Spermatogenesis, Oogenesis And Fertilisation

Question 1

1- what is spermatogenesis?

Answer 1

The production of male gametes (spermatozoa) from a primordial germ cell within the testes

Question 2

1- how many stages is spermatogenesis split into?

Answer 2

1st stage spermatogenesis
-differentiation
-mitosis

2nd stage spermatogenesis
-meiosis 1
-meiosis 2
-spermiogenesis

Question 3

1- describe the first stage of spermatogenesis

Answer 3

Primordial germ cell,
Dofferentiates,
Becomes a spermatogonium (diploid 2n),
Goes through mitosis,
Becomes primary spermatocytes (diploid 2n)

Question 4

1- describe the second stage of spermatogenesis

Answer 4

Starts as primary spermatocyte (diploid 2n),
Goes through meiosis 1- DNA replication and crossing over,
Becomes secondary spermatocytes (haploid n),
Goes through meiosis 2- each chromosome has 2 chromatids and 1 goes into each spermatid,
Becomes spermatid (haploid n),
Goes through spermiogenesis,
Becomes a spermatozoa!

Question 5

2- describe the characteristics of sperm (spermatozoon)

Answer 5

0.017-0.020mm in length
20-100 million in only 3ml of seminal fluid
Travel at 30mph
Survive 2-5 days

Question 6

2- how many segments is a sperms structure split into?

Answer 6

3 parts:
Head- acrosome and nucleus
Midpeice- mitochondria
Tail- flagellum

Question 7

2- what is the function of the sperm head?

Answer 7

Acrosomes- enzymes required for penetration of oocyte
Nucleus- contains chromosomes

Question 8

2- what is the function of the sperm mid piece?

Answer 8

Mitochondria- supply energy

Question 9

2- what is the function of the sperm tail?

Answer 9

Flagellum- transport spermatid using a corkscrew motion

Question 10

3- in one sentence, what is oogenesis?

Answer 10

Growth process in the ovaries where a primary ovum develops into a mature ovum ready fir fertilisation

Question 11

3- describe the state of oogenesis in utero

Answer 11

By 20 weeks gestation- primary ova are all present in the developing foetus if it is female
At time of birth- over 1 million ova are present in the ovaries of the baby
These follicles are immature, they do not develop until menarche

Question 12

3- describe the state of oogenesis during the reproductive cycle

Answer 12

In one cycle, one (rarely more) will mature
Hypothalamus secretes LHRH
Anterior pituitary releases FSH and LH
All of these hormones act on the ovary

The developing follicle is a source of hormones
First half of cycle, the follicle secretes increasing amounts of oestrogen

Before ovulation-
the follicle develops room immature to mature
Follicular fluid inside of the follicle increases
Follicle migrates to ovary surface

Ovulation-
Approx day 14
Follicle ruptures and releases the ovum
Caught by fimbriae
Propelled by cilia along uterine tubes towards the uterus

After ovulation-
the corpus luteum develops and secretes progesterone
This causes LH and FSH to fall
Ovum not fertilised? Degeneration and death of corpus luteum
Ovum is fertilised? Corpus luteum continues to develop and secrete hormones for 3-4 months

Question 13

3- describe the stages of the menstrual cycle in regards to the changes within the uterus

Answer 13

Menstrual (days 1-4):
Progesterone and oestrogen fall
Functional layer of the endometrium is shed
Myometrium contracts

Proliferative (days 5-14):
Regrowth of functional layer of the endometrium
Prepares to receive fertilised ovum
Vascular and rich in mucus

Secretory (days 15-28):
Progesterone stimulates the endometrium to become swollen
Secretory glands produce increasing amounts of watery mucus to assist the spermatic through the uterus

Question 14

4- describe the process of fertilisation

Answer 14

Spermatic are ejaculated from the penis,
Swim up through the vagina and uterus towards floating oocyte in uterine tube,
Both are gametes (containing half of genetic material each),
Capacitation (acrosomes break down to allow spermatic to break into egg membrane),
Sperm penetrates corona radiata and fertilises the egg after acrosome reaction,
Penetration of zona pellucida (glycoprotein layer),
Oocyte completes meiosis 2 to become ovum,
Genetic information combines,
Form a 46 chromosome cell called a zygote,
Zygote starts to divide and multiply,
Travels towards the uterus and becomes a blastocyst,
Blastocyst burrows into uterine wall

Question 15

4- name as many of the generalised acrosome listed process involved in fertilisation as you can

Answer 15

Acrosome reacts with zona pellucida due to enzyme release
Acrosome reacts with perivitelline space of proteins
Nucleus then enters the egg

Question 16

5- what is ‘corona radiata’?

Answer 16

Cellular layer that protects the oocyte

Question 17

5- what is an ‘oocyte’?

Answer 17

An immature ovum/egg cell

Question 18

5- what is ‘zona pellucida’?

Answer 18

Thick extracellular layer that covers the oocyte

Question 19

5- what is the ‘first polar body’?

Answer 19

Smaller cell containing DNA that is created from the first meiosis of the oocyte

Question 20

5- what is a ‘zygote’?

Answer 20

The egg cell after it has been fertilised with the spermatic cell

Question 21

5- what is an ‘acrosome reaction’?

Answer 21

Reaction that allows the sperm to enter the zona pellucida during fertilisation

Question 22

5- what is an ‘acrosome’?

Answer 22

An organelle in the sleep head that releases egg-penetrating enzymes