Anatomy
Abdomen
The bladder receives its efferent parasympathetic fibres derived from spinal cord segments:
Answer:
The bladder receives efferent parasympathetic fibres from the pelvic splanchnic nerves (S2 to S4). Parasympathetic stimulation causes the detrusor muscle of the bladder to contract and the internal sphincter muscle to relax.Urinary Bladder
Anatomy / Abdomen / Urinary Tract
Last Updated: 11th April 2019
The bladder is the most anterior viscera in the pelvic cavity. When empty it is entirely situated in the pelvic cavity, but when full expands superiorly into the abdominal cavity. The bladder is a retroperitoneal structure and when full lies adjacent to the anterior abdominal wall.
Structure
The empty bladder is shaped like a three-sided pyramid that has tipped over to lie on its side and has an apex, a base, a superior surface and two inferolateral surfaces.
- The apex of the bladder is directed towards the top of the pubic symphysis.
- The triangular-shaped base (or fundus) of the bladder faces posteroinferiorly. The two ureters enter the bladder at each of the upper corners of the base, and the urethra drains inferiorly from the lower corner of the base.
- The inferolateral surfaces of the bladder are cradled between the levator ani muscles of the pelvic diaphragm and the adjacent obturator internus muscles above the attachment of the pelvic diaphragm.
- The superior surface is slightly domed when the bladder is empty and balloons upwards as the bladder fills.
Structure of the Urinary Bladder. (Image by OpenStax College [CC BY 3.0 , via Wikimedia Commons)
Relations
In the male the bladder is related:
- anteriorly to the pubic symphysis
- posteriorly to the rectovesical pouch and rectum
- inferiorly to the prostate and the pelvic floor
- superiorly to the peritoneum.
In the female the bladder is related:
- anteriorly to the pubic symphysis
- posteriorly to the vesicouterine pouch, the uterus, the cervix and the vagina
- superiorly to the uterus and the peritoneum
- inferiorly to the pelvic floor.
Relations of the Urinary Bladder. (Image by OpenStax College [CC BY 3.0 , via Wikimedia Commons)
Innervation
The bladder receives efferent sympathetic fibres from the hypogastric plexuses and nerves (T12 - L2).
The bladder receives efferent parasympathetic fibres from the pelvic splanchnic nerves (S2 to S4).
The voluntary external urethral sphincter is innervated by the pudendal nerve (S2 - S4).
Control of Micturition
General visceral afferent fibres from the bladder, which are stimulated by distension (approximately 300 mL for adults), are conveyed in both the sympathetic and parasympathetic nervous system (the latter being the most important in micturition).
Storage Phase:
At low bladder volumes, afferent firing is low. Sympathetic stimulation keeps the detrusor muscle relaxed and keeps the involuntary internal sphincter closed, inhibiting bladder emptying.
Voiding Phase:
At high bladder volumes, afferent firing increases, causing a conscious sensation of urinary urge. During micturition, parasympathetic stimulation causes the detrusor muscle to contract and the involuntary internal sphincter muscle to relax, facilitating emptying of the bladder. The somatic external urethral sphincter is consciously relaxed during micturition.
Neurogenic Bladder
The bladder stretch reflex is a primitive spinal reflex where a full bladder, detected by stretch receptors in the bladder wall, activates visceral afferents resulting in activation of parasympathetic efferents and contraction of the detrusor muscle with resultant micturition. Normally this spinal reflex is overridden by the higher centres of the brain to give voluntary control over micturition via the external urethral sphincter.
In spinal cord injury, two types of clinical syndromes are seen:
- In injuries above the conus medullaris (above vertebra T12), the S2 - S4 levels of the spinal cord are intact and there is a functioning spinal reflex. In this case a reflex bladder will occur, where there is loss of higher control and so the bladder stretch reflex takes over, and the detrusor muscle is stimulated to contract as the bladder fills.
- In injuries affecting the S2 - S4 sacral nerve roots (below vertebra T12) a flaccid bladder will occur, where there is loss of both higher control and of the spinal reflex. In this case when the bladder fills, it becomes abnormally distended until the internal and external sphincters are stretched, allowing urine to pass.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
