The Human Urinary Bladder-a component of the Urinary/Excretory System

1. Summarized Anatomy

2.  Is an organ of the urinary system, situated
anteriorly in the pelvic cavity.
 Is hollow, highly distensible & rounded in shape.
 Main function is to collect, temporarily store, &
expel urine.
 It has a unique muscular structure & a complex
neurological control.
 Embryologically, the bladder is derived from the
Hind-gut.
 An empty bladder lies in the lesser pelvis in adults
but in kids, its in the abdomen till the age of 6
where it goes into the greater pelvis.
 After puberty then it moves into the lesser pelvis.

3.  When EMPTY-flattened by the overlying intestines.
 When FULL-exhibits an oval shape.
 Has an APEX, BODY, FUNDUS/BASE, & NECK.
 Apex-located superiorly, pointing towards the pubic
symphysis. Connected to the umbilicus by the
Median Umbilical Ligament. (Urachus remnant)
 Body-Main part of the bladder, located btw the
apex & the fundus.
 Fundus/Base-Located posteriorly. Is triangular in
shape with the tip of triangle pointing backwards.
 Neck-Formed by the convergence of the fundus &
the 2 inferolateral surfaces. This structure joins the
bladder to the urethra.

4.  Urine enters the bladder by the left & right
ureters, & 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.
 There are 2 sphincters controlling the outflow
of urine; the internal & external urethral
sphincters.
 NB: Trigone is smooth because the mucosa
firmly attaches to the muscularis.

5. The bladder wall contains specialized
smooth muscle, known as Detrusor
muscle.
It receives innervation from both
sympathetic & parasympathetic nervous
system.
There are 2 muscular sphincters located in
the urethra:

6.  Internal urethral sphincter:
 Males-consists of circular smooth fibers which are
under autonomic control. Thought to prevent
seminal regurgitation during ejaculation.
 Females-thought to be a functional sphincter (i.e.
no sphincter muscle present). It is formed by the
anatomy of the bladder neck & proximal urethra.
 External urethral sphincter:
 Has the same structure in both sexes. Skeletal
muscle under voluntary control. During micturation,
it relaxes to allow urine flow.

7. The bladder primarily receives its
vasculature from the internal iliac vessels.
Arterial supply by the Superior Vesical &
Inferior Internal Iliac artery.
Venous drainage achieved by the Vesical
Venous Plexus, which empty into the
Internal Iliac Vein/Hypogastric Vein.

8.  Bladder receives input from both autonomic &
somatic arms of the nervous system.
 Sympathetic nervous system- Hypogastric
nerve (T1-L2). Causes relaxation of the
Detrusor muscle-retention.
 Parasympathetic nervous system- Pelvic
nerve (S2-S4). Causes contraction of the
detrusor muscle-micturation.
 Somatic nervous system-gives us voluntary
control over micturation. It innervates the
external urethral sphincter via the Pudendal
nerve (S2-S5)-constrict or relax.

9. Is a primitive spinal reflex, in which
micturation is stimulated in response to
stretch.
During toilet-training in infants, the spinal
reflex is overridden by the higher centers
of the brain, to give voluntary control over
micturation.

10. 1. Bladder fills with urine, & walls stretch.
Sensory nerves detect stretch & transmit
this into the spinal cord.
2. Interneurons within the spinal cord relay
the signal to the parasympathetic
efferents. (pelvic nerve)
3. The pelvic nerve acts to contract the
detrusor muscle & stimulate micturation.