Formation of zygote

Formation of zygote 

I). Gametes

A). Structure of sperm

1). Head

acromere

2). Midpiece
3). Tail

                                                    

PRIMARY OOCYTE                                                  SECONDARY OOCYTE

     

B). Oocyte

1). Primary oocyte:
2). Secondary oocyte:offspring inherit  mitochondrial DNA from their mothers.

 

After meiosis only one cell contains almost all of the cytoplasm and organelles.

The sperm does not bring in any cytoplasm or organelles

Thus offspring inherit mitochondria (& mitochondrial DNA) from their mothers.

II). How does the sperm penetrate the secondary oocyte?

1.  Oocyte encapsulated

• corna radiata

• 
  

  zona pellucida

2. The sperm becomes capacitated (readied)3.  The enzymes of one acromere are not enough to break through the capsule.
4. Connect to the sperm receptors
5. Sperm and oocyte membranes merge 

III). Immediately after fertilization occurs

Fertilization occurs

sperm loses tail

secondary oocyte undergoes meiosis II

(meiosis I occurred during the female’s fetal development)

eject polar body

female pronuclei & male pronuclei

form a mitotic spindle

 produce a diploid zygote.

undergoes cleavage

trophoblast

IV). Stages of Development

Primary oocyte
Secondary oocyte
OvumZygote
Embryo
Fetus

 V).  Zygote Development

Zygote formation

cleavage

4 cells

Morula

Blastocyst

Blastocysts differentiates into the:

Inner cell mass
Trophoblast cells

 

VI). Embryonic Membranes develop during gastrula

1). Embryonic (Disc) Germ Layers

Ectoderm
Mesoderm
Endoderm

2).  Amnion:
3). Yolk Sac:

•  part of the gut
•  early blood cells
• forms  gonads

4). Allantios:
5). Chorion:

 VII). PlacentaA). What prevents the normal sloughing off of the uterine wall?

The  embryo must maintain the corpus luteum until the placenta can take over its endocrine functions.

 human chorionic gonadotropin (hCG) acts like luteinizing hormone.

B). Formation

Trophoblast

Chorion & chronic villi form:

(Amnion forms around the embryo)

new vessels form, which extend to the embryo

 The endometrium the villi forms the placenta.

Fetal side is flat and smooth and slick

     Maternal side is bumpy

VII). Fetal Circulation 

Blood cells arise in the yolk sac

spaces appear in mesoderm

(middle germ layer)

become network

heart, blood vessels, etc.

by 3.5 weeks heart is formed and beating

1. Umbilical vein (to the heart) transports oxygen rich blood from the placenta to the fetus

2. Blood enters the liver and the ductus venous that shunts blood to the vena cava

3. Most of the blood is than shunted from the right atrium to the left atrium bypassing the pulmonary arteries and lungs.

4. The opening between the atriums of the heart is called theforamen ovale

5. Blood in the pulmonary trunk enters the aorta-bypassing lungs at the ductus arteriosus

6. Blood in the descending aorta branches off into theumbilical arteries and to the placenta

 http://nursingcrib.com/nursing-notes-reviewer/fetal-circulation/