Developmental Anatomy Lecture Syllabus



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Developmental Anatomy

Lecture Syllabus





Department of Histology & Embryology

Peking Union Medical Collage

2007.12
Content


  1. INTRODUCTION TO THE DEVELOPING HUMAN 4

  2. EARLY DEVELOPMENT OF HUMAN EMBRYO 5

  3. chorionic sac 7

  4. 2. Amnion & Amniotic fluid 10

  5. premature rupture of the amnion 11

  6. false knots and true knots 12

  7. intrauterine growth retardation (IUGR) 13

  8. progesterone  estrogens 14

  9. 2. Other multiple pregnancies 14

  10. HUMAN BIRTH DEFECTS 15

  11. DEVELOPMENT OF HEAD AND NECK 18

  12. DEVELOPMENT OF BODY CAVITIES AND DIAPHRAGM 21

  13. DEVELOPMENT OF RESPIRATORY SYSTEMSR.S. 23

  14. DEVELOPMENT OF DIGESTIVE SYSTEMS 25

  15. DEVELOPMENT OF URIGENITAL SYSTEM 29

  16. DEVELOPMENT OF THE NERVOUS SYSTEM 38

INTRODUCTION TO THE DEVELOPING HUMAN
I. Definition:

  1. Embryology: developmental anatomy, the study of the formation and development of embryos.

  2. Human embryology is a science that studies the normal development as well as the birth defects of a human being in the maternal uterus.

II. The History of Embryology

  1. Early History

  2. Renaissance History

  3. Experimental Embryology

  4. Progress of modern embryology: test tube babies & somatic cell cloned animals

III. The main branches of Embryology

  1. Descriptive Embryology

  2. Comparative Embryology

  3. Experimental Embryology

  4. Chemical Embryology

  5. Molecular Embryology

  6. Reproductive Engineering

  7. Teratology

IV. Why a medical student should study Embryology?

V. Introduction of the development of an embryo

prenatal periods

fertilization parturition

38 weeks


fertilization age & gestational age

Three developmental periods are divided:



  1. Preembryonic period (0-2 weeks): fertilization to formation of the bilaminar germ disc.

  2. Embryonic period (3-8 weeks): trilaminar embryonic disc formation & organogenesis

  3. Fetal period (9-38 weeks): growth of the organ systems.


EARLY DEVELOPMENT OF HUMAN EMBRYO
I. Gametogenesis

A process of formation and maturation of the gamete (spermatozoa in male and ova in female), including chromosomal and morphological changes.



  1. Migration of primordal germ cells (PGCs)

  2. Spermatogenesis

  3. Oogenesis


II. Fertilization to Implantation (1st Week of Development)

1. Fertilization: A sperm + an oocyte → zygote

1) before fertilization

(1) male gametes (spermatozoa)

a. number and viability:

b. transport of ejaculated spermatozoa


  • capacitation of spermatozoa:

acrosomal region

  • result: obtaining capacity of fertilizing an egg

(2) female gamete (oocyte)

a. number

b. transport of ovulated secondary oocyte

(3) two gametes meeting

a. time:

spermatozoa: < 48 hours after ejaculation

oocyte: 12 - 24 hours after ovulation

b. site: ampulla of oviduct

2) process of fertilization

(1) acrosome reaction: release of enzymes from acrosome

(2) zona reaction:

zona becomes impenetrable to other sperm (monospermy), through lysosomal enzyme release from cortical granules of oocyte to change structure and composition of the zona.

(3) process of fertilization:

penetration, recognition & fusion

ZP3 is responsible for species-specific fertilization

3) after fertilization

(1) oocyte finishes 2nd meiosis

(2) formation and merge of male and female pronuclei → cleavage

4) Result of fertilization

(1) restoration of diploid number of chromosome

(2) species variation

(3) primary sex determination: Y+X = male, X+X = female

(4) activation of egg metabolism and initiation of cleavage

2. Cleavage and blastocyst formation

mitotic division

zygote blastomeres → morula → blastocyst


  • compaction




(embryoblast)




inner cell mass

blastocyst

blastocyst cavity




trophoblast

  • embryonic stem cell (ES cell)

  • hatching of blastocyst: ~ day 5- 6

3. Implantation: a process of the blastocyst embedding into the endometrium

1) Time: Day 5 - 6 to Day 11 - 12

2) Site: posterior or anterior wall of uterine body

3) Process:

adhesion, expansion, dissolution, invasion, differentiation, repair

4) The main changes during implantation (differentiation)

