Lecture 17: Renal Physiology Flashcards
if RBF is too low, the afferent arteriole:
relaxes
if RBF is too high, the afferent arteriole:
constricts
this vessel is primarily responsible for autoregulation of renal blood flow
afferent arteriole
this vessel is primarily responsible for fine-tuning GFR
efferent arteriole
what effect does increasing afferent arteriole resistance have on glomerular pressure?
decreased glomerular pressure
what effect does decreasing glomerular presure have on GFR?
decreased GFR
what effect does increasing afferent arteriole resistance have on renal blood flow?
decreased renal blood flow
what effect does decreased renal blood flow have on GFR?
decreased GFR
what effect does increasing efferent arteriole resistance have on glomerular pressure?
increasing glomerular pressure
what effect does increasing glomerular pressure have on GFR?
increased GFR
what effect does increasing efferent arteriole resistance have on renal blood flow?
decreased renal blood flow
what effect does increased glomerular pressure have on GFR?
increased GFR
what would cause a decreased renal blood flow?
- increased afferent arteriole resistance
- increased efferent arteriole resistance
what effect would dilation of the afferent arteriole have on GFR?
dilation of afferent > increased glomerular pressure > increased GFR
what effect would dilation of the efferent arteriole have on GFR?
dilation of efferent arteriole > decreased glomerular pressure > decreased GFR
what might cause impediment of arterial dilation?
- being sick/critically ill
- chronic hypertension
- uncontrolled diabetes
GFR autoregulation is dependent on
renal blood flow autoregulation
GFR is better regulated at higher or lower blood pressures?
higher; at pressures of 50 mmHg or lower, GFR has a steeper decline than when BP is closer to 150 mmHg or higher (a more shallow, flatter slope)
GFR autoregulation at high pressures prevents the kidneys from:
spilling massive amounts of fluid into the urine
the normal UOP rate
1 ml/min
as MAP increases, UOP:
increases
as MAP decreases, UOP:
decreases
in terms of autoregulation:
with an initial rise in BP, then we’ll have an increase in RBF, then GFR is increased, UOP ____ and, therefore, blood pressure will _____
- increases
- decrease
in terms of autoregulation:
with an initial decrease in BP, then we’ll have a decrease in RBF, then GFR is decreased, UOP ____ and, therefore, blood pressure will _____
- decreases
- increase
filtration only:
some substances are completely reabsorbed
filtration with partial reabsorption:
some substances are partially reabsorbed
ex) Na+
excessive Na+ in our diet gets partially reabsorbed
filtration with complete reabsorption:
some substances are filtered and secreted
ex) glucose (in a NON-DM patient)
normally, ALL of the glucose gets COMPLETELY reabsorbed in the PCT
filtration with secretion
some substances are filtered and secreted
ex) paramino hippuric acid (PAH)
in filtration with secretion, how much substance gets filtered and how much gets secreted?
- 1/5 gets filtered
- 4/5 gets secreted
what is PAH and why is it used?
paramino hippuric acid
it is used as a diagnostic compound to measure renal blood flow by observing how much of the compound is cleared by the kidneys
the more PAH that is cleared by the kidneys, the higher the RBF is
the less PAH that is cleared by the kidneys, the lower the RBF is
what is the normal reabsorption rate?
124 ml/min
urinary excretion = ?
filtration - reabsorption + secretion
NFP = ?
