Lecture 2 - Basic Embryology and Developmental Periods

Question 1

Prenatal period divided into (2)

Answer 1

Embryonic period - fertilization through 8 weeks

fetal period - 9 weeks until birth

Question 2

Major events of week 1

Answer 2

fertilized oocyte (zygote) –> morula (day 3-4) –> blastocyst (4-5) –> embryo (from layer of blastocyst)

Question 3

Major events of week 2

Answer 3

produces 2 germ layers

 - trophoblast
 - embryoblast

Question 4

Major events of week 3

Answer 4

produces 3 germ layers and layers fold into recognizable 3D shape

Question 5

define gastrulation

Answer 5

production of 3 germ layers

Question 6

what are the two folds that happen in week 3

Answer 6

lateral and cranio-caudal folds

Question 7

when does organogenesis happen

Answer 7

weeks 4-8

Question 8

_______ refers to growth in size of organs

_______ refers to rapid increase in cell number

Answer 8

hypertrophy

hyperplasia

Question 9

mature organ function is not achieved until after birth EXCEPT for which system?

Answer 9

cardiovascular (heart pumps blood to developing organs, which is necessary for their development_

Question 10

______ axis gives top and bottom

______ axis gives us front and back

Answer 10

cranial-caudal

dorsal-ventral

Question 11

pathway of sperm in male reproductive system

Answer 11

seminiferous tubules in testes –>(epididymis) –> ductus (vas) deferens –> ejaculatory duct –> urethra (3 parts) –> out

Question 12

pathway of oocyte in female reproductive system

Answer 12

ovary –> uterine (fallopian tubes) –> uterus

Question 13

meiosis in a nutshell

Answer 13

SINGLE duplication of DNA followed by TWO cell divisions

Question 14

what happens in first meiotic division

Answer 14

1 cell divides into two - goes from diploid to haploid

crossing over of genetic material happens in prophase I

Question 15

what happens in second meiotic division in sperm

Answer 15

secondary spermatocyte (23X, 23Y) –> spermatids x 4

Question 16

Three reasons why meiosis is so important

Answer 16

constancy of chromosome number

random assortment of genetic material and paternal chromosomes

crossing over of chromosome segments (genetic variation)

Question 17

Parts of mature sperm

Answer 17

Head - contains nucleus and covered by acrosome

Middle piece - contains ATP for energy

Tail - single flagella for locomotion

Question 18

first division of oogenesis happens when?

Answer 18

2 million oocytes have completed prophase I by birth

remain in prophase I until right before ovulation, during puberty the rest of the phase is completed (40,000 oocytes)

Question 19

second division of oogenesis happens when?

Answer 19

an ovulated egg or secondary oocyte (400 oocytes) is arrested at metaphase II
metaphase II is ONLY COMPLETED IF FERTILIZED

Question 20

the secondary oocyte gets released from the ovary and contains the zona pellucida and corona radiata. What are these?

Answer 20

zona pellucida - protective glycoprotein layer

corona radiata - follicular cells from ovary that get “stuck” to oocyte with ovulation

Question 21

when do the two polar bodies arise?

Answer 21

first polar body - arises from unequal cytoplasm division in meiosis I

second polar body - arises once egg is fertilized, in meiosis II

Question 22

female reproductive cycle is controlled by (3)

Answer 22

hypothalamus - GRH
pituitary gland - FSH and LH
ovaries

Question 23

what does follicle-stimulating hormone do?

Answer 23

development of ovarian follicles and produces estrogen

Question 24

what does luteinizing hormone do?

Answer 24

stimulates the follicular cells and corpus luteum to produce progesterone

Question 25

Describe the ovarian cycle

Answer 25

Many primary follicles (oocyte protected by follicular cells) start growing each month

Secondary follicles - have acquired fluid filled cavities (antrums) and zona pellucida

one lucky follicle is the mature follicle that is released during ovulation - which happens within 24 hours of a surge of LH production

follicle collapses and form corpus luteum

Question 26

Describe the menstrual cycle (endometrium)

Answer 26

Day 1-5 - Menses (functional layer of endo is sloughed off to prepare for new tissue)

Day 5-14 - Proliferative phase (tissues increases and thickens, controlled by estrogen from follicles; spiral arteries elongate)

Day 14 - Ovulation

Day 14-28 - Luteal phase (tissue increases and progesterone surges from corpus luteum; if no pregnancy, endometrium becomes ischemic due to spiral arteries contracting)

Question 27

where does fertilization happen?

Answer 27

Ampulla of uterine tubes

Question 28

Describe steps of fertilization

Answer 28

sperm enters through corona radiata and lyses zona pellucida (acrosome)

cell membranes of oocyte and sperm fuse
- creates a change in zona pellucida layer and
no other sperm can enter

second meiotic division of oocyte happens - female and male pronuclei formed and fuse together = ZYGOTE