The genitourinary system Flashcards
What is the function of the kidney?
Excretion of metabolic products e.g. urea, uric acid, creatinine
Excretion of foreign substances e.g. drugs
Homeostasis of body fluids, electrolytes and acid-base balance
Regulates blood pressure
Secretes hormones e.g. erythropoietin, renin
How does blood flow through the kidneys?
Renal artery -> segmental artery -> interlobar artery -> arcuate artery -> interlobular artery -> afferent arteriole -> glomerular capillaries -> efferent arteriol -> peritubular capillaries -> interlobular vein -> arcuate vein -> interlobar vein -> renal vein
What is the function of the peritubular capillary?
Provides O2 and nutrients to nephron
Helps in reabsorption of different substances
Helps in secretion of substances into intertubular fluid
What is the function of the detrusor muscle?
contracts to build pressure in the urinary bladder to support urination
What is the function of the trigone?
stretching of this triangular region to its limit signals the brain about the need for urination
What is the function of the internal sphincter?
involuntary control to prevent urination
What is the function of the external sphincter?
Voluntary control to prevent urination
What is the function of the bulbourethral gland?
produces thick lubricant which is added to watery semen to promote sperm survival
How does the superficial nephron compare to the juxtaglomerular nephron?
~10:1 ratio for superficial nephron to juxtaglomerular nephron
Juxtaglomerular nephron has a long loop of Henle that goes deep into inner medulla
Loop of Henle of superficial nephron only goes into outer medulla
Glomerulus of juxtaglomeluar nephron is deeper than glomerulus of superficial nephron
Juxtaglomerular nephron gives a striated appearance
What makes up the juxtaglomerular apparatus?
Macula densa (distal convoluted tubule) Extraglomerular mesangial cells Juxtaglomerular cells (afferent arteriole)
What is the function of the juxtaglomerular apparatus?
GFR regulation through tubulo-glomerular feedback mechanism
Renin secretion for regulating blood pressure
What is glomerular filtration?
Passive process: fluid is driven through semi-permeable glomerular capillaries into bowman’s capsule space by hydrostatic pressure of the heart
The filtration barrier is highly permeable to fluids and small solutes and is impermeable to cells and proteins
The capillary is fenestrated
Below the capillary is the glomerular basement membrane which is lined with negative charged proteins and prevents any negatively charged molecule passing through
Below the basement membrane are epithelial podocytes with gaps between them
What causes the movement of fluid through the glomerular capillaries?
Fluid exerts hydrostatic pressure which is a pushing force
Solutes exert an oncotic pressure which is a pulling force
How do you calculate net ultrafiltration pressure (Puf)?
HPgc= hydrostatic pressure in glomeluar capillaries
HPbw= hydrostatic pressure in bowman’s capsule
πgc= Oncotic pressure of plasma proteins in glomellular capillaries
Osmotic pressure in bowman’s capsule is negligible as large proteins/ cells can’t get through therefor force they exert is very small
Puf = HPgc- HPbw- πgc
What is glomerular filtration rate (GFR)?
The amount of fluid filtered from the glomeruli into the bowman’s capsule per unit time (mL/min)
GFR = Puf x Kf
Where Kf is ultrafiltration coefficient
Any changes in filtration force or Kf will result in GFR imbalances
In a healthy individual GFR is 90-140 mL in male and 80-125mL in female
Fall in GFR is a key feature of renal failure
Through what mechanisms is GFR regulated?
- Myogenic regulation
2. Tubulo-glomerular feedback mechanism
How does myogenic mechanism regulate GFR?
Arterial pressure increases Afferent arteriole stretches Arteriole contracts Vessel resistance increases Blood flow reduces GFR stays same
How does tubulo-glomerular feedback mechanism regulate GFR?
Increase/Decrease in GFR
Increases/Decrease in NaCl in loop of Henle
Change detected by macula densa
Increase/Decrease in ATP and adenosine discharge
Afferent arteriole constricts/ dilates
GFR stabilises
What is renal clearance?
Renal clearance is the number of litres of plasma that are completely cleared of the substance per unit time
Renal clearance is only concerned with excretory role played by the kidneys
How is renal clearance calculated?
C= UV/P mL/min U= conc. of substance in urine V= rate of urine production P= conc. of substance in plasma
C is the conc. of a substance that plasma has been cleared off per minute
Define freely filtered
If a molecule is freely filtered and neither reabsorbed nor secreted in the nephron then amount filtered equals amount excreted.
GFR can be measured by measuring renal clearance of a freely filtered molecule
What molecules can be used to measure GFR?
Insulin and creatinine
How is insulin measured to determine GFR?
Insulin is a plant polysaccharide, is freely filtered and neither reabsorbed or secreted, is not toxic and is measurable in urine and plasma.
Its the ideal molecule to measure GFR however it is not founding mammals so needs to be transfused
How is creatinine measured to determine GFR?
Creatinine is commonly used to determine GFR
Its a waste product from creatine 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
