Genitourinary system Flashcards
What are the 3 major functions of the kidneys?
Excretion
-Of metabolic products e.g uric acid
-Of foreign substances e.g drugs
Homeostasis
-Body fluid, electrolytes, acid-base balance
-Blood pressure
Secretion
-Hormones e.g EPO, renin
Top>Bottom
Cortex, Major calyx, Minor calyx, Medulla
What is route of blood supply to, through and out of the kidneys(all 13 vessels)?
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
Function of the detrusor muscle
Contracts to build up pressure around the bladder to support urination
Function of the trigone
Stretching of this triangular region to its limit signals the brain about the need for urination
Function of the internal sphincter
Involuntarily prevents urination
Function of the external sphincter
Voluntary control to prevent urination
Function of the bulbourethral gland
Produces thick lubricant to be added to watery semen to increase likelihood of sperm survival
Describe the difference in density of mitochondria in different epithelium within a nephron
Mitochondria are rich in all tubule epitheliums
except
Thin descending loop
Thin ascending loop
Collecting duct principal cells
-All have a low mitochondria density
How does thickness change as you move through the loop of henle?
Thin on descending end, ascending is thin first then thickens
What is the ratio of superficial to juxtamedullary nephrons?
~10:1
What is the difference between a superficial and a juxtamedullary nephron?
A superficial nephrons’ loop of henle only goes as deep as the outer medulla whereas a juxtamedullary nephrons’ LOH goes into the inner medulla
What are the components in the juxtaglomerular apparatus and where are they?
Macula densa-Distal CT
Extraglomerular mesangial cells
Juxtaglomerular cells (Afferent arteriole)
What is the function of the macula densa?
GFR regulation through tubulo-glomerular feedback mechanism(Na+/Cl-sensing in the DCT)
What is the function of the juxtaglomerular cells?
Renin secretion to regulat blood pressure
Glomerular filtration
Left>Right
Reabsorption, secretion
Excretion
What is the difference between oncotic pressure and hydrostatic pressure?
Oncotic->Pulling force
Hydrostatic->Pushing force
both are across a semipermeable membrane
What does HPgc denote?
Hydrostatic pressure in glomerular capillaries
What does HPbw denote?
Hydrostatic pressure in bowmans’ capsule
What does πgc denote
Oncotic pressure of plasma proteins in glomerular capillaries
How do you calculate net ultrafiltration pressure(Puf)?
Puf = HPgc - HPbw - πgc
Puf = Glomerular capillary hstatic pressure - Bowmans capusle hstatic pressure - plasma protein onc pressure
GFR def
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 work out GFR?
GFR = Puf * Kf
Kf = Ultrafiltration constant(membrane permeability and surface area available for filtration)
What 2 factors influence GFR apart from net filtration pressure?
Membrane permeability
+
Surface area available for filtration
What is the cardinal feature of renal disease, with a buildup of waste product in the plasma
A drop in GFR
What are the healthy GFR ranges for men and women?
Men: 90-140 mL/min
Women: 80-125 mL/min
What 2 things can cause GFR imbalances?
Change in Kf or filtration forces(derived from formula)
How is GFR regulated myogenically?
Arterial pressure increases
Afferent arteriole stretches
Arteriole contracts
Vessel resistance rises
Blood flow lowers
GFR stabilizes
-Vice versa for decreased pressure
How is GFR regulated through tubulo-glomerular feedback and what cells detect the intial change?
Increase/Decrease in GFR
Increased/Decreased NaCl in LOH
Change detected by macula densa
Increased/Decreased ATP + adenosine discharged
Increases/Decreases osmotic pressure in afferent arteriole
Afferent arteriole contracts/dilates
GFR stabilizes
(This mechanism relies on myogenic regulation)
If C = 50mL/min for a substance, how much is cleared in 3 mins?
150mL
Renal clearance def
Renal clearance is the number of litres of plasma that are completely cleared of the substance per unit time.
How do you calculate renal clearance?
U = Conc of substance in urine
V = Rate of urine production
P = Conc of substance in plasma
What does is mean if a molecule is freely filtered?
Has the same concentration in the glomerular capillaries as in bowmans capsule
(Same ratio as water)
What is an ideal molecule to measure GFR and why?
Inulin
-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 molecule is commonly used to measure GFR in humans and why is it not a perfect molecule to use for this?
Creatinine
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
Is not perfect as a small amount is secreted into the nephron
What is renal plasma flow?
The volume of plasma delivered to the kidneys per unit time
Under what conditions is renal plasma flow equal to renal clearance?
When the amount of a molecule entering the kidney is the same as the amount excreted(Fully removed from plasma)
What molecules’ levels are measured to gauge renal plasma flow and why?
