Applied Renal Physiology Flashcards
Why is renal physiology important
Kidneys interact with other organs to maintain homeostasis- heart, lungs, liver. Drug pharmacodynamics and pharmacokinetics depend upon renal mechanisms
What are the kidneys for
Fluid and osmotic balance, excretion of waste products, blood manufacture (EPO), acid/ base metabolism, blood pressure, electrolyte metabolism, gluconeogenesis
Where does metabolism of vitamin D occur
In the kidneys, this is essential for bones
How much of the total body is water
~60%
How much of the body’s water is made up of extracellular fluids
1/3 which is exchanged across capillary all, plasma, interstitial composition, kidneys maintain ECF
How much of the body’s water is made up of intracellular fluids
2/3, individual mixture but equivalent
What is glomerular filtration rate
The volume of fluid filtered by the glomerular capillaries per unit time
What is glomerular filtration rate (GFR) determined by
Hydrostatic pressure, oncotic pressure and properties of the barrier
What is oncotic pressure determined by
Osmotic relative substances (proteins)
What is net filtration rate
Glomerular hydrostatic pressure (60 mmHg)- Bowman’s capsule pressire (18 mmHg)- glomerular oncotic pressure (32 mmHg)
What is Kf determined by
Hydraulic properties and surface area
What does GFR equal
GFR= Kf x net filtration pressure
What is estimation of GFR used to assess
Degree of kidney impairment and follow the disease
How is diagnosis achieved
By analysis of urine, measuring protein excretion rate, radiological studies and/or renal biopsy
What do GFR quantitate
Effectiveness of renal excretion
What does normal GFR value depend on
Age, gender and body size
What is GFR for men
Approx 130ml/min/1.73m2
What is GFR for women
Approx 120ml/min/1.73m2
What happens to GFR as you get older
Definite decline when over 40
What is normal GFR
~100ml/min
When can GFR be obtained directly
In isolated nephrons
How can GFR be estimated
By measuring the rate of excretion of substances that are freely filtered but then are neither absorbed nor secreted by renal tubules
What should substances used to estimate GFR have no influence on
Any physiological parameter that may alter renal function such as blood pressure or blood flow
What substance can be used to estimate GFR
The plant ploysaccharide inulin which is secreted by the kidneys in direct proportion to its plasma concentration over a very wide range
What is the rate at which a substance is excreted
Its concentration in urine (Uinulin) multiplied by the amount of urine produced per minute (V)
What does rate of excretion equal
Uinulin x V mg/min-1
For a substance not reasborbed or secreted by the renal tubules what must the rate of excretion by the same as
The plasma concentration (Pinulin) multiplied by the rate at which is it filtered
What does rate of filtration equal
Pinulin x GFR mg/ml-1
Therefore what does GFR equal when estimating GFR
GFR = Uinulin x V / Pinluin ml/min
What is the GFR measured rate of inulin excretion called
The inulin clearance
What is inulin clearance
Generally about 120-130 ml/min-1 for adult men and about 10% less for women of a similar body size
Why is the use of inulin not very convenient for clinical purposes
A steady concentration needs to be maintained in the plasma for measurement and you need to accurately measure flow rate of urine coming out meaning that a person has to be cathaterised
What is creatine derived from
Skeletal muscle
Describe the activity of creatine in the kidney
Freely filtered at the glomerulus, not reabsorbed or metabolised, some secretion in the proximal tubule
When is plasma creatinine constant
If GFR, diet and muscle mass are all constant
What can creatine be used for
It can be measured in the blood and is related to renal function. It is released at a constant rate so value today and tomorrow should be the same
If GFR is less than 60-90 what are you likely to miss
The fact that someone has chronic kidney disease as creatinine is relatively unchanged
In which stage of chronic kidney disease may you over interpret small changes in creatinine
Stage 5
How can you improve on creatinine
By encorporating demographic changes
What do you used in Wales to incorporate demographic changes and what does it include
MDRD. Includes 4 variables- age, gender, creatine and ethnicity
What happens to creatinine as you get older
There is muscle mass atrophy therefore a decrease in creatine production
Why do women have a lower creatine productionq
They have a lower muscle mass
Why is ethnicity important in relation to creatinine
Afro-Caribbean people have a different body muscle ratio
What is eGFR
Estimated GFR
Where does the MDRD formula come from
A population of patients in the USA that had renal kidney impairment
Describe the performance of the MDRD eCFR vs GFR graph
Performs well in the mid-range of GFR but less well as higher GFR levels. At the top of the graph the scatter of data is much greater meaning that your confidence that measured GFR= MDRD GFR is much less
What is pyelonephritis
A cortex infection
What is pyonephrosis
An infection in the pelvis of the kidney
What is rigors
An exaggerated response to infection and means that someone shales
What are the symptoms of a lower tract infection
Dysuria, frequency, haematuria, nocturia, suprapubic pain, urgency, foul urine
What are the symptoms of acute pyelonephritis
Fever, malaise, nausea, vomitting, abdominal pain
What are the symptoms of pyonephrosis or perinephric abscess
Rigors, loin pain, scoliosis, loin swelling, weight loss, night sweats
What is ‘honeymoon’ cystitis due to
Women first becoming sexually active
Why are you more likely to get an infection during pregnancy
Due to physiological changes that occur
What does ureteric reflux mean
That urine usually only flows in one direction
What happens if the valve between the ureter and bladder is incomplete
Urine goes back up from the bladder to the kidneys as sits as a static pool- vesico-ureteric reflux
Describe primary vesico-ureteric reflux
Incompetent ureterovesicle junction, shortening of intravsicle ureter (if ureter is shorter then reflux is more likely), spontaneous resolution with growth
Describe secondaet vesico-ureteric reflux
High pressure bladder, dysfunctional voiding or neurogenic bladder (distended= abnormal)
What can cause a functional obstruction during pregnancy
The pressure in the uterus causes pressure in the pelvis which can cause a functional obstruction in the ureter
What is acute pyelonephritis
An inflammatory process occurring within the renal parenchyma caused by bacterial infection
What does acute pyelonephritis most commonly result from
Ascending infection within the urinary tract
What is the definition of pyelonephritis
Fever (>38.5), loin pain and cystitis. Frequently associated with vomiting and dehydration. Significant and potentially life threatening infection
Why do you get vomiting in pyelonephritis
Sympathetic response to pain and fever
Describe the pain associated with pyelonephritis
Localised pain tends to be in the back but can also be in the front of the abdomen. Remember anatomical location of the kidney retroperitoneal but inflammation-peritoneal irritation
What are host factors of acute pyelonephritis
Congenital abnormalities of the tract- vesicoureteric reflux, anatomical abnormalities, dilation +/- obstruction (incomplete fusion of the kidneys). Acquired abnormalities- prostatic enlargement. Calculi (kidney stones). Haematuria- increased Fe (blood loss into urinary system)
What are the symptoms of acute pyelonephritis
High urinary luekocyte count, high bacterial count, haematuria, high systemic leukocyte count, malaise, fever, rigors, loin pain +/- nausea or vomiting
Sequelae to acute pylenephritis
Rarely leads to acute renal failure (ANT). Modern imaging techniques= small defects or scars not uncommon. Very rare for long term renal problems but co-morbidity will increase the possibility. Most patients with acute pyelonephritis get better with antibiotics, it is very rare to cause long term renal problems
How many women get a recurrent UTI within 6 months of their first UTI
27%, more common with E.Coli
What does recurrent mean
That it is a different organism
What does relapse mean
Same organism within 2 weeks of treatment
What is the marker of choice to assess GFR
Creatinine
