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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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. Gastrulation attribute. Manners of gastrulation in vertebrates.

  2. Human gastrulation early stage. Manners of germ layers and extraembryonic organs formation.

  3. Gastrulation late stage. Formation of the trilaminar embryo.


Real-life situations to be solved:

  1. At the age of 14 days there are two vesicles inside the embryo. What they are? What germ layers are the contacting walls presented by?

  2. The cell material of embryoblast becomes bilaminar. What are the age of the embryo, the stage of embryogenesis and the mechanism of embryo layers appearance?

  3. In the specimen you can see the trilaminar human germinal disk. What layers are there? Where is the place of their development? What is their origin? What is the age of the embryo?

  4. There is coordinative blastomers movement in cranio-caudal turn in the external layer of the embryonic disk. What structure appears? What are the age of the embryo and the stages of embryogenesis?


^ Students' Practical Activities:

Students must know and illustrate such histologic specimens:

Specimen 1. Embryo at the primitive streak stage.

Stained with iron hematoxylin.

In the low magnification you can see the primitive streak consisting of dense cord of cells. Laterally to the primitive streak there are three germ layers, which lie separately: primary ectoderm, endoderm and mesoderm, which appear due to the primitive streak cells migration.

Illustrate and indicate: 1. Epiblast – ectodermal germ layer; 2. Primitive streak; 3. Material of the primitive streak; 4. Hypoblast – endodermal germ layer. 5. Mesoderm.

  • At what stage of embryo development does the primitive streak appear?

  • What germ layer does originate from the primitive streak?


References:

        1. Human embryology. Seventh edition. Indermirg Singh, G.P.Pal. Macmillan Indian Ltd. New Delhi.2001. P. 39– 43.

        2. Embryology /Early human development. Fetal membranes. Comparing embryology. N.K.Kashirina, K.S.Volkov. Ternopil, TSMU. Ukrmedknyha.2006. P.53-57.


^ MODULE І. Fundamentals of Cytology and General Embryology

Content module 2. General and comparative embryology

Practical class № 11.

Duration of the practical class: 2 hours.

Theme: IFFERENTIATION OF THE GERM LAYERS.


Professional Motivation: In normal development the cells of three primary germ layers (ectoderm, mesoderm and endoderm) make specific contributions to the formation of different tissues and organs. These germ layers formed during gastrulation give rise to all tissues and organs. Surface ectoderm, Neural crests and neural tube are derivations of the ectoderm. Surface ectoderm gives rise to: epidermis and its derivatives, adenohypophysis, enamel of teeth, lens of eye, internal ear. Neural crests give rise to: neurons of the spinal ganglia, autonomic ganglia, some cranial ganglia, meningeal coverings of the brain and spinal cord, pigment cells, chromaffin cells of adrenal gland, parafollicular cells of thyroid glands. Neural tube gives rise to: brain and spinal cord. Mesoderm consists of three main parts: somites, intermediate mesoderm (nephrogonotome), lateral mesoderm. Somites are subdivided into sclerotome, myotome and dermatome. Sclerotome gives rise to vertebral column. Myotome gives rise to: striated skeletal muscles. Dermatome gives rise to: dermis and subcutaneous tissue of the skin. Intermediate mesoderm gives rise to: urinary system, gonads and accessory glands. Lateral mesoderm differentiates into somatic and splanchnic mesoderm layers and gives rise to: serous membranes, adrenal gland cortex, myocardium and endocardium of heart, germinal epithelium of gonads.

There is a mesenchyme inside the embryo between the germ layers. Mesenchyme gives rise to: connective tissues, dentin of teeth, smooth muscle tissue, microglia.

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.

^

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. Derivates of the ectoderm germ layer.

  2. Derivatives of the mesoderm germ layer.

  3. Derivatives of the endoderm germ layer.

  4. Histo- and organogenesis.


Real-life situations to be solved:

  1. The axial germ organs are seen in the histological specimen. What is the age of the embryo? What is the stage of embryogenesis?

  2. In the serial cross sections of a human embryo the nervous tube is closed for the all space. What is the age of the embryo?

  3. In the histological specimen under the ectoderm germ layer is visible a cross sectioned tube. What is this tube? Where is this tube originated from?


