Ana&Physio 16 - Human Development

7/29/2019 Ana&Physio 16 - Human Development

1/37

Embryology

Prof. Yvette Marris E. Legaspi, RN, MAN


2/37

Fertilization

An egg must be

fertilized within 12 to

24 hours of ovulation

It takes about 72 hours

for an egg to reach the

uterus.

The sperm mustencounter the egg

somewhere in the

uterine tube

2


3/37

3

Fertilization

A sperm can survive for 48-72 hours in the femalereproductive tract

It takes about 10 hours to navigate into theampulla of the fallopian tube where fertilization

occurs.


4/37

Fertilization

When the sperm

encounters and egg, it

undergoes an acrosomal

reaction- exocytosis of the

acrosome, releasing the

enzymes needed to

penetrate the egg.

Sperm must penetrate the

granulosa cells and zona

pellucida that surrounds

the egg

4


5/37

5

Zygote

A zygote is formed when thenucleus of the sperm andovum combine to create a

cell with 23 pairs ofchromosomes. (prior to thestart of cleavage)

Fertilization occurs in theampulla of the uterine tubewithin 24 hours afterovulation (oocyte dies after

24 hours)


6/37

6

From Fertilization to Implantation


7/37

7

Formation of the Morula

Cleavage: Rapid mitotic

cell division (without cell

growth) that subdivides the

cytoplasm of the zygote Cleavage produces

daughter cells calledblastomeres

The zona pellucida remainsaround the entire group ofcells.

About 3 days


8/37

8

Morula

After 3 days of

cleavage, a solid ball

of cells has formed

that resembles a

mulberry (similar to

a Marion berry)

This Morula contains

16 or more cells


9/37

9

Blastocyst

By the fourth or fifth day the morula developsinto a a fluid-filled hollow sphere called ablastocyst

Blastocyst : contains 3 parts Trophoblast: The outer layer of cells

Take part in placenta formation

Inner cell mass: A group of cells clusteredat one side of the blastocyst Becomes the embryo

Blastocoele: The fluid filled cavity


10/37

10

Blastocyst


11/37

11

Implantation

By day six or seven the trophoblast willadhere to the endometrium with the innercell mass side facing the uterine wall

The trophoblast cells proliferate and formtwo distinct layers

Syncytiotrophoblast: Cells on the

perimeter touching the endometrium. Cytotrophoblast: Cells on the interior of

the trophoblast that retain their cellboundaries


12/37

12

Implantation


13/37

13

Implantation


14/37

14

Syncytiotrophoblast

At the point of contact between the trophoblast

and the endometrium, the dividing cells lose

their plasma membranes

This creates a syncytium in which there is alayer of cytoplasm containing multiple nuclei

The syncytiotrophoblast erodes a path

through the uterine endometrium by secretinghyaluronidase

The implanted blastocyst will eventually becovered over by endometrial cells


15/37

15

Implantation

Viability of the corpus luteum is maintained byhuman chorionic gonadotropin (hCG) secreted

by the trophoblast hCG prompts the corpus luteum to continue to

secrete progesterone and estrogen

Between the second and third month, theplacenta assumes the role of progesterone andestrogen production


16/37

16

Chorionic Villi

Chorionic villi are

extensions of the cytotrophoblast coveredwith syncytiotrophoblast that extend into

the maternal blood filled spaces (lacunae)

Maternal blood will exchange nutrientsthrough these villi that will eventually

contain embryonic vessels.


17/37

17

Embryonic Disc

The inner cell mass organizes into an oval sheet

with two layers (the embryonic disc)

Ectoderm: The layer closest to the attachment of

the trophoblast

Endoderm: The layer closest to the blastocoele


18/37

18

Amniotic Cavity

The inner cell masswill separate from the trophoblast during

implantation The ectoderm cells will migrate and form a

fluid-fill chamber (the amniotic cavity)

Amnion: Mesodermal cells will soon createthe outer second layer of the amnion

The fluid and membranes will surround andcushion the developing embryo and fetus


19/37

19

Yolk Sac

Begins as the endodermalcells spread around theouter edges of the

blastocoele.

The yolk sac is completed as the mesodermcells migrate around the pouch.

Site of embryonic blood cells and gonadalstem cells


20/37

20

Gastrulation

This is the term for the process by which a third

layer of cells called the mesoderm, forms

between the ectoderm and endoderm.

Primitive streak: raised dorsal groove that

establishes the longitudinal axis of the embryo

Gastrulation sets the stage for organogenesis;the formation of body organs


21/37

21

Gastrulation


22/37

22

Gastrulation


23/37

23

Primary Germ Layers

Serve as primitive tissues from which all body

organs will be derived

Endoderm:

Epithelial lining of GI & lower respiratory tract

All ducts entering the GI tract

Urinary bladder

Ectoderm: Nervous system

Epidermis

Lining of mouth, and anus

Sense organs such as eyes


24/37

24

Primary Germ Layers

Mesoderm:

Muscle

Bone Cartilage

Blood

Dermis and hypodermis

Kidneys, ovaries, testes

Lining of body cavities


25/37

25

Ectoderm

Mesoderm

Endoderm

Approximately 13 days after fertilization


26/37

26

21-23 Days After Fertilization

Actual Size 1.0

1.5 mm

28 D Aft


27/37

27

28 Days After

Fertilization

By the end of week 4 theres significantdevelopment of the nervous system, heart, bodyform and placenta.

The embryo starts receiving nutrients and

oxygen through the placenta.

Actual Size: 4-6 mm

E b i M b


28/37

28

Embryonic Membranes:

Chorion and Allantois

Allantois: a small outpocketing at the caudal end of the

yolk sac

Structural base for the umbilical cord Becomes part of the urinary bladder

Chorion

Becomes the embryonic contribution to the placenta Derived from trophoblast & mesoderm lining it

Contains the chorionic villi


29/37

29

Umbilic

al


30/37

30

Umbilical

Cord

Connects the

embryo/fetus

to the

placenta

Contains

2 arteries

and 1 vein


31/37

31

2 Arteries

1 Vein


32/37

32

Placenta

The placenta is fully formed and functional by the 3rdmonth of pregnancy

Chorion of embryo & stratum functionalis layer of

uterus Chorionic villi extend into maternal blood filled

intervillous spaces: maternal & fetal blood vessels donot join & blood does not mix

Diffusion of O2, nutrients, wastes Stores nutrients & produces hormones

Barrier to microorganisms, except some viruses

AIDS, measles, chickenpox, poliomyelitis,encephalitis


33/37

33

Endocrine Placenta

Human Chorionic Gonadotropin (hCG):

Maintains the integrity of the corpus luteum

and promotes the continued secretion of

progesterone

Human Placental Lactogen (hPL) and

Placental Prolactin: Prepare the mammary

glands for milk production


34/37

34

Endocrine Placenta

Relaxin: which relaxes connective tissue of

pelvis and cervix

Suppresses the release of oxytocin by the

hypothalamus

Progesterone and Estrogens: Maintain the

endometrial lining


35/37

35

Placenta

This side faces the baby This side touches the uterus


36/37

36

Gestation

Fetal period: Begins at week 9

All major organs have been established

This is the time of growth

Gestation: 40 weeks measured from the first

day of the uterine cycle (day one of

menstruation)

Actually only 38 weeks from fertilization

Fetal


37/37

37

Fetal

Period

56 days after

fertilization Actual Size:

30 mm

Documents

Ana&Physio 16 - Human Development