Urethra

Key takeaways

Urethra belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Urethra to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Urethra from memory before moving on to harder problems.

Reference excerpt

The urethra (pl.: urethras or urethrae) is the tube that transports urine from the bladder to the urethral meatus of the penis or vulva in placental mammals. In males, it also transports semen through the penis during ejaculation. The external urethral sphincter is a striated muscle that allows voluntary control over urination. The internal urethral sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, is innervated by the sympathetic division of the autonomic nervous system in males and females.

Structure The urethra is a fibrous and muscular tube which connects the urinary bladder to the external urethral meatus. Its length differs between the sexes, because it passes through the penis in males.

Male

The human male urethra is on average 18 to 20 centimeters (7 to 8 inches) long and opens at the end of the external urethral meatus. The urethra is divided into four parts in men, named after the location:

There is inadequate data for the typical length of the male urethra; however, a study of 109 men showed an average length of 22.3 cm (SD = 2.4 cm), ranging from 15 cm to 29 cm. The urethra in male placental mammals is typically longer than in females.

Female The human female urethra is about 4 cm long having 6 mm diameter,, extending from the internal urethral orifice of the bladder to the urethral meatus below the clitoris. The meatus is placed behind the symphysis pubis, embedded in the anterior wall of the vagina, and its direction is obliquely downward and forward; it is slightly curved with the concavity directed forward. The proximal two-thirds of the urethra is lined by transitional epithelial cells, while the distal third is lined by stratified squamous epithelial cells. Between the superior and inferior fascia of the urogenital diaphragm, the female urethra is surrounded by the urethral sphincter. The urethra in female placental mammals is typically shorter than in the male.

Microanatomy The cells lining the urethra (the epithelium) going all over transitional cells as it exits the bladder, which are variable layers of flat to cuboidal cells that change shape depending on whether they are compressed by the contents of the urethra. Further along the urethra there are pseudostratified columnar and stratified columnar epithelia. The lining becomes multiple layers of flat cells near the end of the urethra, which is the same as the external skin around it. There are small mucus-secreting urethral glands present in the urethral wall. In females, the paraurethral glands secrete mucous to lubricate the urethra; in males, the homologous bulbourethral glands. The urethra consists of three coats: muscular, erectile, and mucous, the muscular layer being a continuation of that of the bladder.

Blood and nerve supply and lymphatics Somatic (conscious) innervation of the external urethral sphincter is supplied by the pudendal nerve.

Development

In the developing embryo, at the hind end lies a cloaca. This, over the fourth to the seventh week, divides into a urogenital sinus and the beginnings of the anal canal, with a wall forming between these two inpouchings called the urorectal septum. The urogenital sinus divides into three parts, with the middle part forming the urethra; the upper part is largest and becomes the urinary bladder, and the lower part then changes depending on the biological sex of the embryo. The cells lining the urethra (the epithelium) come from endoderm, whereas the connective tissue and smooth muscle parts are derived from mesoderm. After the third month, urethra also contributes to the development of associated structures depending on the biological sex of the embryo. In the male, the epithelium multiples to form the prostate. In the female, the upper part of the urethra forms the urethra and paraurethral glands.

Function

Urination

The urethra is the vessel through which urine exits the bladder. During urination, the urethra's smooth muscle relaxes as the bladder contracts to expel urine in a pressurized stream. Following this, the urethra re-establishes muscle tone by contracting the smooth muscle layer, and the bladder returns to a relaxed, quiescent state. Urethral smooth muscle cells are mechanically coupled to each other to coordinate mechanical force and electrical signaling in an organized, unitary fashion.

Ejaculation The male urethra is the conduit for semen during orgasm. Urine is removed before ejaculation by pre-ejaculate fluid – called Cowper's fluid – from the bulbourethral gland.

Clinical significance

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Urethra

Start with the simplest possible case. Write down what Urethra claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Urethra before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Urethra ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Urethra

In research: Urethra appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Urethra in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Urethra is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human reproductive system, Mammal reproductive system, Urethra, so understanding it makes those chapters shorter.
In everyday life: Look for Urethra outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Urethra in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Urethra means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Urethra out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Urethra in simple terms?

The urethra (pl.: urethras or urethrae) is the tube that transports urine from the bladder to the urethral meatus of the penis or vulva in placental mammals. In males, it also transports semen through the penis during ejaculation.

Why does Urethra matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Urethra?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Urethra.