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Lernmaterialien für Embryology an der Medical University Varna

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Embryology

(Gr. embryon, unborn)

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The sequence of events in the organism from fertilization to birth

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Divisions of embryology


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General embryology

  • Gametogenesis: conversion of germ cells into male and female gametes
  • 1st week of development: ovulation to implantation
  • 2nd week of development: bilaminar germ disc
  • 3rd week of development: trilaminar germ disc 
  • 3rd to 8th week: embryonic period
  • 3rd month to birth: fetus and placenta

 Special embryology

  • Skeletal system 
  • Cardiovascular system
  • Respiratory system
  • Nervous system, etc…. systems
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Meiosis creates genetic diversity



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  • Each individual gamete contains either maternal or paternal version of each chromosome

→ the choice of maternal or paternal occurs independently and randomly for each pair of homologous chromosomes

  • Crossing-over :  the maternal and paternal versions of each chromosome undergo genetic recombination during meiosis
  • Sexual reproduction gives organisms a competitive advantage
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Meiosis

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A special form of nuclear division involved in sexual reproduction

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Meoisis vs Mitosis

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  • Meoisis - a diploid precursor cell gives rise to haploid progeny cells
  •  Mitosis - a diploid precursor cell gives rise to diploid progeny cells;

 In vertebrates, only the diploid cells proliferate: the haploid gametes exist only briefly, do not divide at all, and are highly specialized for sexual fusion

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Spermiogenesis (transformation of spermatids into spermatozoids)

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  •  Golgi phase
  • Cap phase
  • Acrosomal phase
  • Maturation phase
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Stages of prenatal development

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  • Preembryonic stage – weeks 1 & 2
  • Embryonic stage – weeks 3 ÷ 8
  • Fetal stage - months 3 ÷ 9
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The Preembryonic stage

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-> The first 2 weeks of development

- Steps:

> cleavage

> implantation

> embryogenisis

- Final outcome → embryo

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Specific characteristics of male meiosis

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  •  Begins at puberty
  • Goes on continuously, without stop and start mechanisms
  • It takes about 24 days for a human spermatocyte to complete meiosis
  • Very low error rates – 3-4% → if meiosis goes wrong, a a quality control system is activated, which arrests meiosis and leads to apoptosis
  • By the end of meiosis, a sperm has only just begun its differentiation
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Nondisjunction - homologs fail to separate properly


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  •  Some of the haploid gametes produced > lack a particular chromosome, while others have more than one copy of it
  • Cells with the correct number of chromosomes : euploid
  • Cells with an abnormal number of chromosomes:  aneuploid  (most embryos die, … but some survive)
  • Down syndrome – the leading single cause of mental retardation; caused by an extra copy of chromosome 21
  • Klinefelter syndrome – nondisjunction of the XX homologues → extra X chromosome
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In case pregnancy occurs

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  • Human chorionic gonadotropin (hCG), secreted by the placenta, maintains the corpus luteum for 3 months → corpus luteum of pregnancy
  • Grows to a diameter of 5 cm and continues to secrete hormones necessary for the maintenance of pregnancy
  •  Placenta becomes the main site of production of the various hormones involved in maintaining pregnancy, but corpus luteum continues to form these hormones for several months
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3rd-8th week → embryonic period

(= period of organogenesis)

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  • Each of the 3 germ layers (ectoderm, mesoderm, and endoderm) gives rise to a number of specific tissues and organs
  • By the end of the 2nd month, the main organ systems have been established → the major features of the external body form are recognizable
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  • 28845 Karteikarten
  • 248 Studierende
  • 18 Lernmaterialien

Beispielhafte Karteikarten für deinen Embryology Kurs an der Medical University Varna - von Kommilitonen auf StudySmarter erstellt!

Q:

Embryology

(Gr. embryon, unborn)

A:

The sequence of events in the organism from fertilization to birth

Q:

Divisions of embryology


A:

General embryology

  • Gametogenesis: conversion of germ cells into male and female gametes
  • 1st week of development: ovulation to implantation
  • 2nd week of development: bilaminar germ disc
  • 3rd week of development: trilaminar germ disc 
  • 3rd to 8th week: embryonic period
  • 3rd month to birth: fetus and placenta

 Special embryology

  • Skeletal system 
  • Cardiovascular system
  • Respiratory system
  • Nervous system, etc…. systems
Q:

Meiosis creates genetic diversity



A:
  • Each individual gamete contains either maternal or paternal version of each chromosome

→ the choice of maternal or paternal occurs independently and randomly for each pair of homologous chromosomes

  • Crossing-over :  the maternal and paternal versions of each chromosome undergo genetic recombination during meiosis
  • Sexual reproduction gives organisms a competitive advantage
Q:

Meiosis

A:

A special form of nuclear division involved in sexual reproduction

Q:

Meoisis vs Mitosis

A:
  • Meoisis - a diploid precursor cell gives rise to haploid progeny cells
  •  Mitosis - a diploid precursor cell gives rise to diploid progeny cells;

 In vertebrates, only the diploid cells proliferate: the haploid gametes exist only briefly, do not divide at all, and are highly specialized for sexual fusion

Mehr Karteikarten anzeigen
Q:

Spermiogenesis (transformation of spermatids into spermatozoids)

A:
  •  Golgi phase
  • Cap phase
  • Acrosomal phase
  • Maturation phase
Q:

Stages of prenatal development

A:
  • Preembryonic stage – weeks 1 & 2
  • Embryonic stage – weeks 3 ÷ 8
  • Fetal stage - months 3 ÷ 9
Q:

The Preembryonic stage

A:

-> The first 2 weeks of development

- Steps:

> cleavage

> implantation

> embryogenisis

- Final outcome → embryo

Q:

Specific characteristics of male meiosis

A:
  •  Begins at puberty
  • Goes on continuously, without stop and start mechanisms
  • It takes about 24 days for a human spermatocyte to complete meiosis
  • Very low error rates – 3-4% → if meiosis goes wrong, a a quality control system is activated, which arrests meiosis and leads to apoptosis
  • By the end of meiosis, a sperm has only just begun its differentiation
Q:

Nondisjunction - homologs fail to separate properly


A:
  •  Some of the haploid gametes produced > lack a particular chromosome, while others have more than one copy of it
  • Cells with the correct number of chromosomes : euploid
  • Cells with an abnormal number of chromosomes:  aneuploid  (most embryos die, … but some survive)
  • Down syndrome – the leading single cause of mental retardation; caused by an extra copy of chromosome 21
  • Klinefelter syndrome – nondisjunction of the XX homologues → extra X chromosome
Q:

In case pregnancy occurs

A:
  • Human chorionic gonadotropin (hCG), secreted by the placenta, maintains the corpus luteum for 3 months → corpus luteum of pregnancy
  • Grows to a diameter of 5 cm and continues to secrete hormones necessary for the maintenance of pregnancy
  •  Placenta becomes the main site of production of the various hormones involved in maintaining pregnancy, but corpus luteum continues to form these hormones for several months
Q:

3rd-8th week → embryonic period

(= period of organogenesis)

A:
  • Each of the 3 germ layers (ectoderm, mesoderm, and endoderm) gives rise to a number of specific tissues and organs
  • By the end of the 2nd month, the main organ systems have been established → the major features of the external body form are recognizable
Embryology

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