Transcript Reproductive hormones

Pituitary gland
• Embryonic origin
– Anterior pituitary gland (adenohypophysis)
• Rathke’s pouch
– Roof of the embryonic mouth
– Glandular tissue containing secretory cells
– Posterior pituitary gland (neurohypophysis)
• Infundibulum/brain floor)
– Part of the CNS
– Contains axons of the hypothalamic neurons
– Housed in a bony capsle called sella turcica
Pituitary hormones
• Anterior pituitary gland
– Five different hormones
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Gonadotropins (LH and FSH, gonadotroph)
GH (somatotroph)
Prolactin (lactotroph)
Adenocorticotropic hormone (corticotroph)
Thyroid-stimulating hormone (thyrotroph)
• Posterior pituitary
– Two hormones
• Oxytocin
• Vasopression/ADH
Gonadotropins
• Crucial for proper gonadal functions
– Production of steroid hormones
– Development and function of cells
• Steroidogenic cells
– Process of gamete development
• Re-initiation of meiosis (oocytes)
– Physical process of ovulation
• Rupture of follicle
Gonadotropin receptors
• Member of G-protein coupled receptors
– Seven trans-membrane receptor
• Coupled with G-protein complex
– Interaction with gonadotropin
• N-terminus of the protein (extracellular domain)
• Causes shift in conformation/structure of the
receptor
– Activation of G-protein complex
• Activated G-protein
– Activates adenyl cyclase (production of cAMP)
Gonadotropin receptors
• Member of G-protein coupled receptors
– Seven trans-membrane receptor
– Interaction with gonadotropin
• cAMP
– Secondary messenger
– Activates protein kinase A pathway
Neural regulation of gonadotropin
production
• Hypothalamus
– Release of GnRH
– Frequency of GnRH release by GnRH pulse
center
• Frequency of gonadotropin pulses
• Types of gonadotropin being released
– Slower pulse frequency – FSH
– Faster pulse frequency – LH
Gonadal regulation of gonadotropin
secretion
• Production of sex steroid hormones
– Results of gonadotropin actions on testicular or
ovarian cells
– Form feedback system with hypothalamus and
anterior pituitary gland
• Negative
• Positive
• Ovarian proteins (inhibins and activins)
– Inhibition or stimulation of gonadotropin release by
anterior pituitary
• Primarily on FSH
Steroid hormones
• Estrogens
– Estradiol-17 beta (E2-17b)
• Principle estrogen produced by the ovarian follicles
– Most potent
• Produced by the granulosa cells of the follicle
– Androgen from theca cells being converted by aromatase
• Estrogens
OH
OH
– Predominant female
sex steroid hormone
• Development and
function of reproductive
organs
• Fertility
• Development of
mammary alveolar
structure
• Reproductive behavior
• Protestins/progestagens
– Progesterone
• Principle progestin
• Hormone of pregnancy
– Essential for the
maintenance of
pregnancy
– Preparation of uterus for
implantation
– Relaxation of uterine
smooth muscle
– Development of
mammary duct system
• Produced by the corpus
luteum/corpola lutea
– Placenta in some
species
• Androgens
– Testosterone
• Primary male steroid
hormone
• Critical for development and
function of male reproductive
organs
– Masculinization of brain
• Critical for sperm production
– Number
– Quality
• Development of male
secondary sex characteristics
• Substrate for estradiol
production
• Libido
Relationship between steroid
hormones and gonadotropins
• Gonadotropins
– Essential for production of steroid hormones
• Steroid hormones
– Regulate release of gonadotropins via
feedback system
• Estradiol
– Inhibition of FSH release by the anterior
pituitary gland
– Dual feedback on LH release
• Low concentrations = inhibitory (prepubertal period
and non-breeding season)
• High concentrations = stimulatory
– Triggers preovulatory surge of GnRH and LH
• Progesterone
– Inhibits surge-like release of LH
• Inhibits GnRH surge center within the
hypothalamus
– Allows activity of tonic GnRH release center
• Pulsatine secretion of GnRH (high amplitude, low
frequency)
– Pulsatile secretion of LH
• Testosterone
– Inhibits activity of GnRH surge center
• Hypothalamic nuclei organization
• Blocking surge center function
– Inhibits LH secretion
• Regulation of GnRH release
Sexual dimorphism of
neuroendocrine system
• Differences in organization of
hypothalamus
– Transplantation of ovaries to mature castrated
male animal has no effects
– Transplantation of ovaries to male animal
castrated at birth triggers female reproductive
cycle
• Organization of hypothalamus
– Androgens
• Masculinization of brain/hypothalamus
– Male hypothalamus becomes unresponsive to increased
concentrations of estradiol (no GnRH and LH surge)
– Prenatal in most species
• Prevention of estradiol positive feedback
– Primates
• Affect development of female
– Masculinization when exposed to high dose of
androgens during fetal life
Changes in hormone
concentrations
• Female
– Cyclic changes in production of ovarian
steroid hormones
• Correspond to cyclic pattern of GnRH and
gonadotropin secretion
• Male
– Constant production of androgens by testis
• Critical for sperm production
Stages of female reproductive
cycle
• Two phases
– Follicular phase
• Preovulatory follicle
• High concentrations of Estradiol
– Luteal phase
• Corpus luteum/corpora lutea
• High concentrations of progesterone
Stages and phases of the estrous
cycle
Follicular
Phase
18
4
16
3.5
14
3
12
2.5
10
2
8
1.5
6
1
4
0.5
0
Estrus
Metestrus
Diestrus
Proestrus
18
16
14
3
12
2.5
10
2
8
1.5
6
1
4
2
0.5
0
0
2
0
Blood Estradiol
Luteal Phase
Blood Estradiol
Blood Progesterone
3.5
Follicular
Phase
Blood Progesterone
4