1.2 Origin of the gametes

Question 1

What is gamete maturation in males known as?

Answer 1

spermatogenesis

Question 2

What is gamete maturation in females known as?

Answer 2

oogenesis

Question 3

What 3 things occur after germ cells colonise the gonad (medulla and cortex)?

Answer 3

1) proliferate by mitosis
2) reshuffle genetically and eventually reduce to haploid by meiosis
3) cyto-differentiate into mature gametes

Question 4

When are max numbers of oogonia reached in female

Answer 4

Mid-gestation (most die during gestation)

Question 5

When do female gametes enter meiosis I?

Answer 5

Before birth

Question 6

What stimulates entry into meiosis I of female gametes?

Answer 6

follicular cells (these later differentiate into granulosa cells)

Question 7

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 ______.

Answer 7

oogonia, mitosis, gestation, primary oocytes, follicular, primordial follicles, diplotene, prophase

Question 8

The primary oocyte surrounded by the follicular cells is known as the what?

Answer 8

Primordial Follicle

Question 9

What is secreted that causes the female gametes to halt in the arrested stage before birth?

Which cells secrete this?

Answer 9

OMI - oocyte maturation inhibitor secreted by follicular cells

Question 10

How many gametes in the female complete meiosis one each month?

Answer 10

1-2

Question 11

What occurs after puberty in a female?

Answer 11

A small proportion of primordial follicles restart meiosis I to develop furthur

Question 12

Formation of a mature gametes requires the follicle to undergo 3 stages, what are these?

Answer 12

1) pre-antral ➞ primordial follicle
2) antral ➞ graafian follicle
3) tertiary ➞ mature follicle

Question 13

What is menstruation

Answer 13

When the lining of the uterus sheds due to unsuccessful cycle (no fertilisation)

Question 14

How long is the menstrual cycle and by definition when does it start?

Answer 14

28 days, starts on the first day of last period

Question 15

What are the 3 phases of the menstrual cycle? (Incl timeline of each)

Answer 15

1) Preparatory Phase: Days 0-12 (Follicular/proliferative phase)
2) Ovulation: Around days 12-14
3) Waiting Phase: Days 14-28 (Luteal/secretory phase)

Question 16

Describe the pre-antral phase of follicular development

Answer 16

** 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)

Question 17

Describe the Antral phase of follicular development

Answer 17

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)

Question 18

Describe the tertiary/pre-ovulatory phase of follicular development

Answer 18

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.

Question 19

What triggers ovulation?

What happens to the remains of the ruptured follicle and what is the purpose of this?

Answer 19

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

Question 20

Describe the division of the gamete in females (during the completion of meiosis I)

Answer 20

Divisions are UNEQUAL in females (cytoplasm remains with 1 daughter cell and the other forms the first polar body)

Question 21

What occurs following ovulation and when does meiosis II resume in the secondary oocyte?

Answer 21

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)

Question 22

When does the corpus luteum die and why? What happens to it once it dies?

Answer 22

Dies after 14 days if pregnancy does not occur

It then fills with scar tissue and becomes the corpus albicans

Question 23

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 ______.

Answer 23

Medulla, spermatazoa, spermatogonia, spermatogonia, rete testis, epididymis

Question 24

What cells in a male secrete testosterone?

Answer 24

Leydig cells

Question 25

What are the ‘supporting cells’ located in the seminiferous tubules known as?

Answer 25

Sertoli cells

Question 26

Define spermatogenesis and state when it begins

Answer 26

The sequence of events by which spermatogonia are transformed into mature sperm

Begins at puberty

Question 27

Explain the process of spermatogenesis

Answer 27

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

Question 28

How are primary spermatocytes linked?

Answer 28

By cytoplasm bridges

Question 29

Following meiosis, how are the spermatids transformed? (describe shape)

What is this process known as?

Answer 29

Round spermatids are remodelled into elongated spermatozoa

Process = Spermiogenesis

Question 30

What happens to spermatozoa following spermiogenesis?

Answer 30

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

Question 31

What are the components of semen? (4)

Answer 31

Secretions of seminal vesicle (60% )

Secretions of Prostate (20%)

Sperm (via vas deferens)

Secretions of bulbo-urethral glands

Question 32

What NS control is an erection vs ejaculation under?

Answer 32

Erection = POINT = Parasympathetic NS (S2-S4)

Ejaculation = SHOOT = Sympathetic NS (L1-L2) + Somatic innervation from the Pudendal nerve (S2-S4)

Question 33

What is emission?

What NS control is this under?

Answer 33

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)