Bladder

Overview

The Urinary Bladder is an organ involved in the homeostatic process of excretion, and is the situated in the pelvic floor. It is linked to the kidneys via the descending structures called ureter, which move fluid down from the kidneys with the aids of gravity and peristalsis. The fluid being removed from the body by the bladder is produced by the kidneys through ultrafiltration, and is composed mainly of urea, salts, water and other organic compounds. 

Histology

The walls of the main body of the bladder consist of three layers of different tissues:

• An inner epithelial layer, 3-6 cells thick, called the Urolthelium. [1]

• A middle layer consisting of connective tissuse called the lamina propria and the submucosa. [2]

• An outer layer formed from varying arrangements of smooth muscle. [3]

The smooth muscle of the bladder walls is found in 3 different layers:

• The inner layer of loose spiral muscle lies in longitudinal formation.

• The middle layer lies in a circular manner, continuously with the outer layer of the ureter. 

• The outer layer sees the muscle fibers arranged similarly to the inner layer. [4]

Another function of muscle in the bladder is in the internal and external sphincters, which control urine flow out of the badder into the urethra.

• The internal sphincter is controlled by the autonomic nervous system, and is a continuation of the bladder wall. It is permanently tonated to stop urine voiding the bladder, although when maximum bladder capacity is reached, signals from the autonomic nervous system will relax the muscle automatically.
• The extrernal sphincter is controlled by the somatic nervous system and is made of voluntary, or striated muscle, and can therefore be conciously controlled. [5]

Blood supply to the bladder

Oxygenated blood is supplied to the bladder via the inferior and superior vesical arteries, and the umbilical artery. 
Deoxygenated blood is removed via the vesical venous plexus. [6]

Nervous supply to the bladder

Sympathetic nervous fibres, called the hypogastric plexuses and nerves, reach from levels of the upper spinal cord, including the inferior thoracic and upper lumbar.  [6]

Parasympathetic nervous fibres originate from the sacral spinal cord level and travel via the inferior hypogastric plexus and the pelvic splanchnic nerves. [6]

References

[1] Jost S P, Gosling J A, Dixon J S. Journal of Anatomy. 1989. Volume 167, pages 107-115; Morphology of normal human bladder urothelium.

[2] Cao, Liu, Mei, Cunha, Benchun, Baskin, Laurence. Journal of Pediatric Research. 2008. Volume 64, Issue 4, pages 352-357. Urothelium patters in bladder smooth muscle location.

[3] Drake R L. 2010. Gray's Anatomy for Students

[4] Stevens A, Lowe J. 2005. Human Histology. 3rd edition. Pages 324-325. London: Mosby. 

[5] Silverthorn, D U. 2010. Human Physiology: An Intergrated Approach. San Francisco: Pearson Education Inc. 

[6] Moore K L, Dalley A F, Agur A M R. Clinically Orientated Anatomy. 6th edition. Pages 364-368. Philadelphia, Pa; London: Lippincott, Williams & Wilkins.