Unit 5 Lecture 33 Flashcards
Define glomerular filtration
portion of glomerular blood PLASMA is filtered into capsular space
Define tubular reabsorption
water and useful substances are reabsorbed into blood from tubular fluid
Define tubular secretion
certain wastes are removed from blood by secretion into tubular fluid (soon to be called URINE)
function of collecting ducts
reabsorption and secretion
Define excretion
eliminating waste from body
Formula for rate of excretion
Rate of filtration, plus rate of secretion, minus rate of reabsorption
What causes filtration to occur and what percent becomes filtrate?
blood pressure –> ~20% filtrate
What increases % filtration?
- thin membrane
- large surface area of glomerular capillaries
- high glomerular capillary blood pressure (bc SMALL SIZE OF EFFERERNT ARTERIOLE)
What are the 3 filtration barrier layers that make up the glomerular capillaries?
- fenestrations (pores)of endothelial cells
- basal lamina
- slit membrane
What do fenestrations prevent and allow from being filtered into nephron
prevents: blood cells
allows: components of blood plasma
What does the basal lamina prevent being filtered?
larger proteins
What does the slit membrane prevent being filtered?
medium sized proteins
What type of cells are found within the top of the ascending limb of loop Henle
Macula densa cells
What do the macula densa cells interact with?
juxtaglomerular cells in afferent arteriole lining
Define net filtration pressure
The pressure that allows water and small solutes to pass through the renal corpuscle
What is the largest contributor to NFP?
glomerular blood hydrostatic pressure
Define glomerular blood hydrostatic pressure
The pressure that pushes plasma filtrate from glomerular capilalries into capsular space
What changes the glomerular blood hydrostatic pressure?
afferent and efferent arterioles
Define capsular hydrostatic pressure
the MECHANICAL pressure from the glomerular capsule pushing back on the filtrate coming out of the glomerular capillaries
Define blood colloid osmotic pressure
the force caused by differences in WATER CONCENTRATION GRADIENT that pulls water from filtrate back into plasma in glomerular capillaries because nutrients/ proteins were not able to be filtered through capillaries
Formula for NFP
= GBHP - (CHP + COP)
What is the normal NFP?
10 mmHg
Define glomerular filtration rate
the amount of filtrate formed in all renal corpuscles of both kidneys / minute
What is the average GFR?
125 mL/min
What happens if GFR is too high?
useful substances are lost bc speed of fluid passage through nephron
What happens if GFR is too low?
sufficient waste products may not be removed from the body
What determines if GFR is consistent?
a consistent NFP
What is NFP reliant on?
GBHP
What determines GBHP?
Mean arterial pressure (MAP)
What is the normal range of MAP?
80-180 mmHg
What are the 3 ways that GFR is regulated?
- Autoregulation
- Neural regulation
- Hormonal regulation
What is autoregulation of GFR?
mechanisms that maintain a constant GFR despite changes in arterial blood pressure
What two things perform autoregulation of GFR?
- Myogenic mechanism
2. tubuloglomerular feedback
What happens during myogenic mechanism (fast)?
When increased blood pressure stretches efferent arteriole, smooth muscle (MYO*genic) contracts the afferent arteriole diameter to restore GFR level
What happens during tubuloglomerular feedback (slower)?
- Increased blood pressure increases BFR which causes blood to flow fast through renal tubule –> Na+ and Cl- aren’t reabsorbed (stays in urine)
- Macula densa in ascending limb of Henle detects Na+ and Cl- –> inhibits release of Nitric Oxide (vasodilator) from juxtaglomerular apparatus
- afferent arterioles constrict –> reduced GFR
What system is the neural regulation of GFR controlled by?
sympathetic nervous system
What are the blood vessels of the kidneys supplied by?
sympathetic fibers
What do the sympathetic fibers do to afferent arterioles?
vasoconstrict arterioles
What specifically is released by sympathetic postganglionic neurons that causes vasoconstriction?
NE
What does NE bind to to cause vasoconstriction?
alpha 1 adrenergic receptors
Besides from NE, what else does the SNS release and from where?
Renin from juxtaglomerular cells
What happens to renal blood vessel diameter with minimal sympathetic activity?
blood vessel diameter is maximally dilated
What regulation prevails with max dilation and minimal SNS activity
renal autoregulation
What happens to blood vessel diameter with moderate SNS stimulation?
Afferent and efferent arterioles constrict equally
What happens to GFR during moderate SNS activity and moderate constriction of arterioles?
GFR decreases slightly
What happens to blood vessel diameter with extreme SNS stimulation?
vasoconstriction of AFFERENT arterioles predominates
What happens to GFR, urine output, and blood flow to other tissues during extreme SNS activity and vasoconstriction of afferent arterioles
- GFR decreases substantially
- lowers urine output to maintain blood volume
- permits greater blood flow to other tissues (ie muscles)
What two hormones regulate GFR?
- Atrial Natriuretic Peptide (ANP)
2. Angiotensin II
Atrial Natriuretic Peptide does what to GFR?
INCREASES GFR
Angiotensin II does what to GFR?
DECEASES GFR
How does ANP get released?
Increased blood volume stretches the atria which releases ANP
How does ANP increase GFR?
It relaxes glomerular mesangial cells increasing glomerular capillary surface area –> increased GFR
How does angiotensin II get released?
it’s activated by ACE (angiotensin converting enzyme) in lungs following the release of renin from juxtaglomerular cells
How does angiotensin II decrease GFR?
it’s a vasoconstrictor that narrows both afferent and efferent arterioles reducing GFR
