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184 Cards in this Set

  • Front
  • Back
What organs comprise the urinary system?
-Urine forming organs: Kidneys
-Urine storing and transport organs: ureters, bladder and urethra.
What are the urine forming organs?
The kidneys
What are the three regions of the internal Kidney?
-Renal Cortex: outer layer
-Renal Medulla: Inner layer: darker in color
-Renal Pelvis
What is the smallest functional unit of the Kidney?
The nephron
How many neprhons are present in each kidney?
1 million
What tissues make up the vascular component of the nephron?
-Afferent arteriole (branch of the renal artery)
-Glomerulus (tuft of capillaries)
-Efferent Arteriole
-Peritubular capillaries: drain blood back to the renal vein
In general, what makes up the tubular component of the Nephron?
-Bowman's capsule
-Proximal convoluted tubule
-Descending and Ascending Loop of Henle
-Distal convoluted tubule
-Collecting Duct
How many nephrons drain into a common collecting duct?
About 6-8
What is the Juxtaglomerular Apparatus?
Area where distal tubule comes in very close to the glomerulus and regulates the formation of urine by the nephron
What are the 3 regional differences in the 2 types of nephrons?
1. How superficial or deep the glomerulus sits in the cortex
2. The length of the loop of henle
3. A portion of their vasculature
What are the 2 types of nephrons?
What percentage of each is present in the kidneys?
1. Superficial Cortical Nephrons (80%)
2 Juxtamedullary nephron (20%
Describe the (Superficial) Cortical Nephrons.
- In the outer cortex
-Short loops of henle that dip shallowly into the renal medulla
-Have peritubular capillaries that surround the entire nephron
Describe Juxtamedullary Nephrons.
-Have very long loops of henle that extend deep into the renal medulla (tips are close to renal pelvis)
-Instead of peritubular capillaries they have VASA RECTA
What is the vasa recta?
The vasculature that specifically travels alongside the loop of henle in the juxtamedullary nephrons.
Why does the Vasa Recta only run alongside the loop of henle in the juxtamedullary nephrons?
-To not disturb the osmolarity inside the medulla.
-Prevents excess fluid exchange
What key role do the juxtamedullary nephrons play in the body?
-They allow us to create urine of varying concentrations
-Allow for our body's ability to conserve or excrete water
What type of nephrons predominate the kidneys of camels?
Juxtamedullary nephrons (allow for more water conservation)
What are the 3 basic renal processes?
1. Glomerular filtration
2. Tubular Reabsorption
3. Tubular Secretion
What percentage of the CO is received by the kidneys?
About 20%
What is the perenchyme?
They actual tissue of the kidney
What is the movement called if substances are filtered from the tubule into the periuibular capillaries?
Tubular reabsorption
What is tubular secretion?
Substances from the peritubular capillaries move into the renal tubule to become part of urine
Where does blood go first after being filtered by the glomerulus?
Proximal Convoluted Tubule
What section of the tubular system do we make the most adjustments?
Proximal Tubule
What is the renal corpuscle?
Glomerulus + Bowman's Capsule
What are the 3 layers of the glomerular membrane from capillary side --> out?
1. Innermost: Endothelial wall of glomercular caps
2. Basement membrane: acellular layer, small sheet of CT covering glomerular caps
3. Inner layer of bowman's capsule: composed of podocytes
What are podocytes?
Comprise the inner layer of bowman's capsule

-have long foot processes that wrap around the glomerular membranes and interdigitate
What are the 3 layers of the glomerular membrane designed to do?
Ensure NO plasma proteins and no cells can get filtered and end up in the urine
What is the fluid that is filtered in the capsule called?
Protein-free plasma (plasma free filtrate)
What can the presence of protein in the urine be an indicator for?
Hypertension
What are the forces involved in GLOMERULAR FILTRATION?
Like the Starling forces

1. Capillary blood pressure
2. Plasma Oncotic Pressure
3. Hydrostatic pressure (in bowman's capsule

**No oncotic pressure for bowman's capsule because proteins don't get through glomerular membrane
What kind of force is Capillary blood pressure in glomerular filtration?
-Pushing pressure that promotes glomerular FILTRATION
What kind of pressure is exerted by plasma oncotic pressure in glomerular filtration?
-osmotic pressure from the proteins in the plasma
-pulling pressure that opposes glomerular filtration
What does hydrostatic pressure do to glomerular filtration?
-Is the fluid in Bowman's capsule causes a pushing pressure fromt the capsule.

