W3: Urinary system

Question 1

Where are kidneys located (level)

Answer 1

T12-L3 - lateral to transverse processes
Left T12- L3/L4 Right L1-L4
Paraverebral gutters - deep to 11th and 12th ribs - quite high up

Question 2

Which kidney is lower? Why?

Answer 2

The superior pole of the right kidney, due to the presence of the liver, sits around 2.5cm lower than the left kidney’s superior pole

Question 3

How many vertebrae is each kidney?

Answer 3

About 3

Question 4

Discuss adrenal gland

Answer 4

Endocrine organ

Between kidney and diaphragm

The right gland is pyramidal in shape, contrasting with the semi-lunar shape of the left gland.

Retroperitoneal

Cortex - outside - zona glomerulosa, fasciculata and reticularis (mineralocorticoids eg aldosterone, corticosteroids, androgens respectively)

Medulla -> catecholamines - adrenaline

Preganglionic sympathetic innervation of adrenal medulla

Question 5

Vasculature of adrenals

Answer 5

The adrenal glands have a rich blood supply via three main arteries:

Superior adrenal artery – arises from the inferior phrenic artery

Middle adrenal artery – arises from the abdominal aorta.

Inferior adrenal artery – arises from the renal arteries.

Right and left adrenal veins drain the glands. The right adrenal vein drains into the inferior vena cava, whereas the left adrenal vein drains into the left renal vein.

Question 6

Innervation of adrenals

Answer 6

Sympathetic innervation to the adrenal medulla is via myelinated pre-synaptic fibres, mainly from the T10 to L1 spinal cord segments.

Question 7

Functions of kidney

Answer 7

1. Filtration of the blood and formation of urine.
2. Maintenance of systemic blood pressure, through the RAA axis.
3. Production and secretion of erythropoietin and 1,25-dihydroxycholecalciferol (activated vitamin D3). 4. Electrolyte and fluid balance.

Question 8

Layers of/around kidney

Answer 8

Renal capsule – tough fibrous capsule.

Perirenal fat – collection of extraperitoneal fat.

Renal fascia (also known as Gerota’s fascia or perirenal fascia) – encloses the kidneys and the suprarenal glands.

Pararenal fat – mainly located on the posterolateral aspect of the kidney.

Question 9

Lobules

Answer 9

In fetus and newborn – kidney has 12 lobules; in adult – lobules fused to form a smooth surface, although remaining traces of lobulation can mimic a renal masses on radiological imaging.

Question 10

Arrangement of hilum of kidney

Answer 10

Vein (anterior)→ artery (middle) → ureter (posterior)

Question 11

Renal pyramids. What is the apex called? Decribe direction of drainage of urine.

Answer 11

There are between 10-18 renal pyramids within the renal medulla, which are the locations of the loops of Henle and renal collecting ducts

The apex of a renal pyramid is called a renal papilla. Each renal papilla is associated with a structure known as the minor calyx, which collects urine from the pyramids. Several minor calices merge to form a major calyx. Urine passes through the major calices into the renal pelvis, a flattened and funnel-shaped structure. From the renal pelvis, urine drains into the ureter, which transports it to the bladder for storage.

Question 12

*Renal vasculature

Answer 12

• Renal artery – Origin : Abdominal aorta (L2) , branches : inferior suprarenal arteries, ureteric and capsular branches.
• Renal Vein drains into Inferior Vena cava.
• Left renal vein drains -left suprarenal vein and left gonadal vein.

Question 13

Which renal artery is longer? Why? What does it cross and where?

Which renal vein is longer?

Answer 13

Due to the anatomical position of the abdominal aorta (slightly to the left of the midline), the right renal artery is longer, and crosses the vena cava posteriorly

Left renal vein is longer - travels anteriorly to abdominal aorta

Question 14

Divisions of main renal artery

Answer 14

Anterior - divides into 4 segments - mid zone and upper - 75% blood
Posterior - lower lobe - 25% blood

‘End arteries’ - no anastomoses between each other - key - obstruction of one artery will eventually lead to ischaemia and necrosisof the renal parenchyma supplied by this vessel

5 segmental arteries arise from these two divisions

Question 15

Where does left renal vein run?

Answer 15

Under sup mes and over aorta

Question 16

Variations in the number and patterns of branching of the renal artery.

