The Hormones

The Reproductive System of a woman The Menstrual Cycle The Hormones The Reproductive System of a Man The Role of Testosterone The Sperms Odyssey in the Female Reproductive Tract The Process of FertilisationThe Hormones Reproduction is like an orchestra - and the reproductive organs need to be synchronised to perform at just the right time for them to work properly. It is the fertility hormones which play the conductors role. Hormones are chemicals the body makes to carry messages from one part of the body to another. There are two major female hormones - estrogen and progesterone - which are produced by the ovaries. The cycle of ovarian hormone production has two phases. In the first half called the follicular phase, estrogen plays a dominant role. During this phase the egg matures inside the ovary in its follicle. The egg; the surrounding cells (which nurture the egg and are called granulosa cells and theca cells); and the fluid (called follicular fluid) which accumulates in progressively larger amounts during this phase, is called a follicle. The follicle secretes a large amount of estrogen (produced by the granulosa cells) into the bloodstream, and the estrogen circulates to the uterus where it stimulates the endometrium to thicken. The second phase of hormone production begins at ovulation, midway through the cycle, when the follicle changes into the corpus luteum. This produces estrogen; and also large quantities of progesterone throughout the second half of the cycle. Travelling through the bloodstream to the uterus, progesterone complements the work begun by estrogen by stimulating the endometrium to mature and making it possible for a fertilized egg to implant in it. In case pregnancy does not occur, production of estrogen and progesterone falls 10 to 14 days after ovulation as the corpus luteum dies, and the endometrium is shed from the body as the menstrual period. How is the release of hormones regulated by the body? This is a complex self-regulating system, which uses negative feedback control loops, much like a thermostat for an oven does. As the temperature increases, the thermostat shuts off the heater to reduce its heat output. When the temperature falls below the thermostats setting, the thermostat signals the heater to turn up the heat again, thus maintaining the desired temperature. A similar signaling relationship exists between the pituitary gland and the ovaries in women; and the testes in men. For example, as the concentration of gonadotropins in the blood rises, this signals the womans ovaries to increase hormonal output of estrogen. In turn, when the blood levels of estrogen rise, the pituitary gland slows its release of gonadotropins, thus maintaining the desired equilibrium.

The Reproductive System of a woman
The Menstrual Cycle
The Hormones
The Reproductive System of a Man
The Role of Testosterone
The Sperm's Odyssey in the Female Reproductive Tract
The Process of Fertilisation

The Hormones

Reproduction is like an orchestra - and the reproductive organs need to be synchronised to perform at just the right time for them to work properly. It is the fertility hormones which play the conductor's role.

Hormones are chemicals the body makes to carry messages from one part of the body to another. There are two major female hormones - estrogen and progesterone - which are produced by the ovaries.

The cycle of ovarian hormone production has two phases. In the first half called the follicular phase, estrogen plays a dominant role. During this phase the egg matures inside the ovary in its follicle. The egg; the surrounding cells (which nurture the egg and are called granulosa cells and theca cells); and the fluid (called follicular fluid) which accumulates in progressively larger amounts during this phase, is called a follicle. The follicle secretes a large amount of estrogen (produced by the granulosa cells) into the bloodstream, and the estrogen circulates to the uterus where it stimulates the endometrium to thicken.

The second phase of hormone production begins at ovulation, midway through the cycle, when the follicle changes into the corpus luteum. This produces estrogen; and also large quantities of progesterone throughout the second half of the cycle. Travelling through the bloodstream to the uterus, progesterone complements the work begun by estrogen by stimulating the endometrium to mature and making it possible for a fertilized egg to implant in it. In case pregnancy does not occur, production of estrogen and progesterone falls 10 to 14 days after ovulation as the corpus luteum dies, and the endometrium is shed from the body as the menstrual period.

How is the release of hormones regulated by the body? This is a complex self-regulating system, which uses negative feedback control loops, much like a thermostat for an oven does. As the temperature increases, the thermostat shuts off the heater to reduce its heat output. When the temperature falls below the thermostat's setting, the thermostat signals the heater to turn up the heat again, thus maintaining the desired temperature. A similar signaling relationship exists between the pituitary gland and the ovaries in women; and the testes in men. For example, as the concentration of gonadotropins in the blood rises, this signals the woman's ovaries to increase hormonal output of estrogen. In turn, when the blood levels of estrogen rise, the pituitary gland slows its release of gonadotropins, thus maintaining the desired equilibrium.