The Genitourinary System Flashcards
What are the functions of the kidney? (5)
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
What is the anatomical structure of the kidney?
Renal artery
Renal vein
Ureter
Medulla
Minor calyx
major calyx
Cortex
What does the ureter do?
connects kidney to bladder
What is the basic role of erythropoietin?
RBC production
What are the 3 functions of the peritubular capillaries?
- reabsorption
- secretion
- providing O2 and nutrients to nephron so it can do its job
What are the peritubular capillaries?
network surroudnign the nephron
What is a schematic of the renal blood supply to the kidneys?
(entering blood)
renal artery
segmental artery
interlobar artery
arcuate artery
interlobular artery
(reaches nephron)
afferent arteriole
glomerular capillaries
efferent arteriole
peritubular capillaries
(leaving blood)
interlobular vein
arcuate vein
interlobar vein
renal vein
What at the anatomical parts of the bladder and urethra?
Detrusor muscle
Trigone
Internal sphincter
External sphincter
Bulbourethral gland
What at the anatomical parts of the bladder and urethra?
Detrusor muscle
Trigone
Internal sphincter
External sphincter
Bulbourethral gland
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?
I I
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.
What can lead to urinary incontinence?
weakening of sphincters
What are the structures in the nephron?
Glomerulus
Bowman’s capsule
Thin descending and thin ascending loop of Henle
Thick ascending loop of henle
Proximal convoluted tubule
Distal convoluted tubule
Collecting duct
What is the mitochondrial distribution in the nephron?
PCT= epithelial cells are RICH in mitochondria (lot of transport, e.g., 100% glucose reabsorbed)
Thin descending and ascending LOH= low density (due to passive reabsorption)
Thick ascending LOH= epithelial cells are RICH in mitochondria (active reabsorption)
DCT= RICH in mitochondria (salt modulation)
Collecting duct=
- Principal cells have low density
- Intercalated cells are RICH in mitochondria
What are the types of nephron?
superficial and juxtamedullary
What is the difference between superficial and juxtamedullary nephrons?
Superficial=
- LOH is shorter
- only crosses the cortex and outer medulla
- much more abundant (10:1 ratio)
Juxtamedullary=
- LOH is longer
- crosses cortex, outer and inner medulla
Why is the medulla striated?
LOH stretches into medulla
What are the constituents of the juxtaglomerular apparatus?
Macula Densa (DCT)
Extraglomerular mesangial cells
Juxtaglomerular cells (afferent arteriole)
What is the function of the macula densa?
GFR regulation through tubulo-glomerular feedback mechanism
What is the function of the juxtaglomerular cells?
renin secretion for regulation blood pressure
Where is the macula densa, juxtaglomerular cells, and extraglomerular mesangial cells?
Where is the macula densa on this diagram?
What are the different possible renal processes and what is their direction?
Glomerular filtration
Reabsorption (back into blood)
Secretion (into nephron)
Excretion
Are all substances limited to one renal process?
Different substances undergo a different combination of these renal processes.
- dependent on needs of the body as well
How is fluid driven into the bowman’s capsule?
It’s a passive process
Fluid is ‘driven’ through the semipermeable glomerular capillaries into the Bowman’s capsule space by the hydrostatic pressure of the heart.
What is the filtration barrier?
size and charge dependent
Highly permeable to fluids and small solutes. Impermeable to cells and proteins.
What is the filtration barrier made of?
1) fenestra
2) Glomerular basement membrane
3) slit diaphragm
What is the fenestra?
70 nm diameter, water, ions and small proteins can pass
(On capillary lumen with a capillary endothelium)
What is the glomerular basement membrane?
Lined with negatively charged proteins, so negatively charged proteins can’t pass through
What is the slit diaphragm?
Thin, porous and small solutes can pass
Has slits
cell-cell junction of epithelial PODOCYTES
What are the pressures action on the glomerular filtration?
Hydrostatic pressure: pushing
- Fluid exerts this pressure
- Solute and fluid molecules shoved out
Oncotic pressure: pulling
- Solute (e.g., proteins) exerts this pressure
- Fluid molecules drawn in across a semipermeable membrane (osmosis)
What is the net ultrafiltration pressure?
(Puf)
HPgc= hydrostatic pressure in glomerular capillaries
HPbw= Hydrostatic pressure in bowman’s capsule
(pi)gc= oncotic pressure of plasma proteins in glomerular capillaries
Oncotic pressure in glomerular capillaries is so small it’s negligible
Puf= HPgc - HPbw - (pi)gc
what is the GFR?
glomerular filtration rate
It is the 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
How do you calculate GFR?
GFR= Puf x Kf
What is kf?
ultrafiltration coefficient (membrane permeability and surface area available for filtration)
What can result in GFR imbalances?
any changes in filtration forces or Kf
e.g., inflammation, infection, tumour causes changes in membrane permeability and surface area so Kf changes)
What is a normal GFR for male and females?
For healthy male & female adults, the GFR can be between 90-140 mL/min & 80-125 mL/min respectively.
What is a fall in GFR a cardinal feature of?
A fall in GFR is the cardinal feature of renal disease, with a build up of excretory products in the plasma.
What are the mechanism to regulate GFR?
Myogenic mechanism
Tubulo-glomerular feedback
How does the myogenic mechanism work?
- Arterial pressure increases
- afferent arteriole stretches
- arteriole contracts
- vessel resistance rises
- blood flow reduces
- GFR stays the same
How does the tubulo-glomerular feedback mechanism work?
