functions of male accessory glands

 Seminal Vesicles , prostate gland and Cowper's glands are associated with human male reproductive system .

1 ) Seminal Vesicles : 

( i ) Seminal vesicles occur in pair present on the posterior side of urinary bladder Its secretion consists about 60 % of the total volume of the semen . The secretion is an alkaline seminal fluid containing fructose, fibrinogen and prostaglandins. 

iii) Fructose helps in the movement of sperms by providing energy to them. 

iiii) Semen is coagulated in bolus by fibrinogen. This helps in faster movements of sperms in vagina after insemination . 

 (iv) Reverse peristalsis in vagina and uterus for faster movement of sperms towards the egg in the female body is aided by prostaglandins. 

 2 ) Prostate gland : 

( i ) It is a single gland located under the urinary bladder . It has about 20 to 30 separate lobes which open separately into the urethra. 

 ( ii ) Prostatic fluid secreted by this gland is milky white and slightly acidic . It forms 30 % of the semen and is secreted in urethra . 

 (iii) Its contents are citric acid, acid phosphatase and various other enzymes. 

 (iv) The sperms are protected from the acidic environment of vagina by acid phosphatase. 

 ( 3 ) Cowper 's glands ( Bulbo - urethral glands ) : 

( 1 ) Cowper 's glands occur in pair on either side of urethra . They are small and pea shaped . 

 2) Cowper's glands secrete an alkaline, viscous, mucous like fluid. It helps as lubricant during copulation. 

Accessory Sex Glands

The ducts of the male reproductive system store and transport sperm cells, but the accessory sex glands secrete most of the liquid portion of semen. The accessory sex glands include the seminal vesicles, the prostate, and the bulbourethral glands.

Seminal Vesicles

The paired seminal vesicles (VES-i-kuls) or seminal glands

are convoluted pouchlike structures, about 5 cm (2 in.) in length, lying posterior to the base of the urinary bladder and anterior to the rectum . Through the seminal vesicle ducts they secrete an alkaline, viscous fluid that contains fructose (a monosaccharide sugar), prostaglandins, and clotting

proteins that are different from those in blood. The alkaline nature of the seminal fluid helps to neutralize the acidic environment of the male urethra and female reproductive tract that other

wise would inactivate and kill sperm. The fructose is used for ATP production by sperm. Prostaglandins contribute to sperm motility and viability and may stimulate smooth muscle contractions within the female reproductive tract. The clotting proteins help semen coagulate after ejaculation. Fluid secreted by the seminal vesicles normally constitutes about 60% of the

volume of semen.

Prostate

The prostate is a single, doughnut-shaped gland about the size of a golf ball. It measures about 4 cm (1.6 in.) from side to side, about 3 cm (1.2 in.)

from top to bottom, and about 2 cm (0.8 in.) from front to back. It

is inferior to the urinary bladder and surrounds the prostatic urethra . The prostate slowly increases in size from

birth to puberty. It then expands rapidly until about age 30, after which time its size typically remains stable until about age 45,when further enlargement may occur. The prostate secretes a milky, slightly acidic fluid (pH about

6.5) that contains several substances. 

(1) Citric acid in prostatic

fluid is used by sperm for ATP production via the Krebs cycle.

(2) Several proteolytic enzymes, such as prostate-specific antigen

(PSA), pepsinogen, lysozyme, amylase, and hyaluronidase, even-

tually break down the clotting proteins from the seminal vesicles.

(3) The function of the acid phosphatase secreted by the prostate

is unknown. 

(4) Seminalplasmin in prostatic fluid is an antibiotic that can destroy bacteria. Seminalplasmin may help decrease the

number of naturally occurring bacteria in semen and in the lower

female reproductive tract. Secretions of the prostate enter the

prostatic urethra through many prostatic ducts. Prostatic secretions make up about 25% of the volume of semen and contribute to sperm motility and viability.

Bulbourethral Glands

The paired bulbourethral glands (bul-boˉ-uˉ-RE¯-thral), or Cow-

per’s glands (KOW-pers), are about the size of peas. They are located inferior to the prostate on either side of the membranous urethra within the deep muscles of the perineum, and their ducts open into the spongy urethra . During sexual arousal,

the bulbourethral glands secrete an alkaline fluid into the urethra

that protects the passing sperm by neutralizing acids from urine in

the urethra. They also secrete mucus that lubricates the end of the

penis and the lining of the urethra, decreasing the number of

sperm damaged during ejaculation. Some males release a drop or

two of this mucus upon sexual arousal and erection. The fluid does not contain sperm cells.

Semen 

(- seed) is 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 mil-

lion sperm per mL. When the number falls below 20 million/mL,

the male is likely to be infertile. A very large number of sperm is

required for successful fertilization because only a tiny fraction

ever reaches the secondary oocyte.

 Despite the slight acidity of prostatic fluid, semen has a slightly

alkaline pH of 7.2–7.7 due to the higher pH and larger volume of fluid from the seminal vesicles. The prostatic secretion gives semen a milky appearance, and fluids from the seminal vesicles and

bulbourethral glands give it a sticky consistency. Seminal fluid  provides sperm with a transportation medium, nutrients, and protection from the hostile acidic environment of the male’s urethra and the female’s vagina.

