renal filtration Flashcards
each nephron is independent until ___
each nephron is independent until cortical collecting tubule where multiple nehrons merge
riltration occurs in the ______ ________ the nthe rest of the nephron selectively _____ & ________ solutes
filtration occurs in the renal corpuscle then the rest of the nephron selectively reabsorbs and secretes solutes
Describe the nephrons
- nephron types
- cortical nephrons
- glomeruli in the outer cortex
- short loops of henle, descending into the outer medulla
- 90%
- juxtamedullary nephrons
- glomeruli nearthe corticomedullary border
- larger and longer loops of henle, descinding into the inner medulla and papilla.
- higher GFR
- 10%
- cortical nephrons
list the segments of the nephron, in oreder, in abbrevated form
- PCT
- PST
- tDLH
- tALH
- TAL
- DCT
- CNT
- ICT
- CCT
- OMCD
- IMCD
- duct of Belini
besure to designate cortical from juxtamedullary
What % of the systemic blood flows into the kidneys?
how does blood pressure affect the renal system?
25%
hypetension due to renal artery stenosis is not infrequent
what are the parts of the capillary bed to the nephrons?
They are nephron specific
- cortical nephrons
- first capillary bed
- glomerular capillaries
- second capillary bed
- peritubular capillaries (absorbs solutes and water)
- first capillary bed
- juxtamedullary nephrons
- first capillary bed
- glomerular capillaries
- second capillary bed - two sections
- first = peritubular capillries( absorbs solutes)
- second = vasa recta (osmotic exchangers)
- first capillary bed
four functions of the nephrons
- filtering
- plasma is filtered in corpuscle
- this is moderatly selective process
- the filtered fluid id called the ultra filtrate
- reabsorption
- solute and water can be taken back up from tubule to blood tream along the entire length of the tubule from PCT to CCD
- secrete
- additional molecules can be selectively secreted into the tubule in the PCT, DCT, and CCD
- excrete
- what remain in the tubule after the CCD and enters the renal pelvic travels to the bladder and is excreted from the body as urine
define
- glomerulus
- tubule
- bowmans capsule
- glomerulus = capillary bed
- tubule = blind ended nephron lumen
- bowmans or glomerular capsule = capsule surrounding bowmans space and glomerulus
space between capsule and glomerulus
bowmans space
what defines the following structures: glomerulus, bowmans space and bowmans capsule?
renal corpuscle
where does filtration occur in the kidney?
filtration occurs only in the renal corpuscle
describe the contents of the glomerular capillaries
the glomerular capillaries have three layers
- fenestrated endothelium
- basal lamina
- podocytes and their foot proccesses
- proteins interlink podocytes feet
describe the filtration barriers and function/mechanism in the glomerular capirllaries
- fenestrated capilaries- size and charge
- endotherlium are small enough to exclude blood cells from leaving capillary.
- negative charge
- on the pore surfaces repel negatively charged plasma
- basal lamina - charge
- consists of negatively charged glycoproteins further limiting negatively charged plasma proteins
- podocytes foor processes
- form narrow filtration slits that contain negtively charged proteins which further limits negatively charged large substances from entering filtrate
What is the diameter of the most common protein in the blood? what about the glomerular membran? What is the result?
- albumin - most common protein in the blood
- 6nm
- negatively charged
- glomerular membran pore
- 8nm
- negatively charged
- result
- electrostatic repulsion exerted by negative chareges of the glomerular capillary wall proteoglycans
- any albumin that is filtered is re-absorbed by PT
- making measurment of albumin in urine a good indicator of health.
what do the following mean?
- nephropathy
- nephrosis
- nephritis
- nephropathy
- general term for renal diseases
- nephrosis
- non-inflammatory disease (diabetes)
- nephritis
- inflammatory disease (lupus)
what are the freely filtered compound?
compounds that are not hindered by the filtration filters 9capillaries, basal lamina, podocytes
- Na+
- K+
- Cl-
- Urea
- Glucose/sucrose
describe the composition of the glomerular filtrate
- isoosmotic
- nearly protein-free
- devoid of cellular elements
- most salts and organic molecules similar to plasma
normal ultrafiltrate is ______ and contains
normal ultrafiltrate is isoosmotic ( same as the blood)
- isoosmotic
- little proteins
- no cells salts
- small organic molecules in the same concentration as the plasma
limits size and charge of molecules moving into bowmans space
filtration barrier in the glomerular capillary
- endothelial fenetratsion
- basal lamina
- podocytes with foot processes
describe the amount of fluid filtered by the nephrons daily. Explain the equation governeing this process
glomerular filtration rate averages 180 L/day
- starlings equation govern GFR
- sum of hyodrostatic and oncotic forces across the glomerulu, whic gives the net filtration pressure
- glomerular capillary reflection coefficient = product of the permeability and filtering surface area of the capillaries
- Puf =Kf[(Pgc-Pbs)-(Ogc-Obs)]
diagram the pressure along the capillary network
- normally
- pressure in the glomerular capillaries and bowmans capsule do not change over the length of glomerulus.
- difference from the rest of the circulatory system
- pressure in the glomerular capillaries and bowmans capsule do not change over the length of glomerulus.
