Gametogenesis, Fertilisation and the Blastocyst

Question 1

What is teratology ?

Answer 1

Study of birth defects

Question 2

Label the 4 parts of the Fallopian tube

Answer 2

Question 3

The Fallopian tubes end in …

Answer 3

Fimbrae

Question 4

Oogenesis

explain what happens in stages 4 and 5

Answer 4

most growing follicles degenerate to form corpus acreticum

fluid filled antrum made by the follicular cells

thecal layer forms around the growing follicle

follicle call secondary follicle now

Question 5

How does the ovum get into the Fallopian tube?

what consequences does this have ?

Answer 5

Ovum is shed into abdominal cavity and then caught by the fimbrae

makes infection more likely

Question 6

Female gametogenesis (oogenesis)

explain what happens in the first three stages

Answer 6

1. Primary oocyte is surrounded by a single layer of follicular cells = primary follicle
2. At beginning of each monthly cycle, 5-12 primary follicle develop to become growing follicles (only one reaches full maturity however)
3. growing follicles are multiple layered; separated from ovum via the septum pellucidium

Question 7

Where do the follicular cells come from?

Answer 7

Ovarian epithelium

Question 8

What is the septum pellucidum made from ?

Answer 8

Acellular mucopolysaccharide(aka GAGs) layer

Question 9

What two parts does the thecal layer divide into ?

Answer 9

1. Vascular theca interna - produces oestrogen
2. Avascular inactive theca external

Question 10

What happens to the cells of the theca interna and stratum granulosum after the ovum is released?

Answer 10

They enlarge , turn yellowish and form the corpus luteum to secrete lots of progesterone and some oestrogen

Question 11

Oogenesis

explain what happens in stages 6&7

Answer 11

Follicle now called a mature/Graafian follicle

the majority of the follicular cells form the stratum granulosum and secrete progesterone

the others form the outer layer called the cumulus oophorus ; now called secondary oocyte

mature follicle ruptures to release the ovum

ovum covered by corona radiata now

septum pellucidum expanded to become the zona pellucida

Question 12

What happens to the corpus luteum if fertilisation does not occur after 12 days

Answer 12

Corpus luteum degenerates into the corpus alibicans which terminates hormonal output leading to menstruation

Question 13

What happens to the corpus luteum if pregnancy occurs ?

Answer 13

Corpus luteum is sustained by HCG produced by conceptual and forms a large corpus luteum of pregnancy

eventually forms a large corpus albicans

Question 14

Male gametogenesis

(Spermatogenesis)

Answer 14

Occurs in testes

stem cells divide by mitosis to for spermatogonium with 46 XY chromosomes

spermatogonium divide to form primary spermatocytes (still with 46 XY)

1st meiotic division to form secondary spermatocytes with 23X or 23Y chromosomes (double chromatids present at this point)

2nd meiotic division = spermatids with 23X/Y (single chromatid)

spermatids mature to form spermatozoa

Question 15

Label the diagram with he terms :

Acrosomal cap

nucleus

mitochondria

axial bundle

Answer 15

Nucleus covered by sparse cytoplasmic layer

Question 16

Purpose of acrosomal cap in spermatozoa and where is it derived from?

Answer 16

Derived from the Golgi apparatus

contains enzymes that aid in penetration of ovum

Question 17

Describe the structure of the middle piece of the sperm

how does this relate to its function ?

Answer 17

Helically wound mito surrounds central axial bundle of fibril

fibrils have a 9+ 2 arrangement

Question 18

How are ova moved along Fallopian tubes?

Answer 18

Via the action of cilia

Question 19

Main difference between male and female gametogenesis

Answer 19

Spermatogenesis occurs continuously throughout a males life

Females are already born with their lifetime supply of oogonia ; they mature throughout their , once every month and the supply runs out between 45 and 55

Question 20

Compare oogenesis and Spermatogenesis :

which process of division are involved ?

is it continuous/discontinuous ?

how long does it take ?

how many produced in each cycle ? / how many in one ejaculate ?

motile or non/motile?

cytoplasmic:nuclear ratio

does it require additional substances ?

Answer 20

Question 21

Label the prostate gland

Answer 21

Question 22

Label this Sagittal section of the female reproductive system

Answer 22

Question 23

The abdominal cavity in a male is ….