- increase/ decrease in GFR
- increase/ decrease NaCL LOH
- change detected by macula densa
- increased/ decreased ATP and adenosine discharged
- afferent arteriole constricts/ dilates
- GFR stabilizes
What is renal clearance?
Renal clearance is the number of litres of plasma that are completely cleared of the substance per unit time.
What is renal clearance only concerned about?
Renal clearance is only concerned with the excretory role played by the kidneys, i.e., rate of removal of a substance X from the blood and excretion through urine.
- this is why it can be used in calculations with GFR and RPF
What does renal clearance help with, using GFR and RPF?
understanding the excretory of a substance (only filtered or a combination of filtered and secretion)
What is RPF?
renal plasma flow
- the volume of blood plasma passing through the kidneys per minute
How do you calculate the amount of plasma that has been cleared of a substance per minute?
e.g., If C = 50 mL/min for a substance, this means 50mL of plasma has been cleared of that substance per minute.
What concept does the practical determination of GFR need?
concept of renal clearance to calculate GFR
What type of molecule needs to be used for the practical determination of GFR?
If a molecule is freely filtered and neither reabsorbed nor secreted in the nephron then the amount filtered equals amount excreted. Thus GFR can be measured by measuring renal clearance of this molecule.
conc in plasma= conc in bowman’s capsule
What molecules can be used to determine GFR?
Inulin and creatinine
Why is inulin an ideal moecule and what is its fault?
A 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.
What is creatinine, why is creatinine an ideal molecule and what is its fault?
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 creatinine
may indicate renal failure.
It is freely filtered and not reabsorbed.
But a small amount is secreted into the nephron therefore its not a perfect molecule. However, the process for estimating creatinine in blood and urine can account for that to allow for GFR calculations.
When does renal clearance equal the renal plasma flow?
If the total amount of a molecule entering the kidney equals amount excreted, then the renal clearance of this molecule equals the renal plasma flow (RPF).
What is PAH and what is it used to do?
PAH (Para aminohippurate) is used as all the PAH is removed from the plasma passing through the kidney through filtration and secretion.
- helps calculate RPF and renal clearance as they would be the same for para aminohippurate
What is filtration fraction?
The ratio of the amount of plasma which is filtered, and which arrives via the afferent arteriole is defined by the Filtration fraction (FF).
Its value ranges from 0.15-0.20 normally. A value of 0.15 implies 15% of the plasma has been filtered.
FF= GFR/ RPF
If FF is about 20% it indicates the remaining 80% continues its pathway through the renal circulation.
What will be the concentration of creatinine in efferent arteriole if its concentration in afferent is 1.5mmol/L?
1.5 mmol/L (as its freely filtered)
What are the different transport mechanism?
Passive transport:
- diffusion
- osmosis
- electrical gradient difference
Active transport:
1) primary active
- ATPase Pump
- endocytosis
2) secondary active/ coupled transport
(Movement of one solute along its electrochemical gradient provides energy for the other solute to move against it)
- symporter (same direction)
- antiporter (different directions)
What are transport pathways in renal tubules?
Transcellular pathway (across a cells)
- e.g., aquaporins transporting water across a cell
- e.g., transcellular Na+ reabsorption
Paracellular pathway (between epithelial cells)
- e.g., Water, CVa2+, K+, Cl-, urea
What regulates Na+ reabsorption and how in the early PCT?
Angiotensin II regulates Na+ reabsorption by increasing Na+ - H+ antiporters.
What is reabsorbed and secreted in the early PCT?
Substances reabsorbed: 67% Na+, 67% Cl-, 80% HCO3-, 100% Glucose, 67% Water, 100% amino acids, 50% urea
Substances secreted: Drugs, ammonia, bile salts, prostaglandins, vitamins (folate & ascorbate)
What is reabsorption like in early PCT?
Sodium and bicarbonate reabsorption:
1) carbonic anhydrase reaction
2) Na+H+ antiporter
3) Na+HCO3- symporter
Glucose reabsorption:
1) na+K+ ATPase pump
2) Na+ glucose symporter (SGLT2)
3) glucose transporter
How does CO2 enter the epithelial cells in the PCT?
by diffusion
How is a hyperosmotic medullary interstitium formed?
descending LOH is not permeable to salt (Na+ and Cl-)
What side of LOH is permeable to what?
ascending impermeable to water not salt
descending permeable to water not salt
What is reabsorbed at he LOH?
25% Na+, 25% Cl-, 15% water
How is reabsorption at the LOH?
Why is no wate absorbed at the early distal tubule?
because aquaporins are absent
How is reabsorption at the DCT?
1) the Na Cl symporter then the others for Na+ and Cl- reabsorption
What does aldosterone do?
Regulates Na+ reabsorption by increasing apical Na+ channels & basolateral Na+ - K+ - ATPase pumps.
apical= closer to tubular fluid
basolateral= closer to blood
What does anti-diuretic hormone do?
regulates water reabsorption by increasing apical aquaporins
What are the 2 types of cells at the DCT and collecting duct?
Principal cells
Intercalated cells
What happens with principal cells?
low density of mitochondria
What are the types of intercalated cells?
⍺-Intercalated cell: HCO3- reabsorption & H+ secretion.
β-Intercalated cell: HCO3- secretion & H+ reabsorption.
- dependent on acidosis and alkalosis status
What happens at the intercalated cells?
