Course 114 - scholar.cu.edu.egGeneral Embryology PART V [email protected] Dr. Karim M. Khalil Lecturer of Veterinary Anatomy and Embryology Cairo University / Karim Khalil

Course 114

General EmbryologyPART V

[email protected]

Dr. Karim M. Khalil

Lecturer of Veterinary Anatomy and EmbryologyCairo University

/ Karim Khalil

1

Four mammalian embryos at various stages of development:

• A Pig

• B Calf

• C Rabbit

• D Human

“Please, note the similarities in the different developing mammalian species!”

2

Refers to the study of the development of an

embryo immediately after conception to the

fetal stage.

Embryology

Embryo = unborn ology = science

3

Development

Prenatal Postnatal

From fertilization onset up to time of birth

After birth up to time of death .

Fertilization stage: 1st week

Embryonic stage: 2nd – 8th week

Fetal stage: 8th – birth date 4

Embryogenesis

Action Day

Fertilization - Zygote1 – 2

Zygotic stage - Morula 2 – 5

Blastocyst – Implantation6 – 7

Embryonic disc & Germinal layer8 – 12

Neural tube - Notochord 15 – 20

Fetal membranes & Placenta21 - 25

Organogenesis & Heart beating26 – 355

6

Embryogenesis

• The process by which the embryo is formed and

develops.

• It starts with the fertilization of the ovum (or

egg) which, after fertilization, is referred to as

a zygote.

• The zygote undergoes rapid mitotic divisionswith no significant growth (a process knownas cleavage) and cellular differentiation,leading to development of an embryo. 7

8

Division

Mitosis Meiosis

9

10

Differences between Mitosis and Meiosis

MEIOSISMITOSISEvents

Only in the germ

cells.

In somatic & germ

cells.Occurrence

reductional

division.

It is an equational

division.Definition

FourOnly twoDaughter cells

Occurs Does not occur.Synapsis

Occurs Does not occur.Crossing over

Do not split Each centromere

splits into two.Centromeres

HaploidDiploidChromosomes No. 11

Gametogenesis

Spermatogenesis Oogenesis

The term is applied for the development of male gametes

(Spermatogenesis) and female gametes (Oogenesis)

12

13

14

The difference between spermatogenesis and oogenesis

OogenesisSpermatogenesisComparison

Ovary, cortexSeminefrous Tubules (Testes)Occurrence

Ootid + 3 polar bodies4 spermEnd result

LargerSmallerSize of Gametes

Puberty up to

menopausePuberty up to deathContinuity

Immotile ovaMotile spermMotility

Only XX or YChromosomes

AnabolicCatabolicMetabolic activity

AbsentPresentSpermiogenesis

Stimulate follicular

development

Act on sertoli cells (stimulate

spermatogenesis)FsH

Ho

rmo

nal

acti

vity

Stimulate ovulationAct on leydig cells to secrete

testosteroneLH 15

16

A repeated cyclic changes occurs in the

uterus and ovary accompanied by shedding

of endometrium.

Oestrous cycle Menstrual cycle

17

18

19

20

21

Animals are classified according to repetition of oestrous cycle into:

Type of estrous

Polyestrous

Cow Sow

Woman

Monoestrous

Wild Animals

Seasonal Polyestrous

MareCatEwe

Seasonal Monoestrous

BitchBear

22

23

24

Classification of ova according to Amount and Distribution of yolk

Acc

ord

ing

to: Amount of

yolk

Microlecithal

(oligolecithal)Mesolecithal

Macrolecithal

(megalecithal)

Distribution

of yolkisolecithal

Heterolecithal

Extreme

telolecithalTelolecithal Centrolecithal

CleavageTotal (complete) Holoblastic

Partial (incomplete)

Meroblastic

Equal Unequal Discoidal Superficial

Animal speciesMammals

and

Amphioxus

Amphibian Birds Insects

Figure

25

• Corpus luteum of menstruation (cyclic) persists

for 10-14 days in non fertilizing ovum.

• Corpus luteum of pregnancy persists up to 6

months then degenerated as its function

being carried out by the placenta.

Fate of Corpus Luteum

26

Fertilization

27

28

29

30

Cleavage: rapid succession of cell divisions... without cellgrowth - no increase in size, only an increase incell numbers forms hollow ball of cells calledBLASTULA or blastocyst, with internal fluidcavity is called the blastocoel.

• Animal pole: portion of embryo housing primary tissues.• Vegetal pole: portion of embryo containing "yolk“.

31

Classification of ova according to Amount and distribution of yolk

Acc

ord

ing

to: Amount of

yolk

Microlecithal

(oligolecithal)Mesolecithal

Macrolecithal

(megalecithal)

Distribution

of yolkisolecithal

Heterolecithal

Extreme

telolecithalTelolecithal Centrolecithal

CleavageTotal (complete) Holoblastic

Partial (incomplete)

Meroblastic

Equal Unequal Discoidal Superficial

Animal speciesMammals

and

Amphioxus

Amphibian Birds Insects

Figure

32

Embryogenesis

Action Day








34

1. Cleavage

2. Morula

3. Blastula

4. Implantation

Blastogenesis includes:

35

Implantation

The process of embedding the blastula in the endometrium of the uterus.

• It occurs on 7th day after

fertilization.

