Male reproductive organs (Male reproductive system)

Summary

The male reproductive system consists of the penis, testes, epididymis, ejaculatory ducts, prostate, and accessory glands. These organs function together to produce sperm and deliver semen from the testes via ejaculation. For more information on the embryological development of the male reproductive system, see development of the reproductive system.

Penis

Function

Urination and release of semen

Gross anatomy [1][2]

Primarily composed of erectile tissue, blood vessels, nerves, and connective tissue

Structure

Arteries[2][3][1]

Course Supplies
Internal pudendal artery
  • External genitalia

Bulbourethral artery

Deep artery of the penis
  • Erectile tissue
Dorsal artery of the penis
Urethral artery
External pudendal artery

Veins

Vein Anatomy Drains into
Deep dorsal vein of the penis Prostatic and pelvic venous plexuses
Superficial dorsal vein of the penis
  • Travels along the superficial and deep fascia
→ External pudendal veins → greater saphenous vein

Lymphatics

Structure Lymph nodes Course
Perineum, penis, and scrotum Superficial inguinal lymph nodes external iliac nodes → para-aortic nodes
Glans penis Deep inguinal lymph nodes → internal iliac nodes → common iliac nodes → para-aortic nodes
Corpora cavernosa Internal iliac nodes → common iliac nodes → para-aortic nodes

Innervation

Innervation Structures Function
Parasympathetic Pelvic splanchnic nerves (S2-S4) Erection (see below)
Sympathetic Hypogastric nerve (T11-L4) Emission (see below)
Sensory Dorsal nerve of the penis (a branch of the pudendal nerve) Innervates the skin, prepuce, and glans

Point and Shoot": Parasympathetic Points it up (erection), Sympathetic Shoots out the semen (ejaculation).

Microscopic anatomy [1][2]

Embryology [1]

Testes, scrotum, and spermatic cord

Gross anatomy

Structure [1][2][4]

Remember the spermatic cord layers with “TIE turns into ICE”:
- Transversalis fascia Internal spermatic fascia
- Internal oblique → Cremasteric muscle and fascia
- External oblique → External spermatic fascia

Vasculature, lymphatics, and innervation of the testes and scrotum [4]

Testes Scrotum
Arteries
Veins
  • Scrotal veins drain to external pudendal vein

Lymphatics

Autonomic Innervation

  • Abdominal aortic plexus
  • T10 → testicular plexus
Motor innervation
  • None
Sensory innervation
  • Anterior scrotal nerves (genital branch of the genitofemoral nerve and ilioinguinal nerve)
  • Posterior scrotal nerves (perineal branch of the internal pudendal nerve and posterior femoral cutaneous nerve)

Microscopic anatomy

Microscopic anatomy [1][2]

Spermatogonia

  • Description: Undifferentiated germ cells lining the seminiferous tubules
    • Type A (dark): do not undergo mitosis
    • Type A (pale): form type B spermatogonia
    • Type B: undergo mitosis → mature into primary spermatocytes
  • Function: site of primary spermatocyte production

Sertoli cells

Leydig cells

Sperm

Blood-testis barrier

Spermatogenesis and spermiogenesis

Spermatogenesis and spermiogenesis [1][2]

Spermatogenesis

Spermiogenesis

GONIUM is GOING be sperm: speramtogonia → spermatid. ZOON ZOOMS to the egg: mature spermatozoon travel to the egg.

Embryology

Embryology [1]

Epididymis, ductus deferens, and accessory glands

Epididymis [1]

  • Gross anatomy: long, coiled duct along the posterior aspect of the testis → distal end is continuous with ductus deferens
  • Function
    • Storage and maturation of spermatozoa
    • Propulsion of spermatozoa into the ductus deferens
  • Embryology: derived from the mesonephric duct (differentiation requires testosterone)

Ductus deferens [1]

Ejaculatory ducts [1]

Accessory glands

Prostate (see below)

Seminal vesicles [2]

Bulbourethral gland (Cowper gland) [2]

Prostate gland

An accessory gland of reproduction located at the base of the bladder and composed primarily of glandular, fibrous, and smooth muscle tissue.

