Week 9- Genitourinary System Flashcards
On an average day what is salt and water consumption like?
More than we need so that excess must be excreted
What is the function of the kidney?
Excretion of metabolic products, foreign substances
Regulation of body fluids, electrolytes and acid base balance
Control of blood pressure
Secrete hormones
What is the function of the detrusor muscle?
Contracts to build up pressure in the bladder to support urination
What is the function of the trigone?
Stretching of this region to its limit signals to the brain about the need for urination
Describe the flow through a nephron
Glomerulus, bowmans capsule, proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting duct
At the proximal convoluted tubule where does water flow and why?
Out of the tubule because sodium and proteins are pumped out so water follows
What is special about primary and distal convoluted tubule epithelial cells?
They have a lot of mitochondria
What is special about ascending loop of henle epithelial cells?
They have few mitochondria
What are the 2 cell types in the collecting duct and how do they differ?
Principal cells- low mitochondrial density
Intercalated cells- rich in mitochondria
What are the 2 types of nephron?
Superficial and juxtamedullary
What type of nephron is more abundant and by how much?
Superficial- 10 times as many
What makes up the juxtaglomerular apparatus?
Macula densa (distal convoluted tubules) Extraglomerular mesangial cells Juxtaglomerular cells (afferent arterioles)
What is the function of the juxtaglomerular apparatus?
GFR regulation through tubulo-glomerular feedback mechanism
Renin secretion for regulating blood pressure
Is glomerular filtration active or passive?
Passive
How permeable are glomerular capillaries?
Semi permeable
Where does glomerular filtrate go through to?
Bowmans capsule
How is net ultrafiltration pressure calculated?
Hydrostatic pressure in glomerular capillaries - hydro pressure in bowmans capsule - oncotic pressure of plasma proteins in glomerular capsule
What is glomerular filtration rate (GFR)?
The amount of fluid filtered from the glomeruli into the Bowmans capsule per unit time
What is the unit for GFR?
mL/min
How is GFR calculated?
Sum of filtration rate of all functioning nephrons
Pressure of ultrafiltration x ultrafiltration coefficient (membrane permeability and surface area available for filtration)
Describe the myogenic mechanism of regulation of GFR?
Arterial pressure increases, afferent arteriole stretches, arteriole contracts, vessel resistance rises, blood flow reduces, GFR stays the same
What is renal clearance?
The number of litres of plasma that are completely cleared of substance per unit time
How is renal clearance calculated?
(conc of substance in urine x rate at which urine is produced)/ conc of substance in plasma
What are the units of renal clearance?
mL/min
why is liv such a legend?
who knows? theories are still being thought up- maybe it’s her biochemistry, the very molecules she is made from? more likely its the fact she is an anomaly and has the love of her one and only wifey xox
Describe renal blood supply through the kidney
renal artery segmental artery interlobar artery arcuate artery interlobular artery afferent arteriole glomerular capillary efferent arteriole peritubular capillary interlobular vein arcuate vein interlobar vein renal vein
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 a thick lubricant that mixes with watery semen to promote survival of sperm
How do the descending and ascending limbs of the loop of Henle differ?
Descending limb: water moves out, impermeable to sodium
Ascending limb: impermeable to water, sodium pumped out at the top
Describe osmolarity at the lowest point of the loop of Henle
High osmolarity (hyperosmolar), this can be adjusted to change the amount of water that is conserved
Describe osmolarity at the top of the loop of Henle
Iso-osmolar to blood plasma
What are the 4 main renal processes?
Glomerular filtration Secretion Reabsorption Excretion Different substances undergo a different combination of these processes
Why is glomerular filtration a passive process?
Because its driven by the hydrostatic pressure of the heart
Describe the glomerular basement membrane
It is around 70nm in diameter, permeable to water and small solutes but impermeable to cells and proteins
What 2 pressures influence glomerular filtration?
Hydrostatic (pushes fluid out) and oncotic (draws water in)
What is the average GFR for males?
90-140 mL/min
What is the average GFR for females?
80-125 mL/min
What is the main feature of renal failure?
