13. Urinary System

Question 1

Describe the position of the kidneys within the abdomen.

Answer 1

• Hilum of the kidneys is about 5cm lateral to the midline
• The upper poles are not symmetrical:
  
  • Left at T11
  • Right at T12

Question 2

Which kidney lies higher in the abdomen and why?

Answer 2

Left, because of the liver.

Question 3

Describe the position of the kidneys in relation to the muscles in the abdomen.

Answer 3

The kidneys lie on the muscles of the posterior abdominal wall: Psoas, quadratus lumboram and transversus abdominis.

Question 4

Describe the position of the kidneys in relation to the peritoneum. What is the name for this?

Answer 4

They are posterior to the peritoneum -> This is called being retroperitoneal.

Question 5

Describe how the kidneys relate in position to the duodenum, pancreas and spleen.

Answer 5

• Duodenum passes on the right-hand side of the body, covering the hilum of the right kidney
• Pancreas covers hilum of the left kidney
• Spleen covers left border of the left kidney

Question 6

Describe the position of the kidneys.

Answer 6

The kidneys are found within the para-vertebral gutters, with the superior parts lying deep to the 11th and 12th ribs. They have an oblique orientation with the renal hila facing slightly anteriorly and medially.

Question 7

What are the functions of the kidneys?

Answer 7

• Filtration of the blood and formation of urine.
• Maintenance of systemic blood pressure, through the RAA axis.
• Production and secretion of erythropoietin and 1,25-dihydroxycholecalciferol (activated vitamin D3).
• Electrolyte and fluid balance.

Question 8

Describe the structures at the renal hilum and their organisation.

Answer 8

• Most anterior: Renal vein
• Middle: Renal artery
• Most posterior: Renal pelvis (urine)

Question 9

Describe what can be seen in this image.

Answer 9

Also note: ureters extend caudally, over the psoas muscle.

Question 10

Describe the structure and different layers of the kidneys, starting from the outside and going in.

Answer 10

• Capsule -> Tough, fibrous layer
• Cortex -> Contains the nephrons
• Medulla -> Contains the collecting ducts
• Pelvis -> Drains the collecting ducts (via minor and major calyces) -> This is at the hilum of the kidney
• Ureter -> Pelvis then drains into the ureter

Question 11

Which is longer: the right renal artery or left renal artery?

Answer 11

Right renal artery -> Because it passes behind the IVC.

Question 12

What are the major and minor calyces?

Answer 12

Areas of the kidney draining into the renal pelvis. The minor calyces drain into the major calyces.

Question 13

Describe the innervation to the kidneys.

Answer 13

Sympathetic fibres arise from the renal plexus, and travel along the renal arteries to reach each kidney.

Question 14

Describe the position of the adrenal glands.

Answer 14

• Primary retroperitoneal
• Endocrine glands
• Sit superior to the kidneys at the level of T11-T12 within the renal fascia and adipose tissue.

Question 15

Describe the course of the ureters.

Answer 15

• Pass inferiorly from the pelvis
• Along the medial border of the psoas major muscle, just medial to the tips of L2-L5 transverse processes, to the pelvic brim.
• Here, the ureters are crossed by the gonadal vessels.
• As they course inferiorly to the sacroiliac joints, the ureters pass anterior to the bifurcation of the common iliac arteries to reach the pelvic side wall.
• At the level of the ischial spines, the ureters turn anteromedially to reach the lateral angle of the bladder.
• Both ureters pass obliquely through the bladder wall to open at the posterolateral angles of the bladder trigone.

Summary:

• It is retroperitoneal
• Emerges from the hilum of the kidney
• Passes across psoas
• Then over the common iliac artery and vein
• Enter the bladder at the posterior wall

Question 16

Describe the renal and ureteric calculi. Where is the pain distributed?

Answer 16

• These are kidney stones.
• These stones are formed of varying amounts of calcium salts, cystine and uric acid.
• Large renal calculi may fill an entire calyceal system and are referred to as staghorn calculi.
• Stones may cause severe intermittent pain in the flank and lower abdomen, nausea, vomiting and blood in the urine.
• Treatment involves facilitating the passage of the calculus, either with medications, lithotripsy device or endoscopic removal.
• The normal diameter of the ureter is 3mm, but there are three physiological constriction points where renal calculi usually lodge. These are:
  
  • The pelvi-ureteric junction – where the renal pelvis forms the ureter
  • As the ureter crosses over the common iliac bifurcation
  • The vesico-ureteric junction – where the ureter obliquely enters the bladder wall

Question 17

On what side and in which direction do the ureters enter the bladder? What is the function of this?

Answer 17

• Posterior side of the kidney
• Enter obliquely -> Prevents backflow of urine and increased pressure within the bladder compresses the distal ends of the ureters shut -> “sphincter”

Question 18

What does the bladder rest on?

Answer 18

Pelvic floor and pubis

Question 19

What are the different parts of the bladder?

Answer 19

• Apex
• Body
• Fundus
• Base
• Neck

Question 20

Describe the surface markings of the empty and full bladder.

Answer 20

• Empty bladder lies almost entirely within the pelvis, resting on the pelvic floor and pubis.
• As the bladder fills, it ascends into the abdomen and may ultimately reach the height of the umbilicus.

Question 21

What is the trigone?

