Bladder

Bladder

Structure of the Bladder
1. Body: Lying above the uretheral orifices
2. Base: Consisting of trigone and bladder neck
3. Detrusor:Muscular wall formed of smooth muscle cells
4. Ureteral Orifice: The opening of ureter into one corner of Trigone
5. Walls of the Bladder
  1. Urothellum
    1. Ubrella cells, Basal Cells.
      1. Apical:Largest epithelial cells 100-200um
      2. Intermediate layer (20 um in diameter)
      3. Basal layer (5-10 um in diameter)
    2. secretory and sensory functions
      1. Influences the activity of both nerves and under lying tissue layers
  2. Lamina Propria
  3. Submucosa
  4. Detrusor muscle
    1. Smooth Muscle
  5. Adventitia
Interstitial cells (ICs)
1. Recently identified population of cells
2. Morphology similar to interstitial cells of Cajal (ICC in the gut)
3. Found immediately beneath the urothelium as well as on the outer detrusor layer on the boundary of smooth muscle bundles
4. Play Role in processing of sensory information, pace making and modulating detrusor contractility
Spontaneous Activity
1. Non-stimulated contractions that occur in detrusor
2. Enhanced SA in bladder is associated with pathological conditions such as overactive bladder
3. Can stimulate afferent activity
Trigone
1. Area is very sensitive to expansion
  1. Once stretched to a certain degree, urinary bladder signals the brain of its need to empty
Urethra
1. Male 20cm
2. Female 4cm
3. The wall consists of deep mucosa and superficial muscularis
  1. Around the opening to the urethra the circular fibres form internal urethral sphincter
    1. Inferior to IUS is the external urethral sphincter composed of skeletal muscle
      1. Which controls the opening and closing of the bladder.
Innervation of the Bladder
1. Parasympathetic (from pelvic nerves)
  1. Motor to detrusor - to contact
    1. Relaxes Internal sphincter
2. Sympathetic (from pelvic part of sympathetic chain)
  1. Inhibitory to detrusor
    1. Contract internal sphincter
3. Somatic (Pudendal nerve)
  1. Motor to external sphincter
    1. Both afferent and efferent nerves
The micturition Reflex
1. The micturition relex (Storage)
  1. Cortical & suprapontine centers inhibits micturition
    1. Strech receptors send afferent signals to the brain through pelvic nerve
      1. They become active 120 ml of urine in bladder. sympathetic control results in smooth muscle relaxation
        Internal urethral sphincter contraction. Until a socially acceptable.
        Voiding efferent impulses from the brain inhibits parasymathetic neurons in spinal cord.
        Voluntary contractions of external urinary sphincter also contribute to storage.
2. The micturition reflex
  1. Intense vesical afferent activity
    1. The parasympathetic outflow to the bladder
      1. Internal sphincter smooth muscle
        (Ach main stimulus for muscle relaxation)
        Contraction of destrusor and relaxation of internal urethral sphincter

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