(1) Formation of bilaminar embryonic disc

(embryoblast) epiblast

inner cell mass → embryonic disc

hypoblast

(2) Decidual reaction




decidua basalis

Decidua

decidua capsularis → degeneration




decidua parietalis

(3) Formation of the early fetal membranes






cytotrophoblast

trophoblast






syncytiotrophoblast



epiblast

hypoblast






amnioblasts

exocoelomic membrane (& cavity)













amnion

extraembryonic endoderm

of primary yolk sac



primitive streak




late early















extraembryonic mesoderm

secondary yolk sac







allantois










extraembryonic somatic mesoderm

connecting stalk

extraembryonic splanchnic mesoderm





extraembryonic

coelom





cytotrophoblast

syncytiotrophoblast umbilical cord



chorion chorionic cavity





chorionic sac


5) Requirements of implantation

(1) Zona pellucida disappears in time

(2) Normal development and transport of the young embryo

(3) Endometrium in secretory phase

(4) Normal endocrine regulation

6) Abnormal implantation

(1) Ectopic pregnancy

(2) Placenta previa

7) Contraception

(1) Intervening the processes of gamete production: contraceptive pills

(2) Intervening the processes of fertilization

a. condom & diaphragm

b. terilization: vasectomy & tubal ligation

(3) Intervening the processes of implantation

a. intrauterine devices (IUD)

b. post-coital contraception



4. Human assistant reproductive technology

1) Artificial insemination

2) In vitro fertilization-embryo transfer, IVF-ET

2nd week -- “ the period of twos”

two embryonic layer: epiblast & hypoblast

two trophblast layers: cytotrophoblast & syncytiotrophoblast

two cavities: amniotic cavity & yolk sac
III. Formation of three germ layers (3rd Week)

1. Gastrulation: Gastrula

epiblastic cells proliferation & migration

bilaminar embryonic disc trilaminar embryonic disc

1) Formation of the primitive streak

primitive streak & primitive groove

epiblastic cells →

primitive knot & primitive pit

2) Formation of intraembryonic endoderm and mesoderm

3) Formation of trilaminar germ disc

All 3 germ layers are derived from the epiblast.



  • There are two areas that have no mesoderm:

prechordal plate → oropharyngeal membrane

cloacal membrane

4) Formation of the notochord

(1) Process:

primitive node & primitive pit (median cranial migration) → notochordal (head) process → notochordal canal (neurenteric canal) → notochordal plate → notochord

(2) Function: primary inductor, induction of neural plate formation

5) Fate of the notochord & primitive streak

(1) The fate of notochord: degeneration, forming the nucleus pulposus of intervertebral disc

(2) The fate of primitive streak: degeneration

(3) Teratoma: oropharyngeal & sacrococcygeal teratoma



2. Neurulation: the process of neural tube formation Neurula

1) Formation of the neural tube

proliferation invagination

ectoderm cells (overnotochord) neural plate

neural groove & neural fold → neural tube

The neural tube is the primordium of the central nervous system (CNS).

2) Formation of the neural crest

The neural crest is the primordium of the peripheral nervous system (PNS).

3rd week -- “period of threes”

three germ layers: ectoderm, mesoderm & endoderm

three important structure: primitive streak, notochord & neural tube
IV. Differentiation of Germ Layers and Establishment of Body Form (3rd to 8th Week)

1. Differentiation of ectoderm

1) Neural ectoderm

(1) neural tube → CNS


  • rostral (anterior) neuropore: closed by 25-26 days

  • caudal (posterior) neuropore: closed by 27-28 days

(2) neural crest → PNS, the chromaffin cells of the adrenal medulla, parafollicular cells of the thyroid, melanocytes, and part of mesenchyme in the pharyngeal apparatus.

(3) anencephaly & myeloschisis (spina bifida)

2) Surface ectoderm

(1) epidermis and its appendages

(2) adenohypophysis

(3) sensory epithelium of the ear, nose, tongue

(4) lens of the eye

(5) enamel of the teeth



2. Differentiation of mesoderm

paraxial mesoderm → somites

mesoderm → intermediate mesoderm

lateral mesoderm

1) Derivatives of the somite

somites ( 3 pairs/day, 42 - 44 pairs in total )

sclerotome → paraxial skeleton

somite → myotome → muscles

dermatome → dermis

2) Derivatives of the intermediate mesoderm

the primordium of the urogenital system forming the kidneys and gonads, etc.

3) Derivatives of the lateral mesoderm






somatic mesoderm →

bones, muscles and C.T. and mesothelium

lateral




lining inner surface of body wall

mesoderm→

intraembryonic coelom




splanchnic mesoderm

→ muscles and C.T. of viscera, and mesothelium covering them


3. Folding of the embryo

the embryonic disc

r
Folding
apid growth of CNS rapid growth of somites

head and tail folds lateral fold


cylindrical embryo

4. Formation of primitive gut

york sac → primitive gut (foregut, midgut, hindgut) → primordium of digestive and respiratory systems



5. Differentiation of endoderm

endoderm → epithelial of digestive & respiratory tract, and bladder, urethra; parenchyma of liver, pancreas, tonsil, thyroid, parathyroids, thymus; epithelium of tympanic cavity and Eustachian tube.


