Problem 5 – Pinel + Kalat
Hormones influence sex in 2 fundamental ways
1. By influencing the development from conception to sexual maturity of the
anatomical, physiological, and behavioral characteristics that distinguish one as
female and male
2. By activating the reproduction related behavior of sexually mature adults
Neuroendocrine System
Only the organs whose primary function appears to be the release of hormones are
referred to as endocrine glands.
Glands: 2 types
o Exocrine glans (e.g. sweat glands) release their chemicals into ducts which
carry them to their targets
o Endocrine glands (ductless glands) release their chemicals which are called
hormones directly into the circulatory system and these hormones travel via
the circulatory system until they reach their target
Gonads: the male testes and the female ovaries. After copulation (sexual
intercourse) a single sperm fertilizes on ovum to from one called zygote. Each cell of
the human body contains 23 pairs of chromosomes. The ova and sperm only contain
half the number.
Sex chromosomes: they contain the genetic programs that direct sexual
development. Females have 2 large X chromosomes. Males have one X and one Y
chromosome. The sex is determined by the father’s chromosomes.
Classes of Hormones
1. Amino acid derivatives: hormones that are synthesized from an amino acid
molecule. E.g. epinephrine is released from adrenal medulla and synthesized from
tyrosine
2. Peptides and proteins: chains of amino acids- peptide hormones are short chains and
protein hormones are long chains
3. Steroids: hormones that are synthesized from cholesterol. They influence sexual
development and the activation of adult sexual behavior.
Most other hormones produce their effects by binding to receptors in cell
membranes. Steroid also do this but they can also penetrate cell membranes because
they are small and fat soluble. Steroid hormones tend to have the most diverse and
long-lasting effects on cellular function.
Sex steroids: The gonads produce and release steroid hormones. The main classes of
gonadal hormones are androgens (testosterone) and estrogens (estradiol). Ovaries
release more estrogen and testes release more androgen but they shouldn’t be
called male or female hormones, men and women both have these.
3rd class of steroid hormone that ovaries and testes release is called progestin
(progesterone). It prepares women’s uterus and breasts for pregnancy but its
function is unclear for men.
Adrenal cortex also releases small amounts of all the sex steroids released by the
gonads. (even though its main purpose it to regulate glucose and salt levels)
, Organizing effects of sex hormones: produce long lasting effects especially during a
sensitive stage of early development, determine whether the body develops into a
male or female.
Activating effects of sex hormones: more temporary, when a hormone increases
some activity that lasts only while the hormone is present, can occur at any time in
life.
Pituitary Gland: often referred as the master gland because most of its hormones are tropic
hormones. Tropic hormones influence the release of hormones from other glands. E.g.
gonadotropin stimulates the release of gonadal hormones.
It’s divided into two as: posterior and anterior pituitary gland
Posterior pituitary develops from a small outgrowth of a tissue that dangles from the
hypothalamus on the end of pituitary stalk
Anterior pituitary pinches off and migrates upward during development, releases the
tropic hormones, which qualifies as the master gland
The major difference between the endocrine function of women and men is that in woman
the levels of gonadal and gonadotropic hormones go through a cycle that repeats itself
called the menstrual cycle. But men have a steady state that change little from day to day.
Menstrual cycle: after the end of a menstrual period the anterior pituitary releases
follicle stimulating hormone (FSH) which promotes growth of follicle in the ovary.
The follicle nurtures ovum (egg), and produces several types of estrogen including
estradiol. Toward the middle of the cycle, the follicle builds up more receptors to FSH
and the follicle produces increasing amounts of estradiol. This increase in estradiol
causes an increased release of FSH and a sudden release of luteinizing hormone (LH)
from the anterior pituitary. FSH and LH combine to release an ovum. The remnant of
the follicle releases the hormone progesterone which prepares the uterus for a
fertilized ovum. Progesterone also inhibits further release of LH. Toward the end of
the cycle, levels of LH, FSH, estradiol and progesterone all decline. If the ovum is not
fertilized the lining of the uterus is cast off.
Hypothalamus is the regulator of the anterior pituitary but we don’t know how it’s carried
out. There are 2 different mechanisms by which the hypothalamus controls the pituitary:
1. For posterior pituitary: two major hormones in the posterior are vasopressin
(antidiuretic hormone – facilitates the reabsorption of water by the kidneys) and
oxytocin (stimulates contractions of the uterus during labor and ejection of milk).
These are peptide hormones that are synthesized in the cell bodies of neurons in
paraventricular nuclei and supraoptic nuclei. They are stored in the axons of
neurons in the posterior and released with action potentials.
2. For anterior pituitary: anterior is neuron free that’s why the anterior itself is
regulated by hormones released from the hypothalamus. The hypothalamopituitary
portal system carries the hormones from the hypothalamus to the anterior. The
hypothalamic hormones that stimulate the release of anterior pituitary hormones
are releasing hormones and those that inhibit the release of anterior pituitary
hormone are release-inhibiting hormones.
