation of endothelial & mesangial cells → glomerular capillaries compressed → occlusion
  of capillary loops → decrease surface area for filtration → decrease GFR → decrease urine
  production (oliguria)
• Proteinuria causes inflammation and scarring in the renal tubules → nephron loss → decrease GFR

Question 31

Lab Tests – Urine

Answer 31

• Proteinuria and hematuria is found in this patient

Question 32

Glomerular Filtration of Proteins

Answer 32

Permselectivity – restriction of permeation of macromolecules across a glomerular capillary wall on the basis of molecular size, charge, and physical configuration
* Size-selectivity – glomerular permselectivity based on molecular size (cutoff – 8 nm)
* Charge-selectivity – glomerular permselectivity based on net electric charge (repel molecules with net negative charge)

Question 33

Renal Protein Reabsorption

Answer 33

• Almost all (protein) reabsorption takes place in proximal tubules (PT).
• Only ~1% goes to the final urine (normal).
• The proteins cross the apical membrane by endocytosis.
• In PT epithelial cells, the absorbed proteins are degraded in lysosomes into amino acids.
• The amino acids are transported across the basolateral membrane by amino acid transporters.

Question 34

Explanation on Proteinuria in PSGN

Answer 34

• The affected nephrons – progressive loss of function
• In glomeruli of affected nephrons, inflammation may result in:
  – 1. Endothelial cell swelling of glomeruli → larger fenestrae
  – 2. Damage to process of podocytes
  – → loss of glomerular permselectivity, allowing the passage of proteins (albumin & larger proteins) to glomerular space
• Renal tubules of affected nephrons – large filtered loads of proteins exceed the capacity of reabsorption by the tubules → overwhelm the capacity to reabsorb proteins by PT epithelial cells → proteinuria

Question 35

Foamy Proteinuria

Answer 35

• Normally, most proteins are too big to pass through the holes on glomerulonephritis.
• If the glomeruli are inflamed and damaged (such as in PSGN), many proteins will leak into urine through filters of glomeruli, thus leading to proteinuria.
• If there is too much protein in urine, the urine will become foamy and smelly (degradation of proteins)

Question 36

Blood Volume – Exchange of Fluid

Answer 36

• Fluid movement = fluid out - fluid in = (Pc +
  pi) - (Pi + pp)
  – Pc = hydrostatic P of blood (push fluid out)
  – Pi = hydrostatic P of interstitial (tissue) fluid (push fluid in)
  – pp = colloid osmotic (oncotic) P of plasma
  (pp = plasma proteins) (keeps fluid from going out)
  * Promotes fluid re-absorption into
  circulatory system
  – pi = colloid osmotic P of interstitial fluid (push fluid out)
• Movement of solutes
  – At arteriolar end of capillary – +11 mm Hg (pushes fluid out)
  – At venular end of capillary – -9 mm Hg (favors fluid coming back in)
• What happen to the remaining fluids (+11
  mmHg vs. -9 mmHg)?

there will be some fluid retained in interstitial fluid

Question 37

Lymphatic System

Answer 37

• Explanation – excess tissue fluid returned to venous system by lymphatic vessels (lymph)
• Functions of lymphatics
  – Transports interstitial fluid (lymph)
  – Transports absorbed fat from small
  intestine to blood
  – Lymph nodes and lymphocytes –
  immunological defense
• Lymphatic vessels
  – Lymphatic capillaries – closed-ended
  – Lymph enters into systemic circulation
  from thoracic duct into vena cava

Question 38

Mechanisms of Edema Formation

Answer 38

• Albumin – the major protein in the blood which maintains colloid osmotic (oncotic) pressure
• The colloid osmotic pressure hold water to remain within blood vessels, thus prevent leakage of water into tissues.
• increase Permeability to proteins → albuminuria → hypoalbuminemia → decrease plasma colloid osmotic P (oncotic P) → increase accumulation of interstitial fluid → decrease plasma volume → edema
• Edema → swelling (common in PSGN patients)

Question 39

This patient has edema on face and lower legs.
How might the edema occur?

