Module І. Fundamentals of Cytology and General Embryology. Content module 2 icon

Module І. Fundamentals of Cytology and General Embryology. Content module 2




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MODULE І. Fundamentals of Cytology and General Embryology.

Content module 2. General and Comparative Embryology

Practical class № 8

Duration of the practical class: 2 hours

Theme: Gametogenesis. Sex cells


Professional Motivation: Decreasing population in high developed countries on the one hand and its noncontroled increast in the countries of the "third world” on the other hand is one of the most important problem of the contemporary medicine. That's why for future doctors it is necessary to know the human embryogenesis. It begins with progenesis which results in gametogenesis. Different influences can destroy these processes and result in infertility or development of congenital malformation. At the same time there may be some reasons which prevent fertilization. Deep knowledge of all these processes will help doctors to make a correct diagnosis and prescribe an adequate treatment to the patients with sterility and to prevent n on desired pregnancy.


Basic Level:

1. Human Anatomy department.

2. Course of school Valeology.

^

Students’ Independent Study Program:


I. Objectives for Students' Independent Studies

You should prepare for the practical class using the existing textbooks and lectures. Special attention should be paid to the following:

  1. Embryology, as the science that studies the embryo development.

  2. Philogenesis and ontogenesis conception. Human embryogenesis periods.

  3. Progenesis: oogenesis and spermatogenesis. Meioses.

  4. Spermatozoon microscopic and submicroscopic characteristics. Biological importance in fertilization.

  5. Ovum types. The structure and function of a human ovum.


Real-life situations to be solved

  1. There is a cross section of spermatozoon in an electron micrograph. Mitochondrial sheath wrapped around the axial filaments is seen. What part of spermatozoon is cuted?

  2. In histological specimen of a human ovum there is a small amount of yolk inclusions, settled uniformly in cytoplasm. What type of ovum is this?


^ VISUAL AIDS AND MATERIAL TOOLS:

Electron microphotographs

  1. Spermatozoon.

  2. Oocyte (fragment of the ovary follicle).


Students' Practical Activities:

Students must know and illustrate such histological specimens and diagrams:

Specimen 1. Oocyte of mature follicle. (cat ovary).

Stained with hematoxylin and eosin.

Under low magnification find mature follicle with oocyte. Under high magnification explore the structure of oocyte, which is located on the cumulus oophorus and surrounding tunics. Pay attention – nucleus of the female sex cell is situated eccentrically. Follicular cells (small cells with violet nuclei) and their processes form the radiant crown of oocyte.

Illustrate and indicate: 1. Tertiary follicle; 2. Cumulus oophorus; 3. Oocyte.

  • What type is the human ovum?

  • Which cytoplasmic organelle is absent in ovum?

Diagram 1. General structure of the ovum.

Oocyte contains the nucleus, cell membrane (oolemma) and cytoplasm. Oocyte is surrounded by 3 membranes: oolemma, zona pellucida and corona radiate. The nucleus contains haploid amount of chromosomes and is located eccentrically. Cell membrane has microvilli and receptors. Receptors can be divided into 3 types: Zp3 – are receptors for spermatozoa, Zp2 - are receptors, that prevent from polyspermy, Zp1 – collect together Zp2 and Zp3. Cytoplasm contains yolk inclusions and cortical granules. The oocyte is surrounded by translucent glycoprotein layer – zona pellucida. Outer to the zona pellucida are placed follicular cells.

Illustrate and indicate: 1. Nucleus; 2. Nucleolus; 3. Oolemma; 4. Zona pellucida: a) receptors; 5. Corona radiata: b) follicular cells; 6. Cortical granules; 7. Yolk inclusions.

  • Which types of receptors does ovum have?

  • What is the function of the cortical granules?

Specimen 2. Human spermatozoa (smear).

Stained with nigrosin and eosin.

Find spermatozoa under low magnification and then investigate male sex cells under high magnification. Pay a special attention on flagellate form of these cells.

Illustrate and indicate: 1.Spermatozoa: a) head; b) tail.

  • Are spermatozoa haploid or diploid cells?

  • What kind of cell division is characteristic for spermatozoa?

Diagram 2. Structure of the human spermatozoon.

The spermatozoon is an extremely elongated cell consisting of three main components: the head, neck and tail. The tail is subdivided into three segments, the so-called, middle piece, principal piece and end piece. In man, the head has a flattened pear-shape. The nucleus occupies most of the head. Surrounding the anterior two-thirds of the nucleus is the acrosome, a flattened, membrane-bound vesicle containing variety hydrolytic enzymes, principally hyaluronidase. The neck is very short segment, contains two centrioles: proximal and distal. The distal centriole gives rise to the axoneme of the flagellum. The tail consists of the axoneme arranged longitudinally. External to this axoneme within the middle piece, elongated mitochondria are arranged in a tightly packed helix.

Illustrate and indicate: I. Head: 1. Nucleus; 2. Acrosome; 3. Receptors; II. Neck: 4. Proximal centriole; 5. Distal centriole; III. Tail: 6. Mitochondria; 7. Axial thread of the tail.

  • What structures does the spermatozoon body contain?

  • What is the structure and functions of spermatozoon tail?

  • What is the disposition of spermatozoon nucleus?


References:

        1. Human embryology. Seventh edition. Indermirg Singh, G.P.Pal. Macmillan Indian Ltd. New Delhi.2001. P. 11– 25.

        2. Embryology /Early human development. Fetal membranes. Comparing embryology. N.K.Kashirina, K.S.Volkov. Ternopil, TSMU. Ukrmedknyha.2006. P.9-26.


