(Lectures 16-17, Chapter 19) Urinary System Flashcards
Functions of the urinary system (6)
1) Detoxification: removal of metabolic and foreign waste
2) Regulation of Plasma Ion Consumption: regulates secretion of ions
3) Regulation of Plasma Osmolarity: adjusts rate of water excretion relative to plasma solutes
4) Regulation of Plasma Volume + Blood Pressure: controls rate of water excreted in urine, which directly affects BV/BP
5) Regulation of Plasma pH: controls [HCO3-] and [H+] in plasma
6) Endocrine Functions: secretion of erythropoietin and renin, activation of vitamin D3
What is the functional unit of the kidney? What is its main purpose?
Nephron; gets rid of unwanted substances in the blood plasma as blood passes through the kidneys
What is the outer tissue of the kidney called?
Cortex
What is the middle/inner layer of tissue in the kidney called?
Medulla
These channels collect urine and direct it out of the kidney.
Minor/major calyces
What happens once urine reaches the end of the major calyx?
- Enters renal pelvis
- Travels into the ureter, which leads into the bladder
Where is most plasma filtered in the nephron?
Glomerulus
What substance is generated when plasma is filtered in the glomerulus?
Filtrate
T/F: all of the material in the filterate ends up being part of the urine
False: some substances are reabsorbed into the bloodstream as tubular fluid (i.e. filterate) passes through the renal tubules
Renal Corpuscle
Part of the nephron; receives blood supply and generates filterate
The glomerulus is enclosed in the _____ ______
Bowman’s capsule
What is the first region to emerge from the renal corpuscle?
Proximal convoluted tubule (PCT)
What is the purpose of the loop of Henle/nephron loop?
Concentration of filterate
What part of the nephron follows after the loop of Henle?
Distal convoluted tubule (DCT)
Multiple DCTs join at the ______ ___, which sends the remaining filterate to the ____ ______, and the filterate enters the minor/major calyces in the kidney.
Collecting duct, renal papulla
Where are the most adjustments made to tubular fluid in the nephron?
PCT
T/F: once the tubular fluid enters the collecting duct, no more adjustments can be made to it (re: solute/water content)
True
Cortical Nephrons
- Account for ~80% of all nephrons
- located mostly in the cortex
- Regulate substances: water/nutrient retention, electrolyte balance, drug/waste elimination
Juxtamedullary Nephrons
- Account for ~20% of all nephrons
- Renal corpuscle is located in the cortex, very long loop of Henle is located in the medulla
- Same roles as cortical nephrons
- Long loop of Henle makes them important for water retention
Glomerular Capillaries
- Let fluid + solutes flow out of capillaries and into Bowman’s capsule
- high pressure
Peritubular Capillaries
- Let fluid + solutes flow from nephron tubes to capillaries (i.e. they join the venous return)
- low pressure
Vasa Recta
- Capillaries of JM nephrons in the medulla
- Blood flow is v. slow
What blood vessels enter and exit the glomerulus? What is their purpose?
Enter - Afferent Arterioles
Exit - Efferent Arterioles
Purpose is to regulate kidney function
Between afferent and efferent arterioles, which ones are larger? What does this size difference/structure create?
Afferent arterioles
Structure generates backflow, pressure
A group of crowded-together epithelial cells near the afferent/efferent arterioles form a _____ _____
macula densa
What are the smooth muscle cells of the afferent arteriole (located near the macula densa) called?
Juxtaglomerular cells
Juxtaglomerular cells + macula densa = ?
Juxtaglomerular Apparatus
Renal Functions (3)
1) Filtration of blood in the glomerulus; blood pressure forces water/solutes into the capsular space (across membranes of glomerular capillaries)
2) Reabsorption; water/solutes move from tubular fluid to peritubular fluid, across the tubular epithelium
3) Secretion; solutes move from peritubular fluid to tubular fluid
Once filtered, most substances are reabsorbed in the ___
PCT
Permeability of the loop of Henle
Desc. loop: permeable to/allows reabsorption of water
Asc. loop: permeable to/allows reabsorption of ions
Based on the ____ _____ ____, more adjustments are made to the tubular fluid in the DCT.
body’s specific needs
Do kidneys always work at 100% capacity?
No; it’s possible to live with only one kidney
Where is the filtration membrane located? How many layers does it have that plasma solutes must pass through? What are they called?
- Located in the renal corpuscle
- Has 3 layers
1) Glomerular Endothelium (fenestrated layer)
2) Basement Membrane of glomerular capillary
3) Filtration Slits, formed from the extensions of podocytes that cover the glomerular capillaries
Sufficient ____ is needed for glomerular filtration
pressure
What creates the main pressure into the glomerulus?
