Genitourinary System Flashcards
What are functions of the kidney? (5)
Excretion of metabolic products e.g urea, Uric acid, creatinine
Excretion of foreign substances eg drugs
Homeostasis of body fluids, electrolytes & acid-base balance
Regulates blood pressure
Secretes hormones eg erythropoietin, renin
Renal blood supply to kidneys:
Describe the flow of blood from the renal artery to the glomerular capillaries
Describe the flow of blood from the renal vein to the glomerular capillaries
Renal artery -> segmental artery -> interlobar artery -> arcuate artery -> interlobular artery -> afferent arteriole -> glomerular capillaries
Renal vein -> interlobar vein -> arcuate vein -> interlobular vein -> peritubular capillaries -> efferent arteriole -> glomerular capillaries
Bladder & urethra: anatomical diffs in males & females
What are the functions of:
Detrusor muscle
Trigone
Internal sphincter
External sphincter
Bulbourethral gland
Detrusor muscle - contracts to build pressure in the urinary bladder to support urination
Trigone - stretching of this triangular region to its limits signals the brain about the need for urination
Internal sphincter - involuntary control to prevent urination
External sphincter - voluntary control to prevent urination
Bulbourethral gland - produces thick lubricant which is added to watery semen to promote sperm survival
Which structures in the nephron are rich in mitochondria and which structures have a low density of mitochondria?
Epithelial cells Rich in mitochondria: Proximal convoluted tubule Distal convoluted tubule Thick ascending loop of henle Intercalating cells in the collecting duct
Low density mitochondria:
Thin ascending and descending loop of Henle
Principal cells of the collecting duct
What are the two types of nephrons and what are the differences between them?
Superficial nephron and juxtamedullary nephron
Juxtamedullary nephron has a longer loop of henle than superficial nephron
10:1 ratio for superficial to juxtamedullary nephron
What are the constituents of the juxtaglomerular apparatus?
What are the functions of the juxtaglomerular apparatus?
Constituents:
Macula densa (distal convoluted tubule)
Extraglomerular mesangial cells
Juxtaglomerular cells (afferent arteriole)
Functions:
GFR regulation through tubulo-glomerular feedback mechanism
Renin secretion for regulating blood pressure
Glomerular filtration
What type of process is glomerular filtration?
Where does fluid flow into from the glomerular capillaries?
What is the filtration barrier permeable and impermeable to?
What are the fenestrae?
What is the purpose of the slit diaphragm in the capillary endothelium?
Passive process - fluid is driven through the semipermeable glomerular capillaries into the bowmans capsule space by the hydrostatic pressure of the heart
The Filtration barrier (size and charge dependent) - highly permeable to fluids and small solutes. Impermeable to cells and proteins
Fenestra (space between capillary basement membrane)
Slit diaphragm - thin & porous, water & small solutes can pass
Glomerular filtration: participating pressures
Describe the two types of participating pressures involved in glomerular filtration and what substances exert which types of pressure and the effect of the pressures
Hydrostatic pressure:
‘Pushing’
Fluid exerts hydrostatic pressure on capillary walls
Solute & fluid molecules molecules shoved out
Oncotic pressure:
‘Pulling’
Solute (eg proteins) exerts this pressure
Fluid molecules drawn IN across a semipermeable membrane
How do you calculate net ultrafiltration pressure (Puf) ?
What do the following abbreviations stand for?
HPgc
HPbw
Pi (symbol)gc
HPgc = hydrostatic pressure in glomerular capillaries
HPbw = hydrostatic pressure in bowmans capsule
Pi gc = oncotic pressure of plasma proteins in glomerular capillaries
Puf = HPgc - HPbw - pi gc
Glomerular filtration: glomerular filtration rate (GFR)
What is GFR?
How do you calculate GFR?
What is Kf?
What leads to GFR imbalances?
What is the healthy GFR range for male & female adults?
What is a fall in GFR the cardinal feature of?
Glomerular filtration rate (GFR): the amount of fluid filtered from the glomeruli into the bowman’s capsule per unit time. Sum of filtration rate of all functioning nephrons.
GFR measured in - mL/min
GFR = Puf x Kf
Kf = ultrafiltration coefficient (membrane permeability and surface area available for filtration)
Any changes in filtration forces or Kf, will result in GFR imbalances
Healthy male adults GFR: 90-140 mL/min
Healthy female adults GFR: 80-125 mL/min
A fall in GFR is the cardinal feature of renal disease, w a build up of excretory products in the plasma
What is the myogenic mechanism of regulating GFR (to maintain the rate of GFR)?
Arterial pressure increases -> afferent arteriole stretches -> arteriole contracts -> vessel resistance rises -> blood flow reduces -> GFR stays same
What is the tubulo glomerular feedback mechanism to stabilise GFR?
Increase/decrease in GFR -> increased/decreased NaCl in loop of henle -> change detected by macula densa -> increased/decreased ATP & adenosine discharged -> afferent arteriole constricts/dilates -> GFR stabilises
Renal clearance:
What is renal clearance?
How do you calculate renal clearance?
Renal clearance = the number of litres of plasma that are completely cleared of the substance per unit time
Renal clearance is ONLY concerned w the excretory role played by the kidneys eg rate of removal of a substance X from the blood and excretion through urine
C = U x V / P mL/min
U = conc of substance in urine V = rate of urine production P = conc of substance in plasma
If C = 50 mL/min for a substance, this means 50 mL of plasma has been cleared of that substance per minute
Practical determination of GFR:
Why can you measure the GFR of a freely filtered molecule by measuring renal clearance of the molecule?
What is the ideal molecule for measuring GFR and why?
If a molecule is FREELY FILTERED and neither reabsorbed nor secreted in the nephron then the amount filtered equals amount excreted.
Hence, GFR can be measured by measuring renal clearance of this molecule
Ideal molecule to measure GFR: Inulin
Plant polysaccharide
Freely filtered and neither reabsorbed nor secreted
Not toxic
Measurable in urine and plasma
However not found in mammals so needs to be transfused
Practical determination of GFR:
What are the benefits and limitations to using creatinine to measure GFR?
Creatinine:
Waste product from creatinine in muscle metabolism
Amount of creatinine released is fairly constant
If renal function is stable, creatinine amount in urine is stable
Low creatinine clearance or high plasma creatine may indicate renal failure
Creatinine is freely filtered and not reabsorbed but a small amount is secreted into the nephron, therefore it’s not a perfect.
GFR calculations can take this into account
