Session 1 Flashcards
What is the broad function of the glomerulus
Filtration
What does the glomerulus filter
Water, sodium, chloride, potassium, bicarbonate, amino acids, glucose, creatinine, urea
What is reabsorbed at proximal convoluted tubule
Potassium, 67% sodium and chloride, 100% amino acids and glucose, 90% HCO3- and 65% water
What is secreted (cleared from body) at proximal convoluted tubule
Uric acid and organic acids
What happens at descending limb of loop of Henle
10% water reabsorbed
What happens at ascending limb of loop of Henle
Impermeable to water
25% Na+ and Cl- reabsorbed
What controls resorption of water and sodium at distal convoluted tubule
Aldosterone
What is secreted at distal convoluted tubule
K+ and H+
What controls resorption at collecting duct
ADH
What is reabsorbed at collecting duct
Urea, Na+, Cl-, water
What is excreted at end of nephron
Water, Na+, Cl-, HCO3-, Creatinine, Urea
Nephron gets blood supply from
Renal arteries
Why are kidneys vulnerable to ischeamic damage
They take about 20-25% of whole cardiac output
Big difference between cortical or juxtamedullary nephrons
Juxtamedullary have bigger loop of Henle
Broad nephron functions
Filters and cleans blood, enables site for secretion and resorption
Concentrates or diluted urine to control body fluid osmolality and fluid volume
How much that enters the glomerulus ends up filtered
20%
What is clearance
Rate at which glomerulus cleans blood
What is filtrate
What the substances are called once they leave the capillaries and end up being filtered into the Bowman’s capsule and tubule
What is GFR
Glomerular filtration rate= rate of solutes pushed out of blood into Bowman’s space
Excretion function of kidney and urinary tract
Excrete waste products and drugs
Regulation function of kidney and urinary tract
Body fluid volume and ionic compounds, major role in homeostasis and acid-base balance
Endocrine function of kidney and urinary tract
Synthesis of renin (bp and sodium balance), erythropoietin (erythrocyte production) and prostaglandins (involved in regulation of renal function)
Metabolism function of kidney and urinary tract
Vit D is metabolised to active form, metabolism of low molecular weight proteins e.g. insulin, parathyroid hormone, calcitonin
4 broad functions of kidney and urinary tract
Excretion, regulation, endocrine and metabolism
Anatomical location of kidney and urinary tract
Retroperitoneum on the posterior abdominal wall, either side of vertebral column, between T12 and L3, partially protected by ribs 11 and 12
Where is the hilum
L1
Why is right kidney lower
Liver pushed it down
What is yellow
Kidney
What is blue
Renal capsule
What is green
Perirenal fat
What is red
Renal fascia
What is pink
Pararenal fat
What do podocytes wrap around
Capillaries
What is the broad function of the Juxtaglomerular apparatus
Senses composition of contents
3 key cell types in juxtaglomerular apparatus
Macula densa cells, extraglomerular mesangial cells, granular cells
What do macula densa cells do
Sense salt, send signal to granular cells
What do granular cells control
Renin and constriction
What do extraglomerular mesangial cells do
Pass messages, secretes substances, hold skeleton
Order of blood flow from renal artery to efferent arteriole
Renal artery, segmental artery, interlobar artery, arcuate artery, interlobal artery, afferent arteriole, glomerulus, efferent arteriole
Blood flow from efferent arteriole to renal vein
Splits into 2- peritubular capillaries (associated with convoluted tubules), Vasa recta (associated with loop of Henle), interlobular vein, arcuate vein, interlobar vein, renal vein
What is the ureter made from and where is it
Smooth muscle fibres that propel urine (peristaltic waves) to urinary bladder
Retroperitoneal, lateral to tips of transverse processes of lumbar vertebrae
Ureter beyond the pelviureteric junction PUJ divided into
Proximal (abdominal), Middle (pelvic), Distal part (intramural)
Most common area of uteretic injury?