Afferent/efferent arterioles (i.e. regulation by arteriole size
What causes hydrostatic backpressure in the glomerulus?
Fluid in the renal tubules and Bowman’s capsule, including fluid that has already been filtered
What causes resistance pressure (aka colloid osmotic pressure) in the glomerulus? Is it good to for this to be elevated?
- Caused by proteins in the Bowman’s capsule
- No, it should be 0; there should be no proteins in the filterate in a healthy kidney
What causes pulling pressure (aka plasma colloid osmotic pressure) in the glomerulus? What does this pressure do?
- Caused by differences in solute concentration; it’s higher in blood plasma than in filterate
- pulls water out of filterate and into capillaries/bloodstream
The sum of all pressures acting on fluids in the glomerulus is:
Net filtration pressure
What substances are reabsorbed at the PCT? How is this accomplished?
> 99% of the glucose filtered at the glomerulus, amino acids, ions, organic nutrients; moved via transport proteins (active transport)
Water is reabsorbed via ______, which can also regulate the permeability of parts of the nephron to water.
aquaporins
How much of the initial fliterate reaches the DCT?
15-20%
Examples of reabsorption/secretion at the DCT (3)
- Na+ reabsorbed in exchange for K+
- H+ secreted in exchange for Na+; makes body fluid less acidic (i.e. increases pH)
- Secretion of toxins/drugs via carrier proteins
The permeability of these parts of the nephron to water can be regulated/changed.
DCT, collecting duct
What is the measure of the concentration of solutes in a solution (specifically in tubular fluid)?
Osmolarity (mOsm/L)
What happens if the kidneys don’t filter out enough water?
Blood volume + blood pressure increase
In which part of the loop of Henle does tubular fluid become more concentrated?
Desc. loop, as the reabsorption of water occurs here
How does tubular fluid become less concentrated in the asc. loop of Henle?
Ions pumps allow for reabsorption of ions
T/F: urine is concentrated (i.e. has a lot of solutes)
False; it’s dilute, with a typical osmolarity of 65 mOsm/L
Anti-Diuretic Hormone (ADH); examples of effects
Causes water retention by stimulating aquaporins to allow water to exit the DCT and collecting duct
More ADH = more water reabsorbed
High blood volume = low ADH = less water reabsorbed
Urine is concentrated by this process, which allows for the exchange of fluid and solutes:
Countercurrent Multiplication - exchange of solutes/water between vasa recta and interstitial fluid of renal medulla
Countercurrent = exchange between fluids moving in opposite directions Multiplication = effect increases as fluid moves through
Effects of Countercurrent Multiplication
- Creates concentration gradient in interstitial fluid of renal medulla
- Allows for production of highly-concentrated urine (removal of water required)
- Transport of ions from asc. loop to peritubular fluid drives osmosis of water out of the desc. loop (multiplication effect)
How does the vasa recta act as an ‘exchanger?’
Exchanges solutes and water between the interstitial fluid in the renal medulla and the blood; it surrounds the nephron loop in the renal medulla
What effects do blood volume and blood pressure have on urine concentration?
Low BV/BP = more water drawn out from tubular fluid = concentrated urine
High BV/BP = less water drawn out = dilute urine
Obligatory Water Reabsorption
Presence of aquaporins means that the rate of water reabsorption cannot be regulated; occurs in PCT, desc. loop of Henle
Facultative Water Reabsorption
- ADH-dependent, tightly-controlled water reabsorption; ADH must stimulate aquaporins
- Occurs in DCT, collecting duct
How does ADH stimulate aquaporins for facultative water reabsorption?
- Aquaporins are contained in vesicles; their release forms channels
- ADH controls aquaporin activity; stimulates the movement/integration of aquaporins to the membrane
Why is ADH ineffective in stimulating water reabsorption in the asc. loop of Henle?
There are no aquaporins
Glomerular Filtration Rate
- Amount of filterate formed per minute; measure of kidney function
- Determined with blood/urine tests
High levels of this breakdown product from muscles in the blood indicates a low GFR:
Creatinine
What could the presence of proteins in urine indicate?
Breakdown of filtration membranes, because proteins shouldn’t be in there!
What are some possible effects of a low GFR? (2)
- Low tubular fluid flow in nephron
- Reabsorption of unneeded materials
GFR regulation moderates these two things:
- Blood flow into the kidney
- Size of capillaries in the glomerulus (dilated capillaries = more surface area to filter things)
The juxtaglomerular apparatus has specialized cells. What are some of their functions? What does this allow for?
