Term
| what are the major functions of the kidneys? |
|
Definition
Maintain H2O balance, osmolarity,
plasma volume
• Regulate quantity/concentration of
most ECF ions
• Acid-base adjustment (with lungs)
• Excreting (eliminating) waste
products, foreign compounds
• Endocrine (erythropoeitin, renin)
• Converting vitamin D into active form |
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Term
|
Definition
Functional unit of the kidney
(performs all functions); 1 million
per kidney
• Two components
– Vascular component
– Tubular component
• Two distinct regions (nephrons
organized accordingly)
– Cortex (outer granular
appearance)
– Medulla – renal pyramids |
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Term
| what are the two different types of nephrons? |
|
Definition
Juxtamedullary nephrons (20%)
• glomerulus in cortex-medulla border
• long loops of Henle traverse medullary region
• Peritubular capillaries (vasa recta) travel with loops
– Cortical nephrons
• glomerulus in cortex
• most abundant
• Hairpin turns at medulla |
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Term
| what is the vascular component of the nephron? |
|
Definition
Glomerulus primarily– balllike tuft of capillaries
– From renal artery to afferent
arterioles (blood to
glomerulus)
– Efferent arteriole from
glomerulus
– Efferent arteriole to
peritubular capillaries -surround tubular part of
nephron
• Peritubular capillaries join
into venules to renal vein |
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|
Term
| what do the peritubular capillaries do? |
|
Definition
| run along the tubules and allow further exchange of ions and substances. |
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Term
| what is the tubular component of a nephron? |
|
Definition
Hollow-fluid filled tube, single
epithelial layer
– Bowman’s capsule – collects
glomeruls filtered fluid
– Proximal tubule – limited control
of reabsorption, selective filtration
– Loop of Henle
• establishes osmotic gradient
in medula needed for
concentrating urine
• descending and ascending
– Juxtaglomerular apparatus - this is where the distal tubule passes right by the glomerulus
– Distal tubule and collecting duct –
variable controle reab/secretion
with collection from all nephrons |
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|
Term
|
Definition
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|
Term
| what are some important parts of the juxtaglomerular apparatus? |
|
Definition
macula densa - macula densa is an area of closely packed specialized cells lining the wall of the distal tubule at the point of return of the nephron to the vascular pole of its parent glomerulus, (glomerular vascular pole).
The cells of the macula densa are sensitive to the concentration of sodium chloride in the distal convoluted tubule - can increase renin concentration, extraglomerular mesangial cells - are specialized cells around blood vessels in the kidneys, at the mesangium. They are specialized smooth muscle cells that function to regulate blood flow through the capillaries, and juxtaglomerular (granular) cells are cells in the kidney that synthesize, store, and secrete the enzyme renin |
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Term
| what is the basic renal filtration process? |
|
Definition
Glomerular filtration
– non-discriminant filtration of
protein-free plasma
– Glomerulus to Bowman’s
Capsule
• Tubular reabsorption -selective mvmt of filtered
substances from tubular
lumen to peritubular
capilaries
• Tubular secretion –
selective mvmt of nonfiltered substance from caps to lumen
80% of the plasma that enters the glomerulus is not filtered and leaves through the efferent arteriole. 20% is filtered |
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|
Term
| how does glomerular filtration work? |
|
Definition
Fluid filtered from glomerulus into Bowman’s capsule via “barriers”
– Glomerular capillary wall
• Single layer of endothelial cells
• More permeable to water and solutes (limited proteins)
– Basement membrane
– Inner layer of Bowman’s capsule - podocytes that encircle the
glomerulus tuft |
|
|
Term
|
Definition
glomerular filtration rate = filtration coefficient (K
f) * net filtration pressure
–Kf = permeability * surface area
– subject to physiological control - (contractile membrane activity) |
|
|
Term
| what things can affect glomerular filtration |
|
Definition
– Altered capillary wall permeability
– BM resists plasma proteins
– Podocytes – create filtration slits. have foot-like
projections (pedicles)
– Small filtration slits regulate
permeability, negative charge particles have a more difficult time being filtered |
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|
Term
| What are the major forces involved in glomerular filtration? |
|
Definition
Glomerular capillary blood pressure - favors filtration
• Plasma-colloid osmotic pressure (high in glomerulus, zero in bowmans capsule, therfore opposes filtration)
• Bowman’s capsule hydrostatic pressure - opposes filtration. |
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Term