Near pelvic brim
Bony landmarks to approximate course of ureter (Hilium to bladder)
L1- hilium
Tip of lumbar transverse processes
Crosses sacrum at S1
Ischial spine- ureter kink towards bladder
Run around pelvis and enter bladder posteriorly
What is the detrusor muscle
1 massive bladder muscle- weakens and goes wrong = incompetence
What acts instead of a sphincter in the bladder
Vesicoureteral junction- oblique angle
Bladder surface
Muscular folds called rugae- contract and expand
Lined with transitional epithelium- urothelium
When empty the bladder rests on
Symphysis pubis in front of rectum (and vagina and uterus in women)
Bladder can hold on average
750ml
Lumen or ureter is coated in
Urothelium
urothelium is
Continuous lining of the bladder, ureter and pelvis of kidneys
Why do women get more UTIs
Shorter distance from opening
Urethral divisions female
Ureteric openings, internal urethral sphincter, urogenital diaphragm, urethra
Urethral divisions made
Prostatic urethra, Urogenital diaphragm, membranous urethra, Bulbous urethra, penile/spongy urethra, navicular fossa, external urethral meatus
What does euvolemic mean
In fluid balance
What is osmolality
Solute per kg of solvent
What is osmolarity
Number of osmoles of solute per unit
A large volume of what type of plasma comes out as filtrate
Protein free
Plasma contains
Proteins, electrolytes, amino acids, glucose
Give an example of protein too large to fit through holes
Albumin- has charge which helps osmotic force
What is RBF
Renal blood flow- amount of blood that flows through glomeruli per minute Litres/minute
What is RPF
Renal plasma flow- amount of plasma in ml/minute
Renal plasma flow =
Renal blood flow x (1-Hct)
Hct= haematocrit = 40/45% usually
Average GFR
125 ml/min
FF =
(Filtration fraction)
GFR/RPF
Usually around 20%
What does FF represent
Proportion of fluid reaching the kidneys that passes into the renal tubules
Glomerular filtrate usually contains
No blood cells or platelets, virtually no proteins
Mostly organic solutes with a low molecular weight, and inorganic ions
The end product of filtration is identical to
Plasma without the large proteins and cells
What do podocytes help with
Forming a barrier as negatively charged - closely associated with capillary membrane. In Bowman’s capsule epithelium
What is proteinuria
Negative charge on filtration barrier lost so proteins more readily filtered hence in urine
The amount of filtrate is determined by the product of
The average filtration of each nephron in each kidney
A decrease in GFR means
Kidney function has worsened- less nephrons or lower GFR within nephrons
When kidney function declines slowly, what process may happen
Individual nephrons may hypertrophy, so actual kidney function may not fall significantly until kidney damage has occured
What is the issue with GFR
Can’t measure actual GFR so need surrogate marker- renal clearance
What is C
Clearance- volume of plasma that is cleared of a substance in a unit time
Clearance of y =
Urine conc of y
x
urine flow rate
/
plasma conc of y
When is renal clearance not accurate
If substance does not stay with filtrate and is altered by kidney (reabsorbed, secreted, synthesised or metabolised)
Why is clearance an imaginary concept
Describes a volume of plasma completely cleared of solute
Formula for filtration rate
Plasma conc x urine flow rate
Formula for excretion ate
Urine conc x flow rate
How does being a baby affect GFR
Premature and LBW infants often have lower nephron numbers
Fetal excretion predominantly via placenta
Normal GFR by 18 months
Nephron development is finished by
35th-36th week of fetal development
GFR starts declining when, features
30 years old, 6-7ml/min per decade, loss of functioning nephrons, some compensatory hypertrophy
Pregnancy and GFR
GFR increases by about 50%, 130-180ml per minute
Kidney size increases by about 1cm (increased fluid volume vascular and interstitial)
Nephron number same
Back to pre pregnancy levels 6 months postpartum
If used to measure kidney clearance a substance should
Be produced at constant rate, be freely filtered across glomerulus, not be reabsorbed in nephron and not be secreted into nephron
Inulin is a
Plant polysaccharide, ingested, freely filtered, not reabsorbed and not secreted
Why dont we use inulin
Required continuous IV to maintain steady state, required catheter and timed urine collections
What do we use to measure clearance hence GFR
51 Cr-EDTA
Why uses 51 Cr-EDTA
Radioactive labelled marker
Cleared exclusively by renal filtration
Timed injection with blood samples taken 2,3,4 hours after
Approx 10% lower clearance than insulin
When is 51 Cr-EDTA used clinically
In children, where indication of renal function required e.g. transplant or donation
What is creatinine
Endogenous, end product of muscle breakdown
Creatinine is measured by
Urine creatinine over 24 hours, serum creatinine
Disadvantages of measuring creatinine
Cumbersome- carrying bottle of urine, frequently inaccurate
Over estimated GFR by 10-20% due to creatinine secretion (more with more severe renal impairment)
When is measuring creatinine used
In pregnancy
Things that affect creatinine levels in an individual
Intake, muscle mass, renal filtration, renal secretion, renal secretion
Renal secretion makes up proportionately more of total renal excretion as
GFR declines
Things which increase serum creatinine
Large muscle bulk, young, male, creatine supplements, high intake of meat, certain drugs e.GFR. Trimethoprim
Things which reduce serum creatinine
Reduced muscle mass, old, female, vegetarian
What is eGFR
Estimated GFR
Problems with eGFR
Inaccurate in mild kidney disease,
Why is eGFR not reliable in mild kidney disease
reduction in GFR causes increase in blood flow
Reduced nephron number leads to hypertrophy so no change in GFR
Reduced filtration of creatinine due to reduced GFR results in increased serum creatinine and increased secretion into the tubule
How long is urethra in male vs female
Female 4cm, male 15-20cm
What is the area of the bladder compromising of steric openings and internal urethral meatus
Trigone
Which urethral sphincter is under voluntary control
External urethral sphincter
Segmental artery splits to become the
Interlobar artery
Kidneys generally located between
T12-L3
Ureter is narrowest at the
Vesicoureteral junction, the point where it enters bladder
Which arteriole has reduced volume with age
Efferent
Which fluid can escape during collecting duct injury
Urine
