Bladder Anatomy and Function

• This section focuses on bladder and bowel anatomy and function, necessary for treating related conditions.

Bladder Anatomy

• The bladder is an organ of the urinary system.

• From innermost to outermost, the bladder layers consist of epithelium, lamina propria, muscularis propria (detrusor muscle), and perivesical soft tissue.

  • Epithelium: Innermost lining.
  • Lamina propria: Connective tissue, muscle, and blood vessels.
  • Muscularis propria (detrusor muscle): Contracts to expel urine; relaxes during urine storage; innervated by sympathetic and parasympathetic nerves.
  • Perivesical soft tissue: Outermost layer made of fat, fibrous tissue, and blood vessels.

• Trigone: A triangular area inside the bladder.

• Bladder neck: The area at the base of the trigone surrounding the internal urethral orifice, adjacent to the prostate gland in males.

• The bladder neck is supported by pubocervical/pubourethral ligaments and fascia, active support of the pelvic floor muscles (PFM), and endopelvic fascia.

• Internal Urethral Sphincter: A band of circular smooth muscle surrounding the preprostatic urethra in males, under autonomic control, relaxes during micturition and contracts during ejaculation to prevent retrograde ejaculation.

• Functional Sphincter (Female): Formed by bladder neck and proximal urethra.

• External Urethral Sphincter: Skeletal muscle under voluntary control surrounding the urethra, more complex in males due to correlation with fibres of the rectourethralis and the levator ani.

Bladder Innervation

• Sympathetic: Hypogastric nerve (T10-L2) causes detrusor muscle relaxation, promoting urine retention.
• Parasympathetic: Pelvic nerve (S2-S4) causes detrusor muscle contraction, stimulating micturition.
• Somatic: Pudendal nerve (S2-4) innervates the external urethral sphincter, providing voluntary control over micturition.
• Sensory (afferent) nerves in the bladder wall signal the need to urinate when the bladder becomes full.

Bladder Stretch Reflex

• The bladder stretch reflex is a primitive spinal reflex where micturition is stimulated by stretch of the bladder wall.
• Reflex arc:
  • Bladder fills -> walls stretch.
  • Sensory nerves detect stretch, transmit info to spinal cord.
  • Interneurons relay signal to parasympathetic efferents.
  • Pelvic nerve contracts detrusor muscle, stimulates micturition.
• The bladder temporarily stores urine, accommodating 300-600ml in healthy adults, and assists in urine expulsion through muscle contraction and sphincter relaxation.

Normal Voiding Requirements

• A functioning central nervous system is required.
• A functioning/contractile bladder is required.
• Urethral relaxation or manageable outflow resistance is required.

Normal Bladder Function

• Normal bladder holds 300-400ml each void during the day and 500-600ml overnight.
• Normal Voiding Frequency: About six times per day and zero to once overnight for people under 65.
• Over 65: Daily void frequency increases to around seven times a day and once overnight.
• Voiding eight times a day and twice overnight is considered pathological.

Bladder Diaries

• Bladder diaries collect data on urinary storage and output.
• Assists in developing treatment programs.
• Typically completed for three days.
• Fluid intake include timing, amount, type of fluid.
• Output measures include bladder volumes, voiding frequency, time of voiding, bladder urge experienced each void, and can include urinary leakage.

Bowel Anatomy

• The bowel digests food, absorbs nutrients, processes, and expels waste.
• Food travels the digestive tract in 12-48 hours.
  • Small intestine: 6 meters long, absorbs nutrients.
  • Colon: 1.5 meters long, absorbs water.
  • Rectum: Stores waste.
• Sacral flexure: Anteroposterior curve that follows the curve of the sacrum and coccyx.
• Anorectal flexure: Anteroposterior curve formed by the puborectalis muscle, a key contributor to faecal continence.
• Sympathetic supply: Lumbar splanchnic nerves and the superior and inferior hypogastric plexuses.
• Parasympathetic supply: S2-4 via pelvic splanchnic nerves and inferior hypogastric plexuses (S2,3,4 keep the poo off the floor!).
• Anal canal: Located within the anal triangle, collapsed by internal and external anal sphincters except during defecation.
  • Internal anal sphincter: Involuntary smooth muscle in the upper 2/3 of anal canal.
  • External anal sphincter: Skeletal muscle in the lower 2/3 of anal canal, blending with puborectalis muscle.
• Puborectalis muscle: Encircles rectum, maintaining faecal continence.