Hormones influence sex in 2 fundamental ways
1. By influencing the development from conception to sexual maturity of the
anatomical, physiological, and behavioral characteristics that distinguish one as
female and male
2. By activating the reproduction related behavior of sexually mature adults
Neuroendocrine System
Only the organs whose primary function appears to be the release of hormones are
referred to as endocrine glands.
Glands: 2 types
o Exocrine glans (e.g. sweat glands) release their chemicals into ducts which
carry them to their targets
o Endocrine glands (ductless glands) release their chemicals which are called
hormones directly into the circulatory system and these hormones travel via
the circulatory system until they reach their target
Gonads: the male testes and the female ovaries. After copulation (sexual
intercourse) a single sperm fertilizes on ovum to from one called zygote. Each cell of
the human body contains 23 pairs of chromosomes. The ova and sperm only contain
half the number.
Sex chromosomes: they contain the genetic programs that direct sexual
development. Females have 2 large X chromosomes. Males have one X and one Y
chromosome. The sex is determined by the father’s chromosomes.
Classes of Hormones
1. Amino acid derivatives: hormones that are synthesized from an amino acid
molecule. E.g. epinephrine is released from adrenal medulla and synthesized from
tyrosine
2. Peptides and proteins: chains of amino acids- peptide hormones are short chains and
protein hormones are long chains
3. Steroids: hormones that are synthesized from cholesterol. They influence sexual
development and the activation of adult sexual behavior.
Most other hormones produce their effects by binding to receptors in cell
membranes. Steroid also do this but they can also penetrate cell membranes because
they are small and fat soluble. Steroid hormones tend to have the most diverse and
long-lasting effects on cellular function.
Sex steroids: The gonads produce and release steroid hormones. The main classes of
gonadal hormones are androgens (testosterone) and estrogens (estradiol). Ovaries
release more estrogen and testes release more androgen but they shouldn’t be
called male or female hormones, men and women both have these.
3rd class of steroid hormone that ovaries and testes release is called progestin
(progesterone). It prepares women’s uterus and breasts for pregnancy but its
function is unclear for men.
Adrenal cortex also releases small amounts of all the sex steroids released by the
gonads. (even though its main purpose it to regulate glucose and salt levels)
, Organizing effects of sex hormones: produce long lasting effects especially during a
sensitive stage of early development, determine whether the body develops into a
male or female.
Activating effects of sex hormones: more temporary, when a hormone increases
some activity that lasts only while the hormone is present, can occur at any time in
life.
Pituitary Gland: often referred as the master gland because most of its hormones are tropic
hormones. Tropic hormones influence the release of hormones from other glands. E.g.
gonadotropin stimulates the release of gonadal hormones.
It’s divided into two as: posterior and anterior pituitary gland
Posterior pituitary develops from a small outgrowth of a tissue that dangles from the
hypothalamus on the end of pituitary stalk
Anterior pituitary pinches off and migrates upward during development, releases the
tropic hormones, which qualifies as the master gland
The major difference between the endocrine function of women and men is that in woman
the levels of gonadal and gonadotropic hormones go through a cycle that repeats itself
called the menstrual cycle. But men have a steady state that change little from day to day.
Menstrual cycle: after the end of a menstrual period the anterior pituitary releases
follicle stimulating hormone (FSH) which promotes growth of follicle in the ovary.
The follicle nurtures ovum (egg), and produces several types of estrogen including
estradiol. Toward the middle of the cycle, the follicle builds up more receptors to FSH
and the follicle produces increasing amounts of estradiol. This increase in estradiol
causes an increased release of FSH and a sudden release of luteinizing hormone (LH)
from the anterior pituitary. FSH and LH combine to release an ovum. The remnant of
the follicle releases the hormone progesterone which prepares the uterus for a
fertilized ovum. Progesterone also inhibits further release of LH. Toward the end of
the cycle, levels of LH, FSH, estradiol and progesterone all decline. If the ovum is not
fertilized the lining of the uterus is cast off.
Hypothalamus is the regulator of the anterior pituitary but we don’t know how it’s carried
out. There are 2 different mechanisms by which the hypothalamus controls the pituitary:
1. For posterior pituitary: two major hormones in the posterior are vasopressin
(antidiuretic hormone – facilitates the reabsorption of water by the kidneys) and
oxytocin (stimulates contractions of the uterus during labor and ejection of milk).
These are peptide hormones that are synthesized in the cell bodies of neurons in
paraventricular nuclei and supraoptic nuclei. They are stored in the axons of
neurons in the posterior and released with action potentials.
2. For anterior pituitary: anterior is neuron free that’s why the anterior itself is
regulated by hormones released from the hypothalamus. The hypothalamopituitary
portal system carries the hormones from the hypothalamus to the anterior. The
hypothalamic hormones that stimulate the release of anterior pituitary hormones
are releasing hormones and those that inhibit the release of anterior pituitary
hormone are release-inhibiting hormones.
