Physiology and Pharmacology: Reproduction/sex steroid axis Flashcards
Development of the egg?
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Methods of assisted conception?
IVF (in vitro fertilisation)
Intrauterine insemination
Time period for oogenesis?
Takes many years to complete
Process of oogenesis?
- Begins in utero, where there is mitotic division of oogonia (diploid cell)
- Commencement of 1st meiotic division forms the primary oocyte
- There is arrest in prophase
- It is then suspended for many years; following puberty, it begins again, prior to ovulation
- The entire process is completed at fertilisation
What are polar bodies?
1st polar body is 1 of 2 products in the first stage of meiosis; both are relatively small and contain little cytoplasm
Presence of 2 polar bodies signifies sperm entry and completion of the 2nd meiotic division
No. of eggs at different times in the human biological clock?
Very high no. of germ cells mid-trimester; at birth, this drops to below half
Even less by the time puberty begins and even fewer are ovulated (300-400)
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Time period of the menstrual cycle?
Lasts for an average of 28 days
2 phases of the menstrual cycle?
Follicular phase - 1st half of the cycle that allows:
• Maturation of the egg so that it is ready for ovulation at mid-cycle
Ovulation signals end of the follicular phase
Luteal phase - 2nd half of the cycle that allows:
• Development of corpus luteum
• Induction of preparation of reproductive tract for pregnancy (if fertilisation occurs)
What is the primary follicle?
Before birth, primary oocyte is surrounded by a single layer of granulosa cells; each of these primary follicles can produce a single ovum
Until puberty, all primary follicles degenerate to scar tissue (atresia) before ovulation
Development of the secondary follicle?
After puberty, secondary follicles develop cyclically
Oocyte grows and the follicle expands and become differentiated; after puberty, 300-400 are ovulated and rest undergo atresia
What occurs in the luteal phase?
Follicular cells left behind after ovulation undergo luteinisation (transformation to the corpus luteum)
Function of the corpus luteum in the luteal phase?
Secretes progesterone and oestrogen
Oestrogen secreted in the follicular phase and progesterone in the luteal phase are essential for:
• Preparation of uterine lining for implantation
What happens to the corpus luteum after ovulation?
Grows for 8-9 days
If no fertilisation has occurred, it survives no longer than 14 days after ovulation; the corpus albicans forms (a white body of fibrous tissue) and progesterone and oestrogen production decresease
If fertilisation has occurred, corpus luteum persists and produces increasing progesterone and oestrogen until after pregnancy
What does degeneration of the corpus luteum signal?
Start of a new follicular phase
Production and release of GnRH?
AKA Gonadotrophin-releasing hormone
Synthesised by hypothalamic neurons and is released in a pulsatile manner
Function of GnRH?
Stimulates synthesis and release of hormones from the anterior pituitary:
• FSH (low frequency pulses)
• LH (high frequency pulses)
Functions of FSH?
Stimulates follicular development and thickens the endometrium
Functiosn of LH?
LH peak stimulates ovulation
Stimulates corpus luteum development
Thickens endometrium
Secretion of oestrogen?
Primarily by the ovaries
Also be adrenal cortex and, in pregnancy, by the placenta
Functions of oestrogen?
- Thickens endometrium
- Responsible for fertile cervical mucous
- Maturation of ovarian follicles
- Mildly accelerates sodium and water reabsorption by kidney tubules; this increases water content of the uterus
- Responsible for development of secondary sexual characteristics
- High oestrogen conc:
• Inhibits secretion of FSH and prolactin
• Stimulates secretion of LH - Low oestrogen conc. after pregnancy:
• Stimulates secretion of prolactin
Consistency of fertile cervical mucous?
Clear, stringy, stretchable and slippery
Has fern patterns when dry
Production of progesterone?
Secreted by the corpus luteum; also, by the placenta during pregnancy
Functions of progesterone?
- Inhibits LH secretion
- Has a thermogenic effects (increases basal body temp)
- Relaxes smooth muscles
- Responsible for inferile mucous
- Maintains thickness of endometrium
- Maintains pregnancy
Consistency of infertile cervical mucous?
