Block 1 - kidneys Flashcards
(31 cards)
Define filtration fraction
The % of total plasma volume that filters into the tubule
How much cardiac output do the kidneys receive?
20%
Define GFR and what is it determined by?
Is the volume of filtrate formed by all the nephrons in both kidneys per unit time.
Determined by glomerular capillary filtration coefficient (Kf) and net filtration pressure (NFP)
GFR= Kf x NFP
What does Kf reflect?
- surface area of the glomerular capillaries available for filtration
- hydraulic conductivity (permeability) of the filtration barrier)
What is the net filtration pressure?
Is given by the sum of the pressures acting across the filtration barrier. Sum of the hydrostatic and colloid osmotic pressures
What is a typical NFP
10mmHg
Effect of afferent arteriole dilation and efferent arteriole constriction on GFR?
Increases GFR
Effect of afferent arteriole constriction and efferent arteriole dilation on GFR?
Reduces GFR
Effect of angiotensin-2 on glomerular hydrostatic pressure & GFR?
Preferentially constricts efferent arteriole, therefore increasing pressure & increasing GFR
Effect of prostaglandin & atrial natiuretic peptide on glomerular hydrostatic pressure & GFR?
Vasodilator afferent arteriole, therefore increasing hydrostatic pressure & increasing GFR
Effect of noradrenaline, adenosine & endothelium on glomerular hydrostatic pressure & & GFR?
Tend to vasoconstrict afferent arteriole therefore reducing hydrostatic pressure & reducing GFR
What systemic blood pressure is GFR & renal blood flow relatively constant over?
About 80 to 180mmHg
What is myogenic autoregulation?
Is the inherent ability of smooth muscle in afferent arteriole to respond to changes in vessel circumference by contracting or relaxing. Helps to keep GFR constant & protect filtration barrier damage from high blood pressures.
Describe the process of myogenic autoregulation
- increase in arterial blood pressure
- increased renal blood flow & GFR
- increased stretch of afferent arteriole smooth muscle cells
- muscle cells depolarise
- opens calcium ion channels
- reflex contraction of AA vascular smooth muscle
- vasoconstriction of AA
- increase resistance to flow, prevents changes in renal blood flow & GFR
Where are macula densa cells located & what do they do?
Located in early part of distal tubule.
Sense [NaCl], involved in tubuloglomerular feedback
Describe the process of tubuloglomerular feedback
- increase in arterial pressure, renal blood flow & GFR
- increased [NaCl] delivered to macula densa cells
- release of paracrine factors e.g. Adenosine
- constriction of AA smooth muscle so vasoconstriction of AA
- increased resistance to flow, restores GFR
Signs & symptoms of Hypovalaemia (dehydrated)
Symptoms: thirst, dizziness on standing, confusion
Signs: low JVP, postural hypotension, weight loss, dry mucous membrane, reduced skin turgor, reduced urine output
Signs and symptoms of hypervolaemia (fluid overload)
Symptoms: ankle swelling, breathlessness
Signs:raised JVP, oedema, weight gain, hypertension
What is osmolality?
The concentration of a solution expressed as the total number of solute particles per litre.
Osmoles excreted/day = urine osmolality (Osm/L) x urine output (L/day)
What the minimum, maximum & normal urine production volumes per day?
Minimum:500ml
Maximum: 20000ml
Normal:1500ml
How much waste solutes are excreted in the urine each day?
On average 600mOsm
Define obligatory urine volume
Is the minimum volume of urine that needs to be produced each day to excrete waste solutes
What are the causes of polyuria?
Increased water excretion due to excessive water ingestion or inability to concentrate urine (tubular damage, diabetes insipid us)
Increased solute excretion due to diuretics or glycosuria (diabetes mellitus)
What are the causes of oliguria?
Decreased water/solute excretion due to dehydration/low extracellular volume or poor renal perfusion