 Once ejaculated, liquid semen coagulates within 5 minutes

due to the presence of clotting proteins from the seminal vesicles. The functional role of semen coagulation is not known,but the proteins involved are different from those that cause

blood coagulation. After about 10 to 20 minutes, semen reliquefies because prostate-specific antigen (PSA) and other proteolytic enzymes produced by the prostate break down the

clot. Abnormal or delayed liquefaction of clotted semen may

cause complete or partial immobilization of sperm, thereby inhibiting their movement through the cervix of the uterus. After

passing through the uterus and uterine tube, the sperm are affected by secretions of the uterine tube in a process called capacitation . The presence of blood in semen

is called hemospermia most cases, it is caused by inflammation

of the blood vessels lining the seminal vesicles; it is usually treated with antibiotics.

Penis

The penis (tail) contains the urethra and is a passageway for

the ejaculation of semen and the excretion of urine .It is cylindrical in shape and consists of a body, glans penis, and a root. The body of the penis is composed of three cylindrical

masses of tissue, each surrounded by fibrous tissue called the tunica albuginea . The two dorsolateral masses are called the corpora cavernosa penis (corpora -main bodies;

cavernosa - hollow). The smaller midventral mass, the corpus

spongiosum penis, contains the spongy urethra and keeps it open

during ejaculation. Skin and a subcutaneous layer enclose all

three masses, which consist of erectile tissue. Erectile tissue is

composed of numerous blood sinuses (vascular spaces) lined by

endothelial cells and surrounded by smooth muscle and elastic connective tissue.

 The distal end of the corpus spongiosum penis is a slightly

enlarged, acorn-shaped region called the glans penis; its margin is the corona (koˉ-RO¯ -na). The distal urethra enlarges

within the glans penis and forms a terminal slitlike opening,

the external urethral orifice. Covering the glans in an uncircumcised penis is the loosely fitting prepuce (PRE¯-poos), or foreskin. The root of the penis is the attached portion (proximal portion). It consists of the bulb of the penis, the expanded posterior continuation of the base of the corpus spongiosum penis,

and the crura of the penis the two separated and tapered portions of the corpora cavernosa penis. The bulb of the penis is attached to the

inferior surface of the deep muscles of the perineum and is enclosed by the bulbospongiosus muscle, a muscle that aids ejaculation. Each crus of the penis bends laterally away from

the bulb of the penis to attach to the ischial and inferior pubic

rami and is surrounded by the ischiocavernosus muscle 

The weight of the penis is supported by two ligaments that are continuous with the fascia of the penis. 

(1) The fundiform ligament (FUN-di-form) arises from the inferior part of the linea alba. 

(2) The suspensory ligament of the

penis arises from the pubic symphysis.

 Upon sexual stimulation (visual, tactile, auditory, olfactory, or imagined), parasympathetic fibers from the sacral portion of the spinal cord initiate and maintain an erection, the enlargement and stiffening of the penis. The parasympathetic fibers produce and release nitric oxide (NO). The NO causes smooth muscle in the walls of arterioles supplying erectile tissue to relax, which allows these blood vessels to dilate. This in turn causes large amounts of blood

to enter the erectile tissue of the penis. NO also causes the smooth

muscle within the erectile tissue to relax, resulting in widening of

the blood sinuses. The combination of increased blood flow and widening of the blood sinuses results in an erection. Expansion of the blood sinuses also compresses the veins that drain the penis; the slowing of blood outflow helps to maintain the erection.

 The term priapism (PRI¯-a-pizm) refers to a persistent and usually painful erection of the penis that does not involve sexual desire or excitement. The condition may last up to several hours

and is accompanied by pain and tenderness. It results from abnormalities of blood vessels and nerves, usually in response to

medication used to produce erections in males who otherwise

cannot attain them. Other causes include a spinal cord disorder,

leukemia, sickle-cell disease, or a pelvic tumor. Ejaculation (e¯-jak-uˉ-LAˉ-shun; ejectus- - to throw out), the

powerful release of semen from the urethra to the exterior, is a

sympathetic reflex coordinated by the lumbar portion of the spinal cord. As part of the reflex, the smooth muscle sphincter at

the base of the urinary bladder closes, preventing urine from being expelled during ejaculation, and semen from entering the urinary bladder. Even before ejaculation occurs, peristaltic contractions in the epididymis, ductus (vas) deferens, seminal vesicles, ejaculatory ducts, and prostate propel semen into the penile

portion of the urethra (spongy urethra). Typically, this leads to

emission (e¯-MISH-un), the discharge of a small volume of semen before ejaculation. Emission may also occur during sleep (nocturnal emission). The musculature of the penis (bulbospongiosus, ischiocavernosus, and superficial transverse perineal

muscles), which is supplied by the pudendal nerve, also contracts at ejaculation .

 Once sexual stimulation of the penis has ended, the arterioles

supplying the erectile tissue of the penis constrict and the smooth

muscle within erectile tissue contracts, making the blood sinuses

smaller. This relieves pressure on the veins supplying the penis

and allows the blood to drain through them. Consequently, the

penis returns to its flaccid (relaxed) state.