Opaque, sticky, thick, non-stretchable mucous
No fern patter when dry
Effects of different hormones in the follicular phase?
- FSH stimulates follicular development
- Dominant follicle develops and produces increasing follicular fluid (contains oestrogen)
- Oestrogen stimulates endometrial thickening
- Increased serum oestrogen:
• Suppresses FSH secretion
• Favours LH secretion - LH stimulates ovulation and initiates corpus luteum development
What happens during the luteal phase?
Cavity of the ruptured follicle replaced with the corpus luteum, which secretes progesterone and oestrogen
Progesterone stimulates secretory changes in endometrium to prepare for implantation; also, maintains endometrium during early phase of pregnancy
What happens during the menstrual phase?
Corpus luteum degenerates
Progesterone and oestrogen production by the corpus luteum ceases, so endometrium degenerates and menstruation occurs
What stimulates production of FSH and a new cycle?
Drop in blood levels of oestrogen and progesterone
What happens during the LH surge?
Oocyte resumes meiosis; secondary oocyte + polar bodies (degenerates)
Stops at metaphase II (only complete if fertilisation has occurred)
Cytoplasmic maturation occurs
LH receptors are stimulates to synthesise progesterone
When does ovulation occur?
36.5 hours after the LH surge
What happens after the ovulation?
Collapsed follicle forms corpus luteum
How is ovulation detected?
Detect the LH surge (blood tesT)
Basal body temperature rises during ovulation (track over 6 months)
Test urine with LH detection kits
Gross appearance of corpus luteum?
Lutein is a carotenoid pigment that makes it orange/yellow
What day of the cycle would progesterone be measured to assess if ovulation has occurred?
Day 21
Functions of the male genital tract?
Acts as a route for sperm
Production of testosterone
Route of sperm?
- Testes
- Epididymis
- Vas deferens
- Ejaculatory duct
- Urethra
Describe spermatogenesis
Occurs within the seminiferous tubules of the testes; germ cell mitosis is reactivated at puberty and is constant
Control of testes?
LH - acts on Leydig cells to regulate testosterone secretion
FSH - acts on Sertoli cells to enhance spermatogenesis (essential for spermatic re-modelling)
Both of these hormone are released due to the action of GnRH
Functions of Leydig and Sertoli cells?
Leydig - secrete testosterone
Sertoli (in seminiferous tubules) - secrete androgen binding globulin (ABG) and inhibin; also, support germ cells in development
Functions of dihydrotestosterone?
- Enlargement of male sex organs
- Secondary sexual characteristics
- Anabolism
Describe feedback effects of testosterone
Feedback to anterior pituitary:
• Reduces sensitivity of LH-secreting cells to GnRH; LH is inhibited more than FSH
Feedback to hypothalamus:
• Suppression of GnRH bursts
Describe feedback of inhibin
Feedback to anterior pituitary:
• Suppress FSH-secreting cells production of FSH
Effects of testosterone on different body systems?
Skin:
• Produces facial and body hair
• Supports collagen production
Male sex organs:
• Produces sperm
• Prostate growth
• Erectile dysfunction
Brain:
• Responsible for sex drive
• Produces feelings
• Aids memory
Bone marrow:
• Produces RBCs
Bone:
• Maintains bone density
Stages of germ cell development?
- Spermatogonia
- Primary spermatocytes
- Secondary spermatocytes
- Spermatids (Early to elongated)
- Testicular spermatozoa
Special structures developed by the mature sperm cell?
Golgi (acrosome)
Cilium (tail)
Cytoplasm is reduced, as several spermatids link via cytoplasmic bridges
Factors that have adverse effects on human spermatogenesis?
Heat (Taxi Driver’s syndrome - sitting increases temp by 2 degrees within 2 hours)
Alcohol
Smoking
Chemo/radiotherap
Vasectomy (minor effect based on time)
If sperm cannot be collected from ejaculate, what should be done?
Surgical sperm aspiration (indicated for azoospermia)
What does a high FSH level signify?
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Key differences between oogenesis and spermatogenesis?
Oogenesis only leads to production one final ovum
Production of an ovum occurs only once a month
Also, in oogenesis, polar bodies are formed and these eventually disintegrate
