13.10: Duct System and Accessory Glands
- Page ID
- 121767
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Sperm begin in the seminiferous tubules, mature in the epididymis, and travel through the duct system with support from accessory gland secretions for successful transport out of the body.
- Explain the role of the epididymis in supporting sperm.
- Identify how the male accessory glands contribute to seminal fluid and why this is essential.
- Describe the path of sperm from their site of production to their exit from the body.
From the Seminiferous Tubules to the Epididymis
In the previous section, you have learned that sperm are produced inside the seminiferous tubules of the testes, where Sertoli (sustentacular) cells support them as they develop. As they mature, the young sperm move toward the center of the testis and then enter small passageways that guide them out of the testis and toward the epididymis. During this short transition, the surrounding fluid is modified and some water is removed, helping to concentrate the sperm.
From there, sperm enter the long, coiled epididymis. Their journey through this tube takes about 12 days, during which they continue to mature, gradually gaining the ability to swim. The most fully developed sperm are stored in the tail of the epididymis, where they remain until ejaculation.
From Testes to Exit and the Role of Seminal Fluid
The testes provide the environment needed for sperm formation, from external temperature control to the highly organized seminiferous tubules inside. The scrotum and its muscles keep the testes slightly cooler than body temperature, allowing normal sperm production. Within each testis, the seminiferous tubules, Sertoli cells, Leydig cells, and surrounding tissues support the ongoing development of sperm from stem cells to nearly mature spermatozoa. After leaving the testes, these sperm still require final maturation in the epididymis before they are ready to leave the male body and look for that rare ovum.
However, sperm alone cannot accomplish fertilization. They require a specialized fluid environment that nourishes them, protects them, and allows them to move effectively through the male and female reproductive tracts. This crucial support comes from the accessory male glands, which add the components that transform sperm into semen. In this section, we will explore how the seminal vesicles, prostate gland, and bulbourethral glands each contribute to creating a fluid medium that enables sperm survival and successful transport.
Accessory Glands and Seminal Fluid Production
Sperm make up only about 5 percent of the total volume of semen, the thick, milky fluid released during ejaculation. Most of the semen comes from three important accessory glands of the male reproductive system: the seminal vesicles, the prostate gland, and the bulbourethral glands. Together, their secretions form the seminal fluid, which supports, nourishes, and transports the sperm.
Figure \(\PageIndex{1}\): Male Accessory Glands and Their Position. In the sagittal section on the left, the three major accessory glands that contribute to seminal fluid are pointed out by arrows. The paired seminal vesicles sit behind the bladder and add a fructose-rich secretion that fuels sperm. Just below them, the prostate gland surrounds the proximal urethra and contributes a slightly alkaline fluid that supports sperm survival in the acidic female reproductive tract. The bulbourethral glands lie inferior to the prostate and release a small amount of mucus that lubricates and neutralizes the urethra before ejaculation.
The diagram on the right provides an anterior view of the three male accessory glands shown in context with nearby ducts and reproductive structures. (Image on the right credits: "Male Reproductive Organs - Anterior View" by Jennifer Lange is licensed under CC BY-NC-SA 4.0, modification of original by StacyRed-Wiki via Wikimedia Commons; "Leiden - Drawing Male bladder and urethra from posterior - no labels" by Bas (S) Blankevoort, LUMC and Marco C DeRuiter, LUMC, is licensed under CC BY-NC-SA, modifications and labeling by Jennifer Lange.)
Seminal Vesicles
The paired seminal vesicles contribute most of the fluid in semen, producing an alkaline secretion that makes up about 60 percent of the total volume. As sperm enter the ampulla of the ductus deferens during ejaculation, they mix with this fluid, which supplies fructose for ATP production and helps activate their movement. The alkaline pH helps neutralize the acidic environment of the vagina, improving sperm survival. Seminal vesicle fluid also contains prostaglandins, hormone-like molecules that encourage the cervical opening to dilate so sperm can more easily pass from the vagina into the uterus.
Prostate Gland
The prostate gland sits just below the urinary bladder and surrounds the first portion of the urethra, as shown in the figure above. About the size of a walnut, it contains both glandular and muscular tissue. The prostate adds a milky, slightly acidic fluid rich in citric acid to the semen. This fluid briefly thickens semen after ejaculation, helping it remain in the female reproductive tract while sperm begin using the fructose supplied by the seminal vesicles. An enzyme called prostate-specific antigen (PSA) then liquefies the semen, allowing sperm to move farther into the reproductive tract. Prostatic secretions also include seminalplasmin, an antimicrobial substance that helps limit bacterial growth.