PAH (Para-aminohippurate) is used as all the PAH is removed from the plasma passing through the kidney through filtration and secretion.
What are the 2 types of active transport, give their divisions and give examples of each?
Primary Active
Na+/K+ ATPase transport
Endocytosis(e.g small protein reabsorption in the PCT)
Secondary active/Coupled transport
Movement of one solute along its electrochemical gradient provides energy for the other solute to move against it.
Symport
-Molecules travel in the same direction
Antiport
-Molecules go opposite directions
How is Na+ moved between the renal tubules into the blood transcellularly?
Na+/K+ ATPase on basal membrane pulls Na+ out of the cell into the blood, causing a diffusion gradient into cell, drawing in Na+ from the tubule
What are the 3 types of passive transport?
Diffusion
Osmosis
Electrical gradient difference
How does Ca2+, K+, Cl- and urea move between the renal tubules and blood?
Through the paracellular pathway
How does water move in between the renal tubules and blood?
Aquaporins on the basal and apical membrane move water from the tubules to the blood vessels
How does angiotensin II increase Na+ reabsorption?
By increasing the number of Na+/H+ antiporters
Outline the reabsorption pathway of sodium and bicarbonate, including what transport pumps are used
Na+/K+ ATPase pump
Na+/HCO3- symporter
Na+/H+ NHE3 antiporter
Reversible reaction(carbonic anhydrase) (H+ + HCO3- <-> H2O + CO2)
How many HCO3-‘s are exported from the epithelial cell per Na+ through the Na+/HCO3- pump?
3:1 HCO3-:Na+
What molecules are 100% reabsorbed from the renal tubule?
Glucose and amino acids
What percentage of Na+, Cl- and H2O are reabsorbed in the LOH?
Na+: 25%
Cl-: 25%
H2O: 15%
How much of HCO3- is reabsorbed from the renal tubule?
80%
Outline how glucose is reabsorbed into the blood from the renal tubules including the transporter proteins used
Na+/K+ ATPase pump
GLUT 2
Na+/Glucose symporter(SGLT2)
Concentration gradient produced by the Na+/K+ ATPase pump causes Na+ to be pulled into the cel from the renal tubule alongside glucose through the Na+/Glucose symporter
What substances are fully secreted into the renal tubules?
Drugs, ammonia, bile salts, prostaglandins, vitamins (folate & ascorbate)
Outline the movement of Na+/Cl- and water through the LOH
Descending
Water passively leaves
Na+/Cl-cannot leave
Thin ascending
Water cannot leave
Na+/Cl- passively leaves
Thick ascending
Na+/Cl- actively leaves
Hypo-osmotic fluid leaving the LOH
What molecules are reabsorbed in the PCT and DCT?
PCT:
Glucose, Na+, HCO3-
DCT:
Na+, Cl-, Ca2+
How is Na+/Cl- reabsorbed from the thick ascending limb in the LOH into the blood?
Na+/K+/Cl- symporter moves the ions into the epithelial cell
Na+/K+ ATPase exchanges Na+(out) for K+(in)
K+/Cl- symporter also move the ions into the blood through the basal membrane
K+ and Cl- also recycle back into the renal tubule and blood respectively
How is Ca2+ reabsorbed in the early DCT?
Ca2+ enters the epithelial cells freely
-Water can’t move into the epi cell
-All transporter proteins on the basal membrane
Na/K+ ATPase
Na+/Ca2+ pump
Ca2+ ATPase pump
How is Na+/Cl- reabsorbed in the early DCT?
Na+/K+ ATPase
Na+/Cl- symporter
K+/Cl- symporter
Water can’t move into epithelium
Cl- leaks out through basal membrane
How is Na+ reabsorbed and K+ secreted in the distal DCT and collecting duct and through what cell?
Through a principal cell
Na+ enters freely
K+ leaves through both membranes freely
Na+/K+ ATPase
-Aquaporins transport water through both membranes into the blood
What is the function of aldosterone on the reabsorption of Na+?
Aldosterone increases apical Na+ channels & basolateral Na+ - K+ - ATPase pumps
What is the function of AVP/ADH on water reabsorption?
Increases water reabsorption by increasing the amount of aquaporins on the apical membrane
What is the function of an a-intercalated cell and where can you find them?
HCO3- reabsorption and H+ secretion
-Distal DCT and collecting duct
-Cl- leaks into blood
-HCO3-/Cl- antiporter on basal membrane
-H+ ATPase pump on apical membrane
What is the function of a B-intercalated cell and where can you find them?
HCO3- secretion and H+ reabsorption
-Distal DCT and collecting duct
-Cl- leaks into blood
-HCO3-/Cl- antiporter on apical membrane
-H+ ATPase pump on basal membrane
