Testicle

Key takeaways

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

Reference excerpt

A testicle, also called testis (pl. testes) is the male gonad in all gonochoric animals, including humans, and is homologous to the ovary, which is the female gonad. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone. The release of testosterone is regulated by luteinizing hormone (LH) from the anterior pituitary gland. Sperm production is controlled by follicle-stimulating hormone (FSH) from the anterior pituitary gland and by testosterone produced within the gonads.

Structure

Appearance

Male humans have two testicles of similar size contained within the scrotum, which is an extension of the abdominal wall. Scrotal asymmetry, in which one testicle extends farther down into the scrotum than the other, is common. This is because of the differences in the vasculature's anatomy. For 85% of men, the right testis hangs lower than the left one.

Measurement and volume The volume of the testicle can be estimated by palpating it and comparing it to ellipsoids (an orchidometer) of known sizes. Another method is to use calipers, a ruler, or an ultrasound image to obtain the three measurements of the x, y, and z axes (length, depth and width). These measurements can then be used to calculate the volume, using the formula for the volume of an ellipsoid:

V o l u m e = 4 3 ⋅ π ⋅ l e n g t h 2 ⋅ w i d t h 2 ⋅ d e p t h 2 {\displaystyle Volume={\frac {4}{3}}\cdot \pi \cdot {\frac {length}{2}}\cdot {\frac {width}{2}}\cdot {\frac {depth}{2}}}

≈ l e n g t h ⋅ w i d t h ⋅ d e p t h ⋅ 0.52 {\displaystyle \approx length\cdot width\cdot depth\cdot 0.52}

However, the most accurate calculation of actual testicular volume is gained from the formula:

≈ l e n g t h ⋅ w i d t h ⋅ d e p t h ⋅ 0.71 {\displaystyle \approx length\cdot width\cdot depth\cdot 0.71}

An average adult testicle measures up to 5 cm × 2 cm × 3 cm (2 in × 3⁄4 in × 1+1⁄4 in). The Tanner scale, which is used to assess the maturity of the male genitalia, assigns a maturity stage to the calculated volume ranging from stage I, a volume of less than 1.5 cm3; to stage V, a volume greater than 20 cm3. Normal volume is 15 to 25 cm3; the average is 18 cm3 per testis (range 12–30 cm3). The number of spermatozoa an adult human male produces is directly proportional to testicular volume, as larger testicles contain more seminiferous tubules and Sertoli cells as a result. As such, men with larger testicles produce on average more sperm cells in each ejaculate, as testicular volume is positively correlated with semen profiles.

Internal structure

Duct system The testes are covered by a tough fibrous shell called the tunica albuginea. Under the tunica albuginea, the testes contain very fine-coiled tubes called seminiferous tubules. The tubules are lined with a layer of cells (germ cells) that develop from puberty through old age into sperm cells (also known as spermatozoa or male gametes). The developing sperm travel through the seminiferous tubules to the rete testis located in the mediastinum testis, to the efferent ducts, and then to the epididymis where newly created sperm cells mature (spermatogenesis). The sperm move into the vas deferens, and are eventually expelled through the urethra and out of the urethral orifice through muscular contractions.

Primary cell types Within the seminiferous tubules, the germ cells develop into spermatogonia, spermatocytes, spermatids and spermatozoa through the process of spermatogenesis. The gametes contain DNA for fertilization of an ovum. Sertoli cells are the true epithelium of the seminiferous epithelium, critical for the support of germ cell development into spermatozoa. Sertoli cells secrete inhibin, a hormone that plays a crucial role in regulating spermatogenesis by inhibiting the secretion of FSH from the pituitary gland, thus helping to regulate sperm production. Peritubular myoid cells surround the seminiferous tubules. Between the seminiferous tubules are interstitial cells called Leydig cells that produce and secrete testosterone and other androgens important for puberty (including secondary sexual characteristics like facial hair), sexual behavior, and libido. Testosterone controls testicular volume. Immature Leydig cells and interstitial macrophages and epithelial cells are also present.

Blood supply and lymphatic drainage The testis has three sources of arterial blood supply: the testicular artery, the cremasteric artery, and the artery to the ductus deferens. Blood supply and lymphatic drainage of the testes and scrotum are distinct:

The paired testicular arteries arise directly from the abdominal aorta and descend through the inguinal canal, while the scrotum and the rest of the external genitalia is supplied by the internal pudendal artery (a branch of the internal iliac artery). The testis has collateral blood supply from the cremasteric artery (a branch of the inferior epigastric artery, which is a branch of the external iliac artery), and the artery to the ductus deferens (a branch of the inferior vesical artery, which is a branch of the internal iliac artery). Therefore, if the testicular artery is ligated, e.g., during a Fowler-Stevens orchiopexy for a high undescended testis, the testis will usually survive on these other blood supplies. Lymphatic drainage of the testes follows the testicular arteries back to the paraaortic lymph nodes, while lymph from the scrotum drains to the inguinal lymph nodes.

Layers

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Illustrations

Worked examples

Example 1 — a first encounter with Testicle

Start with the simplest possible case. Write down what Testicle 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 Testicle 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 Testicle 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 Testicle

In research: Testicle 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 Testicle 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: Testicle is common in secondary-school and first-year university syllabi. It links to neighbouring topics Endocrine system, Glands, Human male reproductive system, so understanding it makes those chapters shorter.
In everyday life: Look for Testicle 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 Testicle in 20 minutes

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

Frequently asked questions

What is Testicle in simple terms?

A testicle, also called testis (pl. testes) is the male gonad in all gonochoric animals, including humans, and is homologous to the ovary, which is the female gonad. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone.

Why does Testicle 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 Testicle?

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 Testicle.