Chapter 27 - Glomerular Filtration Flashcards
Glomerular filtrate composition
- protein-free
- devoid of cellular elements
- similar concentration of salts and organic molecules as the concs in plasma
(True/False)
Fatty acids are completely filtered in the glomerular
False
low-molecular weight substances such as calcium and fatty acids are not completely filtered in the glomerulus do to it being partially bounded to plasma proteins
Glomerular filter fluid rate is determined by:
(1) the balance of hydrostatic and colloid osmotic forces acting across the capillary membrane
(2) the capillary filtration coefficient (Kf) , the product of permeability, and filtering surface area of the capillaries
High filtration rate of the glomerulus is due to
- high glomerular hydrostatic pressure
- large capillary filtration coefficient
GFR of an average adult human
125 ml/min or 180L/day
Fraction of renal plasma flow that is filtered
0.2
20% of plasma flowing through the kidney that is filtered
Filtration fraction
filtration fraction = GFR / Renal plasma flow
3 major layers of the glomerular capillary membrane - as the filtration barrier
(Lumen)
(1) endothelium of the capillary with fenestrae
(2) basement membrane
(3) a layer of epithelial cells (podocytes) surrounding the outer surface of the capillary basement membrane
ALL LAYERS of the glomerular capillary wall provide a (1) barrier to filtration of plasma protein and
(2) a means to rapid filtration of water and most solutes in the plasma
A. Capillary endothelium
(1) fixed negative charges
(2) holes or fenestrae
B. Basement membrane
(1) strong negative electrical charges from proteoglycans
(2) collagen and proteoglycan fibrillae meshwork with large spaces
C. Epithelial cells - podocytes
(1) negative charges
(2) gaps (slit pores) along the footlike processes (pedicles)
Filterability:
(1) 100% -
(2) 75% -
(3) 0% -
(1) substance is filtered as freely as water
(2) substance is filtered only 75% as rapidly as water
(3) substance is not filtered
Pore size of glomerular membrane
8nm
Proteins excreted in urine
proteinuria or albuminuria
(True/False)
The cause of minimal change nephropathy are unclear but are partially related to an immunological response and abnormal T-cell secretion of cytokines - injuring podocytes and increasing premeability
True
GFR
GFR = (Kf) x (net filtration pressure)
Where net filtration is the sum of osmotic forces (PG - PB - πG + πB)
Osmotic forces in the glomerulus:
1.) PG
2.) PB
3.) πG
4.) πB
1.) hydrostatic pressure in the glomerulus - favors filtration (60mmHg)
2.) hydrostatic pressure in the bowman’s capsule - opposes filtration (18mmHg)
3.) colloid osmotic pressure of the glomerulus - opposes filtration (32mmHg)
4.) colloid osmotic pressure of the bowman’s capsule - favors filtration (0mmHg)
Net filtration pressure
10mmHg
Kf of the glomerulus
12.5 ml/min/mmHg of filtration pressure
400 times as high as Kf of most capilliaries
distention and dilation of the renal pelvis and calyces
hydronephrosis
Osmotic pressure of plasma in:
(1) afferent arteries
(2) glomerular capillaries
(3) efferent arteries
(1) 28 mmHg
(2) 32 mmHg
(3) 36 mmHg
Two factors that influence the glomerular capillary colloid osmotic pressure:
(1) the arterial plasma colloid osmotic pressure
(2) fraction of plasma filtered by the glomerular capillaries - filtration fraction
INCREASED GLOMERULAR CAPILLARY COLLOID OSMOTIC PRESSURE () GFR
DECREASES
INCREASED GLOMERULAR HYDROSTATIC PRESSURE () GFR
INCREASES
Primary means for physiological regulation of GFR
changes in glomerular hydrostatic pressure
Glomerular hydrostatic pressure is determined by
1.) arterial pressure
2.) afferent arteriolar resistance
3.) efferent arteriolar resistance
Donan Effect
the higher the protein concentration, the more rapidly the colloid osmotic pressure rises because of the interaction of ions bound to the plasma proteins
combined blood flow through both kidneys in a 70 kg man
1100 ml/min or about 22% of the cardiac output
percent of total body weight of 2 kidneys combined
0.4%
(True/False)
The arterial-venous extraction of oxygen in the kidneys is low but is twice the rate of the brain
True
Renal oxygen consumption varies in proportion to ()
renal tubular sodium reabsorption
Renal Blood Flow
Renal vein pressure
3 to 4 mmHg
GFR arterial pressure range
80 to 170 mmHg
(True/False)
Blood flow in renal medulla accounts for only 1% to 2% of total renal blood flow
True
Activation of sympathetic nerve fibers in the renal arteries lead to
decrease renal blood flow and GFR
Norepinephrine, epinephrine, and endothelin (1) renal blood vessels and (2) GFR
(1) constrict
(2) decrease
(True/False)
Angiotensin II preferentially constricts efferent arterioles raising glomerular hydrostatic pressure while reducing renal blood flow
True
Endothelin-Derived nitric oxide (1) renal vascular resistance and (2) GFR
(1) decreases
(2) increases
In afferent arterioles of the kidneys, (1) and (2) are released to counteract the vasoconstrictor effects of angiotensin II
(1) nitric oxide
(2) prostaglandins
Prostaglandins and Bradykinin (1) renal vascular resistance and (1) GFR
(1) decreases
(2) increases
Tubular reabsorption is () leaving 1.5L/day to be excreted in urine
178.5 L/day
The juxtaglomerular complex is composed of
(1) macula densa cells in the initial portion of the distal tubule
(2) juxtaglomerular cells in the walls of the afferent and efferent arterioles
Macula densa cells sense
sodium chloride delivery to the distal tubule
Decrease in sodium chloride concentration (detected by the macula densa) intiates
(1) decrease resistance to blood flow in the afferent arterioles - raises glomerular hydrostatic pressure
(2) INCREASES RENIN RELEASE FROM THE juxtaglomerular cells of the afferent and efferent arterioles
GFR changes by only a few percentage points, even with large fluctuations in arterial pressure between ()
75 - 160 mmHg
Myogenic mechanism
the ability of individual blood vessels to resist stretching during increased arterial pressure to prevent an excessive increase in renal blood flow and GFR
