Glomerular Filtration Flashcards
glomerular filtration creates
a plasma like filtrate of blood
glomerular filtrate description of formation
water and substances that are dissolved in blood plasma get forced out of the glomerular capillaries into Bowman’s capsule and form glomerular filtrate
composition of glomerular filtrate
consists of water, electrolytes, glucose, fatty acids, amino acids, vitamins, and nitrogenous wastes
are formed elements and proteins in the filtrate?
no, they are too big to leave the blood vessels.
how is the filtration membrane formed
endothelial cells in glomerular capillaries join podocytes to form a filtration membrane that filters water and small solutes, but not plasma proteins or formed elements
glomerular endothelial cells
have large fenestrations through which solutes pass
basement membrane
restricts passage of particles due to their size and their electronegativity
large plasma proteins
like albumins, are too big to pass through the membrane; glomerular filtrate is only 0.3% protein while blood plasma is 7% protein
pedicels
foot-like extensions from podocytes that wrap around glomerular capillaries to form filtration slits that can block passage of negative ions
kidney infection or kidney trauma
can damage the filtration membrane and allow plasma proteins and/or formed elements to enter the filtrate causing proteinuria and hematuria
what principles does glomerular filtration follow
the same principals that govern capillary bulk flow, but glomerular filtration involves much more fluid
glomerular capillaries
long and provide large surface area for filtration
filtration membrane
thin and porous
blood pressure in glomerular capillaries
is high
glomerular blood hydrostatic pressure
GBHP- the main force responsible for moving water and solutes out of blood plasma through the filtration membrane
capsular hydrostatic pressure
CHP- opposes additional filtration because there is a high rate of filtration and because fluid is already present in the renal tubule
blood colloid osmotic pressure
BCOP- also opposes filtration because of the plasma proteins that are present in blood plasma
net filtration pressure promotes
filtration out of the glomerular capillaries
NFP=
GBHP - (CHP + BCOP)
glomerular filtration rate
GFR- refers to the amount of filtrate that is formed per minute in all of the renal corpuscles of both kidneys
GFR for males
125 mL/min; which produces 180L of filtrate per day
GFR for females
105 mL/min; which produces 150L of filtrate per day
GFR relationship to NFP
GFR is directly proportional to NFP, so changes in GBHP, CHP, or BCOP will affect GFR
if the GFR is too high
filtrate will flow through the renal tubules too quickly for them to reabsorb water and solutes
urinary output (if GFR is too high)
rises and creates a risk for becoming dehydrated
if the GFR is too low
filtrate will flow through the renal tubules too slowly and wastes will get reabsorbed
risk of GFR being too low
creates a risk for developing azotemia
renal autoregulation
the ability of the kidneys to maintain constant renal blood flow and glomerular filtration despite changes in arterial blood pressure
myogenic mechanism
occurs when arterial blood pressure changes, which affects smooth muscle cells in walls of afferent arterioles
when blood pressure rises
smooth muscle fibers contract and constrict afferent arteriole, which decreases blood flow into glomerulus to reduce GFR
when blood pressure drops
smooth muscle fibers relax and dilate afferent arteriole, which increases blood flow into glomerulus to raise GFR
tubuloglomerular feedback involves the
juxtaglomerular apparatus
when GFR is elevated
filtrate flows through renal tubule too fast to reabsorb enough NaCl
macula densa cells
release vasoconstrictor that reduces flow of blood from afferent arteriole into glomerulus to reduce GFR
when GFR falls
flow of blood from afferent arteriole into glomerulus is increased
autoregulation and changes in GFR
autoregulation does not completely block changes in GFR, but it allows for fluctuations within narrow limits
autoregulation and variations in blood pressure
autoregulation cannot compensate for extreme variations in blood pressure but it will prevent large changes in water and solute excretion
neural regulation
uses sympathetic nerve fibers to send signals to afferent arterioles that constrict them and decrease the flow of blood into the glomerular capillaries in order to reduce GFR and maintain systemic blood pressure
the renin-angiotensin mechanism
is activated by a drop in blood pressure
juxtaglomerular cells
secrete renin (an enzyme), which triggers conversion of angiotensinogen to angiotensin II
angiotensin II constricts
both afferent and efferent arterioles to reduce GFR
angiotensin II stimulates adrenal cortex to
secrete aldosterone to promote water retention and sodium retention
angiotensin II stimulates pituitary gland to
secrete ADH to increase water absorption