- sense Na+/NaCl levels
- release renin (hormone)
- contract
- allows for autoregulation of GFR
Why are the macula densa important for glomerular filtration?
They contain chemoreceptors that sense the NaCl content of the filterate
Granular/Juxtaglomerular Cells
- Enlarged smooth muscle cells in arteriole
- Act as mechanoreceptors; they sense BP in the afferent arteriole
- Contain secretory granules that contain renin
Mesangial Cells
- Pass signals between macula densa and granular cells
- Found between arteriole and tubular cells
- Interconnected by gap junctions
- Ensures unification of entire JGA in regulating GFR
Autoregulation of GFR
- Stimulus disrupts homeostasis, which decreases blood flow to the kidneys, which then decreases filtration pressure and results in decreased filtrate/urine production
- Contraction of mesangial cells + dilation of aff. arteriole + constriction of eff. arteriole = increased glomerular BP + restoration of homeostasis
Central Regulation of GFR - Endocrine Response
- Release of renin into the bloodstream increases systemic BP by working w/enzymes (e.g. increase in glomerular BP)
- Can cause hypertension, which would lead to overfiltration
What is aldosterone? What effects does it have?
- Release in central GFR regulation increases Na+ retention, which causes increased BP/BV and glomerular BP
Central Regulation of GFR - Neural Response
Activation of nervous effectors leads to increased BP/BV and increased glomerular BP
- Stimulation of thirst = more fluid consumption
- ADH production = fluid retention
- Sympathetic motor tone = constriction of systemic veins, increased cardiac output
T/F: urine must contain exact amounts of different substances
False; each component of normal urine falls within a range (e.g. pH, solute/water content, volume, osmolarity)
What are some abnormal (i.e. shouldn’t be there) components of urine?
- Proteins (e.g. albumin)
- Glucose
- Ketones
- Red blood cells
- Pus
What is renal failure?
Occurs when kidneys are no longer able to maintain homeostasis
What are some ways in which renal failure can affect the body (excluding the urinary system)?
- Toxin buildup due to reduced urine production (i.e. can’t get rid of waste)
- Ionic/fluid imbalances
- Increased BV/BP = issues with cardiovascular system
- Issues with CNS
How does chronic renal failure differ from acute renal failure?
Chronic = gradual deterioration of kidney function Acute = sudden deterioration of kidney function
Can chronic renal failure be reversed?
No; issues will accumulate over time, but the deterioration can be slowed down
How is chronic renal failure managed? How is this effective?
- Reduced water/salt/protein intake
- Less work for kidney, reduced chance of protein in urine due to faulty filtration membrane
Acidosis can occur due to chronic renal failure. What does this mean? What effects does this have? (Hint: doesn’t have to do w/urinary system!)
- Reduced blood pH (i.e. acidic blood)
- Linked to elevated respiratory function - faster breathing rate taxes respiratory muscles
Chronic renal failure is precipitated by….
Elevated (too much filterate) or decreased (not enough filterate) BP in the kidneys
What are some possible causes of acute renal failure?
- Exposure to toxic drugs
- Renal ischemia (inadequate blood supply)
- Urinary obstruction
- Trauma
- Allergic response to antibiotics or anaesthetics
T/F: at least some function can be recovered in cases of acute renal failure
True, if patients survive the initial incident that caused the renal failure. With proper treatment, the survival rate is ~50%
The first approach to treating renal failure is usually medication. What would be the goal of doing this?
Treating BP, water/Na+ retention
What is the basic premise of dialysis?
Passive diffusion across a selective-permeable membrane
What is hemodialysis?
- Regulation of blood composition using a machine and an artificial membrane that “replaces” the membrane around the glomerulus
- Pores in the artificial membrane allow for the diffusion of ions, nutrients, and organic waste out of the blood (i.e. takes over the kidney’s filtration function
T/F: for hemodialysis, the composition of the dialysis fluid is the same for every patient
False; solute concentrations are tailored for each patient
T/F: hemodialysis is an invasive process that must be done often
True; involves direct exchange of blood (drawn out of patient and into machine), usually done 3x per week, in 2-4hr sessions
How does peritoneal dialysis work?
- Peritoneal lining of lower abdomen is used as a membrane, and dialysis fluid enters the belly via a catheter
- Solution sits for several hours and exchange w/blood occurs across peritoneal membrane; solution is then drained out
How often does peritoneal dialysis occur for a patient? Is it an invasive procedure?
Occurs several times a day, or overnight
Noninvasive procedure
What is the time where dialysis solution sits in the abdomen called?
Dwell time
