Renal Test Two Flashcards
What is the final step in reabsorption of water and sodium?
Water sodium and everything else dissolved in interstitial fluid move by bulk flow into peritubular capilllaries as final step
What organ is most responsible for homeostasis?
Kidneys
Fill in equation: Na excreted = ______
Na filtered - Na reabsorbed
What are the receptors for reflexes that control body sodium?
Baroreceptors in the cardiovascular system and sensors in the kidney that monitor filtered load of sodium
What is the most abundant cation in the ECF?
sodium
How does sodium link to low blood pressure?
low body sodium leads to low ECF volume and plasma which leads to low artery and venous pressure
What are the corrective reflexes to fix low BP?
Control the amount of sodium filtered by controlling GFR. This happens by activating cardiovascular baroreceptors to regulate the MAP
What is the “more important” pathway for correcting low plasma volume?
Increase activity in the sympathetic nerves to the kidneys in response to low BP from low plasma volume. Which will cause constriction of renal arterioles and decrease the net GFR to decrease sodium and water excretion.
Renin aldosterone system?
Angiotensinogen is produced by the liver and in response to low BP renin is released from the kidneys. Renin cleaves angiotensiongen to angiotensin I. AcE comes from the lungs to cleave angiotensin I into angiotensin II which is active and can then act on the adrenal glands to secrete aldosterone to cause an increase of Na reabsorption.
What sends the signal to produce Renin?
Macula densa sends a signal to the juxtaglomerurlar cells in the kidney to produce renin
In the absence of aldosterone where is most of the filtered sodium reabsorbed?
In the proximal tubule (65%)
and 30-32% in loop of henle and distal tubule
What is the rate limiting step of producing aldosterone?
Renin secretion
What are three inputs to the juxtaglomerular cells that increase the secretion of renin?
Sympathetic nerves activated by the baroreceptor reflex to JG cells
Baroreceptors within the kidney due to a decreased stretch from decreased BP
Paracrine factors released from macula densa
What plays a role in the long term regulation of arteriole BP?
an increase in body sodium causes water to be re absorbed so this re absorbed water along with the retained sodium increases the ECF and plasma volume.
When is the later tubule permeable to water?
In the presence of ADH
How can the heart impact high blood pressure?
With high plasma volume there is distension in the atria. This increases secretion of ANP into the plasma and causes decreased Na re absorption and dilation of afferent arterioles and constriction of efferent to raise GFR which increases the excretion of NA
What hormone directly inhibits aldosterone to increase sodium excretion?
ANP
Describe how water is regulated without altering Na.
Sodium will stay in the ECF when added to the body, but water distributes throughout all compartments so pure water gains/losses only slightly change BP
What reflexes alter water excretion without sodium excretion?
Osmoreceptors in the hypothalamus detect ECF and are mediated by ADH
What happens to the hypothalmic osmoreceptors when they shrink?
they increase their frequency of action potentials.
Osmoreceptors synapse on neurons that have c ell bodies in hypothalamus and axons that travel down into posterior pituitary
When excess water is ingested what is the pathway that leads to water excetion?
ECF osmolarity goes down and inhibition of hypothalmic osmoreceptors occurs.
ADH secretion and therefore plasma concentration of it is decreased due to lack of osmoreceptor firing.
Permeability of renal collecting ducts is decreased due to lack of ADH, so decreased water reabsorption and increased excretion occurs
How does ADH influence TRP?
it causes widespread constriction of arterioles
In order to excrete a concentrated urine to allow water reabsorption without concurrent sodium reabsorption what needs to happen?
The hyperosmotic renal interstitial fluid is coupled with collecting ducts that are permeable to water due to ADH. Water will be reabsorbed .
How is dilute urine excreted?
Though a lack of ADH which will result in collecting ducts that are not water permable
In congestive heart failure are renin angiotensin II and aldosterone high or low?
High, which leads to retention of water and sodium leading to the edema
How does severe sweating impact sodium excretion?
It decreases plasma volume and therefore pressure, which leads to an increase in aldosterone to decrease sodium excretion
How does severe sweating impact water excretion?
It increases plasma osmolarity which increases ADH to decrease water excretion
In general how much potassium is reabsorbed/excreted?
Most filtered potassium is NOT excreted in urine because almost all filtered potassium is reabsorbed
Is K secreted regulated or not?
Regulated by the cortical collecting duct according to body’s need
Describe what happens when there is an increase in K intake?
Secreted K can be added to the filtered and not reabsorbed potassium and the amount that is excreted in the urine (small) goes up a small degree.
Potassium depletion, what happens?
There is no secretion so the only potassium that is excreted is what was filtered
How does potassium move from renal interstitial fluid to the tubular fluid?
The Na/K pump moves from renal interstitial fluid across the basolateral membrane of tubule cells into the cells. Then potassium moves by diffusion through K channels into tubular fluid after crossing the luminal membrane
How does aldosterone impact potassium?
it acts on CD cells to increase the rate of K secretion (which leads to increase Na reabsorption)
What are a few things calcium is important for?
Cell division, enzyme function, heart electrical activity, neurotransmitter secretion and Hm. oocyte activation, blood clotting, muscle contraction, bone/teeth formation
What metabolic shift can cause a depressed nervous system and increased muscle activity?
Hypercalcemia
What can cause nervous system excitement and tetany?
Hypocalcemia
Where is calcium concentration greater, ECF or Intracellular compartment?
ECF
How is calcium stored in plasma?
50% ionized Ca in plasma, 9% combined with citrate and PO4, 41% bound to plasma proteins
What promotes absorption of dietary calcium across intestinal walls?
Vitamin D
What is the organic matrix of bone?
Collagen fibers and ground substance
If ECF Ca is low what happens to raise it?
Osteoclasts are activated indirectly by PTH, which increases resorption of bone and causes phosphate ions to leave bone matrix and enter ECF
How are vitamin D and PTH related?
In the absence of active vitamin D the effect of PTH is reduced. So there is decreased bone resorption
What happens if there is excess calcium in the ECF?
Osteoblasts incorporate it into bones
How much calcium is re absorbed?
~99% of filtered calcium is re absorbed and 59% of calcium in plasma is available for glomerular filtration
Where does most Ca reabsorption occur?
In proximal tubule loop of henle and early distal tubule and is mostly not under hormonal control
Where is calcium reabsorption regulated?
IN the late DT and early collecting duct. Low Ca concentration increases PTH which increases calcium reabsorption in the DT/CD
A small change in blood calcium levels above normal causes what?
decreased PTH and increase calcium excretion in the urine
What hormone activates an enzyme that catalyzes conversion of inactive vitamin D into the active form?
PTH
In order for vitamin D to become actiove it undergoes a reaction in ___ and ___.
Liver and final activation in the kdineys
Describe calcitonin?
acts on bone to decrease ECF calcium concentration and is of little importance in normal calcium regulation
Inorganic phosphate in the plasma is filterable or not?
about half of plasma phosphate is filterable and most that is filtered is reabsorbed in the proximal tubule
What decreases renal reabsorption of phosphate ions?
PTH
so when calcium is low and PTH secretion and ca reabsorption are increased phosphate ion excretion in urine is increased
