The Genitourinary System Flashcards
What is the kidney?
On an average day, how much water and salt do we consume?
The central regulator of homeostasis
Take in more water and salt than we need as we do not know how much we will need in a given day (e.g. hot or cold day, amount of exercise, etc.). This means the excess must be excreted (e.g. as urea)
Out of Na+, K+, H2O and urea - which of these do not have a pump?
H2O and urea
What are the 5 main functions of the kidney?
Excretion of metabolic products - urea, uric acid, creatinine etc.
Excretion of foreign substances - drugs, etc.
Regulation of body fluids, electrolytes and acid-base balance
Control BP
Secrete hormones - erthropoietin, renin, etc.
What is the anatomical structure of the kidneys? Fill in the missing labels below:
Cortex = outer layer
Medullary region = inside the cortex
Renal artery = blood in
Renal vein = blood out
Ureter = urine out
What are the different blood vessels in the renal blood supply, starting from the renal artery, through the glomerular capillaries to the renal vein? Fill in the flow diagram below:
What is the function of the bladder and urethra? How do they work together and urine fills the bladder?
What are the functions of the: detrusor muscle, trigone, internal sphincter, external sphincter, bulbourethral gland and label them on the diagram below:
The kidney eventually produces urine, which travels down the ureter to the bladder
The bladder fills to a particular volume (around 200ml) - and then is detected by the detrusor muscle and trigonal region
Detrusor muscle = contracts to build pressure in the bladder to support urination
Trigone = stretching in this region signals to the brain for the need of urination
Internal sphincter = involuntary control to prevent urination
External sphincter = voluntary control to prevent urination
Bulbourethral gland = produces thick lubricant that is added to watery semen to promote sperm survival
What is the structure of a functional unit (nephron) in the kidney? Fill in the missing labels on the diagram below:
What is the function of the nephron at the start, during the PCT?
What are some key properties of the epithelial cells to support this function?
A level notes - look at picture
As solutes are pumped out of the filtrate / reabsorbed, the glomerular filtrate has a lower osmolarity, so water follows and moves out as well
Around the same amount of solute and water are reabsorbed
Many mitochondria - provides ATP for all the pumps (to pump out the solutes)
What is the function of the nephron for the Loop of Henle?
How are the epithelial cells of the loop of henle adapted to its functions?
Counter current system - a level notes
Again, epithelial cells contain many mitochondria in the thick ascending limb of the loop of henle to provide ATP for the pumping activity
Epithelial cells of the thin decending loop of henle = passive movement of water = low mitochondria density as less ATP is needed
What is the function of the nephron in the distal convoluted tubule (DCT) and collecting duct (CD)?
How can the amount of water reabsorption be varied in the DCT / CD?
Put in A level notes
Vary water reabsorption in the CD via vasopressin and aquaporins - it also changes the osmolarity surrounding the loop of Henle affecting the concentration gradient for reabsorption of water
What are the properties of the cells found in the DCT and CD?
What are the 2 cell types in the CD and their properties?
Epithelial cells of the DCT = rich in mitochondria
Principal cells = low mitohondrial density; Intercalated cells = rich in mitochondria
What are the 2 types of nephron?
What are the 3 depths of the nephron?
Which is more abundant that the other?
- Superfiial nephron; 2. Juxtamedullary nephron
- Cortex; 2. Outer medulla; 3. Inner medulla
10: 1 ratio for superficial to juxtamedullary
Why is the cortex of the kidney granular looking, whereas the medulla of the kidney is striated looking?
Where is the glomerulus found in comparison to the rest of the nephron?
All the glomerulae are found in the cortex (not organised into a pattern); all the Loops of Henle are found in the medulla
Almost always found near the early DCT
What does GFR stand for? How is GFR regulated?
What is the juxtaglomerular apparatus? What is its function?
What are the 3 types of cells found in the juxtaglomerular apparatus?
