Week 3 Flashcards
What is renin?
a protein enzyme released by the kidneys when BP is too low
decreased GFR= increased renin release
Increased renal arterial pressure increases the delivery of fluid and sodium to the macula densa. ATP is released and calcium increases in granular and smooth muscle cells of the afferent arteriole, causing arteriole constriction and decreased renin release.
What is the autoregulatory pressure range in the kidney?
80-180 mmhg
What is the site of renin synthesis?
Juxtaglomerular apparatus
What are the 4 components of the JGA?
- modified smooth muscle cells in the afferent arteriole
-modified smooth muscle cells in the efferent arteriole
-extraglomerular mesangial cells
-macula densa cells in the distal tubule**
What is the macula densa?
Chemoreceptors located in the thick ascending limb (TAL) and distal tubule which detect sodium concentration.
macula densa cells trigger the contraction of afferent arteriole
Increased sodium = contraction of afferent arteriole–> decrease blood flow and decreased GFR
increased sodium= decreased GFR
What are the 2 major regulatory functions that are performed by the JGA?
the high distal tubular nacl induced afferent arteriolar vasoconstriction (tubulaoglomerular feedback)
the low tubular nacl induces renin release
what is the JGA’s main function?
regulate blood pressure and the filtration rate of the glomerulus
what is the JGA formed by?
DCT and afferent arteriole
What are the actions of angiotensin 2?
Increased aldosterone synthesis and release
increased ADH release
increased thirst
inhibition of renin release
released prostaglandins which act to maintain GFR
What is the stimulation for aldosterone release?
Increased levels of K+ in ECF
Angiotensin 2
Decreased Na+ levels
** Aldosterone is the final common pathway in the complex response to decreased effective arterial volume
What are the actions of aldosterone?
acts on the distal tubule and collecting ducts to cause K+ and H+ secretion for Na+ retention
Helps control blood pressure by holing onto salt and losing K+ from the blood. = increased GFR = decreased renin
What atrial natriuretic hormone?
promotes the excretion of sodium and water
A majority of ANP is synthesized and secreted from cardiac muscle cells, particularly in the atria
ANP can be thought of as an anti-hypertensive hormone and plays a central role in the regulation of blood pressure.
What is conn’s syndrome?
(HYPERALDOSTERONISM) Aldosterone-secreting tumor causes:
-HTN
-HYPERnatremia
-HYPOkalemia
What are the renal concentrating and diluting mechanisms?
-ADH
-ANP
-the countercurrent multiplier
-urea
Why is it important to be able to concentrate of dilute urine?
- for cells to function they must be bathed in extracellular fluid w a stable concentration of electrolytes and solutes
-the kidney can excrete excess water by forming a dilute urine
-the kidney conserves water by concentrating the urine
What must the normal 70 kg human excrete in solute each day?
600 mOsm of solute each day
What is the maximum urine concentrating ability?
1200 mOsm/L
what is the obligatory urine volume?
0.5L/day
What is ADH?
octapeptice- synthesized in the hypothalamus
-stored and released from the posterior pituitary
-plays a major role in conserving water by concentrating urine.
What does plasma hypotonicity do?
suppresses ADH release = excretion of dilute urine
What does plasma hypertonicity do?
stimulates ADH= enhanced water reabsorption
What does an increase in extracellular fluid osmolarity cause?
causes osmoreceptors cells in the anterior hypothalamus near the supraoptic nuclei to shrink
as they shrink, they fire and stimulate release of ADH
The increased water permeability in the distal nephron segment caused by ADH causes:
increased water reabsorption and excretion of a small volume of concentrated urine.
where are osmoreceptors located?
anterior hypothalamus
increased osmolality stimulates:
ADH release
mechanoreceptors in the atria and aorta will detect __________ and stimulate ADH release
decreases in volume
other stimulators of ADH include:
angiotensin 2
fright
nausea
pain
anesthesia
nicotine
Alcohol does what to ADh?