- oncotic pressure increases with distance due to concentration of protein in plasma
- unlike other capillaries, the kidny fluid movement into Bowmans space is favored along the entire distance of the capillary
what is different about the movement of fluid in the kidey compared to other capillaries?
- unlike other capillaries, the kidny fluid movement into Bowmans space is favored along the entire distance of the capillary
what promotes filtration in the glomerular capillaries? What apposes filtration?
use the GFR comonents to explain
promottion
- of all the differences hydrostatic pressure (Pgc) inside the glomerular capillaries promotes filtration
- colloid osmotic pressure of the proteins in bowmans capsule (Obs), promote filtration
opposition
- hydrostatic pressure in Bowman’s capsule (Pbs) outside the capillaries which opposes filtration
- unlike typical intersitial fluid, capsule is a close sttructture and thus exerts significant pressure
- oncotic osmotic pressure of the glomerular capillary plasma proteins opposes filtration
*
what acells type contributes to the adjustment in the glomerular filtration (before the filter)?
mesangial cells
- smooth muscle in origin
- contract in response to angiotensin 2
- funtion - reduction of the capillary surface area
- this adjusts the constant in the GFR formula (Kf)
how doe the mesangial cells adjust the GFR?
reduction of the Kf constant,
What starts at 40 yrs old
aging and GFR changes
- hylinization of afferent arterioles
- development of aglomerular arterioles
- development of sclerotic glomeruli
list the stages and % compliance of filtration involved with the kidneys
- normalGFR =90% and above
- stage 2 =mild loss, 60-89%
- stage 3a = mild to moderate, 45-59%
- stage 3b = moderate to severe loss, 30-44%
- stage 4, severe, 15-29%
- stage 5, kidney failure 0-15%
explain the law of mass balanse with regard to the filtration of plasma
(total amout of substance)(in the body) = intake + production - excretion - metabolism
- for any substance tha is neither synthesized or metabolized in the kidney, the amount that enters the kidneys is equal to the amount that leaves the kidneys in the urine plus the amount that leaves the kidneys in the renal venous blood
explain the clearance of the substances in the plasma
clearance has dimension of volume/time and it represents the volume of plasma from which all the substance has been removed and excreted into urine per unit time
what is the criteria of a substance for measuring GFR?
- substance must be frewwly filterable in the glomeruli
- substance must be neither reabosrbed nor secreted by the renal tubules
- substance must not be synthesized, borkwn down, or accumulated by the kidney
- substance must be physiologically inert (not toxic and without effect on renal function)
describe the process of measuring GFR
the measure GFR, we need a substance that will be filtered by the kidney. By comparing the amount entering with that excreted, we can detemrmine GFR.
criteria
- substance must be freely filterable in the glomeruli
- substance must be neither reabdorbed nor secreted by the renal tubules
- substance must not be synthesized, borkwn down, or accumulated by the kidney.
- Substance must be physiologically inert (not toxic and with effect on renal function)
explain the production and excretion of creatinine
endogenous substance
- product of muscle creatine phosphate metabolism
- backup energy source in muscle is phosphocreatinine
- when the energy is needed, creatine kinase transfers the phosphate group to form phosphcreatine ADP and creatinine.
- the creatinine is secreted into the plasma
- produced at a steady rate in the body
- rate of urinary creatinine ecretion equals rate of metabolism production
- it is freely filtered
- it is not metabolized in the kidney
- its not absorbed in the kidbey
estimate of FGR in humans
easy, noninvasive and reliable
rate of creatinine secretion into plasma per sex. what is normal?
what can affect the creatinine levels and ultimatly reading?
- male
- 20-25 mg/kg body weigt/day
- female
- 15-20mg/kg body weight/day
normal [creatinine] = ~1mg/dL
- caveats
- meat has high creatinine levels so the have steady state urine collectin is done over 24 hr fast and blood drawn after overnight fasting
- exercise can alter creatinine levels
- non-steady state production due to pathologies
- altered by muscle wasting
- 10% secretion by tubules -> overestimated balanced by measurment underestimate2
compare the measurment of creatinine in the plasma and urine vs just plasma
- most accurate GFR
- creatinine measurment in plasma and urine
- simpler
- plasma alone
- after a 24 hr fast
if GFR increase/ decreases what happens to the plasma creatinine?
if GFR decreases than plasma creatinine increases
if GFR increases thatn plasma creatinine decreases
what is the normal GFR?
normal GFR = 125ml/min
what does a high creatine blood work up mean for the GFR? Low creatinine blood work up?
high creatinine blood workup = low GFR
low creatinine blood workup = high GFR
what asseses the GFR?
measurement of GFR is obtained by assessing creatinine clearance
define and explain the following. what are the normal values of each
- GFR
- RPF
- RBF
- FF
- GFR
- glomerular filtration rate
- the total volume of plasma actually filtered through the glomerulus per unit of time
-
normal value =
- male:125ml/min/1.73m^2
- female:110
- RPF
- the total volume of plasma (not blood), passing throug hthe kidney per unit of time
- this includes both the portion of plasma which is filtered and athe portion which is not filtered
- normal ~600ml/min or 864L/day
- the total volume of plasma (not blood), passing throug hthe kidney per unit of time
- RBF
- ~25% of cardiac output goes to kidneys
- highest blood flow per gram of organ weight in the bodyd at 1L/min/g
- FF = filtration volume, GFR/RPF)
- 0.20
explain the measurement of RBF/RPF
drugs can be used to infuse and then measured in urine.