Bowel Habits

• Normal bowel habits vary from several times a day to several times a week.
• Defecation often occurs 30 minutes after a meal, commonly after breakfast.
• Stool formation and ease of defecation is more important than frequency.

Bristol Stool Chart

• Medical aid to classify faeces into seven categories based on shape and type.
• Stool type depends on time spent in the bowel.
• Well-formed, soft, and easy-to-pass stools are ideal.

Bristol Stool Chart Types

• Types 1-2: Indicate constipation.
• Types 3-4: Ideal stool, easier to pass.
• Types 5-7: May indicate diarrhea and urgency.

Colorectal Motility

• Colorectal/Colonic motility: Movement of food and waste through the colon. The colon propels its contents towards the anus for evacuation.
• Propagating sequences occur less frequently in the distal colon.
• They propagate for shorter distances, at a faster velocity, than in the proximal colon.
• More non-propagating (segmenting) pressure waves occur in the distal colon.

Types of Contractions

• Phasic contractions include segmental (non-propagating) and propagating contractions.
  • Segmental (non-propagating) complexes: Last a few seconds, move contents short distances. Mix colonic contents.
• Propagating contractions involve large bowel segments.
  • High amplitude: 6-20 times/day. Propel contents toward anus.
  • Low amplitude: Hundreds of times/day.
• Anterograde contractions propel gut contents towards the anus (approximately 50 times/24 hours).
• Retrograde contractions propel gut contents towards the mouth (approximately 30 times/24 hours).
• Rectal motility: Periodic motor activity lasting up to 30 minutes, triggered by stool arrival, increased postprandially.

Control of Colonic Motility

• Sleep has an inhibitory effect on the gut; REM sleep increases gut activity.
• Gut activity triples upon waking.
• Eating increases both segmental and propagating complexes, increases overall colonic tone, sensitivity, and rectocolonic reflexes.
• Physical stress causes increased segmental contraction via autonomic pathways, resolving after stress stops.
• Psychological stress slows gastric emptying but accelerates colonic transit, with increased activity persisting.

Normal Bowel Function

• Holding for a short time after feeling the first urge is normal with no faecal incontinence.
• Passing stool within approximately 1 minute of sitting to defecate is normal.
• Passing stool without strain or pain is normal.
• Completely emptying the bowel during defecation is normal.

Bowel Diary

• A bowel diary records stools and defecation.
• Assists in the treatment of bowel dysfunction.
• Should be recorded for seven days.

Fibre

• Fiber is important for general, and gut health and motility.

• Soluble fibre forms a gel, swelling the stool, slowing stomach emptying, lowering cholesterol, and stabilising blood glucose; found in fruit/vegetable insides, psyllium, oats, barley, legumes.

• Insoluble fibre acts as a broom, softening bowel contents and supporting regular movements; found in grains, seeds, fruit/vegetable skins, whole grains, cereals, nuts.

• Recommended intake is 25g/day for adult females and 30g/day for adult males.

Water

• Water is essential for gut motility and defecation.
• Foods provide about 20% of water requirements, digestion by-product provides 10%, and fluids provide 70%.

Flatulence

• Flatulence is a normal bodily function resulting from bacteria breaking down food in the large intestine.
• Fart sounds vary based on gas amount, speed, and anal sphincter tightness.
• The average adult produces 705ml (24 ounces) of gas daily.
• Volume varies by swallowed air and bacterial production from undigested carbohydrates like raffinose.