ZOODSE - 601: Reproductive Biology (Theory)
Gonadal hormones
Gonadal hormones are hormones produced by the gonads, which are the testes
in males and the ovaries in females. These hormones play a critical role
in regulating reproductive function and secondary sexual characteristics.
In males, the primary gonadal hormones are testosterone and
dihydrotestosterone (DHT). Testosterone is responsible for the development
of male secondary sexual characteristics, such as facial hair growth,
deepening of the voice, and increased muscle mass. It also plays a
critical role in the regulation of sperm production. DHT is involved in
the development of male genitalia, prostate gland, and secondary sexual
characteristics.
In females, the primary gonadal hormones are estrogen and progesterone.
Estrogen is responsible for the development of female secondary sexual
characteristics, such as breast growth and widening of the hips. It also
plays a critical role in the regulation of the menstrual cycle.
Progesterone is involved in the preparation of the uterus for pregnancy
and the maintenance of pregnancy.
Gonadal hormones are regulated by the hypothalamus and pituitary gland
through the hypothalamic-pituitary-gonadal (HPG) axis. The hypothalamus
releases gonadotropin-releasing hormone (GnRH), which stimulates the
pituitary gland to release follicle-stimulating hormone (FSH) and
luteinizing hormone (LH). FSH and LH then stimulate the gonads to produce
and release gonadal hormones.
In summary, gonadal hormones play a critical role in regulating
reproductive function and secondary sexual characteristics, and their
production and release are regulated by the hypothalamus, pituitary gland,
and HPG axis.
Mechanism of gonadal hormone action in male
The primary gonadal hormones in males are testosterone and
dihydrotestosterone (DHT), which are produced by the testes. The
mechanism of hormone action involves these hormones binding to specific
androgen receptors that are present in many different types of cells
throughout the body, including the testes, prostate gland, muscle
tissue, and bone.
Once the androgen hormones bind to the androgen receptors, they activate
a signaling cascade that ultimately results in changes in gene
expression, protein synthesis, and cellular function. In the case of
male gonadal hormones, these changes lead to the development of male
secondary sexual characteristics such as facial hair growth, deepening
of the voice, and increased muscle mass.
Testosterone also plays a critical role in the regulation of sperm
production. It acts on the Sertoli cells in the testes to promote the
maturation of sperm cells. Testosterone also acts on the Leydig cells in
the testes to promote the production of more testosterone, creating a
positive feedback loop that helps to maintain normal levels of
testosterone in the body.
DHT, on the other hand, is involved in the development of male
genitalia, prostate gland, and secondary sexual characteristics such as
facial hair growth and balding.
the mechanism of gonadal hormone action in males involves the binding of
testosterone and DHT to androgen receptors, which activates a signaling
cascade that leads to changes in gene expression, protein synthesis, and
cellular function. These changes ultimately result in the development of
male secondary sexual characteristics and the regulation of sperm
production.
Mechanism of gonadal hormone action in female
In females, the primary gonadal hormones are estrogen and
progesterone, which are produced by the ovaries. The mechanism of
hormone action involves these hormones binding to specific estrogen
and progesterone receptors that are present in many different types of
cells throughout the body, including the reproductive organs, brain,
bone, and adipose tissue.
Once the estrogen or progesterone hormones bind to their respective
receptors, they activate a signaling cascade that ultimately results
in changes in gene expression, protein synthesis, and cellular
function. In the case of female gonadal hormones, these changes lead
to the development of female secondary sexual characteristics such as
breast growth, widening of the hips, and redistribution of body fat.
Estrogen also plays a critical role in the regulation of the menstrual
cycle. It acts on the hypothalamus and pituitary gland to regulate the
release of follicle-stimulating hormone (FSH) and luteinizing hormone
(LH), which in turn stimulate the ovaries to produce and release eggs.
Progesterone, on the other hand, is involved in the preparation of the
uterus for pregnancy and the maintenance of pregnancy. It promotes the
thickening of the uterine lining and inhibits contractions of the
uterus to prevent early delivery.
The mechanism of gonadal hormone action in females involves the
binding of estrogen or progesterone to their respective receptors,
which activates a signaling cascade that leads to changes in gene
expression, protein synthesis, and cellular function. These changes
ultimately result in the development of female secondary sexual
characteristics and the regulation of the menstrual cycle and
pregnancy.
Steroid Hormone
Steroid hormones are a class of hormones that are derived from
cholesterol and have a characteristic four-ring structure. They
include hormones such as testosterone, estrogen, progesterone,
cortisol, and aldosterone.
