Biology Today — January 2018

(Jacob Rumans) #1

Ejaculation


The penis is inserted into the vagina of female and the friction
of rhythmic movements of penis stimulates the release of semen
into urethra (referred to as emission). The wave-like contractions
of muscles at the base of penis cause forceful discharge of semen
from urethra into the vaginal canal and is called ejaculation.
It is usually the result of sexual stimulation, including prostate
stimulation. However, it may occur spontaneously during sleep,
also known as “wet dream”.


Subsidence of Erection


After ejaculation, the arterioles to the penis contract, reducing the
flow of blood to penis. This gradually subsides erection of penis.


ACCESSORY GLANDS


The secretions of accessory glands produce seminal fluid as well as
lubricate the urethra. These glands are seminal vesicles, prostate
gland, bulbourethral or Cowper’s glands.


Bulbourethral Glands or
Cowper’s Glands


  • These are paired, pea sized tubuloalveolar
    glands present on either side of
    membranous urethra. Its ducts open
    into the urethra.

  • Function : These glands secrete an
    alkaline fluid, which neutralises the
    acidity of urine in urethra. They secrete
    mucus which lubricates the penis for
    frictionless movements during copulation.


Mucous
glands

T.S. of bulbourethral gland

Prostate Gland



  • It is a large, chestnut shaped spongy
    and lobulated gland which surrounds
    the proximal part of urethra. It remains
    sheathed in the muscles of pelvic floor. It
    pours its alkaline secretion into urethra by 20-30 openings.

  • Function : Prostate produces a slightly acidic milky fluid with pH of 6.5, constituting
    20-30% of the volume of semen. It contains citric acid, enzymes (acid phosphatase, amylase,
    etc.), and prostaglandins. Its secretion nourishes and activates the spermatozoa to swim.
    Secretion of prostate

  • Citric acid : Acts as a nutrient for sperm and imparts acidity to fluid.

  • Enzymes : Like acid phosphatase, amylase, pepsinogen, etc.

  • Prostaglandins : Activates the sperms to swim.


Prostatic
glands

T.S. of prostate gland

Urinary
bladder

Ureter

Ejaculatory duct

Prostate
gland
Prostatic
urethra

Bulbourethral glands

Seminal vesicle
Ampulla of
ductus deferens

Fig.: Accessory glands of male reproductive system

Seminal Vesicles



  • These are a pair of elongated (5 cm), muscular and sacculated glands situated in the pelvis between the bladder and rectum. The ducts of
    seminal gland join the vasa deferentia to form ejaculatory ducts.

  • Function : They produce an alkaline secretion that forms about 60-70% of the volume of semen. The pH of seminal fluid is 7.4. It helps to neutralise
    the acidity of male urethra as well as vaginal tract, thus prolonging the lifespan of sperms.
    Secretion of seminal vesicles

  • Fructose : Provide energy for the sperms.

  • Prostaglandins : Stimulate uterine contractions that help the sperm to propel towards female’s oviduct.

  • Clotting proteins : Facilitates coagulation of semen after ejaculation. Smooth
    muscle


Lumen

T.S. of seminal gland

Prostate Prostate
glandgland

Sperm and semen travel through urethra
and are ejaculated out of the penis.

Fig.: Passage of sperms during ejaculation

Seminal vesicles and prostate produce
semen, which is carried along with
sperm to urethra.

Sperms are
produced in
testis.

Sperms travel
through vas
deferens to
urethra.

Urethra

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