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HISTOLOGY & EMBRYOLOGY Teaching PPT Dept. of Anat., Hist. & Embry. School of Medicine Xi’an Jiaotong University PowerPoint Presentation
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HISTOLOGY & EMBRYOLOGY Teaching PPT Dept. of Anat., Hist. & Embry. School of Medicine Xi’an Jiaotong University. HUMAN EMBRYOLOGY. Introduction. Tianbao Song ( 宋 天 保 ). 1. What is embryology?. normal development. Twins. Triplets. Congenital malformations(Birth defects).

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slide1

HISTOLOGY &

EMBRYOLOGY

Teaching PPT

Dept. of Anat., Hist. & Embry.

School of Medicine

Xi’an Jiaotong University

slide2

HUMANEMBRYOLOGY

Introduction

Tianbao Song (宋 天 保)

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1. What is embryology?

normal development

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Embryologyis a science that studies the normal development as well as birth defects of a human being in the maternal uterus.

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2. Historical gleanings

Hippocrates : first recordedembryological studies; bird embryo can be likened to that of man.

Aristotle: studied chick and other embryos, which resulted from union of semen with menstrual blood.

Father of Medicine

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Preformation theory

Leeuwenhoek : a miniature human being in sperm

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Theory of epigenesis

Wolff(1733-1794): layer concept (4 layers)

Baer: First reported mammalian and human ovum;

The 3 germ layer theory;

Found notochord;

developmental law.

Remark (1815-1865): gave names of 3 germ layers

Father of Modern Embryology

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Darwin (1859): On the Origin of Species emphasized thehereditary nature of variability in evolution.

Recapitulation theory

Müller and Haeckel(1860’): Ontogeny is a brief recapitulation of phylogeny.

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Hans Spemann (1869-1941): theory of organizer andembryonic induction.

Noble prizewinner in medicine and physiology (1935).

Needham(1900-1995): chemical embryology

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Progressof modern embryology:

Test tube babies

Edwards,Steptoe (1978): first TTB in the world (Louise Brown)

Zhang Lizhu, Liu Bin(1988):

first TTB in China (Zheng Mengzhu)

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Somatic cell Cloned animals

Wilmut & Campbell (1997): first cloned sheep in the world(Dolly)

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3. Normal development

38 weeks from fertilization to parturition

1)Preembryonic period: First 2 weeks;Fertilization to formation of the bilaminar germ disc.

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2) Embryonic period: Weeks 3 - 8; Primordia of all major organs develop from the 3 germ layers.

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3) Fetal period:Week 9 – birth.

Growth of the organ systems

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4. Birth defects

4.1 Definition: structural and functional

defects present at birth (congenital

malformations).

teratology: study of congenital malformations

  • 4.2 Causes
  • 1) Genetic factors (25%)
  • 2)Environmental factors(teratogens) (10%)
  • 3)Interaction of genetic and environmental
    • factors (65%)
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4.2.1 Genetic factors

1) Numerical abnormalitiesof chromosomes

Autosomes -- Trisomy 21 (Down’s syndrome):

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Down’s syndrome:

special face,

mental retardation,

heart defect,

simian crease.

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Sex chromosomes

Turner’s syndrome (XO):

short stature

webbed neck

no ovary

mental retardation

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Klinefelter’s syndrome (XXY):

testicular atrophy

sterility

gynecomastia

(mental impairment)

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2) Structural abnormalities of chromosomes:

break, deletion, insertion, etc.

e.g.: 5p- → cat cry syndrome

3) Mutationsof genes

metabolic or functional disorders (e.g.

phenylketonuria, galactosemia);

a few malformations(e.g. microcephaly,

achondroplasia, polycystic kidney)

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4.2.2. Environmental factors (teratogens)

  • 1) Biological
  • Viruses:
    • rubella virus→ cataracts, deafness, cardiac defects;
    • cytomegalovirus→blindness, microcephaly, hepatosplenomegaly;
    • herpes simplex virus→ microcephaly, microphthalmus.
  • Toxoplasma gandii (Toxoplasmosis)
  • Treponema pallidum(Syphilis)
  • Chlamydia trachomatis, ureplasma urealyticum
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2) Physical

radiation, mechanical pressure, traumas

Radiation: World War II: atomic bomb

explosion over Japan.

Survived pregnant women:

28% aborted;

25% delivered children died <1 year;

25% infants with CNS malformations.

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3) Chemical

  • chemicals: nitrite, benzol; lead, arsenic, cadmium, mercury, etc.
  • drugs: thalidomide (amelia and meromelia),
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aminopterin (anencephaly, hydrocephalus,

cleft lip),

streptomycin (deafness).

hormones: estrogens, progestins

social drugs: cigarettes (small babies),

alcohol (fetal alcohol syndrome).

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4) Others

hypoxia(small babies);

nutritional deficiencies

(Vitamins, iodine).

4.2.3. Interaction of genetic and environmental factors: (Cleft lip, heart defect, spina bifida…)

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4.3 Susceptible period

1) Dependent on the developmental stage.

The embryonic period (weeks3-8) is

highest susceptible because of intensive

differentiation.

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2) Different organs have different susceptible period corresponding to their own critical development stage.

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3) Different teratogens also have different susceptible period.

Rubella virus:1st month 50%;

2nd month 22%;

3rd month 7%.

Thalidomide:20 days after gestation