Kidneys Flashcards
Describe the surface anatomy of the kidneys
Between vertebral levels T11-L2/3, the right is lower and the hila sit around L1
Sit under 12th rib with the left under 11th & 12th rib
What is the renal angle?
Between 12th rib and lateral border of vertebral column extensor muscles
Describe the surface anatomy of the ureters
Run vertically inferior to pelvic cavity; follow tips of lumbar vertebrae
transverse processes
What protective layers cover the kidneys?
Perinephric fat
Renal fascia
Paranephric fat
Psoas fascia
Renal fascia is loose & kidneys can move with body position. What occurs if they move too much? And what can be a sign of this?
Nephroptosis
Blood in urine when running
What tissue type do kidneys derive from?
Metanephros - mesoderm
Ureteric bud
What can happen if the ureteric bud develops abnormally?
Bifid Ureter
Duplicated ureter
Absent
During what time frame do the kidneys ascend to their adult position?
Week 6-9
Start in pelvic cavity
Migrate superiorly
Receive new blood supply as they move upwards and take the ureters with them
What is a pelvic kidney?
One kidney never migrates and so remains in the pelvic cavity
If there is no impingement then it doesn’t matter
What is a horseshoe kidney?
Two kidneys fused and not ascended. Gets stuck on IMA, can block it so ischemic bowel
What is a polar renal artery?
Artery not running into hilum. Squash ureter so renal pelvis enlarges
What is the allantois?
Passes from cloaca to umbilicus
What is the adult remnant of the allantois?
Urachus
Name 3 remnants of the allantois that can cause clinical problems
Urachal fistula/patent - urine can leak out
Urachal cyst - can get infected
Urachal sinus - blind ended tract from umbilicus, cheesy discharge
Describe the blood supply to the kidneys
Renal arteries at L1/2 (listen for bruits)
Run posterior to renal vein & IVC
Segmental supply (4/5 end arteries)
Describe venous drainage of the kidneys
Right renal vein directly join IVC
Left veins receive gonadal & suprarenal veins
Left renal vein runs under SMA to join IVC
Describe nerve supply to the supra renal glands
Preganglionic sympathetic fibres (T10-L1)
Synapse directly with chromaffin cells in medulla
What arteries do the ureters receive blood supply from?
Renal Gonadal Aortic Internal iliac Vesical/prostatic
Which direction should the ureters be displaced in order to prevent disrupting their blood supply?
Displace ureter medially in abdo cavity
Displace ureter laterally in pelvic cavity
What pain pattern occurs with renal calculi?
Shifting loin to groin pain T12-L1/2
What is the main differential concern for an elderly patient presenting with presumed left sided renal colic?
Dissecting aortic aneurysm
What are potential sites for stones?
Renal tract (urolithiasis) Gallbladder/biliary tree (cholelithiasis) Salivary glands (sialolithiasis) Appendix (faecolith) Prostate Veins (phleboliths)
How do stones form?
Increased concentration of solutes causing supersaturated solution
Stasis
Infection
What effects can stones have?
Block ducts: colic, jaundice, renal failure
Chronic inflammation: Cholecystits, cystitis, sialadenitis
Infection
Describe salivary stones
Occur more in females Usually Wharton’s duct Pain and swelling of gland Idiopathic, infection, drugs Remove stone – open/endoscopic
Describe gallstones
Common (10%), more in females
GB stores & concentrates bile
Most stones cholesterol based due to high fat diets/hypercholesterolaemia
Pigment stones found in haemolytic disorders (high serum bilirubin)
Ratio of cholesterol:bile salts & lecithin
How do gallstones present?
Asymptomatic
Abdominal pain
Jaundice
Fever
How do you investigate gallstones?
Bloods – LFT, amylase
USS
ERCP (endoscopic retrograde cholangio pancreatography)/MRCP
Describe what factors can affect the likelihood of developing renal stones
Common (10%) Males > females
Varies with geography/climate
Age, Peak onset 20-30
Fluid intake, Family history, Affluence/diet/BMI
Describe how renal stones form pathophysiologically
Urine normally supersaturated but metastable
Crystal growth more than normal
Crystals aggregate to form small stones
Symptomatic stones require particle retention to enlarge
What different types of renal stones can form?
Ca oxalate 60% - visible on xray Ca phosphate 20% - visible on xray Urate 7% - not visible on xray, but will show on USS and CT Struvite 7% Cysteine 2% Others
Where do renal stones get stuck?
