Renal - filtration Flashcards
Although still ___, pressure is higher in these than in any other capillaries in the body
capillaries
Characteristics of glomerulus
Larger surface area
Larger fenestrations for easier filtration
Efferent arteriole is smaller than the afferent
This then requires more pressure to get plasma OUT of the glomerulus through the efferent arteriole
This pressure builds backwards into the glomerulus increasing filter pressure (positive pressure)
Efferent arteriole is smaller than the afferent
Pressure in glomerulus pushing outward into capsular space
Glomerular blood hydrostatic pressure (GBHP)
Glomerular blood hydrostatic pressure (GBHP) normal?
Usually 55mmHg
Hydrostatic pressure exerted by the fluid in capsular space that pushes inward on the visceral glomerular membrane
Capsular hydrostatic pressure (CHP)
“back pressure”
Capsular hydrostatic pressure (CHP)
Normal Capsular hydrostatic pressure (CHP)?
15 mmHg
Pressure due to proteins in blood plasma (mainly albumin)
Blood colloid osmotic pressure (BCOP)
“gravitational pull”
Opposes filtration
Blood colloid osmotic pressure (BCOP)
Pulls on fluid/solutes to keep them in the glomerulus if possible
Blood colloid osmotic pressure (BCOP)
Usually 30mmHg
GBHP-CHP-BCOP
NFP
NFP= 55mmHg-15mmHg-30mmHg
NFP
GBHP-CHP-BCOP
As long as the NFP is a ___ number, filtration will occur
positive
If NFP calculates into a ___ number, NO FILTRATION is occurring
negative
Promoting filtration eventually leads to ___
urine production
the amount of blood filtered by the kidneys’ glomeruli into capsular space per unit time
Glomerular Filtration Rate
Glomerular Filtration Rate
the amount of blood filtered by the kidneys’ glomeruli into capsular space per unit time
Normal GFR?
125 mL/min
If GFR too fast?
filtrate may pass too quickly and required substances may not be reabsorbed
If GFR too slow?
nearly all filtrate may be reabsorbed and certain wastes may not be excreted efficiently
GFR is calculated as an estimated rate (no actual measurements).
Using what 5 components?
Creatinine
Age
Race
Weight
Gender
waste from the breakdown of muscle (normal)
Creatinine
As blood is filtered through the nephrons, the kidney neither reabsorbs or metabolizes this substance?
Creatinine
Should freely pass through the filtration membrane and be urinated out?
Creatinine
In a normal healthy adult, the serum level should be near or at the same level of the urine creatinine clearance (24hour urine collection)
Creatinine
If the urine level is low, this means the kidneys are not filtering the serum ___ properly (kidney damage)
creatinine
Usually means that the creatinine serum level will be elevated if what is low?
urine level (i.e., not be excreted thus held in the serum)
GFR directly related to pressures that determine ____
net filtration pressure
Ex: Severe blood loss reduces mean arterial pressure as well as glomerular blood hydrostatic pressure
If GBHP drops by even 10mmHg, filtration in the glomerulus ___ (remember the NFP is what is needed to force filtration)
stops
Mechanisms that regulate GFR
Renal autoregulation
Neural regulation
Hormonal regulation
Renal autoregulation
Neural regulation
Hormonal regulation
Mechanisms that regulate GFR
Innate actions that occur within the kidney
Mechanisms that regulate GFR
Renal autoregulation
Sympathetic nervous system input (or reduction of input)
Mechanisms that regulate GFR
Neural regulation
Angiotensin II
Atrial natriuretic peptide (ANP)
(Mechanisms that regulate GFR)
Hormonal regulation
GFR- Renal Autoregulation Mechanisms
Myogenic mechanism
Tubuloglomerular feedback
increased BP (as in exercise) causes stretching of afferent arteriole, this causes smooth muscle contraction of afferent arteriole, reduces renal blood flow, which reduces GFR
Myogenic mechanism
This helps to preserve nephron integrity with increased blood pressure
When threat of increased BP is reduced, afferent arteriole may vasodilate to increase GFR to balance out the system
Myogenic mechanism
When GFR increases, rate through the tubules increase
Reabsorption of Na+, Cl- and water reduce due to rate of flow
Macula densa cells sense the increased levels of these in filtrate
These levels inhibit the release of nitric oxide (NO; vasodilator)
If NO inhibited, afferent arterioles constrict, lowers GFR
Lowered GFR slows rate through tubules
Tubuloglomerular feedback
GFR- Renal Autoregulation
DCT runs very close to the JGA… the macula densa cells (of DCT) sense a chemical shift in the JGA (through extraglomerular masangial cells cells)
leading to constriction… slide 91ish
A complex structure that has the ability to affect systemic blood pressure through the autoregulation of tubuloglomerular feedback
Juxtaglomerular Apparatus (JGA)
There is one JGA for every nephron
JGA contains?
