finals- male repro

• Reproductive organs grouped by function

  • Gonads (testes in males, ovaries in females) - produce gametes and secrete sex hormones
  • Ducts - store and transport gametes
  • Accessory sex glands - produce substances that protect gametes and facilitate their movement
  • Supporting structures - e.g. penis in males, uterus in females
• Urology


  Study of the urinary system. Urologists also diagnose and treat diseases and disorders of the male reproductive system.
• Scrotum


  • Supporting structure for the testes, consists of loose skin and an underlying subcutaneous layer that hangs from the root of the penis
  • Raphe - single pouch of skin separated into lateral portions by a median ridge
  • Scrotal septum - divides the scrotum into two compartments, each containing a single testis
  • Dartos muscle - composed of bundles of smooth muscle fibers found in the subcutaneous layer of the scrotum
  • Cremaster muscle - a series of small bands of skeletal muscle that descend as an extension of the internal oblique muscle through the spermatic cord to surround the testes
  • Normal sperm production requires a temperature about 2–3°C below core body temperature, maintained within the scrotum as it is outside the pelvic cavity
  • In response to cold temperatures, contraction of the cremaster muscles moves the testes closer to the body, where they can absorb body heat
• Testes


  • Paired oval glands in the scrotum measuring about 5 cm long and 2.5 cm in diameter
  • Produce sperm and hormones
  • Each testis has a mass of 10–15 grams
  • Develop near the kidneys, in the posterior portion of the abdomen
  • Tunica vaginalis - partially covers the testes
  • Hydrocele - a collection of serous fluid in the tunica vaginalis, may be caused by injury or inflammation
  • Tunica albuginea - a white fibrous capsule composed of dense irregular connective tissue that surrounds the testis
  • Lobules - tunica albuginea extends inward, forming septa that divide the testis into a series of internal compartments called lobules
  • Each lobule contains one to three tightly coiled seminiferous tubules where sperm are produced
• Spermatogenesis


  1. Stem cells called spermatogonia develop from primordial germ cells

  2. Spermatogonia undergo mitosis and differentiation into primary spermatocytes

  3. Primary spermatocytes undergo meiosis I to form secondary spermatocytes

  4. Secondary spermatocytes undergo meiosis II to form four haploid spermatids

  5. Spermatids undergo spermiogenesis to develop into mature sperm cells

  6. Spermiation - sperm are released from their connections to sustentacular cells and enter the lumen of the seminiferous tubule
• Spermatogenic cells


  • The sperm-forming cells
• Sustentacular cells or Sertoli cells


  • Have several functions in supporting spermatogenesis
• Cryptorchidism


  A condition in which the testes do not descend into the scrotum. Occurs in about 3% of full-term infants and about 30% of premature infants. Untreated bilateral cryptorchidism results in sterility because the cells involved in the initial stages of spermatogenesis are destroyed by the higher temperature of the pelvic cavity.
• Interstitial cells or Leydig cells


  • Clusters of cells in the spaces between adjacent seminiferous tubules, secrete testosterone
• Androgen


  Hormone that promotes the development of masculine characteristics. Testosterone also promotes a man's libido (sexual drive).
• In humans, spermatogenesis takes 65–75 days
• Spermatogenesis stages


  1. Spermatogonia (2n)

  2. Primary spermatocytes (2n)

  3. Secondary spermatocytes (n)

  4. Spermatids (n)

  5. Spermiogenesis
• A single primary spermatocyte produces four spermatids via two rounds of cell division (meiosis I and meiosis II)
• About 300 million sperm complete the process of spermatogenesis each day
• Sperm


  • About 60 μm long and contains a flattened, pointed head with a nucleus and an acrosome, and a tail subdivided into four parts: neck, middle piece, principal piece, and end piece
  • The acrosome is a caplike vesicle filled with enzymes that help a sperm to penetrate a secondary oocyte to bring about fertilization
  • The middle piece contains mitochondria that provide the energy (ATP) for the locomotion of sperm to the site of fertilization and for sperm metabolism
• Once ejaculated, most sperm do not survive more than 48 hours within the female reproductive tract
• Hormonal control of testicular function