Inhibits!
the rate of ADH secretion determines:
whether the kidney excretes dilute or concentrated urine
When will you have increased ADH?
increased plasma osmolarity
decreased blood volume
decrease BP
nausea
hypoxia
drugs:
morphine
nicotine
cyclophosphamide
when will ADH secretion decrease?
decreased plasma osmolarity
increase blood volume
increase blood pressure
drugs:
alcohol
clonidine
haloperidol
what are the functions of ADH?
decreased urine production
decreased sweating
increased BP
dehydration=
stimulation of ADH release
overhydration=
inhibition of ADH
Vasopressin’s CV effects are predominately mediated through which receptors?
V1 receptors
located in the cell membranes of vascular smooth muscle
When is a vasopressin infusion indicated?
for tx of severe HoTN after prolonged CPB in pts who are otherwise unresponsive to phenylephrine or NE
What does the supraoptic hypothalamic nuclei regulate?
Water metabolism and are anatomically and functionally associated with the posterior lobe of the pituitary.
What is the nucleus tractus solitarius?
located in the medulla-
the primary area for relay of afferent chemoreceptor and baroreceptor information from the glossopharyngeal and vagus nerves.
What do increased afferent impulses from the glossopharyngeal and vagus nerves cause?
inhibit peripheral SNS vascular tone= vasodilation
-increases vagal tone= bradycardia
How does ADH work?
increases the permeability of the collecting system to water
in the absence of ADH the collecting system is relatively impermeable to water leading to decreased water conservation and a dilute urine
fluid leaving the ascending loop of henle and early distal tubule is always:
DILUTE - regardless of the level of ADH
fluid leaving the ascending loop of henle and early distal tubule is always:
DILUTE - regardless of the level of ADH
in the absence of ADH, the collecting system is relatively impermeable to water leading to:
Decreased water conservation and dilute urine (concentrated plasma, dilute urine)
in the absence of ADH, the collecting system is relatively impermeable to water leading to:
Decreased water conservation and dilute urine (concentrated plasma, dilute urine)
the basic requirements for forming concentrated urine are:
a high level of ADH
a high osmolarity of renal medullary interstitial fluid
water
the basic requirements for forming concentrated urine are:
a high level of ADH
a high osmolarity of renal medullary interstitial fluid
water
What are the key features of the countercurrent multiplier?
-U shape of the loop of Henle
What makes up the counter current mechanism?
loop of Henle and vasa recta
What is the normal plasma osmolarity?
300 mOsm/L
What is the osmolarity of the glomerular filtrate?
iso-osmotic= 300mOsm/L
what is the thin descending limb of the loop of henle?
less permeable to solutes, more permeable to water
Hypertonic- reabsorbs water into the hypertonic medullary interstitium. concentrated urine
What concentration is the urine in the TAL?
dilute
what parts of the nephron are impermeable to water?
ascending limb, DCT, collecting ducts all and urea impermeable to water
What are the major factors that contribute to the buildup of solute concentration in the renal medulla?
TAL: active transport of NA+, K+, Cl—> medullary interstitium
Collecting ducts: active transport
inner medullary collecting ducts: facilitated diffusion
medullary tubules: diffusion
What are the major factors that contribute to the buildup of solute concentration in the renal medulla?
TAL: active transport of NA+, K+, Cl—> medullary interstitium
Collecting ducts: active transport
inner medullary collecting ducts: facilitated diffusion
medullary tubules: diffusion
What is the role of urea?
what is urea?
a byproduct of amino acid metabolism- consists of 2 ammonia molecules
How much urea is made per day?
approx 25-30g/day are made in the liver
What happens in the case of liver failure?
ammonia levels accumulate and encephalopathy and coma develop
How much does urea contribute to osmolarity?
40-50% (500-600 mOsm/L)
Passively reabsorbed from the tubule.
what part of the nephron has a high concentration of urea?
medullary interstitium
- plays an important role in generating a hypertonic interstitium
what part of the nephron has a high concentration of urea?
medullary interstitium
- plays an important role in generating a hypertonic interstitium
the TAL is impermeable to:
water and urea
when ADH is present, water is reabsorbed into the ____ and _____
cortex and outer medulla = tubular contents become more concentrated
What are the 2 functions of the vasa recta?
-remove reabsorbed fluid from the interstitium
-minimize solute uptake from the medulla (maintains medullary hypertonicity)
