Male reproductive organs-2

Penis

Males' perineal region extends into the penis. It is comprised of erectile tissue and is soft. The penis is made up of a free, pendulous body (corpus) that is completely covered by skin and has an attached root (radix) in the perineum. During urination, it transports urine through the urethra, and during ejaculation, it transports semen through the urethra.

Structure of the Penis

The body of the penis is composed of three cylindrical mass of erectile tissue:

• Corpora Cavernosa: The two lateral columns of masses are called the corpora cavernosa. There is one in either side in front of the urethra. The corpora cavernosa are surrounded by a dense, relatively inelastic connective tissue called tunica albuginea. It also contains numerous vascular cavities called venous sinusoids.

• Corpus Spongiosum: This is a posterior column of mass that contains the urethra. The corpus spongiosum extends distally beyond the corpora cavarnosa and becomes expanded at the tip of the penis, which is called glans penis. Lower two thirds of the penis is covered in skin. The loosely fitting skin of the penis is folded forward over the glans to form the prepuce or foreskin, which usually excised during circumcision. The penis is extremely vascular and during  an erection, the blood spaces are filled and it becomes distended.

Internal Genitalia of Male

The internal genitalia consist of epididymis, ductus deferens (vas deferens), ejaculatory ducts, urethra and accessory sex glands such as seminal vesicles, prostate and bulbo-urethral glands. The sperm produced in the testes are carried to the point of ejaculation from penis by a system of ducts.

 Epididymis

The epididymis is a comma-shaped, 4 cm long organ that is located in the back of each testis. It has a tail, a body, and a head. The tail continues as vas deference and the head unite with efferent duct (ductus deferens). The epididymis is created when the semniferous tubules of the testes' central posterior region combine. The pseudo-stratified columnar epithelium lines these tubels, which are encircled by layers of smooth muscle.

Functions of the Epididymis

• Storage of Sperm: It stores sperm until sperm acquire motility and ability to fertilize ovum (maturity). The sperm stored here remains viable for several months.
• Movement of Sperm: It helps to propel sperm to the ductus (vas deferens).

Ductus Deferens (Vas Deferens)

The story of the epididymis continues directly into the ductus deferens, also known as the vas deferens. It is 45 cm long and travels along the back of the testis before exiting the scortum and entering the abdominal cavity through the inguinal canal. Each vas deferens in the abdomen crosses its corresponding ureter to get to the region between the bladder and the rectum. It ultimately comes to an end when it combines with the seminal vesicle duct to produce the ejaculatory duct. It carries sperms through peristaltic contractions of its muscular coat at maximal stimulation and stores them for several months, similar to the epididymis. The sperm that has been stored but hasn't yet been ejaculated is reabsorbed in this process. Vasectomy, a surgical male permanent contraceptive procedure, is typically done over it.

Spermatic Cord

The spermatic cord is the supporting structure of the male reproductive system which suspend the testes in the scortum. There are two spermatic cords, one of each testes. Each cord contains a testicular artery, testicular veins, lymphatics, a deferent duct with artery to ductus deferens and testicular nerve. The spermatic cord passes upwards through the inguinal canal and behind the bladder where it merges with the duct to form the seminal vesicle. Then it passes through the prostate gland as the ejaculatory duct to join the urethra.

Ejaculatory Duct

The ductus deferens joins to the duct of seminal vesicle at ejaculatory duct. It is about 2cm long and is formed by the union of the duct from the seminal vesicle and vas deferens. They receive secretion from the seminal vesicles and pass through the prostate gland where they receive additional secretion. It carries seminal fluid and spermatozoa to the urethra.

Urethra

Urethra is the final section of the reproductive system. It is about 20 cm long and passes through the rostate, the deep muscle of the perineum and the penis. The urethra is the tube that carries urine from he bladder to outside of the body. In males, it has the additional function of ejaculating semen when the nan reaches orgasm. When the penis is erect during sex, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm. It is subdivided into three parts:

• Prostatic Urethra: is about 2-3 cm long and passes through the prostate.
• Membranous Urethra: is about 1 cm long that passes through the deep muscles of the perineum.
• Spongy Urethra (external): is about 15-20 cm long and passes through penis and ends at external urethral orifice.

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. These sex glands include the seminal vesicles, prostate and bulbo-uretral glands.

Seminal Vesicles

The paired seminal vesicles, also known as seminal glands, are a secretary structure that are located anterior to the rectum and posterior to the base of the urine bladder. It is located adjacent to the ducts deferens' ampulla. Each vesicle is around 5 cm long when coiled and increases in length to 10-15 cm when uncoiled. When testosterone is present, it secretes an alkaline, viscous fluid. Water, fructose, prostaglandin, clotting proteins, and vitamin C make up the majority of its composition. The alkaline seminal fluid keeps sperm active by helping to balance the acidic environment of the female reproductive tract.

 Prostate Gland

The prostate is a single doughnut-shaped gland and slightly larger than a walnut. It measure about 4 cm from side to side, about 3 cm from top to bottom, and 2 cm from front to back .The mean weight of the normal prostate in adult males is about 11 grams, usually ranging between 7 and 16 grams and increase with age. It lies inferior to the urinary bladder surrounding the first portion of urethra. It secretes a thin, milky lubricating fluid that adds about 30% volume to the semen. The secretion of prostate makes sperm motile and neutralizes vaginal acidity. This milky, slightly acidic fluid mainly contains water, acid phosphate, proteolytic enzymes, lysozyme, amylase and cholesterol. It also contains and antibiotic called seminalplasmin which can destroy bacteria in semen.

Bulbo-uretheral Gland

The paired bulbo-urethral glands or Cowper's gland, are about size of peas. They are located one in each side of the urethra. They lie directly below the prostate. The bulbo-urethral glands secret clearly alkaline fluid during the onset of sexual excitement which neutralizes the acidity of urine. They also secrete mucus that lubricates the penis.

Semen                           

Semen is a mixture of sperm and seminal fluid. Seminal fluid is a liquid that consists of the secretion of the seminiferous tubles, seminal vesicles, prostate, and bulbo-urethral glands. The volume of semen in a ejaculation is about 2.5-5 ml per ejaculation with 50-150 million sperm per ml. sterility occurs when sperm count falls below 20 million/ml. After ejaculation, sperm can survive for 24-48 hours. A pH of semen is 7.5 i.e. alkaline that is due to the prostatic fluid. Sperm make up only 10% of semen and the remaining part is a fluid, secreted from the accessory glands, which provide fructose to nourish sperm and alkaline medium to neutralize urethral (acidity because of urine) and vaginal acidity. It also contains vitamin C, and trace elements like calcium, zinc, magnesium, copper and sulfur. Once ejaculated, liquid semen coagulates within 5 minutes due to presence of clotting proteins from the seminal vesicles.

Hormonal Regulation in the Male

Follicular Stimulating Hormone (FSH) and Leutinizing Hormone (LH) produced by the anterior pituitary gland are chiefly responsible for stimulating spermatogenesis and testosterone secretion in male. FSH acts indirectly to stimulate spermatogenesis. LH stimulates leydig cells of the testes to secrete the hormone testosterone. The testosterone hormone promotes spermatogenesis along with development of male sexual characteristics. The sertoli cells of the testes also release a protein hormone called inhibin which inhibits FSH secretion by the anterior pituitary.