Bulbourethral (Cowper’s) Glands
The final addition to the seminal fluid comes from the two bulbourethral glands. They produce a thick, slippery mucus that is released early in sexual arousal, before ejaculation. This mucus lubricates the urethra and vagina and helps wash away traces of acidic urine from the urethra. Because this “pre-ejaculate” can pick up sperm left in the urethra from earlier ejaculation, it can occasionally contain sperm and may still lead to pregnancy.
Prostate Specific Antigen (PSA) is an enzyme made almost entirely by the cells of the prostate gland. Its main job is to help liquefy semen after ejaculation, allowing sperm to move more easily through the female reproductive tract.
Although PSA is mostly found in semen, a small amount normally enters the bloodstream. Because the prostate releases PSA, a blood test for PSA can give information about prostate health.
Higher-than-expected blood PSA levels can occur for several reasons, including prostate enlargement, inflammation or infection of the prostate, and prostate cancer. The PSA test is therefore used as part of screening and evaluation for prostate disorders, but the results always need to be interpreted in context because many non-cancerous conditions can raise PSA levels.
The prostate normally doubles in size during puberty. At approximately age 25, it gradually begins to enlarge again. This enlargement does not usually cause problems; however, abnormal growth of the prostate, or benign prostatic hyperplasia (BPH), can cause constriction of the urethra as it passes through the middle of the prostate gland, leading to a number of lower urinary tract symptoms, such as a frequent and intense urge to urinate, a weak stream, and a sensation that the bladder has not emptied completely.
By age 60, approximately 40 percent of men have some degree of BPH. By age 80, the number of affected individuals has jumped to as many as 80 percent. Treatments for BPH attempt to relieve the pressure on the urethra so that urine can flow more normally. Mild to moderate symptoms are treated with medication, whereas severe enlargement of the prostate is treated by surgery in which a portion of the prostate tissue is removed.
Prostate cancer is the second most common cancer in men, and while some forms grow very slowly and may never need treatment, aggressive forms can spread to organs such as the lymph nodes, lungs, and brain. There is no link between benign prostatic hyperplasia (BPH) and prostate cancer, although both can cause similar urinary symptoms.
Diagnosis typically includes taking a medical history, measuring prostate-specific antigen (PSA) levels in the blood, and performing a digital rectal exam. Because the prostate sits just in front of the rectal wall and below the bladder, a clinician can easily palpate its posterior surface by inserting a gloved, lubricated finger into the rectum to check for enlargement, tenderness, or abnormal nodules. If a suspicious mass is found, a biopsy confirms the diagnosis. Treatment options depend on how advanced the cancer is and may include active surveillance, hormone therapy, surgery, chemotherapy, or radiation therapy. For additional details, readers can visit the National Cancer Institute’s page on prostate cancer.
Image credits: Top right - "Prostate (Normal and Enlarged)" by Alan Hoofring for the National Cancer institute is in the public domain. Bottom left: "Exam, Digital Rectal" by the National Cancer Institute is in the public domain.
Ductal System
During ejaculation, mature sperm leave the tail of the epididymis and are propelled by smooth muscle contractions (peristalsis) into the ductus deferens (vas deferens), a thick, muscular tube bundled with blood vessels and nerves inside the spermatic cord. The ductus deferens travels upward through the inguinal canal into the pelvic cavity and curves around the bladder.
Because the vas deference is easily accessed within the scrotum, male sterilization can be achieved by cutting and sealing it in a vasectomy. (See image on the right). Although reversal is sometimes possible, vasectomies are considered permanent and are recommended only for individuals who are certain they no longer wish to father children.
Mature sperm leave the tail of the epididymis and enter the vas deferens that propels them forward with peristaltic contractions. The vas deferens travels within the spermatic cord, loops into the pelvic cavity, and joins the duct of the seminal vesicle to form the ejaculatory duct. This short duct passes through the prostate gland and empties into the prostatic urethra, where additional fluid from the prostate mixes in.
As sperm move along this route, the key glandular contributions they receive converts the fluid into semen.
The bulbourethral glands release a small amount of clear mucus early in arousal that lubricates the urethra.
During ejaculation, the combined fluid is pushed through the urethra and exits the body through the penis. Because the urethra carries both urine and semen, the nervous system coordinates ejaculation so that urine flow is temporarily blocked. This one-way routing ensures that semen can pass efficiently to the outside of the body. The urethra is subdivided into three regions: the prostatic urethra (within the prostate gland), the membranous urethra (passing through the pelvic floor), and the spongy urethra (within the penis).
