Anatomy
Abdomen
Which of the following parts of the male urethra passes through the urogenital diaphragm:
Answer:
The membranous part of the urethra is the narrowest part and passes through the urogenital diaphragm. During its transit through the pelvic floor, in both men and women, it is surrounded by skeletal muscle of the external urethral sphincter.Urethra
Anatomy / Abdomen / Urinary Tract
Last Updated: 11th April 2019
The urethra begins at the base of the bladder and ends with an external opening in the perineum.
Female urethra
In women the urethra is short (about 4 cm long). It passes inferiorly through the urogenital diaphragm into the perineum before opening in the vestibule that lies between the labia minora. The inferior aspect of the urethra is bound to the anterior surface of the vagina. The urethral opening is anterior to the vaginal opening in the vestibule.
Male urethra
Beginning at the base of the bladder and passing inferiorly through the prostate, the urethra passes through the deep perineal pouch and perineal membrane and immediately enters the root of and travels the length of the penis. The external urethral orifice is the sagittal slit at the end of the penis.
ANGLES:
The male urethra (spongy part) has two angles:
- Infrapubic angle - where the urethra bends anteriorly in the root of the penis after passing through the perineal membrane
- Prepubic angle - where the urethra curves inferiorly when passing from the root into the body of the penis
The infrapubic angle is a fixed angle, but the more distal prepubic angle can be diminished by holding the penis upwards during urinary catheterisation. This angle also disappears during erection.
![By Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/02/Male.png)
Angles of the Male Urethra. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
PARTS:
In men the urethra is long (about 20 cm) and is divided into four parts; preprostatic, prostatic, membranous and spongy:
- The preprostatic part is about 1 cm long, extending from the base of the bladder to the prostate and is associated with the internal urethral sphincter (which prevents retrograde movement of semen into the bladder during ejaculation).
- The prostatic part is about 3 - 4 cm long, is the widest part, and is surrounded by the prostate. In this region the lumen of the urethra is marked by a longitudinal midline fold of mucosa (the urethral crest). Midway along its length the urethral crest is enlarged, marked by the openings of the prostatic utricle and ejaculatory ducts. The prostatic ducts empty into the prostatic sinuses on either side of the urethral crest.
- The membranous part is the narrowest part and passes through the urogenital diaphragm. During its transit through the pelvic floor, in both men and women, it is surrounded by skeletal muscle of the external urethral sphincter.
- The spongy part is the longest part and is surrounded by the corpus spongiosum of the penis. It is enlarged to form a bulb at the base of penis and again at the end. The bulbourethral glands open into the bulb of the spongy urethra.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/02/Urethra-1.png)
Parts of the Male Urethra. (Image modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
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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 |
