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BRS Urology and Renal Medicine > The Genitourinary System > Flashcards

The Genitourinary System Flashcards

1
Q

List the functions of kidney.

A

Excretion of metabolic products; e.g. urea, uric acid, creatinine and also of foreign substances (drugs)
Homeostasis of body fluids, electrolytes and acid-base balance.
Regulates BP
Secretes hormones e.g. erythropoietin

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2
Q

What is the outer region of the kidney called?

A

Renal cortex

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3
Q

What is the inner region of the kidney called?

A

Renal medulla

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4
Q

Explain the renal pyramid structure and the hierarchy of drainage.

A

Within the medulla, renal pyramids separated by renal columns.
Renale pyramids produce urine and terminates into the renal papilla → Drains into a collecting pool, minor calyx. Multiple minor calyces to form a major calyx. Major calyces connect to form a major calyx. Major calyces connect to single renal pelvis → Ureter

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5
Q

Outline renal blood supply in the correct order starting from renal artery.

A

Renal artery > Segmental artery > Interlobar artery > Arcuate artery > Interlobular artery > AA > Glomerular capillaries > EA > Peritubular capillaries > Interlobular vein > Arcuate vein > Interlobar vein > Renal vein

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6
Q

List the different components of the bladder and urethra

A

Detrusor muscle
Trigone
Internal and external sphincters
Bulbourethral gland (only present in men)

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7
Q

What is the function of the detrusor muscle?

A

Contracts to build pressure in the urinary bladder to support urination

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8
Q

What is the function of the trigone?

A

Stretching of this triangular region signals to the brain about the need for urination.

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9
Q

What is the function of the external and internal sphincters and what type of control are they under?

A

Both prevent urination

Internal - Involuntary control
External - Voluntary control

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10
Q

What is the function of the bulbourethral gland?

A

Produces thick lubricant which is added to watery semen to promote sperm survival.

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11
Q

What is the structure and functional unit of the kidney?

A

Nephron

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12
Q

Explain the function of the nephron.

A

Nephrons regulate + balance circulatory constituents to homeostatic set points through the processes of filtration, reabsorption and secretion.
AA → towards glomerulus → Filtration occurs within Bowman’s capsule producing filtrate. Proximal end of the tubule that surrounds glomerulus, and receives filtrate is the glomerular capsule.
Renal corpuscle = Glomerulus + Bowman’s capsule

Filtrate filtered by PCT → Loop of Henle → DCT→ Collecting duct

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13
Q

What are the 2 cell types present in the collecting duct and which is rich in MC?

A

Principal cells > low MC

Intercalated > high MC

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14
Q

In the nephron, epithelial cells present where are rich in MC?

A

Thick ascending LoH
DCT
PCT

(Thin descending and thin ascending loops low density of MC)

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15
Q

What are the 2 types of nephron?

A

Superficial nephron - only go as far as outer medulla.
Juxtamedullary nephron - go all the way into the inner medulla.

10:1 ratio for superficial to juxtamedullary nephron.

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16
Q

Why do you think cortex is granular looking whereas medulla has a striated appearance?

A

Glomeruli reside within cortex; the glomerulus is associated with the early DCT.

Medulla → collecting tubules and Loops of Henle give striated appearance.

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17
Q

What are the constituents of the juxtaglomerular apparatus?

A 
Macula densa (DCT) 
Extraglomerular mesangial cells 
Juxtaglomerular cells (Afferent arteriole)
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18
Q

What is the function of the juxtaglomerular apparatus?

A

Sympathetic innervation to beta-1 adrenoreceptors on juxtaglomerular cells signals signals renin secretion (activates renin-angiotensin system).
GFR regulation through tubulo-glomerular feedback mechanism.

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19
Q

Where does glomerular filtration occur?

A

Happens at Bowman’s Capsule

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20
Q

What type of process of glomerular filtration?

A

Passive process - fluid is ‘driven’ through the semi-permeable glomerular capillaries into the Bowman’s capsule space by the hydrostatic pressure of the heart.