Answer 39

excess tissue fluid returned to venous system by lymphatic vessels (lymph)

Question 40

Hematuria

Answer 40

• Hematuria is the presence of RBC & WBC in urine. If WBCs are also found in urine analysis → renal infection
• Hematuria includes microscopic (only viewable under microscopy) and gross (many RBCs, urine will become red or pink) hematuria
• In PIGN, the filters in kidneys (glomeruli) are damaged → fail to maintain blood cells in glomerular capillaries → hematuria
• Etiology
  – Kidney (GN, damages in renal parenchyma, urinary tract, others)
  – Hematological – defects in coagulation, use of anticoagulants (warfarin, heparin) & others

Question 41

PIGN may Develop into Nephrosis

Answer 41

• Nephrosis – non-inflammatory nephropathy, any degenerative disease of renal tubules
• Nephrotic syndrome occurs in 2% children and 20% of adults with PIGN
• Nephrotic syndrome
  – Urinalysis – proteinuria (> 3.5 g/day), oval fat bodies, minimal or microscopic hematuria
  – Hypoalbuminemia
  – Edema
  – Hyperlipidemia
  – Hypercoagulability state

Question 42

Hyperlipidemia and Lipiduria

Answer 42

• Hypoalbuminemia → increase compensatory response in liver (increase production of albumin plus increase synthesis of apolipoproteins & increase
  processing of lipid) → change in lipid & lipoproteins profile
• Plasma levels – increase cholesterol, increase LDL, increase VLDL
• Nephrotic patients – a 5x increase risk of coronary death
• Loss of lipoprotein in urine → lipiduria
  Oval fat body
  Fatty cast

Question 43

Hypercoagulability

Answer 43

• Hypercoagulability – increase risk of thrombus formation
• PSGN → increase urinary loss of clotting (coagulation) factors → increase
  compensatory response in the liver
• → increase Hepatic synthesis of clotting factors
• → Altered coagulation cascade (intrinsic, extrinsic & common PWs
• → increase Platelets aggregability → hypercoagulability
• → increase Formation of venous and arterial clots

Question 44

Infections

Answer 44

• Loss of IgG & complement factors in urine → increase susceptibility to bacterial infections
• Loss of zinc & transferrin in urine (important for lymphocyte function)
• Loss of cytokines → abnormal neutrophil functions
• → increase risk of bacterial infections

Question 45

• Oligouria results from lower GFR. Lower GFR refers to obstructed glomerular fenestrae, whereas proteinuria and
  hematuria means that the glomerular fenestrae are big
  enough for proteins and blood cells to pass through.
• Clinically it is common for PSGN patients to have oligouria,
  proteinuria and hematuria at the same time.
• By which mechanisms could the seemingly contradictory
  symptoms of oligouria, proteinuria and hematuria occurs on
  a patient simultaneously?

Answer 45

• Total surface area for filtration is reduced due to infiltration of
  inflammatory cells & proliferation of mesangial cells → fewer
  fenestrae → decrease surface area → decrease GFR → oligouria
• Proteinuria & hematuria may be due to:
  – Some fenestrae are bigger due to endothelial cell swelling
  – Podocyte injury → detachment from the glomerular basement
  membrane → loss of permselectivity (size & charge)
  – The remaining functionally normal nephrons → compensatory
  hypertrophy & renal tubular dilatation

Question 46

Treatment of PSGN

Answer 46

• Treatment of PSGN is mainly supportive, because there is no
  specific therapy for renal disease.
• Record the urine amount daily for 2-3 wks
• Diet – low salt, high-quality protein & limited water
• Antibiotics to treat the underlying infections
• decrease Hypertension – ACE inhibitors or/and Ca2+ channel inhibitor
• Diuretics
• Monitor/control blood potassium
• Temporary hemodialysis — to help remove toxins and excess
  fluids.