Glomerular filtration rate - regulated by controlling how much liquid is coming into the glomerulus and renin production
It is located next to the glomerulus, between the afferent arteriole and the distal convoluted tubule of the same nephron. It is responsible for regulating GFR
- Macula densa (found in the DCT) = regulates GFR through the tubulo-glomerular feedback mechanism; 2. extraglomerular mesangial cells; 3. juxtaglomerular cells = produce renin to regulate BP
How does glomerular filtration work?
What are the different processes that can occur within the nephron?
Put in A level notes (basement membrane, podocytes etc.) - A passive process where fluid is driven through the glomerular capillaries into the Bowman’s capsule due to the hydrostatic pressure of the heart, which pushes small enough molecules through the semipermable membrane of the glomerular capillaries. It is impermeable to cells and proteins
Glomerular filtration, reabsorption, secretion, excretion - different substances undergo these processes in different amounts
What is meant by the terms hydrostatic and oncotic pressures?
How do these 2 pressures interact in the glomerulus?
In the glomerulus:
Hydrostatic pressure = fluid exerts this pressure (pressure comes from BP / heart contracting) so solutes and fluid are pushed out into the glomerular filtrate
Oncotic pressure = cells and protein are left behind in the glomerulus, creating an osmotic gradient, drawing the fluid back across the semi-permeable membrane
What is HPgc?
What is HPbw?
What is πgc?
So what is the equation to calculate Puf (filtration pressure)?
HPgc = hydrostatic pressure in the glomerular capillaries - drives fluid into the glomerular filtrate
HPbw = hydrostatic pressure in the bowman’s capsule - pulls fluid back into the glomerulus (HPgc works against this)
πgc = oncotic pressure of plasma proteins in the glomerular capillaries - pulls fluid back into the glomerulus
Puf = HPgc - HPbw - πgc
What is GFR?
How is GFR calculated?
Amount of fluid filtered from all the glomeruli into the bowman’s capsule in the kidneys per unit time (mL/min) - sum of filtration rate of all functioning nephrons
GFR = Puf x Kf
Where Puf = filtration pressure, and Kf = ultrafiltration co-efficient taking into account membrane permeability and surface area available for filtration
What are the 3 main factors that can be altered to affect / change GFR?
What are healthy GFRs in males and females respectively?
What occurs with GFR in renal disease?
Change in surface area, permeability or pressure
Males = 90-140mL/min; Females = 80-125mL/min
GFR falls - things that should be excreted via the kidneys remain in the plasma and build up over time
What are the names of the 2 mechanisms to regulate GFR?
- Myogenic mechanism
- Tubulo-glomerular mechanism
What is the myogenic mechanism to regulate GFR?
- Arterial pressure increases - this may be due to exercise, an adrenaline rush, etc. This in turn will increase the hydrostatic pressure of glomerulus (HPgc), increasing GFR
- Afferent arteriole stretches
- Afferent arteriole contracts - this is to resist the force of stretching due to the increased BP
- Vessel resistance increases - as the diameter of the arteriole decreases
- Blood flow reduces
- GFR returns to normal
What is the tubulo-glomerular feedback mechanism to regulate GFR?
- Increase / decrease in GFR
- Increase / decrease in salt absorption in the Loop of Henle - due to increase / decrease in GFR respectively
- Change in salt absorption is detected by the macula densa cells - due to change in their intracellular osmolarity, which changes their size
- increase / decrease in ATP and adenosine discharge
- The discharge of those molecules causes the afferent arteriole to constrict / dilate respectively
- GFR stabilises
After a certain point - results in renin prduction and secretion, leading to angiotension II production (for further arteriole constriction) - to try and retain water
What is meant by the term ‘renal clearance’?
Why is this important?
What is the equation to determine clearance rate?
The volume of plasma that is completely cleared of of the substance per unit of time e.g. 0.05L of plasma is completely cleared of urea per minute
This concept can be used to: 1. calculate GFR, 2. calculate renal plasma flow (RPF), 3. understand the excretory route of a substance (filtration, secretion, reabsorption, etc.)
Label on the diagram below all the different rates:
Rate in = ?
