Module 4 - Reproduction Flashcards
What does the ovary contain
- stromal matrix
(connective tissue,
nerves, lymphatic and
blood vessels) - follicles
- tunica albuginea
- surface epithelium
List the stages of Ovarian Follicles during Folliculogenesis
- primordial follicles (non-growing)
- preantral follicles (early growing)
- early antral follicles
- antral follicles
Describe Primordial to preantral
stages:
- Gonadotropin INDEPENDENT i.e. no exogenous factors
- Intraovarian/paracrine factors
- Balance of stimulatory (activation/recruitment) and
inhibitory (quiescence/apoptosis) factors
Describe Early antral and beyond stage
- Gonadotropin DEPENDENT i.e. FSH and LH
- Follicle cells acquire FSHR and LHR
- Dominant follicle is selected
- Some regulation by intra-ovarian factors (inhibin and activin)
➢ via +ve and –ve feedback loops
When does the preantral stage occur in the menstrual cycle
Throughout
When does the very early antral stage occur in the menstrual cycle
throughout
When does the early antral stage occur in the menstrual cycle
1-6
When does the expanding antral stage occur in the menstrual cycle
6-10
When does the expanded antral stage occur in the menstrual cycle
10-12
When does the preovulatory stage occur in the menstrual cycle
13-14
Overview of meiosis
Prophase I
Metaphase I
Anaphase I
Telaphase I
Prophase II
Metaphase II
Anaphase II
Telaphase II
Define meiosis
Meiosis is a type of cell division that occurs in sexually reproducing organisms and reduces the number of chromosomes in gametes (the sex cells, or egg and sperm).
- During meiosis, the four daughter cells produced are haploid, meaning they only have half the number of chromosomes of the parent cell
- Meiosis produces our sex cells or gametes (eggs in females and sperm in males)
- Meiosis II is an equational division analogous to mitosis, in which the sister chromatids are segregated, creating four haploid daughter cells
FOLLICULOGENESIS
growth and
development of the follicle. it accompanies and supports oogenesis
OOGENESIS
growth and maturation of
the oocyte
Events of oogensis
- Before birth EVENTS
At birth, all
primordial follicles
are already present
and contain primary
oocytes arrested in
prophase I. - Throughout life
until menopause
Primordial follicles
begin to grow and
develop. (Before
puberty all
developing follicles
undergo atresia.) - From puberty to
menopause
After puberty, some
antral follicles are
rescued from atresia
each month and the
primary oocyte in one
(the dominant follicle)
completes meiosis I.
Regulation of the ovarian cycle
- GnRH stimulates FSH and LH secretion
- FSH and LH stimulate follicles to grow,
mature and produce steroid hormones
2-cell 2 gonadotropin hypothesis - Negative feedback inhibits gonadotropin
release - Positive feedback stimulates
gonadotropin release
- Estrogen levels continue to rise as a result
of continued release by dominant follicle
- When levels reach a critical high value, a
brief positive feedback occurs on brain and
anterior pituitary
- Triggers LH surge - LH surge triggers ovulation and formation
of the corpus luteum
- LH surge triggers primary oocyte to
complete meiosis I to become the secondary
oocyte
- Secondary oocyte enters meiosis II and
arrests at metaphase II
- Shortly after ovulation:
Estrogen levels decline
LH transforms ruptured follicle into corpus
luteum
LH stimulates corpus luteum to secrete
progesterone (and some estrogen)
almost immediately - Negative feedback inhibits LH and FSH
release
- Negative feedback from rising plasma
progesterone and estrogen levels
- Inhibin enhances inhibitory effect
- Declining LH inhibits follicle development
- If no fertilisation occurs:
* Corpus luteum degenerates
* Sharp decrease in progesterone and
estrogen
* Ends the negative feedback and cycle
starts again
The uterine (menstrual) cycle
Cyclic changes in the endometrium that occur in response to fluctuating ovarian hormone levels
Three phases:
1. Days 1–5: menstrual phase
2. Days 6–14: proliferative (preovulatory) phase
3. Days 15–28: secretory (postovulatory) phase
Days 1–5: menstrual phase
- Gonadotropin levels beginning to rise
- By day 5, growing follicles starting to
produce more estrogen - Functional layer of the endometrium shed
Days 6-14: proliferative phase
- LH steadily rising with surge just before
ovulation - FSH declining with increase just before
ovulation - Rising estrogen levels → regeneration of
the functional layer of the endometrium - Ovulation at end of the proliferative phase
on day 14.