Pcap - Pisf - Picap + Piisf
what is the innermost layer of the glomerular capillaries?
endothelium
these are MORE permeable than generic capillaries
the porous openings in the glomerular capillary endothelium
fenestrations
the layer superficial to glomerular endothelium capillaries
basement membrane
what is the purpose of the epithelium in glomerular capillaries?
houses podocytes which provide structural support; the capillary beds resist a lot of increased pressure and the podocytes provides structural support to prevent glomerular swelling
the podocytes have foot processes that have openings called:
split pores
the glomerular capillaries have a (positive/negative) charge within membrane
negative
what is the benefit to having negative charges scattered within the glomerular capillary?
to repel negatively charged proteins
describe the role of renal podocytes
- to provide structural support to the glomerular capillaries
- to prevent glomerular swelling (with structural support) d/t high BP
- to regulate surface area of glomerular capillaries
what is dextran?
a synthetic sugar that is modifiable in compound size
polycationic dextran is (more/less) filterable
more filterable
polyanionic dextran is (more/less) filterable
less
the larger a compound is, the _____ filterable it is
less
what is inulin?
a synthetic compound used to accurate way to estimate GFR (similar to creatinine clearance)
a filterability of 1.0 =
high filterability
i.e. H2O
a filterability of .005 =
a low filterability
i.e. albumin
roles of the kidney include (9)
- LT BP regulation
- LT pH regulation
- LT [RBC] regulation
- LT [electrolyte] regulation
- LT vitamin D regulation
- LT serum glucose regulation
- drug clearance
- LT metabolic waste disposal
- osmolarity regulation
all these roles are accomplished with a normal GFR
chronic HTN is a ____ issue
kidney
how does the kidney regulate pH levels?
- the kidneys produce HCO3-
- the kidneys control how much HCO3- gets reabsorbed
- the kidney can get rid of excess protons (H+)
what is the short-term pH regulator of the body?
the lungs - can blow off excess CO2 (but not H+ directly)
how does the kidney regulate [RBC] levels?
- O2 sensors deep in medullary portions of kidney
- low O2 levels > stimulates bone marrow > to produce erythryopoietin (epo) > increase more RBCs
- RBCs will travel to wherever O2 is needed and transport O2 there
how does the kidney regulate vitamin D levels?
- the kidney activates vitamin D
- activated vitamin D helps the kidney reabsorb Ca2+
the more glucose that is filtered, the ____ that is reabsorbed
more
if serum glucose is past transport max of the kidney, what happens to the glucose?
in extreme hyperglycmia, glucose gets lost/”skimmed off” via excretion in the urine
drug clearance occurs mostly in the:
liver
some clearance occurs via the kidney
how does the kidney regulate osmolarity?
- the kidney is able to differentiate water from NaCl, so it can selectively reabsorb water
- the kidney can also get rid of excess NaCl
- this process is regulated by ADH and osmoreceptors in the BRAIN
delineate the circulation flow from renal artery to renal vein
- renal artery
- segmental arteries
- interlobar arteries
- arcuate arteries
- interlobular arteries
- aferrent arteriole
- glomerular capillaries
- efferent arteriole
- peritubular capillaries
- arcuate veins
- interlobar veins
- segmental veins
- renal vein
which structures make up a nephron?
- afferent arterioles
- glomerular capillaries
- efferent arterioles
- peritubular capillaries
PLUS tubular network:
* PCT
* DCT
* Loop of Henle
* cortical collecting tubule
* collecting duct
each KIDNEY has how many nephrons at birth?
1 million
at birth how many nephrons do we have?
2 million
at what age do we start to lose nephrons (d/t “wear & tear”)
40 yrs old
superficial nephrons AKA
cortical nephrons
deep nephrons AKA
inner medullary nephrons
what percentage of our nephrons are cortical?
90-95%
what percentage of our nephrons are inner medullary?
5-10%
there are fewer peritubular capillaries in the (outer medulla/inner medulla)?
inner medulla
the outer medulla’s peritubular capillaries reabsorb compunds from:
the cortical nephrons
between ascending & descending blood vessels in the inner medulla, there are more of the:
ascending blood vessels
why are there more ascending blood vessels in the inner medulla?
there are more split points in the ascending blood vessels
why is it important to have “split points” in the ascending blood vessels in the inner medulla?
