Embryology: Overview and Terminology

Question 1

Where does spermatogenesis occur?

Answer 1

in the seminiferous epithelium of the testis

Question 2

Where does oogenesis occur?

Answer 2

in the cortex of the ovary

Question 3

What is meiosis I called?

Answer 3

The reductional division (takes weeks)

Question 4

What is the longest phase of meiosis 1 and why?

Answer 4

Prophase 1, where crossing over occurs (exchange of genetic material between homologous chromatids). Each homologous chromatid becomes unique. This phase can last weeks

Question 5

What happens after completion of prophase 1?

Answer 5

Completion of meiosis 1 is rapid, the chromatids do not separate but rather one homolog of each chromosome goes into each of the daughter cells

Question 6

What is meiosis II called?

Answer 6

The equatorial division (happens rapidly, in hours)

Question 7

What happens in meiosis II?

Answer 7

chromatids separate from the centromeres like in mitosis. One chromatid in each daughter cell. Daughter cells are haploid

Question 8

Is a germ cell haploid or diploid?

Answer 8

diploid - it is the precursor to spermatogenesis or oogenesis

Question 9

what are the two functions of the testes?

Answer 9

1. Spermatogenesis

2. Steroidogenesis - Leydig cells (testosterone)

Question 10

Where are sperm stored?

Answer 10

Ductus (vas) deferens

Question 11

What is a quiescent primordial follicle?

Answer 11

Structures containing oocytes arrested in meiosis 1. Every month, 10-20 are stimulated to develop, but only one reaches full maturity.

Question 12

What does an ovarian follicle contain?

Answer 12

1. Oocyte - developing gamete
2. Granulosa and theca internal cells - Steroid-secreting cells which mainly produce estrogen during follicle development.

Question 13

During ovulation, what stage of meiosis is the mature egg in?

Answer 13

Metaphase II - does not resume meiosis until fertilization

Question 14

What is the myometrium?

Answer 14

The thick layer of smooth muscle around the uterus. Contraction is prevented during pregnancy by progesterone levels

Question 15

What does estrogen cause in the uterine cycle?

Answer 15

High estrogen levels cause the endometrium of the uterus to rebuild and prepare itself for possible implantation (proliferation)

Question 16

What is the function of the corpus luteum?

Answer 16

Maintains the endometrium during the secretory phase by releasing progesterone. If fertilization does not occur, it degenerates, blood progesterone falls, and the endometrium is sloughed off (menses)

Question 17

What is the function of hCG?

Answer 17

Produced by the embryo, it maintains the corpus luteum so it continues to produce progesterone

Question 18

What is the menstrual phase of the uterine cycle?

Answer 18

Corpus luteum degenerates in the ovary, blood progesterone and estrogen levels drop. The endometrium degenerates and is sloughed off

Question 19

What is the proliferative / follicular phase?

Answer 19

Follicles develop in the ovary, blood estrogen rises, endometrium is rebuilt

Question 20

What is the secretory / luteal phase?

Answer 20

Corpus luteum is present in the ovary, blood progesterone levels are high. Endometrium of uterus prepares for implantation

Question 21

What are the two sub-periods of embryonic development (0-8 weeks)?

Answer 21

0-3 weeks post fertilization - early development including cleavage and gastrulation
4-8 weeks post fertilization - embryonic organogenesis - organ primordia are established

Remember this period is where all the precursors of the organs are developed

Question 22

What are the effects of teratogens in the developmental periods?

Answer 22

0-3 weeks: not sensitive to malformation -> spontaneous miscarriage / lethal
4-8 weeks: most susceptible, especially 4 to 6 weeks. Big congenital defects
Fetal period: 9-38 weeks. Organ systems are maturing, may cause many congenital malformations but they tend to be minor

Question 23

What is the difference between fertilization age and menstrual age?

Answer 23

Fertilization age - dates pregancy from time of fertilization (ovulation). This is 38 weeks full term
Menstrual age - dates pregenancy from start of last menstrual period (LMP). This is 40 weeks full term

Question 24

What are three ultrasound measurements to determine age of embryo or fetus?

Answer 24

1. Gestational sac diameter - also called chorionic cavity, used when embryo is too small to see
2. Crown rump length - measurement from top of head to buttock. Best in the first trimester
3. Size of head or femur length in later pregnancy

Question 25

How often do major and minor anomalies occur?

Answer 25

2-3% of live-born have major, another 2-3% will be recognized by age 5.
Minor anomalies happen in about 15% of newborns

Question 26

What is the leading cause of infant mortality?

Answer 26

Birth defects. Cause of 40-60% of these is unknown

Question 27

What is induction?

Answer 27

The process by which one tissue or group of cells (inducer) produces a signal that changes the fate of an adjacent tissue or set of cells

Question 28

What is totipotent vs pluripotent vs multipotent?

Answer 28

Totipotent - can differentiate into all cell types of the body and placental structures (i.e. zygote and blastomere)
Pluripotent - Can differentiate into all cell types of the body (i.e. embryonic stem cells)
Multipotent - Can differentiate into a limited number of cells. (I.e. mesenchymal cells)

Question 29

What is morphogenesis?

Answer 29

Establishment of form and structure - cells become organized into tissues and organs

Question 30

What are rostral and caudal?

Answer 30

Rostral - towards head. Also cranial

Caudal - towards the tail (feet)

Question 31

What is a sagittal plane?

Answer 31

Any vertical plane the is parallel to the median plane