renal physiology pt 1 (and small add on from thursday) Flashcards
what is filtration
conversion of blood plasma into primary tubular fluid, glomerular filtrate
where does filtration occur
in the glomerulus, which is a network of capillaries
the driving hydrostatic pressure of filtration in the glomerulus is controlled by:
the afferent and efferent arterioles and provided by arterial pressure
what is the golumerular filtration rate (GFR)
about 20% of renal plasma is filtered each minute
forces of filtration (2)
hydrostatic pressure and oncotic pressure
what is PGC
hydrostatic pressure in the glomerular capillary
what is PBS(Pt)
hydrostatic pressure in the bowmans space - nonexistent in healthy animals
what is ||GC
oncotic pressure in the glomerular capillary
what is ||BS
oncotic pressure in the bowmans space - minimal in healthy animals
what determines the hydrostatis pressure in the glomerular capillary and what does it determine
- it determines the rate of filtration as well of the tubular fluids/urine flow to renal pelvis
- determined by blood input from afferent arterioles and tonus of efferent arterioles
- primary target of regulatory mechanisms that control GFR
what is plasma oncotic pressure determined by
difference of protein concentrations between blood plasma and glomerular filtrate
is plasma oncotic pressure a primary target of regulatory mechanisms that control GFR
no
how does plasma oncotic pressure affects the rate of filtration
there is a net filtration along the entire length of the glomerular capillaries
hydrostatic pressure in the bowmans space
- BS insignificant for a healthy animal
- can dramatically rise and prevent filtration upon obstruction of ureters
permeability
- sieve function
- contributes to the co-efficient of ultrafiltration (Kf) along with filtration surface
what is the co-efficient of ultrafiltration
Kf
what are the factors affecting permeability of polypeptides
- size
- shape
- charge
how does size affect permeability of polypeptides
proteins the size of plasma albumins or larger are not efficiently filtered compared to smaller peptides
how does shape affect permeability of polypeptides
long flexible proteins are filtered more efficient than globular proteins
how does charge affect permeability of polypeptides
positively charged polypeptides are filtered more efficiently than negatively charged molecules
what is renin
a polypeptide hormone, produced by specialized cells of the wall of the afferent arteriole (JG cells)
what is the release of renin stimulated by
a decrease in renal perfusion
what is angiotensin II
potent peptide vasoconstrictor that acts directly and indirectly
how does angiotensin II act directly
contricts arterial blood vessels to increase systemic blood pressure and renal perfusion pressure
how does angiotensin II act indirectly
stimulates the release of:
* the mineralocorticoid steroud hormone aldosterone from the adrenal gland
* polypeptide hormone vasopressin (ADH, anti-diuretic hormone) from the pituitary gland
what stops vasocontriction
NO
PgE2
PgI2
what is the relationship between glomerular arteriolar resisitance, GFP and renal plasma flow (RPF)
- constriction of the afferent
- contriction of the efferent
what does contriction of the afferent do
arteriole increases renal vascular resistance (therby reducing RPF) and decreases the intraglomular pressure and GFR
what does constriction of the efferent do
arteriole also lowers RPF but tends to elevate the intraglomerular pressure and GFR
the intrarenal pressure distal to stenosis should be lower than the arterial pressure. as a result, lowering systemic blood pressure AND preventing ability of AII to compensate for that by constricting the efferent arteriole can dramatically decrease GFR and may lead to:
acute renal failure
within the kidney itself, there are mechanisms that directly control the glomerular capillary perfusion (2)
- myogenic reflex
- tubulo-glomerular feedback
which intrinsic factor regulating GFR is independent of renal innervations but might be influenced by levels of prostaglandings and NO
myogenic reflex
what is the myogenic reflex
- glomerular arterioles respond to changes in arteriolar wall tension
- immediate arteriolar constriction in response to an increase in this wall tenstion
- a decrease in arteriolar wall tension results in virtually immediate arteriole dilation
what is the macula densa
a morphologically distinct cluster of epithelial cells, located in the distal portion of the thick ascending limb of the loop of henle
what are macula densa cells sensitive to
an increase in the tubular flow rate
what does an increase in tubular flow rate lead to
decrease in the filtration rate of glomerulus of the same nephron by yet poorly characterized mechanism
what is inulin
- a zenobiotic
- an indicator substance of choice because the rate of its disappearance from plasma strictly relates to the rate of GFR
in clinical practice, the most widely used indicator substance to measure GFR is
creatinine
what is creatinine
a byproduct of muscle metabolism that is handled by kidney similarly to inulin
what test is not applicable in birds as avian renal tubules can both secrete and re-absorb it
creatinine
what is filtration fraction (FF)