OE = out for excretion
OR = out for recirculation
Rate in = rate out
Rate in = OE + OR
Rate in = RPF (renal plasma flow rate) = OE + OR = rate out
GFR = OE (if the substance is freely filtered, and there is no secretion or reabsorption)
RPF = OE (if this substance is completely secreted, and not reabsorbed)
What are theideal properties of a molecule to practically measure GFR?
Which is the ideal molecule that could be used to practically measure GFR?
What is the common molecule used practically to measure GFR?
Ideal properties = measure a freely filtered molecule in the urine that is neither secreted nor reabsorbed in the kidneys (as GFR = OE). So GFR can be measured by measuring renal clearance of this molecule
Ideal = inulin
Common = creatinine
What is good about using creatinine clinically? What are some issues with creatinine?
Why is creatinine concentration unchanged between the afferent and efferent arterioles?
Creatinine does not need to be infused, muscles are continuously producing it - large volumes of urine can be collected over long periods of time. However, muscle wasteage raises creatinine levels and a small amount of creatinine is secreted in the nephron
Because it it freely filtered
What is RPF?
What is PAH? How does PAH pass through the kidneys?
How and why can RPF be calculated using RAF?
Renal plasma flow (RPF) rate - volume of plasma delivered to the kidneys per unit time
Para aminohippurate (PAH) - all the PAH is removed from the plasma passing through the kidneys through filtration and secretion
Because all of the PAH that enters the kidney is excreted, so the renal clearance of PAH must equal RPF
What is FF?
What is the equation to calculate FF?
What is considered a normal FF?
Filtration fraction (FF) - usually calculated as a percentage and represents the proportion of the fluid reaching the kidneys that passes into the renal tubules
FF = [GFR] / [RPF] x 100
Between 15 - 20%
What are the 2 types of transport mechanisms?
What are the 3 different types of passive transport?
What are the 2 different types of active transport and their subtypes?
Why might some people argue diffusion down the electrochemical gradient is secondary active rather than passive?
- Passive transport, 2. Active transport
Passive = diffusion, osmosis, electrochemical gradient
Active: primary = pumps, endocytosis; secondary = movement of one solute along its electrochemical gradient provides energy for the movement of another solute against the oncentration gradient - symport (bring something else with it), antiport (pump something out in the opposite direction)
Electrochemical gradient only exists due to pumps creating that different in electrical potential
What are the passive transport mechanisms in the renal tubules?
What are the active transport mechanisms in the renal tubules?
All 3 passive mechanisms take place in the nephrons
Both, primary and secondary active mechanisms are in the nephrons. Na+ /K+ ATPase pump = lowers Na+ concentration in the cell, so Na+ moves down the concentration gradient, the movement can be used to bring something else in / pump something else out
What is the paracellular pathway? Which molecule often uses this pathway?
What is transcellular reabsorption? How does water use this pathway? How does Na+ use this pathway?
Substances, other than travelling through cells, also go between cells, known as the paracellular pathway. Often water uses the path, and with it other solutes also use this pathway
Transcellular = through the cell. As the membrane is made of lipids, water requires a protein channel (e.g. aquaporin) to travel through cells. Most of the Na+ reabsorption requires Na+/K+ ATPase
In which part of the nephron is most of the substances reabsorbed?
What substances are reabsorbed in the early PCT?
What substances are secreted in the early PCT?
PCT - around 70%, including water as it follows the substances via osmosis
Reabsorbed = 67% Na+, 67% Cl-, 90% HCO3-, 100% glucose, 67% water, 100% amino acids, 50% urea
Secreted = drugs, ammonia, bile salts, prostaglandins, vitamins (folate and ascorbate)
How is the Na+ and HCO3- reabsorbed in the PCT?
How does angiotensin II regulate Na+ reabsorption?
Carbonic anhydrase is present in the tutbular fluid - it converts H+ and HCO3- into H2O and CO2 so CO2 can diffuse into the cells
Inside the cells carbonic anhydrase then coverts back the H2O and CO2 into H+ and HCO3-. The H+ is then exhcanged for an Na+ molecule via an antiportar, so H+ exits the cell whilst Na+ enters it
To prevent HCO3- build up, it is goes through a symporter where both, Na+ and HCO3- leave the cell
Increasing the number of Na+/H+ antiportars
How does angiotensin II work on the PCT when Na+ levels are low / blood volume is low?
