The Genitourinary System (38) Flashcards
What are the functions of the kidney?
- excretion of useless metabolic products: urea, uric acid, creatinine
- excretion of foreign substances: drugs
- regulation of body fluids, electrolytes and acid-base balance
- control of blood pressure
- secretion of hormones: erythropoietin, renin
What is the structure of the kidney?
cortex- outer layer medulla- middle region renal artery- blood in renal vein- blood out ureter- urine out
What is the passage of blood into and out of the kidney?
renal artery–> segmental artery–> interlobar artery–> arcuate artery–> interlobular artery–> afferent arteriole–> glomerular capillaries–> efferent arteriole–> peritubular capillaries–> interlobular vein–> arcuate vein–> interlobar vein–> renal vein
What is the function of the detrusor muscle in the bladder?
contracts to build pressure in the urinary bladder to support urination
What is the function of the trigone in the bladder?
stretching of this triangular region to its limit signals the brain about the need for urination
What is the function of the internal sphincter in the bladder?
involuntary control to prevent urination
What is the function of the external sphincter in the bladder?
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
What is the structure of the nephron?
- glomerulus
- Bowman’s capsule
- proximal convoluted tubule
- loop of Henle
- distal convoluted tubule
- collecting duct
What is reabsorbed into the bloodstream at the proximal convoluted tubule?
Na+
Cl-
most solutes
water follows bc dec. osmolarity in tubule (higher w.p.)
What occurs at the loop of Henle?
- countercurrent flow
- pump salt out at the top of the thick, ascending loop
- salt gradient generated
- lots of mitochondria here in epithelial cells bc pumping activity
- water leaves at thin descending limb bc interstitial fluid = hyperosmolar (N.B. ascending limb impermeable to water)
- epithelial cells here have low density of mitochondria bc passive movement
What occurs at the distal convoluted tubule?
- impermeable to water
- salt pumped, so epithelial cells rich in mitochondria
What cells are rich in mitochondria at the collecting duct of the nephron?
intercalated cells, whereas principal cells have low mitochondrial
What are the 2 types of nephron?
- superficial/cortical nephron: glomeruli in outer portions of renal cortex, short loops of Henle
- juxtamedullary nephrons: glomeruli in juxtamedullary region of cortex, long loops extending down into medullary pyramids
- only 15% of human’s nephrons have long loops
What is the juxtaglomerular apparatus?
- between glomerulus and DISTAL convoluted tubule
- macula densa (distal convoluted tubule)
- extraglomerular mesangial cells
- juxtaglomerular cells (afferent arteriole)
What are the functions 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 the semipermeable glomerular capillaries into the Bowman’s 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
What features enable glomerular filtration?
- fenestrated endothelium of glomerular capillaries, surrounded by glomerular basement membrane
- podocytes w/ numerous pseudopodia that interdigitate to form filtration slits
What is hydrostatic pressure?
a force that compels a fluid to move out of a vessel
fluid exerts this pressure
What is oncotic pressure?
type of osmotic force exerted on fluids by presence of proteins in blood and tissues
What are the participating pressures involved in glomerular filtration?
- blood hydrostatic pressure exerted–> drives fluid into
- lower oncotic pressure from interstitial fluid bc no proteins vs. there are proteins in blood–> attempts to draw fluid molecules in
- HPgc drives fluid into primary urine
- HPbw works against this = -ve pressure
- πgc of plasma proteins in gc = -ve pressure
What is the equation for net ultrafiltration pressure (Puf)?
Puf= HPgc - HPbw - πgc
What is glomerular filtration rate?
- amount of fluid filtered from the glomeruli into the Bowman’s capsule per unit time (ml/min)
- sum of filtration rate of all functioning nephrons
- GFR= Puf X Kf ultrafiltration coefficient (membrane permeability and SA available for filtration)
What is a healthy GFR?
- 90-140ml/min in males
- 90-125ml/min in females
- a low GFR is the cardinal feature of renal disease–> buildup of excretory products in plasma
How do we regulate GFR?