Filtration barrier (size and charge dependent): Highly permeable to fluids and small solutes. Impermeable to cells and proteins.

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21
Q

Outline the process of glomerular filtration.

A

Blood into glomerulus via AA of renal artery. Sufficient hydrostatic pressure required to force fluid through fenestrations between endothelial cells of glomerular capillaries. Relatively large diameter of AA in comparison to EA generates sufficient pressure gradient to enable constituents of plasma to pass through with exception of erythrocytes and plasma proteins.

Glomerular capsule captures filtrate generated by the glomerulus → PCT

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22
Q

What does the filtration membrane prevent from being reabsorbed?

A

Prevents passage of blood cells, large plasma proteins and -ively charged particles. -ively charged particles → Difficulty filtering into capsular space as proteins associated with filtration membrane repel -ively charged substances.

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23
Q

What is the purpose of epithelial podocytes in glomerular filtration?

A

Podocytes with pedicels cover glomerular capillaries. GBM between glomerular endothelium and podocytes. Pedicels interdigitate to form filtration slits, ensuring that platelets and plasma proteins don’t filter through tubule. Maximises absorption of filtrate.

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24
Q

What is hydrostatic pressure?

A

‘Pushing’ > Fluid exerts this pressure.

Solute and fluid molecules shoved out.

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25
Q

What is the oncotic pressure?

A

‘Pulling’ > Solute exerts this pressure. Fluid molecules drawn in across a semi-permeable membrane.

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26
Q

What is the diameter of the filtration membrane and what passes through?

A

70nm diameter

Water, ions and small proteins can pass.

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27
Q

What is the purpose of mesangial cells?

A

Contract to help regulate the rate of filtration of glomerulus.

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28
Q

What is HPgc, HPbw and pi.gc?

A

HPgc - Hydrostatic pressure in glomerular capillaries.
HPbw - Hydrostatic pressure in Bowman’s capsule.
pi.gc - Oncotic pressure of plasma proteins in glomerular capillaries.

(pi.bw is negligible)

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29
Q

How do you calculate Net ultrafiltration pressure (Puf)?

A

Puf = HPgc - HPbw - pi.gc

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30
Q

What is GFR?

A

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.

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31
Q

Equation for GFR?

A

GFR = Puf x Kf

Kf - ultrafiltration coefficient
Puf - Net ultrafiltration pressure

32
Q

What is Kf?

A

An ultrafiltration coefficient (membrane permeability and SA for available for filtration)
Any changes in filtration forces will result in GFR imbalances.

33
Q

What is a healthy GFR in men and women respectively?

A

Men - 90-140mL/min

Women - 80-125mL/min

34
Q

What is a fall in GFR the cardinal feature for?

A

Renal disease, with a build up of excretory products in the plasma.

35
Q

Outline the regulation of GFR via the myogenic mechanism.

A

Arterial pressure increases (BP increases).
AA stretches (activation of mechanoreceptors)
Arteriole constricts (vasoconstriction - occurs to resist the pressure)
Vessel resistance increases
Blood flow reduces
GFR stays the same.

36
Q

Outline the regulation of GFR via the tubulo-glomerular feedback mechanism.

A 
Increase/decrease in GFR 
Increased/decreased NaCl in LoH 
Change detected by MD 
Increased/decreased ATP and adenosine discharged. 
AA constricts/dilates. 
GFR stabilises.
37
Q

Define renal clearance

A

Number of litres of plasma that are completely cleared of the substance per unit time.

(RC 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).

38
Q

What can RC be used to calculate and state the equations?

A

GFR and renal plasma flow (RPF)

C = (UxV)/ p mL/min

U = concentration of substance in urine 
V = rate of urine production 
P = concentration of substance in plasma
39
Q

What does it mean if C=50mL/min?

A

Means 50mL of plasma has been cleared of that substance per minute.

40
Q

Explain the practical determination of GFR.

A

If a molecule is freely filtered and neither reabsorbed nor secreted in nephron, then amount filtered is equal to the amount excreted. Therefore GFR can be measured by evaluating renal clearance of this molecule.

