S3 GFR and Filtration Flashcards
how does blood flow from the aorta to the glomerulus and back to the aorta ?
aorta - renla artery - segmental artery - lobular artery - arcuate artery - interlobular artery - afferent arteriole - glomerulus - efferent arteriole - peritubular capillaries (cortical) or Vasa recta ( Juxtamedullary) - interlobular vein - arcuate vein - lobular vein - segmental vein - renal vein - IVC
what are the differences in the cortical and juxtamedullary nephrons
Ratio - c - 90% J - 10%
Location - C - cortex outer J - Cortex inner
Glomerulus cortex - C - Small J - Large
Loop of Henle - C - short, next to outer cortex J - longer, goes into the inner part of the cortex, dips into medulla
Diameter of arterioles - C - AA>EA J- AA=EA
EA - C - forms peritubular capillary J - forms vasa recta
Sympathetic innervation - C - rich J - poor
describe renal blood flow
renal blood flow is 1.1 L/min
all blood flows through the glomeruli in the cortex
haemotocrit is the volume percentage of red blood cells in blood and is normally ~0.45 so renal plasma flow is RPF 0.55 X 1.1L/min = 605ml/min of plasma
what happens when blood enters the glomerulus
blood enters through Afferent A( pores wide enough for plasma, salts and small molecules, but not RBCs and large proteins) 20% of blood from renal artery if filtered at any one time and 80% of blood arriving exits via efferent arteriole (unfiltered)
what is the glomerular filtrate or ultrafiltrate
water and solutes that have been forced out of the glomerular capillaries as they are too big pass into bowmans space
what are the three layers to the filtration barrier in the glomerulus
- Capillary endothelium
- water, salts, glucose
- filtrate moves between cells - Basement membrane
- permeable to small proteins
- glycoproteins (-ve charge) repel protein movement - Podocyte layer
- contain filtration slits
what substances can and cant get through the GFB
can - inulin (largest), Na +, K+, Cl-, H20, urea, glucose, PEG
can’t - haemoglobin, albumin
what is the effect of charge on filtration and its clinical significance
neutral molecule - bigger size is likely to get through
anions - negative charge also repels, more difficult to get through
cations - positive charge allows slightly bigger molecules through
in many disease processes, the - charge on the filtration barrier is lost so that proteins are more readily filtered. the condition is called proteinuria (protein in the urine)
why is there a higher hydrostatic pressure in the glomerulus
the AA is wider than the EA, so more blood can get in that can escape
how is plasma filtered and what are the forces involved ?
Hydrostatic capillary forces (Pgc) : regulated, is greater than the oppositional forces so net movement is from the capillary into the bowmans space then into the tubule
Hydrostatic pressure in Bowman’s Capsule (Pbc) : where the ultra-filtrate collects
why is auto-regulation of GFR needed ?
keeps GFR and renal blood flow (80-180 mmHG) within normal limits. Without regulation slight changes in BP would cause significant change in GFR
what is the myogenic mechanism ?
arterial smooth muscle responds to increases and decreases in vascular wall tension
what happens if the AA constricts ?
limits blood entering
Pgc falls
GFR falls
what happens if the AA dilates ?
more blood enters
Pgc rises
GFR rises
What happens if the EA constricts ?
less blood can leave - GFR increases
what happens if the EA dilates ?
more blood can leave - GFR decreases
what is the clinical significance of the myogenic mechanism
with an increased BP, AA constricts so GFR remains unchanged and with a decreased blood pressure the AA dilates so GFR remains unchanged. thus maintains GFR within physiological limits (80-180mmHG)
describe what is tubular glomerular feedback
increase in arterial pressure increases glomerular capillary pressure so GFR increases
Increased GFR means more (Na+) and (Cl-) reaches the distal tubule
Macula densa cells in the DCT respond to changes in NaCl in the lumen. They stimulate juxtaglomerular apparatus to release chemicals depending on the NaCL conc
how does the body respond to increased NaCl in the lumen
adenosine is released to vasodilate the EA, so decreases GFR
prostaglandins are released to vasodilate the AA so increases GFR
how does the nervous system regulate the GFR ?
sympathetic nerve fibres innervate AE and EA. Normally sympathetic innervation is low (no effect on GFR). Fight or flight ischaemia can stimulate renal vessels causing vasoconstriction which conserves blood volume (haemorrhage) and can cause a fall in GFR
what is the glomerulotubular balance
whilst myogenic and TGF responses are the first way to stop GFR changes, the GTB is the second line of defence which blunts Na + excretion in response to any GFR changes
how much water and sodium is absorbed in the PT,
PT -s- 67% water - 65%
