Basic Embryology for pharmacist - PowerPoint Presentation

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Basic Embryologyfor pharmacist

by

Krisztina

H.-Minkó Semmelweis University, Department of Anatomy, Histology and Embryology

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Question of time (anatomy vs. gynecology)

Zero time?

Fertilization (anatomy) – clinically usually impossible to determine, uncertain

Last menstruation (gynecology) – certain, but just an estimate, not actual age (ovulation usually 14 days after mestr., fertilization within 2 days)

Length of pregnancy: 280 days (40 weeks) after the last menstruation, 266 days (38 weeks) after conception

Trimesters:

1st: 0-12 weeks

2nd: 12-25 weeks

3rd: 25-40

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Developmental events in the first 3 weeks after fertilizationFertilization

CleavageGastrulationNeurulationPlacenta formation(Spermio- and oogenesis)

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Mitosis vs. meiosis

Number of chromosomes in somatic cells: 22 pair XX (females) or 22 p. XY (males).

During mitosis equal, diploid daughter cells are produced.

During meiosis the number of chromosomes is halved (22X or 22Y – haploid cells). This is achieved by DNA duplication followed by two cell divisions.Normal chromosome number is restored at fertilization, where two haploid cells fuse.Increases variability!

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Crossing over

Identical regions of homologous pairs of chromosomes exchanged. Further increases variability to infinitely high values.

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Oogenesis

Starts in the embryonic period, arrested

a

t the first prophase till puberty. The first meiotic division completed upon ovulation, the second division at fertilization. In humans, usually only one oocyte is ovulated in each menstruational period, between puberty and menopausa, when further maturation cases.Four cells are produced, but only one is functional, the rest (polar bodies) are defective. The oocyte gives the cell organelles the cytoplasm, mitochondria and yolk to the embryo.

Some oocytes may rest in the vulnerable period of arrested meiosis for 40-50 years, resulting in increased ratio of genetic defects with maternal age.

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Spermiogenesis

Starts at puberty, continuously active, high number of sperms are produced, ideally no age limit exists.

Four functional, mobile cells are produced.

22X or 22Y: determines the genetic sex of the embryo.

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Spermiohistogenesis

Production of mobile cells from spermatids.

Chromosome condensation to decrease the amount of transportable materials, tail formation (motor), acrosome formation (digestive enzymes to penetrate zona pellucida), mitochondria (energy).

Only the genetic material is used!Strong selection: defective cells will not usually reach the site of fertilization

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ovulation

fertilisation

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1st week

Ovulation, fertilization, cleavage, transport to uterus, implantation

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Fertilization 1

Spermia must penetrate the corona radiata

and the zona pellucida by active movement and by the help of acrosomal enzymes. When the first sperm reaches the cell membrane, they fuse, and the genetic material (male pronucleus) enters the cell. This is the activating signal for the oocyte to finish the second meiotic division.

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Fertilization 2

Two pronuclei unite

Cleavage starts

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Cleavage

2 cells 4 cells 16 cells: morula cavity: blastula

Inner cell mass = embryoblast

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Timing of Cleavage

Embryo reaches the lumen of uterus by the

4

th day after fertilization – at a blastula stage. By this time zona pellucida has disintegrated, the trophobalst layer invades the endometrium, implantation begins.

The embryo may implant anywhere once the zona pellucida has disappeared. If there is a problem with transportation, it will implant to the uterine tube or other abdominal organs. This state is referred to as extra uterine (ectopic) pregnancy.

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Extrauterine (ectopic) pregnancy

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Implantation (d6-d9)

Trophobalst layer invades the endometrium

App. at the 6

th

day after fertilizationUterine mucosa must be in receptive stage

(secretory phase)

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2nd week

Bilaminar germ disc

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Gastrulation 1(7-14 days a.f.)

Implantation proceeds, trophoblast differentiates.

Embryoblast cells differentiate, bilaminar germ disc appears, with epiblast and hypoblast layers

.

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3rd week

Trilaminar germ discNeurulation begins

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Gastrulation 2(trilaminar germ disc)

14

th

-16th days after fert.Epiblast cells proliferate, move in a central direction, form an invagination (primitive streak and node). Cells migrate to the hypoblast and to the intermediate layer to form the endoderm and mesoderm respectively.

Animation of gastrulation:

https://www.youtube.com/watch?v=sUuX-4fEF3A

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Ectoderm

Neural fold

17th day: early differentiation of mesoderm

Notochord will induce the development of the nervous system from ectoderm.

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Late differentiation of mesoderm, neurulation (day 17-21)

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D 21

Developing aorta, and heart tube is visible, heart pulsation is detectable in ultrasound imaging.

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D 21

Dermatome: connective tissue derivates (dermis) of dorsal skin

Intermediate mes

oderm: urinary system (male genital tract)Somatopleura: parietal layer of serous membranes, lateral and ventral body wall (except for epithelia of skin)Splanchnopleura: visceral layer of serous membranes CT and smooth muscles of intestine

Sclerotome: vertebrae

Myotom

e

: axial muscles

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Neurulation (Day 17-29)(4.w)

Neural tube: central nervous system

Neural crest: peripheral nervous system, etc…

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Neurulation

Animation of neurulation:

https://www.youtube.com/watch?v=iHmBIJs77ZQ&t=91s

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Folding

(3.-6.w)

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Thank You for attention!

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Literature

T.W. Sadler: Langmann’s Medical Embryology, 7th edition, 1995, Baltimore, Maryland, USA - pictures

Papp Z: Szülészet és nőgyógyászat tankönyve, Semmelweis Kiadó, 1999, Budapest

Previous authors of the lecture: Ákos Lukáts, Nándor Nagy