Answer 21

This triangular part of the bladder which lies between the urethra and two ureters.

Question 22

What are the structures on this image?

Answer 22

• Arrows point towards the ureters
• The triangle is the trigone of the bladder

Question 24

What forms the majority of the bladder walls?

Answer 24

• Smooth detrusor muscle
• Lined by transitional epithelium

Question 25

What is the relation of the bladder to the retro-pubic space?

Answer 25

The retro-pubic space is anterior to the bladder, separating it from the pubic symphysis.

Question 26

What are the relations of the bladder to the peritoneum?

Answer 26

The peritoneum reflects onto the superior aspect of the bladder, creating a pouch posterior to the bladder in which fluid can collect.

Question 27

What are the relations of the bladder to the uterus and vagina?

Answer 27

The vesicouterine pouch lies posterior to the bladder and separates it from the uterus and vagina.

Question 28

Describe blood supply and drainage of the bladder.

Answer 28

Arterial supply:

• Superior vesical branch of internal iliac artery (supplies fundus)
• Inferior vesical branch of internal iliac artery (aupplies base)

Venous drainage follows the arterial supply.

Question 29

Summarise the innervation of the bladder.

Answer 29

• Parasympathetic: Pelvic splanchnic nerves from the pelvic plexus (S2-S4) -> Stimulates micturition through contraction of the detrusor muscle and relaxation of the internal urethral sphincter
• Sympathetic: Hypogastric nerve (T11-L2/L3) -> Causes relaxation of detrusor muscle and contraction of internal urethral sphincter
• Somatic: Pudendal nerve (S2-S4) -> Innervates external urethral sphincter, allowing voluntary control over micturition

Also:

• Afferent sympathetic innervation passes to the lumbar spinal cord -> Senses bladder distension

Question 30

How can urinary incontinence occur?

Answer 30

Damage to efferent tracts to the bladder from higher control centres within the brainstem to the S2-4 spinal levels can lead to involuntary detrusor contractions or conversely detrusor paralysis.

Question 31

What is overflow incontinence?

Answer 31

• Blockage of the bladder outflow tract, due to conditions such as prostate cancer or urethral strictures, can lead to a build-up of urine within the bladder.
• This may also occur following damage to detrusor innervation and bladder wall atony.
• When the bladder reaches a threshold volume, urine involuntarily passes out, often in the absence of an urge to urinate.
• This is known as overflow incontinence and may be managed with catheterisation or surgery to remove the obstruction.

Question 32

What is the lining of the urethra?

Answer 32

Stratified columnar epithelium with mucus glands

Question 33

What are the differences between the male and female urethra?

Answer 33

• Male is much longer (20cm compared to 4cm)
• Male has three parts (prostatic, membraneous and penile)

Question 34

What are the 3 parts of the male urethra?

Answer 34

• Prostatic -> Passing through the prostate just after leaving the bladder
• Membranous -> Passing through the perineal membrane
• Penile -> In the penis

Question 35

Describe the features of the prostatic urethra.

Answer 35

Contains:

• Urethral crest -> This has lateral prostatic sinuses which drain prostate secretions.
• Seminal colliculus -> This is an elevation on the urethral crest where the ejaculatory ducts drain.
• Prostatic utricle -> This is a blind ending duct on the urethral crest.

Named features on spec: Seminal colliculus, prostatic utricle, openings of ejaculatory duct

Question 36

Describe the features of the membraneous urethra.

Answer 36

Contains the external (voluntary) urethral sphincter.

Question 37

Which part of the male urethra is shortest?

Answer 37

Membraneous

Question 38

What innervates the external urethra sphincter?

Answer 38

Pudendal nerves (voluntary)

Question 39

Describe the features of the penile urethra.

Answer 39

• Contains the bulbous urethra -> Dilated part at the proximal end where the bulbourethral glands drain
• Mucous urethral glands drain here

Question 40

What are the narrow points of the male urethra?

Answer 40

• Membranous urethra is narrow
• External urethral meatus of penile urethra is also narrow

Question 41

Describe benign prostatic hyperplasia (BPH).

Answer 41

• BPH is a non-malignant growth of the prostate gland that affects around 20% of men aged 55-74.
• Due to the close association with the urethra, symptoms, if present, are ones of bladder outlet obstruction, including poor urinary stream, hesitancy, urinary urgency, frequency and terminal dribbling.
• Occasionally, patients may present with complete urinary retention due to the obstruction.
• Treatment includes medication to reduce the size of the prostate and surgery to remove the obstruction from the prostatic urethra.

Question 42

Describe urethral strictures.

Answer 42

• Scarring of the urethra can result in obstruction of its lumen.
• Common causes of scarring include trauma and sexually transmitted infections, such as gonorrhoea.
• Strictures may result in a double urinary stream, obstructive symptoms as with BPH and frequent urinary tract infections.
• Treatment may include endoscopic dilatation, catheterisation or open surgery to excise the stricture point.

Question 43

Describe bladder catheterisation.

Answer 43

• This is a common medical procedure in which a plastic tube is passed through the external urethral meatus, along the urethra and into the bladder.
• This may be done for a number of reasons, including bladder drainage if in retention, bladder irrigation and acquisition of a urine sample.
• The major complications of bladder complication include urethral/bladder trauma and high incidence of urinary tract infections.