Answer 16

Accessory arteries are common (in about 25% of patients). An accessory artery is any supernumerary artery that reaches the kidney. If a supernumerary artery does not enter the kidney through the hilum, it is called aberrant.

Usually in development kidney supplied by consecutive branches of iliac vessels and aorta - could be remnants of these

Accessory vessels to the inferior pole cross anterior to the ureter and can, by obstructing the ureter, cause hydronephrosis (build up of urine in the kidney)
• In children with ureteropelvic junction obstruction, a crossing vessel is found in 28% of cases

Question 17

What is renal sinus?

Answer 17

‘Empty space’
Where the vessels travel, not for collection of fluid?

Question 18

Where kinday transplant?

Answer 18

Iliac fossa - suitable for US assessment, won’t affect other structures

Question 19

Renal stone impaction
Where is pain commonly felt?

Answer 19

Known as renal and ureteri calculi

• Narrowest sites
• The ureteropelvic junction
• Site of Crossing of common
iliac artery
• Ureterovesical junction

The pain is often located in the ipsilateral flank but can radiate depending on its location. For example, stones in the upper ureter can cause pain in the abdomen, while stones in the lower ureter can cause pain in the genital

Question 20

Horseshoe kidney

Answer 20

A horseshoe kidney (also known as a cake kidney or fused kidney) is where the two developing kidneys fuse into a single horseshoe-shaped structure.

This occurs if the kidneys become too close together during their ascent and rotation from the pelvis to the abdomen – they become fused at their lower poles (the isthmus) and consequently become ‘stuck’ underneath the inferior mesenteric artery.

This type of kidney is still drained by two ureters (although the pelvices and ureters remain anteriorly due to incomplete rotation) and is usually asymptomatic, although it can be prone to obstruction.

Question 21

Innervation of kidney

Answer 21

Thoracolumbar outflow from T10 to L1 (pass through sympathetic trunk without forming a synapse) provide vasomotor supply via the thoracolumbar splanchnic nerve, after synapsing at the renal and coeliac ganglia.

Innervate afferent and efferent arteriole - promote vasoconstriction - decreased GFR

PT cells - stimulates Na+ reabsorption

To granular cells of JGA - renin secretion - important role in blood pressure regulation

Question 22

Discuss path of ureter

Answer 22

The ureters, which are around 25cm in length, convey urine from the renal pelvis to the urinary bladder within the pelvis. The muscular tubes pass inferiorly from the renal 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.

Question 23

Arterial supply of ureter

Answer 23

• It has good longitudinal anastomosis
• Ureter can be safely transected at any level intraoperatively, and a uretero-ureterostomy performed during ureteric trauma/injury), without compromising its viability
• The branch from the renal artery is also constant and is preserved whenever possible in renal transplantation to ensure good vascularity of the ureter.

Abdominal – renal artery, testicular/ovarian artery, and ureteral branches directly from the abdominal aorta

Pelvic – superior and inferior vesical arteries.

Venous drainage is carried out by vessels that correspond to the aforementioned arteries.

Question 24

Discuss path of ureter

Answer 24

The ureters, which are around 25cm in length, convey urine from the renal pelvis to the urinary bladder within the pelvis. The muscular tubes 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 anter- omedially 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.

Question 25

Function of bladder

Answer 25

Temporary storage of urine – the bladder is a hollow organ with distensible walls. It has a folded internal lining (known as rugae), which allows it to accommodate up to 400-600ml of urine in healthy adults.

Assists in the expulsion of urine – the musculature of the bladder contracts during micturition, with concomitant relaxation of the sphincters.

Question 26

Parts of bladder

Answer 26

1. Apex – the anterior-most part of the superior aspect of the bladder, lying behind the pubic symphysis. The bladder attaches to the umbilicus via the median umbilical ligament, which inserts into the apex.
2. Body – the large chamber of the bladder.
3. Fundus – extends from the apex, surround the superior aspect of the bladder, to the point at which the
   ureters drain into the bladder.
4. Base – the posterior surface of the bladder, extending from the two ureteric orifices superiorly to the single
   internal urethral orifice inferiorly. Internally, the base is largely formed by the bladder trigone.
5. Neck – the point of transition from the bladder to the urethral, which is surrounded by the internal urethral
   sphincter.

Question 27

What is the neck of the bladder related to?