- more split points will cause a decreased blood flow velocity in the ascending blood vessels
- this is important to maintain solute concentration in the interstitium of the inner medulla
- decreased blood flow velocity in the ascending blood vessels prevents “wash out” of solutes
concentrated solutes in the renal interstitium is beneficial for the process of
reabsorption
accomplished with the help of decreased blood flow velocity in ascending blood vessels
deep/inner medullary peritubular capillaries AKA
vasa recta capillaries
which type of nephron is more sensitive to low perfusion in terms of oxygen delivery?
- deep medullary nephrons d/t there only being 5-10% of this type of nephron vs cortical nephrons
- there is a limited supply of peritubular capillaries located in the deep medulla
PT capillaries play a large role in reabsorption AND O2 delivery
kidneys lie underneath the
diaphragm
renal artery and vein lie deep to the
mesenteric arteries
which arteries supply blood to the intestines?
mesenteric arteries
how many adrenal glands do we have?
2
1 adrenal gland lies on top of each kidney
how many ureters do we have?
2
suprarenal glands AKA:
adrenal gland
supra = above; above renal
this kidney comes into contact with the liver
RIGHT kidney
the liver is on the right side
this kidney comes into contact with the stomach, spleen, and the pancreas
LEFT kidney
which kidney comes into contact with the colon?
both
relate renal surface anatomy to cancer
- kidney cancer is RARE
- surface area contact with other organs is important in terms of cancer spreading to the kidney (i.e. pancreatic cancer will spread to the middle of the LEFT kidney)
why is renal cancer rare?
- the kidneys do not produce new nephrons
- since there is no cell proliferation, the risk of renal cancer is rare
heart CA is also rare
which quadranst of the abdomen do the kidneys lie?
RUQ - R kidney
LUQ - L kidney
kidney stones exhibit this type of pain
referred pain in the lower back
the urethra is shorter in:
females
the pudendal nerve originates from these spinal nerves
S2, S3, & S4
S 2-3-4 keeps things off the floor
pudendal nerve functions (3)
- bladder emptying
- fecal waste emptying
- boners
prostate gland removal increases risk for:
- erectile dysfunction
- incontinence
corpuscle AKA:
bowman’s capsule
which part of the Loop of Henle is thick? thin?
TAL - thick ascending limb
DTL/ATL - descending thin limb AND ascending thin limb
the macula densa lies in:
TAL (thick ascending limb)
what do the macula densa cells do?
- “speedometer” of the blood flow/filtration rate
- if low flow is sensed, communicates with juxtaglomerular cells
what do the juxtaglomerular cells do?
- releases renin that release AT-II to preferentially relax/constrict the efferent arteriole
renin > angiotensinogen > AT I > ACE > AT II > efferent arteriole
if low flow is sensed by MD cells, what happens?
- JG cells release RENIN
- renin releases AT II to **preferentially **constrict EA
- constricted EA > decreased RBF > occludes outflow from GCs
- GCs hydrostatic pressure increases
- increased GC pressure > increased filtration rate
if high flow is sensed by MD cells, what happens?
- JG cells restrict RENIN release
- EA dilates > increases RBF
- GCs hydrostatic pressure decreases
- decreased GC pressure > decreased filtration rate
clearance rate =
equation
Cx = V̇ x Ux/Px
ml/min
GFR =
equation
GFR = Uinulin x V̇/Pinulin
RBF =
amount
1100 ml/min
~ 22% of CO
RPF =
equation for renal plasma flow
RPF = (1-Hct) x RBF
RPF = 0.60 x 1100 ml/min
ml/min
1-0.40 (Hct) = plasma volume (0.60)
excretion rate
equation
= Ux x V̇
mg/min, mmol/min, mEq/min
ERPF (effective renal plasma flow) =
equation
EPRF = CPAH = UPAH x V̇/PPAH
ml/min
reabsorption rate =
equation
= filtered load - excretion rate
= (GFR x Px) - (U x V̇)
mg/min, mmol/min, or mEq/min