Juxtaglomerular cells
Macula densa cells
Lacis cells (modified mesangial cells)
Found in the walls of the afferent arteriole
Juxtaglomerular cells
Found in the walls of the distal convoluted tubule
Macula densa cells
Located between afferent arteriole, efferent arteriole, and DCT
Lacis cells (modified mesangial cells
The afferent arterioles contain juxtaglomerular cells
Modified smooth muscle cells that have two functions
Detect when blood pressure is too low (by sensing the lack of stretch of the afferent arteriole wall)
They synthesize, store, then secrete hormone/enzyme Renin (described later in RAAS)
Renin causes a cascade of events that helps to increase blood pressure when needed
Modified smooth muscle cells that have two functions
Detect when blood pressure is too low (by sensing the lack of stretch of the afferent arteriole wall)
They synthesize, store, then secrete hormone/enzyme Renin (described later in RAAS)
Renin causes a cascade of events that helps to increase blood pressure when needed
juxtaglomerular cells
Detect increase in NaCl (Sodium Chloride) concentrations in the filtrate
In response to this concentration check, these cells release
ATP, Adenosine in various concentrations which act locally
These trigger contraction of afferent arteriole
This causes GFR to reduce, which reduces the rate tubule flow
macula densa of DCT (part of JGA)
located in between the afferent, efferent and distal convoluted tubule junction
Contract or relax to make small regulatory changes in response to the signals that the other JGA cells are sending
Lacis Cells (Modified Mesangial cells)
Together the macula densa, juxtaglomerular cells, and Lacis cells make the ____
Juxtaglomerular Apparatus
This is tubuloglomerular feedback
Together the macula densa, juxtaglomerular cells, and Lacis cells make the Juxtaglomerular Apparatus
Depending on the filtrate analysis at this location, the filtration performance of the glomerulus can be changed
Helps regulate blood pressure within the kidneys
This can eventually effect systemic blood pressure
This is tubuloglomerular feedback
Blood vessels of the kidney are supplied by __ nervous system fibers only
sympathetic
At rest, sympathetic stimulation is low, so?
Afferent and efferent arterioles are dilated
Blood flow into and out of the glomerulus is relatively equal
With greater sympathetic stimulation, what happens to the kidneys?
Vasoconstriction of the afferent arteriole occurs
Blood flow decreases into glomerulus
GFR decreases
We need blood elsewhere in the body during these times
This also protects the nephrons from the rapid rise in blood pressure
Two hormones control regulation of GFR
Angiotensin II
Atrial natriuretic peptide (ANP)-
Very potent vasoconstrictor
Mostly acts on efferent arterioles
Reduces renal blood flow
Angiotensin II- reduces GFR
reduces GFR (hormone)
Angiotensin II
Secreted by the atria (heart)
Usually secreted in response to increase in volume
Markedly vasodilates afferent and efferent arterioles
GFR increases
Atrial natriuretic peptide (ANP)-
increases GFR
hormone
Atrial natriuretic peptide (ANP)
Glomerular filtration occurs from pressures alone, not from ATP expenditure
Passive Movement
Epithelial cells all along the renal tubule and ducts reabsorb, but the ___ make the largest contribution to reabsorption
PCT cells
Solutes that are both actively and passively reabsorbed include
Glucose, amino acids, urea, sodium, potassium, calcium, chloride, magnesium, bicarbonate, and phosphates
CCUBA GSMPP
Once fluid passes through the PCT, cells located more distally “fine tune” the reabsorption process. Where?
