Reproductive Systems and Fertility - 1 and 2 Flashcards
How many chromosomes are involved in mitosis and what offspring is produced?
1 maternal and 1 paternal chromosome
–> 2 genetically identical daughter cells
produced
How many chromosomes are involved in meiosis and what offspring is produced?
1 maternal and 1 paternal chromosome
Meiosis 1 = crossing over of chromosomes
Meiosis 2 = 4 genetically different
chromosomes produced
= 4 genetically different offspring cells
produced
What causes differences between siblings?
= Meiosis - crossing over = independent assortment of chromosomes
What is a gonad?
The organ where gametes are produced
They also produce hormones that control secondary sexual characteristics.
What is the female gonad and what is the male gonad?
Ovary in female
Testes in male
What are germ cells?
Any cell in the series of the germ line that eventually become gametes
Often indicate the cells before meiosis
What are the germ cells called found in the testis and in the ovary?
Spermatogonia in the testis
Oogonia in the ovary
What is the origin of germ cells?
Germ cells originate from primordial germ cells (PGCs)
How are primordial germ cells (PGCs) formed?
PGC arises in the posterior yolk sac and stay there until gonads are formed
Gonads form from the genital ridge and become testis or ovary
PGCs migrate into the gonad and then reside as germ cells
What is spermatogenesis?
The production of sperm from the primordial germ cells.
When are primordial germ cells formed?
- 3-6 weeks of embryogenesis - PGCs are
formed - 2-3 months of embryogenesis PGCs migrate
into the gonad (future testis) becoming
dormant
What happens at puberty in males ?
Testosterone causes maturation of seminiferous tubules in the testis.
Allowing spermatogonia to proliferate and enter meiosis. = commencement of meiosis in a wave
Some spermatogonia remain - functioning as stem cells
What is the testis made out of ?
= Seminiferous tubules
What is the order of spermatogenesis?
Primordial germ cell (PGC) enters gonad –> Spermatogonium (puberty) –> diploid spermatogonia proliferate by mitotic cell division inside testis –> Primary spermatocyte –> Meiotic division 1 = Secondary spermatocyte –> Meiotic division 2 = Spermatids —> differentiation => Spermatozoa = Sperm
Where does spermatogenesis take place?
In the seminiferous tubule
- In close relation to Sertoli cells
Where are Sertoli cells located?
Span from the basement membrane to the lumen, surrounding differentiating spermatogonia
What is the function of Sertoli cells?
Produce enzymes and growth factors required for spermatogenesis
Also a function as a phagocyte to clean up residual cytoplasm of sperm
What are Leydig cells?
Interstitial cells
Secrete testosterone in response to LH
Where are Leydig cells located?
Reside outside of seminiferous tubules
When do sperm undergo most of their differentiation?
= after the completion of meiosis
How do sperm share the cytoplasm?
via cytoplasmic bridges
How is sperm sharing the cytoplasm via cytoplasmic bridges during spermatogenesis beneficial?
After meiosis some cells only have Y chromosomes and no X chromosomes.
By sharing the cytoplasm until the last stage of differentiation, sperm with Y chromosomes can be supplies with essential proteins encoded by genes on the X chromosomes.
What is spermiogenesis?
= differentiation step of spermatids becoming a highly specialised spermatozoa
Where does spermiogenesis occur?
In the seminiferous tubules
What are the 5 key stages of spermiogenesis?
- Nucleus condense
- Formation of acrosome
- Formation of flagellum
- Mitochondria gathered at the midpiece –>
generate ATP for movement of cilia - Removal of excess cytoplasm
After spermiogenesis where do sperm go?
Sperms are released to the lumen and then transferred to the epididymis
What is spermiation?
The process of sperm being released from the Sertoli cells to the lumen.
Sperms are not motile (cant move) when released
What is the epididymis?
A long single duct with peristaltic contraction
What is the function of the epididymis?
Serves as a reservoir for sperm - their passage takes 1-21 days
Concentrates the fluid x100
Sperm undergo further maturation, acquiring mobility, increasing dependence on fructose for energy production
What is the path of the sperm?
Testis –> Epididymis –> Ductus deferens = Vas deferens –> Vesicular gland = Seminal vesicle –> prostate –> Bulbourethral gland –> Urethra
What is capacitation?
The final stage of maturation of sperm
Where does capacitation take place?
In the female’s genital tract for ~ 7 hrs
What are the 2 key features for capacitation?
- Hyperactive tail movement
- Acrosome reaction: plasma membrane and
acrosome membrane fuse in the tip. Other
parts fuse with the plasma membrane of the
oocyte
What is the definition of infertility?
Inability to conceive within 12 months
What is the probability of achieving pregnancy per menstrual cycle ?
= 20 -25% - in a healthy young couple
- So in theory 98% of couples should be pregnant within 13 months. Reality is 85% in 12 months
What % male and female factors is a couples infertility attributed to?
Male factors - 25%
Female factors - 58%
- the rest unexplained
What % of women are estimated to be infertile?
14%
Why has the proportion of couples without children risen but the infertility rate has not changed?
= due to a trend in delaying childbearing
What are some causes of male infertility?
- Primary hypogonadism ( absence of testis,
chemotherapy, radiation) 30-40% - Secondary hypogonadism ( hypothalamic -
pituitary disease) 2% - Disordered sperm transport 10-20%
- Unknown 40-50%
What is a deferentectomy (vasectomy) ?
- common method of male sterilisation
- Cut and ligated ductus deferens
What happens in a deferentectomy (vasectomy) as sperm is constantly produced?
- Unexpelled sperms degenerate in the
epididymis - Fluid is ejaculated from the seminal glands,
prostate and bulbourethral glands
What is oogenesis?
