The Genitourinary System Flashcards
What is the kidney?
Why do we need it?
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
We have evolved acutally pumps for the ions
What are the 5 main functions of the kidney?
Excretion of metabolic products - urea, uric acid, creatinine
Excretion of foreign substances - drugs
Regulation of body fluids, electrolytes and acid-base balance
Control BP
Secrete hormones - erthropoietin, renin
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:
Describe the order of blood flow in the kidney
Renal artery
Segemental artery
Interlobar artery
Arcuate artery
Interlobular arterty
Afferent areteriole
Glomerular capillaries
Efferent arteriole
Peritubular capilaries
Interlobular vein
Arcuate vein
Interloar vein
Renal vein
What is the function of the bladder and urethra? How do they work together and urine fills the bladder?
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
What are the functions of the:
detrusor muscle
trigone
internal sphincter
external sphincter
bulbourethral gland
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?
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
What are some key properties of the epithelial cells to support this function?
Many mitochondria - provides ATP for all the pumps (to pump out the solutes)
Drives Na/K ATPase
What is the function of the Loop of Henle?
Counter current system
Pump salt out at the top (thick ascending limb)
Generates salt gradient
Water comes out on thin descending limb (passive)
How are the epithelial cells of the loop of henle adapted to its functions?
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
How can the amount of water reabsorption be varied in the DCT / CD?
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?
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
What are the 3 types of cells found in the juxtaglomerular apparatus?
- Macula densa (found in the DCT) = regulates GFR through the tubulo-glomerular feedback mechanism;
- extraglomerular mesangial cells;
- juxtaglomerular cells = produce renin to regulate BP
How does glomerular filtration work?
What are the different processes that can occur within the nephron?
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
Endothelium wiht fenstrations
Basement membrane
Podocytes with slits
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 stays the same
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’?
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
What can renal clearance be used to calculate?
This concept can be used to:
- calculate GFR
- calculate renal plasma flow (RPF)
- 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 the ideal 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 passive transport mechanisms in the renal tubules?
What are the active transport mechanisms in the renal tubules?
Diffusion
Osmosis
Electrical gradient difference
What are the active transport mechanisms used in renal tubules?
Primary active
Secondary active/ coupled transport
Na conc used to drive other things- energy used from moving Na down a conc gradient to move other substances
- Symport
- Antiport
How does reabsorption take place in the early proximal convoluted tubule?
Requires the enzyme carbonic anhydrase
Proton from bicarbonate can be transported out by bringing a sodium in via a antiporter
Bicarbonate-sodium symporter also used
In which part of the nephron is most of the substances reabsorbed?
What is the Na and HCO3 reabsorption in the PCT?
PCT - around 70%
67% Na+, 67% Cl-, 90% HCO3-, 100% Glucose, 67% Water, 100% amino acids, 50% urea
How does angiotensin II work on the PCT?
Increases the number of Na/H antiporters
Increases sodium reabsorption
Inreases blood pressure
What is reabsorbed in the Loop of Henle?
25% Na+, 25% Cl-, 15% Water
What is reabsopred in the early distal convuluted tubule?
Na+
Cl-
Ca2+
What is reabsorped in the distal convuluted tubule and collecting duct?
Na+
Maintains acid-base balance
Which hormones act on the DCT and CD?
- Aldosterone regulates Na+ reabsorption by increasing apical Na+ channels & basolateral Na+ - K+ - ATPase pumps.
- Anti-Diuretic Hormone regulates water reabsorption by increasing apical aquaporins.
Which cells are responsible for maintaing the acid-base balance?
⍺-Intercalated cell: HCO3- reabsorption & H+ secretion.
β-Intercalated cell: HCO3- secretion & H+ reabsorption.
