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Serosal Layer: The bladder consists of four structurally distinct tissue layers. The outermost of these, known as the serosal or tunica seros is derived from the peritoneum and covers only the upper and lateral surfaces of the bladder. (3,5)
Detrusor Muscle: Adjacent to and inward of the serosa layers is the muscle layer of the bladder, also known as the tunica muscularis and more commonly as the detrusor muscle (4), a name derived from the Latin detrudere meaning "to thrust out (5)" and related to the contractile function of this muscle in expelling urine from the bladder.
Submucosal Layer: Internally adjacent to the tunica muscularis is the third layer of the bladder tissue, the submucosal layer, which is also known as the lamina propria (1,5). This layer consists of blood and lympathic vessels and nerves within a stroma of fibrous connective that join the tunica muscularis to the innermost of the bladder tissue layers, the tunica mucosa or mucosal layer (1,2,4,5).
Mucosal Layer: The mucosal layer is the innermost tissue of the bladder. Also known as the urothelium because it consists of the transitional epithelial cells that also line the ureters and urethra (2), the mucosa of the bladder is continuous with the lining of the tubular structures. The epithelial tissue layer of the bladder consists of from five to seven strata of transitional epithelial cells, also called urothelial cells. The deepest of these, made up of the mucosa, of which the uppermost lines the inner surface of the bladder and comes into contact with the urine (2). The uppermost cells of the urothelium at the inner surface of the bladder, are knows as umbrella cells. These cell, which extend over smaller cells in the new lower layer epithelium, are impermeable, resistant to infection and to the adherence of many foreign substances (6) and thus provide protection for underlying cells of the urothelium, the umbrella cells at the surface of this tissue layer secrete a protective substance known as mucin, which protects the underlying bladder cell from irritating substances present in urine.
Mast cells participate in allergic and inflammatory reactions in the body's tissues. Un allergic reactions, antibodies of the immunoglubulin E (IgE) class become bound in a highly selective manner to specialized receptors on the surface of mast cells, prompting them to release various biologically active substances that promote different reactions in the surrounding tissues. Among those substances are heparin, which inhibits blood clotting, protease enzymes that break down proteins, histamine that triggers pain and other signals in local nerve cells, chemotactic substances that attract immunologically active cells into the region of activated mast cells, vasoactive substances that promote dilation of blood vessels and substances such as the prostaglandins and leukocrienes, which promote localized inflammation (7).
The GAGs, or mucin of the bladder urothelium, are first line defense of the urinary bladder against penetration into the bladder wall of bacteria and potentially harmful chemical substances in adjacent urine (6,8,9,11,12). Because GAGs carry a negative electrical charge, the oxygen atoms of the sulfate groups that are chemically bound to many GAG units have a strong tendency to bind to the positively charges hydrogen atoms and water molecules. This tight bonding produces a stable water layer around the coating of the bladder urothelium, preventing urea, calcium, barium, and other irritating solutes in the urine from binding to the sulfate groups of the GAGs (11). This shielding water layer prevents most solutes dissolved in the urine from entering the bladder wall and appears to be of utmost importance for regulation of the permeability of the bladder urothelium (6,8,9,11).
Understanding Your Bladder
Protected Inner Layer of the Bladder (Bladder Wall & Tissue Layers)
Mast Cells
Normally the bladder, like a great many other organizations and tissues of the body, contain some specialized cells knows as mast cells. Theses cells are especially present in connective tissue and often tend to aggregate near blood vessels. Of the several different types of mast cells found in the body, those known as atypical mast cells are most commonly found in the gastrointestinal tract and the bladder (7). Within the bladder, mast cells are normally present in the muscle layer and in larger numbers in the submucosal layer or lamina propria (7,13).
Glycosaminoglycans
At its interior surface, the mucosal layer of the bladder is covered by a film of mucin, which is secreted by the urothelial cells at the surface of this tissue layer and consists largely of the substances known as glycosaminoglycan (GAG) (8,9). These substances are long polymeric molecules held closely to one another by interactions between their atoms, which bind GAGs into a continuous protective mucin film. An individual GAG unit consists, in turn, of these molecules, each derived from sugar glucose and bound chemically to one another. Among the major GAGs are hyaluronic acid, heparin and chondroitin (10).
References
(1) Crouch JE. Functional Human Anatomy 4th ed. Philadelphia, Pa: Lea & Febiger, 1985;533-537
(2) Peterson RO. Urologic Pathology 2nd ed. Philadelphia, Pa: JB Lippincott, 1992; Ch. 4
(3) Culp DA, Fallon B, Loening SAH. Surgical Urology. 5th ed. Chicago, Ill: Year Book 1975; Ch.6
(4) Hollinshead WH, Rosse C. Textbook of Anatomy. 4th ed. Philadelphia, Pa: Harper & Row, 1985;767
(5) Moore KL. Clinically Oriented Anatomy. 2nd ed. Baltimore, MD: Williams & Wilkens, 1985;Ch. 3
(6) Parsons CL, Lilly JD, Stein P. Epithelial dysfunction in nonbacterial cystitis (interstitial cystitis). J Urol 1991;145:732-735
(7) Sant GR, Theoharides TC. The role of mast cell in interstitial cystitis. Urol Clin North Am 1994;219(1):41-51
(8) Sant GR, Meares EM Jr. Interstitial cystitis: pathogenisis, diagnosis, and treatment. Infect Urol January/February 1990;24-30
(9) Parsons CL. The therapeitic role of sulfated polysaccharides in the urinary bladder, Urol Clin North Am 1994;21(1):93-99
(10) Ruggieri MR, Chelsky MJ, Rosen SI, Shickley TJ, Hanno PM. Current findings and future research avenues in the study of interstitial cystisi. Urol Clin North Am 1994;21(1):163-176
(11) Parsons CL, Parson JK. Interstitial cystitis. In Raz S, (Ed.) Female Urology. 2nd Ed. Philadelphia: WB Saunders, 1996; Ch 15
(12) Ratliff TL, Klutke CG, McDougall EM. The etiology of interstitial cystitis. Urol Clin North Am 1994;21(1):21-30
(13) Mesing EM, Stamey TA. Interstitial cystitis: early diagnosis, pathology, and treatment. Urology 1978;12(4):381-392