**opposes glomerular filtration**
Glomerular filtration is highly dependent on what force?
Capillary blood pressure
What value must the net filtration pressure be to have urine formation?
Must have a + number!
What does the Net filtration pressure depend on?
Capillary blood pressure
What is the glomerular filtration rate (GFR)?
mLs/min the kidneys are filtering and is an important measure of renal function
What does the GFR depend on?
1. Status of Net Filtration Pressure (determined by Capillary Blood Pressure)
2. SA available for filtration
3. Permeability of the glomerular membrane
What is glomerulonephritis? What can it lead to?
-active inflammation of the glomerular membrane
-can lead to glomerulosclerosis (scarring)
-Scar tissue reduces permeability, so GFR suffers
What 2 types of control are used in GFR regulation?
1. Autoregulation
2. Extrinsic control of the GFR
What is the overall purpose of autoregulation of the kidneys?
-Since our BP is fluctuating often, the kidneys use this method to prevent the normal BP fluctuations from affecting GFR
What response occur through autoregulation of the glomerulus if there is a drop in BP?
Drop in BP --> more blood flow through afferent arteriole --> rise in glomerulus BP --> rise in NFP--> rise in GRF

**Here, autoregulation kicks in and causes constriction of the afferent arteriole**
What happens in the glomerulus if the afferent arteriole is constricted?
What is this a response to?
-Get less blood in the glomerulus --> CBP drops down

*This would occur if the bodies BP were to rise**
Why would autoregulation kick in to dilate the afferent arteriole?
To prevent a drastic change in GFR in a response to a drop in systemic BP
How does autregulation sense and correct for a change in GFR?
-Through the JGA
What two types of cells are located in the JGA?
1. granular cells
2. Macula densa cells
What 2 functions do the cells of the JGA have?
1. sensory function
2. secretory function
What do the cells of the JGA sense?
Can sense pressure within their lumen
What is the job of the granular cells of the JGA?
Sense pressure within the afferent arteriole
The macula densa cells are responsible for what?
Sensing the rate of fluid flow through the distal tubule
Which cells are responsible for regulating the diameter of the afferent arteriole?
-Granular cells

-If there is a rise in GFR, they secrete a vasoconstricor
-A drop in GFR will result in a vasodilator
What is the tubuloglomerular feedback system?
The macula densa cells reinforce the message sent by the granualr cells.

-Is the mechanism behind GFR autoregulation!

-Constant monitoring of arteriole BP
-consequent adjustment of the afferent arteriole
Does the GFR stay stable during changes in BP?
Yes because of tubuloglomerular feedback system!
What entails extrinsic control of the GFR?
When the sympathetic NS intervenes and effects GFR
What is the goal of extrinsic control of GFR?
to OVERRIDE AUTOREGULATION!!!

-Alters GR in an attempt to control BLOOD VOLUME and therefore BP
Is there any parasympathetic innervation to the kidneys?
NO, the vagus nerve does not innervate the kidneys

-sympathetic input is either high or low
If sympathetic NS causes you to INCREASE GFR, what reaction will you feel in the body?
-Increase in urine output
-Peeing off volume
What affect does sympathetic STIMULATION have on the afferent arteriole?
constrict it!
-NE and E bind to alpha 1 adrenergic receptors on the afferent arteriole --> decreasing GFR
Where does the 80% of plasma, not filtered into the glomerulus, go?
-Into the peritubular capillaries and is subject to tubular secretion and tubular reabsorption
What process of tubular filtration is ALWAYS SELECTIVE?
Tubular REABSORPTION!
-can happen through passive or active transport
What 2 layers must substances cross in order to get reabsorbed into the peritubular capillaries?
1. Luminal membrane: faces the lumen of the tubule
2. Basolateral membrane: faces the interstitial space
What percentage of H2O, glucose, Na+ and K/Cl- that was filtered get reabsorbed?
Water: 99%
Glucose: 100%
Na+: 99.5%
K/Cl-: 50%
What does Na+ need to be reabsorbed?
Energy (actively reabsorbed)
Why is Na+ so draining and yet important in the kidney?
-89% of the energy requirements of the kidney is used in the transport of Na+
-But we COUPLE the transport of many substance to the movement of Na+
Na+ requires energy to get across what membrane?

Which membrane does it move passively over?
-Energy: basolateral membrane

-Passive: luminal membrane
Where is the largest portion of Na+ reabsorbed?
Proximal Tubule
What role does the reabsorption of Na play in the ASCENDING loop of Henle?
-Role in the kidney's ability to concentrate urine and conserve water
What controls the Na reabsorption in the distal tubule and the collecting duct?

