case 4: Post-Streptococcal Glomerulonephritis (PSGN) Flashcards
1
Q
Lactate Dehydrogenase (LDH)
A
- 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
2
Q
Erythrocyte Sedimentation Rate
A
- 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
3
Q
C-Reactive Protein (CRP)
A
- 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
4
Q
Diagnosis
A
- 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)
5
Q
Renal Blood Flow – Magnitude
A
- 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
6
Q
Structure of Kidneys – Gross View
A
- 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
7
Q
Structure of Kidneys – Nephrons
A
- Nephrons – the basic functional unit to form urine
- 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
- Renal tubular components
- Renal vascular components (glomeruli and peritubular capillary network)
8
Q
Glomerular Filtration
A
- 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
9
Q
Glomerulus – Functional Analogies
A
- Filter paper – filtration barrier
- Glomerulus – a blood filtering device, large pores
- Structure of a balloon and a fist
10
Q
Renal Corpuscle
A
- 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
11
Q
The Glomerulus
A
- 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
12
Q
Glomerulus Capillary – Fenestrae
A
- 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
13
Q
Glomerulus Capillary – Visceral Layer
A
- 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
14
Q
Glomerular Capillary – Basement Membrane
A
- 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
15
Q
The Glomerular Filtration Barriers
A
- Fenestrated glomerular capillary endothelium – prevents large proteins from passing through
- The glomerulus basement membrane – contains a negative charge mainly due to heparan sulfate
- Podocytes (visceral epithelial cells) – contain intercellular junctions that prevent further protein loss
16
Q
Movement Across Capillary Wall
A
- 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
17
Q
Basic Nephron Processes
A
- 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?
18
Q
Factors Affecting Filtration
A
- 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 - 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
- Fenestrae are covered by negatively charged glycocalyx
- 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
- The glomerular mesangial cells
19
Q
Filtration – Summary
A
- 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
20
Q
Glomerulus Filtration
A
- 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
21
Q
Acute Glomerulonephritis
A
- 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
22
Q
Acute Post-Streptococcal GN – Background
A
- 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
23
Q
Acute Post-Streptococcal GN – Symptoms
A
- 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)
24
Q
In acute post-Streptococcal glomerulonephritis, why would C3 and CH50 (total hemolytic complement) be reduced?
A
25
Q
Complement System
A
- 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
26
Q
Complement Component 3 (C3)
A
- 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)
27
Q
The CH50 Test
A
- 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
28
Q
Acute PSGN – Pathogenesis
A
- 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
29
Q
Acute Post-Strept. GN – Pathogenesis
A
- 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
30
Q
Why might the oliguria occur in PSGN (PIGN)?
A
- 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
31
Q
Lab Tests – Urine
A
- Proteinuria and hematuria is found in this patient
32
Q
Glomerular Filtration of Proteins
A
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)
33
Q
Renal Protein Reabsorption
A
- 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.
34
Q
Explanation on Proteinuria in PSGN
A
- 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
35
Q
Foamy Proteinuria
A
- 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)
36
Q
Blood Volume – Exchange of Fluid
A
- 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
37
Q
Lymphatic System
A
- 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
38
Q
Mechanisms of Edema Formation
A
- 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)
39
Q
This patient has edema on face and lower legs.
How might the edema occur?
A
excess tissue fluid returned to venous system by lymphatic vessels (lymph)
40
Q
Hematuria
A
- 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
41
Q
PIGN may Develop into Nephrosis
A
- 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
42
Q
Hyperlipidemia and Lipiduria
A
- 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
43
Q
Hypercoagulability
A
- 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
44
Q
Infections
A
- 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
45
Q
- 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?
A
- 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
46
Q
Treatment of PSGN
A
- 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.