• The blastocyst is

implanted inside the

maternal endometrium

by its embryonic pole.36

How the blastocyst is implanted?

37

The eroded endometrium

is now called

Decidua

38

Complete implantation Incomplete implantation

Blactocyst is completely

hidden inside the

endometrium

Chorionic villi lie in

opposition to endometrium

without penetration

All mammals except >>Ruminant ,mare ,sow and

dolphin (Marine mammals)

True placenta False placenta

Types of Implantation

39

Gastrulation

• Means the process of development of the 3

germinal layers of the embryo.

• The developmental events from the Blastula

up to Gastrula (Chorionic vesicle) including

germ layers, neural tube and notochord.

40

http://www.answers.com/topic/germ-layer

41

Day 8 - 1042

Day 1243

44

45

46

47

• Formation of Notochord.

• Development of the neural tube and neural

crest.

48

49

50

51

52

Derivatives of the neural tube and neural crest

C. N. S. (Brain and spinal cord)

1. Sensory ganglia.2. Autonomic ganglia.3. Pigment cells

(melanocytes).4. Schwann cells

(neurolemma).5. Sympathatic chain.6. Adrenal medulla.7. Arachnoid and pia

mater. 53

Differentiation of intraembryonic

mesoderm

1. Dorsal (Paraxial) mesoderm. (Somites)

a) Sclerotome ->> bones, cartilage, connective tissue.b) Myotome ->> skeletal Muscles.c) Dermotome ->> Dermisof the skin.

2. Intermediate mesoderm.

3. Lateral mesoderm.54

55

Ectoderm Mesoderm Endoderm

• C. N. S. • (Brain and spinal

cord)• Epidermis of the

skin.• Ear and Eye.• Pituitary gland• Adrenal medulla

• Connective tissue• Cartilage and

Bones.• Muscles• Dermis of the skin• Urogenital system.• Cardiovascular• Lymphatic• Body Cavities• Respiratory system• Alimentary tract• Adrenal cortex

• Epithelial lining of respiratory system.

• Epithelial lining of Digestive system.

• Epithelial lining of urinary bladder and urethra.

• Epithelial lining of ear

• Parenchyma of glands

Main Derivatives of the 3 germ layers

56

Embryogenesis

Action Day








58

Day 8 - 1059

Day 1260

61

62

63

64

65

Development of the chorionic villi

66

67

Placenta

68

Placenta

A circular disc (15 cm. diameter, 4cm thickness and 500 gm/weight) .

It has 2 surfaces:

• Maternal surface: rough irregular has from 15-20

cotyledons.

• Fetal surface : smooth and shiny covered by the

amnion. It gives attachment to the umbilical cord

69

I. The pattern of implantation.

II. Anatomically based on placental shape and

contact points or distribution of the chorionic

villi

III. Histologically based on the structure of

attached surface (penetration of villi into the

decidua)

Classification of placenta according to

70

Complete implantation Incomplete implantation

Blactocyst is completely

hidden inside the

endometrium

Chorionic villi lie in

opposition to endometrium

without penetration

All mammals except >>Ruminant ,mare ,sow and

dolphin (Marine mammals)

True placenta False placenta

I. Patterns of Implantation


71

II. Anatomically, based on placental shape


72

III. Histologically based on the structure


73

The

pat

tern

of

imp

lan

tati

on

Placenta Non deciduated

False placenta

Deciduated

True placentaImplantation Incomplete Complete Bleeding in

parturation - +

Shedding of

endometrium - +

Anatomically Diffuse Cotyledonary Zonary Discoidal

HistologicallyEpithelio

chorial

Syndesmo

chorial

endothelio

chorial

Hemo

chorial

Animal species Mare and

SowCow and Ewe

Bitch and

Queen

Man

,Monkey

and

Rodent

Types of Placenta

74

Foetal membrane of mammals & umbilical cord

Foetal membrane Embryonic origin Function

AmnionExtraembryonic mesoderm

lined by ectoderm

1. Protection against external risk.

2. Prevent adhesion.

3. Give aseptic medium.

4. Facilitate free movement.

5. Good cervical dilator during

delivery.

6. Provide equal pressure on fetus.

Primary yolk

sac

Roof by endoderm while the

rest by exocoelomic membrane Give rise: primary sex cells ,midgut

and allantois.

Its main function is nutrition

through the vitellinointestinal

duct.

Secondary yolk

sacCompletely lined by endoderm

Definitive yolk

sac

Lined by endoderm and

covered by mesoderm derived

from trophoblast

AllantoisEndodermal protrusion from

the caudal wall of yolk sac Excretion

75

Foetal membrane Embryonic origin Function

Chorion Syncitio and cytotrophoblast Part of placenta

PlacentaChorioallantoic membrane +

endometrium

1. Nutritive material.

2. Oxygen.

3. Waste products.

4. Act as barrier against

bacteria and drugs.

5. Endocrine function

(progesterone).

Umbilical cordMesoderm from connecting

stalk covered by amnion.

It is forms the Wharton,s jelly.

Connects the fetus with mother

through 2 umbilical artery and 1

left umbilical vein

Foetal membrane of mammals & umbilical cord

Documents

Course 114 - scholar.cu.edu.egGeneral Embryology PART V [email protected] Dr. Karim M. Khalil Lecturer of Veterinary Anatomy and Embryology Cairo University / Karim Khalil