Pelvic ureteric junction (PUJ)
Pelvic brim
Vesicoureteric junction (VUJ)
Bladder urethra outlet
What can cause calcium oxalate stones to form?
Hypercalciuria: Idiopathic, Rare genetic disorders,Hyperparathyroidism, Malignancy, Sarcoidosis/TB
Hyperoxaluria: Primary hyperoxaluria, Secondary- Dietary, Enteric
Describe struvite stones
Triple phosphate
Urinary infection by urea-splitting bacteria (split urea to CO2 and ammonia) so alkaline urine
Proteus mirabilis, Klebsiella, Pseudomonas, Providentia
Even low colony numbers produce urease
Struvite stones cause most staghorn calculi
Describe the 2 types of staghorn calculi
Struvite stones cause most staghorn calculi
Partial staghorn – renal pelvis stone extending into at least 2 calyceal groups
Complete staghorn – renal pelvis stone extending into all major calyceal groups filling at least 80% of collecting system
What are risk factors for struvite stones?
Risk factors all related to UTIs Female Indwelling catheters Neurogenic bladders Urinary tract abnormalities Stagnant urine
Describe the formation of cysteine stones
Autosomal recessive disorder affecting dibasic amino acid transporter in tubule
Cystine not reabsorbed – crystalizes
Faintly radio-opaque, Often staghorn
Young, mulitple stones
5% get ESRF
Hard to manage; drink more, alkalinise urine
Describe uric acid stones
Purine metabolism Associated with metabolic syndrome and acidic urine Radiolucent Gout Some medications
How will a patient with renal stones present?
Loin to groin pain (renal colic), Can’t get comfortable, Radiates to testicle Haematuria Vomiting Irritative voiding symptoms Exclude leaking AAA
What history information do you need from someone presenting with renal stones?
No of stones passed Frequency of stone formation Age at first onset Kidney(s) involved Stone type Previous interventions
What initial investigations would you perform on someone presenting with renal stones?
Urine dipstick (haematuria, pH)
Serum creatinine/electrolytes, calcium, urate
Urine microscopy & culture
Imaging: Urgent, Immediate if fever - pyonephrosis
KUB- Sensitivity 50% Ca>struvite>cystine>urate, USS- Sensitivity 60% (80% for obstruction), CT KUB
What is the initial management of a patient with renal stones?
Infected obstructed kidney requires immediate drainage
Need to remove them if: Pain/failure to pass, Recurrent infection, Renal impairment, Bleeding, Some jobs (airline pilot)
How can renal stones be removed?
Fragmentation: Extracorporeal shockwave lithotripsy (ESWL), Focussed shockwave
Removal: PCNL Percutaneous nephrolithotomy, surgery, laser
What are complications of Extracorporeal shockwave lithotripsy (ESWL)?
Haematuria
UTI
Steinstrasse (stone fragments block ureter)
Tubular damage
What are the functions of the kidneys?
Removal of toxins Electrolyte balance Acid base regulation Fluid and volume regulation Endocrine functions
What cell types are found in the loop of Henle?
Thin - cuboid cells
Thick - columnar cells
What do cells in the distal convoluted tubule look like?
Virtually no brush border
Active cells with lots of cytoplasm
What type of cells are found in the ureters?
Transitional epithelium
Folded to allow stretch
Multiple layers for protection
Where do the kidneys sit in the abdomen?
Paired retroperitoneal organ located on posterior abdominal wall
Hilum at L1
What are the posterior relations of the kidneys?
Costodiaphragmatic recess
Quadratus lumborum
Psoas major
12th rib
What is the renal papilla?
Drainage point into calyxes
What is Psoas fascia?
Forms sheath down to hip region – infection can spread down this route; abscess can form under fascia
What is Thoracolumbar fascia?
Tough covering of intrinsic vertebral column muscles
What is Renal fascial space?
Communicates across midline, and serves as route for infection spread
What is nephroptosis?
Renal fascia is loose & kidneys can move with body position
Nephroptosis occurs if they move too much
What does the kidney develop from?
Metanephros (mesoderm) & ureteric bud
Describe the blood supply of the kidneys
Renal arteries at L1/2 (listen for bruits) behind IVC on right
Run posterior to renal vein & IVC
Segmental supply (4/5 end arteries)
Describe the venous drainage of the kidneys
Right renal vein directly join IVC
Left veins receive gonadal & suprarenal veins
Left renal vein runs under SMA to join IVC
Describe the blood supply to the supra renal glands
Left vein drains to renal vein
Right vein drains to inferior vena cava
Describe the nerve supply to the supra renal glands
Preganglionic sympathetic fibres (T10-L1)
Synapse directly with chromaffin cells in medulla
What do the ureters develop from?