These hormones are produced by the adrenal glands, testes, ovaries,
and placenta in response to specific signals from the body. Once they
are produced, steroid hormones bind to specific receptors inside the
cell or on the cell surface, depending on the hormone and the type of
receptor.
Inside the cell, steroid hormones bind to specific proteins called
nuclear receptors, which are located in the cytoplasm or nucleus of
the target cell. Once the hormone-receptor complex is formed, it can
enter the nucleus and directly interact with the DNA to regulate gene
expression.
On the cell surface, steroid hormones bind to specific membrane
receptors, which then activate intracellular signaling pathways that
lead to changes in gene expression and cellular function.
Steroid hormones play important roles in regulating a wide range of
physiological processes in the body, including growth and development,
metabolism, immune function, and reproduction. Their effects can be
widespread and long-lasting, making them powerful signaling molecules
in the body.
Testosterone: This is the primary male sex hormone, produced by the
testes in men and in smaller amounts by the ovaries in women.
Testosterone plays a critical role in the development of male
secondary sexual characteristics, such as facial hair growth,
deepening of the voice, and muscle mass.
Estrogen: This is a group of female sex hormones, produced primarily
by the ovaries. Estrogen is important for the development of female
secondary sexual characteristics, such as breast growth and widening
of the hips, as well as for the regulation of the menstrual cycle.
Progesterone: This hormone is produced by the ovaries and is important
for the preparation of the uterus for pregnancy and the maintenance of
pregnancy.
Cortisol: This hormone is produced by the adrenal glands and plays a
critical role in the body's stress response. It regulates glucose
metabolism, blood pressure, and immune function.
Aldosterone: This hormone is also produced by the adrenal glands and
regulates the balance of salt and water in the body, helping to
maintain blood pressure.
Glycoprotein hormones
Glycoprotein hormones are a class of hormones that consist of a
protein subunit and a carbohydrate (sugar) subunit. They are produced
by specialized cells in the pituitary gland, and they act on target
cells in various parts of the body to regulate a wide range of
physiological processes.
There are three main types of glycoprotein hormones:
Follicle-stimulating hormone (FSH): This hormone stimulates the growth
and development of follicles in the ovaries in women and stimulates
the production of sperm in the testes in men.
Luteinizing hormone (LH): This hormone stimulates ovulation in women
and stimulates the production of testosterone in men.
Thyroid-stimulating hormone (TSH): This hormone stimulates the thyroid
gland to produce thyroid hormones, which are important for regulating
metabolism in the body.
The protein subunit of these hormones is similar among the different
types of glycoprotein hormones, while the carbohydrate subunit varies,
giving each hormone its unique function.
The mechanism of action of glycoprotein hormones involves binding to
specific receptors on target cells, which activates intracellular
signaling pathways that lead to changes in gene expression and
cellular function. Dysregulation of glycoprotein hormone production or
action can lead to various disorders, such as infertility, thyroid
dysfunction, and pituitary tumors.
prostaglandins
Prostaglandins are a group of hormone-like lipid compounds that are
produced by almost all tissues in the body, including reproductive
tissues. They are derived from fatty acids and act as local hormones,
meaning they are produced and act in the same tissue or cell that they
affect.
Prostaglandins are involved in a wide range of physiological
processes, including inflammation, pain, fever, blood flow regulation,
and reproduction. They play a crucial role in reproductive biology,
including ovulation, menstrual cycles, and childbirth.
There are several different types of prostaglandins, designated by
letters (such as PGD2, PGE2, and PGF2alpha), each with its own unique
functions and effects on the body. They act by binding to specific
receptors on cell membranes, triggering a cascade of signaling events
that lead to a variety of physiological responses.
Prostaglandins are a group of hormone-like lipid compounds that are
produced by almost all tissues in the body, including reproductive
tissues. They are derived from fatty acids and act as local hormones,
meaning they are produced and act in the same tissue or cell that they
affect.
Prostaglandins are involved in a wide range of physiological
processes, including inflammation, pain, fever, blood flow regulation,
and reproduction. They play a crucial role in reproductive biology,
including ovulation, menstrual cycles, and childbirth.
There are several different types of prostaglandins, designated by
letters (such as PGD2, PGE2, and PGF2alpha), each with its own unique
functions and effects on the body. They act by binding to specific
receptors on cell membranes, triggering a cascade of signaling events
that lead to a variety of physiological responses.
Prostaglandins are important mediators of many physiological
processes, including those involved in reproductive biology. In
particular, prostaglandins play a role in ovulation, menstrual cycles,
and childbirth. Here are some ways that prostaglandins are involved in
reproductive biology:
Ovulation: Prostaglandins are involved in the process of ovulation,
which is the release of an egg from the ovary. Prostaglandins are
produced in the follicle, the structure in the ovary that contains the
developing egg, and help to stimulate the rupture of the follicle and
release of the egg.