What role does it play?
Hormonal control
-Plays a role in regulating the ECF volume, blood volume and BP
What is the only tubule that does not have Na Reabsorption?
The descending limb of the Loop of HENLE
What pump is used to get Na+ back to the bloodstream and where is it located?
Na/K ATPase pump

-clustered along the basolaterl membrane of the renal epithelial cells
What is Na+ job in the proximal convoluted tubule?
In the PCT, Na+ is DIRECTLY couple to the reabsorption of glucose, AA and water soluble vitamins
What type of transporters are along the luminal membrane of the PCT?
COTRANSPORTERS for glucose, AAs and water soluble vitamins.

-Couple with Na+
How do glucose, AAs and water soluble vitamins get across the basolateral membrane once Na has transported them into the tubule cell?
-They cross the membrane usually through facilitated diffusion by a protein carrier.
-Diffuse into the pertitubular capillaries
Why is there a LIMIT to how fast substances can be transported across the tubules?
Because it requires carriers
-at some point we could potetially saturate all the transporters
What is the Tubular Maximum?
-the maximal RATE of transport of a substance
What is the RENAL THRESHOLD? how is it different from the tubular maximum?
-Renal threshold: max plasma concentration (plasma concentration that pushes you to your tubular maximum)

-Tubular maximum: max RATE of reabsorption.
How much higher than the normal plasma concentration for glucose is needed for it to be seen in the urine?
3x
What happens to the renal threshold if the GFR decreases?
It increases: it takes a higher plasma concentration to get you to the tubular max
-Can occur in elderly due to age related decline in GFR
What does the degree to which Na is reabsorbed in the distal and collecting duct depend on?
-Varies on the body's contol of overall blood volume

-Under hormonal control
What does Na transport in the distal tubule and how?
Transports chloride
-uses cotransporter!
How does Na get into the collecting duct?
Crosses through a leak channel
What tubule is the only place where WATER is not reabsorbed?
the ascending loop of henle
What is the most important substance to be coupled with Na?
WATER!
How much water is reabsorbed in the proximal tubule and the descending loop of henle?
80%
What are the 2 mechanisms that water is reabsorbed?
1. Paracellular Route
2. Transcellular Route
What is the paracellular route of water reabsorption?
-Occurs between epithelial cells through leaky tight junctions (majority in the PCT)

-After Na is pumped across basolateral, it accumulates and creates a strong OSMOTIC gradient that allows for movement of water in between these epithelial cells
What is the transcellular route of water reabsorption?
-water moves THROUGH epithelial cells
-Requires aquaporins (always on the BASOLATERAL membranes on tubular epithelium cells)
What are luminal aquaporins?
-Present in the PCT and descending LofH
-Under hormonal (ADH) control in the
DT and CD
What hormone controls the luminal aquaporins in the DT and CD?
What is its function?
ADH!!!
-Regulates the extend of water reabsorption in these parts of the nephron
How and where does chloride reabsorption occur?
-in the -PCT

-After water leaves the tubule it concentrates everything left behind and creates a gradient for Cl, urea and Potassium to exit through tight junctions

-Cl is secondary to K
Where does the electrical gradient occur in the PCT?
In the lateral spaces where there is a high density of Na.

-Cl's movement through leaky tight junctions is promoted!
What substance in the PCT is both a byproduct and also used to create urine?
Urea
What % of urea do we reabsorb and what is its reabsorption connected to?
50%

-connected to the extent of Na-water reabsorption

(urea reabsorbed secondary to water)
What does it mean if a person has high BUN levels?
They may be dehydrated

-urea reabsorption follows H2O reabsorption
What dictates the reabsorption of K and where does it occur?
-in the PCT

-reabsorbed secondary to Na/water
Do the kidneys help control blood glucose levels?
NO, there is no homeostatic feedback loop that allow for an error of 300%
Do the kidneys help regulate the blood levels of Ca++ and Phosphate?
Yes!