Ureteric bud of mesonephric duct
Which arteries supply the ureters?
Renal Gonadal Aortic Internal iliac Vesical/prostatic
What is the main differential concern for an elderly patient presenting with presumed left sided renal colic?
Dissecting aortic aneurysm
Which sensory nerves are involved in renal calculi pain?
Renal plexus at renal pelvis Abdomino-aortic plexus at pelvic brim Hypogastric plexus (superior) at vesico ureteric junction
What do the ureters cross to enter the pelvic cavity?
Iliac vessels
How much of an adult male is water?
60% so in 70kg male, 42 Litres
What are the 2 main compartments of ECF?
Interstitial fluid which surrounds the cells
Plasma which is non-cellular component of blood
What differences exist between Interstitial fluid and plasma?
Proteins which remain in plasma
What is osmosis?
Net diffusion of water across a selectively permeable membrane from a region of high water concentration to a region of low water concentration
What are osmoles?
Number of osmotically active particles in a solution
What are the endocrine functions of the kidney?
Production of EPO
Alpha hydroxylase production for vit D activation
RAAS system
What is EPO?
Erythropoietin, produced by interstitial cells in cortex & outer medulla
Growth factor, stimulates production of RBC precursors in bone marrow
Stimulus for its release is hypoxia
Kidneys are major source, disease can therefore result in anaemia (normochromic normocytic)
What is the functional unit of the kidney?
Nephron
What are the 3 main processes performed by the nephron?
Filtration
Reabsorption
Secretion
What is urinary excretion rate?
Filtration rate + Secretion rate – Reabsorption rate
What is renal blood flow rate? And what is renal plasma rate?
1 litre per min renal blood flow
600ml per min renal plasma flow
What make up the layers of the glomerular filtration barrier?
Capillary endothelium (fenestrated) Basement membrane (negative charge) Epithelial cells (foot processes - podocytes & filtration slits)
How is the passage of substances limited across the glomerular filtration barrier?
By their size, shape and charge
What cells are excluded from glomerular filtrate?
Blood cells and plasma proteins
What effect do disease processes have on filtrate in the kidneys?
Alter the properties of barrier allowing protein to appear in the filtrate
What factors determine filtration?
Glomerular capillary filtration coefficient, Kf (leakiness of barrier)
Net filtration pressure (NFP)
GFR = Kf x NFP
What is glomerular filtration rate?
GFR
The volume of filtrate formed by all the nephrons in both kidneys per unit time
What is the glomerular filtration coefficient Kf?
Reflects:
Surface area available for filtration
Hydraulic conductivity (permeability) of the filtration barrier
How might Kf be affected in disease processes?
Reduced number of nephrons or processes which damage the filtration barrier will ↓surface area or ↓permeability & ∴decrease GFR
What is net filtration pressure?
Sum of pressures acting across the filtration barrier (Starling forces) Sum of the hydrostatic pressures
Sum of the colloid osmotic (oncotic) pressures
NFP = PG (glomerular hydrostatic) – PB (bowmanns capsule hydrostatic) – πG (glomerular colloid osmotic) + πB (bowmanns capsule colloid osmotic)
Typical is 10mmHg
What does glomerular hydrostatic pressure rely on?
Arterial pressure
Afferent arteriole resistance
Efferent arteriole resistance
How does most regulation of GFR occur?
Changes in glomerular hydrostatic pressure
How can you increase GFR?
Afferent arteriole dilation &/or Efferent Arteriole constriction
How can you decrease GFR?
Afferent Arteriole constriction &/or Efferent Arteriole dilation
What factors can cause Afferent Arteriole dilation and therefore lead to increased GFR?
Prostaglandins Kinins Dopamine low dose Atrial natriuretic peptide Nitrous oxide
What factors can cause Afferent Arteriole constriction and therefore lead to decreased GFR?
Angiotensin II high dose Noradrenaline Endothelin Adenosine Vasopressin
Describe the relationship between GFR and Arteriole resistance
Changes in AA resistance, effect on GFR is fairly linear
For EA resistance, effect on GFR is biphasic: Initial EA constriction causes ↑GFR by ↑glomerular hydrostatic pressure
Severe EA constriction slows down renal blood flow so that glomerular osmotic pressure rises more than hydrostatic & ∴GFR falls
What effect does angiotensin II have on GFR?