Menstruation: Prostaglandins are also involved in menstrual cycles.
During the menstrual cycle, the lining of the uterus builds up in
preparation for pregnancy. If pregnancy does not occur, prostaglandins
are released and cause the uterus to contract and expel the lining,
resulting in menstruation.
Childbirth: Prostaglandins are important in the process of childbirth.
As labor begins, prostaglandins are released, causing the cervix to
soften and dilate, allowing the baby to pass through the birth canal.
Fertility treatments: Prostaglandins can be used as part of fertility
treatments. For example, synthetic prostaglandins can be used to
stimulate ovulation in women who are having difficulty getting
pregnant.
Contraception: Prostaglandins may also play a role in contraception.
Some studies have suggested that inhibiting the production of
prostaglandins may prevent ovulation and act as a form of
contraception.
prostaglandins are important regulators of reproductive biology and
play a vital role in many aspects of human fertility and reproduction.
hypothalamo – hypophyseal – gonadal axis
The hypothalamo-hypophyseal-gonadal (HHG) axis is a complex regulatory
system that controls the function of the reproductive organs in both
males and females. It involves the hypothalamus, the pituitary gland
(also known as the hypophysis), and the gonads (ovaries in females and
testes in males).
The hypothalamus, located in the brain, releases
gonadotropin-releasing hormone (GnRH) into the bloodstream, which
stimulates the pituitary gland to release luteinizing hormone (LH) and
follicle-stimulating hormone (FSH). These hormones then travel through
the bloodstream to the gonads, where they stimulate the production of
sex hormones (estrogen and progesterone in females, testosterone in
males).
The sex hormones produced by the gonads then feedback to the
hypothalamus and pituitary gland, inhibiting the release of GnRH, LH,
and FSH, thus maintaining a balance of hormone levels in the body.
This axis is essential for the development and maintenance of
reproductive function in both sexes, including the regulation of
menstrual cycles and ovulation in females and sperm production in
males. Disruption of the HHG axis can result in a range of
reproductive disorders, including infertility, menstrual
irregularities, and hormonal imbalances.
or
The hypothalamo-hypophyseal-gonadal (HHG) axis is a complex endocrine
system that involves the hypothalamus, pituitary gland, and gonads
(ovaries in females and testes in males). It plays a critical role in
regulating reproductive function and maintaining fertility.
The hypothalamus produces gonadotropin-releasing hormone (GnRH) in a
pulsatile fashion, which stimulates the pituitary gland to produce
follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH
and LH then act on the gonads to stimulate the production of sex
hormones (estrogen and progesterone in females, testosterone in
males).
As sex hormone levels rise, they provide feedback to the hypothalamus
and pituitary gland, which helps regulate the release of GnRH, FSH,
and LH. This feedback loop helps maintain a delicate balance of
hormones in the body, regulating reproductive function and maintaining
fertility.
Disruptions in the HHG axis can lead to a range of reproductive
disorders, including infertility and hormonal imbalances.
How its work hypothalamo – hypophyseal – gonadal axis
The hypothalamo-hypophyseal-gonadal (HHG) axis works by a series of
hormonal signals and feedback loops.
Hypothalamus: The hypothalamus is a part of the brain that produces
gonadotropin-releasing hormone (GnRH) in a pulsatile fashion. This
hormone stimulates the pituitary gland to produce follicle-stimulating
hormone (FSH) and luteinizing hormone (LH).
Pituitary Gland: The pituitary gland is a small gland located at the
base of the brain that produces and secretes FSH and LH in response to
GnRH from the hypothalamus.
Gonads: The gonads (ovaries in females and testes in males) are the
primary reproductive organs responsible for producing sex hormones
(estrogen and progesterone in females, testosterone in males). FSH and
LH from the pituitary gland stimulate the gonads to produce these
hormones.
Hormonal Feedback Loop: As sex hormone levels rise, they provide
feedback to the hypothalamus and pituitary gland, which helps regulate
the release of GnRH, FSH, and LH. In females, estrogen and
progesterone provide negative feedback to the hypothalamus and
pituitary gland, inhibiting the release of GnRH, FSH, and LH. In
males, testosterone provides negative feedback to the hypothalamus and
pituitary gland.
This feedback loop helps maintain a delicate balance of hormones in
the body, regulating reproductive function and maintaining fertility.
Disruptions in the HHG axis can lead to a range of reproductive
disorders, including infertility and hormonal imbalances.
