Urology Care Today

URINARY TRACT AT A GLANCE

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Overview of the urinary tract

Passing urine is something most of us do not give a thought about, as it is part of everyday lives.

However, it is a more complex process than is apparent, as all elements of the urinary tract need to

be functioning and working together, and the three micturition centres in the body, which control

filling and emptying of the bladder via the autonomic and somatic nervous systems, also need

to work in harmony to urinate successfully. Here, Rachel Leaver, lecturer practitioner, urological

nursing, UCLH and London South Bank University, UCLH NHS Foundation Trust, provides an

overview of the male and female urinary tracts.

The urinary tract is divided into:

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The upper tract, which includes

the kidneys and ureters

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The lower tract, which consists of

the bladder and urethra.

Urine is formed by the kidneys

which filter blood passing through

them to remove excess ions,

metabolic waste and chemicals. The

urine passes down the ureters to the

bladder, a hollow muscular organ

which lies to the front of the pelvis

behind the pubic bone.

The bladder has four layers, the

outermost of which is continuous

with the peritoneum. The innermost

layer is the internal mucosa made

of transitional epithelium. This is

surrounded by a muscle layer made

up of circular and longitudinal

muscles forming a sort of net around

the bladder. The mucosal layer is

connected to this muscle layer by the

lamina propria, a connective-tissue

layer. The bladder muscle layer is called

the detrusor muscle. It is studded

with stretch receptors and as the

bladder fills with urine and stretches

to accommodate it, nerve impulses

relay the message via the sacral spine

up the vertebral column to the higher

micturition centres in the brain, i.e. the

pons, and then to the cerebral cortex

(Fillingham and Douglas, 2004).

The micturition centres in the

brain and sacral spine must all be

functioning and able to communicate

with each other via the nerves

connecting them for the bladder to

fill and empty normally.

The normal adult bladder usually

holds between 300–600ml of urine

and this empties out via the urethra.

An internal sphincter made of

smooth muscle lies at the base of

the bladder at the bladder neck.

There is also an external sphincter,

consisting of striated muscle which is

lower down the urethra and in close

contact with the pelvic floor. Both are

closed while the bladder is filling, but

open when the bladder needs to be

emptied (Urology textbook, 2018).

The male urethra is between

15–22cm long, while the female

urethra is only 3–5cm in length.

The male urethra extends from the

bladder neck, through the prostate

gland and the pelvic floor, then down

to the external urethral opening.

The female urethra extends

from the bladder neck and through

the pelvic floor to the external

opening and shares a wall with the

vagina, which is situated behind it

(Fillingham and Douglas, 2004).

EMPTYING THE BLADDER

The sensation of fullness when the

bladder fills with urine triggers off a

response, which alerts that it needs to

be emptied. For this to happen, both

sphincters need to relax and open

while the bladder muscle contracts

and expels the urine out of the body

via the urethra. Unlike the internal

sphincter muscle, which is not

under voluntary control, the external

sphincter can be controlled, and

when it is time to void, this muscle

relaxes to allow it to open.

Meanwhile, the pelvic floor moves

downwards allowing‘funnelling’of

the bladder, which means it is in the

best position to empty (Fillingham

and Douglas, 2004). At the same

UROLOGY AND CONTINENCE CARE TODAY

2018,Vol 1, No 1

time, nerve impulses send messages

from the cerebral cortex via the

pons and down the spine to the

bladder, allowing relaxation of the

internal sphincter and contraction

of the bladder muscle. The muscle

squeezing the bladder causes a rise

in bladder pressure, which pushes

the urine out past the open bladder

neck, down the urethra, past the open

external sphincter and then the rest

of the urethra and out of the body.

When empty, both sphincters close

again, the pelvic floor moves back

up and the bladder relaxes allowing

it to continue to fill. Again, to fill and

empty normally, the bladder muscle

and sphincters need to coordinate

when they open and close with muscle

contraction and relaxation. This means

that the nerves which supply the

bladder, sphincters and pelvic floor

must all be functioning properly (Royal

College of Nursing [RCN], 2012).

Anything which interrupts this

coordination, for whatever reason, will

cause the patient to have filling and

voiding problems, which may lead to

incomplete emptying or incontinence.

REFERENCES

Fillingham S, Douglas J, eds (2004)

Urological Nursing

. 3rd edn. Bailliere

Tindall, UK

Royal College of Nursing (2012)

Catheter

care RCN guidance for nurses

. RCN,

London. Available online: http://

studyres.com/doc/8027570/catheter-

care-rcn-guidance-for-nurses?page=2

Urology textbook (2018)

Anatomy of the

Bladder

. Available online: www.urology-

textbook.com/bladder-anatomy.html

(last accessed 30 January, 2018)