Loop of Henle, DCT, Collecting duct
If small proteins and peptides are passed through the glomerular filter, they are ____
reabsorbed by pinocytosis (usually in PCT)
between adjacent tubule cells
Passive movement only
Thought to account for up to 50% of reabsorption
Paracellular reabsorption
through the tubule cell itself
(e.g., active transport, pinocytosis)
Passive and Active movement
Transcellular reabsorption
the lumen side of the cell
Apical membrane
the interstitial side of the cell
Basolateral membrane
Solute reabsorption drives water reabsorption via osmosis
This is called obligatory water reabsorption
90% of actual water reabsorption by the kidneys occurs with the reabsorption of
Sodium (Na+)
Chloride (Cl-)
Glucose
These segments are always permeable to water!!!!!!!!!
PCT and the descending limb of the loop of Henle
facultative water reabsorption
Regulated by ADH
Occurs in the late DCT and collecting ducts
Regulated by ADH
Occurs in the late DCT and collecting ducts
facultative water reabsorption
The transfer of materials from the capillaries (peritubular and/or vasa recta), interstitial spaces and tubule cells into the filtrate
Tubular Secretion
Secreted substances include (but not limited to)?
Hydrogen ions
Secretion of hydrogen ions helps to control the blood pH
Potassium
Ammonium ions
Creatinine
Certain drugs like penicillin
There is a constant turnover of new blood coming into the kidney’s
The body signals the need for certain elements to be reabsorbed or secreted based on an attempt for homeostasis
This constant movement generates an osmotic gradient as well as an electric gradient (+/-)
The body signals the need for certain elements to be reabsorbed or secreted based on an attempt for homeostasis
Because of this, there is constant movement of things across these membranes (tubule cell : interstitial fluid : capillary)
nitrogenous waste created when proteins are catabolized (broken down)
Ammonia
much less toxic than ammonia, but can still be deadly if left to accumulate
Urea
Urea plays a significant role in creating and maintaining the osmotic gradient in the renal medulla
Most of the ___ is reabsorbed in the PCT.
This “safeguards” the body’s supply of an important buffer
bicarb (HCO3-)
slide 116
Largest amount of solute and water reabsorption from filtered fluid occurs in the PCT
100% of glucose, amino acids, vitamins
i.e., not in DCT
80-90% of filtered HCO3- (bicarb)
Proximal Convoluted Tubule
~65% of Na+, K+, and water
Proximal Convoluted Tubule
Sodium (Na+) is actively transported out of tubule and into interstitial fluid
Glucose and amino acids are co-transported with Na+
Proximal Convoluted Tubule
As Na+ moves into blood, this creates a significantly positive environment in blood, so ___ ions passively move from filtrate into interstitial fluid to help balance this
(PCT)
Cl-
Cells lining the PCT and the descending LOH are especially permeable to water because of the presence of
aquaporin-1 channels
These are protein water channels that increase the rate of water movement
aquaporin-1 channels
Movement of Na+ and Cl- into interstitium creates a significant osmotic imbalance now, so water is obligated to move out of filtrate and into interstitum by ___
osmosis
The osmosis of water will often bring K+ and Ca++ with it in a motion called ___
solvent drag
stimulates cells in the PCT to secrete phosphate
stimulates calcitriol (Vitamin D) to be made in PCT cells and then be absorbed into blood
stimulates cells in the DCT to reabsorb more calcium
Parathyroid Hormone (PTH)