9.1 Structure and Function of the Urinary System

Question 1

Describe the blood supply and drainage of the kidneys (incl spinal level)

Answer 1

• Arterial: renal arteries around L1/L2 directly from aorta
• Venous: renal veins through hilum, directly into IVC

Question 2

What is contained within a renal lobe?

Answer 2

• Renal pyramid
• Overlying renal cortex
• Adjacent renal columns

Question 3

Describe the flow of urine through the different components of the renal cortex and medulla, all the way to the ureters

Answer 3

• Starts in blood
• Substances filtered into nephron at glomerulus

Question 4

Which limb of the loop of Henle is thick vs thin?

Answer 4

• Descending: thin (all the water’s being sucked out of it; shrunk like a sponge)
• Ascending: thicker (higher can afford to give some sodium to the poor)

Question 5

Explain counter-current multiplication (and its effect on urine conc)

Answer 5

• Ascending limb actively pumps out sodium (not permeable to water)
• Descending limb is permeable to water; it follows the sodium from the ascending
• This increases the conc of descending filtrate contents, meaning - when it reaches the ascending limb - it can pump more sodium out, pulling more water
• This is a positive feedback loop that increases urine conc, thus conserving resources for the organism to use

Question 6

Are the minority of nephrons juxtamedullary or cortical?

Answer 6

Juxtamedullary (more concentrated; rarer. most are superficial/cortical). It’s rare to find someone who can concentrate.

Question 7

Location of cortical vs juxtamedullary nephrons. Why does this make sense?

Answer 7

• Cortical have a loop of Henle entirely within cortex; main function is reabsorption/secretion (which is why they’re more common)
• Juxtamedullary have a longer loop of Henle, meaning more water and sodium can be pumped out as the LoH runs deeper into the renal medulla. This means their main function is to concentrate urine

Question 8

Minor vs major calyces of the kidney

Answer 8

• Minor carry urine from one papilla (which is the tip of one pyramid)
• Major carry urine from the joining of multiple minor calyces, into renal pelvis (bowl)

Question 9

What are the two parts of the ureter? Where do the ureters enter the pelvis?

Answer 9

• Abdominal and pelvic parts
• Enter the pelvis at the bifurcation of the common iliac arteries

Question 10

Are the aorta/common iliac arteries intra or retroperitoneal? What does this tell us about the peritoneal position of the ureters (and why else does this make sense?)

Answer 10

• Aorta is retroperitoneal
• Since the ureters cross the common iliac bifurcation (just distal to the aortic bifurcation), it makes sense that the ureters are also retroperitoneal
• (Also makes sense, since the kidneys and the adrenals are retroperitoneal)

Question 11

Describe the two muscular layers of the ureter? Where else do we see this, and why does it make sense?

Answer 11

• Inner circular, outer longitudinal
• Also seen in the GI tract; makes sense, since it allows contraction of both (or either) without preventing the function of the other

Question 12

Where in the body can transitional epithelium be found? Why is it called transitional, and what is another name for it?

Answer 12

• Found in pelvis, ureters (which are continuations of each other), bladder, and urethra
• Called transitional because it can distend (“transition” between shapes) without damage to accomodate varying volumes of urine
• Also called urothelium, since it’s present in the urinary tract as outlined above

Question 13

What are the two nerves involved in neurogenic control of the bladder? From what spinal levels do they arise?

Answer 13

• Pudendal and pelvic nerves
• Arise from the S2-S4 region

Question 14

Describe in full, including the nerves involved, neurogenic bladder control

Answer 14

• When the bladder fills, this is detected by stretch receptors in the urothelium; message is relayed to the spinal cord by parasympathetic fibres from the pelvic nerve
• As per the micturition reflex, this information is processed by interneurons, and then an efferent signal is sent out
• This efferent signal travels via the pelvic nerve also, causing detrusor muscle contraction (parasympathetic) and internal urethral sphincter relaxatrion (loss of sympa input)
• A signal also travels to the pontine micturition centre. If we decide to void, a somatic signal from the pudendal nerve causes EUS relaxation

Question 15

Is erection sympa/parasympathetically mediated? What triggers it, and how does it occur?

Answer 15

• Response to stimulation from genital branches of splanchnic nerves
• Vasodilation of arteries in the corpus cavernosum
• Engorgement (+ suppression of venous outflow)

Question 16

Describe what fluids go where during ejaculation, and which arm of the autonomic nervous system this is implicated in

Answer 16

• Sperm travels from the epididymis (where it waits) into the vas deferens
• Vas deferens travels up over the public bone, over/around the bladder, and makes its way towards the prostate
• But this is only sperm. We also need seminal fluid. Therefore, the seminal vesicle connects to the vas deferens, forming an ampulla (= “flask”, Romans used for perfume)
• Then connects with prostate, which also sends out products, all of which accumulate in the urethra
• This whole process is sympathetically mediated

Question 17

Describe the cell layers of urothelium

Answer 17

• Umbrella cells: one layer thick, tight junctions (high-resistance barrier)
• Intermediate cells, can be multiple layers (attached w/ desmosomes)
• Basal cells (attached to basement membrane w/ hemidesmosomes)

Question 18

What are the two kinds of muscle in the bladder? What are their functions?

Answer 18

• Detrusor: contracts during voiding to empty the bladder
• Trigone (contracts to keep vesiculouretertic junction open during filling of bladder