  1. At puberty, hypothalamic neurosecretory cells increase secretion of GnRH, which stimulates the anterior pituitary to increase secretion of LH and FSH

  2. LH stimulates interstitial cells to secrete testosterone

  3. In some target cells, the enzyme 5 alpha-reductase converts testosterone to dihydrotestosterone

  4. Inhibin, a protein hormone, inhibits FSH secretion by the anterior pituitary. If spermatogenesis is proceeding too slowly, less inhibin is released, which permits more FSH secretion and an increased rate of spermatogenesis
• Reproductive system ducts in males

  • Seminiferous tubules -> Straight tubules -> Rete testis -> Epididymis -> Ductus deferens -> Ejaculatory ducts -> Urethra
• Epididymis


  • Site of sperm maturation, where sperm acquire motility and the ability to fertilize an ovum (occurs for about 14 days)
  • Helps propel sperm into the ductus deferens during sexual arousal by peristaltic contraction of its smooth muscle
  • Stores sperm, which remain viable here for up to several months
• Ductus deferens


  • Conveys sperm during sexual arousal from the epididymis toward the urethra by peristaltic contractions of its muscular coat
  • Can also store sperm for several months
• Spermatic cord


  • Supporting structure of the male reproductive system that ascends out of the scrotum
  • Varicocele - a swelling in the scrotum due to a dilation of the veins that drain the testes
• Ejaculatory ducts


  • Two tubes that carry semen from the seminal vesicles and vas deferens to the urethra
• Accessory sex glands


  • Seminal vesicles
  • Prostate
  • Bulbourethral glands
• Seminal vesicles


  • Secrete an alkaline, viscous fluid that contains fructose, prostaglandins, and clotting proteins
• Prostate


  • Secretes a milky, slightly acidic fluid that contains enzymes that break down clotting proteins from the seminal vesicles
• Bulbourethral glands


  • Secrete an alkaline fluid that neutralizes the acidic environment of the urethra and mucus that lubricates the lining of the urethra and the tip of the penis during sexual intercourse
• Semen


  A mixture of sperm and seminal fluid, a liquid that consists of the secretions of the seminiferous tubules, seminal vesicles, prostate, and bulbourethral glands
• The volume of semen in a typical ejaculation is 2.5–5 milliliters (mL), with 50–150 million sperm per mL. When the number falls below 20 million/mL, the male is likely to be infertile.
• Capacitation


  After passing through the uterus and uterine tube, the sperm are affected by secretions of the uterine tube.
• Hemospermia


  Presence of blood in semen
• Penis


  • Contains the urethra and is a passageway for the ejaculation of semen and the excretion of urine
  • The body of the penis is composed of three cylindrical masses of tissue, each surrounded by fibrous tissue called the tunica albuginea: two dorsolateral corpora cavernosa penis and a smaller midventral corpus spongiosum penis
  • The distal end of the corpus spongiosum penis is the glans penis, with a margin called the corona
  • The prepuce or foreskin covers the glans in an uncircumcised penis
  • The root of the penis is the attached portion, consisting of the bulb of the penis and the crura of the penis
• Erection


  1. Initiated and maintained by parasympathetic fibers from the sacral portion of the spinal cord upon sexual stimulation

  2. Erotic sights, sounds, smells, and thoughts can also stimulate erection, involving descending inputs from the brain (hypothalamus and limbic system) to the spinal cord

  3. Negative stimuli can inhibit erection through these descending pathways
• Sexual intercourse or coitus


  Insertion of the erect penis into the vagina
• Priapism


  A persistent and usually painful erection of the penis that does not involve sexual desire or excitement
• Ejaculation


  The powerful release of semen from the urethra to the exterior, is a sympathetic reflex coordinated by the lumbar portion of the spinal cord
• Emission


  Discharge of a small volume of semen before ejaculation. May also occur during sleep (nocturnal emission)
• Premature ejaculation


  Ejaculation that occurs too early, usually caused by anxiety, other psychological causes, or an unusually sensitive foreskin or glans penis
• Circumcision


  A surgical procedure in which part of or the entire prepuce is removed