biology

Human penis

Human penis is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Human penis rather than just read about it. In short: In human anatomy, the penis (; pl.: penises or penes; from the Latin pēnis, initially 'tail') is an external sex organ (intromittent organ) through which males ejaculate and urinate. Together with the testes and surrounding structures, the penis functions as part of the male reproductive system.

Key takeaways

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

Reference excerpt

In human anatomy, the penis (; pl.: penises or penes; from the Latin pēnis, initially 'tail') is an external sex organ (intromittent organ) through which males ejaculate and urinate. Together with the testes and surrounding structures, the penis functions as part of the male reproductive system. The main parts of the penis are the root, body, the epithelium, including the shaft skin, and the foreskin covering the glans. The body of the penis is made up of three columns of tissue: two corpora cavernosa on the dorsal side and corpus spongiosum between them on the ventral side. The urethra passes through the prostate gland, where it is joined by the ejaculatory ducts, and then passes through the corpus spongiosum. The external opening of the urethra at the tip of the glans is the urinary meatus. An erection is the stiffening expansion and orthogonal reorientation of the penis, which occurs during sexual arousal. Erections can occur in non-sexual situations; spontaneous non-sexual erections frequently occur during adolescence and sleep. In its flaccid state, the penis is smaller, gives to pressure, and the glans is covered by the foreskin. In its fully erect state, the shaft becomes rigid and the glans becomes engorged but not rigid. An erect penis may be straight or curved and may point at an upward angle, a downward angle, or straight ahead. As of 2015, the average erect human penis is 13.12 cm (5.17 in) long and has a circumference of 11.66 cm (4.59 in). Neither age nor size of the flaccid penis accurately predicts erectile length. There are several common body modifications to the penis, including circumcision. The penis is homologous to the clitoris in females.

Structure

Three main parts of the human penis include:

Root: It is the attached part, consisting of the bulb in the middle and the crura, one crus on either side of the bulb. It lies within the superficial perineal pouch. The crus is attached to the pubic arch. Shaft: The pendulous part of the penis. It has two surfaces: dorsal (posterosuperior in the erect penis) and ventral or urethral (facing downwards and backwards on the flaccid penis). The ventral surface is marked by the penile raphe. The base of the shaft is supported by the suspensory ligament, which is attached to the pubic symphysis. Epithelium of the penis consists of the shaft skin, the foreskin (prepuce), and the preputial mucosa on the inside of it. The foreskin covers and protects the glans and shaft. The epithelium is not attached to the underlying shaft, so it is free to glide to and fro. The human penis is made up of three columns of erectile tissue: two corpora cavernosa lie next to each other (separated by a fibrous septum) on the dorsal side and one corpus spongiosum lies between them on the ventral side. These columns are surrounded by a fibrous layer of connective tissue called the tunica albuginea. The corpora cavernosa are innervated by lesser and greater cavernous nerves and form most of the penis containing blood vessels that fill with blood to help make an erection. The crura are the proximal parts of the corpora cavernosa. The corpus spongiosum is an erectile tissue surrounding the urethra. The proximal parts of the corpus spongiosum form the bulb and the distal ends form the glans penis. The enlarged and bulbous-shaped end of the corpus spongiosum forms the glans penis with two specific types of sinusoids, which supports the foreskin, a loose fold of skin that in adults can retract to expose the glans. The area on the underside of the glans, where the foreskin is attached, is called the frenulum. The rounded base of the glans is called the corona. The inner surface of the foreskin and corona is rich in sebaceous glands which secrete smegma. The structure of the penis is supported by the pelvic floor muscles.

The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum (spongy urethra) and opens through the urinary meatus on the tip of the glans.

The penile raphe is the visible ridge between the lateral halves of the penis, found on the ventral or underside of the penis, running from the meatus and continuing as the perineal raphe across the scrotum and the perineum (area between scrotum and anus). The human penis differs from those of most primates, as it has no baculum and relies entirely on erectile tissue. A distal ligament buttresses the glans penis and plays an integral role to the penile fibroskeleton, and the structure is called "os analog", a term coined by Geng Long Hsu in the Encyclopedia of Reproduction. It is a remnant of the baculum that has likely evolved due to change in mating practice. The human penis cannot be withdrawn into the groin, and it is larger than average in the animal kingdom in proportion to body mass. The human penis is reciprocating from a cotton soft to a bony rigidity resulting from penile arterial flow varied between 2–3 to 60–80 mL/Min implies the most ideal milieu to apply Pascal's law in the entire human body; the overall structure is unique.

Size

Penile measurements vary, with studies that rely on self-measurement reporting a significantly higher average size than those which rely on measurements taken by health professionals. A 2015 systematic review of 15,521 men in which the subjects were measured by health professionals showed that the average length of an erect human penis is 13.12 cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66 cm (4.59 inches). Among all primates, the human penis is the largest in girth, but is comparable to the chimpanzee penis and the penises of certain other primates in length. Penis size is affected by genetics, but also by environmental factors such as fertility medications and chemical/pollution exposure.

Normal variations

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Human penis

Start with the simplest possible case. Write down what Human penis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, 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 Human penis 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 Human penis 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 Human penis

In research: Human penis appears in biology 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 Human penis 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: Human penis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human anatomy, Human male reproductive system, Human penis, so understanding it makes those chapters shorter.
In everyday life: Look for Human penis 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.

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How to study Human penis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Human penis 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 Human penis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Human penis in simple terms?

Why does Human penis matter?

Because it connects several biology 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 Human penis?

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 Human penis.