41
Q

What is the ideal molecule for practical determination of GFR?

A

Inulin

42
Q

What is inulin?

A

A PLANT polysaccharide that is freely filtered and is neither reabsorbed nor secreted.

43
Q

Is inulin toxic?

A

No

Measurable in urine and plasma.

44
Q

What is creatine?

A

Waste product from creatinine in muscle metabolism.

Amount of creatinine released is fairly constant. If renal function is stable, creatinine amount in urine is stable.

45
Q

What does low creatinine clearance or high plasma creatine indicate?

A

Renal failure

46
Q

Explain how creatinine is used in the practical determination of GFR.

A

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.

47
Q

What does it mean if the total amount of a molecule entering the kidney equals the amount secreted?

A

Renal clearance of this molecule = renal plasma flow

48
Q

Why is PAH (para aminohippurate) used for renal plasma flow measurements?

A

All the PAH is removed from the plasma passing through the kidney through filtration and secretion.

49
Q

What is the filtration fraction?

A

The ratio of the amount of plasma which is filtered, and which arrives via the afferent arteriole.

50
Q

What is the equation for FF?

A

FF = GFR/RPF

Its value ranges from 0.15 to 0.20 normally.

51
Q

What does a value of 0.15 for the FF imply?

A

Implies 15% of the plasma has been filtered.

52
Q

What is the difference betwen primary and secondary active transport?

A

Primary - Uses ATP directly to transport molecules in and out of the cell.

Secondary - Movement of one solute along its electrochemical gradient provides energy for the other solute to move against its own electrochemical gradient.

53
Q

Is endocytosis a primary or secondary active transport mechanism?

A

Primary - small proteins are reabsorbed in the PCT using an ATP molecule

54
Q

Explain how the Na+/Glucose symporter works.

A

Na+ moves down its concentration gradient into the cell providing energy to transport Glucose against its concentration gradient into the cell.

55
Q

Explain how the Na+/H+ antiporter works.

A

Na+ moves down its concentration gradient into the cell providing energy to actively transport H+ against its electrochemical gradient out of the cell

56
Q

In the epithelial cell layer of the renal tubules, how does water follow the transcellular pathway?

A

It is transported from tubular fluid → Epithelial cells → blood via AQUAPORINS in the epithelial cells.

57
Q

How does trancellular Na+ reabsorption occur in the renal tubules?

A

3Na+ are transported from epithelial cells into blood via Na+/K+ ATPase (basolateral cell membrane) creating concentration gradient for Na+ as it is lower in the epithelial cell so Na+ from the tubular fluid diffuses into cell down concentration gradient.
2 K+ is transported from blood into epithelial cells via Na+/K+ ATPase so this is primary active transport as ATP is used.

58
Q

What is meant by the paracellular pathway in the renal tubules?

A

Substances (such as water, Ca2+, K+, Cl- and urea) are transported through the tight junctions between the epithelial cells.

59
Q

How does Na+ and bicarbonate reabsorption occur in the early PCT?

A

Na+/K+ ATPase creates a low Na+ concentration in the epithelial cell. CO2 enters epithelial cell by diffusion and binds to H20 (carbonic anhydrase) forming bicarbonate and H+.
Na+/H+ antiporter then transports Na+ down its concentration gradient into the cell from tubular fluid and H+ out into the tubular fluid against concentration gradient using the energy from transportation of Na+.
Na+/HCO3- symporter transports Na+ down concentration gradient into blood and bicarbonate is transported into blood against conc. gradient using energy from transportation of Na+.

60
Q

How does Angiotensin II regulate the Na+ reabsorbed?

A

Increase number of Na+/H+ antiporters.

61
Q

How does glucose reabsorption occur in the early proximal convoluted tubule?

A

Na+/K+ ATPase > concentration gradient with less Na+ in epithelial cell.
Na+/Glucose symporter (SGLT2) transports Na+ from tubular fluid into epithelial cell providing energy transporting glucose against its gradient from the tubular fluid into the epithelial cell. Glucose transporter (GLUT2) transports glucose into blood from epithelial cell via FD.

