Lecture 42 - Reproductive Physiology Flashcards
Posterior pituitary
Secretes hormones synthesized in the hypothalamus into circulation
Oxytocin
Anti-directed hormone (ADH) (aka vasopressin)
anterior pituitary
Hypophyseal portal system
Hormones synthesized in the hypothalamus control release of hormone release from the anterior pituitary
Hormones synthesized in anterior pituitary released into circulation to control hormone release from other glands
what are trophic hormones?
o Hormones secreted by the anterior pituitary that stimulate hormone secretion from other glands (aka stimulating hormones – SH)
what are _trophs?
o Cells that secrete trophic hormones (anterior pituitary)
what is _statin?
Inhibiting hormone
the role of positive feedback amplification
o The stimulus evokes a reflex which enhances the stimulus
o Increases the signal to drive the reflex, thus amplifying response
the role of negative feedback regulation
o Self-regulating
o The stimulus which switches on the reflex evokes a response that alleviates the stimulus
o Activating the reflex restores the system to balance
Explain the role of binding proteins in circulation as important mediators in hormone delivery
o Binding proteins regulate the availability of steroid hormones for receptor binding
o Binding proteins can also compartmentalize steroid hormones
Binding proteins found in blood
o Albumin
o Corticosteroid-binding globulin (CBG)
o Sex hormone-binding globulin (SHBG)
Chromosomes in somatic cells
o Diploid cells
o 23 pairs of chromosomes for a total of 46
o Each pair is homologous since contain similar genes in same order
o One member of each pair is from each parent
o 22 autosomal and 1 pair of sex chromosomes
chromosomes in gametes
o Haploid cells
o Single set of chromosomes for a total of 23
o Produced by special type of division – meiosis
mitosis
o Cell division
o After division have diploid cell (2n chromosomes)
o Somatic cell
meiosis
o Gamete formation
o After meiosis haploid cell (n chromosomes)
o Gamete cell (sperm or ovum)
meiosis - sperm
o Four daughter cells
meiosis - ovum
o Single ovum
o + 3 polar bodies (functionally redundant)
spermatogenesis
o Spermatogonia – diploid germ cell
o Undergoes mitosis to produce two daughter cells
Cell 1 (type A) remains a germ cell
Cell 2 (type B) undergoes spermatogenesis
on set of sperm production
puberty
oogenesis
o Begins during fetal development
o Fetal period = Oogonium
o Childhood (no development)
o Puberty to menopause each mouth
oogonium
o Mitotic division during fetal period
o 7 million daughter cells (decreases to 2 million – known as atresia)
o 12-25 weeks = meiosis begins (development of primary oocyte)
o 14-36 weeks = primary follicle forms, arrested meiosis (prophase 1, sister chromatids)
oogenesis - puberty
o FSG stimulates oogenesis to restart
o Primary oocyte develops to secondary oocyte (meiosis I completes, haploid cell)
o Ovulation
o Fertilization (meiosis II completed post fertilization)
describe the hormonal regulation of spermatogenesis
o Regulated by the interplay of GnRH, FSH, LH, testosterone, inhibin and other factors. This system ensures continuous production of sperm cells in the testes and maintenance of male reproductive function.
Gonadotrophin-releasing hormone (GnRH)
o Release of GnRH from hypothalamus begins the process of spermatogenesis
o Released every 60-90 mins
o Stimulates anterior pituitary to release two important hormones (FSH and LH)
Follicle-stimulating hormone (FSH)
o Released by anterior pituitary
o Stimulates Sertoli cells, which provide physical and nutritional support to developing sperm cells
Luteinizing hormone (LH)
o Released from anterior pituitary
o Acts of Leydig cells, which produce testosterone
Testosterone
o Primary male sex hormone
o Stimulates the growth and development of the seminiferous tubules and promotes division of spermatogonia cells into primary spermatocytes
o Also influences the development of secondary sexual characteristics in males
Inhibin
o Hormone produced by Sertoli cells in testes
o Functions as a negative feedback regulator of FSH secretion
sperm maturation and transport
o Sperm cells undergo maturation and storage in the epididymis, where they gain the ability to swim and fertilize an egg
sperm release
When sexual arousal and stimulation occur, the hypothalamus signals the anterior pituitary to release a surge of LH, which stimulates the final stages of sperm development and triggers sperm release (ejaculation) from the epididymis into the vas deferens.
Maintenance of testosterone levels
o Spermatogenesis is most active when testosterone levels are within normal physiological range
o Hormonal regulation of testosterone production is a complex feedback loop with GnRH, LH and inhibin playing important roles.
cells of the follicle
o Granulosa cells
o Basement membrane
o Thecal cells
thecal cells
o Secrete androgen – precursor to estrogen production
o LH hormone sensitive
granulosa cells
o Secrete oestrogen (analogous to Sertoli cells in testes)
o FSH sensitive
o As granulosa cells proliferate the oestrogen contraction in blood increases
dominance
o Single follicle matures for ovulation
o It can take several months
Negative feedback regulation of oestrogen secretion
o As follicles proliferate oestrogen secretion increases
o Oestrogen negative feedback regulation of FSH and GnRH secretion
o Decreased FSH arrest or atresia of follicles, selection of dominate follicles
ovulation
o Triggered by a surge in LH
o Positive feedback amplification – oestrogen concentration above a certain threshold triggers surge in gonadotropin (FSH/LH) release
post ovulation
o Formation of the corpus luteum
o Granulosa and thecal cells used
o Corpus luteum secretes progesterone
daily release of LH and GnRH
o GnRH pulses throughout the day and results in burst of LH release through the day and thus throughout the month
As estrogen concentrations in blood increase, the amount of LH release per burst:
o Increases
o During normal menstrual cycle, estrogen surges just prior to LH surge
Recognize and explain the relationship between the ovarian and uterine cycles
o Closely linked through hormone signalling
o Estrogen produced by developing follicles in ovaries stimulates proliferation of uterine lining (proliferative phase)
o Progesterone produced by corpus luteum in ovaries maintains endometrial lining and prepares it for implantation (secretory phase)
o Hormonal changes in ovaries triggers corresponding changes in the uterus, ensuring that the uterine lining is receptive to a potential fertilized egg
ovarian cycle
follicular phase
luteal phase
uterine cycle
o Menstrual phase
o Proliferative phase
o Secretory phase
Two zones of endometrium
o Functional zone
o Basilar zone
pregnancy and implantation - hCG
hCG sustains the corpus luteum
menopause
o fewer ovarian follicle
o decreased oestrogen secretion
o impaired proliferation phase
o no uterine cycle
o no FSH/LH inhibition
LH and FSH levels in females throughout life
o At Menopause, female oocyte depletion and oocyte insensitivity to gonadotropins (LH and FSH) results in a decrease of follicular estrogen and progesterone release.
o Falls in serum oestrogen and progesterone results in a loss of negative feedback inhibition of GnRH/LH/FSH.
o Produces a dysregulation of gonadotropes