Preferentially constricts Efferent Arteriole – so increases glomerular hydrostatic pressure and therefore increases GFR
Which vasoactive substances dilate the Afferent Arteriole and therefore cause increased glomerular hydrostatic pressure and GFR?
Prostaglandins and atrial natriuretic peptide (ANP)
Which vasoactive substances constrict the Afferent Arteriole and therefore decrease glomerular hydrostatic pressure and GFR?
Noradrenaline (sympathetic nervous system), adenosine and endothelin
What occurs in the peritubular capillaries?
After leaving the glomerular capillaries and passing through the efferent arteriole the blood enters the peritubular capillaries
Changes in hydrostatic pressure and colloid osmotic pressure mean that absorption rather than filtration is favoured
Describe the autoregulation of GFR
GFR and renal blood flow relatively constant across a range of systemic blood pressures (~80–180 mm Hg)
Prevents large changes in renal excretion of water & solutes
Two mechanisms of autoregulation: Myogenic response and Tubuloglomerular feedback
What is Myogenic autoregulation of GFR?
Increase in arterial blood pressure
Increased renal blood flow and increased GFR
↑stretch of afferent arteriole smooth muscle which opens Ca channels Reflex contraction of AA smooth muscle, Vasoconstriction
↑Resistance to flow prevents changes in renal blood flow & GFR
What is a Myogenic response?
Inherent ability of smooth muscle in afferent arterioles to respond to
changes in vessel circumference by contracting or relaxing
What is the Tubuloglomerular feedback to maintain GFR when BP increases?
Mechanism links changes in [NaCl] in tubule lumen to control of afferent arteriole resistance
Utilises juxtaglomerular apparatus, Macula densa cells in initial part of
distal tubule sense [NaCl]
Arterial blood pressure increased, causes a transient ↑GFR which increases [NaCl] delivered to distal tubule
Release of paracrine factors (adenosine) by macula densa cells
Adenosine causes constriction of Afferent Arteriole smooth muscle
Vasoconstriction of AA so ↑Resistance to flow
Restores renal blood flow & GFR
What is the Tubuloglomerular feedback to maintain GFR when BP decreases?
Mechanism links changes in [NaCl] in tubule lumen to control of afferent arteriole resistance
Utilises juxtaglomerular apparatus, Macula densa cells in initial part of
distal tubule sense [NaCl]
Arterial blood pressure decreases, causes a transient ↓GFR which decreases [NaCl] delivered to distal tubule
Release of paracrine factors (renin) by macula densa cells
Renin causes release of Angiotensin II which causes constriction of Efferent Arteriole smooth muscle
Vasoconstriction of EA so ↑Hydrostatic pressure
Restores renal blood flow & GFR
What clinical disorders can occur if the kidneys dysfunction?
Failure of maintenance of fluid volume: Hypertension, Oedema
Failure of fluid composition: electrolyte and acid base disorders
Failure of excretion of waste: uraemia, drug toxicity
Failure of endocrine function: anaemia, renal bone disease
What investigations can be done relating to the kidneys? And what are you looking for?
Urine: What’s being filtered? What’s being excreted? e.g. protein, blood, glucose, leucocytes, osmolarity
Blood: Are waste products accumulating? Electrolyte abnormalities? Evidence of underlying cause? e.g. urea, creatinine, eGFR / GFR, sodium, potassium, pH, osmolarity, autoimmune diseases
Imaging: Any macroscopic structural abnormalities? Any functional abnormalities? e.g. ultrasound, plain X ray, CT, MRI, contrast studies, nuclear imaging
Biopsy: Any microscopic structural abnormalities?e.g. light microscopy, immunohistochemistry, electron microscopy
What are indicators of renal decline?
Proteinuria / albuminuria, Haematuria: Indicate damage
Estimated GFR / GFR, Serum creatinine /urea: Indicate function Calcium / phosphate homeostasis, Electrolytes /pH, Fluid balance / urine volume, Haemoglobin: Indicate function but not quantitative
What does proteinuria show about kidney function? And how can you detect it?
Indicates damage to the filtration barrier
Strong association between proteinuria and rate of disease progression in chronic kidney disease (CKD)
Can be detected by urine dipsticks
More sensitive methods include protein-creatinine ratio (PCR) and albumin creatinine ratio (ACR)
What is haematuria and what can effect its presence?
Blood can originate anywhere in urinary system
Beware menstrual bleeding and false positives on urine dipsticks e.g.
myoglobinuria
May be visible (frank / macroscopic) or non-visible (microscopic)
Age of patient an important factor in differential diagnosis
What is GFR?