- myogenic mechanism: arterial pressure inc.–> afferent arteriole stretches–> arteriole contracts to resist stretch–> vessel resistance rises–> blood flow reduces–> GFR stays the same
- tubulo-glomerular feedback mechanism: inc./dec. GFR–> inc./dec. NaCl in loop of Henle–> change detected by macula densa–> inc./dec. ATP and adenosine discharged–> afferent arteriole constricts/dilates–> GFR stabilises
What is renal clearance?
the number of litres of plasma that are completely cleared of the substance per unit time C= (U x V)/P ml/min U= conc. of substance in urine V= rate of urine production P= conc. of substance in plasma
What is the ideal molecule to use to practically determine GFR?
- ideal molecule: inulin
- plant polysaccharide
- freely filtered and neither reabsorbed nor secreted
- not toxic
- measurable in urine and plasma
N.B. not found in mammals, so needs to be infused
Why is creatinine commonly used to determine GFR?
- waste product from creatine in muscle metabolism, so amount of creatinine released= fairly constant (if muscle mass= constant)
- if renal function is stable–> creatinine amount in urine is stable bc freely filtered and not reabsorbed (BUT a small amount is secreted)
- high plasma creatinine/ low creatinine clearance may indicate renal failure
What substance do we use to measure renal plasma flow (RPF)?
PAH (para aminohippurate) bc all is removed from plasma passing through kidney by filtration and secretion
What is the filtration fraction (FF)?
the ratio of the amount of plasma which is filtered and which arrives via the afferent arteriole
- 0.15-0.20 (15/20% of plasma has been filtered)
- FF= GFR/RPF
What is 2y active/coupled transport?
- a type of active transport
- movement of 1 solute down its electrochemical gradient provides energy for the other solute to move against it
- symport e.g. Na+- glucose symporter
- antiport e.g. Na+- H+ antiporter
What is a paracellular pathway?
- transfer of substances across an epithelium by passing through the intercellular space BETWEEN cells (gap junctions)
- water moves like this, bringing ions w/ it e.g. Ca2+, K+,Cl-, urea etc…
What is a transcellular pathway?
- transfer of water THROUGH cells using aquaporins
- Na+/K+ ATPase transporter for transcellular Na+ reabsorption (bc 3 sodium out, 2 potassium in)–> leads to downhill movement of sodium coupled to other things
How are sodium and bicarbonate reabsorbed in the early proximal convoluted tubule?
carbonic anhydrase converts H+ and HCO3—> CO2+H20–> then back in cell–> H+ brings a sodium in w/ Na+ H+ antiporter–> Na+ and HCO3- move out into blood w/ symporter
What is 100% reabsorbed in the PCT?
glucose
How does angiotensin regulate Na+ reabsorption in the PCT?
increases the number of Na+- H+ antiporters
How is glucose reabsorbed in the early proximal convoluted tubule?
- Na+ - glucose symporter brings in sodium and glucose (bc low sodium in cell due to Na+/K+ ATPase pump)
- glucose then dissolves from cell through GLUT2 transporter into blood down gradient
How are Na+ and Cl- actively pumped/reabsorbed in the loop of Henle?
- at thick ascending limb (vs. passively moved in thin ascending limb)
- Na+ K+ 2Cl- symporter into cell and K+ Cl- symporter out into blood
- cations Na+, Ca2+ etc… reabsorbed by paracellular pathway
How are Na+ and Cl- reabsorbed in the early distal convoluted tubule?
- Na+ Cl- symporter (dependent on Na+/K+ ATPase pump) and K+ Cl- symporter out into blood
How is Ca2+ actively reabsorbed at the distal convoluted tubule?
- Na+ Ca2+ antiporter bring sodium into cell (bc Na+/K+ ATPase pump takes sodium out) and Ca2+ goes into blood
How does ADH regulate water reabsorption at the distal DCT and collecting duct?
causes aquaporins to move to membrane–> inc. water reabsorption
How does aldosterone increase sodium reabsorption at the collecting ducts?
increases apical Na+ channels and basolateral Na+K+ ATPase pumps
How doe we maintain acid-base balance in the collecting ducts?
- alpha intercalated cells: HCO3- reabsorption and H+ secretion
- beta intercalated cells: HCO3- secretion and H+ reabsorption