How is glucose reabsorbed in the early PCT?
When there is low Na+ levels in the blood, or low blood volume, renin is secreted. This causes angiotensin II secretion, which increases the number of antiportars, so more Na+ is pumped out into the tubular fluid and water follows. This causes greater Na+ and water reuptake
Glucose reabsorption dependent on the Na+/glucose symporter. Na+ is pumped out of the other side of the cell into the blood, causing Na+ to move down the electrochemical gradient from the tutbular fluid into the cell, bringing with it a glucose molecule. As the glucose concentration in the cell is higher than in the blood, it diffuses through a glucose transporter (GLUT 2)
What are the substances reabsorbed in the Loop of Henle?
How does salt and water reabsorption take place in the Loop of Henle?
How does the fluid change from the descending to the ascending limb?
Reabosorbed = 25% Na+, 25% Cl-. 15% H2O
Descending limb = impermeable to NaCl, permeable to water
Ascending limb = impermeable to water, permeable to NaCl
Put in A level notes on the counter current system
More salts are reabsorbed than water, so the fluid coming in down the descending limb is hyper-osmolar, and the fluid going out of the ascending limb is hypo-osmolar
What are the different pumps involved in the Loop of Henle?
In the thick ascending limb there is Na+ and Cl- reabsorption
Na+/K+ ATPase pump exchanges one Na+ out of the cell for one K+ entering the cell
There is also an Na+/K+/Cl- symporter, than brings in those salts into the cell
The K+ and Cl- go travel through a symporter into the blood, down the electrochemical gradient
There is also a paracellular pathway for the cations
What substances are reabsorbed in the early DCT?
What are the different transporters / pumps involved in the early DCT?
Reabsorbed = Na+, Cl-, Ca2+
For Na+ and Cl- reabsorption, the Na+/K+ ATPase pump pushes out one Na+ into the blood and brings in one K+ into the cell. Na+ and Cl- enter the cell from the tubular fluid via the Na+/Cl- symporter. The K+/Cl- symporter then pushes out a K+ and Cl- into the blood
Active calcium reabsorption occurs using the Na+/K+ ATPase pump that pushes out an Na+ into the blood and brings in one K+ into the cell. Na+ and Ca2+ enter the cell from the tubular fluid via the Na+/Ca2+symporter. Then via an Na+/Ca2+antiporter, the Ca2+ exits the cell into the blood, and an Na+ enters
The distal DCT and CD contain which 2 types of cells? What are their functions?
Principal cell = Na+ reabsorption, H2O reabsorption, K+ secretion
Intercalacted cell = maintains acid base balance
What substances are reabsorbed in the distal DCT and CD? What substances are secreted in the DCT and CD?
What are the different transporters / pumps involved?
Reabsorbed = Na+, water, HCO3-, and H+; Secreted = HCO3-, and H+
Na+ and water are reabsorbed as the Na+/K+ ATPase pump pushes out one Na+ into the blood and brings in one K+ into the cell. This lowers the concentration of Na+ in cell, so Na+ moves into the cell from the tutbular fluid, and K+ moves into the tubular fluid as there is a higher concetraion of K+ inside the cell than in the tutbular fluid. Water follows behind the Na+, travelling from the tubular fluids through aquaporins into the cell, and through more aquaporins into the blood
What is the primary hormone that regulates Na+ reabsorption and what is the primary hormone that regulates H2O reabsorption? And how?
Aldosterone - regulates Na+ reabsorption by changing the number of Na+ channels and Na+/K+ ATPase pumps
ADH - regulates water by altering the number of aquaporins
How is the acid base balance maintained in the DCT?
What is the difference between an alpha-intercalated cell and a beta-intercalated cell?
Using a proton (H+) pump and a Cl- antiporter
Alpha = HCO3- reabsorption, H+ secretion
Beta = HCO3- secretion, H+ reabsorption