-Renal threshold for Ca++ and phosphate reasorption is set to = the normal plasma concentration of these 2 substances
What does not get reabsorbed in the nephron?
Waste (endogenous or unanticipated *drugs)
What is tubular secretion?
The sending of substances to the tubules from the peritubular capillaries to be excreted in the urine
What type of transport is used in tubular secretion?
Almost always active and selective
Where does H+ secretion occur?
-PCT
-CD
-LofH
How does H+ get secreted?
-Comes from the blood first crosses the basolateral membrane through a proton pump

-Crosses luminal membrane (mechanism depends on the tubule)

--PCT: uses Na+/H+ antiporter (exchanger)
--DC and LofH: facilitated diffusion
What substance is both reabsorbed and secreted?
Potassium
Is potassium secretion regulated by the body?
Yes

-when potassium levels are low, secretion will drop.
What is the mechanism for K secretion?
The SAME as NA REABSORPTION!

-occur simultaneously
Where does K secretion occur?
DT and CD
What happens to K secretion if you enhance Na reabsorption?
K secretion is enhanced
Do we have K secretion everywhere Na is reabsorbed? Why or Why not?
No

-becuase the opportunity for K to cross the luminal memrane is ONLY at the DT and CD

-in the PCT and ascending, the K channels are on the basolateral membrane
What controls the coupling of Na and K?
Aldosterone
What is the function of Aldosterone?
It promotes the reabsorption of Na and the Loss of K!
What tubules does aldosterone act on?

What does it do there?
DT and CD

-Acts to reabsorb Na and secrete K
What 2 effects does aldosterone have?
1. immediate: Na reabsorption and K secretion

2. Long-term: stimulates DT and CD cells to increase production of ATPase pumps in basolateral membrane!!
What is Addison's Disease?
Adrenal cortical dysfunction

