Common Health Issues

Types and Functions of Gonads

• By Rich Health Editorial Team
• January 17, 2024

The sex glands, or gonads, are the testes in men and the ovaries in women. The gonads are stimulated by the pituitary gland, which controls their activity by means of gonadotrophic hormones.

 

These hormones stimulate the testes to make sperm cells and the ovaries to produce egg cells. In addition, the gonads secrete hormones that affect the growth and well-being of the entire body.

 

Types and Functions of Gonads

The following are the types of gonads in the human body and their functions:

The Male Gonads

The testes, or testicles, are a pair of oval glands, each about the size of a small plum. They are suspended in the pouch-like scrotum, and are connected to the body by the spermatic cords.

Sperm passes from the testes through the spermatic cords to the prostate gland and the urethra and out through the penis. Each testicle consists of a set of tubules that produce sperm and a group of cells that manufacture hormones.

 

Starting at puberty, the cells secrete testosterone—the chief male sex hormone. Testosterone is responsible for the development of the male secondary sex characteristics during adolescence—the growth of the penis and the testicles, the deepening of the voice, the growth of pubic and facial hair, and the development of the characteristic male muscle and bone pattern.

 

At the end of adolescence, the hormones speed the fusing of the growing ends of bones with the main shafts, so that the growth of the bones has to stop.

 

The Female Gonads

The ovaries in women correspond to the testes in men. They are a pair of oval white bodies, about 1.5 inches long, lying on each side of the uterus and connected to it by the Fallopian tubes. The function of the ovaries is to produce egg cells, or ova, during a woman’s reproductive years.

At birth the ovaries contain several hundred thousand Graafian follicles. Each follicle is a small, hollow ball about pinhead size in which an egg (ovum) may develop. At puberty the influence of a hormone from the pituitary gland begins to ripen the follicles.

 

Normally, one follicle and egg mature each month, and an ovum is released into one of the Fallopian tubes. It is believed that the ovaries take turns in supplying eggs.

 

The hormones produced by the ovaries are the estrogen and progesterone. Estrogens are responsible for the general growth of the breasts at puberty, and for the development of the other secondary female sex characteristics, i.e. enlargement of the uterus and of the vagina, the distribution of body hair, and the typically feminine narrow shoulders and broad hips.

 

The hormone progesterone chiefly builds up the lining of the uterus to make it ready to receive a fertilized egg cell.

 

Menstruation and Ovulation

Menstruation is the periodic discharge from the body of the extra blood and tissue that have been built up in preparation for pregnancy and have not been used. 

Although menstrual cycles vary, the time from one menstrual period to the next is usually about 28 days.

Doctors customarily count the first day of menstruation as Day 1 in the cycle. During the first 14 days of the cycle, the Graafian follicle and the egg within it grow until the follicle is several times its original pinhead size. While it is growing, the follicle makes the estrogen hormones.

 

On about Day 14, stimulated by the pituitary gland, the follicle bursts and the egg enters the Fallopian tube on its way down to the uterus. If any sperm cells are present in the tube as this time, fertilization may take place.

The fertilized egg continues its 6.5-day journey down the tube and implants itself in the wall of the uterus. Meanwhile, the ruptured follicle from which the egg was discharged is transformed into a yellowish, solid ball called the corpus luteum (Latin for “yellow body”). This body produces another hormone called progesterone.

 

During the last 14 days of the cycle, the hormones produced by the corpus luteum stimulates the development of the tissues and blood supply in the uterus.

 

The fertilized egg secretes its own hormone. This hormone helps the corpus luteum to persist and continue making estrogen and progesterone. In other words, the process is like a chain reaction, with one hormone prodding the other two hormones to keep going.

 

If pregnancy does not occur, the corpus luteum degenerates and its secretions halt. With the stopping of the hormones, the rich blood supply built up in the lining of the uterus sloughs off and leaves the body during menstruation.

 

Scientists have learned how to make synthetic hormones in the laboratory, so that the process of ovulation can be controlled at will. The contraceptive pill prevents pregnancy by halting ovulation.

 

A pregnant woman has an additional powerful producer of sex hormones. This temporary hormone-generator is the placenta, the disk of tissue inside the uterus that acts principally as a bridge between the blood circulations of the mother and the developing baby.

 

The hormones from the placenta include progesterone, estrogen, and gonadotrophin, which stimulates the woman’s ovaries into continued hormone production after the normal commands from her pituitary gland have been switched off.

 

Some of the gonadotrophin is filtered from the blood by the kidneys, and released in the urine. It is the presence of this hormone in a woman’s urine that makes possible one of the most reliable chemical tests for early pregnancy.