V. Fetal membranes and placenta

fetal membranes including chorion, amnion, yolk sac, umbilical cord & allantois

Functions:

nutrition, protection, respiration, excretion, endocrine & immunological barrier preventing rejection of fetus as an allograft



1. Chorion

extraembryonic somatic mesoderm + cytotrophobalst + syncytiotrophoblast

1) Chorionic villi

(1) development of villi:

primary stem villi: cytotrophoblast + syncytiotrophoblast

secondary stem villi: with a core of loose C.T.



tertiary stem villi: with blood vessels in the loose C.T. core

(2) cytotrophoblastic shell (细胞滋养层壳)

stem villi (anchoring villi) , branch villi (terminal villi)

(3) villous chorion (丛密绒毛膜chorion frondosum) & smooth chorion (平滑绒毛膜chorion leave)

2) intervillous space

isolated lacunae in the syncytiotrophoblast → fused to lacunar networks → intervillous space

chorionic plate, primitive uteroplacental circulation

3) abnormal growth of the trophoblast:

Hydatidiform Moles (葡萄胎), Choriocarcinomas (绒毛膜癌)

2. Amnion & Amniotic fluid

1) amniotic sac, amniotic cavity & amniochorionic membrane

2) amniotic fluid

(1) origin: amniotic cells, maternal & fetal blood, tissue fluid and fetal urine etc.

(2) circulation and exchange:

a. by mother b. by fetus

(3) composition:

(4) volume: 10w: 30ml, 20w: 350ml, 37w: 700-1000ml


  • < 400ml → oligohydramnios

  • > 2000ml → polyhydramnios

  • amnionic band

(5) significance:

a. protection

b. prevent adherence of the amnion to the embryo and fetus

c. controlling the embryos temperature

d. enabling the embryo to move freely and grow

e. maintaining homeostasis of fluid and electrolytes

f. permitting normal fetal lung development

g. dilating and washing the cervix during the labor

h. prenatal diagnosis

Amniocentesis -Fetoprotein (-AFP)

premature rupture of the amnion



3. Yolk sac

1) significance:

(1) transfer of nutrients (2-3w)

(2) blood development (mesoderm, 3-5w)

(3) primitive gut (4w)

(4) primordial germ cells (endoderm, 3w)

2) fate:

yolk stalk → Meckels diverticulum(憩室)



4. Allantois

1) origin: finger-like diverticulum from the caudal wall of the yolk sac that extends into the connecting stalk

2) significance:

(1) blood formation: 3-5w

(2) umbilical vein and arteries

(3) a part of urinary bladder

3) fate:

urachus (脐尿管) → median umbilical ligament



5. Umbilical cord

mucous connective tissue covered by amnion, including two arteries, one vein, atrestic allantois and atrestic yolk stalk

1-2cm in diameter, 30-90cm in length (average 55cm)

false knots and true knots



6. Placenta

1) Composes and Shape:

(1) composes: fetomaternal organ

the fetal component: the villous chorion

the maternal component: the decidua basalis

(2) shape: discoid, 15-20cm in the diameter, 2-3cm thickness, 500-600gm weight

a. maternal surface of the placenta: rough

cotyledon(胎盘小叶), groove (placenta septa)

b. fetal surface of the placenta: smooth

amnion, umbilical cord, and radiating chorionic vessels

2) The fetomaternal junction

cytotrophoblastic shell, stem villi (anchoring villi)



placenta accrete (植入胎盘), placenta increta, placenta percreta (穿透性胎盘)

3) Placental circulation

fetal placental circulation

( within the villus )

umbilical A. →→ arterio-capillary-venous system →→ umbilical V.

metabolic gaseous

products products

spiral A. → intervillous space → endometrial V.

maternal placental circulation

intrauterine growth retardation (IUGR)

4) Placental membrane or Placental barrier

(1) < 20w

a. syncytiotrophoblast

b. cytotrophoblast and basal lamina

c. connective tissue in the chorionic villi

e. endothelium and basal lamina of the fetal capillary

(2) > 20w

a. syncytiotrophoblast and basal lamina

b. endothelium and basal lamina

5) Functions of placenta

(1) metabolism

(2) transport of substances

nutrients, gases, waste products, drugs, hormones, Ag, Ab, etc

(3) endocrine secretion

a. protein hormones:

 human chorionic gonadotropin (hCG)

 human chorionic somatomammotropin (hCS) or human placental lactogen (hPL)

 human chorionic thyrotropin (hCT)

 human chorionic corticotropin (hCACTH)

b. steriod hormones:

 progesterone  estrogens

VI. Parturition (分娩)

VII. Twins and other multiple pregnancies

1. Twins

1) dizygotic twins (双卵双胎)



  • same or different sex

  • the external and genetic features are no more alike than other brothers or sisters.

  • separate placenta, chorionic sac and amniotic cavity

  • sometimes two placentas fuse into one

2) monozygotic twins (单卵双胎)

(1) separation of the embryonic blastomere (35%)

  • separate placenta, chorionic sac and amniotic cavity

  • sometimes two placentas fuse into one

(2) separation of the inner cell mass (65%)

  • common placenta and chorionic sac

  • separate amniotic cavity

  • sometimes having placental vascular anastomoses

Twin transfusion syndrome

(3) division of the embryonic disc

a. separate twins

b. conjoined Twins (联胎)

c. parasitic twin (寄生胎)

2. Other multiple pregnancies

1) Triplets

2) Quadruplets

HUMAN BIRTH DEFECTS
I. Introduction

1. What’s birth defect?

Developmental disorders present at birth (congenital malformations)

Structural, functional, metabolic, behavioral or hereditary

2. Teratology




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