Flashcards in Gametogenesis Deck (66):
What is fecundity?
The potential for reproduction
1. Gamete production
3. Carrying a pregnancy to term
What is fertility?
The measure of reproduction
1. Number of children born per person, couple or population
What is fertility rate?
The number of births per time period per person, couple or population
What causes cessation of fecundity in males?
1. Loss of libido
2. Erectile dysfunction (due to diabetes or vascular pathology)
3. Vascular pathology
What causes cessation of fecundity in females?
What is the climacteric?
Period of life when fertility and sexual desire in women are in decline
What is amenorrhoea?
Lack of periods
Primary = no periods ever
Secondary = periods stop
What causes menopause?
1. Ovarian decline and failure
2. Fewer oocytes of lower quality leads to chromosomal anomalies
3. Follicular decline leads to hormone changes and secondary amenorrhoea
When does fecundity begin?
Girls initiate puberty about 2 years earlier than boys
Average age of onset of puberty has been coming down, possibly due to artificial light
Where are the germ cells in the testis?
In seminiferous tubules
Where are the germ cells in the ovary?
What are testicular germ cells called?
Spermatogonial stem cells
What are ovarian germ cells called?
In what stage of differentiation are the testicular stem cells during fetal life?
In what stage of differentiation are the ovarian stem cells during fetal life?
Enter first meiotic division and arrest
How many testicular stem cells survive?
Most germ cells survive to adulthood
Large population of renewable cells remains at puberty
How many ovarian stem cells survive?
Most germ cells die at around the time of birth
Relatively few oocytes left by puberty
How many sperm are made per day?
What fluid are spermatozoa released in?
What fluid are oocytes released in?
What does inhibin do?
In females, output rises pre-oocyte release and remains high after it
Produced by Sertoli cells and granulosa cells
What is the temperature in the testis?
4-7 degrees below body temperature
How does the testis maintain a lower temperature?
1. Position outside the body
2. Pampiform plexus cools arterial blood
3. Divided into compartments
What is the role of the blood/testis barrier?
Testis is a privileged site
1. Prevents penetration of tubular wall so that immune cells cannot gain access
2. Prevents penetration from basal component and adluminal compartment
3. Consequences of breakdown leads to autoallergic orchitis
What do Sertoli cells do?
Produce inhibin and testicular fluid
Where are the Leydig cells located?
Outside the tubules in the interstitium
Where does meiosis occur in spermatogenesis?
In the spermatocytes as they move from the basal to the luminal part of the tubule
What is spermiogenesis?
Maturation of round spermatids through elongating spermatids to spermatozoa
What is spermiation?
Release of spermatozoa luminally into testicular fluid
How long does spermatozoa production take?
How long is the interval of groups of spermatogonia initiating development?
Give four functions of androgens
1. Stimulate accessory sex gland growth and secretion in men
2. Stimulate secondary sex body hair patterns in both men and women
3. Exert anabolic and myotrophic effects to affect body shape
4. Metabolised in target tissues to forms with differential activity
What controls production of testicular androgen?
The pituitary gland
GnRH released from hypothalamus controls pituitary
What does hyphophysectomy cause?
Leydig cell regression
What precedes rise in androgens at puberty?
Rise in LH
Where does LH bind in the testes?
Receptors on Leydig cells
What are the gonadotrophins?
FSH and LH
What is the dictyate stage?
Prolonged resting phase when primordial oocytes arrest in meiotic prophase
Where does the oocyte develop?
Within a follicle
The oocyte-follicular unit
When is the major growth phase of the oocyte?
Primordial - preantral phase
10 --> 110µm diameter
What is the zona pellucida?
Glycoproteins secreted by oocyte during primordial - preantral phase
What do the stromal cells form?
Condense and form thecal cells
What triggers the primordial - preantral phase?
It is spontaneous
It does not depend on exogenous hormones nor does it produce hormones
Give four roles of the granulosa cells?
1. Follicular fluid secretion
2. Formation of an antrum within the follicle
3. Convert androgens to oestrogens in the presence of FSH
4. Produce inhibin
What is the cumulus oophorus?
Inner layer of corona radiata
Projects into antrum from granulosa cells
Connected to oocyte
What happens to the granulosa cells in the preantral - antral phase?
Develop FSH receptors
What happens to the thecal cells in the preantral - antral phase?
Develop LH receptors
What is the role of thecal cells?
Androgen production under LH stimulation
How do oestrogens affect granulosa cells?
Bind and stimulate granulosa cells that made them
What is the role of inhibin in the ovary?
1. Rising inhibin levels stimulate androgen output by thecal cells
2. Stimulate conversion to oestrogens by the granulosa cells
What happens to oestrogen in the pre-ovulatory follicle?
Rapid increase in oestrogen output
What happens to the thecal layer in the pre-ovulatory follicle?
1. Becomes hyperaemic
2. Increased androgen output
2. Increased oestrogen output
What is the endocrine switch?
As follicle approaches ovulation, granulosa cells also develop LH receptors and start synthesising progesterone under LH stimulation
When does oocyte meiosis reactivate?
High levels of LH
How is the secondary oocyte formed?
1. Prophase nuclear membrane breaks down
2. Oocyte enters MI, AI and TI as primary oocyte
3. First meiotic division is unequal and produces a small first polar body and large oocyte
4. Oocyte enters meiosis II
In what stage does the secondary oocyte arrest and ovulate?
What triggers ovulation?
Large spike in LH
Prostaglandins also involved
Where does the follicle surface rupture?
How is the oocyte released to the surface of the ovary?
In its cumulus oophorus carried in follicular fluid
What do the granulosa cells become following ovulation?
Large lutein cells
What do some of the thecal cells become following ovulation?
Small luteal cells
What is the corpus luteum?
The post-ovulatory follicle
What is the corpus luteum made of?
1. Large luteal cells
2. Small luteal cells
What do large luteal cells do?
1. Increase production of progesterone
2. Convert androgens to oestrogens
3. Secrete inhibin in large amounts
What do small luteal cells do?
1. Produce androgens
2. Pass androgens to large luteal cells