Days 15-28: secretory phase
- Begins immediately after ovulation
- Most consistent in duration
- Drop in LH, but level still high enough to
support progesterone (P) production by
corpus luteum - P promotes well-developed blood supply
and endometrial glands provide nutrientrich secretions to prepare for implantation - P thickens cervical mucus to form a plug
that blocks entry of more sperm,
pathogens or debris - If corpus luteum degenerates, P causes
spiral arteries in endometrium to constrict
and endometrial tissue dies
why does the female cycle have 2 phases
The two phases of the female cycle are necessary for the preparation of the uterus for pregnancy and the release of an egg for fertilization. The follicular phase prepares the egg for release, while the luteal phase prepares the uterus for implantation of a fertilized egg.
Identify some actions of estrogen and progesterone on reproductive
organs
- stimulate growth and maturation of reproductive organs and breasts and maintain their adult size and function
- promote the proliferative phase of menstrual cycle
- stimulate production of watery cervical mucus and activity of fimbriae and uterine tube cilia
- promote oogensis and ovulation
- during pregnancy, stimulate growth of uterus and enlargement of external genitalia and mammary glands
- metabolic effects
- neutral effects
- promotion of secondary sex characteristics
Define progesterone
Progesterone is a hormone that plays an important role in the menstrual cycle, pregnancy, and embryogenesis of humans and other species
Define estrogen
Estrogen is a group of hormones that play an important role in the sexual and reproductive development in women.
Estrogen is responsible for developing female sexual characteristics, including breast development, growth of pubic and underarm hair, and the start of menstrual cycles.
Estrogen is produced by the ovaries, adrenal glands, and fat tissues
True or false: Men do not have estrogen
False - they do have estrogen but in smaller amounts.
Testis migration during development
10-15 weeks
- Pelvic position
- Suspensory ligament
lengthens and
regresses
25-28 weeks
- Migrates over pubic
bone
- Reaches scrotum by
35-40 weeks
identify and describe the 2 functional compartments of the testis
The intratubular compartment:
- seminiferous tubules
- lined with complex stratified
germinal epithelium
- contains sperm cells and sertoli cells
- Sperm production
The peritubular:
- neuronal and vascular elements
- connective tissue, immune cells,
interstitial Leydig cells
- Steroid (androgen) production
Function of testis
Sperm and steroid hormone production
Leydig cells
(interstitial cells) =
steroidogenic
(cf theca cells in females)
-synthesize and secrete androgens (testicular hormones).
Summary of events in Spermatogenesis
- Mitotis
- produces large numbers of cells - Meiosis
- generates genetic diversity and ½
chromosomes - Spermiogenesis (Cytodifferentation)
- packages the chromosomes for effective
delivery to the oocyte
Hormonal regulation of testis by HPG
- The hypothalamus releases GnRH,
which reaches the anterior pituitary
via the hypophyseal portal veins. - GnRH causes anterior pituitary
gonadotropic cells to release FSH
and LH. - FSH indirectly stimulates
spermatogenesis by causing
Sertoli cells to release ABP, which
keeps the local concentration of
testosterone high.
ABP = androgen binding protein - LH stimulates Leydig cells to
secrete testosterone, which is
essential for spermatogenesis. - Testosterone acts at other body
sites [e.g., to stimulate maturation
of sex organs, development and
maintenance of secondary sex
characteristics, and libido (sex drive)]. - Negative feedback by testosterone
inhibits FSH and LH release from the
anterior pituitary and GnRH release
from the hypothalamus.
7 Inhibin released by Sertoli cells
feeds back on the anterior pituitary,
decreasing FSH release.
Interstitial Leydig cells
- Large, polygonal
*Lipid droplets
*Elaborate smooth ER
-Testosterone synthesis from
cholesterol - Differentiate to secrete testosterone in
early fetus
*Essential for development of male gonads - Period of inactivity (from about 5 months),
activated at puberty by gonadotropins
Actions of testosterone on reproductive organs
- stimulates formation of male reproductive ducts, glands, external genitilia
- promotes descent of testes
- stimulates growth and maturation of internal and external genitilia at puberty
- promotes long bone growth
promotes growth of larynx - enhances sebum and hair growth
- anabolic
- libido in males - promotes aggressiveness