62
Q

Explain how the general processes of reabsorption involving the Loop of Henle occurs.

A

Na+ and Cl- passively leave thin ascending limb into the medulla and leaves actively from the thick ascending limb. This creates a low water potential in the medulla and so water leaves through the descending limb passively (osmosis).

63
Q

Describe and explain the osmolarity of the tubular fluid in the different parts of the loop of Henle.

A

At the point where the descending limb enters the ascending limb, the tubular fluid is hyperosmolar as water has been passively reabsorbed from the descending limb however since it is impermeable to Na+Cl-, the fluid is hyperosmolar.
At the tip of the thick ascending limb, tubular fluid is hypoosmolar as the salt has been reabsorbed far more.

64
Q

How does Na+Cl- reabsorption in the thick ascending limb of the Loop of Henle occur?

A

Na+/K+ ATPase creates concn. gradient with low Na+ concentration in the epithelial cell.
Na+/K+/2Cl- symporter transports these ions from the tubular fluid into the epithelial cell.
K+ is recycled back out into the tubular fluid.
K+/Cl- symporter allows reabsorption of these ions back into the blood from the epithelial cell.

65
Q

How does Na+ and Cl- reabsorption occur in the early distal convoluted tubule?

A

Na+/K+ ATPase creates concn. gradient with low concn. in the epithelial cell
Na+/Cl- symporter transports Na+ and Cl- into the epithelial cell from the tubular fluid into the epithelial cell.
K+/Cl- symporter then transports the K+ and Cl- from the epithelial cell into the blood.

66
Q

Is the early distal convoluted tubule permeable to water?

A

No

67
Q

How does Active Ca2+ reabsorption occur in the early distal convoluted tubule?

A

Na+/K+ ATPase creates concentration gradient with low concentration in the epithelial cell.
Na+/Ca2+ antiporter transports Na+ into epithelial cell from the blood and Ca2+ is transported from the epithelial cell into the blood against its concentration gradient.
Ca2+ ATPase pump transports Ca2+ against its concn. gradient as well into the blood from the epithelial cell.

68
Q

How do the principal cells work to correct hyperkalaemia?

A

By transporting the K+ out of the epithelial cells and into the tubular fluid.

69
Q

Is the lateral part of the distal convoluted tubule permeable to water?

A

Yes, it has aquaporins

70
Q

How does aldosterone increase Na+ reabsorption?

A

By increasing the apical Na+ channels and basolateral Na+/K+ ATPase pumps

71
Q

How does ADH increase water reabsorption?

A

Increases the apical aquaporins

Basolateral aqauporins are almost always present

72
Q

How does Na+ reabsorption and K+ secretion occur in the principal cells of the DCT and Collecting duct?

A

Na+/K+ ATPase creates concn. gradient with low concn. in the epithelial cell so Na+ is reabsorbed.
K+ is transported into the epithelial cell from the blood and so it is secreted actively.

73
Q

How do the alpha and beta intercalated cells of the DCT and Collecting duct maintain an acid-base balance?

A

The alpha intercalated cells facilitate HCO3- reabsorpion and H+ secretion, whereas the beta intercalated cells facilitate HCO3- secretion and H+ reabsorption.

Alpha intercalated cells have Cl-/HCO3- antiporters on the basolateral side, whereas beta intercalated cell have them on the apical side.

Then the H+ ATPase pump is on the apical side on the alpha intercalated cells and on the basolateral side on the beta intercalated cells.

These two cell types work together to act as a buffer to changes in pH.

74
Q

What substances are reabsorbed in the early PCT (don’t need to remember percentages)?

A

67% Na+, Cl- and water
80% HCO3-
100% Glucose and AAs
50% Urea

75
Q

What substances are secreted in the early PCT?

A

Drugs, ammonia, bile salts, prostaglandins, vitamins (folate and ascorbate)

76
Q

What substances are reabsorbed in the LoH?

A

25% Na+
25% Cl-
15% Water

BRS Urology and Renal Medicine (4 decks)

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