-Vulnerable to orthostatic hypotension b/c their Na levels are so low and they can't control their BP and blood volume
What are the 2 categories of organic compounds secreted in the nephron?
1. Organic Anions
2. Organic Cations
What are endogenous and exogenous compounds secreted from the nephron?
-metabolites of hormones or drugs
-food additives
-environmental pollutants
-recreational drugs
-organic compounds of WASTE
Where are Organic compound secreted?
in the PCT!!
What can be said about the transport mechanisms of organic compound secretion?
There are different mechanisms for cation and anions, but both are COUPLED to Na transport
What is the purpose of the secretory pathway?
-Allows for another opportunity for organic compounds (maybe ones bound to proteins) to be excreted as urine
-Increases the rate of substances' elimination.
What is the range of urine concentration that the kidney can possibly produce?
100mOsm - 1200mOsm
What is the isotonic concentration of urine?
300mOsm
What is the most dilute urine?
100mOsm
What is the smallest volume of urine produced by the kidneys?
0.3ml/mins
Do the kidneys ever stop producing urine?
Why or why not?
No
-called obligatory water loss to remove waste
Can dehydration become more and more severe?
Yes, due to obligatory water loss
What system allow us to produce variable concentrations of urine?
Medullary countercurrent system
Where is the greatest concentration of intersitital fluid located in the Renal Medulla?
Nearest to the renal pelvis
Name the 2 structures of the Medullary Countercurrent System
Superficial cortical nephrons and the Juxtamedullary Nephrons
In the MCCS, what is the function of the juxtamedullary nephrons?
Responsible for establishing for establishing and maintaining the medullary osmotic gradient
Which tubules use the gradient to create different concentrations of urine?
The DT and the CD
What is countercurrent multiplication?
The process by which the vertical osmotic gradient is established
What is permeable across the descending loop?
Permeable to water, NOT Na
What limb is permeable to Na?
Ascending ONLY, IT IS ACTIVELY PUMPED OUT!
What is the osmolarity of the urine as it enters the DT?
100mOsm
The presence of this hormone determines how much water is reabsorbed in the DT and CD.
ADH
What is the function of ADH?
Increases permeability of the DT and CD to water, but in a concentration dependent way
What is occuring in the CD and DT when ADH is nearly 0?
There is no water reabsorption in the DT and CD
What is the interstitial fluid concentration in the CORTEX?
Isotonic
What is the function of the Vasa Recta?
It prevents the medulla interstitial fluid from becoming isotonic.
What happens to the blood in the vasa recta as it moves along the limbs?
It actually gets concentrated and then diluted
What mechanism does ADH use to reabsorb water in the DT and CD?
Binds to receptors on basolateral side of DT and CO
-Stimulates the insertion of LUMINAL AQUAPORINS
-Once the water passes through the luminal aquaporins it then passes through basolateral aquaporins that are ALWAYS PRESENT!
Why do we want a system to control our plasma volume (2)?
1. For long term regulation of BP
2. To ensure that our cells don't swell or shrink because of an unfriendly ECF environment
What would happen to the cells if our ECF is hypertonic?
Pull water out of the cell: Shrinking
What are the first cells to be adversely effected by ECF concentration changes?
The cells of the CNS
What is the MAIN osmostic constituent in regulating ECF volume?
Na!
-Water follows Na
What is the main mechanism of Na gain?
Through ingestion
What are the two mechanisms of Na loss?
Renal and non-renal loss
What is the point of control for Na loss?
Renal loss
What are the 3 sensors for Na concentrations in the body?
Baroreceptors!
1. Aortic Arch
2. Carotid Sinus
3. RENAL BARORECEPTORS
Do our renal baroreceptors adapt?
NO
Where do the renal baroreceptors occur?
In the granualr cells of the Juxtaglomerular apparatus
What are the granular cells designed to monitor?
Stretch as a result of changes in BP
What type of regulation do the renal barorecptors use in the kidney?
Autoregulation of pressures
What action do the renal baroreceptors do when a decrease in plasma volume occurs?
Corresponds to a decrease in BP
-RBs will increase the release of Renin
What is the funciton of Renin?
Enzyme that converts Angiotensinogen to Angiotensin I.
What is the limiting reagent in the production of Angiotensin II?
Renin
What is the purpose of Angiotensin II?
It is our biologically active hormone that corrects for a drop in plasma volume
Why is Renin the limiting reagent for the production of Angtiotensin II?
Because its levels are under regulation and control by renal baroreceptors
What is Angiotensin II's action on the adrenal cortex?
Stimulates the release of Aldosterone
Describe the function of aldosterone
Acts on the DT and CD to enhave Na reabsorption and conserves water
What is an adverse effect of aldosterone?
It promotes the LOSS OF POTASSIUM
What ways does angiotensin II decrease GFR?
1. Vasoconstrict the renal and system blood vessels
2. Enhances the Tubuloglomerular feedback system
How does constriciton of the renal and system blood vessels increase BP?
They reduce GFR and prevent the loss of further plasma by reducing filtration rate
What is the Tubuloglomerular Feedback system?
A way to constrict the afferent arteriole
-Does it indirectly by enhancing autoregulation
-Makes the macula densa cells trigger at a lower threshold
Other than aldosterone release, how does A-II increase Na reabsorption?
Stimulate the Na-H exchangers in the PT, which increases Na reabsorption DIRECTLY!! Also enhaces H+ secretion at the same time!!
How does A-II act to increase water consumption?
Acts on the hypotalamus to increase the sensation of thirst
What 2 functions does the hypothalamus use to increase plasma volume?
1. Stimulates the sensation of thirst
2. Stimulates the release of ADH
What action do the aortic and carotid baroreceptors instantly take to a drop in BP?
They increase sympathetic activity
What are the 2 major effects of increased sympathetic response by the carotid and aortic baroreceptors?
1. Increases renal nerve activity to innervate the vasculature
2. Innervates the juxtaglomerular apparatus (incrases ganular cells to increase release of Renin)
How does ADH effect water and NA?
It increases water reabsorption but does not have an effect on Na
What are the ways that water is gained?
1. Consumed
2. liberated through metabolic processes
What are tehe 3 ways water is lost?
1. Urine (primary)
2. Feces (diarrhea)
3. Profuse sweatig
How does the brain detect plasma osmolarity?
Through Central Osmorespectors
What type of organs are central osmoreceptors?
Circumventricular organs
What are the 2 circumventricular organs that serve as the central osmoreceptors?
1. OVLT
2. SFO
When a rise in plasma omolarity occurs, what action in taken by OVLT and SFO?
they fire action potentials that project to the hypothalamus to tell it to relese ADH from Post Pit
What type of relationship is there between a change in plasma osmolarity and a change in ADH?
Linear relationship! 1% increase in plasma = 1% increase in ADH
What 2 areas of the hypothalamus do the axons of the OVLT and SFO project to?
Paraventricular Nucleus and the Supraoptic Nucleus
Describe the function of PVN and SON?
Continuously synthesize ADH and packages It into secretory vescicles that are stored in Post Pituitary
Once the sensation of the thirst is quenched, have we met our hydration needs?
No, barely half the amount is actually met
A person with liver disease has what [ADH]?
Increased, because the liver decreases the breakdown of ADH
What effect does pain, fear or trauma have on ADH?
Stimulation of release due to increased sympathetic activation
What effect does alcohol have on ADH?
decreases plasma [ADH] concentrations causing more dehydration
What is voluntary dehydration?
The cessation of the thirst before water needs are met by the body.