the fraction of renal plasma flow that is actually filtered by glomeruli
what is fractional excretion (FE)
the rate of urinary excretion of a substance X divided by its rate of filtration
when creatinine does not help much you can use
BUN: blood urea nitrogen
what is GFR directly related to
renal mass/number of functional nephrons
what is an example of a diverse cause for nephrotic syndrome
acute glomerulonephritis
what is tubular reabsorption
a process where the direction of solute transfer is from tubular lumen to the peritubular capillary plasma
what is tubular secretion
the opposite direction from the peritubular capillary plasma to tubular lumen
what is excretion
filtration - reabsorption + secretion
how is renal tubule function assessed
by determining fractional excretion rate (FER) and fractional re-absorption rate (FAR)
what is FER
the percent of a filtered substance that is ultimately excreted in the urine
what is FAR
the proportion of filtered substance X that is reabsorbed by the tubule
what is the proximal tubule responsible for
the reabsorption of the bulk of filtered solutes
anatomo-histologic structure of the proximal tubule facilitates the movement of tubule fluid components inro the blood through two pathways:
- the trans-cellular pathway
- paracellular pathway
in the paracellular pathway, substances are reabsorbed through this pathway move from tubular fluid across the:
tight junctions
what is a tight junction
a highly permeable structure, which attaches the cells of epithelial sheet to each other and forms the boundary between the apical and basolateral membranes
paracellular transport occurs by passible diffusion or by:
solvent drag
what is solvent drag
a mechanism, which is the entrainment of solute by the flow of water
the movement of water and solutes from the interstitial fluid into bloodstream is driven by:
starling’s forces
much of the transport of substances from the tubular fluid to the blood is driven by:
active transport of Na+
re-absorption of filtered peptides:
- a large proportion of filtered peptides are degraded to amino acids by peptidases present in the proximal tubule brush border
- AA are reabsorbed in a co-transport with Na+
why are a wide variety of organic ions secreted into tubular fluid in the proximal tubule
most of them are bound to proteins in the plasma, these substances are not filtered in the glomerulus, so secretion of these substances in the proximal tubule is the major patheay of their excretion
what is an example of an organic ion
hippurates
what is a veterinary importance of proximal tubular secretion
monitoring function of the tubule
in clinical practice what is one of the most important parameters of renal function
GFR
how is GFR determined
the rate of clearance of the plasma of a particular substance
the active transport systems of reabsorption in the renal tubules can have a limit which is called the:
transport maximum (Tmax)
what does Tmax reflect
the amounts of material that can transport per unit time
Tmax of glucose is
amount of glucose transported per unity time to saturate the membrane transporters in the proximal tubule
Tmax equation
GFR X concentration of glucose in ultrafiltrate
the segments that include the thick ascending limb of henle and the distal convoluted tubule are very important for reabsorption of:
Na+, K+, Cl-, Ca+, and Mg2+
the thick ascending limb of the loop of henle and the distal convoluted tubule are able to reabsorb solutes against a
high gradient
the thick ascending limb of the loop of henle and the distal convoluted tubule exhibit poor:
permeability to water
what is reabsorbed in the thick ascending loop of henle
35-40% of the filtered NaCl
what does reabsorption of NaCl in the thick ascending loop of henle allow
formation of osmotic gradient in the interstitium and dilution of urine in the tubule
what are the 5 mechanisms that drive reabsorption in the distal tubule segments
- Na+-K+ ATPase in basolateral membrane of the cells actively transports Na+ from the cells into interstitial fluid and creates an electro-chemical gradient for Na+ across the apical membrane
- gradient drives Na+, K+, 2Cl- co-trasporter in the apical membrane and these ions move from tubular fluid into the cell
- Cl- diffuses down its chemical gradient into the interstitial fluid via Cl- channels in the basolateral membrane
- K+ moves extracellularly down its concentation gradient through K+ channels across both basolateral and apical membrane
- net result of Cl- absorption and K+ secretion: formation of a lumen-to-blood electrical gradient, that moves cations from tubular fluid to blood through paracellular pathway
what is the importance of reabsorption in the distal tubule
resulting dilution of tubular fluid allows the kidney to regulate water excretion without loosing salt - prevents water overload and plasma hypotonicity
what are the two major cell types of collecting ducts
- principal cells
- intercalated cells
what are intercalated cells involved in
K+ and Na+ re-absorption
what are principal cells involved in
K+ secretion
the ultimate rate of renal excretion of K+ and its concentration in the urine is determined by:
the efficiency of intercalated cells and principal cells
