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
Why is creatinine not a perfect molecule to determine GFR?
It is freely filtered and not reabsorbed however a small amount is secreted into the nephron therefor its not a perfect molecule
However process for estimating creatinine in blood and urine can account for that to allow for GFR calculations
What is renal plasma flow?
If the total amount of a molecule entering the kidney equals the amount excreted then the renal clearance of this molecule equals renal plasma flow
What molecule can be used to measure renal plasma flow?
PAH (Para aminohippurate) is used as all PAH is removed from plasma and passes through they kidney through filtration and secretion
What is the filtration fraction?
The ratio of amount of plasma which is filtered and which arrives via the afferent arteriole is the filtration fraction
Its value ranges from 0.15- 0.2 where 0.15 indicates 15% of plasma has been filtered
How is filtration fraction calculated?
FF = GFR/ RPF
What are transport mechanisms in the renal tubules?
PASSIVE:
diffusion
osmosis
electrical gradient difference: charged ions can go to side of membrane with opposite charge
ACTIVE:
Primary active:
-2K+ in, 3 Na+ out using Na+-K+-ATPase pump
-endocytosis e.g. small proteins absorbed in PCT
Secondary active/ coupled transport:
-symport (same direction)- Na+ moves from high to low conc. gradient and creates energy to move glucose
-Antiport (opposite direction)- Na+ moves in along conc. gradient providing energy to move H+ out
What are transport pathways in the renal tubules?
- water moves from tubular fluid through aquaporin in apical membrane of tubule cell and out of aquaporin on basolateral membrane into blood
- Na+ moves from tubular fluid into tubule cell at apical membrane. At basolateral membrane 2K+ pumped in and 3 Na+ pumped out by Na+/K+/ATPase pump
How does sodium and bicarbonate reabsorption occur in the early proximal convoluted tubule?
In cell: H20 and CO2 react in a reversible reaction to form H+ and HCO3-
At apical membrane: Na+ transported into tubule cell and energy is used to pump H+ out into tubular fluid against its conc. gradient via Na+ - H+ - antiporter
At basolateral membrane: 3Na+ pumped out of cell into blood and 2K+ pumped in via Na+/K+/ATPase. Na+ is pumped out of cell providing energy to move 3HCO3- out of cell via Na+-HCO3- symporter
Angiotensin II regulates Na+ reabsorption by increasing Na+ - H+ antiporters
How does glucose reabsorption occur in the early proximal convoluted tubule?
At apical membrane: Na+ moves into cell providing energy to move in glucose via SGLT2 transporter
At basolateral membrane: 3Na+ moves out and 2K+ moves in. Glucose moves out via GLUT2 transporter
How does reabsorption occur at loop of Henle?
Thin descending limb: water passively moves out. Limb is impermeable to Na+ and Cl- so it can’t move out
Thin ascending limb: Limb is impermeable to water so it can’t move out. Na+ and Cl- move out passively
Thick ascending limb: Na+ and Cl- move out passively
At bottom of loop- hyperosmolar tubular fluid (very salty)
At loop of thick ascending limp- hypo-osmolar tubular fluid (low in salt)
How does reabsorption of Na and Cl- occur in the thick ascending limb?
At apical membrane: Na+, 2Cl- and K+ move in via Na+/K+/2Cl- symporter. K+ is moved out through recycling
At basolateral membrane: 3Na+ move out and 2K+ move in. K+ and Cl- move out via K+ - Cl- symporter. Cl- also passively passes out through membrane
How does reabsorption of Na+ and Cl- occur in early distal convoluted tubule?
At apical membrane: Na+ and Cl- move in via Na+ Cl- symporter. Impermeable to water
At basolateral membrane: 3Na+ move out and 2K+ move in via Na+/K+/ATPase pump. K+ and Cl- move out via K+ - Cl- symporter. Cl- passively moves out
How does reabsorption of Ca2+ occur in early distal convoluted tubule?
At apical membrane: Ca2+ passively enters cell. Impermeable to water
At basolateral membrane: 3Na+ move out and 2K+ move in via Na+/K+/ATPase pump. Na+ moves in and Ca2+ moves out via Na+ - Ca2+ antiporter. Ca2+ also moves out via Ca2+ ATPase pump
What 2 cells carry out reabsorption in the distal convoluted tubule and collecting duct?
Principle cell: Na+ reabsorption and K+ secretion
Intercalacted cell: Maintaining acid- base balance
How does reabsorption of Na+ and secretion of K+ take place on the DCT and collecting duct?
At apical membrane: Na+ passively moves in. K+ passively moves out. Water moves in through aquaporin
At basolateral membrane: 3Na+ move out and 2K+ move in via Na+/K+/ATPase pump. K+ passively moves out. Water moves out through aquaporin
Aldosterone regulates Na+ reabsorption by increasing apical Na+ channels and basolateral Na+- K+- ATPase pumps
ADH regulates water reabsorption by increasing aquaporins
How is acid-bace balance maintained in the DCT and collecting duct?
ALPHA INTERCALATED CELL:
At apical membrane: H+ moves out via H+ ATPase pump
Basolateral membrane: HCO3- moves out and Cl- moves in via Cl- HCO3- antiporter. Cl- also passively moves out
BETA INTERCALATED CELL:
At apical membrane: HCO3- moves out and Cl- moves in via Cl- HCO3- antiporter.
At basolateral membrane: H+ moves out via H+ ATPase pump. Cl- passively moves out