Answer 27

Prostate gland

Question 28

Peritoneal relations in male and female

Answer 28

The peritoneum reflects onto the superior aspect of the bladder, creating a pouch posterior to the bladder in which fluid can collect. In males, this area is known as the rectovesical pouch. In females, due to the presence of the uterus and vagina, this is the vesicouterine pouch. (other is rectouterine pouch)

Question 29

Trigone

Difference in walls

Answer 29

Urine enters the bladder through the left and right ureters, and exits via the urethra. Internally, these orifices are marked by the trigone – a triangular area located within the fundus.

In contrast to the rest of the internal bladder, the trigone has smooth walls (this is explained by the different embryological origin: the trigone is developed by the integration of two mesonephric ducts at the base of the bladder)

Question 30

Main muscle in bladder wall

Answer 30

Detrusor

Its fibres are orientated in multiple directions, thus retaining structural integrity when stretched.

Question 31

Sphincter muscles

Answer 31

Internal urethral sphincter:

• Male – consists of circular smooth fibres, which are under autonomic control. It is thought to prevent seminal regurgitation during ejaculation.
• Females – thought to be a functional sphincter (i.e. no sphincteric muscle present). It is formed by the anatomy of the bladder neck and proximal urethra.

External urethral sphincter – has the same structure in both sexes. It is skeletal muscle, and under voluntary control. However, in males the external sphincteric mechanism is more complex, as it correlates with fibers of the rectourethralis muscle and the levator ani muscle.

Question 32

Discuss retropubic space

Answer 32

Retropubic space is a potential avascular space located between the pubic symphysis and the urinary bladder.

Question 33

What is the interal ureteric orifice?

Answer 33

Opening of bladder into urethra

Question 34

What prevents urine from going to into ureter

Answer 34

Ureteric orifices are encircled and tightened by loops of detrusor muscles.
As bladder fills , the increased pressure leads to compression of ureter and acts like a flap value preventing the reflux of urine into the ureter

Question 35

Arterial supply of bladder

Answer 35

The bladder fundus is supplied by the superior vesical artery (umbilical), whilst the base is supplied by the inferior vesical artery in males/vaginal artery in females. Both of the vesical arteries arise from the internal iliac artery. Venous drainage of the bladder is via the corresponding veins.

Question 36

Venous drainage

Answer 36

Venous drainage of the bladder is via the corresponding veins.

Venous drainage is achieved by the vesical venous plexus, which empties into the internal iliac veins. The vesical plexus in males is in continuity at the retropubic space with the prostate venous plexus (plexus of Santorini), which also receives blood from the dorsal vein of the penis

Question 37

Innervation of bladder

Answer 37

• Parasympathetic – Pelvic splanchnic nerves (S2-S4)
Stimulate detrusor muscle contraction
Inhibit/relax the internal urethral sphincter

• Sympathetic – hypogastric nerve (T11-L2/L3)
Relaxation of detrusor muscle
Contraction of smooth muscles in internal urethral sphincter
If faulty, dripping of urine

• Somatic – Pudendal nerve (S2- S4)
Innervates external urethral sphincter, voluntary control over micturition.

• Spinal cord lesion Urinary incontinence

Question 38

Discuss bladder stretch reflex

Answer 38

The bladder stretch reflex is a primitive spinal reflex, in which micturition is stimulated in response to stretch of the bladder wall. It is analogous to a muscle spinal reflex, such as the patella reflex.

During toilet training in infants, this spinal reflex is overridden by the higher centres of the brain, to give voluntary control over micturition.

The reflex arc:

Bladder fills with urine, and the bladder walls stretch. Sensory nerves detect stretch and transmit this information to the spinal cord.

Interneurons within the spinal cord relay the signal to the parasympathetic efferents (the pelvic nerve).

The pelvic nerve acts to contract the detrusor muscle, and stimulate micturition.

Although it is non-functional post childhood, the bladder stretch reflex needs to be considered in spinal injuries (where the descending inhibition cannot reach the bladder), and in neurodegenerative diseases (where the brain is unable to generate inhibition).

Question 39

Spinal cord lesions and continence

Answer 39

Reflex Bladder – Spinal Cord Transection Above T12

In this case, the afferent signals from the bladder wall are unable to reach the brain, and the patient will have no awareness of bladder filling. There is also no descending control over the external urethral sphincter, and it is constantly relaxed.

