Embryology

Question 1

What is the first thing created when the sperm and egg fuse together?

Answer 1

Blastocyst (week 1 and 2)

Question 2

What occurs during gastrulation?

Answer 2

The epiblast gives rise to the 3-layered embryo (week 3)

• ectoderm
• mesoderm
• endoderm

Question 3

What does the ectoderm become?

Answer 3

The skin and neural tube (brain and spine)

Question 4

What does the endoderm become?

Answer 4

the gut tube

Question 5

What does the mesoderm become?

Answer 5

• paraxial -> somites -> vertebral bodies and limbs
• intermediate - urogenital system and reproductive system

lateral - body cavities (pleural cavities, peritoneal cavities)

Question 6

Where does the urinary and reproductive system originate from?

Answer 6

The intermediate plate of the mesoderm

Question 7

What are the 3 sets of kidneys which develop?

Answer 7

• pronephros (degenerate as soon as they’re formed)
• mesonephros (briefly functional)
• metanephros (the definitive kidney)

The metanephros forms from the branches of the mesonephros.

Question 8

What is it that forms the gonads?

Answer 8

The mesonephros, after they are no longer functioning as the kidney.

Question 9

What happens to create the indifferent gonad?

Answer 9

The mesonephros thickens

Primordial sex Cells are imported from the yolk sac to become the germ cells.

Question 10

Which cells form the sperm or ovum?

Answer 10

Primordial sex cells which migrate from the yolk sac.

Question 11

What ate the two tubes around the gonads?

Answer 11

• mesonephric duct

- paramesonephric duct

Question 12

What is the name of the mesonephric duct?

Answer 12

Wolffian Duct

Question 13

What is the name of the paramesonephric duct?

Answer 13

Mullerian Duct

Question 14

How is the male gonad formed?

Answer 14

The indifferent gonad develops into the testis

the mesonephric duct develops into the vas deferens, epididymis, seminal vesicles

the paramesophrenic duct disappears

Question 15

How is the female gonad formed?

Answer 15

the indifferent gonad develops into the testis

the paramesonephric duct forms the Fallopian tube, uterus, cervix of vagina

the mesonephric duct disappears.

Question 16

Which gonad is always made unless instructed otherwise?

Answer 16

ovary.

Question 17

Which gene is expressed on the Y chromosome and what does it code for? (male gonad)

Answer 17

The SRY gene encodes for the TDF (testis determining factor) protein

Question 18

Which cells express the SRY gene?

Answer 18

The primordial cells

Question 19

What action does the SRY gene have?

Answer 19

• It codes for TDF to make the indifferent gonad into a testis.
• it is expressed by the primordial supporting cells and it turns them into Sertoli cells

Question 20

What do the Sertoli cells do?

Answer 20

secrete MIS (Mullerian Inhibiting substance)

Question 21

What is MIS?

Answer 21

Mullerian Inhibiting substance

• it causes the paramesonephric duct to degenerate
• It also transforms mesenchymal cells to form leading cells

Question 22

What is the action of leydig cells?

Answer 22

They produce testosterone which causes the production of the male external genitalia from the mesonephric duct.

Question 23

Where does the prostate originate from?

Answer 23

outgrowth of urethra

Question 24

where do the seminal vesicles originate from?

Answer 24

Mesonephric duct

Question 25

What does the paramesonephric duct become in females?

Answer 25

• fallopian tube
• cervix
• upper part of vagina

Question 26

How does the ovary develop?

Answer 26

the primary sex cords degenerate and secondary sex cords develop.

the primordial sex cells become incorporated in the secondary sex cords

primordial germ cells then bud off with a single layer of the cortical cord to form primordial follicles
the primordial follicles then do active mitosis

Question 27

When are all follicles formed?

Answer 27

Month 7

Question 28

When do oocytes enter meiosis?

Answer 28

By month 7, they complete stage 1 where they stay until puberty

Question 29

How many primordial follicles are there at birth?

Answer 29

2 million - each one has an oocyte.

many follicles atrophy before puberty

Question 30

How many follicles develop in each 28 day cycle?

Answer 30

12-15 develop after puberty

only ONE follicle reaches maturity and ovulation

This continues until menopause

Question 31

Which part of the paramesonephric duct becomes what?

Answer 31

cranial end - ovary

caudal - uterus and superior vagina

Question 32

What creates the inferior part of the vagina?

Answer 32

Urogenital sinus

Question 33

What happens in the descent of the testes?

Answer 33

Week 7 - level T10

week 12 - deep inguinal ring (until 7 months)

Just prior to birth - enters scrotum

Question 34

Which region are the gonads originally in?

Answer 34

The thoraco-lumbar region.

Question 35

What happens in the descent of the ovary?

Answer 35

Week 7 - level T10

week 12 - broad ligament
round ligament drawn through inguinal canal

Question 36

Which fibrous cord causes the descent of the gonads?

Answer 36

The gubernaculum.

Question 37

What is a cause of indirect inguinal hernias?

Answer 37

When the processes vaginallis doesn’t lose its connection with the inguinal canal.

Question 38

What does the gubernaculum become in females?

Answer 38

Both the ovarian ligament and round ligament.

Question 39

What happens to the gubernaculum in males?

Answer 39

It becomes the scrotal ligament, and anchors the testis to the most inferior part of the scrotum.