RBF/RPF
which structure in the kidney plays an important role in concentrating the urine?
the blood supplied to the vasa recta plays an important role in concentrating urine.
which section receives the most blood flow?
renal cortex receives most of the kidney’s blood flow
what is the role of the peritubular and vasa recata capillaries
explain the flow through the peritubular capillary with the following values
- Ppc=20
- Po=10
- Opc=35
- Oo = 8
- O= oncotin, o=interstitial
- role
- reabsorption and delivery of oxygen and nutrients
peritubular capillaries are higher in oncotic pressure, favoring the flow of water into the capillary (ABSORPTION)
- (10-20)-(8-35) = 17
- NET ABSORPTION resemble third of non-kidney systemic capillaries
what assists to remove extra proteins in the interstitium of the kidneys?
lymphatic capillaries found in the cortex. Remove protein that leak from peritubular capillaries to interstitum.
what is responsible for picking up reabsorbed compounds as well as delivery of oxygen and nutrients?
RPF is responsible for picking up reabsorbed compounds as well as delivery of oxygen and nutrients
what is FF?
FF= filtration volume
- FF=GFR/RPF = 125/600 = 0.2
why is the net cosequence an absorption of fluid into the capillaries of the peritubular and vasa recta?
starling equation states that two pressures (physically and oncoctic ) determine the absorption vs secretion.
unlike the situation in the capsule (dependent mostly on the pressure from the artery), the peritubular and vasa recta physical pressure is really low while the oncotic pressure is very high. This leads to a net absorption of fluid into these capillaries.
what is constantly maintained carfully in kidneys?
where is the main site of renal regulation?
2 types of regulation?
RBF and GFR
- intrinsic changes in vascual resistance that maintain constant RBF despite acute changes in renal artery pressure- orthostasis
- afferent arteriole is the main site of renal autoregulation
- intrinsic
- MYOGENIC
- TUBULOGLOMERULAR FEEDBACK
renal vasculature resistance resides in which major segments? What modulates this resistance?
- interlobar arteries
- afferent arterioles
- efferent arteioles
resistance controlled by
- sympathetic
- hormones
- local internal rena lcontrol
what happens to the peritubular function if the physical pressure were to change? How is this maintained?
the RBF(renal blood flow) is controlled by the afferent and efferent arterioles.
- given the follow ing circumstances the physical pressure is modulated at these two locations to maintain contant physical pressure in the peritubular and vasarecta
describe the intrinsic mechanisms involved in blood pressure maintinence
two reactions that decrease the resistance of the afferent arteriole
- myogenic response
- vascular smooth muscles responds to changes in wall tension by contracting or relaxing
- they relax in response to low pressure and contract in response to high pressure
- mechanism
- stretch gated channels(SAC) are activated when the membrane is distorted by the increase in pressure
- the deformation resultts in channel conformational change that leads to opening allowing Na+ and Ca++ to flow into the cell
- this then causes constriction of the smooth muscle
- tubuloglomerular feedback
- location
- TAL passing adjacent to the capsule= JGA with MDcells
- Macula densa cells in the juxtaglomerular apparatus have many NKCC2 facing the DCT.
- increasing MAP->increase RBF->increase GFR->increase [NaCl] in TAL->
- increase in [Na] inctracellular -> increase Na/K pump -> increase ADP ->
- activate nonselective cation channel -> increase [Ca++] -> release ADP ->ADP binds A1 receptors on nearby vascular smooth muscle cells -> contraction -> increase resistance in afferent arteriole -> decrease GFR
- increasing MAP->increase RBF->increase GFR->increase [NaCl] in TAL->
- location
what are the factors that increase sensitivity of TGF(tubular glomerular feedback) volume contraction?
- Angiotensin 2
- thromboxane
- protaglandins E2
TGF = 1 of 2 intrinsic mechanisms that modify the afferent arteriole
what factros decrease sensitivity of TGF volume expansion?
- ANP
- NO
- cAMP
- prostaglandin I2
- High-protein diet
what type of innervation do the kidneys receive?
sympathetic but NOT PARAYMPATHETIC innervation.
postganglion cell body in celiac.
describe the sympathetic tone during normavolemia
normavolemia, sympathetic tone is minimal
describe the sympathetic tone during hypovolemia
in hypovolemia, tone increases and the adrenal medulla is active.
Binding a1 result in vasoconstriction of afferent and efferent arterioles, which decreases in GFR and RBF
TGF relies on what perameters?
TGF relies on JGA where increased salt delivery to TAL signals high GFR and is compensated by inducing contraction
myogenic regulation relies on…..
myogenic regulation relies on SAC to adjust resistance depending on pressure
higher pressure result in higher resistance.