| kidney stones increase hydrostatic pressure in the lumen, reducing filtration. |
|
Definition
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|
Term
| how do we control glomerular filtration rate? |
|
Definition
Blood flow control (20-25% cardiac output)
• GFR ~180 L/day, ~125 ml/min
• Controlled adjustments in GFR – glomerular blood pressure
– Autoregulation (local alterations in GFR)
• Myogenic mechanism
• Increase stretch – constrict
• Decrease stretch – dilate
• Tubuloglomerular feedback
• Smooth muscle cells within
afferent form granular cells
• Tubular cells at JGA form
macula dense (sense NaCl)
• ↑Na (with H20), vasocontrict
afferent, vasodilate efferent
Myogenic and tubuloglomerular feedback regulate GFR/MAP to 80-180 mmHg
• Controlled adjustments in GFR outside of this range
– Extrinsic sympathetic control (long-term control of MAP)
• sympathetic nervous system input to afferent arterioles
• Baroreceptor reflex
– ↓GFR causes ↓urine output, conserving some water and salt,
helping to restore plasma volume to normal
– Hormonal – discussed later |
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Term
| When JGA cells (macula densa) detecs increase in NACL, it signals the granule cells to vasoconstrict. too much fluid in the renal system, causes them to constrict, which reduces filtration and reduces fluid loss. |
|
Definition
|
|
Term
Baroreceptor/Sympathetic influences on
MAP |
|
Definition
| know this slide like the back of your hand |
|
|
Term
| what are some unregulated influences on the GFR? |
|
Definition
– Plasma-colloid osmotic pressure
• Severely burned patient ↑GFR
• Dehydrating diarrhea ↓GFR
– Bowman’s capsule hydrostatic P – kidney stones |
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|
Term
| what is plasma clearance? |
|
Definition
Volume of plasma cleared of a particular substance per minute (not
the amount of the substance removed)
• Varies for different substances, depending on how the kidneys
handle each substance
there is a limit to reabsorption because it is an active process. |
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Term
| how does tubular reabsorption and secretion work? |
|
Definition
Tubular reabsorption -selective mvmt of filtered substances from lumen to
peritubular capilaries
– 99% of solutes, fluid
– Typicallly all glucose
• Tubular secretion –
selective mvmt of nonfiltered substance from caps to lumen |
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|
Term
| how is sodium reabsorbed? |
|
Definition
Na reabsorption - Na
+-K+
ATPase at basolateral
membrane (80% total
energy)
•Na+
is not reabsorbed in
descending loop of Henle
• Water follows reabsorbed
Na+ by osmosis |
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|
Term
| how does passive reabsorption work at the end of the proximal tubule? |
|
Definition
Glu/AAs - reabsorbed by Nadependent, 2⁰transport (typically in
first half of proximal tubule)
• Other electrolytes have their own
carrier systems
• Reabsorption of H
2
0 in proximal tubule
increases [urea] in the tubule
• Generally, unwanted waste products
are not reabsorbed
• Calcium reabsorption/secretion
adjusted by hormonal concedntration
(parathyroid hormone increases Ca
reab. In distal tubules) |
|
|
Term
| is Na+ reabsorption regulatied in the proximal or distal tubule? |
|
Definition
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|
Term
| a change in Na+ or H20 in renal system activates the renin-angiotensin-aldosterone system. |
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Definition
| granular cells release the renin with decreased BP and increased sympathetic activity. Macula densa detects decreased NaCl, triggers granular cells as well. |
|
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Term
| what does angiontensin II trigger? |
|
Definition
| triggers aldosterone aldosterone from adrenal cortex, but also increases vasopressin and thirst. |
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Term
| Renin-angiotensin-aldosterone system. know this well. |
|
Definition
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Term
| what is the difference between aquaporin 1 and aquaporin 2? |
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Definition
| AQP1 is in the proximal tubule and always open. AQP2 is in the dital tubule and is regulared to vasopressin/ADH. |
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Term
| how does tubular secretion of potassium work? |
|
Definition
Keeps plasma K
+
concentration at
appropriate level
– Secreted only in the distal and
collecting tubules w/ aldosterone
potassium is the most important ion to be regulated because your cells are so very very permeable to potassium. |
|
|
Term
| how does tubular secretion of H+ work? |
|
Definition
Regulates acid-base balance
– Secreted in proximal, distal, and
collecting tubules |
|
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Term
| what affect does aldosterone have on K+ and Na+ secretion? |
|
Definition
increased tubular K+ secretion, increased urinary excretion.
