Neurosecretory cells in the hypothalamus of both
males and females secrete pulses of
releasing hormone (GnRH)
into the pituitary blood
supply at regular intervals.
GnRH stimulates the anterior pituitary lobe to secrete
similar pulses of follicle-stimulating hormone (FSH)
and luteinizing hormone (LH) into the bloodstream.
In the male, FSH and LH stimulate sperm development
and testosterone production by the testes. Testosterone
in the blood inhibits secretions of GnRH from the
hypothalamus and LH and FSH secretions from the
In the female, LH and FSH cause the egg cells to
mature and to produce estrogen:
• As the estrogen level increases and an egg develops,
there comes a point when a massive release of LH
and FSH from the pituitary gland occurs, leading to
• After ovulation, the remnants
of the follicle (corpus luteum)
continue to produce estrogen
from the hypothalamus and
LH and FSH secretions from
the pituitary gland.
pituitary gland and inhibit
ovaries produce relaxin to increase the flexibility of
uterine and vaginal smooth muscle in preparation
A hormone released
by the hypothalamus
that stimulates the
gland to secrete
hormone (LH) and
act on the ovaries
R egulation o f sex h o rm o n e secre tio n s by th e hyp o th alam u s,
p itu itary g lan d , and g o n a d s • Figure 9.18
The coordination of GnRH, FSH, and LH
secretion, along with the secretion of sex hormones by the gonads, signal the onset of puberty
and gamete production in both males and females. In addition, this process signals ovulation and maintenance of pregnancy in females.
The hypothalamus releases pulses
of GnRH at regular intervals.
LH and FSH
FSH and LH act on the ovary and lead to development of an egg and
production of estrogen and progesterone. These hormones influence the
hypothalamus and pituitary via either positive or negative feedback,
depending on the point in the menstrual cycle when secretion occurs.
FSH and LH act on the testes and
lead to testosterone production, which
exerts effects on the hypothalamus
and pituitary via negative feedback.
Endocrine Glands Regulate Other Key Body Functions