S3 GFR and Filtration Flashcards

1
Q

how does blood flow from the aorta to the glomerulus and back to the aorta ?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the differences in the cortical and juxtamedullary nephrons

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

describe renal blood flow

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what happens when blood enters the glomerulus

A

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is the glomerular filtrate or ultrafiltrate

A

water and solutes that have been forced out of the glomerular capillaries as they are too big pass into bowmans space

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what are the three layers to the filtration barrier in the glomerulus

A
  1. Capillary endothelium
    - water, salts, glucose
    - filtrate moves between cells
  2. Basement membrane
    - permeable to small proteins
    - glycoproteins (-ve charge) repel protein movement
  3. Podocyte layer
    - contain filtration slits
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what substances can and cant get through the GFB

A

can - inulin (largest), Na +, K+, Cl-, H20, urea, glucose, PEG
can’t - haemoglobin, albumin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is the effect of charge on filtration and its clinical significance

A

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

why is there a higher hydrostatic pressure in the glomerulus

A

the AA is wider than the EA, so more blood can get in that can escape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how is plasma filtered and what are the forces involved ?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

why is auto-regulation of GFR needed ?

A

keeps GFR and renal blood flow (80-180 mmHG) within normal limits. Without regulation slight changes in BP would cause significant change in GFR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the myogenic mechanism ?

A

arterial smooth muscle responds to increases and decreases in vascular wall tension

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what happens if the AA constricts ?

A

limits blood entering
Pgc falls
GFR falls

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what happens if the AA dilates ?

A

more blood enters
Pgc rises
GFR rises

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What happens if the EA constricts ?

A

less blood can leave - GFR increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what happens if the EA dilates ?

A

more blood can leave - GFR decreases

17
Q

what is the clinical significance of the myogenic mechanism

A

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)

18
Q

describe what is tubular glomerular feedback

A

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

19
Q

how does the body respond to increased NaCl in the lumen

A

adenosine is released to vasodilate the EA, so decreases GFR

prostaglandins are released to vasodilate the AA so increases GFR

20
Q

how does the nervous system regulate the GFR ?

A

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

21
Q

what is the glomerulotubular balance

A

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

22
Q

how much water and sodium is absorbed in the PT,

A

PT -s- 67% water - 65%