Answer 23

Closed

Question 24

Describe the events occurring before fertilisation

Answer 24

When the sperm reach the isthmus they become less motile and wait for chemoattractants released from the cumulus cells on ovulation tomake sperm motile again

sperm reach ampulla where fertilisation occurs

Question 25

What is capacitation

Answer 25

Changes to spermatazoa that must occur for successful fertilisation; takes place upon ejaculation - conditioning in female reproductive tract during which acrosomal cap loses glycoprotein coat and increased motility occurs

Question 26

Describe first 3 the events which occur upon fertilisation

Answer 26

Penetration by spermatazoon prompts completion of 2nd meiotic division fusion of plasma membrane of both gametes ; male nucleus is injected Zona reaction occurs ; ovum shrinks to form the perivitelline space

Question 27

What is the role of the acrosomal enzymes in fertilisation

Answer 27

Help disperse corona radiata and aid penetration of zona pellucida

Question 28

What is the zona reaction ? Why is it important

Answer 28

When fertilisation occurs, the permeability of zona pellucida is altered to prevent further penetration enzymes released by cortical granules digest sperm receptor proteins so that they can no longer bind this prevents polyspermy (implantation of more than one sperm)

Question 29

Stage 4/5 of fertilisation

Answer 29

Cleavage ~30h post fertilisation 2 daughter blastomeres formed by mitosis cells continue to cleave to form progressively smaller blastomeres (DNA synthesis occurs but no new proteins)

Question 30

Formation of morula

Answer 30

Stage 6 of fertilisation morula refers to solid ball of cells cytoplasmic:nuclear ratio near normal cytoplasm differential packaged Free within uterine cavity zona pellucida still remains to prevent implantation

Question 31

Blastocyst formation

Answer 31

Occurs during 2nd week morula cells undergo compaction tight junctions between surface cells zona pellucida begins to breakdown (called hatching) Formation of inner cell mass and trophoblast blastocyst now has a cavity

Question 32

Function of inner cell mass and trophoblast

Answer 32

Inner cell mass goes on to form the embryo trophoblast form extra embryonic membranes and placenta

Question 33

Label the inner cell mass and trophoblasts in this image

Answer 33

Question 34

one spermatogonium divides to make _____ spermatozoa one oogonium divides to make ______ ovum due to ______ division of the cytoplasm

Answer 34

4 spermatozoa 1 ovum (asymmetrical division of cytoplasm)

Question 35

what are polar bodies?

Answer 35

small residual cells produced during the first and second meiotic divisions of oogenesis that have very little cytoplasm and no use 1 polar body produced during meiosis I 3 polar bodies formed during meisois II

Question 36

give a brief summary of oogenesis

Answer 36

at foetal stage, female jas 400,000 primary follicles already produced primary oocyte arrested at prophase I of meiosis I until puberty primary oocytes completes meiosis I at beginning of menstrual cycle to form the secondary oocyte secondary oocyte arrested at prophase II of meiosis II until fertilisation occurs meiosis II completed upon fertilisation

Question 37

Where and when does implantation occur

Answer 37

6 days after fertilisation in the posterior wall of uterus nearer the fungus than the cervix

Question 38

What are the 3 words that can be used to describe the trophoblast

Answer 38

Invasive , ingestive and digestive ; can get past the uterine epithelium

Question 39

What is the decidual reaction ?

Answer 39

Upon implantation of the blastocyst in the uterine lining , Thickening of the endometrium occurs increased secretion occurs from the endometrium (uterus lining) Glandular epithelial cells will now contain more glycogen and lipids

Question 40

What are the 3 populations of cells present upon implantation of the blastocyst?

Answer 40

Primitive ectoderm (epiblast) primitive endoderm (hypoblast) trophoblast

Question 41

Events occurring in early implantation

Answer 41

Epiblast surrounds the amniotic cavity hypoblast surrrounds the yolk sac cavity wall of blastocyst is two layered now

Question 42

What happens on day 10 after implantation

Answer 42

Blastocyst completely embedded ; epithelial continuity restored trophoblast produces extra embryonic mesoderm which separates edges of trophoblast and epiblast/hypoblast , thus providing space for expansion of the embryo cavities form in the extra embryonic mesoderm Trophoblast splits into two types - syncytial trophoblast and cytotrophoblast

Question 43

What does conceptus mean ?

