1.2 Origin of the gametes Flashcards
What is gamete maturation in males known as?
spermatogenesis
What is gamete maturation in females known as?
oogenesis
What 3 things occur after germ cells colonise the gonad (medulla and cortex)?
1) proliferate by mitosis
2) reshuffle genetically and eventually reduce to haploid by meiosis
3) cyto-differentiate into mature gametes
When are max numbers of oogonia reached in female
Mid-gestation (most die during gestation)
When do female gametes enter meiosis I?
Before birth
What stimulates entry into meiosis I of female gametes?
follicular cells (these later differentiate into granulosa cells)
Female germ cells in the cortex of the primordial gonad are known as _______. These proliferate rapidly by ______.
Most die during _______ and the remaining begin meiosis I before birth becoming _______.
Entry to meiosis I is stimulated by ______ cells, which surround the primary oocytes to form _________.
Meiosis is then arrested at the _______ stage of ______.
oogonia, mitosis, gestation, primary oocytes, follicular, primordial follicles, diplotene, prophase
The primary oocyte surrounded by the follicular cells is known as the what?
Primordial Follicle
What is secreted that causes the female gametes to halt in the arrested stage before birth?
Which cells secrete this?
OMI - oocyte maturation inhibitor secreted by follicular cells
How many gametes in the female complete meiosis one each month?
1-2
What occurs after puberty in a female?
A small proportion of primordial follicles restart meiosis I to develop furthur
Formation of a mature gametes requires the follicle to undergo 3 stages, what are these?
1) pre-antral ➞ primordial follicle
2) antral ➞ graafian follicle
3) tertiary ➞ mature follicle
What is menstruation
When the lining of the uterus sheds due to unsuccessful cycle (no fertilisation)
How long is the menstrual cycle and by definition when does it start?
28 days, starts on the first day of last period
What are the 3 phases of the menstrual cycle? (Incl timeline of each)
1) Preparatory Phase: Days 0-12 (Follicular/proliferative phase)
2) Ovulation: Around days 12-14
3) Waiting Phase: Days 14-28 (Luteal/secretory phase)
Describe the pre-antral phase of follicular development
** Independent of hormones
1) primary oocyte grows but does NOT resume meiosis I
2) follicular cells transition from flat to cuboidal and then proliferate to from granulosa cells
3) granulosa cells secrete a glycoprotein that surround the primary oocyte forming a zone pellucida
4) surrounding stromal cells form a theca folliculi composed of 2 parts: Interna (endocrine) and Externa (fibrous cap)
5) the theca and granulosa cells begin expressing receptors (later collaborate to secrete oestrogen)
Describe the Antral phase of follicular development
1) granulosa cells continue to grow and proliferate
2) fluid appears between the spaces and forms an antrum ➞ Graafian follicle
3) as more fluid forms the Graafin follicle dramatically expands (upto 2mm) and then hormonal stimulation occurs
4) FSH binds granulosa cells and LH binds theca cells (interna)
5) Theca cells (by LH) secrete androgens which are converted to oestrogen by granulosa cells (by FSH)
Describe the tertiary/pre-ovulatory phase of follicular development
Occurs 37hrs before ovulation
1) under influence of oestrogen LH receptors appear on outer granulosa cells
2) these are stimulated by an LH surge causing the oocyte to re-starts meiosis ➞ first meiotic division is completed.
4) secondary follicle enters meiosis II and arrests again at metapahse 3 hours prior to ovulation
5) follicle size increases dramatically by increase in antral fluid and the structure begins to weaken.
What triggers ovulation?
What happens to the remains of the ruptured follicle and what is the purpose of this?
LH surge stimulates collegenase activity causing the dominant follicle to rupture
The remains of the ruptured follicle reorganise to form the Corpus luteum which grows in the ovary under the influence of LH. It is a endocrine gland whos purpose is to secrete oestrogen and progesterone in preparation for a potential pregnancy
Describe the division of the gamete in females (during the completion of meiosis I)
Divisions are UNEQUAL in females (cytoplasm remains with 1 daughter cell and the other forms the first polar body)
What occurs following ovulation and when does meiosis II resume in the secondary oocyte?
Following ovulation the ovum is carried out in the fluid and gathered up into the fallopian tube by fimbria.
Meiosis II resumes ONLY if the ovum is fertilised (unfertilised cells degenerate 24 hours after ovulation)
When does the corpus luteum die and why? What happens to it once it dies?
Dies after 14 days if pregnancy does not occur
It then fills with scar tissue and becomes the corpus albicans
XY germ cells colonise the sex cords in the ______ of the primordial gonad.
________ develop within cords and proliferate by mitosis before birth to form ________.
At puberty the cords hollow out to become seminiferous tubules where the ________ cluster around the basal membrane.
The tubules empty into the ______ and then into the ______.
Medulla, spermatazoa, spermatogonia, spermatogonia, rete testis, epididymis
What cells in a male secrete testosterone?
Leydig cells
What are the ‘supporting cells’ located in the seminiferous tubules known as?
Sertoli cells
Define spermatogenesis and state when it begins
The sequence of events by which spermatogonia are transformed into mature sperm
Begins at puberty
Explain the process of spermatogenesis
1) spermatogonia are transformed into primary spermatocytes during puberty
2) primary spermatocytes undergo meiosis I to form 2 haploid secondary spermatocytes (reduction division)
3) secondary spermatocytes undergo meiosis II to form 4 haploid spermatids
How are primary spermatocytes linked?
By cytoplasm bridges
Following meiosis, how are the spermatids transformed? (describe shape)
What is this process known as?
Round spermatids are remodelled into elongated spermatozoa
Process = Spermiogenesis
What happens to spermatozoa following spermiogenesis?
Eongated spermatozoa are released into the lumen of the seminiferous tubules
Further functional maturation occurs as they pass down the tubule though the rete testis ➞ ducti efferentes ➞ epididymis -➞ continues once inside the female tract
What are the components of semen? (4)
Secretions of seminal vesicle (60% )
Secretions of Prostate (20%)
Sperm (via vas deferens)
Secretions of bulbo-urethral glands
What NS control is an erection vs ejaculation under?
Erection = POINT = Parasympathetic NS (S2-S4)
Ejaculation = SHOOT = Sympathetic NS (L1-L2) + Somatic innervation from the Pudendal nerve (S2-S4)
What is emission?
What NS control is this under?
Occurs during copulation when contractions of the vas deferens sweep sperm to be mixed with other component of semen from seminal vessicles
NS = Sympathetic (L1-L2)