There is a functioning spinal reflex, where the parasympathetic system initiates detrusor contraction in response to bladder wall stretch. Thus, the bladder automatically empties as it fills – known as the reflex bladder.

Flaccid Bladder – Spinal Cord Transection Below T12

A spinal cord transection at this level will have damaged the parasympathetic outflow to the bladder. The detrusor muscle will be paralysed, unable to contract. The spinal reflex does not function.

In this scenario, the bladder will fill uncontrollably, becoming abnormally distended until overflow incontinence occurs.

Question 40

*Urinary incontinence

Answer 40

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 innerva- tion 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 41

Bladder ligaments

Answer 41

Pubovesicle in female and puboprostatic in male

Medial umbilical ligament connects apex to umbilicus (remnant of the urachus)

Question 42

Lining of urethra

Answer 42

It is lined by stratified columnar epithelium, which is protected from the corrosive urine by mucus secreting glands.

Question 43

What does the male urethra also transport, as well as urine?

Answer 43

Semen - fluid with spermatozoa and sex gland secretions

Question 44

What can the male urethra be divided into?

Answer 44

Prostatic

Membranous

Penile

Question 45

Describe prostatic urethra

Answer 45

Receives the ejaculatory ducts (containing spermatozoa from the testes and seminal fluid from the seminal vesicle glands) and the prostatic ducts (containing alkaline fluid).

Question 46

Describe membranous urethra

Answer 46

Passes through the pelvic floor and the deep perineal pouch.

Surrounded by the external urethral sphincter – which provides voluntary control of micturition.

Voluntary sphincter (pudendal nerve)

It is the narrowest and least dilatable portion of the urethra.

Question 47

Describe penile urethra

Answer 47

Passes through the bulb and corpus spongiosum of the penis, ending at the external urethral orifice (the meatus).

Receives the bulbourethral glands proximally.

In the glans (head) of the penis, the urethra dilates to form the navicular fossa.

Question 48

Seminal colliculus

Answer 48

_Distal to w_here the ejaculatory duct joins prostatic urethra

Elevation of urothelium

Question 49

Prostatic utricle

Answer 49

he prostatic utricle (Latin for “small pouch of the prostate”) is a small indentation in the prostatic urethra, at the apex of the urethral crest, on the seminal colliculus (verumontanum), laterally flanked by openings of the ejaculatory ducts.

Question 50

Bulbourethral gland

Answer 50

The bulbourethral gland or Cowper’s gland, which is homologous to the Bartholin’s gland in females, produces a pre-ejaculate that cleanses and lubricates the urethra prior to the arrival of the semen.

Question 51

Blood upply of urethra in man

Answer 51

Prostatic urethra – supplied by the inferior vesical artery (branch of the internal iliac artery which also supplies the lower part of the bladder).

Membranous urethra – supplied by the bulbourethral artery (branch of the internal pudendal artery)

Penile urethra – supplied directly by branches of the internal pudendal artery.

Question 52

Discuss female urethra

What is the distal end marked by?

Answer 52

Short

Bladder -> perineal membrane -> pelvic floor -> opens into vestibule (area in between labia minora)

he distal end of the urethra is marked by the presence of two mucous glands that lie either side of the urethra – Skene’s glands. They are homologous to the male prostate.

Question 53

Neurovascular supply of female urethra

Answer 53

internal pudendal arteries, vaginal arteries and inferior vesical branches of the vaginal arteries. Venous drainage is given by veins of the same name

Question 54

Where is the external urethral sphincter in women?

Answer 54

.just before passing through the perineal membrane,the urethra is surrounded

by the voluntary external urethral sphinCter (innervated by the pudendal nerve).

Question 55

Benign Prostatic Hyperplasia (BPH)

Answer 55

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, includ- ing 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 56

Urethral Strictures

Answer 56

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 endo- scopic dilatation, catheterisation or open surgery to excise the stricture point.

Question 57

Bladder Catheterisation

Answer 57

This is a common medical procedure in which a plastic tube is passed through the external urethral me- atus, 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.

Catheterisation is more complex in males, as there are two angles to consider – the infrapubic and prepubic angles. The prepubic angle can be diminished by holding the penis upwards during urinary catheterisation.