Physiology of Pregnancy & Reproduction Embryology

Physiology of Pregnancy & Reproduction Embryology
Presentation by: Dr.Anna Mae Smith, MPAS, PA-C
Lock Haven University of Pennsylvania

Stage 1

* Fertilization
* 1 Oocyte
* 300 Million Sperm
* 24 Hours
* 0.1 - 0.15 mm
* 1 day post-ovulation

Fertilization

* SPERM + EGG(OOCYTE) = ZYGOTE
* The fertilization process takes about 24 hours.
* Sperm life = 48 hours
o It takes about ten hours to navigate the female productive track, moving up the vaginal canal, through the cervix, and into the fallopian tube where fertilization begins.

Mr.SPERM
+
Mrs. EGG
Fertilization

* 300 million sperm enter the the vagina... only 1%, 3 million, enter the uterus
* The next step is the penetration of the zona pellucida, a tough membrane surrounding the oocyte.
* Penetration of the zona pellucida takes about twenty minutes.

Fertilization

* Within 11 hours following fertilization, the oocyte has extruded a polar body with its excess chromosomes. The fusion of the oocyte and sperm nuclei marks the creation of the zygote and the end of fertilization.

Stage 2
Cleavage
* First Cell Division, Blastomeres,
* Mitotic division
* 0.1 - 0.2 mm
* 1.5 - 3 days post-ovulation
* The zygote now begins to cleave, with each division occurring into two cells called blastomeres
* The zygote's first cell division begins a series of divisions, with each division occurring approximately every twenty hours
* When cell division ungenerated about sixteen cells, the zygote becomes a morula (mulberry shaped)
* It leaves the fallopian tube and enters the uterine cavity three to four days after fertilization.

Stage 3
Early Blastocyst
* 0.1 - 0.2 mm
* 4 days post-ovulation
* Blastocyst formation
* Two cell types are forming:
o embryoblast (inner cell mass on the inside of the blastocele)
o trophoblast (the cells on the outside of the blastocele).
Stage 4
Implantation Begins
* HCG Levels Rise
* 0.1 - 0.2 mm
* 5 - 6 days post-ovulation
* The trophoblast cells secretes an enzyme which erodes the epithelial uterine lining and creates an implantation site for the blastocyst.
Implantation Begins

* ovary continues producing progesterone
* trophoblast cells continue releasing human chorionic gonadotropin (hCG)
* Endometrial glands in the uterus enlarge in response to the blastocyst and the implantation site becomes swollen with new capillaries. Circulation begins, a process needed for the continuation of pregnancy.

Stage 5
Implantation Complete
* Placental Circulation System Begins to form
* 0.1 - 0.2 mm
* 7 - 12 days post-ovulation
* Trophoblast cells engulf and destroy cells of the uterine lining creating blood pools, both stimulating new capillaries to grow and foretelling the growth of the placenta.
* The inner cell mass divides, rapidly forming a two-layered disc
* The top layer of cells...
o will become the embryo and amniotic cavity
o the lower cells will become the yolk sac.
* Ectopic pregnancies can occur at this time and sometimes continue for up to 16 weeks of pregnancy before being noticed

Stage 6
Gastrulation, Chorionic Villi Formation
* 0.2 mm
* 13 days post-ovulation
* The formation of blood and blood vessels of the embryo begins
* Yolk sac begins to produce hematopoietic or non-nucleated blood cells.
* Gastrulation three layers of the embryo: ectoderm, mesoderm and endoderm.
Stage 7

* Neurulation and Notochordal Process
* 0.4 mm
* 16 days post-ovulation
* Endoderm forms the lining of lungs, tongue, tonsils, urethra and associated glands, bladder and digestive tract.

Stage 7

* Mesoderm forms the muscles, bones, lymphatic tissue, spleen, blood cells, heart, lungs, and reproductive and excretory systems.
* Ectoderm forms the skin, nails, hair, lens of eye, lining of the internal and external ear, nose, sinuses, mouth, anus, tooth enamel, pituitary gland, mammary glands, and all parts of the nervous system

Stage 8

* Primitive Pit, Notochordal Canal and Neurenteric Canals
* 1.0 - 1.5 mm
* 17-19 days post-ovulation
* Neural plate with a neural groove
* The blood cells of the embryo are already developed and they begin to form channels along the epithelial cells which form consecutively with the blood cells.

Stage 9

* Appearance of Somites(condensations of mesoderm, appear on either side of the neural groove
* 1.5 - 2.5 mm
* 19 - 21 days post-ovulation
* Primitive streak
* Endocardial (muscle) cells begin to fuse and form into the early embryo's two heart tubes.

Stage 10

* Neural Folds Begin to Fuse, Heart Tube fuses
* 1.5 - 3.0 mm
* 21 - 23 days post-ovulation
* Cardiac muscle contraction begins
* Eye & ear cells are present
* Neural tube starts closing

Stage 11

* Thirteen to Twenty Somite Pairs, Rostral Neuropore Closes, Optic Vesicle Appears, Two Pharyngeal Arches Appear
* 2.5 - 3.0 mm
* 23 - 25 days post-ovulation
* A primitive S-shaped tubal heart is beating and peristalsis, the rhythmic flow propelling fluids throughout the body, begins.
* At this stage, the neural tube determines the form of the embryo
Stage 12


* Twenty-one to Twenty-nine Somite Pairs, Caudal Neuropore Closes, Three to Four Pharyngeal Arches Appear, Upper Limb Buds Appear
* 3.0 - 5.0 mm
* 25 - 27 days post-ovulation
* The brain and spinal cord together are the largest and most compact tissue of the embryo.

Stage 12

* Valve & septa appear in the heart
* The digestive epithelium layer begins to differentiate into the future locations of the liver, lung, stomach and pancreas.
* The beginning cells of the liver form before the rest of the digestive system.

Stage 13 (approximately 27-29 postovulatory days)

* Forebrain, midbrain and hindbrain.
* Forebrain senses, memory formation, thinking, reasoning, problem solving.
* Midbrain relay station, coordinating messages to their final destination
* Hindbrain regulates the heart, breathing and muscle movements

This presentation covered upto 40th week stage.
Physiology of Pregnancy & Reproduction Embryology.ppt