EmbryologyDavid A Grainger MD, MPH

Objectives

• Review origin and migration of germ cells

• Understand the arrangement of the female gonad

• Describe spermatogenesis and oogenesis

• Outline the steps of fertilization

• Follow preimplantation embryonic development

• Describe the stages of implantation

The “mature” sperm cell1. plasma membrane

2. outer acrosomal membrae

3. acrosome

4. inner acrosomal membrane

5. nucleus

6. proximal centriole

7. rest of distal centriole

8. thick outer longitudnal fibers

9. mitochondrion

10.axenome

11.anulus

12.ring fibers

Stigma

Ovulation

Maturation and activation of

sperm

Epididymis———————Maturation

Ejaculation———————-Activation

Ascension to ovary——-Capacitation

Near the oocyte—Acrosome reaction

Fertilization and Docking

Docking triggers a cascade of events

Polyspermy Block

Hardening of the ZP

Entry of the Sperm into Oocyte

End of Meiosis II - 2nd polar body extruded

Preparation by EGG to unpack paternal DNA

Fertilization (Plan B)

Structure of the ovary -

cortical and medullary

1. primordial follicle

2. primary follicle

3. secondary follicle

4. tertiary follicle

5. antral follicle

6. cumulus oophorus

Follicle structure, Ooctye in

Diakinesis (prophase I)

Secondary Oocyte after

“impregnation”

2 hours after impregnation

2nd polar body extruded

Pronuclei forming

Synthesis phase where DNA is duplicated in each pronuclei;

then DNA condenses into chromosomes

Microtubule formation from paternal

centrosome (3)

Pronuclei approach each other

18 hours after impregnation:

paternal centrosome (3) duplicated in

preparation for upcoming cell division

Paternal pronuclei slightly larger

Maternal pronuclei closer to polar bodies

Pronuclei membranes dissolve

Chromosomes align on spindle

Zygote divides

GOAL ACHIEVED

• Fabrication of a DIPLOID set of chromosomes

• Determination of GENDER of the new individual

• The induction of normal “cleavage division” for

embryogenesis

Blastocyst Development

Hatching

Embryo Polarity

Trophoblast ICM (embryoblast)

Migration of embryo through

fallopian tube

Adhesion of the blastocyst

Embryo in the 4th week• 1 - primordial germ cells

• 2 - allantois

• 3 - rectum

• 4 - ectoderm

• 5 - foregut

• 6 - primordial heart

• 7 - secondary yolk sac

• 8 - endoderm (yellow)

• 9 - mesoderm (red)

• 10 - amniotic cavity

The primordial germ cells come from ectoderm, but

separate from ectoderm very early in development

Embryo in 5th week

• 1 - rectum

• 2 - vitelline

• 3 - allantois

• 4 - nephrogenic cord (pink)

• 5 - gonadal ridge (green)

• 6 - primordial germ cells (red

dots)

• 7 - heart prominence

Immigration of primordial germ cells

into gonadal ridge - 5th to 6th weeks• 1 - proliferating coelomic epithelium

• 2 - thickening of mesenchyma

• 3 - germinal cords

• 4 - primordial germ cells (red dots)

• 5 - mesenchyma

• 6 - allantois

• 7 - vitelline

• 8 - intestinal tube

• 9 - dorsal mesentery

• 10 - gonadal ridge

• 11 - nephrogenic cord

• 12 - mesonephric duct (Wolffian)

• 13 - mesonephric tubule

• 14 - aorta

Primoridial Germ Cells

Undergo

MITOSIS

leading to an

INDIFFERENT STAGE

of gonadal development

The key to sexual differentiation lies on the Y chromosome

If no Y chromosome - and thus no SRY - is present, a feminine phenotype is engendered.

Determining the gender -

testis at week 7• 1 - mesonephric duct (Wollfian)

• 2 - PGC

• 3 - peritoneal cavity

• 4 - aorta

• 5 - mesonephric tubule

• 6 - gonadal cords

• 7 - coelomic epithelium

• 8 - intestine

• 9 - mesenterium

• 10 - anlage of paramesonephric duct (Mullerian)

• 11 - mesonephros - nephron

Convoluted seminiferous

tubule• 1 - basal lamina

• 2 - myofibroblast

• 3 - fibrocyte

• 4 - Sertoli’s cell

• 5 - spermatogonia

• 6 - various stages of sperm cells

during spermatogenesis

• 7 - spermatozoon

• 8 - lumen

Temporal course of spermatogenesis

Spermiogenesis and the

structure of the sperm cell• 1 - axonemal structure

• 2 - golgi complex

• 3 - acromsomal vesicle

• 4 - pair of centrioles

• 5 - mitochondrion

• 6 - nucleus

• 7 - flagellar primordium

• 8 - microtubules

• 9 - sperm cell tail

• 10 - acrosomal cap

Leydig interstitial cells and

hormonal regulation

1. Leydig interstitial cells - active

during embryogenesis

(produce testosterone) -

reactivated at puberty

2. Crystalloids of Reinke - large

protein crystals

The ovary - development of oocytes

A wave of proliferation begins that lasts from the 15th week to the 7th month: primary germ cells arise in the cortical zone via mitosis of

With the onset of the meiosis (earliest onset in the prophase in the 12th week) the designation of the germ cells changes. Th

The primary oocytes become arrested in the diplotene stage of prophase I (the prophase of the

Determining the gender -

ovary at week 8• 1 - mesonephric duct (Wollfian)

• 2 - PGC

• 3 - peritoneal cavity

• 4 - aorta

• 5 - mesonephric tubule

• 6 - degenerated gonadal cords

• 7 - thickened coelomic epithelium

• 8 - intestine

• 9 - mesenterium

• 10 - anlage of paramesonephric duct (Mullerian)

• 11 - atrophy of the mesonephros - nephron

Germ cell count - oocytes

primordial primary

secondary tertiary

Follicular Development