Function [2]

Secretion of:

Gross anatomy [1][2]

Structure

Vasculature, lymphatics, and innervation of the prostate gland [3][6]

Arteries
Veins
  • Prostatic venous plexusinternal iliac vein → internal vertebral plexus (Batson plexus)
    • Located between the true and false capsule
    • Covered by the anterior prostatic fascia and the endopelvic fascia

Lymphatics

Sympathetic innervation
Parasympathetic innervation

Because of the prostate's lymphatic drainage to the para-aortic lymph nodes, prostate cancer often metastasizes to the lumbar spine.

Microscopic anatomy [8][9]

Embryology [8]

References:[10][11]

Male sexual response

There are three parts of the male sexual response: erection, emission, and ejaculation.

Erection [12][2][13]

PDE-5 inhibitors (e.g., sildenafil) inhibit hydrolysis of cGMP → ↑ NO → vasodilation → prolonged erection

Ejaculation [12][2][15]

Emission

Expulsion

Remember the ejaculatory pathway of sperm with SEVEn UP: Seminiferous tubules → Epididymis → Vas (ductus) deferens → Ejaculatory duct → Urethra → Penis

Innervation of male sexual response: Point, Squeeze, and Shoot
1. Parasympathetic → Point (erection)
2. Sympathetic → Squeeze (ejaculation)
3. Somatic (pudendal nerve) → Shoot (emission)

Clinical significance

Penis

Testes and scrotum

Prostate

Other

  • 1. Drake RL, Vogl W, Mitchell AWM. Gray's Anatomy for Students. Churchill Livingstone; 2005.
  • 2. Chung KW, Chung HM. Gross Anatomy. Philadelphia, PA: Lippincott Williams & Wilkins; 2012.
  • 3. Le T, Bhushan V,‎ Sochat M, Chavda Y, Abrams J, Kalani M, Kallianos K, Vaidyanathan V. First Aid for the USMLE Step 1 2019. New York, NY: McGraw-Hill Medical.
  • 4. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Lippincott Williams & Wilkins; 2013.
  • 5. Stocco C. Tissue physiology and pathology of aromatase. Steroids. 2012; 77(1-2): pp. 27–35. doi: 10.1016/j.steroids.2011.10.013.
  • 6. Aaron L, Franco OE, Hayward SW. Review of Prostate Anatomy and Embryology and the Etiology of Benign Prostatic Hyperplasia. Urol Clin North Am. 2016; 43(3): pp. 279–288. doi: 10.1016/j.ucl.2016.04.012.
  • 7. Swanson GP, Hubbard JK. A better understanding of lymphatic drainage of the prostate with modern imaging and surgical techniques. Clin Genitourin Cancer. 2013; 11(4): pp. 431–40. doi: 10.1016/j.clgc.2013.04.031.
  • 8. Goljan EF. Rapid Review Pathology. Philadelphia, PA: Elsevier Saunders; 2018.
  • 9. Bhavsar A, Verma S. Anatomic Imaging of the Prostate. BioMed Research International. 2014; 2014: pp. 1–9. doi: 10.1155/2014/728539.
  • 10. Kaplan. USMLE Step 1 Anatomy Lecture Notes 2016. Kaplan Publishing; 2015.
  • 11. Gartner LP, Hiatt JL. Cell Biology and Histology. Lww; 2014.
  • 12. Dean RC, Lue TF. Physiology of Penile Erection and Pathophysiology of Erectile Dysfunction. Urol Clin North Am. 2006; 32(4): pp. 379–395. doi: 10.1016/j.ucl.2005.08.007.
  • 13. Cunningham GR, Rosen RC. Overview of male sexual dysfunction. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/overview-of-male-sexual-dysfunction. Last updated May 11, 2016. Accessed February 23, 2017.
  • 14. Jonas Boström, Anders Hogner, and Stefan Schmitt. Do Structurally Similar Ligands Bind in a Similar Fashion?. Journal of Medicinal Chemistry. 2006. url: https://pubs.acs.org/doi/10.1021/jm060167o.
  • 15. Alwaal A, Breyer BN, Lue TF. Normal male sexual function: emphasis on orgasm and ejaculation. Fertil Steril. 2015; 104(5): pp. 1051–60. doi: 10.1016/j.fertnstert.2015.08.033.
last updated 12/08/2019
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