^ MODULE І. Fundamentals of Cytology and General Embryo­logy

Content module 2. General and Comparative Embryology

Practical class № 9.

Duration of the practical class: 2 hours

Theme: Fertilization. Cleavage.


Professional Motivation: Cleavage is the next stage of embryogenesis after fertilization. Once a zygote has reached two-cell stage, it undergoes a series of mitotic divisions with short interphase period, resulting in rapid increase in the number of cells. At the same time the common massage of organism is constant during the cleavage. Due to this process a multicellular organism appears. Cleavage disorders may result in malformation of embryo development on the 7-th day of embryogenesis the implantation into the endometrium begins. Sometimes blastocyst cannot move into the uterine and implantation occurs wherever else. They are an abnormal implantation sites. In such a case there is no possibility for normal course of pregnancy because it produces bloodiness. Obstetricians have to remember about such a situation. From the other side some external influence can change the cleavage and produce in twins’ development.


^ Basic Level:

1. Structure of the female reproductive system (Human Anatomy department).

2. Course of school Valeology.


Students’ Independent Study Program:

I. Objectives for Students' Independent Studies

You should prepare for the practical class using the existing textbooks and lectures. Special attention should be paid to the following:

  1. Fertilization, stages and biological significance.

  2. Cleavage. Different kinds of cleavage. Blastula types.

  3. Extracorporal fertilization, medical and social significance.


Real-life situations to be solved:

  1. The cleavage results in a coeloblastula. For what type of the oocyte is characteristic this type of cleavage?

  2. Have investigated two types of the oocytes. The first one contains a few amount of the yolk, the second one contains a large amount of the yolk. How are called these oocytes?


^ Students' Practical Activities

Students must know and illustrate such diagrams:

Diagram 1. Fertilization.

Fertilization is happened in the ampullary region of the uterine (fallopian) tube. Enzymes from the activated sperm penetrate the corona radiata and zona pellucida to enter the egg membrane. Entry of sperm triggers the final maturation of the oocyte (second meiotic division). Egg and sperm nuclei unite to create a single diploid cell. The final of fertilization is the formation of a zygote.

Whole process of fertilization is subdivided into the following stages: penetration, activation and nuclear fusion. During fertilization are happened: acrosome reaction, fusion of oocyte and sperm cell membranes, entering of the sperm nucleus and centrioles into the cytoplasm of the oocyte, cortical reaction, zona reaction and formation of zygote.

Illustrate and indicate: 1,2,3,4 – acrosomal reaction; 5. Zona pellucida; 6. Oolemma; 7. Cortical granules; 8. Cortical reaction.

Diagram 2. Types of the oocytes and cleavage.

The oocytes accordingly to the amount of the yolk can be divided into: alecithal (have helminths), oligolecithal (or isolecithal): primary (have lancet flukes) and secondary (has human) and polylecithal (or telolecithal): medialecithal (have amphibian), megalecithal (have birds) and centrolecithal (have incecticides).

The cleavage in primary oligolecithal oocytes is complete, equal and synchronous. The blastula is called coeloblastula.

The cleavage in secondary oligolecithal oocytes is complete, unequal and asynchronous. The result of the cleavage is formation of the morula, which comes into differentiation and forms the blastocyst.

The cleavage in medialecithal oocytes is complete and unequal. The blastula is called amphiblastula.

The cleavage in megalecithal oocytes is incomplete (discoidal or meroblastic) and unequal. This type of cleavage results in a discoblastula.

The cleavage in centrolecithal oocytes is incomplete and superficial. The blastula is called periblastula.

Illustrate and indicate all types of the oocytes and cleavages.


References

        1. Human embryology. Seventh edition. Indermirg Singh, G.P.Pal. Macmillan Indian Ltd. New Delhi.2001. P. 34– 36.

        2. Embryology /Early human development. Fetal membranes. Comparing embryology. N.K.Kashirina, K.S.Volkov. Ternopil, TSMU. Ukrmedknyha.2006. P.27-41.


^ MODULE І. Fundamentals of Cytology and General Embryology

Content module 2. General and Comparative Embryology

Practical class № 10.

Duration of the practical class: 2 hours

Theme: Gastrulation


Professional Motivation: Gastrulation is the next period of embryogenesis after cleavage. Gastrulation of chordate or vertebrate animals can be classified into 4 types: invagination, epiboly, dilamination, migration. It result is the appearance of three germ layers. The cells of the embryoblast form the ectodermal and endodermal germ layers, the two layers which constitute the bilaminar germ disc. It lies between the amniotic and yolk vesicle which appear from the primary ectoderm and endoderm. At the end of the second week embryogenesis a vaguely defined streak appears on the surface of the ectoderm facing the amniotic cavity. Cells of ectodermal layer migrate along the surface of the disc in the cranio-caudal direction and invaginate between the ectodermal and endodermal layers to form an intermediate cell layer - mesoderm. It consists of three main parts: somites, intermediate mesoderm (nephrogonotome), somatic and splanchnic mesoderm layer. There is a mesenchyme inside the embryo between the germ layers. Different tissues and then organs will develop from these components. It is clear that disorders of these processes will result in malformation. Future doctors should to recognize the significance of this period of embryogenesis to prevent a congenital malformation.


^ Basic Level:

1. Human Anatomy department.

2. Course of school Valeology.

  1   2   3   4   5   6

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