Students' Practical Activities:

Students must know and illustrate such histologic specimens:

Specimen 1. Embryo at the stage of the neural tube, somites and notochord formation

Stained with iron haematoxylin

Place specimen nervous tube up. At low magnification you can recognize the ectoderm covering the embryo and the neural tube under it. There is mesoderm at the sides of the neural tube. Mesoderm is subdivided into three parts: somites, intermediate mesoderm and lateral mesoderm. Lateral mesoderm is two-layered: somatic mesoderm (parietal layer) and splanchnic mesoderm (visceral layer). Down to neural tube there is the notochord. The lowest layer is the endoderm.

Illustrate and indicate: 1. Ectoderm; 2. Endoderm; 3. Derivatives of the mesodermal germ layer: a) somites; b) intermediate mesoderm: c) parietal mesoderm layer; d) visceral mesoderm layer; 4. Coelom; 5. Notochord; 6. Neural tube; 7. Mesenchyme.

  • At what stage of the embryo development the notochord, neural tube and somites do appear?

  • What are the main mesoderm structural parts in the specimen?

  • What does the somite differentiate in?

Specimen 2. Chicken embryo at the stage of the trunk and amniotic folds

Stained with iron haematoxylin

At low magnification, at the cross sectioned chicken embryo you can see the outer most layer: the ectoderm, neural tube and notochord. In the middle part of the embryo is placed the mesoderm (dark violet colour), which is differentiated into somites (paraxial mesoderm), intermediate mesoderm and 2-layerd lateral mesoderm (splanchnotome) - (visceral and parietal). The primordial kidneys are visible laterally to the notochord as circles. The inner most embryo layer is endoderm. At sides of the embryo the ectoderm and parietal layers of the splanchnotome form the amniotic folds, which grow toward to each other above the embryo. At time of their closing the amnion will form. All embryonic layers form the trunk folds, which grow toward to each other too below the embryo. Ta time of trunk folds meeting the gut tube will form. Trunk folds move toward to each other but do not accrete; because of what the connecting stalk is formed. The connecting stalk communicates the gut tube with the yolk sac.

Illustrate and indicate: 1. Embryonic ectoderm; 2. Embryonic endoderm; 3. Dermatome; 4. Primary renal canaliculi; 5. Parietal mesodermal layer; 6. Visceral mesoderm layer; 7. Coelom; 8. Neural tube; 9. Notochord; 10. Dorsal aorta; 11. Primary blood vessels; 12. Trunk folds; 13. Amniotic folds.


References:

  1. Human embryology. Seventh edition. Indermirg Singh, G.P.Pal. Macmillan Indian Ltd. New Delhi.2001. P. 46– 59.

  2. Embryology /Early human development. Fetal membranes. Comparing embryology. N.K.Kashirina, K.S.Volkov. Ternopil, TSMU. Ukrmedknyha.2006. P.68-76.

^ MODULE І. Fundamentals of Cytology and General Embryology

Content module 2. General and Comparative Embryology

Practical class № 12.

Duration of the practical class: 2 hours.

Theme: Extraembryonic organs


Professional Motivation: After the implantation a specific interrelation has established between the embryo and the female organism. The embryo is growing up and developing inside the endometrium of uterine wall. It is covered by chorion. In the early weeks of development the entire surface of chorion has the villi. As pregnancy advances this situation is changed. The villi on the embryonic pole continue to grow and expand, thus giving rise to the chorion frondosum, those on abembryonic pole degenerate and is known as the chorion leave. The difference in the abembryonic poles of the chorion is also reflected in the structure of decidua. The decidua over the chorion frondosum, the decidua basalis, consists of a compact layer which is tightly connected with the chorion. This layer is reffered to as the decidual plate. The decidual layer over the abembryonic pole is known as the decidua capsularis. The rest of uterine endometrium forms the decidua parietalis. Placenta is a unique human organ because it consists of two absolutely different parts and materials: fetal and maternal. It performs many vitally important functions (nutritive, protective, endocrine, respiration). Abnormality of its position and structure may produce interruption of pregnancy. On the other hand there are some especial processes in the course of embryogenesis when the danger to normal human development persists. Doctors have to recognize the significance and peculiarities of critical periods to prevent any negative influence on the human being at these moments.


^ Basic Level:

1. Human Anatomy department.

2. School course of Human Anatomy and Physiology.

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