In order to fully understand the transmission, effccts and complications of STD and to be able to communicate your conerns to the doctor, you must have a reasonable knowledge of the anatomy (structure) of the sexual and reproductive system and the differnt types of sexual practices.

 Male anatomy (Fig 1)

Anus - the opening through which faeces passes.

Bladder - the sac which contains the urine.

Epididymis - this is a coiled structure which lies at the back of the testis. It acts as a storehouse for sperm. An infection of the epididymis is known as epididymitis. Sterility may result if scarring seals off both epididymes.

Glans penis - this is the head of the penis. In uncircumcised men, the glans penis is covered by the prepuce (foreskin). An infection of the glans penis and/or the prepuce is known as balanitis.

Penis - the erectile male organ which conveys urine to the outside and sperm into the vagina during sexual intercourse.

Prepuce - the foreskin which covers the glans penis. An infection of the prepuce and/or glans penis is known as balanitis. The prepuce is removed by circumcision.

Prostate - this gland lies at the neck of the bladder and encircles the urethra. It contributes fluid to semen. An infection of the prostate gland is known as prostatitis.

Rectum - the lower end of the large intestine that ends in the anus. The rectum is lined by a thin mucous membrane and is not naturally lubricated during sex like the vagina. Anal and rectal sex is, therefore, more likely to cause tears in the mucous membrane lining, facilitating the entry of germs. This is why anal or rectal sex is said to be very risky and this may be one reason why infections such as Hepatitis B and AIDS are particularly common among homosexual men. The slight bleeding associated with the passage of hard stools is one indication of how thin the mucous membrane lining of the rectum is.

Scrotum - the sac which contains the testes.

Testis - one of the two sex organs in the scrotum.

Urethra (urine pipe) - the tube through which urine from the bladder flows to the outside. An infection of the urethra is known as urethritis. The male urethra is about 20 cm long compared to 4 cm in the female. Theis makes it more difficult for germs to enter the bladder and this is why cystitis (bladder infection) is relatively uncommon in men.

Vas deferens - the duct which connects the epididymis to the urethra. Sperm travels through the vas deferenss into the urethra.

Female anatomy (Fig 2)

Anus - the opening through which faeces passes. You will also notice from the figure that the anus is quite close to the vagina. This makes it possible for infected secretions from the vagina to flow backwards into the anus and rectum, causing an infection there. Rectal gonorrhoea in women is believed to be due to contamination by vaginal secretions rather than through actual rectal intercourse.

Bartholins gland - this is one of two glands which lie in the lower third of each labium majus. It secretes a fluid during sexual arousal and lubricates the vagina so that intercourse can take place without much discomfort. Infection of the Bartholins gland may lead to the formation of a Bartholins abscess.

Bladder - the sac which stores urine. An infection of the bladder is known as cystitis.

Cervix - the neck of the uterus (womb) which protrudes into the vagina. It is pierced by a canal which connects the cavity of the uterus with the vagina. The canal is called the cervical canal and its opening is called the os. An infection of the cervix is known as cervicitis. Infection there may spread into the uterus through the cervical canal.

Clitoris - the sensuous structure located at the top of the labia. It is the female equivalent of the penis.

Fallopian tube - one of two tubes through which the egg travels down from the ovary into the uterus. An infection of the Fallopian tube is called salpingitis. However, infection there commonly involves other adjacent structures inside the pelvis such as the uterus and the ovary and most doctors use the composite term, pelvic inflammatory disease (PID) to refer to infection of any one or more of these sites.

Labium majus (major lip) - one of the two larger lips of the vagina.

Labium minor (minor lip) - one of the two smaller lips of the vagina.

Ovary - one of two glands that produce eggs and the female hormones.

Rectum - the lower end of the large intestine that ends in the anus.

Urethra - the tube through which urine from the bladder flows to the outside. An infection of the urethra is known as urethritis. The female urethra is about 4 cm long compared to 20 cm in the male. This makes it easier for germs to go straight through the urethra into the bladder and this is why women are more prone to develop cystitis (bladder infection).

Uterus - the womb. It consists of the body and the neck (cervix). The cervix iopens into the vagina and the body of the uterus is joined in each corner by the Fallopian tube. An infection of the uterus commonly involves other structures within the pelvis such as the Fallopian tubes and the ovaries and is called pelvic inflammatory disease (PID).

Vagina - the birth canal which also accepts the penis during sexual intercourse.The adult vagina is lined by a mucous membrane that is several cell layers thick.This is why the vagina can withstand the rigors of childbirth. The vagina is also lubricated during sexual arousal and this allows intercourse to take place comfortably and with the minimum of trauma.