The differentiation of the ovum (egg cell) into a mature ovum to further develop when fertilised.
What are the key steps of oogenesis?
Primordial germ cell (PGC) enters gonad –> Oogonium –> Diploid oogonia proliferate by mitotic cell division inside ovary –> Primary oocyte –> Division 1 of meiosis stops in prophase as the primary oocyte grows –> further development of primary oocyte –> Puberty –> Maturation of primary oocyte - Completion of division 1 of meiosis –> Secondary oocyte –> division 2 of meiosis = Mature ovum (egg)
When are primordial germ cells PGCs formed?
4-6 weeks of embryogenesis
What happens at 6 - 12 weeks of embryogenesis?
PGCs migrate into developing gonad (future ovary)
Now called Oogonia
What happens after the oogonia have formed?
proliferation
What happens at week 12 of embryogenesis?
-Oogonia enter the first mitotic prophase =>
Now called primary oocyte
- Follicle cells in the ovary surround the oocyte, forming the primordial follicle
Do primordial follicles increase or reduce over time?
- 5 months of embryogenesis = 7 million
primordial follicles - at birth: reduced to 0.7 ~ 2 millions after
degradation - at puberty: 700,000 of primordial follicle
What happens to primordial follicles after puberty?
A few primordial follicles re-commence meiosis every day, only one is ovulated every month
What stage of the oocyte does ovulation occur?
The secondary oocyte stage
When will the second meiosis (second polar body) be formed?
ONLY if fertilisation occurs
What is a primordial follicle?
a primary oocyte with enlarged cytoplasm with a flat one cell layer of follicular (granulsoa) cells = the dormant status
What is a primary follicle?
Chosen to re-commence growth. Follicular cells become cuboid and proliferate into multiple layers
What is a preovulatory follicle?
One of the secondary follicles that is chosen to mature for ovulatio
What is a secondary follicle?
With antrum ( a cavity) with fluid from granulsoa cells
What is a follicle with a large antrum called?
a Graafian follicle
What is zone pellucida?
A layer of glycoprotein, translucent
What are the 2 pituitary hormones involved in the menstrual cycle?
FSH
LH
What are the 2 ovarian hormones involved in the menstrual cycle?
Estrogen
Progesterone
What are the 5 stages in the menstrual cycle?
- Preparation for implantation
- Preparation for fertilisation
- Ovulation
- Preparation for implantation
- Preparation for fertilisation
What is day 1-5 of the menstrual cycle called?
Menstrual phase
What is day 5-14 of the menstrual cycle called and what hormone is produced to cause it?
Proliferative Phase
- the follicle and thecal cells proliferate and secrete estrogens.
Estrogens cause the endometrial lining of the uterus to proliferate.
What happens at day 13-14 of the menstrual cycle?
FSH and LH levels rise sharply
It induces ovulation and progresses meiosis
What is day 14-28 of the menstrual cycle called?
Secretory phase
What day is defined as day 1 in the menstrual cycle?
The first day of menstruation
What is and what happens at ovulation?
The expulsion of a mature (secondary) oocyte from the follicle to the abdominal cavity.
Takes place ~ 38 hrs after the LH surge
The ovum is collected by the trumpet shaped distal end of the uterine tube (infundibulum) with fimbriae. –> re start of meiosis
Why don’t eggs in the ovary all mature at the same rate?
A few primordial follicles commence growth every day so there are follicles all at various stages in the ovary.
What happens to most of the follicular cells after ovulation?
- Most stay in the ovary and become corpus
luteum - The ones directly surrounding the oocyte
remain attached to the oocyte after
ovulation.
What are the 3 steps that have to occur when a sperm meets an oocyte?
- Sperm has to migrate through the layer of
follicular cells (corona radiata) - Penetrate the zona pellucia using an
enzyme in acrosome - Fuse the plasma membrane to that of the
oocyte
When does the second division of meiosis complete?
Completes when the sperm enters
Where does the fertilised egg travel?
to the uterus for the development of the human embryo
What does the embryoblast (inner cell mass) mean?
= becoming embryo
What does trophoblast mean?
= becoming extraembryonic tissues
What is the first step of implantation on day 6?
Blastocyst attaches to the endometrium at the embryonic pole
What is the second step of implantation on day 6-7?
Some trophoblast cells (syncytiotrophoblast) invade into the endometrium, beginning to form part of the placenta
What is the third step of implantation on day 8?
The inner cell mass becomes a flat sheet consisting of epiblast and hypoblast
An additional cavity appears on the epiblast side (amniotic cavity)
What happens on day 9 - 10 of implantation?
- Full embedding
- Maternal blood enter cavities in the
trophoblastic layer
What is hCG and what is its function?
hCG = human chorionic gonadotrophin
hCG maintains the hormonal activity of the corpus luteum in the ovary. The corpus luteum secretes estrogen and progesterone to maintain pregnancy
What are the two types of contraceptive pill?
- estrogen and progestogen
- progestogen only
=> both aim to mimic the luteal phase
(secretory phase)
What are some of the causes of infertility in females?
- Amenorrhea - absence of menstruation /
ovulatory dysfunction - 46% - Tubal defect - 38%
- Endometriosis (endometrium like tissue is
found outside the uterus) - 9%
What are the 6 main steps in In Vitro Fertilisation?
- Induce maturation of follicles by hormones,
including FSH and hCG - Several follicles mature (instead of one, as
would naturally) - Collect oocytes by laparoscopy or with
guide of transvaginal sonography - Add sperm
- Successfully fertilised ones undergo
cleavage in vitro - Implant back into the uterus