Glomerular filtration rate (GFR)
The volume of filtrate formed by all the nephrons in both kidneys per unit time
What happens to GFR in disease states?
Directly related to function of nephrons & declines in all forms of progressive kidney diseases
What is the best overall index of kidney function in health &disease?
GFR
What is a normal GFR?
Linked to surface area of body ∴typical young male GFR = 120 ml/min/1.73m2
What factors effect the estimated GFR?
Age, sex and body size – declines with increasing age
What is renal clearance?
Volume of plasma from which a substance is completely cleared by the kidneys per unit time
Urine production x substance concentration in urine / substance concentration in plasma
Which substances have no renal clearance?
Proteins
Which substance is filtered and completely reabsorbed so has no renal clearance?
Glucose
Which substance is filtered but not reabsorbed or secreted and so gives an approximation of GFR?
Inulin
Which substance is filtered and partially reabsorbed?
Urea
Which substance is filtered and secreted?
Creatinine
For renal clearance of a substance to equal GFR, what properties must it have?
Freely filtered across the glomerulus Glomerulus only route of excretion Not reabsorbed or secreted Non-toxic Easily measured
What is creatinine and why is it used as an estimate for GFR?
Formed from breakdown of creatine, a skeletal muscle component
Produced at a steady rate for a given individual
Freely filtered at glomerulus & not reabsorbed
Small amount of secretion means clearance tends to overestimate GFR
Requires 24 hour urine collection – issues with compliance, time and reliability, Not suitable for a routine measure of renal function / GFR
Three tests used routinely to assess renal function, what are they?
Serum urea
Serum creatinine
Estimated GFR (eGFR)
Something normally filtered by kidneys builds up in the blood indicates ↓GFR and therefore ↓renal function
What is serum urea and what does it measure?
Nitrogen containing metabolic waste product of protein breakdown
Also known as: blood urea nitrogen (BUN)
Filtered but also partially reabsorbed
Levels typically rise in kidney disease as GFR falls
Serum levels reflect more than just GFR
What factors can increase serum urea?
Increase production: High protein diet, Increased catabolism (e.g.trauma, infection, surgery, cancer), Gastrointestinal bleed, Drugs e.g. corticosteroids, tetracyclines
Decreased elimination: Renal disease causing ↓GFR, Poor renal blood flow e.g.dehydration, hypotension
Why must a change in urea be compared to creatinine to see if there is a parallel change?
If both increased in parallel ie.both doubled, then a fall in GFR likely
If urea disproportionately higher than creatinine, need to consider:
Dehydration, High protein diet, GI bleed, Catabolic state
What factors can affect normal serum creatinine levels for that person?
Related to muscle mass: Age, sex, amputation, malnutrition, muscle wasting, ethnicity
Diet also affects creatinine levels (vegetarian diet vs. meat rich diet)
What happens to serum creatinine levels with diseased kidneys?
Increase as GFR is reduced
What happens to serum creatinine levels in a body builder with normal kidneys?
Levels will be high due to muscle mass and so will give impression of renal failure despite normal kidney function
What will serum creatinine levels be like in a elderly patient with diseased kidneys?
Levels may appear normal. Decreased GFR increases levels but decreased body mass decreases levels. Kidney disease may be masked and not detected
Why is serum creatinine not a useful measure in early kidney disease?
Can lose ~50% of renal function (GFR) and still appear to have a serum creatinine that lies within the ‘normal’ range
What is Estimated GFR (eGFR)?
Uses equations to calculate the GFR based on a single serum measurement of a substance
Incorporates clinical information along with a single serum measurement to generate an estimated GFR (eGFR)
Most use serum creatinine, age, sex and ethnicity to calculate
CKD-EPI equation (CKD Epidemiology) – recommended by NICE
Why do we need tubular processing?
Fine tune volume and composition of urine & to avoid huge fluid &
solute losses
Reabsorption more important than secretion for most substances
Describe the general mechanisms underlying tubular reabsorption
Utilises passive and active transport mechanisms to move fluid & solutes from tubule lumen to peritubular capillary
Luminal & basal surfaces of tubule epithelial cells have different transporters allowing concentration gradients to be established
Na+/K+ ATPase provides concentration gradient for reabsorption of many substances along the nephron
Water passively reabsorbed and linked closely to sodium reabsorption & permeability of the different parts of the nephron
Where does the majority of reabsorption occur?
Proximal convoluted tubule
Where does most fine tuning of solute concentrations occur?
Distal parts of nephron under hormonal control
How much urine is produced per day?
1.5 litres