Answer 43

Fertilised egg

Question 44

What occurs after the extraembryonic mesoderm is produced ?

Answer 44

The cavities merge to form the chorionic cavity/extraembryonic coelom derivative of trophoblast begin to form the placenta extraembryonic mesoderm connects the conceptus to the trophoblast via the connecting stalk

Question 45

Give a brief summary of what happens in the first 2 weeks after implantation

Answer 45

2 cell layers (Epiblast and hypoblast ) 2 cavities ( amniotic and yolk sac) 2 trophoblast derivatives (cyto and syncytium trophoblast)

Question 46

Describe the structure of the conceptus at the end of the 2 weeks post fertilisation

Answer 46

Bilaminar disc forms where the epiblast and hypoblast meet the majority of the foetus will be produced from this

Question 47

What are dichorionic - diamniotic twins

Answer 47

splitting of zygote at day 3 or separate fertilisation of 2 ova by 2 sperm - comprises almost all cases of dizygotic twins and 1/4 of monozygotic twins lowest mortality risk but still higher than that of singleton

Question 48

Monochorionic twins

Answer 48

2 types : 1. share the same placenta 1. Occurs in most cases of monozygotic twins 2. risk of twin-twin blood transfusion 2. share the same amnion 1. Occurs when split is after 9th day but before 12th day 2. 50% survival risk ; risk of umbilical chord wrapping around babies 3. rarely occurs

Question 49

How do conjoined twins occur

Answer 49

When division of zygote occurs later tha 12 days highest mortality

Question 50

What happens in the third week post fertilisation

Answer 50

process is called gastriculation 3 germ layers - Formation of intraembryonic mesoderm and definitive ecto/endoderm to form trilaminar disc 3 important structures formed : notochord , primitive streak and neural tube

Question 51

Label this cross section of the embryo

Answer 51

Question 52

gastrulation

Answer 52

process of cellular rearrangement within the epiblast that leads to the formation of the 3 germ layers and a trilaminar disc epiblast cells migrate towards primitive pit and penetrate through the epiblast layer

Question 53

What happens at the prochordial plate during the 3rd week post fertilisation

Answer 53

Endoderm thickens and becones firmly adherent to the overlying ectoderm in the region of the prochordal plate this is the future mouth region

Question 54

Formation of the notochord (notogenesis) what is the function of the notochord

Answer 54

Epiblast cells migrate from the primitive node and extend cranially to form a midline structure called the notochordal process. Notochord then forms from the mesoderm - it is a flexible cylindrical tube fucntions: guide the formation of the nervous system and vertebral column induce overlying ectoderm to form the neuroectoderm of the neural plate ; the notochord eventually underlies the neural tube

Question 55

Formation of the neural tube

Answer 55

Neural plater form neural fold which become the neurectoderm the neural fold fuse to form a neural tube which eventually becomes the brain and spinal chord the neural tube loses contact with the overlying ectoderm

Question 56

name the structures derived from the endoderm

Answer 56

Epithelial lining of digestive and respiratory tracts, Lining of urethra, bladder and reproductive System Liver and pancreas

Question 57

name the structures derived from the mesoderm

Answer 57

Notochord Musculoskeletal system Muscular layer of stomach, intestine etc Circulatory system

Question 58

name the structures derived from the ectoderm

Answer 58

Epidermis of skin Cornea and lens of eye Nervous system

Question 59

what is the purpose of the syncytiotrophoblast

Answer 59

syncytiotrophoblast becomes continuous with the uterus maternal blood vessels invade spaces between the syncytiotrophoblast this allows uterplacental circulation to begin

Question 60

what is the primitive streak ? describe its structure

Answer 60

a groove in the midline of the epiblast which appears in the third week post fertilisation primitive node found at cranial end primitive pit within primitive node epiblast cells migrate through the primitive pit to form the notochord between the hypoblast and epiblast

Question 61

how is the endoderm formed ?

Answer 61

formed by epiblast cells that migrate through the primitive pit and displace the hypoblast cells.

Question 62

how is the mesoderm formed ?

Answer 62

formed by epiblast cells that migrate through the primitive pit and lie between the epiblast layer and the newly created endoderm.

Question 63

how is the ectoderm formed?

Answer 63

formed by the epiblast cells that remain in position

Question 64

purpose of notochord

Answer 64

essential for the development of the nervous system and primitive skeletal structures