increased tubular Na+ reabsorption, less urinary excretion. |
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Term
| Regulation of H+ and HCO3- concentrations???? |
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Definition
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Term
| how do the kidneys affect water concentration? |
|
Definition
80% reabsorbed by elevated osmotic pressure of blood
in peritubular capillaries following glomerular filtration
• Countercurrent Mechanism - salvages water from
glomerular filtrate, so produces a concentrated urine |
|
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Term
| how is Urine Excretion and concentration varied? |
|
Definition
With variation in hydration, urine varies
concentrations.
– Too much water in ECF hypotonic ECF
(result = dilute urine)
– A water deficit establishes a
hypertonic ECF (result = conc. urine)
• Large, vertical osmotic gradient
established in medullary interstitial fluid
– follows the hairpin loop of Henle
– Concentration greater with depth of
medulla
– Osmotic gradient between tubular
lumen and interstitial fluid |
|
|
Term
| what is countercurrent multiplication? |
|
Definition
Establishes medullary vertical osmotic gradient
• Comparing the descending and ascending limbs of the loop of Henle:
– descending limb highly H20 permeable, not Na
– ascending limb transports NaCl out of the tubular lumen, impermeable to
H20. (produces hypertonic interstitial fluid)
– “countercurrent flow” produced by proximity of two limbs |
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|
Term
| how does water reabsorption work (vasopressin/ADH)? |
|
Definition
65-80% H20 reabsorption is obligatory in proximal tubule.
• Variable in distal tubule/collecting, based on ADH/vasopression
• ADH/VP secretion
– Hypothalamus production, release from posterior pituitary
– VP/ADH increases tubular H20 permeability w existing osmotic gradient
– Release with thirst, decreased plasma volume/pressure |
|
|
Term
| how does vasopressin work? |
|
Definition
Hypothalamic osmoreceptors – near VP and thirst cells
– Osmolarity increase →vasopressin secretion and thirst
stimulated
– Osmolarity decrease →vasopressin secretion decreased and
thirst suppressed
• Left atrial receptors
– Monitor pressure of blood flowing through (reflects ECF volume)
– Upon detection of major reduction in arterial pressure, receptors
stimulate vasopressin secretion and thirst
– Upon detection of elevated arterial pressure, vasopressin and
thirst are both inhibited
• Angiotensin II – stimulates VP release/thirst (conserve
Na+) |
|
|
Term
| what are some factors affecing vasopressin release? |
|
Definition
| osmolarity greater than mOsM, decreased atrial stretch due to low blood volume, decreased blood pressure. These all end up in increased vasopressin synthesis and increased water reabsorption to conserve water. |
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|
Term
|
Definition
Urine flow to renal pelvis,
ureters to bladder (storage)
• Micturition is the process of
emptying the urinary bladder.
• Bladder filling = increased
tension = micturition reflex |
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