A fall in GFR with a build of excretory products in the plasma
Describe the tubulo- glomerular feedback mechanism of regulation of the GFR
Increase/decrease in GFR
Increase/decrease in Nacl in loop of Henle
Change detected by macula densa
Increase/decrease in ATP or adenosine discharged
Afferent arteriole constricts/dilates
GFR stabilises
What are the 2 ways substances leave the kidneys?
Via excretion or to recirculate
Why can GFR be measured by measuring the renal clearance of a molecule?
If a molecule isn’t resorbed or secreted in the nephron, then the vol filtered is equal to the vol secreted so renal clearance displays GFR
What is the ideal molecule for measuring GFR and what are its limitations?
Inulin, it is freely filtered, not secreted, measurable in urine and plasma BUT not found in mammals so needs to be infused
What molecule is commonly used to measure GFR and what are its limitations?
Creatinine (a waste product from creatine in molecule metabolism) , amount released is fairly constant BUT a small amount is secreted in the nephron- this can be accounted for in calculations
What happens to creatinine clearance and plasma creatinine during renal failure?
Creatinine clearance is low
Plasma creatinine is high
What is filtration fraction?
The ratio of the amount of plasma which is filtered and the amount which arrives via the afferent arteriole
What is the usual filtration fraction?
0.15-0.20
What are the 3 passive transport mechanisms in renal tubules?
Diffusion, osmosis and electrical gradient difference
What are the 2 types of active transport mechanisms in renal tubules?
Primary active and secondary active/coupled transport (movement of one solute along its electrochemical gradient provides energy for the other solute to move against it)
What are the 2 types of primary active transport mechanisms in renal tubules?
Using a pump
Endocytosis eg small proteins in the PCT
What are the 2 types of secondary active transport mechanisms in renal tubules?
Symport (both move in the same direction across the membrane)
Antiport (both move in opposite directions across the membrane)
Describe how sodium and bicarbonate are resorbed in the proximal convoluted tubule
Water and co2 combine to form carbonic acid via carbonic anhydrase which dissociates
H+ ions move out of the cell via Na+/H+ antiporter so Na+ enters cell
Na+ and biacrb move out of cell into blood via symporter
Describe how glucose is resorbed in the proximal convoluted tubule
Na+ and glucose move into the cell via Na+-glucose symporter
Gluscose moves out of cell and into blood via glucose transporter
What hormone regulates Na+ resorption and how?
Angiotensin II, it increases Na+-H+ antiporters
What substances are resorbed in the proximal convoluted tubule?
Na+, Cl-, HCO3-, 100% glucose, water, amino acids, urea
What substances are secreted in the proximal convoluted tubule?
Drugs, ammonia, bile salts, prostaglandins, vitamins (folate and ascorbate)
What substances are resorbed in the loop of Henle?
Na+, Cl-, water
How are Na+ and Cl- resorbed in the ascending limb of the loop of Henle?
Na+, 2x Cl- and K+ move into the cell via symporter, Na+ then moves out into the blood via Na+/K+ ATPase pump and K+ and Cl- move out into the blood via symporter
How are Na+ and Cl- reabsorbed in the distal convoluted tubule?
They enter the cell via symporter, Na+ leaves and enters blood via Na+ K+ ATPase pump and Cl- moves into the blood via K+ Cl- symporter
How is Ca2+ actively resorbed in the early distal convoluted tubule?
Via Na+ Ca 2+ antiporter
Via Ca 2+ ATPase pump
How does aldosterone regulate Na+ reabsorbtion?
It increases apical Na+ channels and basolateral Na+/K+ ATPase pumps
How does ADH regulate water reabsorption?
It increases apical aquaporins
What cells are involved with maintaining the acid base balance and where are they found?
Intercalated cells (alpha and beta), they are found in the distal convoluted tubule
How do the 2 different intercalated cells maintain acid base balance?
Alpha intercalated cell- reabsorption of HCO3- and H+ secretion
Beta intercalated cell- H+ reabsorption and HCO3- secretion
How is renal clearance calculated?
(Urine conc of Y x Urine vol) / Plasma conc of Y
What is the difference between accuracy and precision?
Accuracy: being able to get to where you want
Precision: consistently being able to get where you want
What substance is almost completely secreted in the kidney?
PAH (para amino hippuric acid)
